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Digital image correlation (DIC) technology can capture strain anomalies and predict crack initiation providing early warning of material failure. Herein, DIC technique is used to calculate the full‐field strain by analyzing the grayscale patterns of speckle images during the tensile process. This allowed for an analysis of the microstructure evolution of the 316LN austenitic stainless steel (SS) at cryogenic temperatures. Deformation behavior of the 316LN SS at cryogenic temperatures is further analyzed using electron backscatter diffraction technology and transmission electron microscopy. Based on the strain field obtained by the DIC technique, a comprehensive analysis of the martensite volume fraction at different strains can be conducted. The results show that the strain localization under cryogenic deformation is related to martensitic transformation, while the random distribution of slip bands aligns with local strain peak values. Notably, fracture under cryogenic deformation occurs in regions where the strain field reaches its peak, rather than at locations with the maximum strain value. [ABSTRACT FROM AUTHOR]

This work reports on the possibility of sustaining a stable operation of polarization-doped InGaN light emitters over a particularly broad temperature range. We obtained efficient emission from InGaN light-emitting diodes between 20 K and 295 K and from laser diodes between 77 K and 295 K under continuous wave operation. The main part of the p-type layers was fabricated from composition-graded AlGaN. To optimize injection efficiency and improve contact resistance, we introduced thin Mg-doped layers of GaN (subcontact) and AlGaN (electron blocking layer in the case of laser diodes). In the case of LEDs, the optical emission efficiency at low temperatures seems to be limited by electron overshooting through the quantum wells. For laser diodes, a limiting factor is the freeze-out of the magnesium-doped electron blocking layer for temperatures below 160 K. The GaN:Mg subcontact layer works satisfyingly even at the lowest operating temperature (20 K). [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) from semiconductor-based substrates is often limited by its low enhancement factor (EF). Here, we demonstrate the ultrahigh SERS sensitivity of defect-engineered Nb2O5 nanoparticles through cryogenic temperature measurements. High-energy ball milling was used to produce Nb2O5 nanoparticles with abundant surface defects, specifically oxygen vacancy defects. Owing to these oxygen vacancy defects, these nanoparticles show extraordinary SERS sensitivity toward the detection of methylene blue (MeB) dye as well as other cationic dye molecules such as malachite green (MG) and crystal violet (CV). Further, reducing the substrate temperature to a cryogenic regime (77 K) greatly enhances the photoinduced charge transfer (PICT) efficiency by lowering the phonon-assisted recombination rate, which in turn amplifies the SERS signal by almost 2.5 times. By reducing the lattice thermal vibrations at sufficiently low temperatures, the defect states are populated with a large number of photoinduced electrons, which is reflected in the massive increase in the intensity of the photoluminescence (PL) signal. With this remarkable enhancement, we have detected down to 10–8 M of MeB with an extraordinary SERS EF of 8.38 × 107, which is exceptional for a semiconductor-based SERS substrate. Additionally, other cationic dye molecules (MG, CV) and some volatile organic compounds (VOCs) also exhibited significant enhancement. Further, with the aid of density functional theory (DFT) calculations and finite element method (FEM) based simulations, we sought to investigate the individual contributions of the chemical and electromagnetic enhancement mechanisms to the overall SERS enhancement. These findings are crucial for developing metal-free, high-efficiency SERS substrates. [ABSTRACT FROM AUTHOR]

Consideration is given to the method of parametric identification of a symmetric thermal-conductivity tensor for a cryogenic nitrogen thermal protection thermostatting an aluminum skeleton of a cylindrical nitrogen-filled vessel. This problem is solved as the problem of seeking the global minimum of the root-mean-square residual functional between the theoretical field of temperatures and the registered maximum thermal-protection temperature. To this end, it is necessary to solve the "primal" problem of heat transfer between the thermal protective coating with a selected initial approximation of components of the thermal-conductivity vector and their basis functions taking account of their dependence on temperature. The method of conjugate directions has been selected as the most accurate optimization method of first order of convergence. To implement this method, it is necessary to find components of the gradient of the residual functional under study. The descent step in this method is sought from the minimum of the target functional at each computational iteration, which corresponds to the iterative regularization method. A criterion for the cessation of the iterative process is the superposition of errors that introduce ill-posedness into the formulation of the problem under study. [ABSTRACT FROM AUTHOR]

