Plasma oscillations in two-dimensional semiconductor superstructures in the presence of high-frequency electric field

The effect of a high-frequency field on plasma oscillations in two-dimensional electron gas with a superstructure was studied. A dispersion relationship ω(k) was derived in the case of high temperatures (Δ ≪ T, where Δ the conductivity miniband width and T is the temperature in energy units). The calculations were based on the quantum theory of plasma oscillations in the casual-phase approximation while taking into account the umklapp processes.     

Propagation of ultrasonic waves in neptunium monochalcogenides

The ultrasonic attenuation and acoustic coupling constants due to phonon–phonon interaction and thermoelastic relaxation mechanisms have been studied for longitudinal and shear waves in B₁ structured neptunium monochalcogenides NpX (X: S, Se, Te) along 〈1 0 0〉 direction in the temperature range 100–300 K. The second and third order elastic constants (SOEC and TOEC) of the chosen monochalcogenides are also computed for the evaluation of ultrasonic parameters. The ultrasonic attenuation due to phonon–phonon interaction process is predominant over thermoelastic relaxation process in these materials. The ultrasonic attenuation in NpTe has been found lesser than other materials NpS, NpSe and GdY (Y: P, As, Sb and Bi). The semiconducting or semimetallic nature of neptunium monochalcogenides can be well understood with the study of thermal relaxation time. Total ultrasonic attenuation in these materials is found to be quadratic function of temperature. The nature of NpTe is very similar to semimetallic GdP. The mechanical and ultrasonic study indicates that NpTe is more reliable, perfect, flawless material.     

Nonlinear optical properties of nanospherical layer in the presence of an electric field

The linear and nonlinear optical properties in a spherical nanolayer quantum system subjected to an uniform applied electric field directed with respect to the z-axis have been theoretically investigated within the compact-density matrix formalism and the iterative method. The dependence of the optical absorption coefficients (ACs) and refractive index (RI) changes on the core radius R₁, on the inner radius of the clad R₂, and on the applied electric field F has been investigated detailedly. The results show that the optical ACs and RI changes of the nanospherical layer have been strongly affected by these factors. Moreover, the outcome of the calculation also suggests that all the factors mentioned above can give rise to blue-shift or red-shift significantly.     

钢-铅粘接结构的粘接强度对超声体波反射与 透射特性的影响*

针对多层异种金属粘接结构中粘接强度的超声检测与表征困难的问题,采用线性弹簧模型和等效弹性模量模型来分别表征界面粘附强度和内聚强度,推导了超声体波斜入射N层粘接结构的反射与透射系数表达式。通过在不同入射面和入射声波模式等条件下,同时连续改变两种参数来系统研究粘接层界面粘附强度与内聚强度变化对超声波反射与透射特性的影响关系,确定了能够敏感表征粘接强度的超声参量,为粘接强度的无损检测与评价提供理论依据。     

超声波马达的发展──国内最新动态

基于最新参考文献与ＩＮＴＥＲＮＥＴ网络查询,本文提出超声马达或压电驱动器在我国科技领域最新的研究成果及其未来走向。其中,能够引起研究人员兴趣的尖端性领域包括;超声马达的微型化;具有多个自由度的压电驱动器;具有新颖结构的压电驱动器;超声马达的振动实验测试;高分辨率的压电驱动器;超声马达的使用寿命;超声马达的动力学模型等。     

Self-screening of the polarized electric field in wurtzite gallium nitride along [0001] direction

The strong polarization effect of GaN-based materials is widely used in high-performance devices such as white-light-emitting diodes (white LEDs), high electron mobility transistors (HEMTs), and GaN polarization superjunctions. However, the current researches on the polarization mechanism of GaN-based materials are not sufficient. In this paper, we studied the influence of polarization on electric field and energy band characteristics of Ga-face GaN bulk materials by using a combination of theoretical analysis and semiconductor technology computer-aided design (TCAD) simulation. The self-screening effect in Ga-face bulk GaN under ideal and non-ideal conditions is studied respectively. We believe that the formation of high-density two-dimensional electron gas (2DEG) in GaN is the accumulation of screening charges. We also clarify the source and accumulation of the screening charges caused by the GaN self-screening effect in this paper and aim to guide the design and optimization of high-performance GaN-based devices.     

