Device Operating Temperature Research Articles

Probing the limits for coherent optical control of a mechanically decoupled defect center in hexagonal boron nitride

The coherent control of a two-level system is among the most essential challenges in modern quantum optics. Understanding its fundamental limitations is crucial, also for the realization of next generation quantum devices. The quantum coherence of a two-level system is fragile in particular, when the two levels are connected via an optical transition, which, at the same time, enables the manipulation of the system. When such quantum emitters are located in solids the coherence suffers from the interaction of the optical transition with the solid state environment, which requires the sample to be cooled to temperatures of a few Kelvin or below. Here, we use a mechanically isolated quantum emitter in hexagonal boron nitride to explore the individual mechanisms which affect the coherence of an optical transition under resonant drive. We operate the system at the threshold where the mechanical isolation collapses in order to study the onset and temperature-dependence of dephasing and independently of spectral diffusion. The insights on the underlying physical decoherence mechanisms reveal a limit in temperature until which coherent driving of the system is possible. This study enables to increase the operation temperature of hBN-based quantum devices, therefore reducing the need for cryogenic cooling.

Unveiling Energy Conversion Mechanisms and Regulation Strategies in Perovskite Solar Cells.

Despite recent revolutionary advancements in photovoltaic (PV) technology, further improving cell efficiencies toward their Shockley-Queisser (SQ) limits remains challenging due to inherent optical, electrical, and thermal losses. Currently, most research focuses on improving optical and electrical performance through maximizing spectral utilization and suppressing carrier recombination losses, while there is a serious lack of effective opto-electro-thermal coupled management, which, however, is crucial for further improving PV performance and the practical application of PV devices. In this article, the energy conversion and loss processes of a PV device (with a specific focus on perovskite solar cells) are detailed under both steady-state and transient processes through rigorous opto-electro-thermal coupling simulation. By innovatively coupling multi-physical behaviors of photon management, carrier/ion transport, and thermodynamics, it meticulously quantifies and analyzes energy losses across optical, electrical, and thermal domains, identifies heat components amenable to regulation, and proposes specific regulatory means, evaluates their impact on device efficiency and operating temperature, offering valuable insights to advance PV technology for practical applications.

Spintronic device in SWCNT-FET configuration based on chromium oxides thin films consisting of half-metallic ferromagnetic CrO2

Spintronic device architectures consisting of ferromagnetic chromium oxide electrodes in single-walled carbon nanotubes field effect transistor (SWCNT-FET) configuration have been fabricated to act as strategic building blocks for next generation super-compact high-speed nanoelectronic devices for logic and memory operations. Stable thin films of chromium oxides consisting of half-metallic ferromagnetic chromium-di-oxide (CrO2) were pulsed laser deposited (PLD) over lattice-matched rutile-type-tetragonal intermediate TiO2 thin layers over thermally oxidized Si substrates for engineering of the spintronic device structure. Focused ion beam (FIB) milling was applied to the ferromagnetic chromium oxide thin films for patterning of the source (S) and (D) electrodes. Typical electrical characteristics derived by lnρ vs. T−1/2 plots confirmed spin-dependent transport (SDT) as the dominant mechanism of electrical conduction upto temperatures of ∼280 K along with negative magnetoresistance (MR) of ∼30 % at 278 K. Electrical characteristics (output and transfer) of the spintronic device structure were drawn under application of magnetic field (H) in out-of-plane geometry at the temperatures of 5.6 K, 250 K & 300 K. Drain current (Id) is demonstrated to be controlled effectively as a function of gate bias (Vg) for different fixed Vd-biases at all the device operating temperatures. Change in %MR as a function of gate voltage (Vg) was acquired at T = 250 &T = 300 K that displayed higher %MR change under out-of-plane geometry of applied field of 0.75 T of the spintronic device operation.

Smart fin with automatic evaporation and regeneration for thermal management of high heat flux electronics

The high temperature of modern electronic devices poses great challenges to the safety and reliability of applications. Reasonable and effective control of device operating temperature for enhancing device performance and promoting the development of the electronics industry has a positive effect. Here, an innovative and efficient passive cooling technology is proposed to reduce the device temperature using polymerized metal fin and smart hydrogel to form smart fin. The smart fin carries away the waste heat generated by the device through evaporation and regeneration is accomplished by capturing water molecules from the environment. The smart fin is demonstrated to low down the temperature of a heater with heat flux of 2900 W/m2 by 48.3 °C and restores to its initial state after 160 min. At a threshold temperature of 60 °C, it promoted the maximum usage power by 49.4%. The evaporation and regeneration capacity of the smart fin can be controlled by ambient temperature, relative humidity, and smart hydrogel thickness. Specifically, high temperatures promote water evaporation and absorption, high humidity suppresses evaporation but favors absorption, and excessive thickness impedes water transport. This thermal management strategy with simple structure, low-cost, and easy-preparation is expected to become a universal technology in the electronics industry.

