Optical and atomic force microscopic study on step bunching in BaB_2O_4 crystal growth

The formation of macrostep during high-temperature phase of barium meta-borate （^-BaB204） single crystal growth has been investigated by both optical in-situ observation system and atomic force microscopy （AFM）. The in- si$u observation results demonstrate that the critical linear size of growing facet exceeding the size that the macrostep generates is significantly anisotropic. The critical linear sizes are around 280 ~m and 620 ~m for {1010} and （T010} planes, respectively. AFM study illustrates that macrostep train with a height of 150 nm^200 nm is one typical morphological feature of the as-grown crystal surface. The riser of each macrostep consists of several straight and parallel sub-steps, indicating the occurrence of step bunching. Additionally, triangular sub-steps with heights of several nanometers on the treads of the macrosteps are found to be another typical feature of surface morphology, which implies a microscopically competitive bunching of sub-steps between various crystallographic orientations.

Observation of liquid crystalline collagen with atomic force microscopy(AFM)

The effects of concentration and sonication on the liquid crystalline phases of collagen were investigated by several methods,especially by the atomic force microscopy(AFM).The X-ray diffraction(XRD)results revealed that the triple-helical structure of the collagen was nearly unchanged after sonication.Moreover,the differential scanning calorimetry(DSC)examinations indicated that the thermal stability of the sonicated collagen was close to that of native collagen.The AFM observations showed that collagen with a concentration of 60 mg/mL had more ordered arrays compared to that of 30 mg/mL when both samples were treated by sonication.Furthermore,the 60 mg/mL collagen solution without sonication could still form pre-cholesteric patterns,while the liquid phase could not be observed for the 30 mg/mL collagen solution under the same conditions.Generally,AFM was an effective tool for the study of the liquid crystalline phases of collagen.

Joint Operation of Atomic Force Microscope and Advanced Laser Confocal Microscope for Observing Surface Processes in a Protein Crystal

We demonstrated the insitu observation of a moving atomic force microscope (AFM) cantilever using a laser confocal microscope combined with a differential interference microscope (LCM-DIM). The AFM cantilever scanned or indented the {110} surface of a hen egg-white lysozyme crystal in a supersaturated solution. Using a soft cantilever, we could observe the step growth with high time resolution by LCM-DIM and perform quantitative measurements of the step height by AFM simultaneously. In addition, a hard cantilever was used with LCM-DIM to observe the dynamics of crystal surface scratching and indentation. In the supersaturated solution, the small steps generated from the scratched line aggregated to macro steps, and subsequently flattened the surface.

Observation of atomic steps on CaCO_3 crystal surface

By using scanning polarization force microscopy,the deliquescence process and the atomic steps on the cleavage surface of CaCO3 in air were studied in situ.Under an exposure to medium umidity(-57%),the sloiw step movement has been observed.

In-situ Observation of the Growth of Fibrous and Dendritic Crystals in Quasi-2-dimensional Poly(ethylene oxide) Ultrathin Films

Crystal growth processes of poly（ethylene oxide） were followed from the original nucleation sites by using atomic force microscopy. Two distinct quasi-2-dimensional crystals about 4 nm thick were obtained from as-spun polymer ultrathin films： fibrous crystals, generated by the sheafing field via spin-coating, coexist with con- ventional dendrites. The growth of the two structures is dominated by diffusion limited aggregation, though the growth rate of the fibrous crystals is around one order of magnitude faster than that of the dendrites. The fibrous crystals are more stable than the dendritic ones.

Investigation on the Folding Mode of a Polymer Chain in a Spiral Crystal by Single Molecule Force Spectroscopy

Investigation on the folding mode of a single polymer chain in its crystal is significant to the understanding of the mechanism of the fundamental crystallization as well as the engineering of new polymer crystal-based materials. Herein, we use the combined techniques of atomic force microscopy （AFM） imaging and force spectroscopy to pull a single polyethylene oxide （PEO） chain out of its spiral crystal in amyl acetate. From these data, the folding mode of polymer chains in the spiral crystal has been reconstructed. We find that the stems tilt in the typical flat area, leading to the decrease in the apparent lamellar height. While in the area of screw dislocation, the lamellar height gradually increases in the range of several nanometers. These results indicate that the combined techniques present a novel tool to directly unravel the chain folding mode of spiral crystals at single-molecule level.

