Local anodic oxidation by atomic force microscopy for nano-Raman strain measurements on silicon-germanium thin films

Nanolithography based on local anodic oxidation (LAO) by atomic force microscopy is a promising technique for patterning strained film nanostructures on the silicon substrates. Due to its versatility and precise control, LAO is suited for preparing well defined calibration structures for local strain measurements. We investigated silicon-germanium patterns prepared by LAO and subsequent selective anisotropic wet etching. By combining the nanolithography and etching, dedicated strain test structures with a line width of 65 nm were achieved and utilized for calibration of tip-enhanced Raman measurements.     

Morphology and current-voltage characteristics of nanostructured pentacene thin films probed by atomic force microscopy

Atomic force microscopy was used to study the growth modes (on SiO2, MoS2, and Au substrates) and the current-voltage (I-V) characteristics of organic semiconductor pentacene. Pentacene films grow on SiO2 substrate in a layer-by-layer manner with full coverage at an average thickness of 20 A and have the highest degree of molecular ordering with large dendritic grains among the pentacene films deposited on the three different substrates. Films grown on MoS2 substrate reveal two different growth modes, snowflake-like growth and granular growth, both of which seem to compete with each other. On the other hand, films deposited on Au substrate show granular structure for thinner coverages (no crystal structure) and dendritic growth for higher coverages (crystal structure). I-V measurements were performed with a platinum tip on a pentacene film deposited on a Au substrate. The I-V curves on pentacene film reveal symmetric tunneling type character. The field dependence of the current indicates that the main transport mechanism at high field intensities is hopping (Poole-Frenkel effect). From these measurements, we have estimated a field lowering coefficient of 9.77 x 10(-6) V-1/2 m1/2 and an ideality factor of 18 for pentacene.     

Nanofabrication with atomic force microscopy

Atomic force microscopy (AFM) was developed in 1986. It is an important and versatile surface technique, and is used in many research fields. In this review, we have summarized the methods and applications of AFM, with emphasis on nanofabrication. AFM is capable of visualizing surface properties at high spatial resolution and determining biomolecular interaction as well as fabricating nanostructures. Recently, AFM-based nanotechnologies such as nanomanipulation, force lithography, nanografting, nanooxidation and dip-pen nanolithography were developed rapidly. AFM tip (typical radius ranged from several nanometers to tens of nanometers) is used to modify the sample surface, either physically or chemically, at nanometer scale. Nanopatterns composed of semiconductors, metal, biomolecules, polymers, etc., were constructed with various AFM-based nanotechnologies, thus making AFM a promising technique for nanofabrication. AFM-based nanotechnologies have potential applications in nanoelectronics, bioanalysis, biosensors, actuators and high-density data storage devices.     

Atomic force microscopy and X-ray photoelectron spectroscopy study on nanostructured silver thin films irradiated by atomic oxygen

Nanostructured silver thin films irradiated by atomic oxygen (AO) generated in a ground simulation apparatus were investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM results show that after irradiation, all the grain sizes of the thin films became more or less small, and the compact surface became rough and sparse. From XPS depth profile of an AO-irradiated silver thin film, it can be found that the silver oxides formed exist as two valences, that is, at the surface, the oxide is mainly AgO, and gradually change to Ag₂O, the content of unoxidized silver also increase with depth of film.     

Studying the high-field electron conduction of tetrahedral amorphous carbon thin films by conducting atomic force microscopy

The high-field electron conduction of tetrahedral amorphous carbon (ta-C) thin films substrate has been studied using a conducting atomic force microscope (C-AFM). The ta-C thin films with a high concentration of sp³ bonding (80–90%) were deposited on Si by field arc deposition (FAD). The high-field “conductance” and surface morphology were mapped simultaneously. At low bias, the “conductance” exhibits inhomogeneities on a large scale, presumably due to thickness variations or interface defects. However, at high bias, the small difference in “conductance” due to thickness variations or interface defects was buried by the high intrinsic “conductivity.” It has also been shown that high field causes electric breakdown in these films by converting sp³ bonding to sp² at high electric field.     

