Rapid Formation of Beryllium Nitride and Beryllium Oxide by Excimer Laser Irradiation of Samples Immersed in Liquids
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RAPID FORMATION OF BERYLLIUM NITRIDE AND BERYLLIUM OXIDE BY EXCIMER LASER IRRADIATION OF SAMPLES IMMERSED IN LIQUIDS. 0. DIJKKAMP, X.D. WU*, SIU-WAI CHAN AND T. VENKATESAN Bell Communications Research, Red Bank, NJ 07701 *Physics Department, Rutgers University, Piscataway, NJ 08854 ABSTRACT Excimer laser induced rapid formation of nitride and oxide layers on beryllium samples immersed in liquid nitrogen and water, resp., has been studied. From Rutherford backscattering spectra the amounts of incorporated nitrogen and oxygen were determined. In addition, scanning electron microscopy was used to study the morphology of the irradiated surface and compound formation was confirmed by X-ray diffraction. Our results show that extremely rapid reaction takes place when the laser energy is sufficient to melt the beryllium surface. The amount of reaction is found to be proportional to both the energy density and the number of laser shots, until a nearly stoichiometric layer of Be3 N2 or BeO is formed at the surface, at which point the reaction saturates. Growth rates on the order 20 nm per shot are deduced from the data, which is orders of magnitude higher than those achieved by conventional means. INTRODUCTION Materials modification by means of pulsed laser irradiation offers many interesting possibilities, due to the unique spatial and temporal confinement of such beams, and the ease with which energy can be coupled to reactive interfaces, say in a vacuum environment. Examples include pulsed laser annealing [1], photoablation of metals and insulators [2], in particular polymers [3], laser assisted chemical vapor deposition [4] and laser induced etching [4,5]. The high quench rates which can be obtained may allow the formation of metastable phases with interesting properties, such as high Tc superconductivity [6,7]. Recently, several groups have studied the formation of transition metal nitrides by pulsed laser irradiation of samples immersed in liquid nitrogen [6,8]. The results of similar experiments performed by our group have been presented elsewhere [9]. In this paper we discuss the results of a detailed study of the formation of nitrides and oxides on beryllium. This metal has been chosen as a model system for the following reasons. First, its low mass makes it a convenient substrate for the detection of oxygen and nitrogen by means of Rutherford backscattering. This allows fast, depth-resolved quantitative analysis of the amount of incorporated material. Second, the relevant thermodynamical properties of beryllium are rather similar to those of silicon, as will be discussed in detail below, which allows comparison with experimental and theoretical data of pulsed laser annealing of silicon, an extensively studied system [1].
Mat. Res. Soc. Symp. Proc. Vol. 75. -1987 Materials Research Society
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EXPERIMENT A Lambda Physik EMG-200 KrF excimer laser (248 nm, 30 ns) with a maximum output of 1 J/shot was used in the experiments. The beam was collimated to assure a homogeneous energy density and focussed by a quartz le
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