Research on a Diamond Tip Wear Mechanism in Atomic Force Microscope-based Micro/nano-machining

The object is to investigate the wear of an atomic force microscope (AFM) diamond tip when conducting micro/nano machining on single crystal silicon surface. The experimental research and theoretical analysis were carried out on the worn tip in terms of wear rate, wear mechanism and the effect of the tip wear on micro machining process. The wear rate was calculated as 1.7(10～10mm 3/(N·m) by using a theoretical model combined with the experimental results. Through an integration of an AFM observation on the worn tip features with the FEM simulation of the stress distribution, in addition to the unit cutting force calculation on the AFM diamond tip, the wear mechanism of the AFM diamond tip was concluded as mainly chemical wear, and the wear process was also elaborated as well.

Application of modified quartz crystal sensors:Detection of isobutyl alcohol,ethyl acetate and ethylene

Aroma volatilization is one of the very important attributes of agricultural products during ripening.Ingredients of aroma compounds experience changes over products’different ripening stages.This paper aimed to develop a detection system based on modified quartz crystal sensors to detect volatile organic compounds(VOCs).By drop-coating on sensors’surface,four sensors were made using quartz crystal resonators coated with four different absorbable materials:ethyl cellulose,cellulose acetate,1,2-dioleoyl-sn-glycero-3-[phosphor-L-serine],and galactosyl ceramide.With the diversely coated sensors,three VOCs:isobutyl alcohol,ethyl acetate and ethylene were detected at ppm level.To investigate the structure influence of the coated sensing films on VOCs absorption,the topography of films was imaged in 3D using atomic force microscopy(AFM)in tap mode for qualitative analysis of gas absorption.The selectivity and sensitivity were investigated when sensors were exposed to VOCs with increasing concentrations.The results showed that the frequency shift of sensors was linear to the concentrations of all three VOCs in the range of 5-25 ppm.With values reaching over 4.5 Hz/ppm,the sensitivity of cellulose acetate coated sensor to three VOCs was similar,higher than that of sensors with other coatings.The high sensitivity of the cellulose acetate coated sensor might be due to the film’s rough surface and porous structure.The results may help further research on detection of fruits’organic volatiles during the ripening stage.

Adsorption-desorption of Silica Nanoparticles on Poly（ethylene glycol） Brushes Grafted onto Au Substrate Studied by Quartz Crystal Microbalance

The adsorption-desorption of silica nanoparticles（NPs） on poly（ethylene glycol）（PEG） grafted onto gold（Au） substrate was studied by quartz crystal microbalance with dissipation monitoring（QCM-D） technique. The results of frequency and dissipation show that SiO2 NPs can be adsorbed strongly on PEG-SH brushes at pH of 9.6, and a new dense and rigid construction is formed. Adjusting the pH from 9.6 to 12.3 resulted in the desorption of si- lica NPs from the PEG brushes because of a significant weakening of the hydrogen bond between the silica NPs and PEG chains. In addition, the viscoelastic properties of the system during the adsorption-desorption process were also analyzed via the relationship between the normalized frequency（Af/n） and mass. And the corresponding atomic force microscopy（AFM） images also exhibit morphological changes during the above process, consistent with the changes in viscoelasticity.

Impact of cooling condition on the crystal structure and surface quality of preferred c-axis-oriented AlN films for SAW devices

AlN films with preferred c-axis orientation are deposited on Si substrates using the radio frequency(RF) magnetron sputtering method.The post-processing is carried out under the cooling conditions including high vacuum,low vacuum under deposition gas ambient and low vacuum under dynamic N2 ambient.Structures and morphologies of the films are analyzed by X-ray diffraction(XRD) and atomic force microscopy(AFM).The hardness and Young's modulus are investigated by the nanoindenter.The experimental results indicate that the(100) and(110) peak intensities decrease in the XRD spectra and the root-mean-square of roughness(Rrms) of the film decreases gradually with the increase of the cooling rate.The maximum values of the hardness and Young modulus are obtained by cooling in low vacuum under deposition gas ambient.The reason for orientation variation of the films is explained from the perspective of the Al-N bond formation.

