Search

While NaCl-structure transition-metal nitrides have been widely studied over the past two decades, little is known about the corresponding NaCl-structure rare-earth nitrides. Polycrystalline CeN, for example, has been reported by different groups to be both a wide band-gap semiconductor and a metal. To address this controversy, we have grown epitaxial CeN layers on MgO(001) and measured their physical properties. The films were grown at 700°C by ultrahigh vacuum reactive magnetron sputter deposition in mixed Ar/N[SUB2] discharges maintained at 4 mTorr)(0.53 Pa). X-ray diffraction and transmission electron microscopy results establish the film/substrate epitaxial relationship as cube-on-cube, (001)[SUBCeN]‖(001)[SUBMgO] with [100][SUBCeN]‖[100][SUBMgO], while Rutherford backscattering spectroscopy shows that the layers are stoichiometric with N/Ce=0.99Plusmn;0.02. CeN is metallic with a positive temperature coefficient of resistivity and a temperature-independent carrier concentration, as determined by Hall effect measurements, of 2.8±0.2×10[SUP22]cm[SUP-3] with a room temperature mobility of 0.31 cm[SUP2]V[SUP-1]s[SUP-1]. At temperatures between 2 and 50 K, the resistivity is limited by defect scattering and remains constant at 29 μΩ cm, while at higher temperatures it increases linearly, limited primarily by phonon scattering, to reach a room-temperature value of 68.5 μΩ cm. The hardness and elastic modulus of CeN(001) were determined from nanoindentation measurements to be 15.0±0.9 and 330±16 GPa. [ABSTRACT FROM AUTHOR]

We investigate the effect of N vacancies on the mechanical properties of epitaxial δ-Tin[SUBx](001)layers with x=0.67- 1.0. The relaxed lattice parameter increases linearly with x in good agreement with ab initio density functional calculations, indicating that deviations from stoichiometry are entirely due to anion vacancies. Hardness values increase continuously, while the elastic modulus decreases with increasing N-vacancy concentration. We attribute the observed vacancy hardening to a reduced dislocation mobility arising from an increase in the rate-limiting activation energy for cation migration. [ABSTRACT FROM AUTHOR]

Single-crystal TiN(111) layers, 45 nm thick, were grown on MgO(111) by ultrahigh vacuum reactive magnetron sputter deposition in pure N[sub 2] discharges at T[sub s]=700 °C. Epitaxial Al(111) overlayers, 160 nm thick, were then deposited at T[sub s]=100 °C in Ar without breaking vacuum. Interfacial reactions and changes in bilayer microstructure due to annealing at 620 and 650 °C were investigated using x-ray diffraction and transmission electron microscopy (TEM). The interfacial regions of samples annealed at 620 °C consist of continuous =7-nm-thick epitaxial wurtzite-structure AlN(0001) layers containing a high density of stacking faults, with =22 nm thick tetragonal Al[sub 3]Ti(112) overlayers. Surprisingly, samples annealed at the higher temperature are more stable against Al[sub 3]Ti formation. TEM analyses of bilayers annealed at 650 °C (10 °C below the Al melting point!) reveal only the self-limited growth of an =3-nm-thick interfacial layer of perfect smooth epitaxial wurtzite-structure AlN(0001) which serves as an extremely effective deterrent for preventing further interlayer reactions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses the growth of epitaxial metastable B1 sodium chloride (NaCl) structure tantalum nitrite or TaN layers. Growth of the TaN thin films on magnesium oxide at 600 degrees centigrade; Hardness and elastic modulus; Rutherford backscattering spectroscopy; Room-temperature resistivity.

The defects of GaAs layers grown on Si (001) substrate with patterned SiO2 structures were investigated using transmission electron microscopy. The compressive strain along the <110> direction was induced in selectively grown GaAs epilayers. The defects such as stacking faults or microtwins were trapped near the GaAs/Si interface, over which defect free GaAs regions were formed from the middle of trench walls. It is suggested that the residual compressive strain in defect free GaAs layers is due to the patterned SiO2 structures. [ABSTRACT FROM AUTHOR]