We describe infrared and x-ray photoelectron spectroscopy studies of the interfaces formed when the PMDA/ODA polyamic acid is imidized on gold, chromium, and copper. Polyimide films ranging from 34 ° to 1328 ° are analyzed as part of these studies. The IR and XPS results indicate that the gold interacts very little with the polyimide, while copper produces significant changes in the IR and XPS spectra. At elevated cure temperatures passivated chromium also reacts with the polyimide. In structures with chromium and copper, the thermal stability of the polyimide at the interface is reduced from that of bulk polyimide. The data demonstrate that the metals interact with the polymer structure at the point where ring closure occurs to form the polyimide from polyamic acid.

Adhesion degradation mechanism at the interface of a multilayer thin film was studied as a function of annealing temperature. The multilayer thin films employed for current investigation of the temperature effect were constructed by sputtering 500 Å Cr and 10K Å Cu on both sides of kapton. A steady decrease of adhesion strength was found as a result of increasing the annealing temperature from 150°C to 350°C. Thin film and interfacial properties in association with degradation of adhesion were characterized by several techniques, including intrinsic stress measurement, Auger, TEN and SIMS. Several changes were observed by elevating the annealing temperature. It was found that the intrinsic stress in each layer changed. Both Cu and Cr grain size increased with the annealing temperature. The interface at kapton and metal became more defined. The Cu atoms were found to become mobile and diffused into Cr and kapton layer after a 350 degree annealing. In addition, a change of molecular orientation and chemistry in kapton near the interface was observed by SIMS and XPS studies. A combination of these factors resulted in a decline of adhesion strength.

The influence of the substrate material on the column and grain microstructure, the residual stresses, crack patterns and delamination of Cr films has been investigated using TEM, SEM, and X-ray diffraction. The inter-influence of these factors which determine the long term reliability of microelectronics is discussed. When interfacial adhesion is very low, as may be the case with some polymer substrates, cracking occurs discontinuously during film formation each time the stress exceeds the critical value for fracture.

A new UHV atomic force microscope for the study of micromechanical properties is described. A capacitance technique is used, which enables simultaneous measurement of forces perpendicular and parallel to the surface (i.e., load and friction), and has low noise down to frequencies below 0.1 Hz. Preliminary results for Ir- and W-tips sliding on graphite and silicon, respectively, demonstrate the capabilities of this new instrument.

As surfaces slide over one another, work is done by the forces causing the motion and energy is lost. Origins of this friction behavior can be very complex and are still scarcely understood in molecular terms. Adhesion, plowing and asperity deformation, heat-induced chemical reactions, viscoelastic response of a sbustrate, and still other influences, can all dominate depending on the physical system in question. Conceptually it is convenient to group these many possible origins of energy dissipation into three categories: elastic and plastic deformation of the underlying substgrates, wear (i.e. degradation of the surfaces and substrates during the course of sliding, and surface mechanical properties of the interface itself. In favorable model systems a substantial degree of separation is possible. This paper is concerned with separating the surface chemical contributions to boundary layer friction from the mechanical ones.

This paper reviews the author's research of the adhesion, friction, and micromechanical properties of materials and presents examples of the results. The ceramic and metallic materials studied include silicon carbide, aluminum oxide, and iron-base amorphous alloys. The design and operation of a torsion balance adapted for study of adhesion from the Cavendish balance are discussed first. The pull-off force (adhesion) and shear force (friction) required to break the interfacial junctions between contacting surfaces of the materials were examined at various temperatures in a vacuum. The surface chemistry of the materials was analyzed by x-ray photoelectron spectroscopy. Properties and environmental conditions of the surface regions which affect adhesion and friction - such as surface segregation, composition, crystal structure, surface chemistry, and temperature were also studied.

Fracto-Emission is the emission of particles and photons during and after fracture of materials. The observed emission includes electrons, negative and positive ions, neutral species in both ground states and in excited states, and visible photons. This emission can often serve as a sensitive probe of crack growth and may prove to be a useful tool for investigating molecular and microscopic events accompanying crack growth and for studying the details of failure modes in a variety of materials. Interfacial failure provides unique fracto-emission signals due to the extensive charge separation accompanying separation of dissimilar materials. Here we present the results of several recent studies of interfacial failure involving a variety of materials and relate them to electronic and mechanical processes accompanying failure.

We have constructed an instrument designed to make measurements of interfacial mechanical properties under ultra-high vacuum conditions. The device has been configured to allow two metallic surfaces to be prepared and characterized independently within a single UHV chamber. The two can then be brought into contact to allow measurements of the frictional properties of their interface. In this manner we are able to study the frictional properties of metallic surfaces modified by the presence of mono-molecular films. The instrument is described in this paper as are the results of initial measurements performed on modified tungsten surfaces. In addition we address the question of why it is that such ultra-thin films can modify the mechanical properties of surfaces brought into contact under macroscopic loads.

