R. Mu

F-doping effects on electrical and optical properties of ZnO nanocrystalline films

F-doped and undoped ZnO nanocrystalline films were prepared from thermal oxidation of ZnF2 films deposited on a silica substrate by electron beam evaporation. The F-doped ZnO film has very low electrical resistivity of 7.95×10−4Ωcm and a high optical transmittance. The study also indicated that (1) the substitutional F atoms in the film serve as donors to increase the carrier concentration and the optical band gap with respect to undoped ZnO film, and (2) F passivation reduces the known number of Os2−/Os− surface states and increases carrier mobility.

Room-temperature ferromagnetism in (Mn, N)-codoped ZnO thin films prepared by reactive magnetron cosputtering

(Mn, N)-codoped ZnO films were grown on fused silica substrates by reactive magnetron cosputtering. X-ray diffraction measurements reveal that the films have the single-phase wurtzite structure with c-axis preferred orientation. X-ray photoelectron spectroscopy studies indicate the incorporation of both divalent Mn2+ and trivalent N3− ions into ZnO lattice. Acceptor doping with nitrogen partly compensates the “native donors,” which results in a low electron concentration of 3.16×1016cm−3 though p-type conductivity is not achieved. (Mn, N)-codoped ZnO films show significant ferromagnetism with Curie temperature above 300K. The mechanism of ferromagnetic coupling in codoped ZnO is discussed based on a bound magnetic polaron model.

Optical properties and electrical characterization of p-type ZnO thin films prepared by thermally oxiding Zn3N2 thin films

In this paper, we report a simple method for preparing p-type ZnO thin films by thermal oxidization of Zn 3 N 2 thin films. The Zn 3 N 2 films were grown on fused silica substrates by using plasma-enhanced chemical vapor deposition from a Zn(C 2 H 5 ) 2 and NH 3 gas mixture. The Zn 3 N 2 film with a cubic antibixbyite structure transformed to ZnO:N with a hexagonal structure as the annealing temperature reached 500 °C. When the annealing temperature reached 700 °C, a high-quality p-type ZnO film with a carrier density of 4.16 x 10 1 7 cm - 3 was obtained, for which the film showed a strong near-band-edge emission at 3.30 eV without deep-level emission, and the full width at half-maximum of the photoluminescence spectrum was 120 meV at room temperature. The origin of the ultraviolet band was the overlap of free exciton and the bound exciton. The N concentration was as high as 10 2 1 cm - 3 , which could be controlled by adjusting the parameters of the annealing processes.

The structural and optical properties of Cu2O films electrodeposited on different substrates

Cuprous oxide films were successfully electrodeposited onto three different substrates through the reduction of copper lactate in alkaline solution at pH = 10. The substrates include indium tin oxide film coated glass, n-Si wafer with (001) orientation and Au film evaporated onto Si substrate. The substrate effects on the structural and optical properties of the electrodeposited films are investigated by in situ voltammetry, current versus time transient measurement, ex situ x-ray diffraction, scanning electron microscopy, UV–vis transmittance and reflectance and photoluminescence techniques. The results indicate that the choice of substrate can strongly affect the film morphology, structure and optical properties.

The photoluminescence properties of ZnO:N films fabricated by thermally oxidizing Zn3N2 films using plasma-assisted metal-organic chemical vapour deposition

Nitrogen doped ZnO films are directly fabricated by the thermal oxidation of Zn3N2 films. Zn3N2 films are prepared by plasma-assisted metal-organic chemical vapour deposition (PA-MOCVD). By comparing with undoped ZnO photoluminescence spectra, a much stronger bound exciton emission due to a neutral nitrogen acceptor (A0X) is observed at low temperature. The neutral acceptor level is located at 130 meV above the valence band maximum. To demonstrate the quality of ZnO:N thin films as a p-type, a Zn3N2/n-Si heterojunction structure was first fabricated. With an increase of oxidation temperature, the structure has gradually shown p–n junction rectification characteristics from I–V measurements.

GaAs nanocrystals formed by sequential ion implantation

Sequential ion implantation of As and Ga into SiO2 and α‐Al2O3 followed by thermal annealing has been used to form zinc‐blende GaAs nanocrystals in these two matrices. In SiO2, the nanocrystals are nearly spherical and randomly oriented, with diameters less than 15 nm. In Al2O3, the nanocrystals are three dimensionally aligned with respect to the crystal lattice. Infrared reflectance measurements show evidence for surface phonon modes in the GaAs nanocrystals in these matrices.

Er-doped ZnO films grown by pulsed e-beam deposition

Erbium (Er)-doped ZnO thin films were grown on fused silica (SiO2) substrates by pulsed electron-beam deposition (PED) and analysed by Rutherford backscattering spectrometry (RBS), ultraviolet–visible absorption, and photoluminescence (PL). Subsequent annealing at 700 °C produces remarkable effects on the optical properties of Er-doped films. Under 325 nm excitation, a dramatic increase of deep-level emission from 450 to 680 nm was observed from annealed Er-doped ZnO films. Under 488 nm excitation, the PL spectrum of annealed Er-doped ZnO films revealed sharp and well-resolved Stark-splitting peaks in both the green emission of transition and the red emission of transition of Er3+ ions, which suggests that the Er ions have been incorporated inside the crystalline ZnO grains after thermal annealing.

Increased short circuit current in organic photovoltaic using high-surface area electrode based on ZnO nanowires decorated with CdTe quantum dots

A photosensitized high-surface area transparent electrode has been employed to increase the short circuit current of a photovoltaic device with a blend of poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM) as the active layer. This is achieved by directly growing ZnO nanowires on indium tin oxide (ITO) film via a physical vapor method. The nanowire surface is then decorated with CdTe quantum dots by pulsed electron-beam deposition (PED). The nanowires alone provided a 20-fold increase in the short circuit current under visible light illumination. This was further increased by a factor of approximately 1.5 by the photosensitization effect of CdTe, which has an optical absorption of up to 820 nm.

Effects of interfacial interaction potential on the sublimation rates of TNT films on a silica surface examined by QCM and AFM techniques

The study of 2,4,6-trinitrotoluene (TNT) sublimation rates from the bulk surface and a substrate surface have been evaluated quantitatively with both atomic force microscopy and quartz crystal microbalance (QCM) techniques. A first principle theoretical model is proposed, which allows obtaining three critical parameters, bulk sublimation rate, surface interaction potential, and the effective decay length, with no arbitrary parameters. The bulk sublimation rate predicted by the model is quantitatively confirmed by QCM experiments. The isothermal measurements with QCM showed that the sublimation activation energy of bulk TNT is 131 kJ/mol. More importantly, all results were obtained at one atmosphere and near room temperature. Thus, it should have direct impacts on explosive trace detection device applications.

Annealing behavior of tin implanted silica

Abstract Tin ions were implanted into silica substrates at 275 keV. The samples were annealed at 300–1000°C. The as-implanted and annealed samples were studied by the infrared specular reflectance technique. Kramers–Kronig transformation (KKT) was carried out on the reflectance spectra to obtain n, k, transverse optical (TO), and longitudinal optical (LO) spectra. Based on these spectra, we can understand the effects of ion implantation and annealing on the Si–O–Si bond angle, Si–O–Si bond breaking, and density change of implanted silica.