R. S. Ajimsha

Effect of substrate roughness on photoluminescence spectra of silicon nanocrystals grown by off axis pulsed laser deposition

Silicon nanoparticles were prepared by off axis pulsed laser deposition (PLD) technique. The optical properties of Si nanoparticles grown on quartz substrate have been characterized by optical absorption, photoluminescence, Raman, and transmission electron microscopy. TEM has demonstrated that the radius of nanocrystals decreases from 4to0.8nm as the off axis target to substrate distance increases. A blueshift up to 4.2eV is observed in the optical absorption spectra of the Si quantum dots. The slope of log(hν) vs log(α) graph shows that the optical transitions in Si quantum dots are allowed direct, allowed indirect, and direct forbidden transitions which depend on the nature of the substrate used for the growth of silicon. Relaxation of k selection rule is observed in these samples. Photoluminescence (PL) emission consists of an intense broad emission extending over visible to ultraviolet region. The photoluminescence peak energy and intensity are found to be sensitive to the nature of substrate. Possibl...

Characterization of radio frequency plasma using Langmuir probe and optical emission spectroscopy

The radio frequency plasma generated during the sputtering of Indium Tin Oxide target using Argon was analyzed by Langmuir probe and optical-emission spectroscopy. The basic plasma parameters such as electron temperature and ion density were evaluated. These studies were carried out by varying the RF power from 20to50W. A linear increase in ion density and an exponential decrease in electron temperature with rf power were observed. The measured plasma parameters were then correlated with the properties of ITO thin films deposited under similar plasma conditions.

p-type electrical conduction in α-AgGaO2 delafossite thin films

Thin films of delafossites of α-AgGaO2 were prepared on α-Al2O3 (0001) and on Si (100) single crystal substrates by pulsed laser deposition. The films have a band gap of 4.12eV and a transparency of more than 50% in the visible region. The electrical conductivity at 300K was 3.2×10−4Scm−1. The positive sign of Seebeck coefficient (+70μVK−1) demonstrated the p-type conduction in the films. Transparent p-n heterojunctions on a glass substrate having a structure glass/ITO∕n-ZnO∕p-AgGaO2 were fabricated. The ratio of forward to reverse current was more than 100 in the range of −2to+2V.

Luminescence from Surfactant-Free ZnO Quantum Dots Prepared by Laser Ablation in Liquid

Highly transparent, luminescent and biocompatible ZnO quantum dots were prepared in water, methanol, and ethanol usingliquid-phase pulsed laser ablation technique without using any surfactant. Transmission electron microscopy analysis confirmedthe formation of good crystalline ZnO quantum dots with a uniform size distribution of 7 nm. The emission wavelength could bevaried by varying the native defect chemistry of ZnO quantum dots and the laser fluence. Highly luminescent nontoxic ZnOquantum dots have exciting application potential as florescent probes in biomedical applications.© 2007 The Electrochemical Society. DOI: 10.1149/1.2820767 All rights reserved.Manuscript submitted September 4, 2007; revised manuscript received November 6, 2007.Available electronically December 17, 2007.

Phase-coherent electron transport in (Zn, Al)Ox thin films grown by atomic layer deposition

A clear signature of disorder induced quantum-interference phenomena leading to phase-coherent electron transport was observed in (Zn, Al)Ox thin films grown by atomic layer deposition. The degree of static-disorder was tuned by varying the Al concentration through periodic incorporation of Al2O3 sub-monolayer in ZnO. All the films showed small negative magnetoresistance due to magnetic field suppressed weak-localization effect. The temperature dependence of phase-coherence length ( lφ∝T−3/4), as extracted from the magnetoresistance measurements, indicated electron-electron scattering as the dominant dephasing mechanism. The persistence of quantum-interference at relatively higher temperatures up to 200 K is promising for the realization of ZnO based phase-coherent electron transport devices.

Synthesis of Highly Luminescent, Bio‐Compatible ZnO Quantum Dots Doped with Na

Na doped ZnO quantum dots of average size 6 nm were prepared using wet chemical route at room temperature without any capping agents and the formation of nanoparticles is confirmed by transmission electron microscope (TEM) and x‐ray diffraction (XRD) analysis. Optical band gap of ZnO: Na is found to be blue shifted with decrease in size due to quantum size effects. Incorporation of Na in ZnO quantum dots is confirmed using inductively coupled plasma atomic emission spectroscopy (ICP‐AES). Strong room temperature photoluminescent emissions in the violet region due to native defects of ZnO and yellow region resulting from substitutional incorporation of Na in the Zn site was observed from the ZnO: Na quantum dots. Both emission wavelength and integral intensity of emission in the visible region can be well controlled by adjusting the concentration of the alkaline precursor used as the dopant. Highly luminescent bio‐friendly Na doped ZnO quantum dots can be used as fluorescent probes in biomedical applications.

Growth of zinc oxide thin films for optoelectronic application by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on quartz, silicon, and polymer substrates by pulsed laser deposition (PLD) technique at different oxygen partial pressures (0.007 mbar to 0.003 mbar). Polycrystalline ZnO films were obtained at room temperature when the oxygen pressure was between 0.003 mbar and .007 mbar, above and below this pressure the films were amorphous as indicated by the X-ray diffraction (XRD). ZnO films were deposited on Al2O3 (0001) at different substrate temperatures varying from 400°C to 600°C and full width half maximum (FWHM) of XRD peak is observed to decrease as substrate temperature increases. The optical band gaps of these films were nearly 3.3 eV. A cylindrical Langmuir probe is used for the investigation of plasma plume arising from the ZnO target. The spatial and temporal variations in electron density and electron temperature are studied. Optical emission spectroscopy is used to identify the different ionic species in the plume. Strong emission lines of neutral Zn, Zn+ and neutral oxygen are observed. No electronically excited O+ cations are identified, which is in agreement with previous studies of ZnO plasma plume.