By using lattice matched short period (50 Å) GaInAs/InP superlattices, we are able to extensively characterize, ex-situ, nucleation of thin (20–30 Å) GaInAs layers on InP. Systematic variation of the interface formation technique allows us to understand how parameters such as growth temperature and growth rate can contribute to interfacial roughness, giving rise to growth transients near the interfaces that are unexpected from characterization of thick layers. Growth of multi-period structures such as those studied here enables the use of Raman scattering, photoluminescence, and double crystal x-ray diffraction to determine that Ga incorporation is favored over In incorporation near the InP to GaInAs interfaces. Furthermore, by examining the surfaces and structural properties of epitaxial layers (15 Å-1 μm) of both InP and GaInAs with atomic force microscopy and Raman scattering, respectively, we are able to correlate results on the superlattice structures with results from single layers. Finally, we show how understanding the nucleation of thin films through the process described here enables the growth of complicated, previously unrealizable, heterostructures for use in novel optoelectronic devices.

Stress in thin films plays a critical role in many technologically important areas. The role is a beneficial one in strained layer superlattices where semiconductor electrical and optical properties can be tailored with film stress. On the negative side, residual stress in thin-film interconnects in microelectronics can lead to cracking and delamination. In spite of their importance, however, surface and thin-film stresses are difficult to measure and control, especially on a local level. In recent studies, we used the Interfacial Force Microscope (IFM) in a nanoindenter mode to survey the nanomechanical properties of Au films grown on various substrates. Quantitative tabulations of the indentation modulus and the maximum shear stress at the plastic threshold showed consistent values over individual samples but a wide variation from substrate to substrate. These values were compared with film properties such as surface roughness, average grain size and interfacial adhesion and no correlation was found. However, in a subsequent analysis of the results, we found consistencies which support the integrity of the data and point to the fact that the results are sensitive to some property of the various film/substrate combinations. In recent measurements on two of the original substrate materials we found a direct correlation between the nanomechanical values and the residual stress in the films, as measured globally by a wafer warping technique. In the present paper, we review these earlier results and show recent measurements dealing with stresses externally applied to the films which supports our earlier conclusion concerning the role of stress on our measurements. In addition, we present very recent results concerning morphological effects on nanomechanical properties which add additional support to the suggestion that near-threshold indentation holds promise of being able to measure stress on a very local level

In the present study, the micromechanical properties of single-crystal A12O3 have been tested using a micromechanical depth-sensing testing device. A series of microscratches are produced on the annealed {0001}, {1120} sapphire specimens of special geometry. The scratches were positioned in pre-selected crystallographic directions, determined with the backreflection Laue method X-ray diffraction method.

The microscratch tracks were examined with transmission electron microscopy (TEM). The main emphasis in the analysis of deformation structure of sapphire has been placed on the correlation of irregularities observed on load-displacement curves to the extent of elastically deformed regions, nucleation of the dislocations on the surface, unique nature of the crack-dislocation networks associated the sapphire anisotropic deformation behavior.

The atomic force microscope (AFM) has become a popular tool for characterizing surfaces of many different types of materials. In this paper, an AFM is used to probe the mechanical properties of polymer samples through examination of force curves produced during tip-sample contact and indentation. Three types of cantilever probes with spring constants estimated to be 1–5 N/m, 20–100 N/m, and 400–500 N/m respectively, were used to study different polymer samples with known modulus values ranging from 20 MPa to 3 GPa. A technique is developed that relates the measured sample response to elastic modulus, and illuminates the importance of the relative stiffnesses of the cantilever probe and the sample to the material response.

We study the deformation of nano-scale polymer films which are subject to external bending forces by means of computer simulation. The polymer is represented by a generalized bead-spring-model, intended to reproduce characteristic features of n-alkanes. The film is loaded by the action of a prismatic blade which is pressed into the polymer bulk from above and a pair of columns which support the film from below. The interaction between blade and support columns and the polymer is modeled by the repulsive part of a Lennard-Jones potential. For different system sizes as well as for different chain lengths, this nano-scale experiment is simulated by molecular dynamics methods. Our results allow us to give a characterization of deformed states for such films. We resolve the kinetic and the dynamic stage of the deformation process in time and access the length scale between discrete particle and continuum mechanics behavior. For the chain lengths considered here, we find that the deformation process is dominated by shear.