Damage mode tensile testing of thin gold films on polyimide substrates by X-ray diffraction and atomic force microscopy

In situ tensile testing has been performed on thin gold film, 320 nm thick, deposited on polyimide substrates. During the tensile testing, strain/stress measurements have been carried out by X-ray diffraction using the d-sin²ψ method. The X-ray stress analysis suggests crack formation in the films for stresses greater than 670 MPa. The surface of the deformed specimen observed by atomic force microscopy (AFM) exhibits both cracks and two types of straight-sided buckling patterns lying perpendicular to the tensile axis. These buckling patterns can have a symmetrical or asymmetrical shape. The evolution of these two kinds of buckling structures under tensile stress has been observed in situ by AFM and compared to X-ray stress data. The results indicate that symmetrical straight-sided buckling patterns are induced by the compressive stress during unloading, whereas the asymmetrical result from the delamination of the film during the tensile deformation.     

Observation by atomic force microscopy of calix[n]arene thin films and their thermal rearrangement

Vapor deposited thin films of various calix[n]arenes have been investigated by contact mode atomic force microscopy. Two classes of thin films have been defined. For para-H-calix-4-arene, para-H-calix-6-arene, and para-iso-propyl-calix-4-arene pre-organized structures are observed on deposition. For para-iso-propyl-calix-6-arene, para-tert-butyl-calix-4-arene, para-tert-butyl-calix-6-arene, para-tert-butyl-calix-8-arene glassy unordered systems are obtained on deposition. Annealing of para-iso-propyl-calix-6-arene, para-tert-butyl-calix-4-arene, para-tert-butyl-calix-6-arene at 100°C leads to crystallization either directly from the glass or by migration of nano-crystallites to form microstructures.     

Atomic force microscopy and atomic force acoustic microscopy characterization of photo-induced changes in some Ge-As-S amorphous films

Amorphous Ge₂₇As₁₃S₆₀, Ge₁₄As₂₇S₅₉ and Ge₁₆As₂₆S₅₈ thin films were prepared by thermal evaporation. Well annealed films were photodarkened by the photons with energy little exceeding the band gap energy. Using Atomic Force Microscopy we observed significant photoexpansion of studied films. Atomic Force Acoustic Microscopy revealed domains like structure of the surface and near surface parts of the samples which one was found to be more disintegrated after illumination.     

并五苯薄膜的AFM及XRD研究

报道了以热氧化硅片为衬底,用溶液溶解和真空蒸镀两种方法制备有机半导体材料并五苯薄膜.用原子力显微镜(AFM)分析了薄膜的形貌,用X射线衍射仪(XRD)分析了薄膜的晶体结构,讨论了诸多因素对薄膜的影响以及两种方法制备的并五苯薄膜的相结构.     

Some observations on thin magnetic films made by continuously monitoring the coercive force

Conclusions The experimental method described permits the coercive force/thickness relationship to be reliably determined, and avoids the problems encountered by previous techniques. The experimental values of the critical thicknesses, t ₃ and t ₄, at which coercive force anomalies occur, allow the determination of the exchange constant for the magnetic material. Coercive force monitoring during deposition enables films to be prepared with the desired magnetic parameters for computer storage systems. The method is also a useful tool for determining the critical thickness of an intermediate, non-magnetic layer separating two ferromagnetic thin films.     

A simple atomic force microscopy method for the visualization of polar and non-polar parts in thin organic films

Here we present a scanning probe microscopy method that allows for the identification of regions of different polarity (i.e. hydrophilicity) in thin organic films. This technique is based on the analysis of the difference between phase images generated at different applied bias voltages in tapping-mode atomic force microscopy. We show that, without any chemical modification of the microscope tip, it is possible to investigate surface properties of complex macromolecular layers, yielding new insight into the functional properties of the photosynthetic electron transport macromolecular complex, Photosystem I.     

