刻蚀AlN缓冲层对硅衬底N极性n-GaN表面粗化的影响

研究了等离子体刻蚀AlN缓冲层对硅衬底N极性n-GaN表面粗化行为的影响. 实验结果表明, 表面AlN缓冲层的状态对N极性n-GaN的粗化行为影响很大, 采用等离子体刻蚀去除一部分表面AlN缓冲层即可以有效提高N极性n-GaN在KOH溶液中的粗化效果, AlN缓冲层未经任何刻蚀处理的样品粗化速度过慢, 被刻蚀完全去除AlN缓冲层的样品容易出现粗化过头的现象. 经X射线光电子能谱分析可知, 等离子体刻蚀能够提高样品表面AlN缓冲层Al 2p的电子结合能, 使得样品表面费米能级向导带底靠近, 原子含量测试表明样品表面产生了大量的N空位, N空位提供电子, 使得材料表面费米能级升高, 这降低了KOH溶液和样品表面之间的肖特基势垒, 从而有利于表面粗化的进行. 通过等离子体刻蚀掉表面部分AlN缓冲层, 改善了N极性n-GaN在KOH溶液中的粗化效果, 明显提升了对应发光二级管器件的出光功率.     

超高压高温烧结中金刚石表面石墨化过程再研究

 通过3组模拟实验,考察了低压高温下金刚石表面石墨化条件和超高压高温条件下金刚石表面石墨化过程,发现在钴-碳共晶点以下、超高压高温烧结样品WC-Co基体附近区域金刚石表面已发生石墨化,XRD测试结果表明,超高压高温烧结过程中金刚石表面经历了石墨化初期、高峰期和抑制期三个阶段。     

无规场非晶化表面的临界行为

应用平均场重整化群方法,讨论表面无规场和非晶化存在对S=1和σ=1/2混合自旋伊辛系统表面磁性临界行为的影响,得到在各种情况下系统的表面相图.计算结果表明,非晶化在一定范围内与无规场竞争仍可出现三临界点和重入现象. 关键词：     

InGaAs薄膜表面的粗糙化过程

采用STM分析InGaAs表面形貌演变研究InGaAs表面的粗糙化和预粗糙化等相变过程, 特别针对In_0.15Ga_0.85As薄膜表面预粗糙化过程进行了深入研究. 发现In_0.15Ga_0.85As薄膜在不同的衬底温度和As等效束流压强下表现出不同的预粗糙化过程. 在低温低As等效束流压强下, 薄膜表面将经历从有序平坦到预粗糙并演变成粗糙的过程, 起初坑的形成是表面形貌演变的主要形式, 随着退火时间的延长, 大量坑和岛的共同形成促使表面进入粗糙状态; 在高温高As等效束流压强下薄膜表面将率先形成小岛, 退火时间延长后小岛逐渐增加并最终达到平衡态, 表面形貌将长期处于预粗糙状态.     

激光表面纹理化过程中的Rayleigh-Taylor不稳定性

用表面纹理化的热模型 ,分析了固体表面的熔化和重固化的物理过程 ,计算了在纹理化过程中的表面温度、穿透深度、熔化深度、相面移动速度等物理量 ,提出了 Rayleigh-Taylor不稳定性形成周期化结构的机理。     

准分子激光增强高分子材料粘着力的机理研究

 由热方程计算激光与液体薄膜材料相互作用时的温度场,分析高分子材料表面熔化及材料表面液体膜汽化产生的材料的表面粗化;近一步分析高分子的断裂、F原子 替代等光化学反应;从而提出激光增强高分子材料的粘着力的表面粗化和光化学反应的机理。     

基于磁控溅射和ICP刻蚀的RB-SiC表面平坦化工艺

采用射频磁控溅射技术在RB-SiC表面沉积Si平坦化层,通过正交试验研究了射频功率、Ar流量和工作气压三个因素对薄膜表面质量和形貌的影响规律,以获取最佳的薄膜沉积参数.射频功率120 W、工作气压1.2Pa和Ar流量40sccm条件下获得了最佳质量的平坦化样品,利用电感耦合等离子体对平坦化膜层进行刻蚀抛光,通过Lambda950分光光度计测试不同工艺阶段样品表面的反射率.结果表明,相比于未处理的RB-SiC初始样品,经过平坦化和等离子体刻蚀的样品表面粗糙度标准差值由1.819nm减小至0.919nm,样品表面反射率相应地提高了2%.由此说明射频磁控溅射平坦化沉积与电感耦合等离子体刻蚀的组合工艺可实现RB-SiC表面的高质量加工.     

激光表面纹理化过程中的Rayleight-Taylor不稳定性

 用表面纹理化的热模型,分析了固体表面的熔化和重固化的物理过程,计算了在纹理化过程中的表面温度,穿透深度,熔化深度,相面移动速度等物理量,提出了Rayleight-Taylor不稳定性形成周期化结构的机理。     

分形表面电子态

基于Ｐａｌａｓａｎｔｚａｓ的分形上高度－高度关联函数的近似富里叶变换Ｗ（ｋ）,研究了电子态在分形表面上的局域化,发现电子态与表面粗糙有较强的耦合,而且局域化不仅与粗糙的两个参数－均方根高度σ和关联长度ζ有关,还受表面分维数影响,数值结果显示局域化随分维的增大而加强。     