A Novel Isolated Gate Driver Power Supply Method for Self-Powered SiC DC Solid-State Switch Using Thermoelectric Generation

DC switches using power electronics technology are increasingly used in dc power systems. Unlike other typical power electronic equipment, it is difficult for the DC switch to acquire energy from the primary circuit in the long-term closure state without d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> or potential difference. As a result, the gate drivers of the devices in DC switches can only be powered from the ground via a complicated and expensive secondary isolation power supply system. This paper proposes a novel isolated gate driver power supply method based on thermoelectric generation for SiC DC switches. By utilizing the unique high operating temperature of wide-bandgap devices, self-power generation can be achieved through the temperature difference between the device and the environment even without d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> or voltage difference. Following the comprehensive integration of the thermoelectric generator and the radiator, a 1.7kV/400A DC switch prototype capable of long-term steady self-power supply is developed, proving the efficacy of the proposed method.

The role of vanadium substitution in the oxygen sublattice disorder of Ba7Nb4MoO20-based hexagonal perovskite oxide-ion conductors.

Ba7Nb4MoO20-based hexagonal perovskite derivatives are promising oxygen-ion conductors for solid electrolytes in solid-oxide fuel cells and electrolysers. A thorough understanding of chemical substitution and its impact on structural features conducive to high ionic conductivity is fundamental for decreasing the operation temperature of such devices. Here, a new 7H polytype-based composition, namely Ba7Nb3.9-x V x Mo1.1O20.05, is investigated to assess the effect of vanadium substitution. Structural changes upon V incorporation are studied using X-ray and neutron diffraction, as well as 51V and 93Nb solid-state nuclear magnetic resonance spectroscopy. For the undoped composition at room temperature, two distinct oxygen sites (O1 and O5) are found along the palmierite-like layer, corresponding to a mix of four- and six-fold coordination for adjacent M2 cations. At high temperature (527 °C), reorganization of oxygen results in the major occupation of O1 and four-fold (tetrahedral) coordination of the M2 cations. The same rearrangement is observed upon V-substitution, but already at room temperature. From 51V NMR, we identified a tetrahedral coordination for V5+ cations, indicating their preferential occupation of the M2 site. This preferential occupation by V5+ cations is correlated with increasing tetrahedral coordination of Nb5+ cations as observed from 93Nb NMR. Altogether, these observations indicate that V-substitution impacts the oxygen sublattice so as to mimic the high-temperature structure. Additionally, BVSE calculations demonstrate a decreasing energy barrier for O2- migration associated with the presence of vanadium in the structure. This conclusion corroborates the hypothesis that vanadium's propensity for a lower coordination number is beneficial for promoting high O2- mobility in this promising class of oxide-ion conductors.

Design and simulation of nitrogenated holey graphene (C2N) based heterostructure solar cell by SCAPS-1D

The nitrogenated holey Graphene (C2N) based solar cell has been modeled and analyzed by using SCAPS-1D. Initially, a reported structure (TCO/IGZO/C2N) has been considered and improved by incorporating Al and Pt as front and back contact, respectively. Then, a novel device structure (Al/TCO/IGZO/C2N/CZT/Pt) has been proposed by inserting a BSF layer with heavily doped p-CZT material. The outcomes of the suggested cell structure have been analyzed numerically by changing different physical parameters. The absorber and BSF layer's thickness has been optimized as 0.6 μm and 0.4 μm, respectively. The cell performance is significantly declined when the bulk defect density in C2N exceeds the value of 1015 cm−3. The rising of device operating temperature shows a negative effect on performance. From this analysis, the structure has been optimized according to device performance. The optimized results have been achieved with the VOC, JSC, FF and efficiency (eta) of 1.40 V, 22.59 mA/cm2, 89.02%, and 28.16%, respectively. This research contributes to enriching the knowledge on the field of C2N materials and its use in optoelectronic applications.

