Maskless pendeo-epitaxial growth of GaN films

High-resolution x-ray diffraction (XRD) and atomic force microscopy (AFM) of pendeo-epitaxial (PE) GaN films confirmed transmission electron microscopy (TEM) results regarding the reduction in dislocations in the wings. Wing tilt ≤0.15° was due to tensile stresses in the stripes induced by thermal expansion mismatch between the GaN and the SiC substrate. A strong D°X peak at ≈3.466 eV (full-width half-maximum (FWHM) ≤300 μeV) was measured in the wing material. Films grown at 1020°C exhibited similar vertical [0001] and lateral [11 0] growth rates. Increasing the temperature increased the latter due to the higher thermal stability of the GaN(11 0). The (11 0) surface was atomically smooth under all growth conditions with a root mean square (RMS)=0.17 nm.     

{225}f片状马氏体宏观点阵变形特征的AFM观察与定量分析

利用原子力显微镜(AFM)对Fe-8Cr-1C合金{225}f马氏体的宏观形状应变特征进行了观察与定量分析.结果表明:{225}f片状马氏体宏观形状应变特征表现出与{3 10 15}f全孪晶马氏体不同的特征.{3 10 15}f全孪晶马氏体表面浮凸呈规则的"N"或""型;而{225}f片状马氏体表面浮凸呈不规则"N"型,其"浮凸群"既有均匀切变的特征,又有沿基面堆垛长大的痕迹,其浮凸高度、浮凸角远低于{3 10 15}f马氏体.     

快速热处理对(Ba,Sr)TiO3薄膜晶化行为的影响

采用射频溅射法在Si(111)基片上制备了(Ba,Sr)TiO3(BST)薄膜,并对制备的薄膜进行了快速退火热处理.采用X射线衍射和原子力显微镜分析了退火温度、退火时间和加热速度对BST薄膜晶化行为的影响.研究结果表明,BST薄膜的晶化行为强烈依赖于退火温度、退火时间和加热速度.BST薄膜的结晶度随退火温度的升高而提高.适当的热处理可降低BST薄膜的表面粗糙度,BST薄膜的表面粗糙度随退火温度的升高经历了一个先降低后增大的过程,但退火后BST薄膜的表面粗糙度都小于制备态薄膜的表面粗糙度.BST薄膜的晶粒尺寸随退火温度的升高经历了一个先增大后减小的过程.随退火时间的延长,BST薄膜的特征衍射峰越来越强,薄膜的晶化程度越来越高.随退火时问的延长,BST薄膜的晶粒尺寸和表面粗糙度也经历了一个先增大后减小的过程.BST薄膜的晶粒大小主要由退火温度决定.高的升温速率可获得较小的晶粒.     

不同退火温度下铁基薄带介观结构的AFM研究

用原子力显微镜(AFM)观测了铁基合金(Fe73.5Cu1Nb3Si13.5B9)薄带断口的介观结构.通过对310℃退火样品的观测,可以发现薄带的贴辊面区(SRFA)和自由面区(FFA)存在着非常明显的结构差异;而540℃退火样品的AFM观测结果则显示这种差异并不明显.将310℃和540℃退火的样品在HF酸溶液中进行腐蚀,获得不同腐蚀深度的腐蚀表面,再用AFM观测其表面形貌,则发现:在310℃退火样品的腐蚀表面,自由面和贴辊面形貌各自随腐蚀深度的变化而变化,并且两表面形貌之间在腐蚀前期有差异,但后期无明显不同;而540℃退火样品的两个腐蚀表面,则不存在这样的变化和差异.该观测结果与薄带断口观测到的介观结构相符合.造成这种结构差异的原因是经不同温度退火后,薄带内部残留的内应力不同.     

