Electrostatic forces in micromanipulations: Review of analytical models and simulations including roughness

Manipulations by contact of objects between 1 m and 1 mm are often disturbed by adhesion between the manipulated object and the gripper. Electrostatic forces are among the phenomena responsible for this adhesive effect. Analytical models have been developed in the literature to predict the electrostatic forces. Most models are developed within the framework of scanning probe microscopy, i.e. for a contact between a conducting tip and a metallic surface. Models are reviewed in this work and compared with our own simulations using finite elements modeling. The results show a good correlation. The main advantage of our simulations lies in the fact that they can integrate roughness parameters. For this purpose, a fractal representation of the surface topography was chosen through the use of the Weierstrass-Mandelbrot function. Comparisons with experimental benchmarks from the literature show very good correlation between experimental results and simulations. It demonstrates the importance of surface topography on electrostatic forces at very close separation distances.     

Adsorption characteristics of atomic nitrogen on ruthenium surfaces

We have studied the adsorption, vibration, and diffusion of N atoms on Ru(0 0 0 1), , and surfaces by means of the 5-parameter Morse potential (5-MP) of interaction between atomic nitrogen and a metal surface. The adsorption sites, adsorption geometry, binding energy and eigenvibration of atomic nitrogen on the different ruthenium surfaces are calculated. It is shown that atomic nitrogen always preferably occupies the high coordination sites on Ru surfaces. The 4-fold site is the preferable adsorption site for atomic nitrogen on both open and surfaces while 3-fold site is the most stable adsorption site for atomic nitrogen on both Ru(0 0 0 1) and surfaces. Moreover, we find the lowest energy pathway of diffusion and diffusion barriers of atomic nitrogen on the surfaces.     

Atomistic simulation of Pt trimer on Pt(1 1 1) surface

The diffusion of Platinum trimer on Pt(1 1 1) is studied at different temperatures by molecular dynamics (MD) simulation. The structure stability is studied by cluster binding energy. The interaction between adatoms and surface atoms is discussed based on the calculated phonon density of state of Pt trimer. The diffusion coefficients of Pt trimer are derived from mean square displacement of cluster’s mass-center, which is obtained by long simulation times (?0.2 s) and tracing of interstitial atoms on surface. Then the diffusion prefactor and migration energy are deduced from Arrhenius relation. The calculated results are in reasonable agreement with experiment. In addition, using the diffusion prefactor and migration energy, the efficiency of Pt trimer as a critical nucleus for three-dimensional growth of thin films is discussed.     

The electron counting rule and passivation of compound semiconductor surfaces

A brief review is presented of the role of electron counting rule (ECR) in explaining structural stability and passivation of compound semiconductor surfaces. While III-V(1 1 0) and majority of III-V(0 0 1) and III-V(1 1 1) surfaces reconstruct in accordance with the ECR, there are a few low- and high-index surfaces which disobey the ECR but stabilize by sustaining significant elastic deformation in the surface region. We explain the latter scenario with the help of computational results for the geometric and electronic structure of GaSb(0 0 1)-(1×3), GaSb(0 0 1)-c(2×6), InP(1 1 1)A-(), and GaAs(1 1 1)B-Sb(1×3). We also discuss hydrogen passivation of these surfaces. It is pointed out that the recently observed stable InP(1 1 1)A-() surface can be both chemically and electronically passivated by exposing it to a hydrogen gas of one quarter of a monolayer coverage.     

An example of chemistry-morphology interaction: making up for the geometric and energetic heterogeneities of the (1 0 0) surface of single crystalline silicon by high-temperature treatments in H2

A lot of work has been carried out to prepare chemically homogeneous (1 0 0) silicon surfaces. The hydrogen-terminated (1 0 0) silicon surfaces are the most promising ones, especially in view of their remarkable environmental stability. The simplest way to produce hydrogen-terminated surfaces (attack in water solution of HF of a sacrificial, thermally grown, oxide) results in strongly heterogeneous rough surfaces (although with prevailing dihydride terminations). These surfaces can, however, be flattened and homogenized by treating them in H₂ at high temperature (>850 C). The morphological and chemical changes undergone by the surface during the treatment are studied X-ray photoelectron spectroscopy, atomic force microscopy, scanning tunnelling microscopy, infrared absorption spectroscopy in the attenuated total reflection mode, reflection high energy electron diffraction and thermal programmed desorption, and the mechanisms responsible for them are discussed.     