The application of terahertz (THz) science in industrial technology and scientific research requires efficient THz detectors. Such detectors should be able to operate under various external conditions and conform to existing geometric constraints in the required application. Pyroelectric THz detectors are among the best candidates. This is due to their versatility, outstanding performance, ease of fabrication, and robustness. In this paper, we propose a compact pyroelectric detector based on a bioriented poled polyvinylidene difluoride film coated with sputtered metal electrodes for in situ absorption measurement at cryogenic temperature. The detector design was optimized for the registration system of the electron paramagnetic resonance (EPR) endstation of the Novosibirsk Free Electron Laser facility. Measurements of the detector response to pulsed THz radiation at different temperatures and electrode materials showed that the response varies with both the temperature and the type of electrode material used. The maximum signal level corresponds to the temperature range of 10–40 K, in which the pyroelectric coefficient of the PVDF film also has a maximum value. Among the three coatings studied, namely indium tin oxide (ITO), Au, and Cu/Ni, the latter has the highest increase in sensitivity at low temperature. The possibility of using the detectors for in situ absorption measurement was exemplified using two typical molecular spin systems, which exhibited a transparency of 20–30% at 76.9 cm−1 and 5 K. Such measurements, carried out directly in the cryostat with the main recording system and sample fully configured, allow precise control of the THz radiation parameters at the EPR endstation. [ABSTRACT FROM AUTHOR]

This study investigates the strain rate-dependent deformation behavior of cost-effective twinning-induced plasticity (TWIP) steel, Fe–26Mn-0.4C, at 15 K and reveals intriguing insights into its mechanical properties. The serration type changes from type A to type C with decreasing strain rate, resulting in a quasi-cleavage fracture at the crack initiation site. Microstructural analysis unveils a correlation between strain rate and the evolution of bundle twins, nano-twins, and ε-martensites. These denser networks of deformation twins (DTs) and ε-martensites contribute to impacting the mechanical properties. The mechanism behind the formation of serrations involves a rate-dependent thermal instability effect and the intricate interactions between dislocations and dislocations/Mn–C couples. The distinct findings enhance our understanding of the complex deformation behavior of high-Mn steel at cryogenic temperatures and provide valuable insights into the broader field of high-Mn steel applications in dynamic environments.

In this study, the microstructure evolution and aging behavior of surface-nanocrystallized WE43 Mg alloy induced by ultrasonic shot peening at a cryogenic temperature were examined. The results reveal that the original coarse grains with an average grain size of 46.7 μm were refined to nanocrystalline grains with 31.5 nm in the nanocrystalline region, demonstrating a marked grain refinement effect. After aging treatment, the nanocrystalline region experienced two aging stages. During Stage Ⅰ, there was a rapid increase in hardness, and in Stage Ⅱ, it reached a maximum of 154.2 HV, representing a 105.6% improvement over the solution-treated alloy. Further microstructural characterization indicates that solute segregation initially occurred along the grain boundaries, leading to a rapid increase in hardness during Stage Ⅰ. Subsequently, two types of precipitates were observed both at the grain boundaries and within the grains during Stage Ⅱ, with the combined effects of solute segregation and precipitation contributing to a further increase in hardness.

This study investigates the impact of rare elements on high-entropy alloys (HEAs) and provides significant insights. By integrating varying proportions of Al-Nd and Al-Ce compounds into a CoCrFeNi-based alloy, shifts were detected in the microstructure and phase composition of grains. As the proportion of rare elements rose, their localization within the grain phase structure intensified, leading to overall coarsening. The heat transfer characteristics of HEA alloys containing rare elements exhibited variability, with notable phase transitions occurring at cryogenic temperatures based on the alloying constituents. Among the tested alloys, Ce10 and Ce20 alloys demonstrated the highest heat transfer rates (800 Wg − 1 ). Notably, an escalation in the rare element ratio added to the alloy resulted in a significant augmentation in hardness, nearly doubling the original level. [ABSTRACT FROM AUTHOR]

The deformation behavior of the pure aluminum has been studied at 298 K and 77 K to elucidate the mechanism for dual-enhancement effect at cryogenic temperature. The results reveal that as the deformation temperature decreases from 298 K to 77 K, the tensile strength and elongation increase from 67.9 MPa to 49.1% to 142.4 MPa and 61.9%, respectively. The simultaneous increase in strength and ductility at 77 K is attributed to the higher strain hardening rate and more uniform deformation at cryogenic temperature. Results obtained from quasi in-situ EBSD indicate that at cryogenic temperatures, there is a higher density of dislocations that are uniformly distributed within the grains. It helps alleviate dislocation pile-ups and reduces the likelihood of crack initiation at grain boundaries. Moreover, a significant number of grains align their orientation rotation towards at cryogenic temperature. Multiple fine slip systems initiate within these grains, contributing to improved mechanical properties in pure aluminum. In contrast, samples deformed at 298 K exhibit localized strain during deformation, with the initiation of unfavorable, non-uniform coarse slip bands within the grains. The findings of this study offer insights into the mechanisms of the dual-enhancement effect in pure aluminum at cryogenic temperatures.

Monolayers of transition metal dichalcogenides (TMDCs) demonstrate plenty of unique properties due to the band structure. Symmetry breaking brings second-order susceptibility to meaningful values resulting in the enhancement of corresponding nonlinear effects. Cooling the TMDC films to cryogenic temperatures leads to the emergence of two distinct photoluminescence peaks caused by the exciton and trion formation. These intrinsic excitations are known to enhance second harmonic generation. The nonlinear signal can be greatly increased if these material resonances are boosted by high-quality factor geometric resonance of all-dielectric metasurfaces. Here, we experimentally observe optical second harmonic generation caused by excitons of 2D semiconductor MoSe2 at room and cryogenic temperatures enhanced by spectrally overlapped high-Q resonance of TiO2 nanodisks metasurface. The enhancement reaches two orders of magnitude compared to the case when the resonances are not spectrally overlapped.