A series of boron carbide materials was hot pressed with 0-7% excess carbon. The strength of each material was determined by four point bending, and found to decrease from about 600MPa to 300MPa as the carbon content increased from 0% to 7%. Diamond indentation yielded hardness values that decreased from 28.3 to 25.OGPa and toughness values that increased from 3.5 to 4.5 MPa√mover the same carbon range. Each sample was fractured in situ in ultrahigh vacuum (UHV) and examined by scanning Auger microanalysis (SAM) and XPS to determine both the elemental and chemical state distributions. For the samples with excess carbon, localized carbonrich regions are observed on fracture surfaces by SAM. XPS reveals a 50% enhancement of excess carbon on the fracture surface compared to the bulk for the sample with 7% excess carbon. A correlation was observed between surface carbon composition and the bulk toughness and hardness. The C(ls) XPS spectra were utilized to determine the nature of carbon in B4C on freshly fractured and Ne+ bombarded surfaces. Two distinct peaks were observed in the C(ls) region. Low dose ion bombardment resulted in a single broad C(ls) peak at the midpoint of the two initial peaks. It can be inferred from this data that there are C-C-C intericosahedral linkages in B4C.

The residual stresses of two different film/substrate systems were calculated. Besides, several micromechanical tests were performed. Joining the calculated residual stresses to the analysis of the experimental results, some insight on the interfacial adhesion of film/substrate systems is presented.

Multi-layer thin film which has structure of Cu/Cr/K/Cr/Cu prepared by sputtering process was analyzed for interfacial stresses for as-deposited conditions. This structure was also annealed at 150°C, 250°C, and 350°C for around 15 min. in a vacuum and cooled slowly down for stress analyses.

Equations derived by Osgood [1] for residual stress estimations for homogeneous material system using layer removal technique (stress relief) is now applied for inhomogeneous system (multilayer structure). The results are compared with the data obtained from x-ray diffraction technique by using sin2Ψ-2θ method, for Cu layer.

From the present analyses, the data obatined using layer removal seem to be qualitatively consistent with but not quantitatively in agreement with x-ray method. Data obtained using the layer removal method have some overlaps with those obtained from x-ray technique. However, in details, data from the curvature method present different scattering band from the x-ray method. It is suggested that the layer removal method is more practical to be used to estimate the average residual stress of the multi-layer system not only because the layer removal method estimates the bulk behavior but also when the metal film is thin (e.g., 200A for Cr layer), x-ray technique becomes impractical. By annealing the sputtered structure up to 250°C, the residual stresses, in particularly Cu layer, decreased on both sides in x- and y-directions.

From the main results drawn from the present studies, the layer removal sequence for the curvature method shows significant affects on the obtained results of residual stresses. Minimizing influences caused by layer removal sequences as well as removing duration and temperature provides the most accurate results on residual stress measurements.

The elastic constants of a Σ5 (100) twist grain boundary are calculated on a monolayer-by-monolayer basis, and the elastic behavior is shown to differ by up to an order of magnitude from bulk-like behavior. This unusual elastic behavior is found to be similar to that of uniaxiallystrained crystals, since the grain boundaries themselves are regions which are strained (expanded) in one direction.

Plasma sprayed Hydroxyapatite (HA) coatings are applied to metal prostheses to allow for implant fixation through chemical bonding of the coating with surrounding bone tissue. Without a well-adhering coating, this fixation is threatened. Thus, a thorough characterization of the metal / ceramic interface is necessary. This study used a novel composite short bar interfacial fracture toughness technique with high resolution electron spectroscopic imaging to examine Ti-6AI-4V plasma spray coated with 100μm of HA. For this system, an interfacial fracture toughness value of 1.31 +/− 0.08 MPa·m1/2 was obtained, with a corresponding tensile adhesive bond strength of 6.7 +/− 1.5 MPa. High resolution ESI revealed distinct phosphorous segregation to the interface and diffusion into the underlying titanium. A 24-hour post-heat treatment at 960°C greatly increased the bond strength at this interface. Observations from ESI suggested that this effect may be due to enhanced diffusion of both phosphorous and calcium into the metal substrate.

We report on a novel method for measuring the bond strength of metal/ceramic interfaces. Test specimens are created by vapor depositing a metal film on a ceramic substrate. The specimen is impacted with a thin metal flyer sending a short planar shock pulse into the ceramic. If the shape and amplitude of the wave is properly controlled the interface will spontaneously debond creating new free surfaces.

