
==== Front
iScience
iScience
iScience
2589-0042
Elsevier

S2589-0042(24)02043-1
10.1016/j.isci.2024.110818
110818
Article
Optically induced quantum transitions in direct probed mesoscopic NbSe2 for prototypical bolometers
Jayanand Kishan 1
Saenz Gustavo A. 2
Krylyuk Sergiy 3
Davydov Albert V. 3
Karapetrov Goran 4
Liu Zhonghe 5
Zhou Weidong 5
Kaul Anupama B. anupama.kaul@unt.edu
126∗
1 Department of Materials Science and Engineering, University of North Texas, Denton, TX 76207, USA
2 Department of Electrical Engineering, University of North Texas, Denton, TX 76207, USA
3 Material Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
4 Department of Physics, Drexel University, Philadelphia, PA 19104, USA
5 Department of Electrical Engineering, University of Texas at Arlington, Arlington, TX 76019, USA
∗ Corresponding author anupama.kaul@unt.edu
6 Lead contact

26 8 2024
20 9 2024
26 8 2024
27 9 11081810 3 2024
30 7 2024
22 8 2024
© 2024 The Author(s)
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Summary

Superconducting transition-edge sensors (TES) have emerged as fascinating devices to detect broadband electromagnetic radiation with low thermal noise. The advent of metallic transition metal dichalcogenides, such as NbSe2, has also created an impetus to understand their low-temperature properties, including superconductivity. Interestingly, NbSe2-based sensor within the TES framework remains unexplored. In this work, direct-probed superconducting NbSe2 absorbers led to a proof-of-concept demonstration for the transduction of incoming light to heat, where a thermodynamic superconducting phase transition in NbSe2 was evident to switch it to the normal state, when biased below its superconducting transition temperature. A wavelength-dependent response of its optical absorption properties was observed, based on the incident optical excitation source used. Furthermore, extensive optical characterization studies were conducted using Raman spectroscopy, where the in-plane and out-of-plane thermal conductivity was empirically determined. Our results open possibilities for the use of NbSe2 in superconducting radiation detectors, including in a TES framework.

Graphical abstract

Highlights

• Incoming optical radiation absorbed by superconducting NbSe2

• Heat generated from absorption causes switching to normal state

• Switching characteristics depend on wavelength of incoming radiation

• Superconducting NbSe2 shows promise for bolometers and radiation detectors

Applied sciences; Materials science; Nanomaterials

Subject areas

Applied sciences
Materials science
Nanomaterials
Published: August 26, 2024
==== Body
pmcIntroduction

Layered two-dimensional (2D) materials have intrigued the research community since the mechanical exfoliation of graphene in 2004,1 where their outstanding optical, mechanical, and electronic properties have been at the heart of fundamental studies, including in transition metal dichalcogenides (TMDs).2,3 Studies on TMDs have opened up opportunities for exploring their use in photodetectors,4 zero-dimensional (0D) cage molecule-2D hybrids,5 and quantum multibody systems.6 The TMDs are present in five polytypes: tetragonal (1T), hexagonal (2H), rhombohedral (3R), orthorhombic (1T′), and monoclinic (Td). Each layer consists of a transition metal M (e.g., Mo, Nb, W, and Re) sandwiched between two chalcogen X (e.g., S, Se, and Te) atomic planes that form the X-M-X tri-planar architecture, with the MX2 stoichiometry. In this crystalline structure, strong in-plane covalent bonding arises between the X-M-X complex, while the out-of-plane bonding between adjacent X-X interactions is weak, arising from van der Waals coupling.7 The electronic structure of TMDs ranges from the typical d-block group VI semiconducting (e.g., MoS2, MoSe2, WS2, and WSe2) to the metallic or semi-metallic (e.g., TaS2, TaSe2, NbS2, NbSe2) group V binary chalcogen compounds.8 In the case of group VI semiconducting TMDs, their out-of-plane quantum confinement leads to bandgap tunability, and the transition from indirect bandgap to direct bandgap optical transitions being a characteristic feature.1,9

While the semiconducting TMDs have garnered significant attention from the broader research community, the body of work on superconducting 2D materials, particularly NbSe2, also a TMD, appears to be less extensive. In particular, NbSe2 has distinctive electronic and magnetic properties including emergent superconductivity, which coexists with incommensurate charge density wave (ICDW) states. The latter phenomenon is attributed to a periodic modulation of conduction electrons accompanied with lattice distortions at temperatures T below 33.5 K.10 In single unit cell thick layers of NbSe2 superconductivity is realized via Ising spin pairing due to broken inversion symmetry.11

Cryogenically induced superconducting transitions are at the heart of superconducting tunnel junctions relying on the Josephson effect12 in the superconductor-insulator-superconductor (SIS) configuration, as well as superconducting-quantum-interference-devices (SQUIDs) for high-speed superconductor electronics.13,14 The Josephson junction is comprised of an ultra-thin insulator film sandwiched between two superconducting layers which forms the basis for quantum-limited detection, pivotal in astrophysics applications,15 along with superconducting qubits for quantum computing.16 The latter is a rapidly growing area in recent times toward national security needs involving the broader quantum information science community. More recently lower-dimensional materials such as 0D nanoparticles, 1D nanowires, and 2D materials have been explored for their use in single photon detection, a key component of quantum information science employing photons.17

Another device that leans on superconducting properties for its operation is the transition edge sensor (TES). Here, incoming photons from incident electromagnetic radiation interact with the superconducting sensor which is biased on the steeply rising edge in the resistance R versus T characteristic of the TES. Incoming radiation causes local heating to propel the superconducting sensor to its normal state, forming the basis for radiation detection where sensitivity toward the quantum-limit is a fundamental goal.18 The TES has been implemented for non-destructive analysis of nuclear materials,19 neutrino detection,20 optical and microwave frequency detection21,22 on the European Athena satellite,23 and South Pole Telescope,24 as well as electron-beam ion traps (EBIT).25 The hot-electron bolometer (HEB), based on direct detection or mixing, outperforms SIS and Schottky diodes in astronomical observations significantly above 1 THz which were used on the Herschel space observatory.26 The microwave kinetic inductance detector (MKID),27 the superconducting nanowire single-photon detector (SNSPD),28 and the superconducting stripline detector (SSLD)29 are other variants of detectors relying on superconducting materials. In many situations, the aforementioned devices exhibit low-thermal noise and high sensitivity.18,30-31 Superconducting films employed in the aforementioned detectors typically rely on materials such as Mo,32 Nb,33 NbN,34 and high-Tc superconductors such as YBCO35 and MgB2.36

Although elemental or compound superconducting materials have been extensively studied for their use in TES devices, including some material systems such as Nb and YBCO where investigations have spanned several decades, 2D materials on the other hand, are far less explored for TES applications. Elemental superconductors such as Mo shows a superconducting transition temperature Tc ∼ 0.9 K, while Nb exhibits Tc ∼ 9 K. Binary 3D crystalline compounds, such as the nitride of refractory Nb, i.e., NbN yields Tc in the range of ∼12–16 K dependent on its crystalline quality and offers a more direct comparison to the selenide of Nb which takes up a 2D crystalline host lattice in the form of NbSe2. In comparison to the aforementioned 3D crystalline materials, either elemental or binary, 2D NbSe2 exhibits layer-dependent properties, a feature not commonly observed in 3D crystalline material systems, stemming from the out-of-plane van der Waals bonding in the latter. For example, previous studies conducted on NbSe2 have demonstrated a thickness-dependent magnetic susceptibility and superconducting response.37 This layer-dependent response also likely poses intriguing possibilities when NbSe2 is used as the absorber material in TES architecture, providing another exciting degree of freedom to tune its interaction to incoming radiation. The current study considered in this work on bulk NbSe2 should thus serve as an important benchmark and stepping-stone to extended such empirical analysis in the future for the validation of theoretically proposed phenomena for TES devices based on NbSe2 in the limit of monolayers and thickness-dependent device parameters. Additionally, Xi et al.38 previously demonstrated layer-dependent gate tunability of the superconducting transition of NbSe2, where the transition temperature and superconducting bandgap maybe tuned externally. Through layer engineering and electrostatic tuning, NbSe2 may serve as a candidate bolometer material for high-energy particle detection, as well as a single photon detector for quantum information science applications. Furthermore, large area detectors, such as long-range telescopes, may benefit from the arrangement of NbSe2 pixel arrays capable of capturing and detecting a wide spectral range of energies, on-demand, via layer engineering and electrostatic tuning of the crystallites.