Modelling and simulation of high-frequency (100 MHz) ultrasonic linear arrays based on single crystal LiNbO3

Background

High-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the fabrication of conventional backing-layer structure, which requires a pitch (distance between the centers of two adjacent elements) of half wavelength in medium, is really a great challenge.

Objective and method

Here we present an alternative buffer-layer structure with a silicon lens for volumetric imaging. The requirement for the size of the pitch is less critical for this structure, making it possible to fabricate high-frequency (100 MHz) ultrasonic linear array transducers. Using silicon substrate also makes it possible to integrate the arrays with IC (Integrated Circuit). To compare with the conventional backing-layer structure, a finite element tool, COMSOL, is employed to investigate the performances of acoustic beam focusing, the influence of pitch size for the buffer-layer configuration, and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance.

Results

For a 100 MHz 10-element array of buffer-layer structure, the ultrasound beam in azimuth plane in water could be electronically focused to obtain a spatial resolution (a half-amplitude width) of 86 μm at the focal depth. When decreasing from half wavelength in silicon (42 μm) to half wavelength in water (7.5 μm), the pitch sizes weakly affect the focal resolution. The lateral spatial resolution is increased by 4.65% when the pitch size decreases from 42 μm to 7.5 μm. The crosstalk between adjacent elements at the central frequency is, respectively, −95 dB, −39.4 dB, and −60.5 dB for the 10-element buffer, 49-element buffer and 49-element backing arrays. Additionally, the electrical impedance magnitudes for each structure are, respectively, 4 kΩ, 26.4 kΩ, and 24.2 kΩ, which is consistent with calculation results using Krimholtz, Leedom, and Matthaei (KLM) model.

Conclusion

These results show that the buffer-layer configuration is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays dedicated to volumetric imaging.     

Effect of electric field on the longitudinal ultrasonic waves in Rochelle salt

The temperature dependence of velocity and attenuation for the longitudinal ultrasonic waves propagating along the (100) direction has been measured in the vicinity of the upper transition temperature under the various electric conditions in Rochelle salt.     

Ion acoustic solitary waves in the presence of a high frequency electric field

The propagation of a small but finite amplitude ion acoustic wave in the presence of a radio frequency (frequency below electron plasma frequency) electric field is investigated. The velocity, the amplitude and the width of the solitary wave are found to decrease with increasing intensity of the RF field.     

Field electron emission from carbon nanotubes in the presence of a weak high-frequency electric field

Series of narrow peaks in the frequency range of f ≈ 50–1200 MHz have been revealed in the frequency responses of the emission current from carbon nanotubes in the presence of a weak high-frequency electric field. The analysis makes it possible to attribute these peaks to resonance of the first and second harmonics of forced mechanical vibrations of carbon nanotubes in a high-frequency electric field. The determined Q factor of nanotubes is in the range of 100–300.     

Absorption properties of one- and two-dimensional semiconductor nanocrystals in the presence of an electric field

We have considered the broadening of optical absorption spectra of ensembles of randomly oriented nanorods and nanoplatelets that is caused by the action of a static electric field. It has been found that the linewidth in the spectra of the considered nanocrystals depends nonlinearly on the field strength and attains saturation in fields on the order of 100 kV/cm. We show that, due to a weak confinement, the electrooptical response of nanoplatelets is stronger than that of nanorods, which leads to a number of distinctive features in the field-induced broadening of the spectra of nanoplatelets and gives grounds to state that nanoplatelets are the most promising objects for use in electrooptical devices.     

Low frequency surface waves in the presence of an external high frequency electric field

The problem of surface sound propagation in the presence of external high frequency dipole electric field is investigated using Vlasov-Poisson equations. The structure of the electric field of these surface waves is also determined. It has been found that the ion sound waves that exist in the presence of external high frequency waves are true surface waves while those without the external field are quasi-surface waves as the former waves decay within one wavelength away from the surface.     