Measurements indicate the debonding process occurs in less than 1.0 ns, which we believe is too short for crack propagation along existing flaws. Therefore, we conclude that simultanious breaking of atomic bonds rather than propagation and coalescence of cracks is the means by which the film and substrate are separated. The free surface velocity of the metal overlayer is monitored during spall by laser interferometry. The data constitute a direct measurement of the bond strength. The measured bond strengths are reproducible and do not show a dependence on shock amplitude for identically prepared specimens.

The adhesion of thin evaporated Cu films directly to SiO2 is generally poor. The adhesion can be improved by a variety of treatments, ranging from a pre-deposition Ar ion bombardment of the substrate, to post deposition bombardments with ion beams, photons or electrons. Also, if a thin layer of partially oxidized Cr is deposited onto the SiO2 prior to Cu deposition, the Cu adheres more strongly. The intrinsic mechanism responsible for these adhesion improvements remains to be understood.

We have attempted to characterize the interface of these structures by a combination of Rutherford Backscattering Spectrometry (RBS) and an adhesion peel test to determine the role each treatment plays in the adhesion process.

Wettability and contactibility of selected metals and alloys on superconducting YBa2Cu3O7-x were studied. Droplets of metals and alloys were formed by melting short segments of wires on pellets of YBa2Cu3O7-x The wires were melted in a rapid thermal annealer with an oxygen atmosphere to lessen the oxygen loss from the YBa2Cu3O7-x surface. The contact angles of the solidified droplets on the pellets were measured from the micrographs taken with a scanning electron microscope. Contact angles less than 90° were obtained with Pb and Ag, while angles greater than 90° were obtained with Bi metal, 40Pb/60Sn, and 99Pb/lSb alloys. Pb alloyed with either Sn or Sb increased the wetting angles. The contact angles provided a direct measurement of wetting characteristics and were used to relate various surface energies and the work of adhesion between tested metallic systems and YBa2Cu3O7-x.

Copper and sol-gel processed cordierite were cosintered in oxidizing atmosphere using an eutectic bonding technique. Firing at low and high heating rates leads to interfaces which present different macroscopic properties. These interfaces were therefore investigated on a microscopic scale by SEM, XPS and STEM analyses. Copper diffusion as well as strong chemical and structural modifications were observed in the interface region. Although these interfaces have good adhesion properties, there was no evidence for the formation of some interfacial copper compound.

Measurements of mechanical damping, or internal friction (Q−1), and dynamic Young's modulus (E) have been made near 80 kHz and at strain amplitudes (ε) in the range of 10−8 to 10−4 on small specimens of the following two continuous fiber-reinforced metal matrix composites (MMCs): 6061 aluminum reinforced with alumina (Al/A12O3) and 6061 aluminum reinforced with tungsten (AI/W). Baseline experiments were also performed on 99.999% aluminum (pure Al) for comparison puposes. The temperature (T) dependence of modulus up to 475°C was determined for AI/A12O3 and pure Al. The rate of modulus decrease with increasing temperature for AI/A12O3 and Al was the same, that is, dE/dT was essentially the same for both materials. Thus, the reduction in modulus observed for the Al/Al2O3 was attributed to the reduction in modulus of the Al matrix and not that of the Al2O3 fibers. The strain amplitude dependence of damping was examined for all three materials. The pure Al exhibited classical dislocation damping behavior with strain amplitude dependent damping starting at a strain of 2 × 10−5. The Al/Al2O3 specimens showed only mild dependence of damping on strain amplitude starting at strains near 10−5. The AI/W exhibited significant amplitude dependence of damping starting at strains of 2 × 10−6 with the fiber diameter being a major factor in determining the damping behavior. The Q−1 versus ε data for Al/Al2O3, when analyzed in terms of the Granato-Lücke (GL) theory for dislocation damping, yielded minor pinning lengths of dislocations near 10−8 m and mobile dislocation densities near 1011 m−2. The same analysis for the Al/W data gave values near 10−8 m for the minor pinning lengths and 1012 M−2 for the dislocation density. Relative to the results for pure Al, the minor pinning lengths for Al/Al2O3 and AL/W are comparable (10−8 m for pure Al), but the dislocation densities are much higher (109 m−2 found in the pure Al). The relatively high dislocation densities calculated for these aluminum matrix MMCs agree with previous findings of other researchers and may be associated with the fiber/matrix interface.

The structure of the bond between dental aluminous porcelain and tin oxide coated platinum foils, used in dental jacket crowns, has been studied using analytical electron microscopy of crosssectioned specimens. It has been shown that the tin oxide is in the form of stannic oxide (SnO2) and that some of the oxide dissolves into the glass. It has also been demonstrated that the platinum foil is strained immediately adjacent to the interface.