An accurate determination of minimum ignition energy (MIE) is essential for assessing electrostatic hazards and characterising potential for occurrence of combustion in flammable mixtures. This is of utmost importance for hydrogen-air mixtures characterised by a MIE equal to 0.017 mJ, whereas conventional flammable gases are characterised by MIE typically higher than 0.1 mJ. The study aims at developing and validating a CFD three-dimensional model capable to simulate complex unsteady physical and chemical phenomena underlying capacitive discharge spark. The model accounts for the experimental apparatus details, including the effect of electrodes' gap and associated heat losses. The numerical approach accurately reproduced the experimental measurements of MIE for mixtures of hydrogen with air at initial temperature ranging from ambient (T = 288 K) to cryogenic (T = 123 K). Hydrogen concentration in air was included in the range 10–55% for tests at T = 288 K, and 20–60% for tests at T = 173 K and 123 K respectively. Simulations assess the impact of experimental characteristics and design, such as the electrodes' dimension, and numerical features on process dynamics, growth of the flame kernel and MIE predictions. • Development of a CFD 3D model simulating the phenomena underlying a discharge spark. • Inclusion of effect of conductive and radiative heat losses on the MIE predictions. • Validation against tests on H 2 -air mixtures at ambient and cryogenic temperatures. • Simulations provide insights into the process dynamics and flame kernel development. [ABSTRACT FROM AUTHOR]

This experimental study delves into the intricate mechanics of stress concentration and fatigue behavior exhibited by 9% Ni steel welded joints under cryogenic conditions. The study specifically examines butt-welded, fillet longitudinal, and fillet transverse specimens, comparing their fatigue properties under room and cryogenic temperatures. Notably, determining hot-spot stress presents a challenge, as it cannot be directly obtained through traditional means. To overcome this limitation, a method for predicting hot-spot stress is introduced, which considers the effects of misalignments and weld bead characteristics. The study also highlights the impact of grip-clamping-induced specimen deformation and the reduced middle section on stress concentration resulting from misalignments. Furthermore, it proposes separate consideration of the effects of the weld bead on the axial nominal stress and on the bending stress of the specimen. The accuracy of strain gauge measurements in cryogenic environments is addressed by suggesting a method to correct the output of 2-wire strain gauges using a fixed ratio derived from 2-wire and 3-wire strain gauges. By comparing predicted hot-spot stress with actual measurements, the study validates the reliability of the proposed predictive method. These findings contribute to a deeper understanding of the behavior of 9% Ni steel welded joints under cryogenic conditions and provide valuable insights for design and engineering in similar applications. [ABSTRACT FROM AUTHOR]

Comprehending the mechanical response of materials on an atomic level is pivotal in the optimisation of advanced materials with superior mechanical properties. This research article utilises the atomistic-scale based molecular dynamics simulations to report the uniaxial tensile behaviour of bicrystalline Ni-6Cu (Nickel – 94% and Copper – 6%) alloy incorporated with pre-existing faceted Σ3 [111] 60° {11 8 5} grain boundaries. The primary aim of this investigation is to comprehend the performance of bicrystalline Ni-6Cu alloy under varying thermodynamic conditions and to assess the influence of pre-existing faceted grain boundaries on its tensile behaviour. This work encompasses a range of strain rates (108 to 1010 1/s) and temperatures (spanning from 100 to 900 K) for the uniaxial tensile deformation simulations. The outcomes unveil that the Young's modulus of Ni-6Cu alloy (with pre-existing faceted grain boundaries embedded in its domain) was inversely proportional to temperature and constant with respect to strain rate. For the same configuration, yield stress was inversely and directly proportional to temperature and strain rate, respectively. Interestingly, incipient plasticity in the tensile stress–strain response was observed at lower temperature and lower strain rate. From the microstructural point of view, at lower temperatures, the incoherent twin boundary served as a source for the nucleation of stacking faults; however, as the temperature increased, both the incoherent twin boundary and the tips of coherent twin boundary function as the source for stacking faults formation. Our simulations also verified the GB's anti-thermal (or non-Arrhenius) migration behaviour even under tensile load. [ABSTRACT FROM AUTHOR]

The mechanical properties of a fine-grained (FG) Ti-6Al-4V extra-low interstitial (ELI) alloy were investigated by tensile tests at 298 K and 77 K. The experimental results indicated that, at 77 K, the alloy exhibits a small uniform elongation of 2.65%, but has a fracture elongation of 19.2%, showing superior post-necking elongation. At 298 K, the alloy displays a single dislocation slipping, β→α″ phase transformation occurred, and 6.35% uniform elongation was obtained, whereas the coupling of dislocation slipping and twinning deformation behaviors dominated at 77 K. The limited uniform elongation is attributed to the absence of martensite phase transformation at 77 K, whereas the decent fracture elongation is ascribed to the resistance offered by twinning against plastic instability. [ABSTRACT FROM AUTHOR]