Experimental and theoretical studies on X-ray induced secondary electron yields in Ti and TiO2

Generation of X-ray induced secondary electrons in Ti and TiO₂ was studied from both experimental and theoretical approaches, using X-ray photoelectron spectroscopy (XPS) attached to a synchrotron radiation facility and Monte Carlo simulation, respectively.The experiment revealed that the yields of secondary electrons induced by X-rays (electrons/photon) at photon energies to 4950 and 5000 eV for Ti and TiO₂ are δ_Ti(4950 eV) = 0.002 and δ_Ti(5000 eV) = 0.014 while those for TiO₂ are δTiO₂(4950 eV)=0.003 and δTiO₂(5000 eV)=0.018.A novel approach to obtain the escape depth of secondary electrons has been proposed and applied to Ti and TiO₂. The approach agreed very well with the experimental data reported so far. The Monte Carlo simulation predicted; and while and .An experimental examination on the contribution of X-ray induced secondary electrons to photocatalysis in TiO₂ has also been proposed.     

Atomic geometry, electronic states and possible hydrogen passivation of the InP(1 1 1)A surface

We present a first-principles theoretical study of the atomic geometry and electronics states of the InP(1 1 1)A surface under In- and P-rich conditions. The In-rich surface, characterised by an In vacancy per unit (2×2) cell, obeys the electron counting rule (ECR) and is semiconducting. Under P-rich conditions we have considered two surface reconstructions: (2×2) with 3/4 monolayer (ML) P coverage and () with 1 ML coverage. In complete agreement with a recent experimental work by Li et al., it is found that the () reconstruction is more stable than the (2×2) reconstruction. However, the () reconstruction has a metallic band structure and thus does not satisfy the ECR. The stability of this reconstruction is explained to arise from a competition between the ECR and a significant elastic deformation in the surface region. We confirm the suggestion by Li et al. that this surface can be passivated both chemically as well as electronically with 1/4 ML coverage of hydrogen.     

Pt-induced structures on Si(1 1 0) studied by STM

The structures induced by platinum (Pt) adsorption on Si(1 1 0) surface have been studied by scanning tunneling microscopy (STM) for coverage up to 2 monolayers (ML). Three surface phases have been found to form: “5×4”, “13×2” and “6×5” for Pt coverages 0.3, 0.5 and 1 ML respectively. All structures are formed by one-dimensional rows aligned along the direction. At the coverage >1 ML islands of, probably, Pt silicide start to form in form of 1D nanowires.     

High precision fast projective synchronization in chaotic (hyperchaotic) systems

A high precision fast projective synchronization method was proposed through introducing an impact factor. The numerical simulations indicate that the synchronization precision was increased three orders of magnitude higher than available methods in literature, under the same conditions of numerical method and hardware. The synchronization can achieved after first iteration. The synchronization speed has been increased by 13 484 times and 23 000 times when and , respectively, compared to general methods.     

Diffusion behaviour of Nb in yttria-stabilized zirconia single crystals: A SIMS, AFM and X-ray reflectometry investigations

Using secondary ion mass spectrometry (SIMS) we have investigated the concentration vs. depth profile of Nb, thermally diffused into (1 0 0)-oriented yttria-stabilized zirconia (YSZ) single crystal substrates. The surface morphology of Nb films and YSZ substrates was analyzed using atomic force microscopy (AFM). The structural disorder and the interface configuration of the samples were investigated by X-ray reflectometry (XRR). Two kinds of substrates were used: as-received (AR) and reduced (R) ones. The R-substrates were obtained by thermal annealing of AR-substrates in air for 2 h at 1250 °C. The bulk diffusion coefficients D_T in the temperature range of 780-1000 °C, activation energy Q, and the pre-exponential factor, D₀, have been obtained for Nb in YSZ. For the AR single crystals, the results can be well represented by the expression:

     

Crystallite misorientation analysis in semiconductor wafers and ELO samples by rocking curve imaging

Rocking curve imaging is based on measuring a series of Bragg-reflection digital topographs by monochromatic parallel-beam synchrotron radiation in order to quantify local crystal lattice rotations within a large surface area with high angular and high spatial resolution. In this paper we apply the method to map local lattice tilts in two distinct semiconductor sample types with lattice misorientations up to 0.5° and with spatial resolution from 30  down to 1 . We analyse the measured surface-tilt data volumes for samples with almost smoothly varying specific misoriented defect formation in GaAs wafers and for an inherent subsurface grain structure of epitaxial lateral overgrowth wings in GaN. Back-projected tilt maps and histograms provide both local and global characteristics of the microcrystallinity.     

Crystalline orientation of BiMnO3 thin films grown by rf-sputtering

BiMnO₃ thin films were deposited by means of rf-sputtering onto [1 0 0] oriented SrTiO₃ substrates. X-ray diffraction measurements revealed epitaxial growth with [0 0 l]_m orientation in the monoclinic structure representation, equivalent to the direction of the pseudocubic cationic lattice. This [0 0 l]_m orientation was obtained in a wide deposition parameters range. Preliminary magnetization measurements suggest that these films do not present ferromagnetism below the bulk Curie temperature, T_C=105 K.     

Atomic structure of thin dysprosium-silicide layers on Si(1 1 1)

We report on scanning tunneling microscopy results of thin dysprosium-silicide layers formed on Si(1 1 1). In the submonolayer regime, both a and a 5 × 2 superstructure were found. Based on images taken at different tunneling conditions, a structure model could be developed for the superstructure. For one monolayer, a 1 × 1 superstructure based on hexagonal DySi₂ was observed, while several monolayers thick films are characterized by a superstructure from Dy₃Si₅.     

Optical properties of nickel(II)-azo complexes thin films for potential application as high-density recordable optical recording media

Smooth thin films of three kinds of nickel(II)-azo complexes were prepared by the spin-coating method. Absorption spectra of the thin films on K9 glass substrate in the 300-600 nm wavelength region were measured. Optical constants (complex refractive index ) and thickness of the thin films prepared on single-crystal silicon substrate in the 300-600 nm wavelength region were investigated on rotating analyzer-polarizer type of scanning ellipsometer, and dielectric constants , absorption coefficients α as well as reflectance R of thin films were then calculated at 405 nm. In addition, in order to examine the possible use of nickel(II)-azo complex thin film as an optical recording medium, one of the nickel(II)-azo complex thin film prepared on K9 glass substrate with an Ag reflective layer was also studied by atomic force microscopy and static optical recording. The results show that the nickel(II)-azo complex thin film is smooth and has a root mean square surface roughness of 2.25 nm, and the recording marks on the nickel(II)-azo complex thin film are very clear and circular, and their size can reach 200 nm or less.     

Surface free energy of polypropylene and polycarbonate solidifying at different solid surfaces

Advancing and receding contact angles of water, formamide, glycerol and diiodomethane were measured on polypropylene (PP) and polycarbonate (PC) sample surfaces which solidified at Teflon, glass or stainless steel as matrix surfaces. Then from the contact angle hystereses (CAH) the apparent free energies of the surfaces were evaluated. The original PP surface is practically nonpolar, possessing small electron donor interaction (), as determined from the advancing contact angles of these liquids. It may result from impurities of the polymerization process. However, it increases up to 8-10 mJ/m² for PP surfaces contacted with the solids. The PC surfaces both original and modified show practically the same . No electron acceptor interaction is found on the surfaces.The of modified PP and PC surfaces depend on the kind of probe liquid and contacted solid surface. The modified PP values determined from CAH of polar liquids are greater than that of original surface and they increase in the sequence: Teflon, glass, stainless steel surface, at which they solidified. No clear dependence is observed between and dielectric constant or dipole moment of the polar probe liquids. The changes in of the polymer surfaces are due to the polymer nature and changes in its surface structure caused by the structure and force field of the contacting solid. It has been confirmed by AFM images.