Carrier generation and recombination rate in armchair graphene nanoribbons

Armchair graphene nanoribbons (A-GNRs), with a tunable energy gap, are an alternative structure for use in optoelectronic devices. The performance of these optoelectronic devices critically depends on the carrier generation and recombination rates, which have been calculated in this paper. Because of the 1D band structure of A-GNRs, carrier scattering, generation and recombination rates in these structures would be completely different from those in 2D graphene sheets. In this paper, using the tight binding model, and by considering the edge deformation and Fermi golden rule, we find the band structure, and the carrier generation and recombination rates for pure A-GNR due to optical and acoustic phonons, as well as Line Edge Roughness (LER) scatterings. The obtained results show that the total generation and recombination rates increase with increasing A-GNR width and eventually saturate for wide ribbons. These rates increase as the carrier concentration is increased (which has been considered homogenous along ribbon width) and temperature. Also, despite the large LER scattering in narrow ribbons, the generation and recombination rates are less for A-GNRs than for graphene sheets. Using this theoretical model, one can find the suitable A-GNR structure for the design of optoelectronic devices.     

Influence of grain boundaries on the recombination rate in germanium

The electronic properties of the In (→ Cd) acceptor are studied in polycrystalline germanium by the perturbed angular correlation method (PAC). The time independent anisotropy reveals a strong temperature dependence. This behaviour can be explained quantitatively by a model based on recombination processes at the Cd acceptor. The recombination rates depend on the annealing procedure of the samples, thus indicating a strong influence of the grain boundaries.     

Observation of heterodyne mixing in surface x-ray photon correlation spectroscopy experiments

We report measurements of propagating capillary waves on a liquid water surface at T=5 degrees C with x-ray photon correlation spectroscopy. The experiment has been performed under grazing incidence conditions with an incoming x-ray beam below the critical angle of total external reflection. In the q region investigated the measured intensity-intensity autocorrelation functions of the liquid water surface were found to be heterodyne signals, i.e., a combination of first- and second-order correlation functions g(1)(tau) and g(2)(tau).     

Two photon photoelectric effect in the surface plasma resonance of aluminium

Photoemission from Al films is observed at a photon energy of 2.6 eV in an ATR-experiment. The yield is proportional to the square of the light intensity. Resonances occur at angles corresponding to surface plasma resonances of the fundamental and double frequency.     

Schwarzschild物镜装卡应力对光学元件面形的影响

为了实现接近衍射极限的分辨率,工作在极紫外波段的Schwarzschild物镜要求其光学元件的面形精度达到约1 nm（RMS值）;而在物镜的装配过程中,装卡产生的应力会影响光学元件的面形精度,定量计算装卡应力对元件面形的影响是获得高分辨率成像的关键。在光学设计、公差分析的基础上,采用有限元模型系统地分析了应力对Schwarzschild物镜光学元件面形精度的影响。结果表明：采用自行设计的物镜结构,应力对主镜面形的影响可以达到0.7 nm,而对副镜的影响可以忽略;应力所产生的光学元件面形变化会使系统的几何传递函数(5000 lp/mm)从0.76下降到0.61。     

The effect of the laser pulse shape on the wakefield generation in field-ionized plasma

In this paper, the effect of the laser pulse shape on the generation and evolution of the wakefield during the interaction of the intense laser pulse with the gas have been studied utilizing the parallel relativistic PIC simulation code. In order to reach this aim, three pulses with length 300 fs and different rise-times 30, 45, and 60 are typically selected. Our results show that, the amplitude of the laser wakefield produced in the gas in comparison with the plasma strongly depends on the laser pulse shape. The simulation results indicate that for the high-slope laser pulse time (here 30 fs), ionization and thus density fluctuations have no significant effect on the wakefield generation because of rapid increase of the laser electric field. While by increasing the laser pulse rise-time to 45 fs, the rapid wave breaking due to the change in the medium refractive index during the gas ionization, prevents from the wakefield amplitude growth, so that the wakefield with larger amplitude is emerged in the plasma. For a slow-sloping pulse (here 60 fs), the ratio of the wakefield generation in the gas to the plasma is altered for the different gas densities and laser intensities. Moreover, it is represented that the longer the laser pulse rise-time, the sooner difference between the wakefield produced in the gas and plasma is observed. In fact, the larger the rise-time, the greater the density fluctuations and, consequently, the larger the initial noise is generated to seed the Raman instability.     

