Characterization of transparent conducting oxide thin films deposited on ceramic substrates

In this work, we investigate the optical and electrical properties of various transparent conductive oxide (TCO) thin films deposited on insulating ceramics for emerging optoelectronic applications. Thin films investigated include indium tin oxide (ITO), ruthenium oxide (RuO₂), and iridium oxide (IrO₂) on Al₂O₃ ceramic substrates. The conducting films have been deposited by various techniques including RF magnetron sputtering and low-cost spray pyrolysis. The morphological characteristics of the films were carried out using high magnification optical microscopy and atomic force microscopy (AFM). Optical and electrical characterization was carried out by optical absorbance/transmittance, van der Pauw, current-voltage (I-V), and Hall effect measurements. The results are presented in this paper.     

碳纳米管原子力显微镜针尖及其在生物学研究中的应用

碳纳米管是制作原子力显微镜针尖的理想材料，这是由于碳纳米管具有很小的半径，较高的纵横比，高的柔软性能，独特的化学结构和确定的电子特性，运用碳纳米管针尖成功地获得了免疫球蛋白和单个蛋白分子等的高分辨率结构图像。     

原子力显微镜探针原位有效参数对线宽测量的修正

针对原子力显微镜（AFM）的线宽和轮廓的精确测量，对AFM探针的原位有效参数进行了定义和表征，提出使用AFM探针的原位有效参数对AFM的线宽测量结果进行修正的模型。采用有效半径和半内角表征AFM探针的复合形状，悬臂轴倾角表征探针的安装状态，设计了具有不同梯形截面的两个表征样板，通过对表征样板进行AFM和扫描电子显微镜（SEM）的比对测量获得了探针的原位有效参数。提出了在线宽测量中，当AFM的扫描轮廓线具有不同的斜度时分别采用的不同的修正公式。采用此公式和探针的原位参数对掩膜板的AFM线宽测量结果进行了修正。     

Characterization of ZnO:Al/Au/ZnO:Al trilayers for high performance transparent conducting electrodes

Symmetric ZnO:Al/Au/ZnO:Al trilayers were sputter-deposited and characterized for transparent conducting electrodes, varying the thickness of the ZnO:Al (AZO) and Au layers. The optical transmission for normal light incidence is optimum for an AZO thickness of 50 nm, due to the suppression of reflection. In this case, the transmittance is more than 0.7 for wavelengths above 400 nm and for a Au thickness of 5 nm. At the same time, the sheet resistance is approx. 30 Ω, which can be decreased to 12 Ω with the increase of the Au thickness to 9 nm. This is achieved with a moderate loss in the optical transmission. The figure of merit for transparent conducting electrodes, as introduced by G. Haacke (J. Appl. Phys. 47 (1976) 4086) yields values from 29.4 × 10^− 3 to 6.9 × 10^− 3 Ω^− 1, depending on the Au thickness and the considered wavelength range.     

AFM线宽测量不确定度的分析与评定

详细分析了P47型原子力显微镜线宽测量不确定度的来源,给出了基于几何形状的线宽测量模型,提出了线宽测量不确定度的评定路线和方法。确定了探针针尖引起的测量不确定度是AFM线宽测量不确定度的主要来源,并对其进行了定量分析。普通Si3N4探针针尖引起的不确定度分量约占线宽总量的5%。     

AFM studies of microindented GaN and InGaN

The microhardness characteristics of GaN and GaN/InGaN films epitaxially grown on (0001) sapphire have been investigated using Vickers and Knoop indenters. The variation of H_V and H_K follows a reverse type of indentation size effect (reverse ISE). The microhardness results have also been analyzed using Meyer's law, Hays-Kendall approach and Proportional specimen resistance (PSR) model. The effect of N⁺ implantation on the microhardness of GaN has also been studied. The implanted sample is more resistant to plastic penetration than the unimplanted one and it is found that implantation enhances the surface hardness. Detailed AFM studies around the indented regions of the GaN and GaN/InGaN give the nature and behavior of the deformation on the surface.     

Topographical, compositional and schottky characterization of PtSi/Si schottky diodes

PtSi ultra-thin films were grown on Si-wafer using pulsed laser deposition (PLD). As determined from X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), the compositional structures of the PtSi were discussed. Furthermore, the surface structure of these films was studied by atomic force microscopy (AFM). A possible growth mechanism is presented, on studying the variation of morphological features (i.e., roughness and size of crystallites) with annealing temperature and films thickness. In addition, by the AFM studies and schottky characterization measurements of PtSi films forming during various annealing processing, preferable preparing conditions are proposed to form the continuous and smooth PtSi thin film on Si substrate by PLD.     