The 2D TMD materials family has grown at a rapid pace over the last decade, and much attention has been placed on the large-area synthesis and manufacturing of these van der Waals solids.39 Approaches for the large-scale synthesis of 2D materials include chemical vapor deposition (CVD), liquid exfoliation, and wet chemical synthesis, to mention a few. Of the aforementioned growth approaches, CVD offers the most potential for generating high-crystalline quality materials, while at the same time being largely compatible with the infrastructure of today’s microelectronics industry and semiconductor process technology.40 Recent work has demonstrated the ability to produce high-quality NbSe2 with thicknesses control using CVD processes.41,42,43 This highlights the possibility of manufacturing high-grade and crystalline quality NbSe2 toward future scalable platforms and for the deployment of superconducting NbSe2 toward important applications, including TES devices.

Furthermore, NbSe2 is a refractory material with a melting point >1,573 K from which a high bond strength, as well as high mechanical stability, maybe inferred.44 Specifically, the bulk modulus of NbSe2 is reported to be ∼52 GPa,45 which is similar in magnitude, to first order, to Silicon’s bulk modulus (∼130 GPa),46 where the latter is widely recognized as a robust mechanical support structure for micro-electro-mechanical systems (MEMS), as well as TES devices. Thus, we expect NbSe2 to offer similar structural stability attributes, while its chemical and air-stability is a topic discussed in more detail in the section “Synthesis and materials characterization of 2H-NbSe2”, where experimental analysis was facilitated by Raman spectroscopy and energy dispersive X-ray spectroscopy (EDS). Such spectroscopy analysis revealed no observable degradation for our samples when they were exposed to radiation under ambient conditions, corroborating its stabile nature, which should be beneficial for practical TES devices.

In this work, we demonstrate the use of a bulk NbSe2, as a superconducting bolometer when it couples to incoming electromagnetic radiation. Here, a change in temperature is sensed as a result of absorption of the electromagnetic radiation focused on the crystal, causing the optical-to-thermal transduction to arise from the superconducting-to-normal transition. Direct probing of the bulk NbSe2 crystal in a cryogenic probe stage with optically pumped incoming radiation spanning the ultraviolet (UV, λ = 405 nm), visible (VIS, λ = 660 nm), and near-infrared (NIR, λ = 1060 nm) via an optical fiber at cryogenic temperatures allowed us to observe the superconducting-to-normal state transition. Time-resolved measurements were also conducted with these lasers, which enabled us to estimate switching parameters of bulk NbSe2-based prototypical TES device. The in-plane and out-of-plane first-order temperature and laser power dependent coefficients of the bulk NbSe2 crystallite were tabulated by analyzing the Raman peak shifts with respect to temperature T and power P, which provided insights into the in-plane and out-of-plane thermal conductivities, where the former was found to be a factor of two higher. Our prototypical demonstration shows the optical-to-thermal transduction in the superconducting transition of bulk 2H-NbSe2, driven solely by incoming optical radiation. This work is well positioned to open opportunities for the use of NbSe2 and other superconducting dichalcogenides in superconducting bolometers in the future.

Results

Synthesis and materials characterization of 2H-NbSe2

The 2H-NbSe2 crystals were grown using the chemical vapor transport (CVT) method with SeBr4 as the transport agent, and the details of the growth is discussed in the STAR Methods. Powder X-ray diffraction (XRD) scans depicted in Figure 1A confirms the hexagonal crystal structure of the obtained 2H-NbSe2 flakes (space group P63/mmc). Materials Data Inc (MDI) Jade 6.5 software (Livermore, CA 2015) was used to calculate the lattice parameters of our 2H-NbSe2 crystallites where the parameters were determined to be a1 = a2 ∼ 3.445 Å and a3 ∼ 12.548 Å, which are comparable to lattice constants previously reported47 for 2H-NbSe2 (a1 = a2 = 3.449 Å and a3 = 12.54 Å). Post growth, the CVT grown NbSe2 crystallites were stored in a vacuum desiccator to minimize air-exposure and possiblity of consequent degradation.48Figure 1 NbSe2 crystal structure and phonon modes

(A) Powder XRD diffraction scans of as grown 2H-NbSe2. The peak at 69.3° denoted with ∗ refers to the Si (400) reflection from the sample holder. Inset shows a representative picture of CVT grown NbSe2 flakes.

(B–D) Raman spectroscopy of 2H-NbSe2, where the crystal structure of 2H-NbSe2 (top and cross-sectional views) are shown in (b)-left, while the Raman active vibrational modes comprising of the out-of-plane A1g and the in-plane E1g, E2g1, E2g2 modes are shown in (b)-right.

(C) Schematic of the 2H-NbSe2 crystal placed on an SiO2/Si substrate used for the micro-Raman measurements excited with a 532 nm laser source.

(D) Raman spectra gathered at room T for pristine 2H-NbSe2 shown in the optical micrograph of the inset, where the vibrational modes are located at ∼ 228.2 cm−1 and 238.7 cm−1, corresponding to the A1g and E2g1 Raman modes, respectively.

The bulk NbSe2 flakes were further examined using Raman spectroscopy. The lattice of 2H-NbSe2 is reported to encompass Au, Bg, Bu, Ag, Eu, and Eg, vibrational modes of which one out-of-plane phonon mode (A1g), and three in-plane phonon modes (E1g, E2g1 and E2g2) are reported to be Raman active.49 A schematic of the Raman active vibrational modes in NbSe2 is shown in Figure 1B. In contrast, Raman inactive modes correspond to asymmetric vibrational modes, either stretched or bent, which are detected using Fourier transform infrared spectroscopy (FTIR). In our sample, a thick NbSe2 crystal was placed on a 270 nm thick thermal SiO2 layer on a Si substrate for high optical contrast (see schematic in Figure 1C). The approximate dimensions of the NbSe2 crystallite used in the following investigations were measured to be 2 mm × 1 mm × 13 μm (length × width × height). From the Raman analysis, the vibrational modes occur at ≈ 228.2 cm−1 and ∼238.7 cm−1 which are assigned to the A1g and E2g1 modes, respectively, as shown in Figure 1D, and the data are in close agreement with previous reports.50 The broad line around 180 cm−1 is called the soft mode due to a second-order scattering mechanism,51 and its analysis is beyond the scope of this paper. The E2g2 vibrational mode is reported to occur at ∼ 29.6 cm−1, and we did not observe this mode due to limitations of our micro-Raman instrumentation. Furthermore, the E1g mode signal intensity is reported to be very low because of the small Raman cross-section.49

The T-dependent Raman spectroscopy measurements were then conducted from T ∼ 80 K where cooling was done using liquid nitrogen (LN2), and a heater was used to warm up the sample up to room T ∼ 298 K. The laser was stabilized at a constant laser power P ∼ 0.84 mW at which an appreciable signal-to-noise (S/N) ratio was obtained, without inducing damage to the bulk NbSe2 crystallite. The E2g1 and A1g modes were analyzed using Gaussian peak-fitting to extract the Raman shift. The contour plot in Figure 2A illustrates the Raman map as a function of T for our NbSe2 crystallite. From the data presented in Figure 2B, the in-plane E2g1 and out-of-plane A1g modes were red-shift linearly as T increased from 80 K to 298 K. The first-order T-dependent behavior for the E2g1 and A1g modes was analyzed using,52(Equation 1) ω(T)=ω0+χT

where ω(T) is the Raman peak position as a function of T, ω0 is the vibrational frequency at 0 K, and χ is the first-order T coefficient extracted from the linear fit. In Equation 1, the influence of the higher-order T coefficient term (χ2T2)53 was not examined given that the higher order non-linear trends were not apparent in our data in Figure 2C. Furthermore, the influence of the non-linear χ2T2 term has been previously reported in some TMDs only at T > 350 K,54 while our measurements were well below this T range. From Equation 1, we find that |χE2g1| ≈ 0.0410 cm−1/K and |χA1g| ∼ 0.0174 cm−1/K, as shown by the top and bottom panels in Figure 2C.Figure 2 Temperature and excitation laser power dependent Raman spectroscopy of NbSe2

(A) Contour map of the T-dependent Raman for 2H-NbSe2 from 80 K to 298 K where the data are collected in 20 K increments at a constant laser P of ≈ 0.84 mW.

(B) Stack plot of the Raman spectra of 2H-NbSe2 from 80 K to 298 K. Dashed lines track position of the E2g1 and A1g modes, which exhibits a linear redshift as T increases.

(C) Raman shift as a function of T for which the χE2g1∼ − 0.041 cm−1/K and a χA1g ∼ − 0.0174 cm−1/K were extracted.

