Ductile materials are found to sustain brittle fracture when the crack moves at high speed. This fact poses a paradox under current theories of dislocation emission, because even at high velocities, these theories predict ductile behavior. A theoretical treatment of time-dependent emission and cleavage is given which predicts a critical velocity above which cleavage can occur without emission. Estimates suggest that this velocity is in the neighborhood of the sound velocity. The paper also discusses the cleavage condition under mixed mode loading, and concludes that the cleavage condition involves solely the mode I loading, with possible sonic emission under such loadings

Using a material synthesis technique to optimize the coverage of metals on the surface of silicon, the iron-promoted nitridation of high-purity silicon was studied. The kinetic results indicated that conversions to silicon nitride were directly dependent upon the surface loading by iron up to the point of excess coverage where the rates dropped sharply. A further modification of the iron-promoted system by alkali and alkaline earth metals sharply increased the degree of conversion. The results suggested that the chief effect of the metal promotion was to reduce nitridation induction times and to disrupt the oxided silicon surface. Reaction rates were enhanced by the iron promoter to the extent that the silicon surface was covered and deoxidized by iron.

Electrical conduction in undoped and indium-doped ZnO films in as-deposited, vacuum-annealed and oxygen-annealed states has been studied. The as-deposited and oxygen-annealed films contain a large density (≥ 1017 m−2) of trap states due to chemisorbed oxygen at the grain boundaries. The role of these trap states has been analyzed in terms of the grain boundary carrier trapping model. The vacuum-annealed films are free of chemisorbed oxygen, and the conduction in these films is controlled by scattering due to ionized impurities and grain boundary barriers. In the case of undoped ZnO films, intrinsic trap states at the grain boundaries also play a significant role. The optical behavior of all films in the UV and visible regions is dielectric-like and the optical bandgap shows a dependence on free carrier concentration that is controlled by a bandgap narrowing effect due to electron-electron and electron-impurity interactions as well as the Moss-Burstein effect of bandgap widening. In the IR region the optical behavior is metal-like due to free-electron effects and follows the Drude model.

The effect of lateral cracks on strength controlling contact flaws in brittle materials is examined. Inert strength studies using controlled indentation flaws on a range of ceramic, glass, and single crystal materials reveal significant increases in strength at large contact loads, above the predicted load dependence extrapolated from strength measurements at low indentation loads. The increases are explained by the growth of lateral cracks decohesing the plastic deformation zone associated with the contact from the elastically restraining matrix, thereby reducing the residual stress field driving the strength controlling radial cracks. A strength formulation is developed from indentation fracture mechanics which permits inert strengths to be described over the full range of contact loads. The formulation takes account of the decreased constraint of the plastic deformation zone by lateral crack growth as well as post-contact nonequilibrium growth of the radial cracks. Simple extensions permit the strengths of specimens controlled by impact flaws to be described, as well as those failing under nonequilibrium (fatigue) conditions. The implications for materials evaluation using indentation techniques are discussed and the dangers of unqualified use of strength measurements at large indentation loads pointed out. The work reinforces the conclusion that a full understanding of the residual stress field at dominant contact flaws is necessary to describe the strength of brittle materials.

Molybdenum disilicide thin films having the tetragonal crystal structure were prepared by furnace reaction of ion-beam-sputtered molybdenum layers with silicon substrates. The room temperature intrinsic resistivity is ∼20 μΩ cm. The Hall effect indicates predominantly hole conduction. Geometrical magnetoresistance measurements provide a carrier mobility estimate of 90 cm2 /V.s at room temperature. The Hall mobility is much less than this; the large difference between the two mobility values suggests multiband conduction. An isotropic, degenerate, twoband model may be fitted to the data with a comparatively low majority carrier concentration (holes) of ∼ 1.5 × 1021 cm−3 Regarding the effects of microstructure on transport, the residual resistivity for films formed on 1-0-0 silicon wafers is much greater than for those formed on an (LPCVD) polysilicon layer: 92 vs 29 μΩ cm, respectively. A correlation with average grain size for the two sample types suggests that grain boundary scattering is the principal cause of the residual resistivity. electronic materials; electrical properties; thin film

Substrate material used for fabrication of P/P + epitaxial silicon wafers was preannealed at 650 °C in nitrogen ambient prior to the epitaxial deposition process for various times up to 300 min. The substrate material originated from a characterized crystal ingot. The results show that annealing before epitaxial deposition can preserve oxide precipitate nuclei from dissolution during the epitaxial deposition process. Additional postepitaxial annealing at 750 °C further enhances the growth of bulk defects.

