Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001)

We have investigated the influence of sputtering parameters such as N2 flow ratio, applied dc power and substrate temperature on the formation process of high-quality and low-resistivity HfN film using an ultrahigh-vacuum sputtering system. The obtained film quality was evaluated using X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses. The resistivity values were measured by a four-point probe method. We found that (111) HfN and (100) HfN films with equivalent resistivity to the bulk value can be grown in a single-oriented state at the substrate temperature of 450°C on (111) Si and (001) Si, respectively. Therefore, it is revealed that impurity-free, high-quality HfN film with high crystallinity and low resistivity can be obtained at relatively low substrate temperatures, if appropriate sputtering conditions are satisfied, using an ultrahigh-vacuum sputtering system.

Polycrystalline HfO 2 thin film capacitors were prepared by anodizing sputter-deposited Hf films, and their capacitor and leakage current properties were studied. Electrical measurements were performed for the parallel-plate Hf anodized capacitors with an Al-HfO 2 -Hf (metal-insulator-metal) structure, and high capacitance density (0.6 "F/cm 2 ) and low dielectric loss (0.0095) were obtained for a very thin-oxide capacitor anodized at 10 V. In addition, the leakage current density of this capacitor was about 5 Â 10 À9 A/cm 2 at an applied voltage of 5 V. The leakage current density (J) of HfO 2 capacitors as a function of applied electric field (E) was investigated for several capacitors with different oxide thicknesses, by plotting lnðJÞ vs E 1=2 curves. As a result, it was revealed that the conduction mechanism is due to Schottky emission, irrespective of the oxide thickness.

No abstract

We report the results of Raman, infrared, and inelastic neutron scattering investigations of the vibrational spectrum of the complex p-tert-butylcalix͓8͔arene͑1:1͒fullerene, a system with almost isolated C 60 molecules confined inside neutral cages. All the internal optical-active modes of the C 60 guest have been identified, and further modes which can be attributed to C 60 intramolecular vibrations appear in the neutron scattering function. A comparison with the vibrational spectrum of empty p-tert-butylcalix͓8͔arene indicates that the hostguest interaction is very weak. As solid-state effects are also practically suppressed, the investigated complex gives the unique opportunity to study almost free fullerene balls confined in the solid state.A huge number of theoretical and experimental studies followed the discovery of the new fullerene allotropes of carbon. Much of the interest has been focused on the dynamical properties of C 60 , and a comprehensive picture of the vibrational behavior has been obtained by a combination of neutron, Raman, and infrared scattering experiments. 1-6 However, it is not yet clear to what extent the presence of solid-state effects complicates the comparison of the experimental results with quantum-mechanical calculations performed for isolated C 60 molecules. The splitting of the degenerate molecular modes deserves further investigation as well, being not only a consequence of the crystal field, 6 but also the result of 12 C/ 13 C isotopic effects 7 and of merohedral orientational disorder in crystalline C 60 . 8 Here we present light and neutron spectroscopy results which reveal the existence of a unique opportunity of studying the behavior of fullerene in a quasifree environment. Actually, the experimental findings show that the C 60 molecules, confined in the solid-state complex with p-tert-butylcalix͓8͔arene, are almost isolated.Calixarenes are cup-shaped macrocyclic phenolic oligomers which find increasing applications as building blocks of receptors for the selective complexation of alkali and alkaline-based metal cations. Moreover, for their ability to form inclusion complexes with neutral organic molecules, calixarenes have been the subject of a number of investigations in the framework of the host-guest or supramolecular chemistry. 9 Among this class of synthetic matrices, the p-tert-butylcalix͓n͔arene ͑where nϭ8 refers to the number of phenolic units͒, is able to include the fullerene molecule, and recently a ͑1:1͒ complex of p-tert-butylcalix͓8͔arene with C 60 has been obtained. 10,11 This is an important breakthrough in fullerene chemistry, offering an economic means of C 60 purification and providing, on the other hand, an interesting inclusion system for the study of the C 60 dynamics. Actually, infrared ͑IR͒, visible, and ultraviolet spectra, together with 13 C NMR results, strongly indicate that the C 60 is weakly bound to the upper edge of the calix͓8͔arene cavity ͑Fig. 1͒ and that interactions among the fullerene molecules PHYSICAL