Optimization of lead-free materials-based perovskite solar cell using SCAPS-1D simulation

Perovskite solar cells (PSCs) are the foremost transition in photovoltaics approaching commercialization. The tin-based perovskites take off the toxic lead-based perovskites in the solar cells. The parameters of each layer in the device play a significant role in the device performance graph. The main aim of this simulation is to design a highly efficient and environment-friendly PSC. The influence of parameters such as device temperature, total defect density, work function, thickness, and electron affinity plays a vital role in the photovoltaic response. Here, the active layer is explored in this study. After the SCAPS-1D simulation of FTO (fluorine-dopped oxide)/SnO2/FASnI3/CuI/Au based device, the impact of optimization of the device temperature and active layer, the performance parametric of the device is analyzed, which led to the breakthrough by a surprising rise in PCE of 30.33 %, VOC = 1.28 V, JSC = 27.72 mA/cm2 and FF = 85.33 % with active layer thickness of 450 nm, Nt = 1 × 1013 cm−3 and at the device operating temperature at 300K providing a valuable vision for tin-based perovskite applications.

Nanocavity enhanced photon coherence of solid-state quantum emitters operating up to 30 K

Solid-state emitters such as epitaxial quantum dots have emerged as a leading platform for efficient, on-demand sources of indistinguishable photons, a key resource for many optical quantum technologies. To maximise performance, these sources normally operate at liquid helium temperatures ( ∼4 K ), introducing significant size, weight and power requirements that can be impractical for proposed applications. Here we experimentally resolve the two distinct temperature-dependent phonon interactions that degrade indistinguishability, allowing us to demonstrate that coupling to a photonic nanocavity can greatly improve photon coherence at elevated temperatures up to 30 K that are compatible with compact cryocoolers. We derive a polaron model that fully captures the temperature-dependent influence of phonons observed in our experiments, providing predictive power to further increase the indistinguishability and operating temperature of future devices through optimised cavity parameters.

Bi-parameter thermal-mechanical reliability of miniaturised electromechanical RF relays for space applications

Reliability assessment of the miniaturised RF electromechanical relays under the simultaneously applied thermal and mechanical stresses was studied. This combination of stress factors, commonly overseeing by the existing reliability standards and testing procedures, does occur in certain operation conditions, such as during the spacecraft launch phase. It was demonstrated that the relay robustness for the mechanical vibration is not affected by high temperature up to the maximum device operation T of 100 °C. However, a progressive deterioration of the device performance under mechanical shocks with the temperature increase was observed. The relay exhibits state flipping events at lower shock accelerations under high temperatures. The relay's destruction limits are also lower at the maximum device operation temperature. The observed degradation is not large, and the device performance stays within the required specifications even at the highest operation temperature.

Highly thermal conductive and flame retardant poly(vinyl alcohol) film with synergistic alignments of boron nitride nanosheets/Ti3C2Tx MXene for thermal interface materials

With the development of microelectronics and flexible wearable electronic devices, poly(vinyl alcohol) (PVA) based thermal interface materials (TIMs) have received much attention. However, poor heat dissipation and high flammability have emerged as the key issues that restrict their application. In this work, the directional alignment of phytic acid (PA) modified boron nitride nanosheets (BNNS) and Ti3C2Tx MXene in PVA matrix was achieved by ice-templated assembly, which simultaneously enhanced the flame retardancy and thermal conductivity of PVA composite films (PVA/BTx). Owing to the synergistic effect between oriented BNNS and Ti3C2Tx MXene on forming the thermally conductive network within PVA matrix, the in-plane thermal conductivity of PVA/BTx-30 composite film was increased to 8.54 W m−1 K−1, much higher than that of PVA film (0.30 W m−1 K−1). Meanwhile, the heat dissipation process of PVA films applied as TIMs was simulated, which showed that PVA/BTx-30 films exhibited excellent thermal conduction and significantly decreased the operation temperature of electronic devices. Additionally, the peak heat release rate (PHRR) and total heat release (THR) of PVA/BTx-30 films were reduced by 60.3% and 62.0%, respectively, showing good flame retardancy. Importantly, the flexible Ti3C2Tx nanosheets further enhanced the mechanical properties of PVA/BTx composite films. Therefore, this work provides an effective method for the preparation of high thermal conductivity and flame retardant composite materials, which has important potential applications in the microelectronics industry.

Design of a p-i-n type inverted perovskite solar cell using SiOx as down-conversion material to improve PCE: Simulation and optimization in SCAPS-1D

In this research work, an inverted p-i-n type perovskite solar cell: ITO/PEDOT: PSS/CH3NH3PbI3/PCBM/Au has been simulated and optimized in SCAPS-1D. The optimized parameters in SCAPS-1D that improved solar performance were: perovskite thickness, the total defect density of perovskite, the total defect density of interfaces, series and shunt resistances, and device operating temperature. As a result, the efficiency (PCE) increased to 18.33%. Subsequently, when the silicon-rich oxide (SiOx) material was implemented in the simulation as downconversion energy material on the outside of the cell, a power conversion efficiency (PCE) of 23.7% was obtained. The SiOX film obtained experimentally by sputtering obtained good photoluminescence, absorption coefficient, band gap, and transmittance characteristics before and after thermal annealing. These characteristics have been considered for the proposed device. It is indicated that the inverted perovskite solar cell of type pi-n: SiOx/ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Au has better J-V output values and EQ quantum efficiency than the perovskite solar cell without SiOx.