Frequency modulated atomic force microscopy on MgO(001) thin films: interpretation of atomic image resolution and distance dependence of tip-sample interaction

Atomically resolved images on a MgO(001) thin film deposited on Ag(001) obtained in ultrahigh vacuum by frequency modulated atomic force microscopy at low temperature are presented and analysed. Images obtained in the attractive regime show a different type of contrast formation from those acquired in the repulsive regime. For the interpretation of the image contrast we have investigated the tip-sample interaction. Force and energy were recovered from frequency shift versus distance curves. The derived force curves have been compared to the force laws of long-range, short-range and contact forces. In the attractive regime close to the minimum of the force-distance curve elastic deformations have been confirmed. The recovered energy curve has been scaled to the universal Rydberg model, yielding a decay length of l = 0.3?nm and ΔE = 4.2?aJ (26?eV) for the maximum adhesion energy. A universal binding-energy-distance relation is confirmed for the MgO(001) thin film.     

Single-molecule switching with non-contact atomic force microscopy

We report upon controlled switching of a single 3,4,9,10-perylene tetracarboxylic diimide derivative molecule on a rutile TiO(2)(110) surface using a non-contact atomic force microscope at room temperature. After submonolayer deposition, the molecules adsorb tilted on the bridging oxygen row. Individual molecules can be manipulated by the atomic force microscope tip in a well-controlled manner. The molecules are switched from one side of the row to the other using a simple approach, taking benefit of the sample tilt and the topography of the titania substrate. From density functional theory investigations we obtain the adsorption energies of different positions of the molecule. These adsorption energies are in very good agreement with our experimental observations.     

Nanogoniometry with scanning force microscopy: a model study of CdTe thin films

In this paper scanning force microscopy is combined with simple but powerful data processing to determine quantitatively, on a sub-micrometer scale, the orientation of surface facets present on crystalline materials. A high-quality scanning force topography image is used to determine an angular histogram of the surface normal at each image point. In addition to the known method for the assignment of Miller indices to the facets appearing on the surface, a quantitative analysis is presented that allows the characterization of the relative population and morphological quality of each of these facets. Two different CdTe thin films are used as model systems to probe the capabilities of this method, which enables further information to be obtained about the thermodynamic stability of particular crystallographic facets. The method, which is referred to as nanogoniometry, will be a powerful tool to study in detail the surface of crystalline materials, particularly thin films, with sub-micrometer resolution.     

Space charge limited current measurements on conjugated polymer films using conductive atomic force microscopy

We describe local (~150 nm resolution), quantitative measurements of charge carrier mobility in conjugated polymer films that are commonly used in thin-film transistors and nanostructured solar cells. We measure space charge limited currents (SCLC) through these films using conductive atomic force microscopy (c-AFM) and in macroscopic diodes. The current densities we measure with c-AFM are substantially higher than those observed in planar devices at the same bias. This leads to an overestimation of carrier mobility by up to 3 orders of magnitude when using the standard Mott-Gurney law to fit the c-AFM data. We reconcile this apparent discrepancy between c-AFM and planar device measurements by accounting for the proper tip-sample geometry using finite element simulations of tip-sample currents. We show that a semiempirical scaling factor based on the ratio of the tip contact area diameter to the sample thickness can be used to correct c-AFM current-voltage curves and thus extract mobilities that are in good agreement with values measured in the conventional planar device geometry.     

Microstructure and electrical properties of YBCO thin films

Microstructures of c-axis oriented YBCO thin films made by high-pressure d.c. sputtering on LaAlO₃ and MgO substrates were examined by TEM. The a-axis oriented grains, second phases and micro-twins were frequently observed in the film. The a-axis oriented grains expanded along their c-axis directions during film growth. The a- and b-axis misorientations were observed in the film on MgO due to serious lattice mis-match between YBCO and MgO. The second phases were often accompanied with a-axis oriented grains suggesting they act as nuclei. These observed results were correlated with the measured T _c and J _c of the films.