David B. Bogy

Characterization of diamondlike carbon films and their application as overcoats on thin‐film media for magnetic recording

This paper reviews and analyzes the literature on thin carbon layers with emphasis on their use as protective overcoats for thin‐film magnetic media. We discuss carbon as a material, its preparation as a thin film, and review and evaluate various techniques for characterizing its thin‐film properties.

Static friction coefficient model for metallic rough surfaces

Modele de calcul du coefficient de frottement statique dans le cas de surfaces rugueuses metalliques

On the problem of edge-bonded elastic quarter-planes loaded at the boundary

Abstract The stress field in bonded quarter-planes of different elastic materials due to arbitrary (integrable) normal and shear loading applied at the boundary is given explicitly in terms of the two composite parameters α, β introduced in Dundurs discussion [2] of the authors previous paper [1]. The singularity in the stress field is studied for all physically relevant values of α, β. The singularity is of order r − λ , log r, or 1 depending on the values of α, β. The solution for uniform normal and shearing tractions is also obtained from a limiting case. The general solution is also used to derive a simple algebraic function of α only, that represents the fraction of the applied load borne by each quarter-plane. Finally the loading is specialized to that of a concentrated normal force and the resulting stress components are shown graphically as a function of position along the bonded edge for various values of α, β.

Stress singularities at interface corners in bonded dissimilar isotropic elastic materials

Abstract The plane problem is considered of two materially dissimilar isotropic, homogeneous, elastic wedges that are bonded together along both of their common faces so that the cross section forms a composite fullplane with a single corner in the otherwise straight interface boundary. The loading is due to a regular plane body force field with finite resultant applied to a bounded subregion of one of the wedge domains. Emphasis is placed on determining how the order of the singularity in the stress field at the corner depends on the material constants and corner angle. Numerical results are presented for several chosen angles and all physically relevant composites. In no instance is the stress singularity more severe than that associated with the traction and displacement problems for the reentrant wedge element.

Chemical Structure and Physical Properties of Diamond-Like Amorphous Carbon Films Prepared by Magnetron Sputtering

Thin films of amorphous carbon (a-C) and amorphous hydrogenated carbon (a-C:H) were prepared using magnetron sputtering of a graphite target. The chemical structure of the films were characterized using electron energy loss spectroscopy (EELS) and Raman spectroscopy. The mass density, hardness, residual stress, optical bandgap, and electrical resistivity were determined, and their relation to the films chemical structure are discussed. It was found that the graphitic component increases with increasing sputtering power density. This is accompanied by a decrease in the electrical resistivity, optical bandgap, mass density and hardness. Increasing the hydrogen content in the sputtering gas mixture results in decreasing hardness (14 GPa to 3 GPa) and mass density, and increasing optical band gap and electrical resistivity. The variation in the physical properties and chemical structures of these films can be explained in terms of the changes in the volume of sp{sup 2}-bonded clusters in the a-C films and changes in the termination of the graphitic clusters and sp{sup 3}-bonded networks by hydrogen in the a-C:H films.

Adhesion Model for Metallic Rough Surfaces

An improved DMT adhesion model in conjunction with an elastic-plastic contact model is used to study adhesion of contacting metallic rough surfaces. The effects of surface roughness and surface energy of adhesion on the pull-off force and on the significance of the adhesion force are investigated. It is shown that for clean surfaces the adhesion is quite large even for relatively rough surfaces. Adhesion is negligible only for contaminated rough surfaces or at very high external loading.

Maskless Plasmonic Lithography at 22 nm Resolution

Optical imaging and photolithography promise broad applications in nano-electronics, metrologies, and single-molecule biology. Light diffraction however sets a fundamental limit on optical resolution, and it poses a critical challenge to the down-scaling of nano-scale manufacturing. Surface plasmons have been used to circumvent the diffraction limit as they have shorter wavelengths. However, this approach has a trade-off between resolution and energy efficiency that arises from the substantial momentum mismatch. Here we report a novel multi-stage scheme that is capable of efficiently compressing the optical energy at deep sub-wavelength scales through the progressive coupling of propagating surface plasmons (PSPs) and localized surface plasmons (LSPs). Combining this with airbearing surface technology, we demonstrate a plasmonic lithography with 22 nm half-pitch resolution at scanning speeds up to 10 m/s. This low-cost scheme has the potential of higher throughput than current photolithography, and it opens a new approach towards the next generation semiconductor manufacturing.

Effects of substrate temperature on chemical structure of amorphous carbon films

Amorphous carbon thin films were prepared at 30, 200, and 450 °C by magnetron sputtering of a graphite target. The surface structure and chemical bonding (sp2/sp3) of the carbon films were characterized by scanning tunneling microscopy (STM) and Raman spectroscopy. STM images show that graphite microcrystallites of 20–40 A in size are present at the surfaces of all the films and the number of the microcrystallites increases with increasing substrate temperature. The microcrystallites often contain structural defects. Raman measurements show that increasing the substrate temperature results in an increase in the sp2‐bonded fraction of carbon atoms and a decrease in the microstructural defects. These results indicate that the microstructural changes are correlated with changes in the chemical bonding ratio (sp3/sp3) and no diamond microcrystallites are present in the amorphous carbon. A three‐dimensional atomic structure of the graphite microcrystallites is discussed in terms of turbostratic graphite.

Thermal Stability of Amorphous Hard Carbon Films Produced by Cathodic-Arc Deposition

The thermal stability of amorphous hard carbon films produced by cathodic arc deposition was studied by near edge x-ray absorption fine structure (NEXAFS) spectroscopy, Raman spectroscopy, and nanoindentation evaluation. Pure carbon films of up to 85% sp3 content were deposited using a pulsed biasing technique and annealed in ultrahigh vacuum up to 850 °C. NEXAFS spectra show no change in the film properties up to 700 °C, and a modification of the spectra for 800 and 850 °C, which indicate graphitization. Raman spectra show only a very slight change up to 850 °C. The nanoindentation data show no change in hardness and elastic modulus with annealing up to 850 °C. The study demonstrates the high thermal stability of the films. The difference in the NEXAFS and the Raman and nanoindentation results can be attributed to the surface sensitivity of NEXAFS in comparison to the more bulk sensitivity of Raman spectroscopy and nanoindentation.

Measurement of head/disk spacing with a laser interferometer

A multichannel heterodyne laser interferometer was built to measure the head-disk spacing in magnetic disk drives. The main advantage of the present method compared to white light interferometry and capacitive measurements is that neither the disk nor the slider need be transparent or conductive. The interferometer is described, including the optics and electronics. Experimental results on head-disk spacing during the take-off, flying and landing processes are presented and discussed. It is concluded that the present system is capable of making the desired measurement with minimum modification of the slider. It has a resolution of 2.5 nm and a bandwidth of DC to about 40 kHz. >