In pursuit of a fourth-generation electron cyclotron resonance (ECR) source, a powerful Nb3Sn superconducting magnet system employing a sextupole-in-solenoid configuration has been recently developed at the Institute of Modern Physics (IMP) in Lanzhou, China. These superconducting magnets operate under extreme conditions, experiencing high magnetic fields, cryogenic temperatures, and mechanical stresses. Understanding their stress/strain behaviors, therefore, is of utmost importance to ensure reliable operation and optimal performance. However, the conventional single-point strain gauges commonly exhibit certain limitations that pose challenges in measuring global strain within complex and larger structures. The presence of substantial electromagnetic interference further exacerbates the difficulty in obtaining accurate strain measurements. To address these challenges, a novel approach was undertaken in this study to develop a distributed real-time strain monitoring system specifically designed for the sextupole superconducting magnets, which is based on optical frequency domain reflectometry (OFDR) combined with high spatial resolution distributed optical fiber technology. The strain profile and evolution of the magnets system have been comprehensively monitored throughout the entire operational process, including assembly, cooling down, excitation, and quenching stages. Consequently, valuable insights into the global strain characteristics of the superconducting magnets have been attained, revealing intriguing features such as asymmetrical distribution and extreme values. The development of this distributed real-time strain monitoring system represents a notable advancement in the field of superconducting magnet technology. [ABSTRACT FROM AUTHOR]

This paper investigates the mechanical response and the mechanisms of failure of an ultra-high molecular weight polyethylene under service at cryogenic temperature. The service temperature T s being about 50 ∘ C below its glass transition temperature T g , the study focuses on the experimental techniques to determine both the glass transition temperature T g and the ductile–brittle transition temperature (DBTT). T g was estimated by dynamic mechanical thermal analysis (DTMA) and contrasted with the glassy–rubbery transition defined by using the Young's modulus issued from monotonic tensile tests on smooth specimens at room and low temperature and various cross-head speeds. Concerning the DBTT, two estimators of the transition, based on the fracture surface and the up-to-failure data, were studied. An operating diagram (temperature/cross-head speed) including the probability of ductile failure and both the rubbery and glassy domains is proposed. This diagram aims at finding an optimal compromise of the material response combining stiff versus soft with brittle versus ductile behaviour. [ABSTRACT FROM AUTHOR]

The CrCoNiSi0.3 MEA exhibits excellent cryogenic mechanical properties upon both quasi-static and dynamic tension. Under quasi-static tension at cryogenic temperature, the engineering yield and ultimate tensile strengths (UTS) reach 980 MPa and 1800 MPa, respectively, with notable ductility (62 %). The product of UTS and total elongation (TE) is 111.6 GPa %, surpassing most cryogenic high strength-ductility alloys. The significant mechanical strength enhancement is attributed to the denser deformation twins (DTs), multiple twinning, and extensive face-centered-cubic to hexagonal-close-packed (HCP) phase transitions, resulting in a high work hardening capacity. Upon dynamic tension at cryogenic temperature, the strength and strain hardening are further improved, which originates from the thickening DTs and HCP sequence and localized plastic deformation. The effects of temperature and strain rate on phase transition are studied. It is proposed that there is a competing relationship between high strain rate and increased stacking fault energy (SFE) due to temperature rise. The coupling effect of cryogenic temperature and high strain rate inhibits phase transition due to the deformation inhomogeneity in CrCoNiSi0.3 MEA. The findings make a valuable contribution to understand the influence of temperature and strain rate on the mechanism of FCC-to-HCP phase transition.

The dual-graded structure with both gradients of grain size and coherent L12 precipitation was applied to a (CoCrNi)96Al3Ti3 medium-entropy alloy for achieving superior tensile properties. Simultaneous improvement on yield strength and uniform elongation is observed in the dual-graded structure at cryogenic temperature, compared to those at room temperature. Stronger hetero-deformation-induced hardening and higher density of geometrically necessary dislocations are observed at cryogenic temperature in both single-grain-size-graded and dual-graded structures. The hardening mechanisms at room temperature are characterized by low density of deformation twins and stacking faults (SFs) on one slip system, while are dominated by high density SFs at two slip systems and formation of Lomer-Cottrell (L-C) locks at cryogenic temperature for the single-graded structure. The hardening mechanisms at both room and cryogenic temperatures are revealed by high density of SFs and L-C locks in the dual-grade structure. These SFs and L-C locks can provide strong hardening themselves as dynamic Hall-Petch effect on one hand, and can interact with coherent L12 precipitates for intense precipitation hardening on the other hand. The better tensile properties for the dual-graded structure at cryogenic temperature should be attributed to a special SF-induced plasticity, i.e., the formation of SF networks and their interactions with nanoprecipitates.