(D) Laser power P dependence of the Raman spectra for NbSe2 from ∼11.7 μW to ≈ 4700 μW. For laser power P < 840 μW, a δω/δP(E2g1) of −3.9 cm−1/mW and δω/δP(A1g) of −2.9 cm−1/mW were calculated and a kA1g ∼ 0.07 W/m.K and kE2g1 ∼ 0.13 W/m.K was extracted using Equation 3. Variation of δω/δP at higher laser P > 840 μW is also plotted as shown by the reduced slope region denoted by the dotted line. The change in slope is attributed to dominance of higher-order P coefficient ([(δ2ω/δP2)P2]) which was not addressed in Equation 2 for our computation. We hypothesize that the dominance of ([(δ2ω/δP2)P2]) term in Equation 2 is due to localized heating at P > 840 μW. The inset shows the P-dependent stack plot of the Raman spectra from 11.7 μW to 4,700 μW, revealing the changed nature of the δω/δP for both the low (P < 840 μW) and high slope (P > 840 μW) regions in the E2g1 and A1g peak positions.

Next, the Raman shift of the modes was analyzed as a function of the incident optical excitation power P of the laser, shown in Figure 2D at room T. An increase in P causes an ensuing increase in T locally, which likely results in thermal dilation within the crystal, inducing a shift in the vibrational phonon spectrum. The first-order power P coefficient is described as follows,(Equation 2) ω(P)=ωP0+(δωδP)P

where ω(P) is the Raman peak position as a function of laser excitation power P, ωP0 is the vibrational frequency at p = 0 W, δω/δP is the first-order power P coefficient which denotes the change in the A1g and E2g1 peak positions with increasing laser power P. Incidentally, with Gaussian peak position fitting to the laser power P-dependent Raman spectra presented in the inset of Figure 2D, we observe a red-shift in the A1g and E2g1 peaks with increasing laser power P over the entire range from low P (∼11.7 μW) to high P (∼4700 μW), though two regimes were evident where δω/δP changed more rapidly up to 840 μW, as shown in Figure 2D. Additionally, the laser power P-dependent trend observed in δω/δP (see Figure 2D) was found to be reversible upon reduction of laser power P from 4,700 μW to 11.7 μW. We believe the slower change in δω/δP above P = 840 μW may be due to the influence of the higher-order non-linear term ([(δ2ω/δP2)P2]) which was not considered in Equation 2 for our computation. In the low P range of 11.7 μW–840 μW, our data analysis led us to determine |δω/δP|(A1g) ∼ 2.9 cm−1/mW and |δω/δP|(E2g1)∼ 3.9 cm−1/mW using Equation 2. As a result, the thermal conductivity k is extracted using the following,55(Equation 3) k=χ(12πz)(δωδP)−1

where χ is as described previously, and z is the thickness of the NbSe2. Using the computed values of |δω/δP|(E2g1) and |δω/δP|(A1g) in the low P range (P < 840 μW), measured z ≈ 13 μm for our bulk NbSe2 crystallite, the thermal conductivity was calculated, where kE2g1 ≈ 0.13 W/m.K refers to the in-plane mode, and kA1g ∼ 0.07 W/m.K refers to the out-of-plane mode. It is interesting to note that kE2g1 is almost 2× higher than the kA1g, which is well in line with the earlier observation of |χE2g1| > 2× |χA1g|, highlighting the presence of anisotropy in thermal conductivity caused by T-dependent and P-dependent phonon anharmonicity in the NbSe2. Furthermore, Table 1 summarizes all of the quantitative parameters determined using non-contact Raman spectroscopy on bulk NbSe2 crystallites investigated in our work.Table 1 First-order temperature coefficient and thermal conductivity parameters for NbSe2

Material Property	Measured Value	
In-plane	Out-of-plane	
First-order T-coefficient of phonons (χ)	|χE2g1| ∼ 0.0410 cm−1/K	|χA1g| ∼ 0.0174 cm−1/K	
Thermal conductivity (k)	kE2g1 ∼ 0.13 W/m.K	kA1g ∼ 0.07 W/m.K	
A summary of the in-plane and out-of-plane parameters determined using non-contact Raman spectroscopy on bulk NbSe2.

After extensive T- and P-dependent Raman measurements, the NbSe2 crystallites were once again examined to deduce the possibility of degradation arising from air-exposure or photo-oxidation occurring during these measurements. Thin exfoliated NbSe2 flakes are indeed very sensitive to both air exposure and photo-oxidation. The before and after Raman spectra are shown in Figure S1 (see Supplementary Information) which reveals little shift in the phonon peak positions, indicative of minimal degradation occurring in our samples during the measurements. Incidentally, the phonon peaks of selenium-based 2D materials are reported to shift upon the formation of selenium vacancies, oxygen substitution, or other defects formed through exposure to ambient atmosphere or defect formation through photo-oxidation.56 However, surface and composition sensitive characterization techniques such as X-ray photoelectron spectroscopy (XPS) would allow further validation of photo-oxidation states in the NbSe2 which may be interesting to explore in a future study. In reviewing the existing literature,50,57,58 our measurement range is broad over 80 K–298 K for the T-dependent Raman, to determine χ and k values for bulk NbSe2 crystallites. Furthermore, as reported in a prior study,59 k is strongly dependent on vacancy and defect concentrations. The wide variation in k values found in the literature for the same material has been observed for single layer graphene,60 and incidentally also for NbSe2,61 as reported in the prior literature.41,62,63 Moreover, early studies successfully demonstrated the use of Raman spectroscopy to deduce k in 2D materials including graphene,60 where the T-dependent and P-dependent phonon peak positions shift as the T changes, from which k is inferred. Using the shift in the optical phonon peak positions which are sensitive to local heating effects (e.g., caused by ambient temperature or laser-power induced heating), the thermal conductivity for 2D materials can be estimated using such a noncontact approach, despite the fact that the Raman-active optical phonons play a minor role in directly conducting heat along the flake. Balandin and co-workers pioneered this approach in 2008,60 where the T-dependent and P-dependent G-peak position was used to determine k in graphene. We have used the same approach here following similar guidelines, where the E2g1 and A1g mode variations allowed us to compute k for our bulk NbSe2. However, prior work by Zhang et al.64 has shown modulation of Raman peak positions and their intensities with the choice of substrate for in-plane and out-of-plane phonons modes. The anisotropy in thermal conductivity reported in our work may also be influenced by the interaction of NbSe2 with the substrate. While not within the scope of this paper, future studies elaborating upon thermal conductivity calculations and its anisotropy may be interesting to gather for both supported and suspended NbSe2 to shed insights on the role the substrate plays. Additionally, bulk NbSe2 is less prone to oxidation compared to thin membranes, and thus no additional Raman peaks appeared, for example at ∼ 302 cm−1 ascribed previously to the presence of Nb2O5 formed after laser irradiation.65

Electronic transport measurements

Delta-mode instrumentation

The electronic transport measurements on our bulk NbSe2 samples were conducted using a data acquisition system developed in-house to acquire the superconducting transition temperature Tc using the Lakeshore CRX-4K cryogenic probe stage. The schematic of the instrumentation is shown in Figure 3A. One of the ways in which electronic transport measurements on superconductors are carried out is using a commercially available physical property measurement system (PPMS),11,57 variable T helium cryostat,41,65 or closed-cycle two-stage pulse tube with helium stage.66 In this work, we have developed an approach to make such transport measurements with the CRX-4K probe station using a closed cycle helium refrigerator, where optical radiation is coupled to the device under test (DUT), while the transport measurements are made in vacuum using delta-mode technique.Figure 3 Delta-mode electrical characterization setup for superconducting transition temperature measurement

(A) The instrumentation setup for the electronic transport measurements to determine superconducting Tc using the CRX-4K probe stage. Here, a nano-voltmeter (Keithley 2182A), a precision current source (Keithley 6220), and the Lakeshore 336 temperature controller are interfaced to the CRX-4K probe station, where cooling is achieved using compressed He closed cycle refrigerator.

(B) Input Is and output V measured from V+ to V-, as shown in the schematic in (a), at Is modulated at 12.5 Hz.

(C) The measured R obtained for Nb used as our reference sample for our in-house designed Tc measurement system. The R is plotted as a function of T to tabulate its Tc(R = 0 Ω) which occured at 8.49 K in the CRX-4K, while in the PPMS this transition occurs at Tc(R = 0 Ω) = 9.18 K. The T offset of 0.69 K is attributed to the thermal position of the temperature sensor located well beneath the sample on the SH-2.00-T stage, causing a delta in the actual T on the surface of the sample. The inset shows R as a function of T over a broader T range for the sputtered Nb film from 6 K to 300 K using both the PPMS and the CRX-4K.

The delta-mode technique uses an ambipolar current source Is to the DUT which is squared in amplitude to eliminate the Seebeck voltages at the interfaces. Here, electrical connections and adapters from the instrumentation to the DUT result in a Seebeck coefficient mismatch and a large T gradient in our interconnects on the chip. Since the Seebeck voltages remain constant in magnitude and polarity at a fixed T regardless of current source bias, the average voltage is extracted every n cycles at the maximum operating frequency of 12.5 Hz, as denoted in Equation 4.(Equation 4) Vaverage=∑i=1n(Va,n−2Vb,n+Vc,n4)(−1)n

Here, Vaverage is the measured voltage for the channel R calculation; Va,n, Vb,n, and Vc,n are used to indicate the alternating maximum and minimum measured voltages at each n delta cycle. An example of this cyclical behavior in current and voltage is shown in Figure 3B for a given ambipolar input Is = ± 100 μA, and Vmeasured varies between 13 μV and 17 μV from n = 0 to n = 8 delta cycles, while the output Vaverage = 15 μV was computed from Equation 4, as represented in Figure 3B.

