Nanostructured GaN on silicon fabricated by electrochemical and laser-induced etching

Nanostructured GaN layers have been fabricated by electrochemical and laser-induced etching (LIE) processes based on n-type GaN thin films grown on the Si (111) substrate with AlN buffer layers. The effect of varying current and laser power density on the morphology of the GaN layers is investigated. The etched samples exhibited a dramatic increase in photoluminescence intensity as compared to the as grown samples. The average diameter of the GaN crystallites was about 7-10 nm, as determined from the PL data The Raman spectra also displayed stronger intensity peaks, which were shifted and broadened as a function of etching parameters. A strong band at 522 cm^− 1 is from the Si (111) substrate, and a small band at 301 cm^− 1, due to the acoustic phonons of Si. Two Raman active optical phonons are assigned h-GaN at 139 cm^− 1 and 568 cm^− 1due to E2 (low) and E2 (high) respectively.     

AFM and SEM observation on mechanism of fatigue crack growth in an Fe-Si single crystal

Fatigue crack growth tests are carried out on sheets of an Fe-3.2% Si single crystal with a crystallographic orientation appropriate for striation formation. The behaviour of slip near a crack tip during the loading and unloading parts of a fatigue cycle is observed using an Atomic Force Microscope and a Scanning Electron Microscope. The fracture surfaces are also analysed with an AFM and an SEM. The mechanism of fatigue crack growth is discussed based on the observations, and a fundamental kinematic model for fatigue crack growth is proposed. The model gives a reasonable explanation for both the crack growth and striation formation.     

钛酸纳米管的AFM和STM研究

使用AFM 和STM研究了钛酸纳米管.得到了纳米管表面的精面结构.在纳米管表面观察到一个约0.8nm高的大台阶,这是由于纳米管的螺旋特性造成的.还观察到表面各处有楞边平行于管轴的小台阶.这些小台阶与钛酸片层上的相同,是Ti-O八面体的连接方式造成.这些结果与先前在TEM研究基础上提出的钛酸纳米管模型相符合.     

化学刻蚀法制备多孔硅的表面形貌研究

应用各种表面形貌分析方法如SEM、TEM、AFM等,通过对用化学刻蚀法形成的多孔硅进行表面形貌分析,发现由于横向腐蚀比较严重而使多孔硅层在达到一定深度后就会自动脱落。腐蚀中由于大量H2的析出,对硅晶体产生巨大的应力,这些应力使硅在比较脆弱的晶粒边界或缺陷处产生微裂纹,多孔硅就从这些地方开始和生长。     

SEM/AFM studies of cementitious binder modified by MWCNT and nano-sized Fe needles

Several compositions of cement paste samples containing multiwalled carbon nanotubes were produced using a small-size vacuum mixer. The mixes had water-to-binder ratios of 0.25 and 0.3. Sulfate resistant cement has been used. The multiwalled carbon nanotubes were introduced as a water suspension with added surfactant admixtures. The used surfactant acted as plasticizing agents for the cement paste and as dispersant for the multiwalled carbon nanotubes. A set of beams was produced to determine the compressive and flexural strengths. The scanning electron microscope and atomic force microscope studies of fractured and polished samples showed a good dispersion of multiwalled carbon nanotubes in the cement matrix. The studies revealed also sliding of multiwalled carbon nanotubes from the matrix in tension which indicates their weak bond with cement matrix. In addition to multiwalled carbon nanotubes also steel wires covered with ferrite needles were investigated to determine the bond strength between the matrix and the steel wire. These later samples consisted of 15-mm-high cylinders of cement paste with vertically cast-in steel wires. As reference, plain steel wires were cast, too. The bond strength between steel wires covered with nano-sized Fe needles appeared to be lower in comparison with the reference wires. The scanning electron microscope studies of fractured samples indicated on brittle nature of Fe needles resulting in shear-caused breakage of the bond to the matrix.     