High-entropy alloys (HEAs) demonstrate superior mechanical properties at room temperature, highlighting potential for engineering applications. With the increasing demand for advanced materials, especially in modern applications facing rigorous conditions, it becomes imperative to gain profound insights into the dynamic behavior of HEAs. In this study, the (FeCoNi)86Al7Ti7 HEA, renowned for exceptional printability and room-temperature mechanical properties, has been fabricated by selective laser melting (SLM), and its tensile and impact behaviors at ambient and cryogenic temperatures are systematically investigated. Experimental results reveal enhanced tensile properties as temperature decreases, achieving a high ultimate strength of 1313.6 MPa and impressive ductility of 24.8 % at 77 K. This improvement is attributed to the synergistic deformation mechanisms, including dislocation slip, stacking faults, Lomer and Lomer-Cottrell locks, which maintain a high strain-hardening rate and thus suppress strain localization. In contrast, impact properties deteriorate due to constrained dislocation mobility at high strain rates and low temperatures, with Charpy impact energy decreasing from 8.1 J at 293 K to 5.1 J at 77 K. Consequently, cracks readily initiate at cellular boundaries or defects, propagating in an intergranular manner and inducing localized deformation. This study provides valuable insights for the future applications of 3D-printed HEAs in extreme operational environments.

In this study, a 1 MW double-rotor flux switching machine is designed for high-power density electric motors in all-electric aircraft. The motor features an air core stator that accommodates armature windings and field coils. Armature conductors utilize aluminum Litz wire at T = 20K, while YBCO superconducting tapes are employed for the field coils operating at T = 20 K. The inner and outer rotors are constructed with laminated Hiperco 50. Most notably, superconducting magnetic shields are positioned between the two rotor teeth to minimize leakage flux and guide magnetizing flux on a pre-determined path. This new motor is shown to have widely superior power density and efficiency. The motor design is evaluated across different pole/slot combinations, revealing that higher pole numbers increase power density. Specifically, a 20-pole/15-slot double rotor flux switching motor with a shield achieves a power density exceeding 100 kW/kg, with efficiency reaching up to 99.5%. This was twice the power density of a comparable design without the shield. The thermal management system has been designed for the proposed motor. The result is a machine that satisfies requirements for electric aviation propulsion applications.

Cryogenic data transfer has numerous applications at 4.2 K for extracting data from supercomputers and quantum computers to address interface bottlenecks. The external modulation of data transmission across temperature zones is achieved through the use of electro-optic modulators. The performance of a thin-film lithium niobate (TFLN) Mach-Zehnder modulator was examined at cryogenic temperatures. Low-frequency measurements indicate that the Vπ (voltage needed for π phase shift) of the modulator increases as the temperature decreases from 298 K to 4.2 K. A comparison was conducted between the readout performance of the electrical wire link and the optical fiber link, spanning from 4.2 K to 298 K. Additionally, high-speed data transmission was successfully demonstrated in a 4.2 K environment without the need for cryogenic electric amplifiers, achieving signals of up to 30 Gbps. The proposed solution holds potential benefits for both classical and quantum computers in alleviating interface bottlenecks.

In this paper, we have investigated the flicker noise (1/ $f$ ) in 45-nm RFSOI NFETs for quantum computing applications. 1/ $f$ noise characterization and analysis were performed in linear region at cryogenic temperatures down to 10K. A Lorentzian-like noise is also observed depending on bias conditions, possibly due to the floating body of PDSOI. The extracted frequency exponent $(\gamma)$ shows an inverted U-shape behavior with temperature mainly attributed to non-uniform energy distribution of traps in the gate dielectric. The dominant source of 1/ $f$ noise is carrier number fluctuation. Thermal-activation behavior of 1/ $f$ noise is studied, which shows the traps responsible for noise are not thermally activated. Volume trap densities are also extracted from 300K down to 10K. The volume trap density increases with a decrease in temperature, but no significant increase in normalized noise is observed at cryogenic temperatures in the measured NFETs. The non-uniform distribution along with the thermal inactive behavior of traps over the studied temperature range is expected to be a plausible reason for the temperature-independent behavior of normalized noise.

This study investigated changes in low-frequency noise sources associated with short-channel bulk metal-oxide-semiconductor field-effect transistors (MOSFETs) by analyzing random telegraph noise (RTN) from 300 K down to 3 K. The power spectral density (PSD) of the drain current, which exhibited RTN characteristics in the frequency domain, changed with temperature. In addition, the effect of temperature on the PSD was not monotonic such that peaks were generated at specific temperatures. A comparison between p-type and n-type MOSFETs established that the former exhibited PSD values nearly an order of magnitude smaller than those of the latter. The PSD peaks observed in the temperature domain were analyzed using a theory based on the Shockley-Read-Hall model and the energy levels of the charge traps responsible for RTN were determined. Assessing the temperatures and corresponding energy levels associated with these PSD peaks showed a trend in which energy levels approached band edges as the temperature was decreased. This study assists in the development of strategies to reduce low-frequency noises generated by cryogenic qubit controllers by elucidating the impact of band-tail states on noises at 4 K.

