Structural and optical properties of single crystal Zn 1−x Mg x O nanorods ͑0 Յ x Յ 0.17͒ are studied experimentally and theoretically. Structural analyses indicate that the nanorods grown on Si substrates are oriented in the c-axis direction and the nanorods possess the single-crystalline hexagonal structure with the Mg incorporated within the ZnO nanorods by means of substituting Zn. A blueshift of the near-band edge emission in the photoluminescence spectra by increasing Mg content is observed. Two distinct emission bands are found in the photoluminescence spectra; one is mainly attributed to the delocalized exciton recombination and the other is originating from localized excitons due to the incorporation of foreign impurity of Mg. Enhanced exciton localization with increasing Mg content in Zn 1−x Mg x O nanorods is mainly due to large ionic characters of Mg-O bonding. Structural stability, band structures, projected density of states, and charge distribution in various Zn 1−x Mg x O alloy compounds were further investigated by first-principles calculations. A good agreement between experimental and theoretical results is found.
X-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been performed for Zn1−xCoxO and Zn1−xMgxO to elucidate the effects of the doping of Co and Mg, which have very different electronegativities, on the electronic structures of ZnO nanorods. The intensities of O K-edge near-edge features in the XANES spectra of Zn1−xCoxO and Zn1−xMgxO nanorods are found to be lower than those of ZnO, which suggests that both Co and Mg substitutions of the Zn ions enhance the effective charge on the O ion. The valence-band SPEM measurements show that Mg doping does not increase the density of near-Fermi-level states, which implies that Mg doping will not improve field emission of ZnO nanorods. It is surprising to find that both Co and Mg substitutions of Zn increase the numbers of O 2p dominated valence-band states, despite that Co and Mg have larger and smaller electronegativities than that of Zn.
This paper reports the growth of single-crystalline silicon carbon nitride (Si 1ϪxϪy C x N y ) films on crystal silicon substrate using C 3 H 8 for carbon source by rapid thermal chemical vapor deposition ͑RTCVD͒. Based on the scanning electron microscope analysis, the Si 1ϪxϪy C x N y films are smooth on the surface and at the Si 1ϪxϪy C x N y /Si interface, which is important for device applications. A model to explain the growing mechanism of the Si 1ϪxϪy C x N y film is being proposed.Silicon carbon nitride (Si 1ϪxϪy C x N y ) film has attracted much attention because of its interesting characteristics and wide range of promising applications. 1 The crystalline Si 1ϪxϪy C x N y possesses several physical properties such as hardness, oxidation resistance, and corrosion resistance that can compete with those of cubic boron nitride. A recent study of Si 1ϪxϪy C x N y compounds shows potential applications for blue or ultraviolet optoelectronic and high temperature microelectromechanical system ͑MEMS͒. 1,2 In the past, the fabrications of Si 1ϪxϪy C x N y films by reactive magnetron sputtering, ion implantation, and plasma-assisted chemical vapor deposition have been reported. 1,3-5 However, these methods grow either rod-shaped crystals, mixtures of crystalline and amorphous, or pure amorphous Si 1ϪxϪy C x N y films. No smooth surface morphology and uniform crystalline structure, which are important for applications in high voltage or high temperature electronic devices, have been found.In this study, a cubic single-crystal Si 1ϪxϪy C x N y (c-Si 1ϪxϪy C x N y ) film has been successfully synthesized, for the first time, using C 3 H 8 as the carbon source in a rapid thermal chemical vapor deposition ͑RTCVD͒ system under a wide variety of deposition conditions. The C 3 H 8 gas is selected for the purpose of low cost and the wide utility in industrial manufacture. Moreover, the RTCVD system is adopted for its capability of rapid temperature increases and higher temperature that provide the absorbed pieces a higher surface mobility to form a smoother interface and better microstructure. 6 In addition, Auger electron spectroscopy ͑AES͒, scanning electron microscopy ͑SEM͒, and transmission electron microscopy ͑TEM͒ are employed to characterize the composition and the structure of the films. Based on the analysis, a mechanism of growing cubic structure c-Si 1ϪxϪy C x N y film is being proposed. Fabrication and MeasurementThe Si 1ϪxϪy C x N y films were grown on Si͑100͒ wafers with resistivity of 4-10 ⍀ cm, using a homemade RTCVD system with horizontal fused quartz tube as furnace. The heat source is ultraviolet ͑UV͒ halogen lamps with high energy density. The temperature of the substrate is measured by an optical pyrometer. After chemical cleaning, the substrates were immediately loaded into the reaction tube, and then the system was pumped down to about 10 Ϫ7 Torr. Then follows the process sequence as illustrated in Fig. 1 to deposit the films; ͑A͒ The substrates were held at 900°C for 10 min to remove native oxide la...
X-ray absorption near-edge structure (XANES) and x-ray emission spectroscopy (XES) measurements were used to investigate the effect of Mg doping in ZnO nanorods. The intensities of the features in the O K-edge XANES spectra of Zn 1-x Mg x O nanorods are lower than those of pure ZnO nanorods, suggesting that Mg doping increases the negative effective charge of O ions. XES and XANES spectra of O 2p states indicate that Mg doping raises (lowers) the conduction-band-minimum (valence-band-maximum) and increases the bandgap. The bandgap is found to increase linearly with the Mg content, as revealed by photoluminescence and combined XANES and XES measurements.
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