John T. Grant

Deposition of stoichiometric MoS2 thin films by pulsed laser evaporation

Abstract Thin films of MoS 2 have been deposited on stainless steel substrates by pulsed laser evaporation. The substrates were nominally at room temperature during deposition. In situ surface analysis of the as-deposited films by Auger electron spectroscopy and X-ray photoelectron spectroscopy showed the films to be stoichiometric MoS 2 . Analysis of the films by Raman spectroscopy and X-ray diffraction indicated the films to be hexagonal MoS 2 .

Polyurethane/polysiloxane ceramer coatings: Evaluation of corrosion protection

A series of polyurea and polyurethane ceramer coatings were formulated using hexamethylene diisocyanate (HDI) isocyanurate, alkoxysilane-functionalized HDI isocyanurate, tetraethyl orthosilicate (TEOS) oligomers and cycloaliphatic polyesters. The coatings were prepared as a function of alkoxysilane-functionalized HDI isocyanurate and TEOS oligomers concentration. Also, the effect of acid catalyst was investigated. The corrosion resistance of polyurea or polyurethane ceramer coating systems were evaluated using a prohesion chamber on aluminium alloy 2024-T3 substrate. The polyurethane ceramer coatings were compared with the chromate pretreatment and the epoxy-polyamide primer containing the chromate pigment. In addition to prohesion, the interface between the coating and substrate was characterized using X-ray photoelectron spectroscopy (XPS). The prohesion data showed that the corrosion was inhibited by the TEOS oligomers. However, high concentrations of TEOS oligomers and acid catalyst produced blistering in the polyurea/polysiloxane ceramer coatings. The prohesion data alsoi showed that the corrosion protection of ceramer coatings performed as well as the chromate pretreatment and competitively with the epoxy primer. From the XPS and prohesion data, a self assembling silicon oxide layer at the metal-coating interface was proposed.

Electrostatic self-assembly of sulfonated C60-porphyrin complexes on chitosan thin films

Abstract Sulfonated C 60 , 5,10,15,20-tetra kis 4-[ meso -tetra-methyl (4-pyridinyl)] porphyrin (C 60 (SO 3 − ) n –TMePyP 4+ ) complex films have been prepared by electrostatic self-assembly of each chromophore from solution. When these complex films are formed on a thin film of chitosan polymer, the stacked bilayer films exhibit nearly twice the absorption as those prepared on conventional silanized substrates. X-ray photoelectron spectroscopy measurements disclose a strong interaction between the C 60 (SO 3 − ) n and TMePyP 4+ . Atomic force microscopy results of the surface morphology, hardness, and the chemical functionality are used to explain the differences between substrate treatments.

Surface composition and barium evaporation rate of “pedigreed” impregnated tungsten dispenser cathodes during accelerated life testing

Abstract A study has been made of the surface composition and barium evaporation rate of “pedigreed” impregnated tungsten dispenser cathodes. The effect of air exposure on coated cathodes was examined and was found to have no significant effect on barium evaporation rate although in some cases longer reactivation times were required. No changes in surface topography were apparent following air exposure and reactivation. Life testing was done at 100°C above the typical operating temperature for the cathode, where the typical operating temperature was taken to be 950°C for coated cathodes and 1050°C for uncoated cathodes. The cathodes were examined at different stages of life testing, up to 1200 h. Significant decreases in barium evaporation rates were found after as few as 500 h of life testing. After 1000 h the evaporation rate had decreased more than an order of magnitude. Changes in surface composition were also found. The effects of tungsten particle size, used in manufacture of the billet, on barium evaporation rate were also studied but no correlation was found.

An evaluation of the bremsstrahlung contribution to specimen damage in XPS using Auger peak intensities

Abstract The contribution of the bremsstrahlung radiation from a conventional X-ray source to specimen damage is related to the total amount of X-ray energy absorbed by the specimen. For organic compounds, which contain light elements such as C, O, and N, absorption of X-rays leads primarily to 1s photoemission. In this study the Auger-to-photoelectron peak (KLL/1s) intensity ratio was measured using both conventional and monochromatic AlKα X-ray sources for a series of compounds containing light elements from C to Mg. These ratios show a systematic 15–70% increase with conventional source relative to the monochromatic source, as the atomic number decreases for all elements studied except Mg. Calculations of 1s hole production, based on characteristic line and bremsstrahlung intensities measured with an energy-dispersive X-ray analyzer, showed the same trend, but smaller percentage increases. The differences between the experimental and theoretical values are attributed mainly to an overestimate of the characteristic/bremsstrahlung ratio using the energy-dispersive X-ray data. The bremsstrahlung contribution to specimen damage for carbon was estimated to be between ≈ 4% (calculated from X-ray data) and ≈ 44% (calculated from relative Auger intensities).