Sorption of zinc by novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid

Novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid were applied as adsorbents for the removal of Zn²⁺ ions from aqueous solution. In batch tests, the influence of solution pH, contact time, initial metal ion concentration and temperature was examined. The sorption was found pH dependent, pH 5.5 being the optimum value. The adsorption process was well described by the pseudo-second order kinetic. The hydrogels were characterized by spectral (Fourier transform infrared—FTIR) and structural (SEM/EDX and atomic force microscopy—AFM) analyses. The surface topography changes were observed by atomic force microscopy, while the changes in surface composition were detected using phase imaging AFM. The negative values of free energy and enthalpy indicated that the adsorption is spontaneous and exothermic one. The best fitting isotherms were Langmuir and Redlich-Peterson and it was found that both linear and nonlinear methods were appropriate for obtaining the isotherm parameters. However, the increase of temperature leads to higher adsorption capacity, since swelling degree increased with temperature.     

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.     

Studies using AFM and STM of the correlated effects of the deposition parameters on the topography of gold on mica

A systematic study of the correlated effects of deposition temperature, film thickness and deposition rate on the morphology of gold films on mica was carried out using atomic force microscopy and scanning tunnelling microscopy. For the range of thicknesses, rates and temperatures concerned, a variety of surface structures, mainly in the form of rounded mounds, islands, long channel and short channel plateaux topographical features were formed under various combinations of these three parameters. The rounded mounds and islands formed, respectively, on the mica substrate at room temperature and at 150°C were found to be essentially independent of the film thickness and deposition rate selected. When deposited at higher temperatures (300°C and 440°C), a change from islands to channelled features, via the growth and coalescence of the islands, was observed either on increasing the film thickness for a given deposition rate (≈ 1.0 Å s⁻¹) or on increasing the deposition rate to a given film thickness (400 Å). It is evident from the results presented that, whereas the film thickness and the deposition rate at a given temperature determine to what extent the film has coalesced, the growth temperature influences the lateral size of the surface features formed. In consequence, conducting films were found when the gold coverage was ≥ ≈0.9. Investigation of the vertical characteristics of the films was also conducted. The origin of all the phenomena observed can be attributed to competition between secondary nucleation and thermally enhanced diffusion processes occurring on the gold surface during deposition and film formation.     

AFM study of the surface morphology of L-CVD SnO2 thin films

In this paper we present the results of Atomic Force Microscopy (AFM) characterisation of the surface morphology of the L-CVD SnO₂ thin films prepared by L-CVD technology and studied after exposure to air, dry air oxidation, and ion beam profiling. The L-CVD SnO₂ thin films after air exposure have a very smooth surface morphology with an average surface roughness (RMS) smaller than 0.5 nm, and average and maximal grain heights of about 1 and 2 nm, respectively. After dry air oxidation the L-CVD SnO₂ thin films exhibit an average surface roughness (RMS), as well as the average and maximal grain height, increased by one order of magnitude. Finally, after the ion beam profiling the L-CVD SnO₂ thin films exhibit an evidently disordered structure with a lot of craters. These experiments showed that the L-CVD SnO₂ thin films exhibit a very high quality surface morphology, what can be useful for solar cells and gas sensors application.     

Use of a neural network to link AFM etch patterns to plasma parameters

Plasmas play a critical role in depositing thin films or etching fine patterns while manufacturing integrated circuits. A new model for plasma diagnosis is presented. This was accomplished by linking atomic force microscopy (AFM) to plasma parameters using a neural network. Experimental AFM data were collected during the etching of silicon oxynitride films in C₂F₆ inductively coupled plasma. Surface roughness of etched patterns was characterized by means of discrete wavelet transformation. This led to the construction of three vertical (type I), diagonal (type II), and horizontal (type III) wavelet coefficient-based models. The performance of diagnosis models was evaluated in terms of the prediction and recognition accuracies. Both accuracies were optimized as a function of the number of hidden neurons. Comparisons revealed that the type I model yielded the largest recognition and the smallest prediction error. This was demonstrated even under stricter monitoring conditions. More improved diagnosis is expected by enhancing AFM resolution.     

