Ab initio calculation of stable structures of a Na atomic chain under bias voltages

The stable geometries of a three-atom Na chain connected to two semi-infinite jellium electrodes are studied under bias voltages by performing ab initio force calculations within the density functional theory. At a low bias voltage of 0.01 V, the stable geometry is found to be symmetric, while it becomes asymmetric for higher bias voltages. The displacements of Na atoms in the chain are proportional to the applied bias voltages up to 1 V, while their behavior changes drastically above 1 V. These results can be understood from the behavior of charges induced by the applied voltage. It is also found that the structural relaxation due to the bias voltage also affects the potential drop along the chain and the current—voltage characteristics of the chain.     

反应溅射TiN纳米晶薄膜的结构特征和耐蚀性

利用直流反应溅射技术在不锈钢和硅基体上沉积了TiN纳米晶薄膜,采用场发射扫描电镜(FESEM)、X射线衍射(XRD)和电化学阻抗谱(EIS)技术研究了薄膜的表面形貌、相结构和耐蚀性与偏压的关系。结果表明,TiN薄膜的表面结构明显取决于所施加的偏压,适当提高偏压有利于获得细小、均匀、致密和光滑的膜层。XRD分析发现,TiN薄膜为面心立方结构,其择优取向为(111)面。实验显示,对应0V和-35V偏压的薄膜为欠化学计量比的,而偏压增加至-70V和-105V时的薄膜为化学计量比的TiN。EIS结果表明,较高偏压下的TiN薄膜几乎在整个频率范围内均表现为容抗特征,其阻抗模值明显高于低偏压下的膜层,这主要与较高偏压下的薄膜具有相对致密的微结构有关。较低偏压的TiN薄膜因结构缺陷较多其耐蚀性低于基体不锈钢。EIS所揭示的薄膜结构特征与FESEM观测结果一致。可见,减少穿膜针孔等结构缺陷有利于改善反应溅射TiN纳米晶薄膜耐蚀性。     

低密度聚乙烯基复合导电材料的伏安特性

研究了碳黑含量为２３％～３０％的低密度聚乙烯（ＬＤＰＥ）－碳黑（ＣＢ）复合导电材料的直流Ｉ－Ｕ特性。结果表明，当外加电压小于曲线上的转变电压（或峰值电压）时，电流与电压的关系遵从欧姆定律，近似为一直线，在此区域内测量的体积电阻值重复性好。伏安特性曲线上的峰值电压随温度升高而降低，相对应的电流也减小。电流随时间的响应曲线表明，高电压下，经较长时间才能达到稳定的电流值，而低至１．５Ｖ时，电流几乎一直都是平稳的，测量结果的重复性较好。通过上述试验得到通常的体积电阻的测试条件，由体积电阻求出体积电阻率。     

Dual‐Graphene Rechargeable Sodium Battery

Sodium (Na) ion batteries are attracting increasing attention for use in various electrical applications. However, the electrochemical behaviors, particularly the working voltages, of Na ion batteries are substantially lower than those of lithium (Li) ion batteries. Worse, the state‐of‐the‐art Na ion battery cannot meet the demand of miniaturized in modern electronics. Here, we demonstrate that electrochemically exfoliated graphene (EG) nanosheets can reversibly store (PF₆⁻) anions, yielding high charging and discharging voltages of 4.7 and 4.3 V vs. Na⁺/Na, respectively. The dual‐graphene rechargeable Na battery fabricated using EG as both the positive and negative electrodes provided the highest operating voltage among all Na ion full cells reported to date, together with a maximum energy density of 250 Wh kg⁻¹. Notably, the dual‐graphene rechargeable Na microbattery exhibited an areal capacity of 35 μAh cm⁻² with stable cycling behavior. This study offers an efficient option for the development of novel rechargeable microbatteries with ultra‐high operating voltage and high energy density.     

Comparison of conventional and collapsed region operation of capacitive micromachined ultrasonic transducers

We report experimental results from a comparative study on collapsed region and conventional region operation of capacitive micromachined ultrasonic transducers (CMUTs) fabricated with a wafer bonding technique. Using ultrasonic pulse-echo and pitch-catch measurements, we characterized single elements of 1-D CMUT arrays operating in oil. The experimental results from this study agreed with the simulation results: a CMUT operating in the collapsed region produced a higher maximum output pressure than a CMUT operated in the conventional region at 90% of its collapse voltage (3 kPa/V vs. 16.1 kPa/V at 2.3 MHz). While the pulse-echo fractional bandwidth (126%) was higher in the collapsed region operation than in the conventional operation (117%), the pulse-echo amplitude in collapsed region operation was 11 dB higher than in conventional region operation. Furthermore, within the range of tested bias voltages, the output pressure monotonously increased with increased bias during collapsed region operation. It was also found that in the conventional mode, short AC pulses (larger than the collapse voltage) could be applied without collapsing the membranes. Finally, while no significant difference was observed in reflectivity of the CMUT face between the two regions of operation, hysteretic behavior of the devices was identified in the collapsed region operation.     