We have used the inherent surface sensitivity of second harmonic generation (SHG) to develop an instrument for nonlinear optical (NLO) microscopy of surfaces and interfaces. This optical technique is ideal for imaging nanometer thick self-assembled monolayers (SAM's) which have been patterned using photolithographic techniques. In this paper we demonstrate the application of SHG microscopy to patterned SAM's of the noncentrosymmetric molecule calixarene and discuss other potential applications for this new technique.

Scanning Angle Reflectometry (SAR) is used to investigate the structure of protein layers deposited sequentially, first the antigen and then the antibody, on a silica surface. The reflectivity curves are analyzed by means of the optical invariants, a general description valid in the thin film limit which permits the determination of three and only three structural parameters for a dielectric layer, independent of any model of the layer. The three parameters can be related to the first two moments of the mass density in the layer, or to an average film thickness and density. In addition, a new invariant is constructed which directly yields information about the distribution of mass in the layer, and thus goes beyond the usual uniform layer model.

A soluble, asymmetrically substituted polydiacetylene, poly(BPOD), has been reported to form stable monolayers at the air-water interface by the Langmuir-Blodgett (LB) technique [2]. Preformed polydiacetylene has been deposited onto hydrophobic substrates as multilayers to form second order nonlinear optical thin films. Second harmonic generation was found to increase with the number of layers. From previous atomic force microscopy (AFM) studies backbone orientation along the dipping direction with an interchain spacing of about 5 A° was indicated [2].The film morphology and preferential molecular orientation of these LB films are further investigated by transmission electron microscopy (TEM). A specifically tailored sample preparation method for the ultrathin LB films was used. Multilayer films were deposited on hydrophobic collodion covered glass substrates for this purpose. Electron diffraction was employed to study the crystalline organization of mono and multilayers of LB films as well as cast films.

The effects of instabilities which lead to mound formation and coarsening in homoepitaxial growth on metal (100) surfaces are discussed. These include an instability due to the Ehrlich-Schwoebel step barrier to interlayer diffusion as well as an instability due to step-adatom attraction at ascending steps. A unified picture of the effects of attractive and repulsive interactions at ascending and descending steps on surface morphology and island nucleation is presented. An analytic calculation of the selected mound angle and critical temperature for mound formation as a function of both the Ehrlich-Schwoebel step barrier and the barrier to diffusion towards an ascending step is also presented. Depending on the sign of the step barrier and the magnitude of the prefactor for diffusion over a step various scenarios are possible, including the existence of a critical temperature for mound formation above which (for a positive step barrier) or below which (for a negative step barrier) quasi-layer-by-layer growth will be observed. A theoretical analysis also leads to an accurate prediction of the observed mound angle for Fe/Fe(100) deposition at room temperature. The general dependence of the mound angle, surface skewness, and mound coarsening exponent on temperature, deposition rate, and strength of the step barrier is also studied via kinetic Monte Carlo simulations of bcc(100) growth and compared with recent experiments.

To examine the dependence of in-plane texture development on substrate surface morphology, deposition was performed on an intentionally roughened surface. 2 μm thick sputter deposited Mo films were macroscopically roughened by ion bombardment. This process created aligned mounds on the surface which were ˜1 μm in length, ˜0.1 μm in width and ˜0.04 miimn height. To remove crystallographic orientation effects, this surface was coated with a thin layer of graphite. Using these roughened, coated surfaces as a new substrates, the role of well defined macroscopic roughness in subsequent thin film growth was probed. Mo films were deposited onto these prepared substrates which were placed on a rotating platen under a stationary ion sputter source. When the mounds are aligned with their elongated axes normal to the rotation direction, little to no in-plane texture is found. The same deposition on a flat surface, or on the roughened surface with the mounds oriented parallel to the platen rotation direction, gives films with a high degree of in-plane texture. Scanning electron microscopy, transmission electron microscopy, and transmission electron diffraction data will be presented to corroborate these findings.