In order to corroborate the superconducting transition temperature Tc data deciphered using the above Kelvin sensing delta-mode approach, a calibration test was conducted with a sputtered Nb film before proceeding to our NbSe2 device measurements. For the calibration test, a thick Nb film was deposited on an oxidized Si substrate with a thermal oxide thickness of 270 nm using DC sputtering, with an Ar flow rate of ∼15 sccm, pressure of ≈ 5 mTorr, and plasma power of ∼50 W once the plasma stabilized. The delta-mode transport measurement parameters for our Nb film were conducted at Is = 100 μA (magnitude of Is selected to maximize the S/N ratio), 10 cycles at 12.5 Hz in a T range from 3.88 K to 300 K. Using these parameters, the Tc (R = 0 Ω) was measured to be 8.49 K using the CRX-4K system which is close to Tc = 9.18 K acquired for the same sample using the PPMS system (Quantum Design, model DynaCool), as shown in Figure 3C. This resulted in an offset of ∼0.69 K in our Tc data for the two approaches, which we mostly attributed to the position of the T sensor in our CRX-4K system to be well below the sample chuck, resulting in some thermal offset from the true reading at the surface of the material.

Bolometer measurements for deducing optical-to-thermal transduction

Superconducting TES bolometers rely on the abrupt change in resistivity induced by minute changes in temperature of the TES from the absorbed energy from optical sources which we now describe in our prototypical bolometers. Incidentally, there have been several reports on electronic transport measurements on NbSe2 crystals mechanically exfoliated and transferred onto pre-patterned electrodes by using a polydimethylsiloxane (PDMS) stamping process and subsequent e-beam lithography to define electrical contacts.11,57,65 However, there appears to be no prior reported work on the direct probing of as-grown pristine bulk NbSe2 crystallites to access their intrinsic electronic properties free from surface or interfacial residues commonly associated with post-processing and nanofabrication. The aforementioned delta-mode Kelvin sensing technique allowed us to make measurements on the bulk NbSe2 crystallite which was carefully probed with the Lakeshore tungsten probe tips. A pictograph of our set-up is highlighted in Figure 4A-Left, where the DUT is circled within the red dotted line, and expanded on the right inset. The single-mode fiber-coupled (FC) optical sources utilized were the Thorlabs S3FC405 (λ405nm), S1FC660 (λ660nm), and S1FC1060 (λ1060nm), lasers which were interfaced to the CRX-4K fiber-coupled feedthroughs (manufactured by OZ optics) to focus optical radiation onto the DUT at normal incidence, as shown in Figure 4A-left. We mounted the NbSe2 crystal on a single-side polished Si wafer using VGE-7031 thermal varnish; to further improve the thermal contact between the Lakeshore sample stage SH-2.00-T and the DUT, Apiezon N thermal grease was used between the Si wafer and the chuck, as shown by the sample set-up in Figure 4A-Right. We note the several thermal stray paths within the effective thermal circuit illustrated in Figure 4A-right, where an effective thermal conductance Geff and effective thermal capacitance Ceff are illustrated for our model system.Figure 4 in situ optically induced superconducting transition temperature measurement of NbSe2

(A) Left: a visual of the four-point probing set up used in the CRX-4K cryogenic stage, with the optical fiber and the four terminals for the voltage and current probe connections in the Kelvin-probe set-up. Shown by the dotted-red circle is the DUT which is expanded on the Right. Right: a schematic of our NbSe2 prototypical superconducting bolometer with all the thermal links illustrated until the sample stage SH-2.00-T.

(B) The R is plotted as a function of Tcryo from 0 K up to 40 K, revealing the Tc,onset (R = Rn) occurring at 3.89 K and Tc (R = 0 Ω) occurs at 3.88 K. Inset shows the R as a function of T over a wider T range from 300 K down to the superconducting transition.

(C) Measured R(T)/Rn and from the approximation fit to the R(T)/Rn data modeled using Equation 5, a unitless transition bandwidth α was computed. Through the NRA approximation, α was determined to be ∼196 for NbSe2. Inset shows the measured R(T)/Rn and approximation fit R(T)/Rn for Nb, revealing an α of ∼1639.

(D) Time-resolved photo response of NbSe2 where R is plotted as a function of t using an optical source with λ405nm. The plot is divided into five regions (I to V) with respect to the temporal response of the DUT as a function of the wavelength of the incoming laser source. Inset shows the temporal response in the rising edge and falling edge of the DUT with additional irradiation sources at λ660nm and λ1060nm. Evidently, we observe τr|1060nm<τr|660nm<τr|405nm and τf|1060nm<τf|660nm<τf|405nm.

Electronic transport measurements were initiated through the previously described delta-mode measurements on NbSe2 crystals from 300 K down to 3.88 K, with Is = 1 mA (magnitude of Is selected to maximize S/N). Furthermore, when a lower magnitude of Is < 100 μA was used with the current instrumentation, to possibly reduce the effect of Joule heating and decrease the response time, the signal-to-noise ratio in the ensuing I-V was low and the data were noisy, which can be addressed further in future work. Additionally, between consecutive T-dependent measurements, a 300 s equilibration interval was used, to ensure the surface T of NbSe2 (Tsurface) reaches the T set-point denoted as Tcryo. Figure 4B shows the R−T behavior at Tcryo < 40 K, where a Tc (R=0Ω) was observed at 3.88 K, while the Tc,onset(R=Rn) (Rn ∼ 2.6 mΩ, is the normal state R) was observed at 3.89 K. Moreover, no discernible R hysteresis was found when the DUT was heated and cooled below and above the superconducting transition.

Incidentally, the Tc,onset(R=Rn) and Tc (R=0Ω) noted from our CRX-4K transport measurements are lower than previously reported values of ∼6.5 K–7.2 K for bulk NbSe2.53,54 We believe that the offset in the Tc (R=0Ω) in our NbSe2 bulk crystallite with the CRX-4K is a result of poor thermal coupling associated with the underlying layers in our DUT to the CRX-4K stage. We have used GE-7031 varnish for thermal coupling of the superconducting crystal with the cryostage, as shown by the schematic in Figure 4A-Right. Our assumption is further corroborated by the data in Figure S2 which shows Tc measurements on the same sample obtained using vibrating sample magnetometry (VSM) within a PPMS. As seen from Figure S2, the onset of Tc ∼ 6.78 K for this sample, which is in close agreement with previously reported Tc values for bulk NbSe2.53,54 Additionally, EDS analysis in Figure S3 in the Supplementary Information section, discusses the near stoichiometric ratio of Nb:Se, thus confirming our notion of the lower Tc (R=0Ω) measured with the CRX-4K to be associated with poor coupling of the underlying layers in our DUT to the CRX-4K stage (i.e., GE-7031 varnish). In the case of superconducting thin films that are directly deposited on a substrate using techniques such as physical vapor deposition, this offset in Tc is expected to be smaller given the direct adhesion of the film to the substrate rather than relying on thermal varnish to couple the two. Since the primary objective of our work here was to assess the optically induced superconducting-to-normal-state phase transition in bulk NbSe2, we successfully demonstrate the function of this prototypical bolometer behavior using the CRX-4K. The inset in Figure 4B shows the entire temperature sweep from 300 K down to the superconducting transition, where the residual resistivity ratio (RRR) was tabulated to be ∼13; the RRR in this case was taken as the ratio R300 K/R8 K and these data are consistent with a prior report for CVT synthesized NbSe2 crystallites with RRR ∼ 16.7

For our bolometer measurements, the incident laser power P at the sample was calibrated using a Thorlabs PM100D power meter with a silicon photodiode on the SH-2.00-T. The Tcryo was maintained at near Tc (R = 0 Ω) = 3.88 K, and λ405nm, λ660nm, and λ1060nm optical sources at P ∼ 4.45 mW were then used at normal incidence to shine electromagnetic radiation on the sample surface, which triggered the switch to the normal state. For irradiating with λ405nm, λ660nm, and λ1060nm, the laser spot was placed between the four probes used to measure resistance of the bulk NbSe2 crystal, as depicted in Figure 4A. The approximate laser spot size was ∼250 μm, which is far smaller than the lateral dimensions of the crystal, i.e., 2 mm × 1 mm (length × width). The optical source was thus placed in the middle of the NbSe2 crystal ensuring that the electrically probed region captured the interaction the sample had with the incoming light source. The simplest approximation of the sensitivity of a superconducting absorber layer for TES bolometers is given by a unitless parameter α, which is captured by the following,67(Equation 5) [R(T)/Rn]≈0.5(tanh(πα(Tsurface−Tc))+1)

