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The process of photoelectrochemical etching is employed to comparatively study the properties of nanotextured high density Mg-doped and undoped GaN in the temperature dependent photoluminescence (PL). The analysis reveals that an increase in the potential fluctuation created by the nanotexurization process increases the carrier localization in the substances, which explains the observed asymmetric S-shaped behavior in the GaN compounds.

We have studied the effect of annealing (at temperatures 300, 400, and 500 °C) on nanoparticulate CdS film on silicon substrate deposited by hybrid Langmuir–Blodgett chemical bath deposition technique. Width, intensity, and the line shape of the longitudinal optical phonon in Raman spectra and photoluminescence (PL) spectra suggest that the annealing brings about coalescence of nanoparticles at 300 °C, increasing the size of the nanoparticles and also increases the red region PL related to surface states. Annealing at 400 °C leads to two different coexistent states, showing larger nanoparticles and bulklike film. On further annealing at 500 °C, PL shows a drastic redshift to PL of bulklike CdS. This is well brought out by resonance Raman measurements and later confirmed by scanning electron microscope data. Most interesting observation is that PL and Raman results together are indicative of phase transformation of nanoparticulate hexagonal CdS film to bulklike cubic CdS film on annealing at 500 °C, unlike cubic to hexagonal structural phase transition observed in bulk CdS films. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study of the effects of irradiation by swift heavy ions (SHIs) with Se values ranging from 80 to 1270 eV/Å and fluence ranges varying between 1010 and 1014 ions/cm2 incident on thin films of C60. The control over Se is exercised through the choice of ion species for irradiation (O, Ni, and Au). Structural changes in C60 were investigated quantitatively using Raman spectroscopy. The results indicate that at low fluences polymer formation takes place whereas at high fluences there is complete fragmentation of C60, resulting in amorphous carbon formation. Measured values of band gap and in situ resistivity decrease with fluence. This result is consistent with the structural modifications observed by Raman spectroscopy. The composition of the polymer fraction formed (e.g., the content of two dimensional polymerized network of C60 molecules) as well as that of a-C (e.g., the content of nanographite) also vary with Se of the ion used. A phenomenological model, taking into account the ion track, enables us to explain the trend of polymer formation as well as fragmentation of C60, with increasing fluence of SHI. The cross section for damage (fragmentation of C60 molecules) has two values—one effective at low fluences and the other at high fluences. By arriving at a quantitative formula giving the fraction of polymer/damaged C60 molecules at any given fluence, we are able to predict the fluence and ion species required for a given amount of polymerization/damage or vice versa. Effort has been made to correlate Se and Sn values to the damage cross sections using data from this work along with those from other experiments using keV and MeV ions. [ABSTRACT FROM AUTHOR]

Modification of thin film samples of C[sub 60] on Si and quartz substrates, induced by irradiation of 110 MeV Ni ions at various fluences, was studied. The pristine and irradiated samples were investigated using Raman spectroscopy, electrical conductivity, and optical absorption spectroscopy. The Raman data and band gap measurements indicate that swift ions at low fluences result in aggregate formations involving multiple molecular units such as dimers or polymers. High fluence irradiation results in submolecular formations and amorphous semiconducting carbon, indicating overall damage (fragmentation) of the fullerene molecules. These submolecular units in the amorphous carbon network have been identified as nanocrystalline graphite. [ABSTRACT FROM AUTHOR]

A comparative study is conducted to examine the effects of irradiation by swift heavy ions (SHIs) on thin films of [C.sub.60]. The results are used to derive quantitative formula to obtain fraction of polymer/damaged [C.sub.60] molecules at any given fluence and predict the fluence and ion species required for a given amount of polymerization/damage or vice versa.

High quality CdS nanowires (NWs) are grown at room temperature by electrochemical deposition into the pores of prepared porous alumina templates (PATs) from alkaline aqueous electrolyte solution (pH = 8.5) containing Cd and SO , using high frequency (200 Hz) alternating current (ac, 21 V). PATs with hexagonally ordered nanoporous columns are prepared using relatively simple and faster single step anodizing at 30 V in 0.24 M oxalic acid. The room temperature synthesis of NWs from aqueous solution using ac voltage simplifies the growth process as well as makes it an inexpensive approach for the fabrication of CdS NWs in large density. Atomic force microscopy and scanning electron microscopy (SEM) confirm the formation of spatially regular and well-arranged hexagonal porous structures. SEM further shows that diameter of grown CdS NWs lie in the range ~ 30-50 nm. Raman spectroscopy and X-ray diffraction of as deposited and annealed PAT-CdS nanowires composites confirm the formation of high crystalline quality CdS NWs having hexagonal wurtzite crystal structure. The preparation method and possible mechanism for the synthesis of CdS NWs is discussed. The deposition method can be generalized to a wide range of semiconductors. [ABSTRACT FROM AUTHOR]

Correlation between size, bonding of Si and O at the surface/interface of Si nanocrystals and frequency of Si phonons in Si-SiO 2 nanocomposites is established using Raman mapping and X-ray photoelectron spectroscopy. Corroboration of these results with absorption spectroscopy shows that lowering of direct transition of light electron conduction band to heavy hole valence band ∼2.8 and 2.95 eV is a result of the interplay between effect of electron confinement (increases band gap) and oxidation bonding environment at the surface/interface (decreases band gap) of a nanocrystal in Si-SiO 2 nanocomposites. These studies have generated deeper insight into the fundamental understanding of the nanocomposite, which can allow easy optical microscopy monitoring of Si-SiO 2 based device fabrication. [ABSTRACT FROM AUTHOR]

Raman spectroscopy/mapping is used to investigate the variation of Si phonon wavenumbers, i.e., lower wavenumber (LW ~ 495-510 cm−1) and higher wavenumber (HW ~ 515-519 cm−1) phonons, observed in Si-SiO2 multilayer nanocomposite (NCp) grown using pulsed laser deposition. Sensitivity of Raman spectroscopy as a local probe to surface/interface is effectively used to show that LW and HW phonons originate at surface (Si-SiO2 interface) and core of Si nanocrystals, respectively. The consistent picture of this understanding is developed using Raman spectroscopy monitored laser heating/annealing and cooling experiment at the site of the desired wavenumber, chosen with the help of Raman mapping. Raman spectra calculations for Si41 cluster with oxygen and hydrogen termination show strong mode at 512 cm−1 for oxygen terminated cluster corresponding to the vibration of surface Si atoms. This supports our attribution of LW phonons to be originating at the Si-SiO2 surface/interface. These results along with XPS show that nature of interface (oxygen bonding) in turn depends on the size of nanocrystals and LW phonons originate at the surface of smaller Si nanocrystals. The understanding developed can conclude the ongoing debate on large variation in Si phonon wavenumbers of Si-SiO2 NCps in the literature. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Specially designed laser heating experiment along with Raman mapping on Si-SiO2 nanocomposites elucidates the contribution of core and surface/interface in the intermediate frequency range (511-514 cm-1) Si phonons. The contribution of core to surface/interface increases with the size of Si nanocrystal, which itself increases on laser irradiation. Further, it is found that resonance Raman is crucial to the observance of surface/interface phonons and wavelength dependent Raman mapping can be corroborated with band edges observed in absorption spectra. This understanding can be gainfully used to manipulate and characterize Si-SiO2 nanocomposite, simultaneously for photovoltaic device applications. [ABSTRACT FROM AUTHOR]