Resistance switch employing a simple metal nanogap junction

In recent years, several researchers have reported the occurrence of reversible resistance switching effects in simple metal nanogap junctions. A large negative resistance is observed in the I-V characteristics of such a junction when high-bias voltages are applied. This phenomenon is characteristic behaviour on the nanometre scale; it only occurs for gap widths slightly under 13?nm. Furthermore, such a junction exhibits a non-volatile resistance hysteresis when the bias voltage is reduced very rapidly from a high level to around 0?V, and when the bias voltage is reduced slowly. This non-volatile resistance change occurs as a result of changes in the gap width between the metal electrodes, brought about by the applied bias voltage.     

Influence of ion bombardment on the properties and microstructure of unbalanced magnetron deposited niobium coatings

The effect of the ion bombardment to unbalanced magnetron deposited, approximately 1.5 and 4.5 μm thick, Nb coatings have been investigated as the bias voltage was varied from U_B=−75 to −150 V. Increasing bias voltage increased the hardness of the coating from 4.5 to 8.0 GPa. This was associated with residual stress and Ar incorporation into the Nb lattice. Strong {110} texture developed in the samples deposited at low bias voltages, while beyond U_B=−100 V a {111} texture became dominant. However, strong {111} texture was observed only with the thicker 3Nb coatings. Secondary electron microscopy investigation of the coating topography showed fewer defects in the thicker coatings. All coatings exhibited good corrosion resistance, with the thicker coatings clearly outperforming the thinner ones. Excessive bias voltages (U_B=−150 V) was found to lead to poor adhesion and loss of corrosion resistance.     

Enhancing effect of substrate bias on nanotwin formation of sputtered Ag thin films

In this study, a novel method for producing high-density 〈111〉-oriented nanotwinned Ag film is proposed so as to improve the performance of backside metallization for power devices. Negative bias voltages were applied during sputtering to facilitate the formation of densely stacked nanotwinned columnar structures. In addition, the effects of substrate bias on the properties of Ag films were observed in the lower transition layer thickness, stronger 〈111〉 texture, and higher indentation hardness. The optimal indentation hardness, 1.71 GPa, was found in the nanotwinned Ag film sputtered with a bias voltage of???150 V; it was about twice that of the normal-grained Ag film sputtered without substrate bias, 0.85 GPa. In addition, the results showed that the Ag film sputtered with a bias voltage of???150 V possessed the strongest (111) intensity, and its surface (111) ratio was 98%, much higher than the 77% of the Ag film sputtered without substrate bias. It is concluded that the Ag nanotwinned film sputtered with a bias voltage of???150 V has the potential for application as an interlayer in low-temperature direct bonding.

     

Calibration of Voltage Transformers and High- Voltage Capacitors at NIST

The National Institute of Standards and Technology (NIST) calibration service for voltage transformers and high-voltage capacitors is described. The service for voltage transformers provides measurements of ratio correction factors and phase angles at primary voltages up to 170 kV and secondary voltages as low as 10 V at 60 Hz. Calibrations at frequencies from 50–400 Hz are available over a more limited voltage range. The service for high-voltage capacitors provides measurements of capacitance and dissipation factor at applied voltages ranging from 100 V to 170 kV at 60 Hz depending on the nominal capacitance. Calibrations over a reduced voltage range at other frequencies are also available. As in the case with voltage transformers, these voltage constraints are determined by the facilities at NIST.     

In0.53Ga0.47As PIN光电探测器的温度特性分析

从理论和实验上分析了双异质结In0.53Ga0.47As PIN光电探测器在不同的反向偏置电压下暗电流在甚宽温度范围内的温度特性。结果表明：在反向偏置低压与高压段,产生一复合电流与隧道电流(缺陷隧道电流与带带间隧道电流)分别占主导地位,并呈现出相应的温度特性。还从理论与实验两方面探讨了噪声对探测器R0A的影响,结果表明：在低温段,产生一复合噪声起主要作用,在高温段,俄歇复合噪声起主要作用。     

STM induced modification of gold surface in the presence of TMP amine

In this paper we present scanning tunneling microscopy (STM) investigations of gold with 2,2,6,6-Tetramethylpiperidine (TMP) overlayer. During the STM experiments the creation of holes and hills or no changes of the surface were observed depending on the applied bias voltage and polarity. No modifications were observed in the bias range from −0.5 to +0.5 V. The holes were created for the bias voltages greater than +0.5 V and hills for the bias voltages lower than −0.5 V. The observed changes of the surface morphology suggest the presence of electrochemical reaction between the tip and the surface. Additionally, our results suggest that TMP lowers the electrochemical activation energy of gold to +0.5 eV.     