基片温度对TiO2薄膜表面形貌和性能的影响

利用射频磁控溅射设备在玻璃基片上制备TiO2薄膜,采用AFM、UV-Vis分光光度、接触角测定仪等测试手段,研究基片温度对薄膜表面形貌、粗糙度和表面性能的影响.结果表明,随着基片温度增加,薄膜表面粗糙度增大,薄膜中颗粒由无定形态逐渐向定向排列的晶态转变,而薄膜结构、表面形貌和粗糙度的变化明显影响薄膜表面性能.最后,探讨了薄膜的生长机理.     

AFM轻敲模式中微悬臂振动的研究

针对原子力显微镜AFM（Atomic torce microscope）在轻敲工作模式下微悬臂在谐振频率附近振动的问题，依据振动学理论和仿真分析的方法，建立了微悬臂的振动模型，仿真出了微悬臂前几阶的振动模态。得到了在保证振幅不变的情况下微悬臂各参数与其自由端偏转角的关系，指出了轻敲模式下减小AFM测量误差的方法。     

ZnO growth on Si with low-temperature CdO and ZnO buffer layers by molecular-beam epitaxy

Low-temperature (LT) buffer-layer techniques were employed to improve the crystalline quality of ZnO films grown by molecular-beam epitaxy (MBE). Photoluminescence (PL) spectra show that CdO, as a hetero-buffer layer with a rock-salt structure, does not improve the quality of ZnO film grown on top. However, by using ZnO as a homo-buffer layer, the crystalline quality can be greatly enhanced, as indicated by PL, atomic force microscopy (AFM), x-ray diffraction (XRD), and Raman scattering. Moreover, the buffer layer grown at 450°C is found to be the best template to further improve the quality of top ZnO film. The mechanisms behind this result are the strong interactions between point defects and threading dislocations in the ZnO buffer layer.     

Acquisition of high-precision images for non-contact atomic force microscopy

The atomic force microscope (AFM) system has evolved into a useful tool for direct measurements of intermolecular forces with atomic-resolution characterization that can be employed in a broad spectrum of applications. The distance between cantilever tip and sample surface in non-contact AFM is a time-varying parameter even for a fixed sample height, and typically difficult to identify. A remedy to this problem is to directly identify the sample height in order to generate high-precision atomic-resolution images. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Since in most practical applications only the microcantilever deflection is accessible, we will use merely this measurement to identify the sample height. In most non-contact AFMs, cantilevers with high-quality factors are employed essentially for acquiring high-resolution images. However, due to high-quality factor, the settling time is relatively large and the required time to achieve a periodic motion is long. As a result, identification methods based on amplitude and phase measurements cannot be efficiently utilized. The proposed method overcomes this shortfall by using a small fraction of the transient motion for parameter identification, so the scanning speed can be increased significantly. Furthermore, for acquiring atomic-scale images of atomically flat samples, the need for feedback loop to achieve setpoint amplitude is basically eliminated. On the other hand, for acquiring atomic-scale images of highly uneven samples, a simple PI controller is designed to track the desired constant sample height. Simulation results are provided to demonstrate the feasibility of the approach for both sample height identification and tracking the desired sample height.     

Nanoparticle detachment: a possible link between macro- and nanotribology?

Although particle detachment is a common phenomenon associated with most tribological processes, it seldom occurs that each piece of elemental debris can be considered as the result of a single event. Such an association has been revealed by the systematic study of a specific system, where a pin of graphite is made to rub against thoroughly polished steel. While the discontinuous nature of the transfer film allows a quantitative assessment of the volume of transfer h _e to be made by 3D optical-profilometry, the linear dependence of the rate of particle detachment dh _e/dn (n=number of rubbing cycles) with the logarithm of sliding speed v strongly suggests the existence of a particular type of stick–slip, where each stick may lead to the detachment of a debris particle. The variations in size of these debris with environment as revealed by AFM, further suggest that the global rate of particle detachment is of the form: dh _e/dn=Nx _i , where N is the number of stick–slip events per rubbing cycle, x the proportion of stick events leading to a cohesive rupture, and _i the mean volume of an elemental particle. While this relation is apparently supported by most experimental results, its actual validation can only be made by experiments at the level of single (nanoscale) asperities, carried out under well-controlled experimental conditions.