Obtaining NiAl intermetallic compound using different milling devices

NiAl intermetallic compound was synthesized by mechanical alloying technique in planetary and attritor mills. The starting powders consisted of elemental mixtures of Ni and Al at Ni₅₀Al₅₀ (at%) composition. In the planetary mill, compound formation occurred gradually during mechanical alloying, while the occurrence of a mechanically induced self-propagating reaction (MSR) can be suggested in the attritor mill. The NiAl obtained in both mill types was partially disordered with long-range order parameter not inferior to 0.66. Quantitative phase analysis using the Rietveld method was performed in as-milled samples, and this method was also employed to estimate changes in crystallite size and lattice strain of the NiAl produced during mechanical alloying.     

Heteroepitaxial growth of III–V compound semiconductors for optoelectronic devices

An AlGaAs/GaAs multi-quantum well vertical-cavity surface-emitting laser diode (VCSELD) has been grown on a Si substrate using metalorganic chemical vapour deposition (MOCVD). The VCSELD with a 23-pair of AlAs/Al_0·1Ga_0·9As distributed Bragg reflector on a Si substrate exhibited a threshold current of 223 mA under continuous-wave condition at 220 K. Electroluminescence observation showed that an optical degradation was caused by generation and growth of dark-line defects. An MOCVD-grown InGaN/AlGaN double-heterostructure light-emitting diode on a sapphire substrate exhibited an optical output power of 0·17 mW, an external quantum efficiency of 0·2%, a peak emission wavelength at 440 nm with a full width at half-maximum of 63 nm and a stable operation up to 3000 h under 30 mA DC operation at 30°C. A high current level of 281 mA/mm and a large transconductance (g _m) of 33 mS/mm have been achieved for a GaN metal semiconductor field-effect transistor (MESFET) with a gate length of 2 μm and a width of 200 μm at 25°C. The GaN MESFET at 400°C showed degraded characteristics: a lowg _m of 13·4 mS/mm, a gate leakage and a poor pinch-off.     

Contact and interconnect formation on compound semiconductor devices by ionized-cluster beam deposition

A new deposition technology, namely the ionized-cluster beam deposition method, was applied to form contacts and interconnects on III–V compound semiconductor devices. Au alloy films deposited by this technology had strong enough adhesion to an insulator layer to be a satisfactory interconnection. A step approximately 8 μm high at an angle of 90° to the semiconductor was covered fully with an Au alloy film obtained by this method. Electrical ohmic contacts for p-type GaP and GaAs were successfully obtained at substrate temperatures of 400 °C and 300 °C respectively without any further annealing process; this resulted in better device characteristics because of the lower process temperatures and also made the device less expensive because of a reduction in fabrication time.     

High-frequency strain-gauge installation

Conclusions The strain-gauge equipment developed by us is used for studying bending and twisting vibrations in small-diameter boring bars of diamond-cutting lathes. This equipment served for registering boring bar vibrations at a frequency of 12–15 kHz and a relative deformation amplitude of 10^–5–10^–6. It has been found that these oscillations lower the quality of the machined surface and increase considerably the wear of the cutting tool.One year's utilization of the equipment has shown that it operates reliably with the required precision of measurement over a wide measurement range of vibration frequencies and amplitudes.     

High-frequency membrane hydrophone

A membrane hydrophone with a 37-μm diameter spot poled electrode has been fabricated on a 4-μm-thick film of the piezoelectric copolymer, polyvinylidene fluoride trifluoroethylene (PVDF-TrFE), and initially characterized. The hydrophone has an effective spot size of less than 100 μm, an on-membrane +7-dB gain buffer amplifier, and a -3-dB bandwidth of 150 MHz. The acoustic properties of the hydrophone were investigated with a transducer equivalent circuit model, the electric fringe fields due to poling were characterized with a finite difference electrostatic field model, and the effective spot diameters 2a₃ and 2a₆ were estimated. Measurements on the bandwidth, effective spot size, and sensitivity are presented. This hydrophone appears suitable for the characterization of both the frequency and spatial parameters of high-frequency transducers such as intravascular ultrasound (IVUS) catheter transducers operating in the 10-40 MHz range     

High-frequency moving-iron instruments

Conclusions The instruments developed by us have an almost uniform scale starting at 10% of the full-scale reading. The first design is simpler and more reliable. As far as we know such instruments are not being produced anywhere. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 45–47, November, 1961     

High-frequency measuring impedance-to-voltage converter

An instrumental impedance-voltage converter operating in the 0.1–10 MHz frequency band is described. The impedance measurement error does not exceed 3%. Translated from Izmeritel’naya Tekhnika, No. 8, pp. 54–58, August, 1996.     