High frequency ultrasonic detection of C-crack defects in silicon nitride bearing balls

A non-destructive testing method for silicon nitride bearing balls based on ultrasonic resonance spectroscopy is proposed here. Through the theoretical study of their elastic vibrations, it is possible to characterize the balls using a vibration mode that is similar to surface wave propagation. The study of the influence of C-crack defects on the resonances of Rayleigh modes is presented here. These C-cracks are typically formed by impacts between balls during finishing or handling. They are frequently found on the surface of silicon nitride bearing balls and these C-cracks decrease the rolling contact fatigue life considerably. This kind of defect is difficult to detect because the C-shaped surface crack is very small and narrow (500 μm × 5 μm), and its depth does not exceed 50 μm. The proposed methodology can both excite spheroidal vibrations in the ceramic balls and detect such vibrations over a large frequency range. In particular, high frequency vibrations are considered because these are similar to the surface waves propagating in the cortical zone of the ceramic balls and consequently they can be used to detect C-crack defects.     

Effect of switching ultrasonic amplitude in preparing a hybrid of fullerene (C60) and gallium oxide (Ga2O3)

In this study, we proposed ‘switching ultrasonic amplitude’ as a new strategy of applying ultrasonic energy to prepare a hybrid of buckminsterfullerene (C₆₀) and gallium oxide (Ga₂O₃), C₆₀/Ga₂O₃. In the proposed method, we switched the ultrasonic amplitude from 25% to 50% (by 5% amplitude per 10 min, within 1 h of ultrasonic irradiation) for the sonochemical treatment of a heterogeneous aqueous mixture of C₆₀ and Ga₂O₃ by a probe-type ultrasonic horn operating at 20 kHz. We found that compared to the conventional techniques associated with high amplitude oriented ultrasonic preparation of functional materials, switching ultrasonic amplitude can better perform in preparing C₆₀/Ga₂O₃ with respect to avoiding titanium (Ti) as an impurity generating from the tip erosion of a probe-type ultrasonic horn during high amplitude ultrasonic irradiation in an aqueous medium. Based on SEM/EDX analysis, the quantity of Ti (wt.%) in C₆₀/Ga₂O₃ prepared by the proposed technique of switching ultrasonic amplitude was found to be 1.7% less than that prepared at 50% amplitude of ultrasonic irradiation. The particles of C₆₀/Ga₂O₃ prepared by different modes of amplitude formed large (2–12 μm) aggregates in their solid phase.Whereas, in the aqueous medium, they were found to disperse in their nano sizes. The minimum particle size of the as-synthesized C₆₀/Ga₂O₃ in an aqueous medium prepared by the proposed method of switching ultrasonic amplitude reached to approximately 467 nm. Comparatively, the minimum particle sizes were approximately 658 nm and 144 nm, using 25% and 50% amplitude, respectively. Additionally, Ga₂O₃ went under hydration during ultrasonic irradiation. Moreover, due to the electron cloud interference from C₆₀ in the hybrid structure of C₆₀/Ga₂O₃, the vibrational modes of Ga₂O₃ were Raman inactive in C₆₀/Ga₂O₃.     

The effect of external electric field on mass attenuation coefficients of some semiconductor

In this study, we measured the mass attenuation coefficient of n-type GaAs, p-type GaAs, n-type Si and Au/n-Si/n⁺Si/Al samples with and without external electric field. Samples were set in perpendicular direction to the 100?mCi ²⁴¹Am radioactive source and counts were made with a NaI(Tl) detector. It was observed that when an external electric field was applied onto the samples, mass attenuation coefficients were increased. Results showed that this study is consistent with previous studies.     

Magnetic field dependence optical properties of GaN/AlN multiple quantum wells

In this work, we have investigated the optical properties of some multiple quantum wells under the influence of an external magnetic field and (for the first time) number of wells. We have retained the total length of the structure constant which is technologically important. Then we have detected a blue shift in the absorption peak positions due to the application of the magnetic field and a red shift due to the increasing of the number of wells. The red shift is only seen in the multiple quantum wells with odd number of wells and the absorption peaks of the multiple quantum well with even number of wells are not changed.