The exact scaling form is determined for the size distribution of islands created via irreversible nucleation and growth during submonolayer deposition. This form is controlled by a dependence on size of the propensity for islands to “capture” diffusing adatoms. This sizedependence is determined directly from simulations. It reflects a complex relationship between the size of an island, and the area of its cell in a tessellation of the surface based on the island locations. The relationship corresponds to a correlation between island size and separation.

We present a model for thin film growth by particle deposition that takes into account the possible evaporation of the particles deposited on the surface as well as the effect of point defects. Our focus is on the early formation kinetics of two-dimensional islands on the surface, in particular in the scaling properties of the maximum number of islands formed on the surface. Most of our results are obtained through the analysis of rate equations describing the system. They are supported by simple scaling arguments and are confirmed by extensive computer simulations. We find significant differences with previous studies of this system which arise from different physical hypotheses concerning the mechanisms of island growth in the presence of evaporation.

Ultrathin refractory metal silicide films, such as tungsten silicide (WSix) offer a wide range of applications in VLSI and ULSI circuits such as local interconnects, bit lines and wordlines. One practical way of depositing WSix is by a CVD technique in which WF6, is reduced by either silane (SiH4) or dichlorosilane (SiH2 Cl2 ). In this investigation, step coverage characteristics of silane based and dichlorosilane based tungsten silicide films, deposited by low pressure chemical vapour deposition method will be compared. WSix films of various thicknesses (1200–2000 Å) were deposited on topographies created by patterning poly-Si layers. WSix, step coverage was evaluated as a function of deposition temperature, poly-Si layer thickness and poly-Si line spacing. Field emisssion scanning electron microscopy was used to characterize step coverage profiles. It is clearly shown that, silane based WSix films deposited on poly-Si lines with sub 0.5 micron spacings result in poor step coverage which could lead to higher localized stress, cracking and higher line resistance. Dichlorosilane based WSix, on the other hand showed more conformal step coverage, which results in better process marhin for subsequent patterning steps. Finally, it was also observed that, the final silicide profile is highly dependent on the thickness of the underlying poly-Si layer, as well as poly patterning process margin.

CdTe thin films with thicknesses in the range of 60˜100 nm have been grown on miscut (001) Si surfaces under different precursors, such as Te and As, with one cycle annealing. The thin-film microstructure was studied in cross section using high-resolution electron microscopy. Atomicresolution images revealed several interesting features of the initial growth of the heteroepitaxial CdTe thin films. With As as the precursor, the films initially grew in three different orientation variants (commonly referred to as domains): (A) CdTe (111)//Si (001) with CdTe (1–10)//Si(110); (B) CdTe (111)//Si (001) with CdTe (11–2)//Si(110), and (C) CdTe (001) // Si (001) with CdTe (110) // Si (110). Each variant has demonstrated its own characteristic defects such as twinning, interface Lomer dislocations and {111} stacking faults. With the [001] growth direction, the CdTe film became defect-free by having about 13° tilt relative to Si [001] such that CdTe (1–11) and Si(−111) planes aligned sideways at the interface. With Te as the precursor, A- and B-type variants were mainly observed. The interfaces were sharper, especially for the A-type interface, but the film adhesion was weaker than when As was the precursor.

Organic compounds such as oleic acid, polymethyl methacrylate (PMMA) and polyacrylate (PAA) were coated on slide and silica glass powders. The resulting interaction mechanism was determined by the leaching properties of the glass, and the bond strength of each ion on the glass with coated organics. Soluble components such as sodium and calcium play important roles in the interaction properties of the organics with glass surfaces. The effects of solvent are also discussed.