原子氢与金刚石表面的相互作用

用高分辨率电子能量损失谱研究了氢原子吸附在金刚石表面的各种振动模式,其中主要是位于360meV处的C—H键的伸长振动和位于160meV处的“剪”振动。用氚原子代替氢原子吸附在金刚石表面,观测到上述振动模式所发生的同位素位移。将金刚石表面加热至900℃后,各种振动模式全部消失,这时吸附氢原子全部脱去,金刚石表面的悬键变成平躺在表面上,导致金刚石表面石墨化。由于石墨化后π-带的作用,在损失谱上出现一个非弹性的、连续的损失峰结构。我们用UPS和AES技术进一步证实了脱氢后金刚石表面的石墨化。 关键词：     

Induction of superconductivity by strong electric field

It is shown that strong electric field perpendicular to the surface of a solid with free charges creates the surface inhomogeneous superconducting state with critical parameters depending on the surface electrical potential only.The critical temperature and magnetic field of the surface inhomogeneous state can be high in the strong electric field.     

Numerical Calculations for the Surface on a Semi-Infinite Ising Model with a Random Surface Field

We study the critical behavior of the surface on a semi-infinite simple cubic lattice Ising model with a bimodal random surface field by large cell mean-field renormaliza tion group method and Monte Carlo simulations. Our results show that the surface ferromagnetic phase exists in the weak random field range above the bulk critical temperature. The surface. specific heat is not divergence and the susceptibility show a cusp singularity at the surface ferromagnetic-paramagnetic transition for a relatively large and om field.     

Effects of an intense electric field on metal surface geometry

The effects of a strong positive electric field on the surface geometry of a single crystal, smooth metal surface are discussed. Explicit density functional calculations are presented for the field induced relaxation and evaporation of the Al(111) surface layer of atoms. The results are then explained in terms of a simple model and approximately extended to other metal surfaces. Our model determines the critical field for surface evaporation if there is no reconstruction. Finally, we will briefly mention the possibility of field induced reconstruction and its role in determining the critical field for stripping the surface layer of atoms.     

On the stability of a free surface of a magnetic fluid under microgravity

We have investigated the behavior of a free surface of a suspension of ferrimagnetic particles in heptane under strongly reduced gravity. It was found that the free surface is destabilized when a homogeneous magnetic field parallel to the surface is applied. The strength of the critical magnetic field parallel to the surface varies with the volume concentration of magnetic particles in the suspension. We show that the destabilization of the fluid layer is forced by the influence of the suspension on the homogeneity of the magnetic field producing a magnetic field component normal to the fluid surface. The dependence of the critical magnetic field on the volume concentration of magnetic particles can be explained by applying the theory of the normal-field instability to this field component under conditions of strongly reduced gravity. The experiments were carried out at the drop tower ‘Bremen’ of the Center of Applied Space Technology and Microgravity (ZARM) in Bremen.     

Critical adsorption in the weak surface field limit

We study critical adsorption in the small surface field (h(1)) limit using a homologous series of critical liquid mixtures. The experiment data, in the one-phase regime, is accurately described by a universal surface scaling function G+(z/xi(+),z/l(h)) at distance z from the interface with correlation length xi(+) and surface field length l(h) approximately absolute value of (h(1))(-nu/Delta(1)), where h(1) approximately Deltasigma, the surface energy difference between the two components.     

Elektrophotolumineszenz eines Zink-Cadmium-Sulfid-Phosphors in Abhängigkeit von Anregungswellenlänge und Feldimpulsbreite

Luminescence flashes in an excited ZnCdS (Ag) phosphor occur when electric fields are put on or off. Whether these flashes are positive or negative depends on the length of the field pulse, on the exciting wavelength, and on the polarity of the irradiated electrode. There is a critical duration of the field pulses for which no field-off flash appears. At another but related critical time, the flashes with periodic field applications change sign. These times change with the exciting wavelength. The observations are interpreted as being controlled by the gradual filling of surface traps, which in its turn is influenced by the distribution of electron and hole concentrations produced by the incident radiation and the electric field. The critical time is approximately equal to the time needed for completely filling the surface traps.     

Creasing to cratering instability in polymers under ultrahigh electric fields

We report a new type of instability in a substrate-bonded elastic polymer subject to an ultrahigh electric field. Once the electric field reaches a critical value, the initially flat surface of the polymer locally folds against itself to form a pattern of creases. As the electric field further rises, the creases increase in size and decrease in density, and strikingly evolve into craters in the polymer. The critical field for the electrocreasing instability scales with the square root of the polymer's modulus. Linear stability analysis overestimates the critical field for the electrocreasing instability. A theoretical model has been developed to predict the critical field by comparing the potential energies in the creased and flat states. The theoretical prediction matches consistently with the experimental results.     

Critical nucleation field at the structured surface of a superconductor

The effect of a structured surface of a superconductor on the critical nucleation field is discussed in two cases: one with the magnetic field parallel to the grating wavenumber and the other parallel to the ripples. In the first case, it is found that the critical field is reduced as a function of grating height, whereas in the latter case it is increased.     

Quantum critical surface of the XXZ zigzag spin chain with applied magnetic field and its application

We analyze the exact ground state of XXZ zigzag spin chain with applied magnetic field and find the quantum critical surface. Using the theorem of positive semi-definite matrix, we can prove that the ground states for a specific region are fully polarized state and one-magnon state. We also argue that this is the quantum critical surface in all cases. Applied to the superconducting quantum dots array, our result gives the analytical expression of quantum critical surface for the system in the presence of gate voltage.