Study on surface morphology of GaN growth by MOCVD on GaN/Si(111) template

The surface morphology of GaN grown by MOCVD on GaN/Si template was studied. Rough morphology and deep pinhole defects on some surface areas of the samples were observed and studied. The formation of rough morphology is possibly related to Ga-Si alloy produced due to poor thermal stability of template at high temperature. The deep pinhole defects generated are deep down to the surface of MBE-grown GaN/Si template. The stress originated from the large thermal expansion coefficient difference between GaN and Si may be related to the formation of the pinhole defects. The surface morphology of the GaN can be improved by optimizing the GaN/Si template and decreasing the growth temperature.

Au(111)自组装膜表面原子力显微镜纳米刻蚀

在Au(111)硫醇自组装膜上通过原子力显微镜（AFM）纳米刻蚀加工了各种功能化纳米结构。本论文取得的主要成果如下： 1. “蘸笔”技术移除自组装膜及金基底 以烯丙基溴为墨水，用蘸笔技术在16－巯基十六羧酸（MHA）修饰的Au(111)基底上可以实现对金基底的直接加工，形成阴刻图案；并提出了详细的加工机理。 2. Au(111)自组膜表面的可逆加工 （1）利用乙醇修饰的导电AFM针尖通过电致刻蚀在Au(111)基底的烷基硫醇自组装膜上实现了阴阳刻图案的可逆加工。X射线光电子能谱分析表明阳刻图案的化学组成为氧化金，且此氧化金可被乙醇还原生成金得到阴刻图案。此阴刻图案可用作纳米模板，我们利用此模板加工了氧化铁磁性纳米结构和溶菌酶蛋白质纳米结构。 （2）用修饰硫醇的导电AFM针尖在Au(111)基底上实现了硫醇的可逆书写。 3. Au(111)自组膜表面官能团转化 用硫醇自组装膜修饰的Pt针在Au(111)基底的烷基硫醇自组装膜上实现了表面端基官能团转化。所得亲水性纳米图案可用作物理（如直接吸附纳米粒子）和化学纳米模板（如诱导硅烷自组装）。加工过程中基底自组装膜保持完整，未破坏Au-S键。 4. AFM研究适配子与血小板衍生生长因子－BB的相互作用 利用AFM电致刻蚀在HS-(CH2)12-(OCH2CH2)4-OH（EG4）/Au(111)上选择性移除EG4，在新暴露的金基底上生长血小板衍生生长因子－BB（PDGF-BB）适配子与EG4的混合自组装膜，通过PDGF-BB适配子与 PDGF-BB的特异性键合固定PDGF-BB，得到PDGF-BB的纳米图案。

