We describe the formation and properties of H(2)GaN(3) (1), which is a very simple and stable molecular source for chemical vapor deposition (CVD) of GaN heterostructures. Compound 1 and the perdeuterated analogue D(2)GaN(3) (2) are prepared by the LiGaH(4) and LiGaD(4) reduction of Br(2)GaN(3) (3), respectively. Compound 3 is obtained from the thermal decomposition of the crystalline adduct SiMe(3)N(3).GaBr(3) (4) via loss of SiMe(3)Br. A single-crystal X-ray structure of 4 reveals that the molecule is essentially a Lewis acid-base complex between SiMe(3)N(3) and GaBr(3) and crystallizes in the orthorhombic space group Pna2(1), with a = 14.907(5) Å, b = 7.759(3) Å, c = 10.789(5) Å, V = 1248(1) Å,(3) and Z = 4. The new azidobromogallane HBrGaN(3) (5) is also prepared by reaction of appropriate amounts of 3 and LiGaH(4). Both H(2)GaN(3) (1) and D(2)GaN(3) (2) are volatile species at room temperature and can be readily distilled at 40 degrees C (0.20 Torr) without decomposition. Normal-mode analysis and ab initio theoretical calculations suggest that the vapor phase IR spectra of 1 and 2 are consistent with a trimeric (H(2)GaN(3))(3) and (D(2)GaN(3))(3) molecular structure of C(3)(v)() symmetry. On the basis of the mass spectrum, 1 is a trimer in the vapor phase and decomposes readily at low temperatures by elimination of only H(2) and N(2) to yield pure and highly stoichiometric GaN thin films. Crucial advantages of this new and potentially practical CVD method are the significant vapor pressure of the precursor that permits rapid mass transport at 22 degrees C and the facile decomposition pathway that allows film growth at temperatures as low as 200 degrees C with considerable growth rates up to 800 Å/min.

No abstract

No abstract

An experimental investigation with Nd:YAG laser system was carried out to study the effects of laser hardening process parameters on the microstructure and hardness during laser hardening of EN25 steel. The laser beam is allowed to scan on the surface of the work piece by varying the laser beam power (750–1250 W) and travel speed (500–1000 mm/min) of the work table. The microstructural features of the laser hardened EN25 steel were analysed using optical microscope. The microstructure of the surface layer was found to consist of plate martensite. A substantial increase in surface hardness was achieved, by a factor of 2 times the base material hardness.

No abstract