High-Entropy Proton Conductive Electrolyte for Intermediate Temperature Operation

Due to the high operating temperatures required by commercially available cells, solid oxide electrochemical devices are currently limited in their application to sectors ranging from production to storage of energy, from pollution abatement to pure oxygen distillation. In this study, it is presented a novel electrolyte that promises to dramatically reduce the operating temperature of solid oxide electrochemical devices. Our proposed electrolyte consists of four cations and non-critical raw materials with a stoichiometry that allows for maximum entropy in an ABO3-based oxide. Preliminary results presented in this proceeding indicate that the material outperforms commercial cerates and zirconates in terms of thermal and electrochemical properties, while there is still room for further improvements.

Evaluating high temperature photoelectrocatalysis of TiO2 model photoanode

Sunlight concentration has been demonstrated as one promising strategy for practically photoelectrochemical (PEC) water splitting with exceeding 10% solar-to-hydrogen efficiency. However, the operating temperature of PEC devices, including the electrolyte and photoelectrodes, can be elevated to 65 ℃ naturally due to the concentrated sunlight and the thermal effect of near-infrared light. In this work, high temperature photoelectrocatalysis is evaluated using titanium dioxide (TiO2) photoanode as a model system, which is believed to be one of the most stable semiconductors. During the studied temperature range of 25–65 ℃, a linear increment of photocurrent density with a positive coefficient of 5.02 μA cm−2 K−1 can be observed. The onset potential for water electrolysis shows a significant negative shift by 200 mV. An amorphous titanium hydroxide layer and a number of oxygen vacancies generate on the surface of TiO2 nanorods, promoting the water oxidation kinetics. During long-term stability testing, the NaOH electrolyte degradation and TiO2 photocorrosion at high temperatures could cause the decaying photocurrent. This work evaluates the high temperature photoelectrocatalysis of TiO2 photoanode and reveals the mechanism of temperature effects on TiO2 model photoanode.

Preparation of CuO films at different sputtering powers and the effect of operating temperatures on the photovoltaic characteristics of p-CuO/n-Si heterojunction

With the progressively prominent impact of pollution caused by the extensive use of unsustainable fossil energy on the environment, clean energy with solar energy as an important component is developing rapidly. As a p-type semiconductor material with excellent performance, CuO is expected to become one of the most competitive photovoltaic materials in the field of optoelectronic devices. We first explored the effects of changing the sputtering power on the crystalline quality of CuO thin films, and systematically investigated the crystal structure, surface morphology, optical and electrical properties. Then we fabricated an Au/p-CuO/n-Si/Al heterojunction solar cell by magnetron sputtering and analyzed the influence of the device on the electrical properties at different temperatures. High rectification characteristics typical of diodes were obtained. Finally, by measuring and calculating the photovoltaic performance of the device under simulated sunlight irradiation, we studied the dependence of the device operating temperature on the photoelectric conversion efficiency in detail.

Thermomechanical properties of aluminum oxide thin films made by atomic layer deposition

In microelectromechanical system devices, thin films experience thermal processing at temperatures some cases exceeding the growth or deposition temperature of the film. In the case of the thin film grown by atomic layer deposition (ALD) at relatively low temperatures, post-ALD thermal processing or high device operation temperature might cause performance issues at device level or even device failure. In this work, residual stress and the role of intrinsic stress in ALD Al2O3 films grown from Me3Al and H2O, O3, or O2 (plasma ALD) were studied via post-ALD thermal processing. Thermal expansion coefficient was determined using thermal cycling and the double substrate method. For some samples, post-ALD thermal annealing was done in nitrogen at 300, 450, 700, or 900 °C. Selected samples were also studied for crystallinity, composition, and optical properties. Samples that were thermally annealed at 900 °C had increased residual stress value (1400–1600 MPa) upon formation of denser Al2O3 phase. The thermal expansion coefficient varied somewhat between Al2O3 made using different oxygen precursors. For thermal-Al2O3, intrinsic stress decreased with increasing growth temperature. ALD Al2O3 grown with plasma process had the lowest intrinsic stress. The results show that ALD Al2O3 grown at 200 and 300 °C is suitable for applications, where films are exposed to post-ALD thermal processing even at temperature of 700 °C without a major change in optical properties or residual stress.

