Simone Anders

Nanoindentation and Nanoscratching of Hard Carbon Coatings for Magnetic Disks

Nanoindentation and nanoscratching experiments have been performed to assess the mechanical properties of several carbon thin films with potential application as wear resistant coatings for magnetic disks. These include three hydrogenated-carbon films prepared by sputter deposition in a H{sub 2}/Ar gas mixture (hydrogen contents of 20, 34, and 40 atomic %) and a pure carbon film prepared by cathodic-arc plasma techniques. Each film was deposited on a silicon substrate to thickness of about 300 run. The hardness and elastic modulus were measured using nanoindentation methods, and ultra-low load scratch tests were used to assess the scratch resistance of the films and measure friction coefficients. Results show that the hardness, elastic modulus, and scratch resistance of the 20 and 34% hydrogenated films are significantly greater than the 40% film, thereby showing that there is a limit to the amount of hydrogen producing beneficial effects. The cathodic-arc film, with a hardness of greater than 59 GPa, is considerably harder than any of the hydrogenated films and has a superior scratch resistance.

Hardness, elastic modulus, and structure of very hard carbon films produced by cathodic‐arc deposition with substrate pulse biasing

The hardness, elastic modulus, and structure of several amorphous carbon films on silicon prepared by cathodic‐arc deposition with substrate pulse biasing have been examined using nanoindentation, energy loss spectroscopy (EELS), and cross‐sectional transmission electron microscopy. EELS analysis shows that the highest sp3 contents (85%) and densities (3.00 g/cm3) are achieved at incident ion energies of around 120 eV. The hardness and elastic modulus of the films with the highest sp3 contents are at least 59 and 400 GPa, respectively. These values are conservative lower estimates due to substrate influences on the nanoindentation measurements. The films are predominantly amorphous with a ∼20 nm surface layer which is structurally different and softer than the bulk.

Clusters and magnetism in epitaxial Co-doped TiO2 anatase

We show that under certain conditions, highly Co-enriched TiO2 anatase clusters nucleate on epitaxial TiO2 anatase grown on LaAlO3(001) by oxygen plasma assisted molecular beam epitaxy. In the most extreme cases, virtually all incident Co segregates to the clusters, yielding a nanoscale ferromagnetic phase that is not ferromagnetic in homogeneous films of the same Co concentration. The nucleation of this phase simultaneous with continuous epitaxial film growth must be carefully monitored in order to avoid drawing false conclusions about the film structure.

Transport of vacuum arc plasmas through magnetic macroparticle filters

Vacuum arc plasma deposition combined with magnetic filtering of the plasma to remove macroparticles is a promising technique for the production of metallic, compound and hard amorphous carbon thin films. High efficiency of the magnetic filter is a crucial parameter for the application of this technique. We report investigations of the influence of different filter designs, magnetic field configurations and electric potentials on the filter efficiency. We analyse the transport mechanisms on which the flow of plasma through the filter is based, and describe and discuss the occurrence of instabilities in magnetic filters. With an optimum filter arrangement we were able to obtain a filter output of 25% of the total number of ions produced by the vacuum arc discharge.

Metal plasma immersion ion implantation and deposition using vacuum arc plasma sources

Plasma source ion implantation (PSII) with metal plasma results in a qualitatively different kind of surface modification than with gaseous plasma due to the condensable nature of the metal plasma, and a new, PSII‐related technique can be defined: metal plasma immersion ion implantation and deposition (MPI). Tailored, high‐quality films of any solid metal, metal alloy, or carbon (amorphous diamond) can be formed by MPI using filtered vacuum arc plasma sources, and compounds such as oxides or nitrides can be formed by adding a gas flow to the deposition. Here we describe the plasma formation at cathode spots, macroparticle filtering of the vacuum arc plasma by magnetic ducts, the underlying physics of MPI, and present some examples of MPI applications.

