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Chromium nitride nanoparticles with mean diameter distribution between 0.8 nm and 30 nm were produced by laser irradiation of a chromium target immersed in liquid nitrogen. Cr was directly converted to chromium nitride nanoparticles according to selected-area electron diffraction analyses using the transmission electron microscopy technique. Crystalline nanoparticles mostly consist of Cr 2 N , which is commonly reported together with the conversion of Cr 2 N to CrN and the mixture of chromium oxides. In addition, there is no evidence of oxidation by storage or photodegradation of the nanoparticles in isopropyl alcohol suspensions. The intensity profile of small-angle X-ray scattering indicates that the geometrical shape of the nanoparticles is not spherical but cylindrical with aspect ratio (height-to-radius) of 0.35 – 0.05. UV-Vis absorption spectroscopy reveals the presence of surface plasmon absorption at the ultraviolet region at wavelengths of 350, 372, and 397 nm. First-principles calculations of density of states, dielectric function, and optical conductivity performed within the theoretical framework of density functional theory for Cr 2 N with a hexagonal structure corroborate the formation of surface plasmons. [ABSTRACT FROM AUTHOR]

Research describing the temperature dependence of excitonic energies in AlGaAs alloys is presented. Photoluminescence and photoreflectance studies of structures with varying aluminium concentrations are examined.

The photoluminescence (PL) technique as a function of temperature and excitation intensity was used to study the optical properties of multiquantum wells (MQWs) of GaAs/AlxGa1-xAs grown by molecular beam epitaxy on GaAs substrates oriented in the [100], [311]A, and [311]B directions. The asymmetry presented by the PL spectra of the MQWs with an apparent exponential tail in the lower-energy side and the unusual behavior of the PL peak energy versus temperature (blueshift) at low temperatures are explained by the exciton localization in the confinement potential fluctuations of the heterostructures. The PL peak energy dependence with temperature was fitted by the expression proposed by Pässler [Phys. Status Solidi B 200, 155 (1997)] by subtracting the term σE2/kBT, which considers the presence of potential fluctuations. It can be verified from the PL line shape, the full width at half maximum of PL spectra, the σE values obtained from the adjustment of experimental points, and the blueshift maximum values that the samples grown in the [311]A/B directions have higher potential fluctuation amplitude than the sample grown in the [100] direction. This indicates a higher degree of the superficial corrugations for the MQWs grown in the [311] direction. [ABSTRACT FROM AUTHOR]

X-ray diffraction studies help observe the effective epitaxial growth of Cu/CaF2 bilayers on hydrogen terminated Si(111) wafers by thermal evaporation. Cu films adopt a different growth pattern on CaF2 epitaxially grown on Si(111) than upon direct growth on Si(111). The difference is explained by the CaF2 epitaxial layer that blocks reaction between Cu and Si in as-deposited samples.

The thermal evolution of a ZnSe epilayer grown by molecular beam epitaxy on GaAs(001) has been studied by high resolution x-ray diffraction as well as photoelectron and Raman spectroscopies. Sequential annealing of a relaxed epilayer reveals a fast migration of Ga towards the ZnSe cap layer with a significant accumulation of As atoms near the ZnSe-reacted interface. A Ga[sub 2]Se[sub 3] compound appears as a predominant byproduct whereas Zn atoms are probably diffusing from the reacted interface into the GaAs substrate. [ABSTRACT FROM AUTHOR]

Properties of the interface between the epitaxial layer of heavily doped Al[sub 0.48]In[sub 0.52]As:Si and the InP(Fe) substrate are investigated by photoluminescence in AlInAs:Si/InP(Fe) heteroestructures grown by molecular beam epitaxy. The effect on heterostructure optical properties of including a thin Al[sub 0.22]Ga[sub 0.26]In[sub 0.52]As:Si layer at the interface is investigated as well. To explain the different interface emission energies observed, the results are analyzed by using the mixed-type I-II interface model, which considers in the type II interface a narrow InAs well, with variable width, between AlInAs and InP. The observation of the interface emission at energies as high as 1.36 eV, at low excitation intensity, is explained taking into account the high doping level of the samples. The observed interface transition luminescence thermal quenching is tentatively explained by analyzing the spatial distribution of electrons in the triangular quantum well formed at the type II interface (or at the mixed I-II interface) as a function of the temperature. [ABSTRACT FROM AUTHOR]

The mechanical properties of InSe and GaSe single crystals have been studied by means of nanoindentation tests. Both bulk crystals are well ordered and present a predominant γ-type interlayer stacking sequence as determined by x-ray diffraction and transmission electron microscopy measurements. The course of plastic deformation induced in the crystals by application of a definite shear stress through the penetration of a Berkovich tip indicates that the deformation occurs predominantly by pop-in events along easy slip directions having a fairly elastic character between displacements. Hardness anisotropy along crystal axes is clearly seen and the measured elastic modulus presents a discrepancy smaller than 5% in comparison with theoretical calculations performed using previous experimental values of the elastic constants. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

AlGaAs structures with different aluminum concentration (x=0.0, 0.17, 0.30, and 0.40) were characterized by photoluminescence and photoreflectance techniques. The temperature dependence of optical transitions in the temperature ranging from 2 to 300 K were investigated. Y. P. Varshni [Physica (Utrecht) 34, 194 (1967)], L. Vin˜a et al. [Phys. Rev. B 30, 1979 (1984)], and R. Pa¨ssler [Phys. Status Solidi B 200, 155 (1997)] models were used to fit the experimental points. The Pa¨ssler model gave the best adjustment to the experimental points. The tree models showed that the empirical parameters obtained through the adjustment of the experimental data in the three different models are aluminum composition dependent in the ternary alloy. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High-resolution x-ray diffraction, photoelectron, and Raman spectroscopy is used to study thermal evolution of ZnSe/GaAs epilayer. A fast migration of Ga atoms towards the ZnSe epilayer with an accumulation of As atoms near the ZnSe-reacted interface is revealed.

The properties of the interface between the epitaxial layer of heavily doped Al(sub 0.48)In(sub 0.52)As:Si and the InP(Fe) substrate are examined by photoluminescence in AlInAs:Si/InP(Fe) heterstructures grown by molecular beam epitaxy (MBE). The interface transition luminescence thermal quenching is explained by analyzing the spatial distribution of electrons n the triangular quantum well formed at the type II interface (or at the mixed I-II interface) as a function of the temperature.