Atomic force microscopy (AFM) study of poly(ethylene terephthalate-co-4,4′-bibenzoate): A polymer of intermediate structure

An atomic force microscope (AFM) operating in both tapping and contact modes was used to study the surface topography and the molecular organization of a molded flexural test bar prepared from a poly(ethylene terephthalate-co-4,4'-bibenzoate) copolymer containing a terephthalate:4,4′-bibenzoate molar ratio of 45:55 (PETBB-55). Micrometer-scale (15 × 15 μm) contact-mode AFM images revealed that the PETBB surface contains a deep indentation that forms trenches that extend over the entire surface examined. In addition, the surface may appear as an overlay of fibrils having different orientation. At greater magnification (1 × 1 μm), it is possible to observe the existence of micropores. These results were also observed in images obtained while operating the AFM in the tapping mode. The side of the part is more homogeneous and ordered than is its top surface. It has the appearance of a stacked lamellar structure in which missing fibrils can originate cracks ∼0.5-μm wide. Fine surface details were observed in nanometer-scale images, showing the presence of chains of white spots that could represent molecules or a cluster of molecules. These chains can form domains in which they are almost parallel to each other and have a preferred orientation; this structural organization was generated without any orientation other than that produced during a mold flow. Alternatively, chain lengths are interrupted and white spots form, distorted by easily recognizable hexagonal arrangements. The degree of lamellar order observed in the side of the bar, the area of greatest flow orientation in the part, was not been observed for the PET homopolymer in the past and bears some resemblance to previously imaged liquid crystalline polyester (LCP) structures. Combined with some previously reported LCP-like mechanical properties, we propose that this PETBB copolymer is, in fact, a “frustrated LCP,” one that with some driving force could be converted to liquid crystallinity. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2616–2623, 2001     

Nanotribological characterization of digital micromirror devices using an atomic force microscope

Texas Instruments’ digital micromirror device (DMD) comprises an array of fast digital micromirrors, monolithically integrated onto and controlled by an underlying silicon memory chip. The DMD is one of the few success stories in the emerging field of MEMS. In this study, an atomic force microscope (AFM) has been used to characterize the nanotribological properties of the elements of the DMD. An AFM methodology was developed to identify and remove micromirrors of interest. The surface roughness, adhesion, friction, and stiffness properties of the DMD elements were studied. The influence of relative humidity and temperature on the behavior of the DMD element surfaces was also investigated. Potential mechanisms for wear and stiction are discussed in light of the findings.     

纤维素酶预处理对化机浆磨浆及纤维形态的影响

研究了在精磨前用纤维素酶预处理杨木化学机械浆对磨浆的影响,探讨了纤维素酶用量对能耗、纸浆物理性能和纤维形态的影响,并采用扫描电镜和原子力显微镜对其表面形态进行分析。结果表明,随着酶用量的增加,磨浆能耗逐渐降低,但是纸浆的物理强度性能都有不同程度的降低。通过原子力显微镜和扫描电镜观察发现,酶处理后,纤维在打浆过程中容易分丝帚化和断裂,纤维长度下降,这也是纸浆物理强度性能降低的原因。     

等离子体处理对丙纶纤维表面接触角的影响

论述了等离子体处理后丙纶纤维表面形态以及接触角的变化。利用基于Wilhelmy原理的接触角测量仪测量了纤维的动态接触角,为表征纤维的润湿性能提供了一种很好的途径。通过比较分析得出了等离子体处理后丙纶纤维的表面形态和表面接触角的关系。     

Convenient near-field optical measurement and analysis of polystyrene spheres

The modification of a commercial tapping mode atomic force microscope (AFM) into a transmission mode near-field scanning optical microscope (NSOM) is presented and polystyrene spheres in the diameter of 100 nm are used in this experiment. The detection of near-field signals is based on photodiodes with lock-in technique, and resolutions of topography and near-field signals obtained are about 10 and 20 nm, respectively. Furthermore, it is discovered that the computer-simulated near-field energy distribution profile, obtained by scanning over polystyrene spheres under illumination mode, falls within 5% range as compared with experimental values. The near-field absorption coefficient can be determined by this way. This will be a useful theoretical model to analyze the near-field transmission effect from others.     