Au(111)电极上分子相互作用扫描隧道显微镜研究

本论文利用扫描隧道显微镜(STM)在Au(111)电极上结合电化学方法在分子水平上观察分子的吸附组装和结构调控等。主要内容如下： (1) 用现场电化学扫描隧道显微镜(ECSTM)在Au(111)电极上研究了巯基己醇(MHO)取代六苯并苯的详细过程。取代速度强烈依赖于MHO的浓度。浓度较低时，反应速度较慢，我们可以用现场ECSTM跟踪观察详细的取代过程。取代首先发生在靠近重构线肘部的位置，出现单分子或多个六苯并苯分子的取代而形成的pits。随着取代过程的进行，这些小的pits生长或合并成较大的pits；pits周围的六苯并苯分子逐渐被MHO取代，最终在限定的区域内形成有序的domain。观察局部区域的取代过程，我们发现沿着重构线的方向扩展速度最快。快速取代之后，MHO在Au(111)电极表面形成( )R30°晶格结构，而慢速取代之后，MHO在表面形成c(4×2)超结构。与MHO在干净的Au(111)电极上的吸附相比，在六苯并苯修饰的Au(111)电极上即使在很低的浓度下也没有观察到平躺的物理吸附相，而是直接形成化学吸附相。这可能是由于六苯并苯的存在，MHO的碳氢链不能直接与Au原子接触。通过数据分析，我们发现取代速率曲线呈倒S形状。 (2) 我们用循环伏安法(CV)和ECSTM研究了腺嘌呤(Adenine，A)，胸腺嘧啶(Thymine，T)和鸟嘌呤(Guanine，G)单组分及混合组分(A+T)的电化学二维相变。施加在Au(111)电极上的电位不同，A会呈现不同的吸附状态，包括物理吸附相和化学吸附相。在物理吸附的电势范围，高分辨ECSTM图像显示，同一个电势下共存着多样性的A的吸附结构。当基底电势变得更正时，一种更倾斜的吸附状态也就是A的化学吸附相会形成。在较负电位下，A和T能通过分子之间氢键作用在Au(111)电极上形成一种新的网络结构，而G能形成多层吸附。 (3) 利用STM研究了不同方法移除硫醇自组装膜之后金电极表面的再生情况。分别使用了化学法和电化学还原脱附法。化学法比较简单，使用的试剂有王水，piranha和NaBH4。王水对金电极表面有强腐蚀作用；piranha和NaBH4对金表面的作用较小，但是NaBH4处理之后的金表面上会有较多的亮岛出现。在移除自组装膜之后的电极上直接组装六苯并苯，我们观察到用piranha和NaBH4处理之后的金电极表面上六苯并苯自组装膜缺陷较多，有序domain也比较小。电化学法脱附可以得到比较干净的金表面，直接组装的六苯并苯自组装膜有序性好，缺陷少。而且，电化学脱附法通过控制电位可以实现硫醇自组装膜和六苯并苯自组装膜的相互转换。

Growth of GaN layers on GaAs and GaP (111) and (001) substrates by molecular beam epitaxy

Films of GaN have been grown using a modified MBE technique in which the active nitrogen is supplied from an RF plasma source. Wurtzite films grown on (001) oriented GaAs substrates show highly defective, ordered polycrystalline growth with a columnar structure, the (0001) planes of the layers being parallel to the (001) planes of the GaAs substrate. Films grown using a coincident As flux, however, have a single crystal zinc-blende growth mode. They have better structural and optical properties. To improve the properties of the wurtzite films we have studied the growth of such films on (111) oriented GaAs and GaP substrates. The improved structural properties of such films, assessed using X-ray and TEM method, correlate with better low-temperature FL.

Ordering along <111> and <100> directions in GaInP demonstrated by photoluminescence under hydrostatic pressure

Photoluminescence of GaInP epilayers under hydrostatic pressure is investigated. The Gamma valley of disordered GaInP shifts sublinearly upwards with respect to the top of the valence band with increasing pressure and this sublinearity is caused by the nonlinear dependence of lattice constant on the hydrostatic pressure. The Gamma valleys of ordered GaInP epilayers rise slower than that of the disordered one. Considering the interactions between the Gamma valley and folded L and X valleys, the pressure dependence of the band gap of ordered GaInP is calculated and fitted. The results demonstrate that not only ordering along [111] directions but also sometimes simultaneous ordering along [111] and [100] directions can occur in ordered GaInP. (C) 1996 American Institute of Physics.

High quality CeO2 film grown on Si(111) substrate by using low energy dual ion beam deposition technology

By using the mass-analyzed low energy dual ion beam deposition technique, a high quality epitaxial, insulating cerium dioxide thin film with a thickness of about 2000 Angstrom, has been grown on a silicon (111) substrate. The component species, cerium and oxygen, are homogeneous in depth, and have the correct stoichiometry for CeO2. X-ray double-crystal diffraction shows that the full width at half maximum of the (222) and (111) peaks of the film are less than 23 and 32 s, respectively, confirming that the film is a perfect single crystal. (C) 1995 American Institute of Physics.

