Structural transformation of Ge dimers on Ge（001） surfaces induced by bias voltage

Scanning tunnelling microscopy is utilized to investigate the local bias voltage tunnelling dependent transformation between （2×1） and c（4×2） structures on Ge（001） surfaces, which is reversibly observed at room temperature and a critical bias voltage of -0.80 V. Similar transformation is also found on an epitaxial Ce islands but at a slightly different critical bias voltage of -1.00V. It is found that the interaction between the topmost atoms on the STM tip and the atoms of the dimers, and the pinning effect induced by Sb atoms, the nacancies or the epitaxial clusters, can drive the structural transformation at the critical bias voltage.     

Influence of Si/SiO2 interface properties on electrical performance and breakdown characteristics of ultrathin stacked oxide/nitride dielectric films

In this work, the influence of Si/SiO₂ interface properties, interface nitridation and remote-plasma-assisted oxidation (RPAO) thickness (<1 nm), on electrical performance and TDDB characteristics of sub-2 nm stacked oxide/nitride gate dielectrics has been investigated using a constant voltage stress (CVS). It is demonstrated that interfacial plasma nitridation improves the breakdown and electrical characteristics. In the case of PMOSFETs stressed in accumulation, interface nitridation suppresses the hole traps at the Si/SiO₂ interface evidenced by less negative V_t shifts. Interface nitridation also retards hole tunneling between the gate and drain, resulting in reduced off-state drain leakage. In addition, the RPAO thickness of stacked gate dielectrics shows a profound effect in device performance and TDDB reliability. Also, it is demonstrated that TDDB characteristics are improved for both PMOS and NMOS devices with the 0.6 nm-RPAO layer using Weibull analysis. The maximum operating voltage is projected to be improved by 0.3 V difference for a 10-year lifetime. However, physical breakdown mechanism and effective defect radius during stress appear to be independent of RPAO thickness from the observation of the Weibull slopes. A correlation between trap generation and dielectric thickness changes based on the C-V distortion and oxide thinning model is presented to clarify the trapping behavior in the RPAO and bulk nitride layer during CVS stress.     

In situ monitoring of nucleation and evolution of Ge nanodots on faintly oxidized Si(1 1 1) surfaces

We have investigated the nucleation and evolution of germanium (Ge) nanodot (ND)s taking place while depositing Ge onto the silicon (Si) (1 1 1) surfaces with ultra-thin Si oxide films by using ultra-high vacuum in situ high-resolution transmission electron microscopy in the profile-imaging geometry. Various types of growth phenomena such as nucleation, growth and coalescence of Ge NDs have successfully been observed. The results show that the growth phenomena of the Ge NDs are dramatically rapid after their size reaches the size of the critical nucleus. The critical nucleus size estimated from a model using the cohesive energy of the Ge NDs has been consistent with observed one.     

Analytical approximation to the solution of the Dirac equation with the Eckart potential including the spin-orbit coupling term

By using the supersymmetric WKB approximation approach and the functional analysis method, we solve approximately the Dirac equation with the Eckart potential for the arbitrary spin-orbit quantum number κ. The bound state energy eigenvalues and the associated two-component spinors of the Dirac particles are obtained approximately.     

A local-world node deleting evolving network model

A new type network growth rule which comprises node addition with the concept of local-world connectivity and node deleting is studied. A series of theoretical analysis and numerical simulation to the LWD network are conducted in this Letter. Firstly, the degree distribution p(k) of this network changes no longer pure scale free but truncates by an exponential tail and the truncation in p(k) increases as pa decreases. Secondly, the connectivity is tighter, as the local-world size M increases. Thirdly, the average path length L increases and the clustering coefficient 〈C〉 decreases as generally node deleting increases. Finally, 〈C〉 trends up when the local-world size M increases, so as to kmax. Hence, the expanding local-world can compensate the infection of the node deleting.     

Ultraviolet electroluminescence from ZnO-based light-emitting diode with p-ZnO:N/n-GaN:Si heterojunction structure

A p-ZnO:N/n-GaN:Si structure heterojunction light-emitting diode (LED) is fabricated on c-plane sapphire by full metal organic chemical vapor deposition (MOCVD) technique. The p-type layer with hole concentration of 8.94×10¹⁶ cm⁻³ is composed of nitrogen-doped ZnO using NH₃ as the doping source with subsequent annealing in N₂O plasma ambient. Silicon-doped GaN film with electron concentration of 1.15×10¹⁸ cm⁻³ is used as the n-type layer. Desirable rectifying behavior is observed from the current-voltage (I-V) curve of the device. The forward turn on voltage is about 4 V and the reverse breakdown voltage is more than 7 V. A distinct ultraviolet (UV) electroluminescence (EL) with a dominant emission peak centered at 390 nm is detected at room temperature from the heterojunction structure under forward bias conditions. The origins of the EL emissions are discussed in comparison with the photoluminescence (PL) spectra.     

Alteration of skin light-scattering and absorption properties by application of sunscreen nanoparticles: A Monte Carlo study

We report about the results of our investigations on the alteration of optical properties of the superficial layer of human skin at four UV range wavelengths, 310, 318, 360 and 400 nm, by application of 35-200 nm-sized particles of titanium dioxide (TiO₂), silicon (Si) and zinc oxide (ZnO). The theoretical study based on combination of the Mie theory and Monte Carlo simulations reveals the optimal sizes of the nanoparticles minimizing the light transmittance for the considered wavelengths.     

Isobaric analogue resonances in71As through proton elastic scattering on70Ge

The analogues of the low-lying levels in⁷¹Ge have been observed as resonances in the compound nucleus⁷¹As through proton elastic scattering on⁷⁰Ge in the energy rangeE _p=3.5 to 5.3 MeV. The excitation functions cover the analogue resonances corresponding to states upto 2.3 MeV excitation in⁷¹Ge. The sub-structures in the 5.06 MeV resonance, first observed by Temmer and co-workers have been confirmed in the present experiment. The present investigation reveals similar sub-structures in the 4.13 MeV resonance lending further support to the existence of intermediate structure near an isobaric analogue resonance. The resonance parameters and the spectroscopic factors (for the corresponding parent states) have been extracted. The results are compared with the information available from the⁷⁰Ge(d, p)⁷¹Ge reaction.     

半导体与超晶格的数学模型及其分析Ⅰ:模型

本文论及半导体与超晶格的数学模型方法的一些新近发展动态。介绍了半导体与超晶格的一些背景材料并给出了半导体宏观模型间的层次框架。超晶格中载流子传输的SHE扩散模型也被观察。     

H^＋注入锗酸铋晶体表面层的性质

Ｈ＾＋注入锗酸铋（Ｂｉ４Ｇｅ３Ｏ１２或ＢＧＯ）晶体引起某些效应，如辐射损伤，光学吸收和近表层区域的晶体分解。经Ｈ＾＋注入后，ＢＧＯ晶体的颜色变成棕色，但实验中证实不了该变化是由色心的产生所引起。此外，实验中也示观察到Ｈ＾＋注入ＢＧＯ晶体中有离子束诱发的光学活性变化。可见在注入过程中，未发生从Ｂｉ４Ｇｅ３Ｏ１２转变到Ｂｉ１２ＧｅＯ２０的结构相变，由此预见，注入过程中可能发生离子束引起的晶体分解。Ｈ＾