The effect of molecular shape anisotropy on surface melting

We report molecular dynamics (MD) simulations of the behaviour of the (101̄0) and (0001) crystal-vapour interfaces of Lennard-Jones dimers near the triple point. For slightly anisometric molecules, where the bulk melts from an orientationally disordered state, both interfaces were found to surface melt, with behaviour resembling that of the atomic Lennard-Jones system. In contrast, at larger anisometries, where the molecules are orientationally ordered close to the triple point, the (101̄0) face exhibits a first-order surface melting transition, while the (0001) face does not surface melt at all.     

激光脉冲波形对烧蚀Si靶表面温度的影响

利用双温方程对激光烧蚀Si靶的过程进行了数值模拟,并结合合适的初始条件和边界条件,研究了在飞秒、皮秒激光作用下,脉冲波形（矩形、梯形、三角形和高斯形）对Si靶表面载流子和晶格温度分布的影响。结果表明：激光功率密度是影响载流子温升的主要因素,矩形脉冲激光烧蚀Si靶表面载流子的峰值温度最高,而高斯分布的脉冲引起靶面载流子峰值温度最低。可见,激光脉冲波形对Si靶表面载流子的温度分布具有重要影响。所得结果可为制备高质量的薄膜提供理论依据。     

激光脉冲波形对烧蚀Si靶表面温度的影响

利用双温方程对激光烧蚀Si靶的过程进行了数值模拟,并结合合适的初始条件和边界条件,研究了在飞秒、皮秒激光作用下,脉冲波形(矩形、梯形、三角形和高斯形)对Si靶表面载流子和晶格温度分布的影响。结果表明:激光功率密度是影响载流子温升的主要因素,矩形脉冲激光烧蚀Si靶表面载流子的峰值温度最高,而高斯分布的脉冲引起靶面载流子峰值温度最低。可见,激光脉冲波形对Si靶表面载流子的温度分布具有重要影响。所得结果可为制备高质量的薄膜提供理论依据。     

Influence of surface waves on plasma high-order harmonic generation

The influence of surface plasma waves on high-order harmonic generation from the interaction of intense lasers with overdense plasma is analyzed. It is shown that the surface waves lead to the emission of harmonics away from the optical axis, whereas the high-order on-axis harmonics are lowered in intensity. Our simulation results indicate that surface plasma wave generation plays a crucial role in surface high-order harmonic generation experiments. Furthermore, a novel surface plasma wave generation process different from the well-known two-surface wave decay is observed in the highly relativistic regime.     

Influence of surface defects on high frequency phonon generation

Two experiments on phonon emission into dielectric substrates are described. In both cases the surface phonon mean free path has been greatly reduced. An emitting phonon radiator vacuum deposited on the surface is then seen to overheat, corresponding to passage from the radiation to the diffusion limit.     

Determination of the rate of surface recombination of the base of alloyed germanium transistors

A method of determining the rate of surface recombination of the base of alloyed germanium transistors is described. We take as a basis of the method the switching transients of the emitter junction when the collector is open-circuited and when the collector is biased in the reverse direction. The results of preliminary measurements obtained using type P-5 open transistors (not encapsulated and not coated with lacquer) are presented. The experimental values of the rate of surface recombination lie in the range (2–4) · 10³ cm/sec.     

Influence of nonequilibrium charge carrier recombination on the signal shape and magnitude in the photodeflection spectroscopy method under pulse excitation

A theory of signal shaping is proposed for semiconductor investigation by the method of photodeflection spectroscopy with pulse excitation that would take account of the influence of charge carrier recombination on the temperature distribution in the specimen. Quantitative computations are performed for silicon that demonstrate the change in PDS signal amplitude and shape when taking account of bulk carrier recombination. It is shown that taking account of the influence of bulk recombination discloses the possibility of obtaining additional quantitative information about the charge carrier lifetime in the specimen.Translated from Izvestiya Vysshikh Uchebnykh zavedenii, Fizika, No. 1, pp. 41–45, January, 1991.     

聚乙烯薄膜中空间电荷短路放电复合率的发光法研究

通过对在直流高压作用下低密度聚乙烯薄膜中注入的空间电荷的短路放电发光测量,研究了聚乙烯薄膜中空间电荷的复合率.通过短路放电光子数的测量及定量分析考察了电压极性、场强大小及加压时间对短路下电荷复合率的影响.结果表明发光强度（复合率）随外加场强的变化明显,而与加压时间的关系不显著.但场强高于80 MV/m时发光强度（复合率）的增大速度变慢.结合本实验结果及他人的相关数据,得出了聚乙烯薄膜样品的发光效率约为5.9×10^-6,短路初始阶段的0.2 s内样品的电荷复合率约为2.8%. 关键词： 空间电荷 短路放电 复合发光 复合率