Here, R(T) is the R as a function of T, Rn is the normal state resistance at the onset of the superconducting transition, Tsurface is the temperature at the surface of the NbSe2 under an incoming flux of photons (see Figure 4A-right), and Tc (R = 0 Ω) = 3.88 K is the superconducting transition temperature of the NbSe2 crystallite. We used the R−T data from Figure 4B and performed a non-linear regression analysis (NRA) to fit Equation 5 to our measured [R(T)/Rn] as a function of Tcryo between 3.88 K and 5 K, as shown in Figure 4C. We assumed Tsurface=Tcryo in the laser-off condition, and as noted previously a 300 s interval was used in between sampling the R data to equilibrate Tsurface to the setpoint Tcryo. The sensitivity α was computed to be ∼196 for our direct-probed bulk NbSe2 (αNbSe2) using the NRA fitting technique, with the idea to minimize the sum of squared residuals (SSR); here SSR is the sum square deviation between the measured [R(T)/Rn] values and the fit approximation of [R(T)/Rn] from Equation 5. Similarly, the inset in Figure 4C shows the NRA fit of [R(T)/Rn] to our measured [R(T)/Rn] for direct probed sputtered Nb film (αNb), where the αNb was computed to be ∼1639, evidently it was found that αNbSe2≪αNb. For our direct-probed superconducting NbSe2, the calculated α signifies good electrothermal feedback, exhibiting higher sensitivity compared to, for example, a typical superconducting thermistors in a TES architecture (α∼10).68,69

Next, we have investigated the λ-dependent optical-to-thermal transduction present in our DUT comprising of the NbSe2 van der Waals crystal. To initiate the temporal and λ-dependent measurements, the modulation of R as a function of time t under λ405nm illumination was measured and the data are presented in Figure 4D. The fiber coupled laser at λ405nm was fixed at P ∼ 4.45 mW and Is = 1 mA was used for the delta-mode measurements of R at 300 s intervals. This yielded a transition from R=0Ω|Tsurface=Tc to R=Rn|Tsurface=Tc,onset under the influence of optical irradiation. Five regions of operation are evident denoted as such at the top of Figure 4D, from regions I to V, while the bottom shows the empirically calculated rise time τr,which is defined as the time taken by the NbSe2 sensor to heat up and change its resistance from R=0Ω|Tsurface=Tc to R=Rn|Tsurface=Tc,onset after the laser source was turned on. Similarly on the falling edge, the fall time τf was computed as the time taken for the NbSe2 absorber to transduce from R=Rn|Tsurface=Tc,onset to R=0Ω|Tsurface=Tc (i.e., reverting back to the superconducting state), after the laser was turned off. In region I, the DUT was maintained in the superconducting state such that R=0Ω|Tsurface=Tc, at Tcryo = 3.88 K, with the laser off. In region II, the laser was turned on, which caused R to increase gradually, eventually resulting in the switch from R=0Ω|Tsurface=Tc to R=Rn|Tsurface=Tc,onset. Here, τr was empirically measured to be 25 min for the λ405nm irradiation source on our direct-probed NbSe2 sensor. In region III, with the laser still on, a saturation of R=Rn|Tsurface=Tc,onset came about, as a result of thermal equilibrium between the environment and thermal dissipation to the SH-2.00-T sample stage. For ease of visualization, the increase in T of the bolometer is schematically represented by a broad color change from gray-to-red for the absorber in traversing regions II to III (top panel of Figure 4D). In region IV, the laser is turned off, and there is a dwell time from R=Rn|Tsurface=Tc,onset to R=0Ω|Tsurface=Tc. Finally, in region V, a thermal phase transduction is evident in going from R=Rn|Tsurface=Tc,onset to R=0Ω|Tsurface=Tc. Using the data in regions IV and V, τf was empirically computed to be 55 min for the λ405nm source. Furthermore, the inset in the bottom panel of Figure 4D plots the R−t response of the DUT using other irradiation sources, specifically λ660nm and λ1060nm where the τr and τf values were determined empirically. Interestingly, the λ-dependent trend of our DUT’s time constants was found to follow τr|1060nm(10min.)<τr|660nm(20min.)<τr|405nm(25min.), and similarly τf|1060nm(35min.)<τf|660nm(40min.)<τf|405nm(55min.), which is now elaborated more upon next.

Increasing λ decreased τr, as observed, implying that the higher incident λ value resulted in a faster optical-to-thermal transduction occurring within the NbSe2 TES sensor. We assume that the λ-dependent trend in our DUT’s temporal response is related to the λ-dependent reflectivity of the NbSe2 crystallites previously reported by Liang. et al.70 and Hill. et al.71 who both noted an increased reflectivity in NbSe2 with a decrease in λ; this is also consistent with our observations for λ450nm to λ1060nm. We hypothesize that since a higher ratio of the incident electromagnetic radiation is reflected at lower incident λ values, the DUT takes more time to heat up from R=0Ω|Tsurface=Tc to R=Rn|Tsurface=Tc,onset, leading to our empirical observation that τr|1060nm<τr|660nm<τr|405nm. Furthermore, for all the λ values used in this temporal response study, we see that τf ≫ τr for our prototypical bolometer. We presume this is associated with the poor heat dissipation from the superconducting NbSe2 layer to the Si thermal heat sink, since there is a 10-fold decrease in Si’s thermal conductance at Tcryo < 20 K compared to that at room T,72 limiting the thermal coupling to the SH-2.00-T sample stage, in order for the DUT to revert back to the superconducting state. The τr and τf recorded with the DUT under the optical stimulus is unmistakably linked to the thermal conductivities kE2g1 and kA1g of the bulk NbSe2 evaluated through Raman spectroscopic analyses presented here. However, the response of the system is the sum of the thermal conductivities of the several layers such as Si, thermal grease, thermal varnish and the NbSe2, as described in Figure 4A. To reiterate, the primary focus of this work was to provide a proof-of-concept demonstration of the NbSe2 to optical irradiation in a TES architecture. The emphasis of this study was to highlight the prototypical demonstration of bulk NbSe2 highlighting a transduction from R=0Ω|Tsurface=Tc to R=Rn|Tsurface=Tc,onset by optical stimulation, using the proposed equipment setup. Our study was not motivated by benchmarking because it is heavily dependent on the architecture of the DUT, and the defect concentration in the crystallite, as discussed earlier in this paper. The thermal conductivity of NbSe2 obtained through Raman spectroscopy can be extended to other material systems for determining thermal conductivities using non-contact approaches. Furthermore, the effective heat capacitance Ceff is inversely dependent on k, where higher Ceff values are correlated to a lower thermal noise within the TES device.67 This implies that the anisotropy in k values for NbSe2 reported in our study may perhaps be used to deduce NbSe2 crystal’s orientation to optimize thermal noise performance. In the case when NbSe2 is suspended, the Ceff of the TES maybe further reduced to improve thermal noise performance.

For TES measurements, an alternative unambiguous approach for determining the modulation of Tc (R=0Ω) to Tc,onset(R=Rn) under the influence of optical irradiation maybe possible by extracting DC I-V curves to measure the critical current density and extracting the superconducting energy gap of bulk NbSe2,73,74 as part of a future study. Moreover, our work focuses on analyzing the intrinsic electrical response of NbSe2 biased at its superconducting state, such that with incident optical stimulation, it causes it to switch to the normal state with the proof-of-concept validation of the NbSe2 crystal as a TES. NbSe2 in its 2D form <10 layers, has also shown evidence of superconductivity but the transition temperature appears to decrease as sample thickness decreases.37 While our samples were bulk, the findings of this study can easily be translated to thinner films of NbSe2 approaching the 2D limit. Furthermore, another degree of freedom is afforded in 2D NbSe2 to modulate its transition temperature through the thickness dependent dielectric screening that decreases as the sample thickness decreases for <10 layers. This allows external electric or magnetic fields to couple to the dielectric environment which changes with thickness, as reported previously.38,75

Discussion

In this work, a comprehensive characterization of single-crystalline NbSe2 was conducted toward a prototypical TES bolometer demonstration. A superconducting transition in bulk NbSe2 was determined to occur at ∼ 3.88 K using the delta-mode Kelvin sensing technique by direct electrical probing in a Lakeshore CRX-4K probe stage. Several optical radiation sources from the UV-to-IR (λ405nm, λ660nm and λ1060nm) were used to determine various operational parameters of our sensors. The bolometer’s switching time constants showed a λ-dependent temporal response; for example, the rising time constant showed the following sequence: τr|1060nm<τr|660nm<τr|405nm. The λ-dependent trend in our DUT’s temporal response is attributed to the λ-dependent reflectivity of the NbSe2 crystallites, as explained in the Results section. The temperature and laser power dependent Raman spectroscopy analysis revealed a directional anisotropy in thermal conductivity k, where, kE2g1 ∼ 0.13 W/m.K and kA1g ∼ 0.07 W/m.K was computed, suggesting kE2g1 ∼ 2× kA1g, presumably due to phonon anharmonicity. This work shows a proof-of-concept demonstration of NbSe2 where a transduction from its zero-state resistance to normal-state resistance is evident through optical stimulation and indicates the promise of 2D NbSe2 toward future TES devices and bolometers. These devices maybe further miniaturized through lithographic patterning in the future, for the realization of monolithically integrated sensors which may be coupled to rf, microwave, and quantum photonic components.

