Scanned-cantilever atomic force microscope with large scanning range

A scanned-cantilever atomic force microscope (AFM) with large scanning range is proposed, which adopts a new design named laser spot tracking. The scanned-cantilever AFM uses the separate flexure x-y scanner and z scanner instead of the conventional piezoelectric tube scanner. The closed-loop control and integrated capacitive sensors of these scanners can insure that the images of samples have excellent linearity and stability. According to the experimental results, the scanned-cantilever AFM can realize maximal 100 × 100 (μm) scanning range, and 1-nm resolution in z direction, which can meet the requirements of large scale sample testing.     

Investigation of heteroepitaxial diamond films by atomic force and scanning tunneling microscopy

We report on Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) investigations on chemical vapour deposited heteroepitaxial diamond films. Besides the good macroscopic crystal morphology a statistical tilt up to ±5.2° of the oriented crystallites has been found relative to the silicon substrates. By optimizing the process conditions, however, the crystal tilt of the films can be reduced, resulting in an improved film perfection. On crystallite (001)-surfaces a substructure of growth facets or islands has been found and high resolution STM images have established a 2×1 surface reconstruction on these growth facets. AFM and SEM were applied to study the morphology of diamond nuclei initially grown on the silicon substrate. Strong island like (Volmer-Weber) growth has been found, with a nucleus height to diameter ratio of 1:1. While the islands are growing in size with respect to time of nucleation, its aspect ratio does not change, due to the high surface free energy of the diamond relative to silicon.     

Thermal and kinetic surface roughening studied by scanning tunneling microscopy and atomic force microscopy

Recent studies of thermal roughening on Si surfaces and kinetic roughening of some growing films, copper and tungsten, by using scanning tunneling microscopy and atomic force microscopy are reviewed. A logarithmic divergence of the surface height fluctuations of Si(111) vicinal surfaces is confirmed, in agreement with the theoretical prediction of rough surface in thermal equilibrium. For the kinetically formed rough surfaces, power law dependences of the interface width on the system size are clearly observed. Furthermore, the tungsten films show a short-range scaling regime and a long-range “smooth” regime. The roughness exponents α are compared with theoretical predictions: for the typical Cu electrode position condition (α=1/2), the exponent appears to be close to that found for local growth models, and for tungsten films (0.7～0.8), it is consistent with recent predictions for growth where surface diffusion is predominant.     

Sensing dipole fields at atomic steps with combined scanning tunneling and force microscopy

The electric field of dipoles localized at the atomic steps of metal surfaces due to the Smoluchowski effect were measured from the electrostatic force exerted on the biased tip of a scanning tunneling microscope. By varying the tip-sample bias the contribution of the step dipole was separated from changes in the force due to van der Waals and polarization forces. Combined with electrostatic calculations, the method was used to determine the local dipole moment in steps of different heights on Au(111) and on the twofold surface of an Al-Ni-Co decagonal quasicrystal.     

Electron stimulated desorption induced by the scanning tunneling microscope

The use of the scanning tunneling microscope (STM) as an excitation source and a probe of electron stimulated desorption on the atomic scale is reviewed. The case of H desorption from H-terminated Si(001) is examined in detail. Experimental results on excitation thresholds, desorption cross-sections, isotope effects and site-selectivities are presented. Evidence for mechanisms involving direct electronic and hot ground-state desorption, as well as a novel multiple-vibrational excitation mechanism is discussed. Using the latter mechanism, the ultimate resolution limit of selective single atom desorption is achieved. New results on desorption from Si dihydride, including a proposed mechanism for the STM-induced H/Si(001)-3 × 1 to 2 × 1 conversion, are presented. Possible applications of STM-induced desorption in nanofabrication are considered.     

Scanning tunneling microscope for electrochemistry - a new concept for the in situ scanning tunneling microscope in electrolyte solutions

We have constructed a scanning tunneling (STM) for operation in electrochemical conditions in electrolyte solutions. The electrochemical potentials of the tunneling tip and the substrate with respect to a reference electrode can be simultaneously controlled. The apparatus offers a new possibility for complete in situ observation of electrode surfaces in electrolyte solutions under potentiostatic conditions. The electrochemical deposition and dissolution of Ag have been investigated with this instrument.     