Abstract In this study, a technique is suggested to enhance the temperature difference for cooling and energy efficiency of thermoelectric cooler (TEC) used in cooled detectors when subjected to high current conditions. Embedding a structure for storing heat during phase change is the basis of this method at the heat sink. A simulation model was created for a common two‐stage series TEC with an asymmetrical design, which is coupled with a structure for storing heat through phase change. The research examined how phase transition heat storage impacts the coefficient of performance (COP) and refrigeration temperature difference across various phase‐change substances, heat transfer coefficients at the hot end, currents, and the height of the phase‐change material (PCM). The findings suggest that the suggested approach of combining PCM with TEC can efficiently lower the cold end temperature of TEC by a maximum of 20 K, enhance the temperature gap by a maximum of 16 K, and preserve the consistency of the optimized quantity across various hot end heat transfer coefficients. During the phase‐change process of PCMs, the COP of TECs integrated with PCM is found to increase by an average of 2%–3% compared to TECs without PCM integration. Under the maximum current operating condition, the cryogenic temperature can be optimized to a minimum of 238 K. In summary, the proposed method of integrating phase‐change heat storage with TECs provides a promising solution for improving their cooling performance and energy efficiency in cooled detectors under high current conditions. Additional investigation can be conducted to explore the practical application of this approach and enhance the design parameters for various uses.

This work reports on the possibility of sustaining a stable operation of polarization-doped InGaN light emitters over a particularly broad temperature range. We obtained efficient emission from InGaN light-emitting diodes between 20 K and 295 K and from laser diodes between 77 K and 295 K under continuous wave operation. The main part of the p-type layers was fabricated from composition-graded AlGaN. To optimize injection efficiency and improve contact resistance, we introduced thin Mg-doped layers of GaN (subcontact) and AlGaN (electron blocking layer in the case of laser diodes). In the case of LEDs, the optical emission efficiency at low temperatures seems to be limited by electron overshooting through the quantum wells. For laser diodes, a limiting factor is the freeze-out of the magnesium-doped electron blocking layer for temperatures below 160 K. The GaN:Mg subcontact layer works satisfyingly even at the lowest operating temperature (20 K).

The application of terahertz (THz) science in industrial technology and scientific research requires efficient THz detectors. Such detectors should be able to operate under various external conditions and conform to existing geometric constraints in the required application. Pyroelectric THz detectors are among the best candidates. This is due to their versatility, outstanding performance, ease of fabrication, and robustness. In this paper, we propose a compact pyroelectric detector based on a bioriented poled polyvinylidene difluoride film coated with sputtered metal electrodes for in situ absorption measurement at cryogenic temperature. The detector design was optimized for the registration system of the electron paramagnetic resonance (EPR) endstation of the Novosibirsk Free Electron Laser facility. Measurements of the detector response to pulsed THz radiation at different temperatures and electrode materials showed that the response varies with both the temperature and the type of electrode material used. The maximum signal level corresponds to the temperature range of 10–40 K, in which the pyroelectric coefficient of the PVDF film also has a maximum value. Among the three coatings studied, namely indium tin oxide (ITO), Au, and Cu/Ni, the latter has the highest increase in sensitivity at low temperature. The possibility of using the detectors for in situ absorption measurement was exemplified using two typical molecular spin systems, which exhibited a transparency of 20–30% at 76.9 cm−1 and 5 K. Such measurements, carried out directly in the cryostat with the main recording system and sample fully configured, allow precise control of the THz radiation parameters at the EPR endstation.

Based on the first-order shear deformation theory (FSDT), the large-amplitude vibration behavior of shallow spherical shells made of functionally graded materials (FGMs) due to the rapid decrease of temperature (cooling shock) is investigated. FGM is assumed to be a mixture of stainless steel and low-carbon steel whose properties are considered temperature dependent and are estimated based on the power-law model. According to FSDT and von Kármán assumptions, the governing equations of motion in conjunction with corresponding boundary conditions are obtained using Hamilton's principle. The temperature distribution is also achieved by means of the 1D Fourier transient heat conduction equation, considering two time-dependent thermal loading scenarios. The considered thermal boundary conditions allow that a temperature difference is created with a time delay for the structure under cooling shock. Also, the results of recent experiments are employed to estimate the temperature-dependent properties of structures. In the solution approach, the generalized differential quadrature method and the Newmark-beta integration scheme are utilized. Selected numerical results are presented to study the effects of thermal load rapidity time, geometry, magnitude of thermal load, and material gradient index on the thermally induced vibrations of spherical shells. Stresses generated in the shell due to the thermally induced vibrations are also investigated. [ABSTRACT FROM AUTHOR]