Limitations of the study

Surface and composition-sensitive characterization methods, such as X-ray photoelectron spectroscopy (XPS), may allow for additional confirmation of photo-oxidation states in NbSe2, which may be worth investigating in future work. The interaction of NbSe2 with the substrate may potentially have an effect on the anisotropy in thermal conductivity revealed in our study. Additional research into thermal conductivity calculations and anisotropy for both supported and suspended NbSe2 may thus be useful in shedding insights into the role the substrate itself plays. The current investigation on bulk NbSe2 used in this work should serve as a benchmark for future extensions of this empirical study to validate theoretically predicted phenomena for TES devices based on NbSe2 in the limit of monolayers and extracting thickness-dependent device parameters.

Resource availability

Lead contact

Futher information and requests for resources should be directed to the lead contact, Anupama Kaul (Anupama.Kaul@unt.edu).

Material availability

This study did not generate any new materials.

Data and code availability

• All data reported in this paper will be shared by the lead contact upon request.

• This paper does not report original code.

• Any additional information required to reanalyze the data reported in this paper is available from the lead contact upon request.

Acknowledgments

We thank the 10.13039/100000181 Air Force Office of Scientific Research (grant number FA9550-15-1-0200 and FA9550-21-1-0404 ), the 10.13039/100000001 National Science Foundation (grant number NSF ECCS 1753933 ) and the US Department of Energy (grant number DE-NA0004114 ) who provided funding support that enabled us to pursue this work. G.K. acknowledges support from the US Department of Energy (grant number DE-FOA-0002514 ). S.K. and A.V.D. acknowledge support through the Materials Genome Initiative funding allocated to the National Institute of Standards and Technology.

Author contributions

A.B.K. conceived the overall project. K. J and G. A. S. conducted the experiments related to instrumentation set-up and transport and material characterization. S. K. and A. V. D. synthesized the 2D crystals. G. K. and S. K. conducted the material characterization studies, Z. L. and W. Z. assisted in the device fabrication and measurements. All contributed to discussions related to figure edits. A.B.K. and K. J. analyzed the data, conducted significant manuscript edits and came up with the conclusions. All reviewed the manuscript writing and approved of its content.

Declaration of interests

The authors declare no competing interests.

STAR★Methods

Key resources table

REAGENT or RESOURCE	SOURCE	IDENTIFIER	
Chemicals	
	
Nb powder (99%)	Strem Chemicals	https://www.strem.com/	
Se powder (99.999%)	Strem Chemicals	https://www.strem.com/	
	
Software and algorithms	
	
XRD data Analysis - Jade 6.5 software	Materials Data Inc (MDI)	https://materialsdata.com/	
Data analysis and plotting – Origin	OriginLab Corporation	https://www.originlab.com/	
	
Other	
	
Bruker D8 X-ray diffractometer	Bruker	https://www.bruker.com/en.html	
Horiba LabRAM HR Evolution	Horiba Scientific	https://www.horiba.com/int/scientific/	
Delta-mode measurement, Keithley 2182A and Keithley 6220	Tektronix	https://www.tek.com/en/products/keithley	
Lakeshore CRX-4K	LakeShore Cryotronics	https://www.lakeshore.com/home	
Quantum Design Physical Property Measurement System	Quantum Design	https://www.qdusa.com/index.html	
Thermo Fisher Apreo 2S Lo Vac Scanning Electron Microscope	Thermo Fisher Scientific	https://www.thermofisher.com/us/en/home.html	

Experimental model and study participant details

There are no experimental model and study participants to include in this study.

Method details

Growth of NbSe2 crystallites

Polycrystalline NbSe2 was synthesized during a 72-h reaction between stoichiometric amounts of Nb (99.9%, Strem Chemicals) and Se (99.999%, Strem Chemicals) powders in a vacuum-sealed quartz ampoules at 850°C. The quartz ampoules contained ∼1 g of polycrystalline NbSe2 charge and ∼110 mg (5 mg/cm3) of SeBr4, which were sealed under vacuum and placed in a single-zone furnace. The T at the charge and crystal growth zones (Thot–Tcold) were 825°C–700°C for a growth duration of ∼160 h.

X-Ray diffraction and Raman characterization of the NbSe2 crystal

Powder X-ray diffraction (XRD) scans were produced using a Bruker D8 X-ray diffractometer. Materials Data Inc (MDI) Jade 6.5 software (Livermore, CA 2015) was used to calculate the lattice parameters. The micro-Raman spectroscopy measurements were carried out using a Horiba LabRAM HR Evolution system equipped with a 532 nm laser for excitation and a high spectral resolution grating of 1800 grooves/mm. The optical power P was tuned with a neutral-density filters, which reduces the laser power P from 100% down to 0.01%, and the laser spot size was determined to be ∼2.6 μm for a 10× objective with a numerical aperture (NA) of 0.25.

Delta-mode measurements

The delta-mode technique was used for the bolomter measurements using a nanovoltmeter (Keithley 2182A) interfaced to a precision bipolar current source (Keithley 6220). The base T in our system was readout using the built-in silicon diode sensor (DT-670-CU-HT) underneath the Lakeshore sample stage (SH-2.00-T), as shown in Figure 3A. In the Kelvin sensing technique, the Keithley 6220 sources current in the range of 100 fA to 105 mA, and the nano voltmeter measures the ensuing voltage via the RS-232 communication channel with the trigger link cable 8501 for synchronization. The T is controlled using the Lakeshore 336 temperature controller interfaced to the DT-670-CU-HT, and a built-in heater warms the sample from the base T of ∼3.88 K up to a maximum of 350 K. A Kelvin sensing technique was implemented to null-out the influence of the parasitic resistance R arising at the electrical contacts for the DUT and the external cabling of the instrumentation.

Quantification and statistical analysis

There are no quantification or statistical analyses to include in this study.

Additional resources

Disclosures

Certain commercial equipment, instruments, software or materials, commercial or non-commercial, are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.

Supplemental information

Document S1. Figures S1–S3 and Table S1

Supplemental information can be found online at https://doi.org/10.1016/j.isci.2024.110818.
==== Refs
References