AFM Observation of GaN Grown on Different Substrates at Low Temperatures

Aim To study the relationship between the substrate temperature and the morphology and properties of GaN. Methods\ Applying the hydride chemical vapor deposition method, GaN films were deposited on different kinds of substrates, including sapphire, Si(111),Si(100),GaAs and GaP(111) both on the P face and the Ga face. The growth was performed at low temperatures of below 700℃. XRD, Hall measurement, cathodoluminescence (CL) and atomic force microscopy (AFM) were used to characterise the film properties. Results\ It was found that the temperature and the nature of substrate materials influence the layer morphology. Conclusion\ The analysis shows that no apparent relationship exists between the optical properties and layer morphology.

铜在含SO_2大气中的腐蚀初期规律和机理

利用原子力显微镜 (AFM)原位考察了铜在SO2 质量分数为 0 .9× 1 0 - 6和 90 %相对湿度条件下 ,大气腐蚀过程中表面形貌及结构变化 ,观察到铜在大气腐蚀中高分辨的形貌变化过程 :铜表面逐渐形成纳米级的蚀点 ,并随着时间延长变大和彼此交迭 ,而后开始更大尺度的新一层次蚀点的发展 ,表现出腐蚀微电池层次发展特征。红外反射吸收光谱 (IRAS)表明 ,碱式硫酸盐是构成腐蚀产物膜的主要组分。石英晶体微天平 (QCM)原位测得的动力学曲线表明 ,铜在该条件下的腐蚀速度呈现出随时间延长而逐渐下降的趋势 ,说明形成的腐蚀产物对进一步腐蚀产生抑制作用。

PZT薄膜晶化过程的相变及铁电畴监测

采用射频磁控溅射法，在室温Pt／Ti／SiO_2／Si上制备了非晶态Pb(Zr_(0.48)Ti_(0.52))O_3(PZT)薄膜，经不同温度，相同保温时间快速退火处理使其转化为多晶PZT薄膜。用XRD，AFM测定了PZT薄膜的相组分与表面结构，并利用压电响应力显微镜(piezoresponse force microsco-py，PFM)观察了初始晶化和高度晶化样品自发极化形成的铁电畴。结果表明：PZT薄膜晶化发生在550℃，PFM可观察到自发形成的圆形铁电畴。650℃处理的样品晶化最充分并呈现出(111)择优取向，用PFM观察到该样品形成具有强烈压电信号的电畴。由此分别算得铁电相占薄膜总体积的(7.8±0.2)％和(97.3±0.2)％。PFM结合XRD，AFM的运用为寻求铁电薄膜晶化机理提供了新的途径。

热处理对STO铁电薄膜微结构的影响

系统研究了CFA与RTA两种热处理方式以及热处理温度和时间对STO薄膜微结构的影响.STO薄膜采用脉冲激光沉积法(PLD)制备.采用原子力显微镜(AFM)和XRD分别对薄膜的表面形貌和晶粒结构进行分析.结果表明,在热处理温度650～800℃范围内,相对于CFA、STO薄膜经RTA热处理后,薄膜表面晶粒大小分布均匀、致密.两种热处理方法都使薄膜的晶粒直径随温度升高而增大,并且温度越高,薄膜的晶形越完整,同样热处理温度下,RTA与CFA相比薄膜的晶粒较小,两种热处理方法的最大晶粒尺寸都＜120nm.但XRD分析结果表明,在相同热处理温度下,CFA热处理的结晶转化率较RTA热处理要高.在一定范围内,RTA热处理时间对薄膜晶粒尺寸影响不大,热处理时间越长,晶粒更加完整,表面更加均匀平整,结晶转化率越高.