Photoemission electron microscope for the study of magnetic materials

The design of a high resolution photoemission electron microscope (PEEM) for the study of magnetic materials is described. PEEM is based on imaging the photoemitted (secondary) electrons from a sample irradiated by x rays. This microscope is permanently installed at the Advanced Light Source at a bending magnet that delivers linearly polarized, and left and right circularly polarized radiation in the soft x-ray range. The microscope can utilize several contrast mechanisms to study the surface and subsurface properties of materials. A wide range of contrast mechanisms can be utilized with this instrument to form topographical, elemental, chemical, magnetic circular and linear dichroism, and polarization contrast high resolution images. The electron optical properties of the microscope are described, and some first results are presented.

PRINCIPLES OF X-RAY MAGNETIC DICHROISM SPECTROMICROSCOPY

A review is given of the principles underlying X-ray magnetic circular (XMCD) and linear (XMLD) dichroism spectromicroscopies consisting of polarized X-ray absorption spectroscopy in conjunction with scanning or imaging microscopy. The techniques are shown to have many useful and important capabilities for the study of complex magnetic materials. They offer elemental specificity, chemical specificity and variable depth sensitivity, among others. XMCD microscopy is best suited for the study of ferromagnets and ferrimagnets, and it allows a quantitative determination of the size and direction of spin and orbital moments. XMLD microscopy promises to become a powerful tool for the study of antiferromagnets which are difficult to study by conventional microscopy techniques.

Pulsed dye laser diagnostics of vacuum arc cathode spots

The ignition and arc phases of vacuum arcs were investigated using differential dye laser absorption photography with simultaneous high spatial (micrometer) and temporal (nanosecond) resolution. The discharge duration was 800 ns, the current 50-150 A, the electrode material copper, and the cathode-anode distance less than 50 mu m. A 0.4 ns laser pulse (tunable, gamma =480-530 nm) was used to obtain momentary absorption photographs of the cathode region. During ignition, an optically thick anode plasma expanded toward the cathode, decaying within 25 ns after bridging the electrode gap. In the arc phase, a fragmentary structure of the cathode spots was observed in situ for the first time. The microspots have a characteristic size of 5-10 mu m. They appear and disappear on a nanosecond time scale. The plasma density of the microspots was estimated to be greater than (3-6)*10/sup 26/ m/sup -3/. >

Macroparticle‐free thin films produced by an efficient vacuum arc deposition technique

Macroparticle‐free films of various metals and diamond‐like carbon have been obtained by a pulsed vacuum arc deposition technique. An axial magnetic field (100–200 mT) generated by the discharge current itself was used to focus the plasma produced by the cathode spots and to guide the plasma flow through a macroparticle filter. The films were characterized by scanning electron microscopy, atomic force microscopy, and Rutherford backscattering spectrometry. They were found to be macroparticle‐free. The total efficiency of the combined gun‐filter plasma source is even higher than a standard nonfiltered vacuum arc plasma source in terms of deposited film thickness per discharge, because the plasma losses in the filter are overcompensated by the focused plasma injection into the filter.

Effect of vacuum arc deposition parameters on the properties of amorphous carbon thin films

Abstract Hard and smooth films of amorphous carbon with thicknesses in the nanometer to micrometer range were formed on silicon substrates using a vacuum arc deposition technique. In this technique, a carbon plasma is generated by a vacuum arc plasma source coupled with a magnetic filter for obtaining macroparticle-free amorphous carbon films. The influence of the substrate bias voltage and pulsed bias duty cycle on the film properties was investigated. A significant enhancement of the film quality and adhesion was achieved by applying a negative pulsed bias voltage to the substrate. Nanoindentation, pin-on-disk tribotesting, surface profilometry, Rutherford backscattering spectroscopy, elastic recoil spectroscopy, and Raman spectroscopy were used to characterize the properties and structure of the amorphous carbon films. It was found that the hardest films with the highest density and lowest friction coefficient were obtained at - 100 V pulsed bias voltage, whereas higher pulsed bias voltages improved the film adhesion and reduced the internal stress. For -100 V pulsed bias voltage, the maximum film hardness was achieved with a 50% duty cycle, and was significantly higher than that produced with a d.c. bias.