Effect of bias voltage on microstructure and mechanical properties of arc evaporated (Ti, Al)N hard coatings

In the present study, authors report on the effect that substrate bias voltage has on the microstructure and mechanical properties of (Ti, Al)N hard coatings deposited with cathodic arc evaporation (CAE) technique. The coatings were deposited from a Ti _{0· 5}Al _{0· 5} powder metallurgical target in a reactive nitrogen atmosphere at three different bias voltages: U _B ?=??? 25, ?50 and ?100 V. The coatings were characterized in terms of compositional, microstructural and mechanical properties. Microstructure of the coatings was investigated with the aid of X-ray diffraction in glancing angle mode, which revealed information on phase composition, crystallite size, stress-free lattice parameter and residual stress. Mechanical properties were deduced from nano-indentation measurements. The residual stress in all the coatings was compressive and increased with increasing bias voltage in a manner similar to that reported in literature for Ti–Al–N coatings deposited with CAE. The bias voltage was also found to significantly influence the phase composition and crystallite size. At ?25 V bias voltage the coating was found in single phase fcc-(Ti, Al)N and with relatively large crystallites of ~ 9 nm. At higher bias voltages (?50 and ?100 V), the coatings were found in dual phase fcc-(Ti, Al)N and fcc-AlN and the size of crystallites reduced to approximately 5 nm. The reduction of crystallite size and the increase of compressive residual stress with increasing bias voltage both contributed to an increase in hardness of the coatings.     

Anomalous kink behavior in the current-voltage characteristics of suspended carbon nanotubes

Electrically-heated suspended, nearly defect-free, carbon nanotubes (CNTs) exhibiting negative differential conductance in the high bias regime experience a sudden drop in current (or “kink”). The bias voltage at the kink (V _kink) is found to depend strongly on gate voltage, substrate temperature, and gas environment. After subtracting the voltage drop across the contacts, however, the kink bias voltages converge around 0.2 V, independent of gate voltage and gas environment. This bias voltage of 0.2 V corresponds to the threshold energy of optical phonon emission. This phenomenon is corroborated by simultaneously monitoring the Raman spectra of these nanotubes as a function of bias voltage. At the kink bias voltage, the G band Raman modes experience a sudden downshift, further indicating threshold optical phonon emission. A Landauer model is used to fit these kinks in various gas environments where the kink is modeled as a change in the optical phonon lifetime, which corresponds to a change in the non-equilibrium factor that describes the existence of hot phonons in the system.      

Nanotechnology for next generation Josephson voltage standards

We have developed two voltage standard systems: 1) the programmable Josephson voltage standard and 2) the Josephson arbitrary waveform synthesizer. The programmable system is fully automated and provides stable programmable dc voltages from -1.2 V to +1.2 V. The synthesizer is the first quantum-based ac voltage standard source. It uses perfectly quantized Josephson pulses to generate arbitrary waveforms with low harmonic distortion and stable, calculable time-dependent voltages. Both systems are presently limited to output voltages less than 10 V as a result of frequency requirements and the limits of junction fabrication technology. We describe the development of fabrication technology for these systems and describe the circuit- and fabrication-related constraints that presently limit system performance. Finally, we propose the use of lumped arrays of junctions to achieve higher practical voltages through development of a nanoscale junction technology, in which 13 000 junctions are closely spaced at 50 nm-100 nm intervals     

Flexible Zinc–Tin Oxide Thin Film Transistors Operating at 1 kV for Integrated Switching of Dielectric Elastomer Actuators Arrays

Flexible high‐voltage thin‐film transistors (HVTFTs) operating at more than 1 kV are integrated with compliant dielectric elastomer actuators (DEA) to create a flexible array of 16 independent actuators. To allow for high‐voltage operation, the HVTFT implements a zinc–tin oxide channel, a thick dielectric stack, and an offset gate. At a source–drain bias of 1 kV, the HVTFT has a 20 µA on‐current at a gate voltage bias of 30 V. Their electrical characteristics enable the switching of DEAs which require drive voltages of over 1 kV, making control of an array simpler in comparison to the use of external high‐voltage switching. These HVTFTs are integrated in a flexible haptic display consisting of a 4 × 4 matrix of DEAs and HVTFTs. Using a single 1.4 kV supply, each DEA is independently switched by its associated HVTFT, requiring only a 30 V gate voltage for full DEA deflection. The 4 × 4 display operates well even when bent to a 5 mm radius of curvature. By enabling DEA switching at low voltages, flexible metal‐oxide HVTFTs enable complex flexible systems with dozens to hundreds of independent DEAs for applications in haptics, Braille displays, and soft robotics.     