Vaping preferences of individuals who vaporise dry herb cannabis, cannabis liquids and cannabis concentrates

In 2019 an estimated 200 million people aged 15–64 used cannabis, making cannabis the most prevalent illicit substance worldwide. The last decade has seen a significant expansion in the cannabis vaporiser market, introducing cannabis vaporisation as a common administration method alongside smoking and ingestion. Despite reports of increased prevalence of cannabis vaporisation there has been little research into the use of these devices. To remedy the current dearth of data in this area this study utilised an anonymous online survey of individuals who self-reported past cannabis vaporisation. The respondents (N = 557) were predominantly young (<35 years) and male. Most (91.4 %) stated they had ever vaped dry herb cannabis, 59.1 % reported vaporisation of cannabis oil or liquids, and 34.0 % reported vaporisation of cannabis concentrates. This study identifies the types of vaporisation devices (including brands and models) employed by cannabis vapers, as well as the vaporisation temperatures and puff durations commonly used for dry herb, cannabis liquids and cannabis concentrates. To the best of our knowledge, this is the first time the usual operating temperatures of these vaporisation devices and user specific consumption patterns such as puff duration have been reported for cannabis vaping. This information will allow for a more realistic understanding of patterns of recreational use and improve experimental conditions in research settings to reflect the user’s context.

The Electronic Structure of Cs2AgBiBr6 at Room Temperature

Cs2AgBiBr6 is a stable halide double perovskite with a bandgap of about 2.2 eV. Therefore, it is intensively studied as a potential lead‐free alternative to hybrid perovskite solar cell absorber materials such as methylammonium lead iodide. However, power conversion efficiencies of solar cells with this material have not yet exceeded 3%. A detailed understanding of the electronic structure of this material is difficult, due to the variance of reported data and experimental as well as theoretical difficulties that occur in going beyond a qualitative understanding of such an indirect semiconductor at device operation temperature. Herein, self‐energy‐corrected electronic structure theory including spin–orbit coupling and structural dynamics at room temperature are combined to model and understand this compound in a quantitative manner as compared with experimental findings. It is proposed that the observed low power conversion efficiencies are intrinsic and can be attributed to the density of states in the conduction band region.

Interfacial reaction between Sn-Ag solder and electroless Ni-Fe-P diffusion barriers with different internal microstructure

The increasing operation temperature of electronic devices significantly accelerates the growth of Cu-Sn intermetallic compounds (IMCs) at the interfaces of Sn-Ag solder/Cu substrate which deteriorates the device reliability. A robust diffusion barrier is thus required to suppress the interfacial reactions between solders and substrates. In this work, electroless Ni-Fe-P coatings with three different internal microstructure were prepared to compare their interfacial reactions and diffusion barrier properties in Sn-Ag solder interconnects. Ni-Fe-P coatings can effectively suppress the excessive growth of interfacial IMCs in Sn-Ag solder interconnects during reflow process. It has been found that the Ni-Fe-P coatings with crystalline structure had great influence on IMCs formation and morphology at Sn-Ag/Ni-Fe-P interfaces. Among three types of Ni-Fe-P coatings, the crystalline Ni-Fe-P exhibited the optimal diffusion barrier property owing to the presence of a uniform and thinnest FeSn2 layer at the interface, while the amorphous Ni-Fe-P coating was less effective due to the irregular and thickest Ni3Sn4 IMCs formed at the interface.

Finite Volume Method Modeling of Heat Transfer in Acoustic Enclosure for Machinery.

This paper deals with the problem of heat accumulation in acoustic enclosures. Increased noise levels at production sites or manufacturing lines force the application of acoustic enclosures. Effective noise reduction due to enclosures often comes with the additional thermal insulation of the device, which in many cases causes a strong increase in the device operation temperature. This paper presents the methodology of thermal phenomena numerical modeling based on the potential influence of acoustic enclosures on the increase in device operation temperature. The proposed model consists of an original acoustic enclosure concept design, and the numerical modeling is based on the computational fluid dynamics FVM (finite volume method) conducted in Ansys Fluent. The research comprised a set of simulations at different air flow rates of 52.5 m3/h, 105 m3/h, 210 m3/h and 420 m3/h at the enclosure inlet. The analysis carried out on the basis of flow paths and temperature distribution plots inside the enclosure led to the conclusion that the expected, analytically calculated minimum volumetric flow rate is not sufficient to effectively cool the investigated device to the required temperature of 26 °C, and higher air flow rates should be applied. Simulation results indicated that the numerical tools can be useful in the prediction of the heat exchange process, as well as in the selection of an appropriate source and location of cooling.