Investigation into layers formed by selective transfer CMP mechanisms with atomic force microscope

To understand mechanisms of chemical mechanical planarization (CMP), an atomic force microscope (AFM) was used to characterize polished layer surfaces formed by selective transfer after a set of polishing experiments. It is know that in the process of friction of two materials and in the presence of own lubricants, wear phenomenon itself manifests as a transfer of material from an element of a friction couple on the other, this phenomenon being characteristic to the selective transfer process. A selective transfer can be safely achieved in a friction couple, if there is a favorable energy, and in the presence of relative movement, if in the friction area is a material made by copper and the lubricant is adequate (glycerin or special lubricant). The forming selective layer on the contact surfaces makes that the friction force to be very low because of the structure formed by selective transfer. To optimize the CMP process, one needs to obtain information on the interaction between the slurry abrasive particles (with the size range of about 30–70 nm) and the polished surface. To study such interactions, we used AFM. Surface analysis of selective layer using the AFM revealed detailed surface characteristics obtained by CMP. Studying the selective layer CMP, of which the predominated one is copper (in proportion of over 85%), we found that the AFM scanning removes the surface oxide layer in different rates depending on the depth of removal and the pH of the solution. Oxide removal happens considerably faster than the copper CMP removal from the selective layer. This is in agreement with generally accepted models of copper CMP. It was found that removal mechanisms depend on the slurry chemistry, potential per cent of oxidizer, and the applied load. This presentation discusses these findings. Both load force and the friction forces acting between the AFM tip and surface during the polishing process were measured. One big advantage of using the AFM tip (of radius about 50 nm) as abrasive silica particle is that we can measure forces acting between the particle-tip and the surface being polished. Here, we report measurement of the friction force while scratching and polishing. The correlation between those forces and removal rate is discussed.     

脂质体结构特性的原子力显微镜研究

用原子力显微镜(AFM)研究了1,2二油酸甘油3磷酸1甘油(DOPG)脂质体胞囊的形态和脂双层膜结构.报道了AFM探针与吸附在氧化硅膜上脂质体的相互作用结果.实验结果表明,在液晶态的DOPG中,AFM图像是一些球形或椭球形颗粒.这些球形或椭球形颗粒与液晶态的DOPG脂质体的结构特性有关.当AFM的探针与脂质体表面相互作用力超过某临界值时,脂质体胞囊破裂,变成脂双层结构.从图上可以看到,第二层的DOPG膜吸附在第一层上,膜的厚度约为5nm. 关键词： 原子力显微镜 脂质体 纳米结构     

Conductance through atomic contacts created by scanning tunneling microscopy

We investigate conductance through contacts created by pressing a hard tip, as used in scanning tunneling microscopy, against substrates. Two different substrates are considered, one a normal metal (Cu) and another a semi-metal (graphite). Our study involves the molecular dynamics simulations for the atomic structure during the growth of the contact, and selfconsistent field electronic structure calculations of deformed bodies. We develop a theory predicting the conductance variations as the tip approaches the surface. We offer an explanation for a quasiperiodic variation of conductance of the contact on the graphite surface, a behavior which is dramatically different from contacts on normal metals.     

原子力显微镜探针耦合变形下的微观扫描力研究

原子力显微镜(AFM)的微探针系统是典型的微机械构件，它在接触扫描过程处于耦合变形状态.采用数值模拟方法探究恒力模式下探针耦合变形对微观扫描力信号、微观形貌信号的影响.研究表明，AFM的恒力模式扫描中，法向扫描力并不是恒定大小，与轴向扫描力存在耦合作用，在粗糙峰峰值增加阶段，二力均增加；在粗糙峰峰值减小阶段，二力均减小；该耦合作用随形貌坡度、针尖长度等增加而加强.微观形貌的测试信号和横向扫描侧向力信号受探针耦合变形影响较小，但侧向力与形貌斜率密切相关，且其极值点与形貌极值点存在位置偏差，这些结果均与原子力 关键词： 原子力显微镜 探针悬臂梁 耦合变形 扫描力     

Electroluminescence of diamond films induced by a scanning tunneling microscope

We report the scanning tunneling microscope induced band-A emission from boron-doped polycrystalline diamond films fabricated by chemical-vapor deposition (CVD). The broad blue emission occurs at a bias above ±3.4 V with double peaks at 410 and 450 nm and is attributed to the dislocation-related defect centers. Greatly enhanced green emissions around 530 nm are observed at high positive bias. This, together with strongly bias- and polarity-dependent emission intensities and spectra, leads us to propose that the boost in the green emission at high bias is probably related to the minority electron injection into the boron-related acceptor states in the subsurface.     

Electroluminescence of single CdSe nanocrystals induced by scanning tunneling microscope

Electroluminescence intensity of single CdSe nanocrystals (NCs) excited by the tunnel current of a scanning tunneling microscope (STM) was measured. Samples with NCs do not exhibit plasmon emission. This enables one to measure pure emission from a single NC. Electroluminescence, measured in time, differs considerably from that of photoluminescence in similar NCs. This difference in temporal behavior results from the difference in physical conditions of experiments on photo- and electroluminescence.     