Tribological behaviour of MW PACVD diamond coatings in vibrating contacts

Six diamond coatings were produced by microwave plasma-assisted chemical vapour deposition (MW PACVD) on polished SiC substrates. Process gas pressure and process gas composition were varied systematically, resulting in different coating morphologies, roughnesses and grain sizes. Friction and wear were investigated for unlubricated vibrating contact conditions in air at room temperature. Tribological tests on diamond coatings were performed in a ball-on-disc configuration, with steel balls (100Cr6) and alumina balls acting as counterbodies. For comparison of the tribological performance of the diamond coatings, standard tests were performed with a stroke of 200 μn, a load of 10 N, and a frequency of 20 Hz. The effect of relative humidity (RH) was investigated by testing in dry (3% RH), in normal (50% RH), and in moist air (100% RH), respectively To investigate running-in effects and wear propagation, the test duration (10⁴, 10⁵, and 1.2·10⁶ sliding cycles) was varied. For steel/diamond pairings, high wear at the steel ball and high friction were measured, influenced by roughness and grain size of the diamond coating and by relative humidity. For Al₂O₃ against diamond, a pronounced running-in of friction and wear was found. High friction and high wear at the beginning of each test are followed by a stationary phase with extremely low friction coefficients (⩽ 0.05) and with wear rates below the limit of resolution. This running-in depends on grain size and roughness of the coating, on relative humidity, as well as on the operational parameters. Surface analysis using SEM, EDX, LRS and AFM was conducted, to investigate tribologically induced surface changes.     

AFM分析磁控溅射法制备的TiO2纳米薄膜

采用磁控反应溅射法，在室温条件下制备了TiO2纳米薄膜，用原子力扫描显微镜(AFM)分析考察了溅射功率、溅射时真空室压力等工艺参数对薄膜结晶状态、晶粒尺寸的影响．实验结果表明，在室温下，只有溅射功率大于100W以上时，才能形成粒子结晶完全的纳米薄膜，随着溅射功率的增加，真空室溅射气压的降低，薄膜中TiO2粒子尺寸显著增大；随着溅射时间的延长，薄膜厚度增加．并根据溅射薄膜的成膜机理，讨论了实验工艺参数对薄膜微结构的影响。     

ABRASIVE-BASED NANO-FINISHING TECHNIQUES: AN OVERVIEW

The surface finishing techniques can be divided into two categories: traditional and advanced. To overcome some of the problems of traditional finishing techniques, hybridized processes have been evolved by the researchers. Some of the advanced finishing processes that have been reviewed are abrasive flow machining (AFM), magnetorheological finishing (MRF), magnetorheological abrasive flow finishing (MRAFF), magnetic abrasive finishing (MAF), chemo mechanical polishing (CMP), etc. Most of these processes have been developed in the recent past and they can be employed to produce optical, mechanical, and electronic components with micrometer or sub-micrometer form accuracy and surface roughness within nanometer range with hardly any surface defects. However for large size flat components, MAF seems to be the most suitable finishing process. In MAF, DC power supply is given to the electromagnet hence intermixing of ferromagnetic abrasive particles during the process does not take place and the worn out cutting edges keep interacting with the workpiece surface. As a result, the finishing rate is quite low. The use of pulsed DC power supply to the electromagnet results in pulsating flexible magnetic abrasive brush (P-FMAB), which substantially enhances the finishing rate. The on-line measurement of the forces has helped in understanding the mechanism of material removal during Static-FMAB (S-FMAB) and Pulsating-FMAB. The magnitude of normal magnetic force (originating indentations) in P-FMAB has been found to be dynamic in nature and substantially high in magnitude as compared to S-FMAB.     

Impact of phosphorus doping to multiple-stacked Si quantum dots on electron emission properties

We have fabricated multiple-stacked phosphorous doped Si quantum dots (P-doped Si-QDs) embedded in SiO₂ on n-Si(100) structures and characterized their field electron emission under DC bias application to semitransparent Au top-electrodes. At applied biases of −8 V and over, the electron emission signal with a peak kinetic energy at ~2.0 eV was detected. In addition, we also found that the electron emission was drastically enhanced with an increase in the applied DC bias over −11 V. The applied bias dependence of emission intensities shows that the P-doped Si-QDs is effective to improve electron emission efficiency while undoped Si-QDs stack is suited to low power operation. This indicates that electric field was reduced near the top side of the Si-QDs stack and an increase in electron injection rate from the n-Si(100) to the dots by phosphorus doping plays a role on high efficient electron emission from the Si-QDs stacked structures.     

Optoelectronic properties of a perylene substituted (cholesteryl)benzoateethynylene co-polymer

A perylene cholesteryl-benzoateethynylene co-polymer was synthesized by Sonogashira reaction and characterized by NMR, UV–Vis, static and dynamic fluorescence spectroscopy and cyclic voltammetry. The optical and electrochemical properties in solution are consistent with photoinduced energy transfer from the electron donor conjugated backbone to the electron acceptor perylene substituent. Photovoltaic properties are indeed found, even if the performance of the solar cells is quite low due to the formation of aggregates. The incorporation of (6,6)-phenyl C61–butyric acid methyl ester (PCBM), however, increases by an order of magnitude the efficiency of the prototype (from 10⁻⁴ to 10⁻³%) due to both better phase mixing and improved electrical continuity as supported by Atomic Force Microscopy (AFM) and Electrical Force Microscopy (EFM) studies.