The Optimization of Niobium Diselenide Thin Films Through Control of Pulsed Laser Deposition Parameters
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THE OPTIMIZATION OF NIOBIUM DISELENIDE THIN FILMS THROUGH CONTROL OF PULSED LASER DEPOSITION PARAMETERS
ALLAN E. DAY*, SAMUEL J.P. LAUBE**, M.S. DONLEY*, and J.S. ZABINSKI* *WIJMLB, Materials Directorate, OH, **University of Cincinnati, OH
ABSTRACT Niobium diselenide has potential for use as a conductive lubricant, but to achieve the optimal properties of low friction coefficient, high conductivity and oxidation resistance, the SeJNb ratio and crystallinity must be carefully controlled. It has been shown that Pulsed Laser Deposition (PLD) permits the required degree of control, even over films with complex stoichiometries. (4-8). In this study, PLD was used to grow stoichiometric, crystalline thin films of niobium diselenide and to study the effects of laser deposition parameters on film properties. Film chemistry and crystallinity were evaluated using XPS, RBS, and glancing angle XRD. Friction and wear measurements were taken on a ball-on-flat tribometer. The deposition apparatus incorporates a fully computerized data acquisition and control system that facilitated the correlation of the laser deposition parameters to film properties. This study has shown that film chemistry could be changed from substoichiometric to superstoichiometric and crystallinity varied between amorphous to highly crystalline by appropriate choice of PLD parameters. The property correlations and acquisition system that permitted the identification of the optimal growth conditions will be described. INTRODUCTION Solid lubricant films are required for many high precision, applications such as satellite mechanisms and micro-electromechanical systems. In some of these applications the lubricant needs to be able to conduct electrical currents. Molybdenum disulphide, the current solid lubricant of choice for many applications has excellent wear characteristics but poor electrical properties. Niobium diselenide is a solid lubricant having a hexagonal, tri-layered structure similar to that of MoS2, but it has six orders of magnitude less resistivity. Jamison has reported a technique whereby the NbSe2 structure could be altered using intercalation to substantially improve its friction and wear properties at temperatures up to 350'C [1-2]. Other research has shown that sputtered and compact specimens of NbSe2 have potential uses as a lubricant in moist environments [3]. To date, PLD has been shown to be an excellent technique to deposit adherent, stoichiometric, crystalline thin films of a number of tribologically important materials. Among these is MoS2 whose growth by PLD has been studied and characterized in detail [4-8]. From these studies it was clear that PLD is a complex, highly energetic process where the laser parameters can have a large effect on film properties. To gain control of the PLD process one must understand it. To do this, sensors must be developed to investigate the deposition process in-situ and, thereby, gain a more fundamental understanding of the film growth characteristics. This research was the first step towards gaining
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