An analysis of macroparticle-related defects on CrCN and CrN coatings in dependence of the substrate bias voltage

Chromium nitride coatings with and without a carbon content being assigned as CrCN and CrN were prepared by cathodic arc evaporation. The effect of negative substrate bias voltages (10-300 V) on the microstructure, phase composition and morphology of the coating surface was studied. X-ray diffraction data show that almost all coatings crystallized in the cubic structure with (111) and (200) diffraction lines appearing only for low negative bias voltage and a (220) diffraction line being present for the coatings deposited at higher negative bias voltages. For CrN coatings obtained at −300 V a hexagonal structure was also observed. In case of CrCN coatings the (220) diffraction line shows much higher intensity than in case of CrN coatings and was significantly broadened. On the surface of the coatings a large number of macroparticles of different size was observed. An increase of bias voltage causes a reduction of the areal density of macroparticles and a decrease of the mean surface roughness Ra.     

Preparation and electrical characterization of Cd0.8Zn0.2Te/Si thin films

Thin films of Cd_0.8Zn_0.2Te/Si structures were prepared by vacuum evaporation technique. The electrical properties such as activation energy, barrier height, and transport mechanism along with the capacitance-voltage characteristics are analyzed. The zero field activation energy calculated from the saturation current density with the inverse absolute temperature is found to be 0.37 eV and the barrier height is 0.54 eV. As the applied bias voltage increases the activation energy decreases from 0.3 to 0.22 eV for the bias range of 0-2 V. From the observed current voltage characteristics it is found that the surface state density is high for the films deposited at room temperature. From the high-frequency (1 MHz) C-V measurement the built in voltage is found to be 0.15 V. The plot of 1/C² vs the applied bias voltage behaviour is linear, indicating the presence of abrupt junction. The acceptor concentration as obtained from the 1/C² vs bias voltage is 1.4×10¹⁶ cm⁻³.     

Substrate bias voltage influenced structural, electrical and optical properties of dc magnetron sputtered Ta2O5 films

Tantalum oxide (Ta₂O₅) films were formed on silicon (111) and quartz substrates by dc reactive magnetron sputtering of tantalum target in the presence of oxygen and argon gases mixture. The influence of substrate bias voltage on the chemical binding configuration, structural, electrical and optical properties was investigated. The unbiased films were amorphous in nature. As the substrate bias voltage increased to −50 V the films were transformed into polycrystalline. Further increase of substrate bias voltage to −200 V the crystallinity of the films increased. Electrical characteristics of Al/Ta₂O₅/Si structured films deposited at different substrate bias voltages in the range from 0 to −200 V were studied. The substrate bias voltage reduced the leakage current density and increased the dielectric constant. The optical transmittance of the films increased with the increase of substrate bias voltage. The unbiased films showed an optical band gap of 4.44 eV and the refractive index of 1.89. When the substrate bias voltage increased to −200 V the optical band gap and refractive index increased to 4.50 eV and 2.14, respectively due to the improvement in the crystallinity and packing density of the films. The crystallization due to the applied voltage was attributed to the interaction of the positive ions in plasma with the growing film.     

Bias enhanced nucleation of diamond thin films in a modified HFCVD reactor

In this study we investigated the nucleation of synthetic diamond thin films on Si substrates by double bias enhanced Hot Filament Chemical Vapour Deposition (HFCVD) method. First, we investigated the influence of the bias voltage and secondly the influence of the nucleation time under different bias voltages. The bias voltage was varied from −120 V up to −220 V as well as the nucleation time was changed from 30 up to 120 min in order to obtain the optimized nucleation conditions for following growth of continuous diamond layer. Samples were analyzed by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. SEM was used for determination of cluster sizes and their distribution on the Si surface, while Raman Spectroscopy for determination and analysis of carbon phases.     

Deposition,structure and hardness of Ti–Cu–N hard films prepared by pulse biased arc ion plating

In this work, Ti–Cu–N hard nanocomposite films were deposited on 304 stainless steel (SS) substrate by using pulse biased arc ion plating system with Ti–Cu alloy target. The effects of negative substrate pulse bias voltages on chemical composition, structure, morphology and mechanical properties were investigated. The composition and structure of these films was found to be dependent on the pulse bias, whereas the pulse biases put little influence on hardness of these films. The XPS spectra of Cu 2p showed that obtained peak values correspond to pure metallic Cu. Cu content in Ti–Cu–N nanocomposite films changed with pulse bias voltage. In addition, X-ray diffraction analysis showed that a pronounced TiN (111) texture is observed under low pulse bias voltage while it changed to TiN (220) orientation under high pulse bias voltage. Surface roughness of the Ti–Cu–N nanocomposite films achieved to the minimum value of 0.11 μm with the negative pulse bias voltage of −600 V. The average grain size of TiN was less than 17 nm. The mechanical properties of Ti–Cu–N hard films investigated by nanoindentation revealed that the hardness was about 22–24 GPa and the hardness enhancement was not obtained.