We have developed a cryogenic characterization platform for ultrafast photodiodes, whose time domain responses are extracted by electro-optic sampling using femtosecond laser pulses in a pump-probe configuration. The excitation of the photodiodes with the pump beam and the electro-optic sampling crystals with the probe beam are realized in a fully fiber-coupled manner. This allows us to use the characterization platform at different temperatures, ranging from cryogenic to room temperature. As an application example, we characterize the time-domain response of commercial p-i-n photodiodes with a nominal bandwidth of 20 GHz and 60 GHz at temperatures of 4 K and 300 K and in a large parameter range of photocurrent and reverse bias. For these photodiodes, we detect frequency components up to approximately 250 GHz, while the theoretical bandwidth of our sampling method exceeds 1 THz. Our measurements demonstrate a significant excitation power and temperature dependence of the photodiodes' ultrafast time responses, reflecting, most likely, changes in carrier mobilities and electric field screening. Since our system is an ideal tool to characterize and optimize the response of fast photodiodes at cryogenic temperatures, it has a direct impact on applications in superconducting quantum technology such as the enhancement of optical links to superconducting qubits and quantum-accurate waveform generators. [ABSTRACT FROM AUTHOR]

[Display omitted] Traditional high strength engineering alloys suffer from serious surface brittleness and inferior wear performance when servicing under sliding contact at cryogenic temperature. Here, we report that the recently emerging CoCrNi multi-principal element alloy defies this trend and presents dramatically enhanced wear resistance when temperature decreases from 273 to 153 K, surpassing those of cryogenic austenitic steels. The temperature-dependent structure characteristics and deformation mechanisms influencing the cryogenic wear resistance of CoCrNi are clarified through microscopic observation and atomistic simulation. It is found that sliding-induced subsurface structures show distinct scenarios at different deformation temperatures. At cryogenic condition, significant grain refinement and a deep plastic zone give rise to an extended microstructural gradient below the surface, which can accommodate massive sliding deformation, in direct contrast to the strain localization and delamination at 273 K. Meanwhile, the temperature-dependent cryogenic deformation mechanisms (stacking fault networks and phase transformation) also provide additional strengthening and toughening of the subsurface material. These features make the CoCrNi alloy particularly wear resistant at cryogenic conditions and an excellent candidate for safety–critical applications. [ABSTRACT FROM AUTHOR]

In this study, a technique is suggested to enhance the temperature difference for cooling and energy efficiency of thermoelectric cooler (TEC) used in cooled detectors when subjected to high current conditions. Embedding a structure for storing heat during phase change is the basis of this method at the heat sink. A simulation model was created for a common two‐stage series TEC with an asymmetrical design, which is coupled with a structure for storing heat through phase change. The research examined how phase transition heat storage impacts the coefficient of performance (COP) and refrigeration temperature difference across various phase‐change substances, heat transfer coefficients at the hot end, currents, and the height of the phase‐change material (PCM). The findings suggest that the suggested approach of combining PCM with TEC can efficiently lower the cold end temperature of TEC by a maximum of 20 K, enhance the temperature gap by a maximum of 16 K, and preserve the consistency of the optimized quantity across various hot end heat transfer coefficients. During the phase‐change process of PCMs, the COP of TECs integrated with PCM is found to increase by an average of 2%–3% compared to TECs without PCM integration. Under the maximum current operating condition, the cryogenic temperature can be optimized to a minimum of 238 K. In summary, the proposed method of integrating phase‐change heat storage with TECs provides a promising solution for improving their cooling performance and energy efficiency in cooled detectors under high current conditions. Additional investigation can be conducted to explore the practical application of this approach and enhance the design parameters for various uses. [ABSTRACT FROM AUTHOR]

In this paper, an analysis of the oxide trapped charge noise in a MOSFET operated down to deep cryogenic temperatures is proposed. To this end, a revisited derivation of the interface trap conductance G p and oxide trapped charge noise S Q t at the SiO2/Si MOS interface is conducted under very low temperature condition, where Fermi–Dirac statistics applies. A new relation between the oxide trapped charge noise S Q t and the interface trap conductance G p is established, showing the inadequacy of the Nyquist relation at very low temperature. Finally, a new formula for the oxide trapped charge 1/f noise, going beyond the classical Boltzmann expression, is developed in terms of oxide trap density and effective temperature accounting for degenerate statistics. [ABSTRACT FROM AUTHOR]

High-precision cryogenic micromechanical testing apparatuses are of significant importance in investigating the micro-region mechanical properties and deformation behaviors of materials at cryogenic temperatures. In this study, a modular cryogenic indentation apparatus was designed and developed utilizing a contact-atmosphere hybrid refrigeration technique with a minimum temperature of −150 °C. The temperature of both the indenter tip and the specimen was independently controlled through a dual-channel proportional–integral–derivative (PID) feedback loop to eliminate contact thermal drift to within 0.1 nm/s. The application of cryogenic nitrogen (N2) atmosphere refrigeration eliminated additional stiffness at the indenter tip completely. The feasibility of the apparatus was demonstrated through calibrations and tests conducted on standard fused silica and single crystal nickel. Highly accurate indentation curves and micro-region mechanical properties of single crystal nickel were obtained at variable cryogenic temperatures. With decreasing temperature, both slip bands and pile-up around residual indentation imprints were weakened. Notably, at −150 °C, the slip bands disappeared, and the phenomenon of pile-up was replaced by sink-in. This developed cryogenic indentation apparatus will be a powerful tool to reveal the effect of cryogenic temperatures on the evolution mechanisms of materials’ micro-region mechanical properties.