Substrates effects on the growth behavior of Copper tetra-tert-butyl phthalocyanine films studied by atomic force microscopy

Copper tetra-tert-butyl Phthalocyanine (CuTTBPc) was vacuum deposited onto substrates of hydrophilic glass, hydrophobic silanized-glass, and one layer CuTTBPc LB film. The effects of substrates on the growth behavior and film characteristics of CuTTBPc were studied by atomic force microscopy as well as XRD and dynamic contact angle analyzer. The results show that, in the early growth stage, the island density and coverage ratio of CuTTBPc are small on hydrophilic glass surface. This result is caused from the weak interaction of CuTTBPc molecules to the glass which leads to a small nucleation rate and rougher morphology in the early growth stage. On the contrary, the nucleation rate of CuTTBPc on the silanized-surface is high and thus a much smoother film comprises densely distributed fine-grain clusters was observed. This fact indicates the higher adhesive force of CuTTBPc molecules to the silanized-surface. On the LB film, the CuTTBPc molecules are arranged in aggregative domains which are separately distributed on the glass surface. These domains act as active sites for the nucleation and growth of the later deposition process and thus, high density clusters were found in the early growth stage. The XRD results demonstrate that the film grown on glass has higher degree of crystalline structure than the others which is resulted from the distinction of the initial growth stage.     

Nanomanipulation by Atomic Force Microscopy

The linking of our macroscopic world to the nanoscopic world of single molecules, nanoparticles and functional nanostructures is a technological challenge. Researchers in nanobiotechnology face the questions “How extract and analyze a single nano‐object?”, “How to pick and place nano‐objects?” and “How to prototype a functional nanostructure?”. Here, nanomanipulation by an atomic force microscope (AFM) in combination with optical manipulation by a microbeam laser offers a practicable solution. In such a system, the AFM can be operated as a nanorobot for manipulation purposes allowing for nanometer precision. A contact free manipulation is achieved by the laser microbeam.     

Nanoparticle formation by the debris produced by femtosecond laser ablation of silicon in ambient air

The debris produced by femtosecond laser ablation (180 fs, 775 nm, 1 kHz) of Si in ambient air is deposited around the ablated craters in a circular zone with diameters between ~ 40 and 300 μm for laser fluences (F) in the region F = 0.2-8 J/cm². The debris consists of nanoparticles. The mean height of the nanoparticles increases with laser fluence (from ~ 70 to 500 nm for fluences in the range F = 0.25-4.38 J/cm²) but at high fluences (F = 8 J/cm²) becomes equal to ~ 170 nm. The average horizontal dimension of the nanoparticles increases with laser fluence. Their average vertical dimension increases in proportion to their average horizontal dimension, but at high fluences becomes much smaller than their corresponding average horizontal dimension. The nanoparticles were found to be single crystals with d spacing of 1.71 ± 0.08 Å (corresponding to {311}).     

Time-resolved opto-electronic properties of poly(3-hexylthiophene-2,5-diyl): Fullerene heterostructures detected by Kelvin force microscopy

Thin blend polymer films made of poly(3-hexylthiophene-2,5-diyl) (electron donor) and fullerene derivatives as electron acceptors ([6,6]-thienylC61 butyric acid methyl ester and [6,6]-thienylC71 butyric acid methyl ester) are prepared by the spin-coating technique on indium tin oxide covered glass substrates. Time-resolved photo-induced changes of surface potentials are detected by Kelvin force microscopy (KFM). Changes of surface potentials by 10-150 mV reveal different quality and kinetics of charge generation in the two blends in short (minutes) and long (hours) time periods. This is attributed to a combination of electron accumulation, trapping, and organic material degradation under ambient conditions. As KFM characterizes the blend films directly without metal contact layer, it reveals differences in the opto-electronic behavior of the blends, which are not detected by common photovoltaic cell characterization.     

原子力显微镜研究酸性溶液中羟基磷灰石/胶原体系的微观形态

将纳米羟基磷灰石(Hap)分散在不同pH值胶原稀溶液中，从而得到羟基磷灰石／胶原分散体系。在原子力显微镜(AFM)下观察，发现当pH=2．5时，在酸溶的胶原溶液中获得高分散性的胶原包裹纳米羟基磷灰石体系；而当pH高于或低于此值时，羟基磷灰石与胶原均维持混合前的状态。     

Contribution of material properties of cellular components on the viscoelastic,stress-relaxation response of a cell during AFM indentation

The close relationship between the mechanical properties of biological cells, namely, elasticity, viscosity, and the state of its disease condition has been widely investigated using atomic force microscopy (AFM). In this study, computational simulation of the AFM indentation is carried out using a finite element (FE) model of an adherent cell. A parametric evaluation of the material properties of the cellular components on the viscoelastic, stress-relaxation response during AFM indentation is performed. In addition, the loading rate, the size of the nucleus, and the geometry of the cell are varied. From the present study, it is found that when comparing the material properties derived from experimental force-deflection curves, the influence of loading rates should be accommodated. It also provides a framework that can quantify the variation of the mechanical property with various stages of malignancy of the cancer cell, a potential procedure for cancer diagnosis.