1 Novoselov K.S. Jiang D. Schedin F. Booth T.J. Khotkevich V.V. Morozov S.V. Geim A.K. Two-dimensional atomic crystals Proc. Natl. Acad. Sci. USA 102 2005 10451 10453 10.1073/pnas.0502848102 16027370
2 Zhang X. Tan Q.-H. Wu J.-B. Shi W. Tan P.-H. Review on the Raman spectroscopy of different types of layered materials Nanoscale 8 2016 6435 6450 10.1039/C5NR07205K 26955865
3 Xia F. Wang H. Xiao D. Dubey M. Ramasubramaniam A. Two-dimensional material nanophotonics Nat. Photonics 8 2014 899 907 10.1038/nphoton.2014.271
4 Min M. Sakri S. Saenz G.A. Kaul A.B. Photophysical Dynamics in Semiconducting Graphene Quantum Dots Integrated with 2D MoS2 for Optical Enhancement in the Near UV ACS Appl. Mater. Interfaces 13 2021 5379 5389 10.1021/acsami.0c18615 33471523
5 Jayanand K. Chugh S. Adhikari N. Min M. Echegoyen L. Kaul A.B. Sc3N@C80 and La@C82 doped graphene for a new class of optoelectronic devices J. Mater. Chem. C 8 2020 3970 3981
6 Bandyopadhyay A.S. Adhikari N. Kaul A.B. Quantum Multibody Interactions in Halide-Assisted Vapor-Synthesized Monolayer WSe2 and Its Integration in a High Responsivity Photodetector with Low-Interface Trap Density Chem. Mater. 31 2019 9861 9874 10.1021/acs.chemmater.9b04086
7 Frindt R.F. Superconductivity in Ultrathin NbSe2 Layers Phys. Rev. Lett. 28 1972 299 301
8 Kaul A.B. Two-dimensional layered materials: Structure, properties, and prospects for device applications J. Mater. Res. 29 2014 348 361 10.1557/jmr.2014.6
9 Mak K.F. Lee C. Hone J. Shan J. Heinz T.F. Atomically thin MoS2: A new direct-gap semiconductor Phys. Rev. Lett. 105 2010 2 5 10.1103/PhysRevLett.105.136805
10 Wilson J.A. Di Salvo F.J. Mahajan S. Charge-density waves and superlattices in the metallic layered transition metal dichalcogenides Adv. Phys. X. 50 2001 1171 1248 10.1080/00018730110102718
11 Xing Y. Zhao K. Shan P. Zheng F. Zhang Y. Fu H. Liu Y. Tian M. Xi C. Liu H. Ising superconductivity and quantum phase transition in macro-size monolayer NbSe2 Nano Lett. 17 2017 6802 6807 10.1021/acs.nanolett.7b03026 28967758
12 Josephson B.D. Possible new effects in superconductive tunnelling Phys. Lett. 1 1962 251 253 10.1016/0031-9163(62)91369-0
13 Martinis J.M. Devoret M.H. Clarke J. Quantum Josephson junction circuits and the dawn of artificial atoms Nat. Phys. 16 2020 234 237 10.1038/s41567-020-0829-5
14 Kaul A.B. Whiteley S.R. Van Duzer T. Yu L. Newman N. Rowell J.M. Internally shunted sputtered NbN Josephson junctions with a TaNx barrier for nonlatching logic applications Appl. Phys. Lett. 78 2001 99 101 10.1063/1.1337630
15 Kaul A.B. Bumble B. Lee K.A. LeDuc H.G. Rice F. Zmuidzinas J. Fabrication of wide-IF 200-300 GHz superconductor-insulator-superconductor mixers with suspended metal beam leads formed on silicon-on-insulator J. Vac. Sci. Technol. B Microelectron. Nanom. Struct. 22 2004 2417 2422 10.1116/1.1798831
16 Harris R. Johnson M.W. Han S. Berkley A.J. Johansson J. Bunyk P. Ladizinsky E. Govorkov S. Thom M.C. Uchaikin S. Probing noise in flux qubits via macroscopic resonant tunneling Phys. Rev. Lett. 101 2008 117003 10.1103/PhysRevLett.101.117003 18851318
17 Wang H. Guo J. Miao J. Luo W. Gu Y. Xie R. Wang F. Zhang L. Wang P. Hu W. Emerging Single-Photon Detectors Based on Low-Dimensional Materials Small 18 2022 2103963 10.1002/smll.202103963
18 Zmuidzinas J. Richards P.L. Superconducting detectors and mixers for millimeter and submillimeter astrophysics Proc. IEEE 92 2004 1597 1616 10.1109/JPROC.2004.833670
19 Bacrania M.K. Hoover A.S. Karpius P.J. Rabin M.W. Rudy C.R. Vo D.T. Beall J.A. Bennett D.A. Doriese W.B. Hilton G.C. Large-area microcalorimeter detectors for ultra-high-resolution x-ray and gamma-ray spectroscopy IEEE Trans. Nucl. Sci. 56 2009 2299 2302
20 Irwin K.D. An application of electrothermal feedback for high resolution cryogenic particle detection Appl. Phys. Lett. 66 1995 1998 2000 10.1063/1.113674
21 Hadfield R.H. Johansson G. Superconducting Devices in Quantum Optics 2016 Springer International Publishing 31 60 10.1007/978-3-319-24091-6
22 Giustina M. Versteegh M.A.M. Wengerowsky S. Handsteiner J. Hochrainer A. Phelan K. Steinlechner F. Kofler J. Larsson J.Å. Abellán C. Significant-Loophole-Free Test of Bell’s Theorem with Entangled Photons Phys. Rev. Lett. 115 2015 250401 10.1103/PhysRevLett.115.250401
23 den Hartog R. Barret D. Gottardi L. den Herder J.-W. Jackson B. de Korte P. van der Kuur J. van Leeuwen B.-J. van Loon D. Nieuwenhuizen A. Requirements for the detectors and read-out of ATHENA X-IFU Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray 2014 International Society for Optics and Photonics 91445Q 10.15407/spqeo15.03.193
24 Ruhl J. Ade P.A.R. Carlstrom J.E. Cho H.-M. Crawford T. Dobbs M. Greer C.H. Halverson N.w. Holzapfel W.L. Lanting T.M. The South Pole Telescope Proc.SPIE 5498 2004 SPIE 11 29 10.1117/12.552473
25 Betancourt-Martinez G.L. Adams J. Bandler S. Beiersdorfer P. Brown G. Chervenak J. Doriese R. Eckart M. Irwin K. Kelley R. The transition-edge EBIT microcalorimeter spectrometer Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray 2014 International Society for Optics and Photonics 91443U
26 De Graauw T. Helmich F.P. Phillips T.G. Stutzki J. Caux E. Whyborn N.D. Dieleman P. Roelfsema P.R. Aarts H. Assendorp R. The Herschel-heterodyne instrument for the far-infrared (HIFI) Astron. Astrophys. 518 2010 L6
27 Zmuidzinas J. Superconducting Microresonators: Physics and Applications Annu. Rev. Condens. Matter Phys. 3 2012 169 214 10.1146/annurev-conmatphys-020911-125022
28 Polakovic T. Armstrong W. Karapetrov G. Meziani Z.-E. Novosad V. Unconventional Applications of Superconducting Nanowire Single Photon Detectors Nanomaterials 10 2020 1198 10.3390/nano10061198
29 Bock J. Day P. Goldin A. LeDuc H.G. Hunt C. Lange A. Vayonakis A. Zmuidzinas J. Antenna-coupled bolometer array for astrophysics Proc. Far-IR, Sub-MM, MM Detect. Work 2002 224 229
30 Richards P.L. Bolometers for infrared and millimeter waves J. Appl. Phys. 76 1994 1 24 10.1063/1.357128
31 Morozov D.V. Casaburi A. Hadfield R.H. Superconducting photon detectors Contemp. Phys. 62 2021 69 91 10.1080/00107514.2022.2043596
32 Bleem L. Ade P. Aird K. Austermann J. Beall J. Becker D. Benson B. Britton J. Carlstrom J. Chang C.L. An Overview of the SPTpol Experiment J. Low Temp. Phys. 167 2012 859 864 10.1007/s10909-012-0505-y
33 Gershenzon E.M. Gol’Tsman G.N. Gousev Y.P. Elant’ev A.I. Semenov A.D. Electromagnetic radiation mixer based on electron heating in resistive state of superconductive Nb and YBaCuO films IEEE Trans. Magn. 27 1991 1317 1320
34 Gol’tsman G.N. Karasik B.S. Okunev O.V. Dzardanov A.L. Gershenzon E.M. Ekstrom H. Jacobsson S. Kollberg E. NbN hot electron superconducting mixers for 100 GHz operation IEEE Trans. Appl. Supercond. 5 1995 3065 3068
35 Raasch J. Szwaj C. Thoma P. Zen H. Konomi T. Scheuring A. Siegel M. Ilin K. Hosaka M. Holzapfel B. Electrical field sensitive high-Tc YBCO detector for real-time observation of CSR Proc. IPAC 2014 1 4
36 Bevilacqua S. Novoselov E. Cherednichenko S. Shibata H. Tokura Y. MgB2 Hot-Electron Bolometer Mixers at Terahertz Frequencies IEEE Trans. Appl. Supercond. 25 2014 1 4 32863691
37 de la Barrera S.C. Sinko M.R. Gopalan D.P. Sivadas N. Seyler K.L. Watanabe K. Taniguchi T. Tsen A.W. Xu X. Xiao D. Hunt B.M. Tuning Ising superconductivity with layer and spin–orbit coupling in two-dimensional transition-metal dichalcogenides Nat. Commun. 9 2018 1427 10.1038/s41467-018-03888-4 29650994