Surface reconstruction of silicon and polysilicon by Nd:YAG laser etching: SEM,Raman and PL studies

A comparative study of porous silicon (PS) fabricated by laser-induced etching on n-type crystalline-silicon and n-type polysilicon substrates is presented here under near resonance conditions by employing a Nd:YAG laser. A scanning electron microscopic study of the two PS samples, prepared under identical processing conditions, elucidates differences in surface morphology. An analysis of the Raman and PL spectra from the two PS materials, employing quantum confinement models, is presented and it further elucidates differences in the nanocrystallites size distributions. A qualitative explanation for the differences is presented.     

Morphology and composition of strontium calcium aluminate matrix doped with Dy3+

Abstract

The aim of the present study was to determine the influence of doping rare earth ion on strontium calcium aluminate (CaO–SrO–SiO₂–Al₂O₃). Therefore, the authors have manufactured luminescent material consisting of 40CaO–5SrO–5SiO₂–50Al₂O₃ doped with Dy³⁺. The compositions have been selected on the basis of chemical stability. Five pellets were prepared with different calcination temperatures and times, namely 400 and 600°C for 1 and 2 h, in order to shed light on their luminescence behaviour. X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy elaborate and characterise the formation of small particle of photoluminescent material in the phosphor matrix host material.     

纳米多孔硅的电化学制备及性能研究

纳米多孔硅是一种潜在的化学和生物传感材料,本文采用电化学腐蚀法制备纳米多孔硅。采用SEM技术分析多孔硅的表面形貌,研究了腐蚀条件对多孔硅的孔隙率、厚度、I-V特性的影响。结果表明,多孔硅的孔隙率随着腐蚀电流密度和腐蚀时间的增加而呈线性增大趋势;其厚度随着腐蚀电流密度的增加而近似呈线性增大趋势,随腐蚀时间的成倍增加而显著增大;其I-V特性表现出非整流的欧姆接触。     

OLEDs中CuPc缓冲层作用的AFM与XPS研究

利用AFM对CuPc/ITO样品表面进行扫描,发现其生长较均匀,基本上覆盖了ITO表面的缺陷,且针孔较少.通过样品表面和界面的XPS谱图分析,进一步证实了这一结果,同时发现,CuPc可以抑制ITO中的化学组分向空穴传输层的扩散.有利于器件的性能的改善和寿命的提高.     

壳聚糖与牛血清白蛋白分子印迹聚合物的制备与表征

利用壳聚糖为功能单体,在模板分子牛血清白蛋白存在下,采用滴加成球法制备出对牛血清白蛋白(BSA)具有特异识别性能的分子印迹聚合物,并用原子力显微镜(AFM)及红外光谱进行了表征。实验结果表明,利用壳聚糖制备的牛血清白蛋白分子印迹聚合物对牛血清白蛋白具有特异识别功能,显示出明显的印迹效果。这种特异分子印迹介质的制备,为分离提纯特种结合蛋白提供了一种优良方法。     

Modification of AZO thin-film properties by annealing and ion etching

Effects of annealing and ion etching on the structural, electrical and optical properties of sputtered ZnO:Al (AZO) thin films were investigated. The post-deposition annealing at temperatures T_A = 200-400 °C in the forming gas (80% N₂/20% H₂) for 1 h and ion RF-sputter etching after annealing were used. Ion-sputter etching rate was 7 nm/min. The surface topography changed noticeably after ion-sputter etching: the surface of the sample was rougher (R_a = 33 nm) in comparison with annealed sample only (R_a = 9 nm). After the post-deposition annealing temperature T_A = 400 °C and ion-sputter etching thin films have higher integral transmittance (in the range of λ = 400-1000 nm) than non-etched samples. The figure of merit (F) became higher with increase of annealing temperature and the maximum value was F = 8%/Ω at T_A = 400 °C (R_s = 10 Ω, T_int = 86%).     