High-frequency micromechanical columnar resonators

Abstract

High-frequency silicon columnar microresonators are fabricated using a simple but effective technological scheme. An optimized fabrication scheme was invented to obtain mechanically protected microcolumns with lateral dimensions controlled on a scale of at least 1 μm. In this paper, we investigate the influence of the environmental conditions on the mechanical resonator properties. At ambient conditions, we observed a frequency stability δf/f of less than 10^?6 during 5 h of operation at almost constant temperature. However, varying the temperature shifts the frequency by approximately ?173 Hz °C^{? 1}. In accordance with a viscous damping model of the ambient gas, we perceived that the quality factor of the first flexural mode decreased with the inverse of the square root of pressure. However, in the low-pressure regime, a linear dependence was observed. We also investigated the influence of the type of the immersing gas on the resonant frequency.     

High-frequency graphene voltage amplifier

While graphene transistors have proven capable of delivering gigahertz-range cutoff frequencies, applying the devices to RF circuits has been largely hindered by the lack of current saturation in the zero band gap graphene. Herein, the first high-frequency voltage amplifier is demonstrated using large-area chemical vapor deposition grown graphene. The graphene field-effect transistor (GFET) has a 6-finger gate design with gate length of 500 nm. The graphene common-source amplifier exhibits ～5 dB low frequency gain with the 3 dB bandwidth greater than 6 GHz. This first AC voltage gain demonstration of a GFET is attributed to the clear current saturation in the device, which is enabled by an ultrathin gate dielectric (4 nm HfO(2)) of the embedded gate structures. The device also shows extrinsic transconductance of 1.2 mS/μm at 1 V drain bias, the highest for graphene FETs using large-scale graphene reported to date.     

DD3单晶合金的评估

叙述了北京航空材料研究院和美国普拉特惠特尼公司对ＤＤ３单晶合金的成本，主要力学性能指标和单晶铸性能进行的评估。评估认为：ＤＤ３合金有优良的力学性能和良好的铸造性能性能，     

High-frequency sintering of multilayer ceramic capacitors

Results of sintering multilayer ceramic capacitors by a high-frequency field are presented. It is shown that half-finished multilayer ceramic capacitors subjected to a high-frequency field are sintered in 5–15 min instead of the several hours taken in the conventional method. Possibilities of using high-frequency fields for sintering ceramic materials and electronic products are discussed.Vitebsk Branch of the Institute of Solid State and Semiconductor Physics, Academy of Sciences of Belarus, Vitebsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 1, pp. 143–145, January–February, 1995.     

High-frequency dynamics of ultrasound contrast agents

Ultrasound contrast agents enhance echoes from the microvasculature and enable the visualization of flow in smaller vessels. Here, we optically and acoustically investigate microbubble oscillation and echoes following insonation with a 10 MHz center frequency pulse. A high-speed camera system with a temporal resolution of 10 ns, which provides two-dimensional (2-D) frame images and streak images, is used in optical experiments. Two confocally aligned transducers, transmitting at 10 MHz and receiving at 5 MHz, are used in acoustical experiments in order to detect subharmonic components. Results of a numerical evaluation of the modified Rayleigh-Plesset equation are used to predict the dynamics of a microbubble and are compared to results of in vitro experiments. From the optical observations of a single microbubble, nonlinear oscillation, destruction, and radiation force are observed. The maximum bubble expansion, resulting from insonation with a 20-cycle, 10-MHz linear chirp with a peak negative pressure of 3.5 MPa, has been evaluated. For an initial diameter ranging from 1.5 to 5 microm, a maximum diameter less than 8 microm is produced during insonation. Optical and acoustical experiments provide insight into the mechanisms of destruction, including fragmentation and active diffusion. High-frequency pulse transmission may provide the opportunity to detect contrast echoes resulting from a single pulse, may be robust in the presence of tissue motion, and may provide the opportunity to incorporate high-frequency ultrasound into destruction-replenishment techniques.