The diffusion of Sb in heavily doped n- and p-type Si has been studied to determine the activation energies and charge states of the point defects responsible for Sb diffusion. It is shown that neutral point defects, probably Vx, dominate under intrinsic doping conditions. For samples doped with high-concentration As or P backgrounds, Sb diffusion is dominated by a double-negatively charge point defect that causes an n2 concentration-dependent Sb diffusivity. Electric-field effects also are important. The measured diffusion coefficients are Dix = 17.5 exp(−4.05 eV/kT), and Di= = 0.01 exp(−3.75 eV/kT). The activation energies are consistent with diffusion via Vx and V= vacancies. Retarded diffusion of Sb in p+-doped samples with uniform B profiles fits an ion pairing model where Sb+B− pairs form to reduce the flux of Sb atoms.

The removal of defects in diamond by light-ion bombardment has been studied by means of Rutherford backscattering spectroscopy (RBS) channeling techniques. The damage produced by 1 × 1014 Sb ions cm−2 at 300 keV (below the critical dose for graphitization) was observed to diminish by as much as 50% under bombardment with H and He ions. The ion-beam-induced annealing has been studied as a function of ion dose and incident angle (channeling and random). Although the data sets differ markedly, they nearly coincide when the dose is normalized to the energy deposited by elastic collisions in the damaged region. This may indicate that nuclear and not electronic collisions contribute primarily to the in situ annealing in a reasonably good insulator such as diamond.

The approach to equilibrium of the grain structure and electrical properties has been studied in high-resistivity, As-implanted polycrystalline silicon films on thermally oxidized silicon wafers. Thermal annealing parameters are found to be critical in determining the film sheet resistance. Results from spreading resistance analysis, secondary ion mass spectroscopy, and transmission electron microscopy indicate that As diffusion down the grain boundaries into the film leads to a large fraction of the As being left in inactive grain boundary sites. Reactivation of the As is negligible when processing temperatures are 900 °C or lower. A relatively simple diffusion model has been developed that can fit the As concentration profile over the entire film thickness. This makes the model applicable to normal integrated circuit processing conditions where film thickness effects and nonequilibrium dopant distributions are important.

Galium phosphorus films grown on (211 )Si by molecular beam epitaxy have been investigated using a transmission electron microscope. The main defects observed in the alloy were of misfit dislocations, stacking faults, and microtwins. The misfit dislocations are of the 60° type with Burgers vectors of a/2 ‹110›, and the stacking faults are intrinsic in nature and bounded by Shockley partials and stair-rod partial dislocations. The habit planes of these defect structures were found to depend solely on the crystalline growth orientation with respect to the substrate orientation. A possible mechanism of the formation and growth of these misfit defects has been proposed for the present growth orientation.

An overview is given of a new process that has been used successfully to make numerous ceramic/metal composite materials by directed oxidation of molten metallic precursors. As an example, the formation of A12O3/A1 composites from Al is discussed in detail.

Depth-sensing indentation instruments provide a means for studying the elastic and plastic properties of thin films. A method for obtaining hardness and Young's modulus from the data obtained from these types of instruments is described. Elastic displacements are determined from the data obtained during unloading of the indentation. Young's modulus can be calculated from these measurements. In addition, the elastic contribution to the total displacement can be removed in order to calculate hardness. Determination of the exact shape of the indenter at the tip is critical to the measurement of both hardness and elastic modulus for indentation depths less than a micron. Hardness is shown to depend on strain rate, especially when the hardness values are calculated from the data along the loading curves.

The reactions between bilayered Ni/Pt films and Si (100) substrates induced by thermal annealing and ion mixing were investigated. Thermal annealing of Si/Pt/Ni and Si/Ni/Pt samples led to layer reversal at low temperatures (∼ 300°to 400°C) and the formation of a ternary phase at high temperatures (∼ 700°C). These results are consistent with those reported in the literature. Ion mixing of both types of samples led to silicide formation without layer reversal. This effect is interpreted in terms of a change of moving species from metal (in thermal annealing) to Si (in ion mixing). The mixing efficiency between Pt and Ni is observed to be enhanced when Si is mixed together with these two metals.

Transmission electron microscopy (TEM) has proven to be an invaluable tool in a multifaceted research program at North Carolina State University, which centers on developing β-SiC as a useful semiconducting material. As such, techniques have been developed for fabricating both plan-view and cross-sectional TEM silicon carbide thin films grown by chemical vapor deposition. The results of the TEM observations are used to determine the effectiveness of specific processing parameters in terms of film quality and defect structure as well as oxidation, ion implantation, and annealing procedures.

An x-ray diffraction technique is presented for the determination of the strain tensor in an epitaxial layer grown on a crystallographically distinct substrate. The technique utilizes different diffracting planes in the layer and in a reference crystal fixed to the layer, and is illustrated by application to an ∼4000 Å (001) silicon layer grown on a (01$\overline 1$2 sapphire wafer. The principal strains were measured, and the measured strain normal to the layer was found to agree with the normal strain calculated from the measured in-plane strains within the experimental uncertainty of strain measurement. The principal stresses in the plane of the silicon film, calculated from the measured strains were −0.92 ± 0.16 GPa in the [100] direction and −0.98 ± 0.17 GPa in the [010] direction.