CoFe合金薄膜的制备及原子力表征

室温下采用射频磁控溅射技术在涤纶纺粘非织造布表面沉积钴铁(CoFe)合金薄膜.通过原子力显微镜(AFM)观察了CoFe合金薄膜在无纺织布表面沉积的微观结构,并较为系统地分析了溅射时间、溅射压强及溅射功率对CoFe合金薄膜微观结构的影响.结果表明,磁控溅射的工艺参数配置对CoFe合金薄膜表面形貌的影响很大,溅射时间的长短、溅射功率的大小对成膜的均匀性有很大影响,在一定的溅射压强(0.5Pa)时合金颗粒将会因团聚而急速增大.     

Fabrication of precisely controlled silicon wire and cone arrays by electrochemical etching

There is an exponentially growing need for well-oriented, vertical silicon nano/micro-structure arrays, particularly in high-density integrated electronic devices. Here, we demonstrate that precisely controlled vertical arrays of silicon wires and cones can be fabricated by a combined treatment strategy of electrochemical and chemical etchings. First, a periodically ordered array of silicon wires was readily fabricated at microscale by simple electrochemical etching in which the current density played a critical role in determining the wire diameter and interspacing. The microstructures fabricated by electrochemical etching were more precisely tuned by further chemical etching, thereby transforming into cone arrays with extremely sharp tips where the cone height was controlled by the etching time. This approach could have broad utility in many electronics requiring miniaturization and high-density integration such as field emitters, photovoltaic and thermoelectric devices.     

Prediction of etching results and etching stabilization by applying principal component regression to emission spectra during in-situ cleaning

A method to predict etching results by analyzing plasma emission spectra during in-situ cleaning was investigated, where the plasma emission spectra indicate the surface condition of etching reactor walls. Plasma-wall interaction was evaluated by using both principal component regression of plasma emission spectra and attenuated-total-reflection Fourier-transform infrared spectroscopy. We found that differences in the amount of silicon oxide deposition on the reactor wall affected radical composition in the plasma during in-situ cleaning and consequently affected the etching results. Etching result predictions using the plasma spectra corresponded very well to the etching result measurements, which are used to improve etching stability.     

Mechanical properties of nanoparticle chain aggregates by combined AFM and SEM: isolated aggregates and networks

Mechanical properties of nanoparticle chain aggregates (NCA) including tensile strength and Young's modulus were measured using an instrument incorporating an AFM tip under SEM imaging. The NCA were studied individually and as network films. Carbon NCA were made by laser ablation of graphite, and SnO2 NCA were made by oxidation of a tin compound. The films were deformable and showed elastic behavior. NCA serve as reinforcing fillers in rubber and films of SnO2 NCA for trace gas detection.     

谷胱甘肽和三氧化钨表面微观结构的AFM表征

用AFM表征了络合锌的谷胱甘肽与三氧化钨溶胶掺铂晶化薄膜的表面分子结构,结果表明:络合锌的谷胱甘肽的分子为七连环状结构,七连环上的两个离子或离子基团与两条长链相连,一个离子或离子基团与一条短链相连;这解释了谷胱甘肽与Zn2 、Fe3 等过渡金属离子络合并使其被螯离,消除了其氧化性,从而提高了谷胱甘肽的抗氧化性.三氧化钨溶胶掺铂薄膜经460℃热处理后晶化,其元胞为正六面体,内含一个WO6八面体,氧离子位居六个面心,钨离子处于体心,自然生长面为002面,晶格常数为(0.75±0.05)nm,氧离子的间距为(0.55±0.05)nm.解释了谷胱甘肽与Zn2 、Fe3 等过渡金属离子络合并使其被螯离,从而消除了其氧化性,以及掺杂一定含量的铂后改善了三氧化钨溶胶的氢敏特性的机理.     