原子力显微镜针尖诱导聚氧乙烯熔体结晶的研究

原子力显微镜（AFM）是研究高分子结晶行为的一种重要实验手段．在使用AFM原位观察高分子结晶时，为保证能真实地反映结晶过程，一个必须注意的问题是要避免AFM针尖的影响．与此同时，人们考察了在AFM扫描时针尖诱导高分子结晶成核的情况．若使用AFM接触模式（contact mode），扫描时容易造成较大的横向剪切力，从而增大了针尖诱导成核的可能性，在聚氧乙烯（PEO）体系中，Pearce和Vancso认为AFM针尖没有诱导PEO结晶，而Beekmans和Vancso等，则发现AFM针尖可能会诱导聚己内酯（PCL）分子链沿着AFM扫描方向（水平方向）的成核，并生长大致垂直于扫描方向的edge-on晶体，上述两过程的区别就在于剪切力的大小不同，

纳米压痕硬度尺寸效应的残余面积最大压深模型

针对材料在纳米压痕硬度测试实验中出现的压痕尺寸效应,通过对单晶硅的纳米压痕实验,得到压痕的真实最大压深,再利用原子力显微镜获得压痕的三维形貌,并结合Matlab软件得到压痕的真实残余面积。以残余面积和最大压深为变量,提出了一种新的描述硬度压痕尺寸效应的模型———残余面积最大压深模型,此模型能更好地描述和理解纳米压痕硬度的尺寸效应。

用AFM研究杜仲抗真菌蛋白的晶体生长

随着后基因组时代的到来以及蛋白质组学研究的深入开展,研究蛋白质晶体生长成为生物化学和结构生物学领域一个广泛关注的课题。通过使用原子力显微镜(Atomic Force Microscope,简称AFM)对杜仲抗真菌蛋白(eucommia antifungal protein,简称EAFP)的晶体在有母液存在下原位实时动态地进行了晶面生长观察。研究结果表明:不同过饱和度对EAFP晶体生长形貌的影响较大,较高的过饱和度下生长很快,生长台阶密度高,较高的过饱和度下主要进行各向异性二维台阶的发生、发展,较低的过饱和度下主要采用螺旋位错的生长方式,当过饱和度极低时生长缓慢,且晶体表面有很多小孔存在,晶面生长很不完整;还对不同过饱和度下晶体生长速率进行了定量的测量,也反映了过饱和度对EAFP晶体生长的影响;同时对在AFM观察过程中由探针的扫描速度和方向对表面形貌的影响进行了讨论。

利用无机盐制备γ-Al_2O_3粉体与薄膜的工艺技术研究

发明了γ Al2O3基陶瓷气敏传感器材料体系,并正研究其薄膜型传感器件。本文以廉价的无机盐Al(NO3)3·9H2O为原料,通过溶胶 凝胶法制备了勃姆石(γ AlOOH)溶胶,然后经干燥、煅烧制备了γ Al2O3的粉体,并通过旋转涂覆工艺制备了γ Al2O3的薄膜,应用X射线衍射(XRD)、X射线光电子能谱(XPS)、原子力显微镜(AFM)等现代分析技术对粉体的物相和薄膜的组分及表面形貌进行了表征,对γ AlOOH溶胶制备过程中的一些影响因素进行了探讨,得出了比较好的制备γ Al2O3基陶瓷粉体和薄膜型气敏传感器的工艺技术条件。

Al诱导a-Si:H薄膜的晶化

采用等离子体化学气相沉积方法在镀Al玻璃及单晶Si衬底上制备了氢化非晶硅 (a Si:H)薄膜 ,研究了样品在不同的热处理过程中Al对其晶化过程的影响。X射线衍射测量发现 ,由于Al的存在使a Si:H的晶化温度大幅度降低 ,并得到了有强烈 (111)结晶取向的多晶Si薄膜。X射线光电子能谱分析表明 ,热处理过程中Al向Si薄膜表面的扩散降低了Si的成核温度。

纳米二氧化钛的晶型转变及光催化性能研究

采用溶胶 凝胶法制得稳定的TiO2透明溶胶,凝胶经焙烧制备了纳米TiO2粉体,利用FT IR、XRD和原子力显微镜(AFM)技术对其进行了结构和形貌表征,考察了其对水杨酸的光催化活性。研究结果表明,醇胺不同的加入量,对TiO2从锐钛矿转变为金红石型的晶相转变温度(600～800℃)有很大影响,FT IR谱的423cm-1处吸收峰为金红石型TiO2的特征Ti—O键振动峰,采用310nm的紫外光波长照射时锐钛矿型TiO2粉体具有较高的光催化活性。