Relative work function, surface composition and topography of “pedigreed” impregnated tungsten dispenser cathodes☆

Abstract A study has been made of the variation in work function, surface composition, and topography of 5:3:2 impregnated tungsten dispenser cathodes made under carefully controlled conditions (pedigreed cathodes). Despite these conditions several cathodes had unexpected deposits on their emitting surfaces, and one showed a variation in work function and composition across the surface during activation.

Auger Electron Spectroscopy

Auger electron spectroscopy (AES) is a method for determining the elemental composition of the several outermost atomic layers of materials. The surface layers often have a composition that is quite different from the bulk material due to contamination, oxidation, or processing. In AES, a specimen is probed with an energetic electron beam with an energy fixed between 3 and 30 keV, resulting in the ejection of core-level electrons from atoms. The resulting vacancy in a core level can be filled by an outer-level electron, with the excess energy being used to emit either an x-ray (electron probe microanalysis) or another electron from the atom (AES). This emitted electron is called an Auger electron. AES is a surface-sensitive technique due to the strong inelastic scattering of low-energy electrons traveling within specimens. Auger electrons from only the outermost several atomic layers are emitted from the specimen without energy loss, and contribute to the Auger peak intensities in a spectrum. The Auger electron kinetic energies are characteristic of the emitting atoms, and the measurement of their energies is used to identify the elements that produce them. The concentrations of elements detected can be determined from the intensities of the Auger peaks. Variation of composition with depth can be determined by depth profiling, which is usually accomplished by removing atomic layers by sputtering with inert gas ions and monitoring the Auger signals from the newly created surfaces. For most elements, the detection limit with AES is between 0.1 and 1 at.%. Keywords: Auger electron spectroscopy (AES); scanning Auger microscopy (SAM); surface analysis; surface chemistry; thin film; depth profiling

Plasma enhanced chemical vapor deposition of high refractive index polymer films

The refractive index is a key characteristic of polymer materials in optical applications. For organic polymers, typical refractive indices are in the range of 1.35 to 1.65. Extending the refractive index beyond the limits is of fundamental scientific interest and would enhance the utility of polymers in many applications. Polymeric thin films fabricated by plasma enhanced chemical vapor deposition (PECVD) have been investigated in the fields of electronics and optics and their utility is becoming more widespread in a variety of applications. Outstanding attributes of the PECVD photonic films include a smooth surface, dense crosslinking structure, robustness, environmental resistance, optical transparency in either visible or IR regions, and good adhesion to many optical window and substrate materials. In recent years, our laboratory has fabricated novel polymer optical coatings and films by PECVD. One focus of this research has been to expand the achievable maximum refractive index. This goal has been sought using two approaches including increasing the conjugation and crosslinking of chemical moieties of the bulk film and incorporation of metal ions into the structure. The techniques of XPS, FTIR, HRSEM, and ellipsometry were used to characterize both the optical properties and the chemical structure of plasma polymerized benzene, ferrocene, and metal-phthalocyanine thin films. The structure-property relationship and the effect of PECVD processing conditions are also discussed in this presentation.

Influence Of Structure On The Dielectric Properties Of PECVD Polymer Films

Polymer dielectric films fabricated by plasma enhanced chemical vapor deposition (PECVD) have inherent superiority due to their smooth surface, pin-hole free morphology, and dense crosslinked bulk structure. These spatially uniform films also exhibit good adhesion to a variety of substrates, excellent chemical inertness, high thermal resistance, and are formed from a rapid, inexpensive, solvent-free, room temperature process. In this work, we describe PECVD polymer dielectric films prepared from three precursors including benzene, octafluorocyclobutane (OFCB) and hexamethyldisiloxane (HMDS) using two different feed locations including in the plasma zone center and in the downstream region. The chemical structure of the PECVD films was determined by XPS, FTIR and ESR. The dielectric constant and dissipation of the films were studied over a range of frequencies up to 1 MHz, and the dielectric strength was characterized by the current-voltage method. Spectroscopic ellipsometry was performed to determine the thickness and refractive index of the resultant films. The PP-benzene films showed strong aromatic characteristics, PP-OFCB films maintained a high F/C ratio with a variety of fluorine moieties, and PP-HMDS retained a large fraction of Si-O bonds. All the PECVD films showed higher dielectric constants than those of corresponding conventional polymers. There is a small sharp drop in dielectric constant at low frequencies for all the PECVD films, attributed to the orientational polarization caused by trapped free radicals, oxygenated groups (C=O), and unsaturated moieties. The largest drop occurred for the PP-HMDS films. All films exhibit a continuous increase in dielectric loss as a function of frequency. Among all the PECVD films, the PP-benzene exhibited high breakdown strength. These variations in the dielectric properties are closely associated with the unique structure features of PECVD films.

Densification of Plasma Polymerized TiO x N y C z Films with Air Exposure

TiOxNyCzthin films plasma polymerized at room temperature experienced significant decreases in film thickness and increases in refractive index with time during air exposure. Correlation of optical and structural changes provided insight into densification mechanisms.