Self-trapping and Binding of Particles from Singular Pockets in Weakly Doped AFM Mott Insulator

We consider effects of binding and self-trapping of particles added or excited over the insulating state of an antiferromagnetic Mott insulator. The state of an electron or a hole (as appears in ARPES), or of their bound pair (as appears in optics) can be modified by interactions with collective degrees of freedom—deformations of the lattice or of the spin environment. The resulting self-localized state lowers the total particle energy, enhances its effective mass and splits off the electronic level below the nominal insulating gap. We show theoretically that the effect is particularly pronounced for states near the antinodal (π, 0) type point of the Brillouin zone of the CuO₂ because of proximity to the van Hove singularity. We study also the van Hove enhancements for bound states of the electron with neutral and charged impurities and for inter-gap excitons. The results are clearly important for undoped and electron-doped cuprates where the antinodal points correspond to the spectrum bottom for electrons. The effect is indirectly important for lightly hole-doped cuprates concerning the ARPES spectrum transfer between the nodal arcs and the dark antinodal regions.     

利用SEM、EDS及WDS对铜及其氧化物的价态效应研究

利用扫描电子显微镜(SEM)、X射线能谱仪(EDS)及X射线波谱仪(WDS)研究了铜及其氧化物的I_(Lα)/I_(Kα)和I_(Lα)/I_(Lβ)谱线强度比的价态效应。结果表明,不同价态铜的I_(Lα)/I_(Kα)和I_(Lα)/I_(Lβ)谱线强度比按一定的规律随价态而变化,即谱线强度比值随价数增加而减少。     

Fabrication of Periodic Nanostructures Using AFM Tip-Based Nanomachining: Combining Groove and Material Pile-Up Topographies

This paper presents an atomic force microscopy (AFM) tip-based nanomachining method to fabricate periodic nanostructures. This method relies on combining the topography generated by machined grooves with the topography resulting from accumulated pile-up material on the side of these grooves. It is shown that controlling the distance between adjacent and parallel grooves is the key factor in ensuring the quality of the resulting nanostructures. The presented experimental data show that periodic patterns with good quality can be achieved when the feed value between adjacent scratching paths is equal to the width between the two peaks of material pile-up on the sides of a single groove. The quality of the periodicity of the obtained nanostructures is evaluated by applying one- and two-dimensional fast Fourier transform (FFT) algorithms. The ratio of the area of the peak part to the total area in the normalized amplitude–frequency characteristic diagram of the cross-section of the measured AFM image is employed to quantitatively analyze the periodic nanostructures. Finally, the optical effect induced by the use of machined periodic nanostructures for surface colorization is investigated for potential applications in the fields of anti-counterfeiting and metal sensing.     

Dental Enamel Quality and Black Tooth Stain: A New Approach and Explanation by using Raman and AFM Techniques

This contribution takes in account investigation of dental enamel regarding “quality” of hydroxyapatite material involved in the mineralization process. Areas damaged by black stain were investigated in order to evaluate changes in chemical composition as compared to those of healthy dental enamel.

Different sectors on tooth surfaces were analyzed using micro-Raman spectroscopy. The integral areas of ν₁ (960 cm^?1) phosphate peak as well as of B-type carbonate peak ν₂ (1070 cm^?1) were obtained to investigate structural differences between the specimens (healthy/unhealthy enamel tooth and different sectors on unhealthy surface tooth). A complete list of chemical specimens involved in chemical processes on dental enamel surface was obtained by Energy Dispersive x-rays (EDX) investigation.

It was noticed that mineralized carbonate peak at 1070 cm^?1 decreased significantly for unhealthy tooth enamel or spots areas (as fluorite groups), suggesting that carbonate ions are easily dissolved in the presence of fluoride.

The present study is confirming an organic origin for the dental “black stain.” The “black stain” is the result of a complex generation process from the damaged enamel, thus explaining their reappearance after the mechanical removing. A possible model for the “black stain” generation process is advanced.