38 Xi X. Berger H. Forró L. Shan J. Mak K.F. Gate Tuning of Electronic Phase Transitions in Two-Dimensional ${\mathrm{NbSe}}_{2 Phys. Rev. Lett. 117 2016 106801 10.1103/PhysRevLett.117.106801
39 Choi S.H. Yun S.J. Won Y.S. Oh C.S. Kim S.M. Kim K.K. Lee Y.H. Large-scale synthesis of graphene and other 2D materials towards industrialization Nat. Commun. 13 2022 1484 10.1038/s41467-022-29182-y 35304474
40 Shen P.-C. Lin Y. Wang H. Park J.-H. Leong W.S. Lu A.-Y. Palacios T. Kong J. CVD Technology for 2-D Materials IEEE Trans. Electron. Dev. 65 2018 4040 4052 10.1109/TED.2018.2866390
41 Wang H. Huang X. Lin J. Cui J. Chen Y. Zhu C. Liu F. Zeng Q. Zhou J. Yu P. High-quality monolayer superconductor NbSe2 grown by chemical vapour deposition Nat. Commun. 8 2017 394 398 10.1038/s41467-017-00427-5 28855521
42 Lin H. Chang M. Fu X. Li P. Chen M. Wu L. Yang F. Zhang Q. Tunability of the Superconductivity of NbSe(2) Films Grown by Two-Step Vapor Deposition Molecules 28 2023 1059 10.3390/molecules28031059
43 Zou Y.-C. Chen Z.-G. Zhang E. Xiu F. Matsumura S. Yang L. Hong M. Zou J. Superconductivity and magnetotransport of single-crystalline NbSe2 nanoplates grown by chemical vapour deposition Nanoscale 9 2017 16591 16595 10.1039/C7NR06617A 29068033
44 Lide D.R. CRC Handbook of Chemistry and Physics 2004 CRC press
45 Mkrtchyan V. Kumar R. White M. Yanxon H. Cornelius A. Effect of pressure on crystal structure and superconductivity of NbSexTe2−x (x = 2, 1.5) Chem. Phys. Lett. 692 2018 249 252 10.1016/j.cplett.2017.12.042
46 Hopcroft M.A. Nix W.D. Kenny T.W. What is the Young’s Modulus of Silicon? J. Microelectromech. Syst. 19 2010 229 238 10.1109/JMEMS.2009.2039697
47 Wilson J.A. Yoffe A.D. The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties Adv. Phys. X. 18 1969 193 335 10.1080/00018736900101307
48 Xi X. Wang Z. Zhao W. Park J.-H. Law K.T. Berger H. Forró L. Shan J. Mak K.F. Ising pairing in superconducting NbSe2 atomic layers Nat. Phys. 12 2016 139 143 10.1038/nphys3538
49 Pereira C.M. Liang W.Y. Raman studies of the normal phase of 2H-NbSe2 J. Phys. C Solid State Phys. 15 1982 L991 L995 10.1088/0022-3719/15/27/009
50 Hill H.M. Rigosi A.F. Krylyuk S. Tian J. Nguyen N.V. Davydov A.V. Newell D.B. Walker A.R.H. Comprehensive optical characterization of atomically thin NbSe2 Phys. Rev. B 98 2018 165109 10.1103/PhysRevB.98.165109
51 Tsang J.C. Smith J.E. Shafer M.W. Raman Spectroscopy of Soft Modes at the Charge-Density-Wave Phase Transition in 2H-NbSe2 Phys. Rev. Lett. 37 1976 1407 1410 10.1103/PhysRevLett.37.1407
52 Pawbake A.S. Pawar M.S. Jadkar S.R. Late D.J. Large area chemical vapor deposition of monolayer transition metal dichalcogenides and their temperature dependent Raman spectroscopy studies Nanoscale 8 2016 3008 3018 26782944
53 Herchen H. Cappelli M.A. First-order Raman spectrum of diamond at high temperatures Phys. Rev. B 43 1991 11740 11744 10.1103/PhysRevB.43.11740
54 Huang X. Gao Y. Yang T. Ren W. Cheng H.-M. Lai T. Quantitative Analysis of Temperature Dependence of Raman shift of monolayer WS2 Sci. Rep. 6 2016 32236 10.1038/srep32236
55 Sahoo S. Gaur A.P.S. Ahmadi M. Guinel M.J.F. Katiyar R.S. Temperature-dependent Raman studies and thermal conductivity of few-layer MoS2 J. Phys. Chem. C 117 2013 9042 9047 10.1021/jp402509w
56 Lioi D.B. Gosztola D.J. Wiederrecht G.P. Karapetrov G. Photon-induced selenium migration in TiSe2 Appl. Phys. Lett. 110 2017 81901
57 Xi X. Zhao L. Wang Z. Berger H. Forró L. Shan J. Mak K.F. Strongly enhanced charge-density-wave order in monolayer NbSe2 Nat. Nanotechnol. 10 2015 765 769 10.1038/nnano.2015.143 26192206
58 Méasson M.-A. Gallais Y. Cazayous M. Clair B. Rodière P. Cario L. Sacuto A. Amplitude Higgs mode in the $2H\ensuremath{-}{\text{NbSe}}_{2}$ superconductor Phys. Rev. B 89 2014 60503 10.1103/PhysRevB.89.060503
59 Che J. Çagin T. Goddard W.A. III Thermal conductivity of carbon nanotubes Nanotechnology 11 2000 65 69 10.1088/0957-4484/11/2/305
60 Balandin A.A. Ghosh S. Bao W. Calizo I. Teweldebrhan D. Miao F. Lau C.N. Superior Thermal Conductivity of Single-Layer Graphene Nano Lett. 8 2008 902 907 10.1021/nl0731872 18284217
61 Roeske F. Shanks H.R. Finnemore D.K. Superconducting- and normal-state thermal conductivity of Nb${\mathrm{Se}}_{2 Phys. Rev. B 16 1977 3929 3935 10.1103/PhysRevB.16.3929
62 Nguyen L. Komsa H.-P. Khestanova E. Kashtiban R.J. Peters J.J.P. Lawlor S. Sanchez A.M. Sloan J. Gorbachev R.V. Grigorieva I.V. Atomic Defects and Doping of Monolayer NbSe2 ACS Nano 11 2017 2894 2904 10.1021/acsnano.6b08036 28195699
63 Li Z. Xi X. Ding B. Li H. Liu E. Yao Y. Wang W. Thermodynamics and Kinetics Synergy for Controlled Synthesis of 2D van der Waals Single-Crystal NbSe2 via Modified Chemical Vapor Transport Cryst. Growth Des. 20 2020 706 712 10.1021/acs.cgd.9b01131
64 Zhang X. Qiao X.-F. Shi W. Wu J.-B. Jiang D.-S. Tan P.-H. Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer{,} multilayer to bulk material Chem. Soc. Rev. 44 2015 2757 2785 10.1039/C4CS00282B 25679474
65 El-Bana M.S. Wolverson D. Russo S. Balakrishnan G. Paul D.M. Bending S.J. Superconductivity in two-dimensional NbSe2 field effect transistors Supercond. Sci. Technol. 26 2013 125020 10.1088/0953-2048/26/12/125020
66 Orchin G.J. De Fazio D. Di Bernardo A. Hamer M. Yoon D. Cadore A.R. Goykhman I. Watanabe K. Taniguchi T. Robinson J.W.A. Niobium diselenide superconducting photodetectors Appl. Phys. Lett. 114 2019 251103 10.1063/1.5097389
67 Benford D.J. Chervenak J.A. Irwin K.D. Moseley Jr S.H. Shafer R.A. Staguhn J.G. Wollack E. Superconducting Bolometer Array Architectures Millim. Submillim. Detect. Astron. 4855 2003 148 10.1117/12.459423
68 Lolli L. Taralli E. Portesi C. Rajteri M. Monticone E. Aluminum–Titanium Bilayer for Near-Infrared Transition Edge Sensors Sensors 16 2016 953 10.3390/s16070953
69 Nagler P.C. Sadleir J.E. Wollack E.J. Transition-edge sensor detectors for the Origins Space Telescope J. Astronomical Telesc. Instrum. Syst. 7 2021 1 18 10.1117/1.JATIS.7.1.011005
70 Liang W.Y. Optical anisotropy in layer compounds J. Phys. C Solid State Phys. 6 1973 551 565 10.1088/0022-3719/6/3/018
71 Hill H.M. Rigosi A.F. Krylyuk S. Tian J. Nguyen N.V. Davydov A.V. Newell D.B. Walker A.R.H. Comprehensive optical characterization of atomically thin NbSe2 Phys. Rev. B 98 2018 165109 10.1103/PhysRevB.98.165109
72 Thompson J.C. Younglove B.A. Thermal conductivity of silicon at low temperatures J. Phys. Chem. Solid. 20 1961 146 149 10.1016/0022-3697(61)90146-9
73 Dvir T. Massee F. Attias L. Khodas M. Aprili M. Quay C.H.L. Steinberg H. Spectroscopy of bulk and few-layer superconducting NbSe2 with van der Waals tunnel junctions Nat. Commun. 9 2018 598 10.1038/s41467-018-03000-w 29426840
74 Khestanova E. Birkbeck J. Zhu M. Cao Y. Yu G.L. Ghazaryan D. Yin J. Berger H. Forró L. Taniguchi T. Unusual Suppression of the Superconducting Energy Gap and Critical Temperature in Atomically Thin NbSe2 Nano Lett. 18 2018 2623 2629 10.1021/acs.nanolett.8b00443 29529377
75 Lin H. Zhu Q. Shu D. Lin D. Xu J. Huang X. Shi W. Xi X. Wang J. Gao L. Growth of environmentally stable transition metal selenide films Nat. Mater. 18 2019 602 607 10.1038/s41563-019-0321-8 30858568