Joule heating and spin-transfer torque investigated on the atomic scale using a spin-polarized scanning tunneling microscope

The influence of a high spin-polarized tunnel current onto the switching behavior of a superparamagnetic nanoisland on a nonmagnetic substrate is investigated by means of spin-polarized scanning tunneling microscopy. A detailed lifetime analysis allows for a quantification of the effective temperature rise of the nanoisland and the modification of the activation energy barrier for magnetization reversal, thereby using the nanoisland as a local thermometer and spin-transfer torque analyzer. Both the Joule heating and spin-transfer torque are found to scale linearly with the tunnel current. The results are compared to experiments performed on lithographically fabricated magneto-tunnel junctions, revealing a very high spin-transfer torque switching efficiency in our experiments.     

Nanotubes and force interactions in an atomic force microscope

The conditions for nanotubes to be used as atomic force microscope (AFM) probes are analyzed. It is shown theoretically for the first time that single-and multilayer tubes with diameters ranging from 0.5 to 5 nm give atomic-level resolution of the surface. The presence of cylindrical symmetry makes each surface atom of a nanotube “imaging.” For a definite ratio of the diameter of a single nanotube and the period of the surface structure, the atomic resolution vanishes. Such nanotubes are of special interest for probing the details of the large-scale relief and for investigations in nanotribology. In contrast to silicon and other (solid) probes, nanotubes are not blunted on contact with the surface, but rather they bend and their initial shape is restored when the stress is removed. The critical loads for an AFM to function in the repulsive regime are determined. Zh. Tekh. Fiz. 69, 124–127 (August 1999)     

Vibration of H atomic chains on Ni(110) measured by scanning tunneling microscope light emission spectroscopy

We have measured the visible light spectrum emitted by hydrogen atoms adsorbed on an Ni(110) surface, excited by the tunneling current from the scanning tunneling microscope. The spectrum contains periodic fine structures, whose period corresponds to the vertical vibrational energy of the adsorbed H atom. This energy showed the expected isotope shift when H was replaced by deuterium, and further it depended on the H-atom chain length.     

Tapping mode atomic force microscope combined with reflection scanning near-field optical microscope (AF/RSNOM)

A new kind of scanning probe microscope is introduced in this paper, which is a combination of atomic force microscope and reflection scanning near field optical microscopy (AF/RSNOM) with equi-amplitude tapping mode. The principle and recent experiment result of AF/RSNOM are reported. Besides convenient operation, the bi-functional probe tip of AF/RSNOM brings an even illumination for every sampling position. Experiment result and analysis show that the signal to noise ratio (SNR) of AF/RSNOM optical image is much better than that of other RSNOM without tapping working mode.     

A new organic complex thin film for ultra-high-density data storage with a scanning tunneling microscope

A new organic complex, tetrathiafulvalene/m-nitrobenzylidene propanedinitrile (TTF/m-NBP), was prepared to use as an ultra-high-density data-storage medium. A nanometer-scale recording technique was demonstrated with a scanning tunneling microscope (STM) under ambient conditions. The organic complex thin film was fabricated by using a vacuum thermal deposition method. The results of Fourier transform infrared spectra showed that the structure of the organic complex thin film was the same as that of a complex crystal. Data were recorded by applying voltage pulses between the tip and the substrate. Current–voltage (I–V) curves measured by the STM showed that the conductance of the recorded region is much higher than that of the unrecorded region, which indicated that the data were recorded by a local change of the electrical property of the film. The smallest recorded mark was 1.1 nm in diameter and the width of the pulse voltage has an influence upon the diameter of the recording marks. PACS 73.61.Ph; 71.20.Rv; 72.80.Le; 33.15.Kr; 81.15.Ef     

Local anodization of permalloy film by atomic force microscope

Local anodization on a permalloy (_Ni80Fe20)${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20})$ thin film by an atomic force microscope (AFM) in air was studied. Fabrication of uniform structure on the permalloy film was difficult in comparison with that on a Si(1 0 0) substrate. On the permalloy film, threshold voltage for the AFM anodization increased until 3 h after exposure to air. With passage of time, I–V$I–V$ curves on the permalloy film also changed from metallic behavior to insulating one. In addition, I–V$I–V$ curves varied at positions on the permalloy film. The oxide layer with time- and position-dependencies can induce non-uniform structure in AFM anodization. However, uniformity of structure was able to be improved by using method of fabrication of dots.