Electrical conductivity for polyethylene-carbon black, polycarbonate-carbon black composites was measured for conducting compositions well above the percolation limit. Three conductivity methods were employed in our studies: sputtering coated metal electrodes, painted metal electrodes, and the four-point method. Results suggest that while the two latter methods do not modify substantially the material surface, the former method introduces a low conductivity region at the surface. The effect of contact resistance developed during metal coating is discussed in the light of both fluctuation-induced tunneling predictions and “hopping” transport mechanisms. Experimental results favor the tunneling alternative across the evaporated metalcomposite interphase.

Chemical preparation methods were developed for high-field ZnO varistors which used precipitation techniques to prepare precursor powders. Varistors were made by sintering uniaxially pressed pellets in the range of 675°–740 °C in air. Properties of these varistors included electric fields (E) in the 10–100 kV/cm range at current densities (J) of 5 A/cm2, nonlinearity coefficients (α) greater than 30 for 2.5≤J≤5.O A/cm2, and densities in the range of 65%-99% of theoretical depending both on sintering temperature and composition.

The x-ray photoemission studies of polytetrafluoroethylene (PTFE) bombarded by lowenergy electrons in ultra-high vacuum conditions indicate that the major chemical changes induced by electron bombardment are defluorination of the surface and cross-linking of the polymer chains. The same electron bombardment process, when performed in the presence of 1×10−6 Torr ND3, also results in the adsorption of nitrogen-containing groups at the surface. The rate of nitrogen adsorption is linear for short electron bombardment times while the rates of defluorination and cross-linking are roughly exponential. However, at long bombardment times, the rates of nitrogen uptake, defluorination, and cross-linking become zero at the same time, indicating that defluorination of the surface is the rate-determining step in electron beam-induced adsorption of nitrogen-containing species. Regardless of whether the bombardment is carried out in ultra-high vacuum or in the presence of ND3, the maximum modification depth is less than 30 Å. Pull tests performed on PTFE samples bombarded by electrons in ultra-high vacuum, then removed into air and bonded to epoxy show epoxy-PTFE joint strengths of 280–360 1b/in.2 (psi), are compared to zero psi for untreated PTFE and ≃2000 psi for cohesive failure within the PTFE layer.

Chemical reactions at the Au/InP interface were investigated in the temperature range 25°-510 °C by x-ray diffractometry, scanning electron microscopy (SEM), and energy dispersive x-ray analysis. The samples were prepared by depositing gold films onto clean InP (100) single-crystal substrates under 10∼9 Torr vacuum. Spots appeared in SEM micrographs of the deposited film of a sample annealed at room temperature for 35 days, indicating that a solid-state reaction had occurred. After the sample was heated to 330 °C under flowing N2 gas, £1 dendritic islands were observed in the film. A 365 °C anneal turned the color of the Au film from yellow to pink, and Au, £1 and Au2P3 were identified by x-ray diffractometry. In reacting with the InP substrate, £1 produced silver-colored γ and more Au2P3 at 450 ° C. With respect to InP, γ was relatively stable, and further reactions were minimal even when the sample was annealed at 510 °C for 40 min under atmospheric-pressure N2. The ternary phase diagram for the bulk Au-In-P system provides the basis for understanding the sequence of the above results and much of the information in the literature about Au/InP interfacial reactions.

The structural and electrical properties of a Nb-Si thin alloy film as a function of temperature have been studied by Auger electron spectrometry, Rutherford backscattering spectroscopy, transmission electron microscopies, and in situ electrical resistivity and Hall coefficient measurements. The NbSi2,8 films were deposited by double electron-gun coevaporation onto oxidized silicon. For electrical measurements samples of a van der Pauw pattern were made through metallic masks. In the as-deposited state the coevaporated alloy film was amorphous. Upon annealing a precipitous drop in resistivity near 270°C has been determined to be the amorphous to crystalline phase transformation. The kinetics of the transformation has been determined by isothermal heat treatment over the temperature range of 224°C to 252°C. An apparent activation energy of 1.90 eV has been measured. The nucleation and growth kinetics in the crystallization process show a change in the power of time dependence from 5.5 to 2.4. The microstructures of films at various states of annealing have been correlated to the resistivity change. The crystalline NbSi2 shows an anomalous metallic behavior. The resistivity (p) versus temperature curve has a large negative deviation from linearity (dfl) and it approaches a saturation value (psat) as temperature increases. The resistivity data are fitted by two empirical expressions put forth to explain the resistivity behavior in A15 superconductors at low and high temperatures. One is based on the idea that ideal resistivity must approach some limiting value in the regime where the mean free path becomes comparable to the interatomic spacing and the other is based on a selective electron-phonon assisted scattering. In spite of the wide temperature range of analysis, it is not possible to choose one of them due to the fact that the best fit in both cases is nearly the same. The Hall coefficient (RH) changes sign from negative above ∼250°K to positive below ∼ 250°K.