This work aims to study the constitutive models and microstructures of a novel high-strength and high-ductility (HSHD) steel under cryogenic temperature. A series of cryogenic tensile tests were conducted using a testing machine equipped with a cryogenic chamber. The results showed that the HSHD steel exhibits an obvious temperature-dependence effect. As the temperature decreased, the yield strength and tensile strength gradually increased, while the uniform elongation increased and then decreased. At a cryogenic temperature of −196 °C, the HSHD steel exhibited significantly enhanced mechanical properties. Specifically, the yield strength, tensile strength, and uniform elongation were 1200 MPa, 1620 MPa, and 30 % respectively. Based on the obtained temperature-dependence effect, the classic Ludwigson constitutive model that all parameters were functions related to temperature was developed and its accuracy was verified through numerical analysis. Furthermore, the microstructure of HSHD steel was investigated during the different deformation stages through microstructure characterization techniques. The excellent cryogenic mechanical properties of HSHD steel stem from the synergic effects of high-density dislocations, denser mechanical twins, and Lomer-Cottrell locks as well as their extensive interactions, rarely observed in their siblings deformed at room temperature. Furthermore, the transformation-induced plasticity (TRIP) effect, which is a significant mechanism for plasticity and favors strain hardening, delays the initiation of necking at −196 °C. These findings reveal the relationship between mechanical behavior and deformation mechanisms in HSHD steel within the low-temperature regime, providing valuable insights for the design of HSHD steel in cryogenic applications.

This experimental study delves into the intricate mechanics of stress concentration and fatigue behavior exhibited by 9% Ni steel welded joints under cryogenic conditions. The study specifically examines butt-welded, fillet longitudinal, and fillet transverse specimens, comparing their fatigue properties under room and cryogenic temperatures. Notably, determining hot-spot stress presents a challenge, as it cannot be directly obtained through traditional means. To overcome this limitation, a method for predicting hot-spot stress is introduced, which considers the effects of misalignments and weld bead characteristics. The study also highlights the impact of grip-clamping-induced specimen deformation and the reduced middle section on stress concentration resulting from misalignments. Furthermore, it proposes separate consideration of the effects of the weld bead on the axial nominal stress and on the bending stress of the specimen. The accuracy of strain gauge measurements in cryogenic environments is addressed by suggesting a method to correct the output of 2-wire strain gauges using a fixed ratio derived from 2-wire and 3-wire strain gauges. By comparing predicted hot-spot stress with actual measurements, the study validates the reliability of the proposed predictive method. These findings contribute to a deeper understanding of the behavior of 9% Ni steel welded joints under cryogenic conditions and provide valuable insights for design and engineering in similar applications.

The alloy 21-6-9 is a nitrogen-strengthened austenitic stainless steel often used in aerospace applications due to its high strength, good fabrication properties, and toughness at cryogenic temperatures. However, minimal research has been conducted on alloy 21-6-9 using the additive manufacturing process laser powder-bed fusion (L-PBF). The L-PBF technique has been seen as a key to reducing production time and avoiding costly machining. Therefore, there is an interest in investigating L-PBF-processed 21-6-9 to determine the effects of L-PBF on properties at elevated and cryogenic temperatures. In this study, prior to tensile testing the alloy 21-6-9 underwent heat treatments that simulated aerospace applications and the alloy was analyzed and characterized to evaluate phase stability. The effects of elevated and cryogenic temperatures (77 K) on the tensile behavior and microstructure were investigated using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The tensile tests showed that the yield strength and ultimate tensile strength improved, while ductility varied depending on the conditions and test environment. The ultimate tensile strength was approximately 80% higher at 77 K than at room temperature, although the elongation decreased by around 90%, possibly due to the formation of strain-induced martensite.

Austenitic stainless steels are widely used in cryogenic pressure vessels, liquefied natural gas pipelines, and offshore transportation liquefied petroleum gas storage tanks due to their excellent mechanical properties at cryogenic temperatures. To meet the lightweight and economical requirements, pre-strain of austenitic stainless steels was conducted to improve the strength at cryogenic temperatures. The essence of being strengthened by strain (strain strengthening) and the phase-transformation mechanism of austenitic stainless steels at cryogenic temperatures are reviewed in this work. The mechanical properties and microstructure evolution of austenitic stainless steels under different temperatures, types, and strain rates are compared. The phase-transformation mechanism of austenitic stainless steels during strain at cryogenic temperatures and its influence on strength and microstructure evolution are summarized. The constitutive models of strain strengthening at cryogenic temperatures were set to calculate the volume fraction of strain-induced martensite and to predict the mechanical properties of austenitic stainless steels. [ABSTRACT FROM AUTHOR]