以金属为缓冲层在Si（111）上分子束外延GaN及其表征

用电子束蒸发方法在Si（111）衬底上蒸发了Au/Cr和Au/Ti/Al/Ti两种金属缓冲层,然后在金属缓冲层上用气源分子束外延（GSMBE）生长GaN.两种缓冲层的表面都比较平整和均匀,都是具有Au（111）面择优取向的立方相Au层.在Au/Cr/Si（111）上MBE生长的GaN,生长结束后出现剥离.在Au/Ti/Al/Ti/Si（111）上无AlN缓冲层直接生长GaN,得到的是多晶GaN;先在800℃生长一层AlN缓冲层,然后在710℃生长GaN,得到的是沿GaN（0001）面择优取向的六方相GaN.将Au/Ti/Al/Ti/Si（111）在800℃下退火20min,金属层收缩为网状结构,并且成为多晶,不再具有Au（111）方向择优取向.

低能碳离子束沉积（111）织构的立方SiC薄膜

在硅衬底上利用具有质量选择功能的低能离子束沉积技术沉积碳离子制备出除碳、硅之外无其他杂质元素的纯净的立方SiC薄膜．利用X射线光电子谱、俄歇电子能谱、X射线衍射对样品进行了表征．结果显示常温和400℃制备的样品为非晶结构，在800℃制备的样品由一富碳的表面层和有着良好化学计量比的SiC层组成，碳化硅晶体薄膜是（111）织构的．通过分析可知衬底温度、离子沉积能量和样品保温扩散时间等因素综合在一起对于在硅上沉积SiC薄膜起着重要作用．远远大于TRIM预测厚度的SiC薄膜的获得是高的衬底温度、一定注入能量的碳离子引起的增强扩散以及通道注入效应综合作用的结果。

Preparation of 50mm 3C-SiC/Si(111) as Substrates Suited for Ⅲ-Nitrides

50mm SiC films with high electrical uniformity are grown on Si(111) by a newly developed vertical low-pressure chemical vapor deposition (LPCVD) reactor.Both in-situ n- and p-type doping of 3C-SiC are achieved by intentional introduction of ammonia and boron into the precursor gases.The dependence of growth rate and surface morphology on the C/Si ratio and optimized growth conditions is obtained.The best electrical uniformity of 50mm 3C-SiC films obtained by non-contact sheet resistance measurement is ±2.58%.GaN films are grown atop the as-grown 3C-SiC/Si(111) layers using molecular beam epitaxy (MBE).The data of both X-ray diffraction and low temperature photoluminescence of GaN/3C-SiC/Si(111) show that 3C-SiC is an appropriate substrate or buffer layer for the growth of Ⅲ-nitrides on Si substrates with no cracks.

（111）A InP衬底上MOCVD外延InGaAsP的表面形貌和光学特性

为了研究(111)衬底的特性以及实现等边三角形微腔激光器，利用金属有机化学气相淀积(MOCVD)研究了(111)A InP衬底上InGaAsP外延层的表面形貌和光学特性。考虑到(111)A InP衬底的悬挂键密度比较低，在生长过程中有意提高了V／III比。通过扫描电子显微镜(SEM)和光荧光(PL)谱分别研究了外延层的表面形貌和光学特性。实验发现，表面形貌和光学特性随V／III比和温度的变化非常大。最佳V／IlI比和温度分别为400和625℃。

Si(111)衬底无微裂GaN的MOCVD生长

采用AlN插入层技术在Si(111)衬底上实现无微裂GaN MOCVD生长.通过对GaN外延层的a,c轴晶格常数的测量,得到了GaN所受张应力与AlN插入层厚度的变化关系.当AlN厚度在7～13nm范围内,GaN所受张应力最小,甚至变为压应力.因此,GaN微裂得以消除.同时研究了AlN插入层对GaN晶体质量的影响,结果表明,许多性能相比于没有AlN插入层的GaN样品有明显提高.