M. C. Salvadori

WCCo cutting tool inserts with diamond coatings

Abstract WCCo cutting tool inserts were coated with diamond films using microwave plasma assisted chemical vapor deposition. Several pretreatment processes and combinations were used to enhance the diamond nucleation and growth: mechanical treatments with diamond powder seeding, acid etching of the cobalt using an electrolytic acid bath, and formation of a TiC or DLC interlayer using metal plasma immersion ion implantation and deposition (MePIIID). Scanning electron microscopy (SEM) was used to view the diamond film morphology, and microanalysis was used to examine for cobalt removal after acid etching. The diamond quality was characterized by Raman spectroscopy, and the adhesion between the film and the cutting tool inserts was estimated by indentation tests. The present work compares the different treatments of the WCCo insert surface, with particular reference to the adhesion between the diamond film and the cutting tool insert.

Conducting polymer formed by low energy gold ion implantation

A buried conducting layer of metal/polymer nanocomposite was formed by very low energy gold ion implantation into polymethylmethacrylate. The conducting layer is ∼3 nm deep and of width ∼1 nm. In situ resistivity measurements were performed as the implantation proceeded, and the conductivity thus obtained as a function of buried gold concentration. The measured conductivity obeys the behavior well established for composites in the percolation regime. The critical concentration, below which the polymer remains an insulator, is attained at a dose ∼1.0×1016 atoms/cm2 of implanted gold ions.

Thermoelectric effect in very thin film Pt∕Au thermocouples

The thickness dependence of the thermoelectric power of Pt films of variable thickness on a reference Au film has been determined for the case when the Pt film thickness, t, is not large compared to the charge carrier mean free path, {ell}, that is, t/{ell}. Pt film thicknesses down to 2.2 nm were investigated. We find that {Delta}S{sub F} = S{sub B}-S{sub F} (where S{sub B} and S{sub F} are the thermopowers of the Pt bulk and film, respectively) does not vary linearly as 1/t as is the case for thin film thermocouples when the film thickness is large compared to the charge carrier mean free path.

Simple, safe, and economical microwave plasma‐assisted chemical vapor deposition facility

A simple and economical microwave plasma‐assisted chemical vapor deposition facility has been developed and used for synthesis of diamond thin films. The system is similar to those developed by others but includes several unique features that make it particularly economical and safe, yet capable of producing high quality diamond films. A 2.45‐GHz magnetron from a commercial microwave oven is used as the microwave power source. A conventional mixture of 0.2% methane in hydrogen is ionized in a bell jar reaction chamber located within a simple microwave cavity. By using a small hydrogen reservoir adjacent to the gas supply, an empty hydrogen tank can be replaced without interrupting film synthesis or causing any drift in plasma characteristics. Hence films can be deposited continuously for arbitrarily long periods while storing only a 24‐h supply of explosive gases. System interlocks provide safe start‐up and shut‐down and allow unsupervised operation. Here we describe the electrical, microwave, and mechani...

Diamond synthesis by microwave plasma chemical vapor deposition using graphite as the carbon source

We report on the growth of high‐quality diamond using a microwave plasma chemical vapor deposition (CVD) system in which the feed gas contains no hydrocarbons, but instead the source of carbon is a graphite piece which resides within the plasma volume. Results of experiments using this technique by itself and in combination with the normal methane feed gas method are described. The samples were analyzed by Raman spectroscopy and scanning electron microscopy. Diamond grown in this way was found to be particularly pure and of high crystallinity.

Diamond-like-carbon and molybdenum disulfide nanotribology studies using atomic force measurements

Abstract In this work, some results are presented concerning the studies of friction coefficient distribution in diamond-like-carbon (DLC) and molybdenum disulfide (MoS 2 ) thin films stored in atmosphere environment. Tribological nanoscale analysis using Lateral Force Microscopy (LFM) were performed. Experiments aimed at establishing the tribological properties of sputtered DLC and MoS 2 thin films. For friction measurements the LFM technique requires lateral movement of the Atomic Force Microscopy (AFM) tip in contact with a surface. The lateral force acts on the pyramidal tip attached to the end of the cantilever, due to friction or viscous forces, resulting in the cantilever measurable torsion and deflection related to frictions magnitude. The relationship among data from friction coefficient distribution, surface composition and crystal structure for DLC and MoS 2 are compared and are presented for the first time. Auxiliary characterization techniques as Raman scattering spectroscopy (RSS), and X-ray photoelectron spectroscopy (XPS) for both DLC and MoS 2 thin films are also presented.

Gold-implanted shallow conducting layers in polymethylmethacrylate

PMMA (polymethylmethacrylate) was ion implanted with gold at very low energy and over a range of different doses using a filtered cathodic arc metal plasma system. A nanometer scale conducting layer was formed, fully buried below the polymer surface at low implantation dose, and evolving to include a gold surface layer as the dose was increased. Depth profiles of the implanted material were calculated using the Dynamic TRIM computer simulation program. The electrical conductivity of the gold-implanted PMMA was measured in situ as a function of dose. Samples formed at a number of different doses were subsequently characterized by Rutherford backscattering spectrometry, and test patterns were formed on the polymer by electron beam lithography. Lithographic patterns were imaged by atomic force microscopy and demonstrated that the contrast properties of the lithography were well maintained in the surface-modified PMMA.

Columnar CVD diamond growth structure on irregular surface substrates

Abstract Columnar grain structure is always observed in CVD-diamond growth and is an important parameter to identify the morphology of thin and thick films. Structure defects, aspects of onset nucleation and film growth mechanisms can also be related to columnar growth. In this work we focused our attention on the columnar structure of CVD-diamond grown on irregular surfaces. We observed that there is a relationship among curvature radius of the substrate surface, the spread of the column volume and the growth rate of the diamond film. Growth rates on spherical surfaces of around 0.5 mm curvature radius have been observed to be up to three times bigger than the growth rates on planar surfaces. Also, the grain size distribution on planar and on the corner surfaces as a function of the growth rate has been studied. Characterization with scanning electron microscopy (SEM) and Raman scattering spectroscopy (RSS) has been performed.

Contamination due to memory effects in filtered vacuum arc plasma deposition systems

Thin film synthesis by filtered vacuum arc plasma deposition is a widely used technique with a number of important emerging technological applications. A characteristic feature of the method is that during the deposition process not only is the substrate coated by the plasma, but the plasma gun itself and the magnetic field coil and/or vacuum vessel section constituting the macroparticle filter are also coated to some extent. If then the plasma gun cathode is changed to a new element, there can be a contamination of the subsequent film deposition by sputtering from various parts of the system of the previous coating species. We have experimentally explored this effect and compared our results with theoretical estimates of sputtering from the SRIM (Stopping and Range of Ions in Matter) code. We find film contamination of order 10-4 - 10-3, and the memory of the prior history of the deposition hardware can be relatively long-lasting.

The Effect of a Graphite Holder on Diamond Synthesis by Microwave Plasma Chemical Vapor Deposition

This paper reports that a microwave plasma chemical vapor deposition system using a graphite retaining ring as the sample holder has been used for low pressure diamond synthesis. The hydrogen plasma in this system can etch material from the graphite surface. By conditioning the surface of the graphite ring, this process can be reversed, and material can then be deposited onto the graphite surface by the plasma, rather than being etched from it. The result of conditioning the graphite retaining ring was to cover the graphite with diamond, and hinder plasma etching of carbon from the retaining ring. The samples were characterized using Raman Spectroscopy and Scanning Electron Microscopy, and the surface of the remaining ring was also studied with Raman.