Si1−x−y GexCy epitaxial films offer wider control of strain and bandgap. In such films the morphology is an important indication of the crystalline quality of the material. We report on the morphology of Si1−x−y GexCy epitaxial thin films deposited by Ultra High Vacuum Chemical Vapor Deposition at a temperature of 550° C and deposition pressures ranging from 1 to 10 mTorr. The precursors used were Si2H6, GeH4 and CH3SiH3. Germanium mole fractions ranging from 0% to 40% were studied with carbon concentrations varying from 2×1019 to 2×1021 atoms/cm3. AFM analysis of the surface indicates that the roughness is a function of both the carbon concentration and the film thickness. For high germanium concentrations with thickness beyond the critical thickness (of Si1−xGex), carbon is found to decrease the surface roughness of the film. Thus the surface morphology confirms the strain compensation provided by carbon which is also observed using XRD. For films below the critical thickness, as the carbon concentration is increased, three dimensional islanding is observed by RHEED and AFM, degrading the epitaxial quality of the material.

Microstructure properties, and surface morphology of gold films processed at different temperature were investigated by transmission electron microscopy (TEM) and atomic force microscope (AFM). The film thickness was chosen less than several hundreds angstrong. Previous electrical measurement found that the low temperature (LT=77K) film showed several orders lower resistance compared to the film obtained at room temperature with very thin (about 100Å) thickness. This indicated potential application of these LT films on electronic and optoelectronic devices. TEM study found that the LT films showed much smaller density of grain boundaries than that of the room temperature (RT=300K) samples. In AFM observation, for film thickness of 100Å, LT film showed smoother, and continuous surface while the RT film consisted of discrete islands. When the thickness was increased to 200Å, the LT film showed much larger-sized grains compare to that of the RT film. For LT deposition, 2-dimensional larger-sized grains were first formed at low temperature deposition which later extended to be 3-dimension. The low grain boundary density of the LT film is consistent with its lower resistivity observation.

We have studied the effects of growth parameters and substrate orientations on InGaP quality using Normarski microscopy, photoluminescence (PL) spectrum and atomic force microscopy (AFM). The full width at half maximum (FWHNM) and peak position of PL spectrum were closely related with the surface morphology. The InGaP layers of narrower FWHM and shorter peak wavelength had smoother surface morphology. The InGaP layers grown on (100) substrates at the moderately low reactor pressure showed rougher surface than those on the tilted substrates. But the surface morphology was noticeably improved to be mirror-like at the lower reactor pressure. The surface morphology was inverted between the exact and tilted substrates in this reactor pressure. Furthermore, the samples grown on the tilted substrate exhibited rougher surface than the samples grown on the exact substrate. (111)B-misoriented growth surfaces had smoother than (111)A-misoriented surfaces.

We studied a lattice distortion and relaxation of BaTiO3(BT) thin films grown on SrTiO3 (001) substrates(ST) by a molecular beam epitaxy method using an oxygen radical source RT were prepared by alternately deposition of BaO and TiO2 layers, and the structure of the thin films was evaluated by X-ray diffraction, reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy, coaxial impact collision ion scattering spectroscopy and X-ray photoelectron spectroscopy The lattice constants of the films varied with distance from the interface of BT and ST It was found that lattice distortion and relaxation of BT On the other hand, the surface analysis indicated that adsorbed oxygen was enriched on the BaO-terminated surface in comparison with the TiO2-terminated surface Then we proposed new mechanism of BT thin film growth with adsorbed oxygen.

To obtain informations about the correlation between structure and electrical property in metallic multilayers, we have fabricated Ni/Co superlattices with and without Pb as a surfactant by molecular beam epitaxy. From the observations of RHEED and x-ray diffraction patterns, we confirmed that the surfaces of Ni/Co superlattices with Pb are flatter and the interfaces are sharper than one without Pb, which means that Pb operates as an effective surfactant.We have investigated the electrical properties of superlattices by measuring magnetoresistance. The initial change of resistance with magnetic field from 0 to 1 kOe was larger for the superlattices with a surfactant, while once magnetic field was applied, the effect of a surfactant to resistivity change was not observed. This suggests that Pb also changes the initial magenetic domain structure and the magnetotransport property of Ni/Co superlattice is not sensitive to interface structure.