Papers by Keyword: Photoluminescence (PL)

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Authors: N.A. Asli, Mohamad Rusop, Saifollah Abdullah
Abstract: Nanostructured Porous Silicon templates (NPSiT) were prepared by photo-electrochemical anodization of p-type crystalline silicon in HF electrolyte at different etching time. Five samples were prepared with etching time varied from 10 to 50 minutes at 20 mA/cm2 of current density. The effects of etching time on NPSiT were observed based on nanocrystallite size, photon energy and surface distribution. These studied was demonstrated by Raman spectroscopy, photoluminescence (PL) and Fourier transforms infrared spectroscopy (FTIR). It was found that NPSiT sample with large pore diameter, which is smaller nanocrystallites size of Si between pore. The optical properties of NPSiT were investigated by photoluminescence (PL) and PL peak broadening and shifting towards higher energy can be observed with increasing etching time. The optimum etching time with respect to PL intensity was obtained at 30 minutes, for which uniform pores and a shift of the PL maximum to a higher energy of 1.9 eV is observed.
Authors: Yuan Ming Huang, Bao Gai Zhai, Qing Lan Ma
Abstract: Porous silicon (PS) is usually prepared by means of the anodization under constant current density, and fabrication of PS is a key step towards the realization of all-silicon electronic devices. It is a general belief that the photoluminescent properties of electrochemically etched PS depend on the anodization current density. In this work, we electrochemically prepared a series of PS films in the electrolyte of hydrofluoric acid by varying anodizing current density in the range of 1-70 mA/cm2. In spite of the different anodizing current density, the peak wavelength of the photoluminescence spectrum of the electrochemically anodized PS does not depend on the anodization current density. SEM has been utilized to characterize the morphology of the prepared PS films, and the mechanism is discussed for the anodization current independent photoluminescence of PS.
Authors: John W. Steeds, N. Peng, W. Sullivan
Abstract: 1 MeV ion implantations of 4H SiC have been performed to various doses with ion probes of 5 µm diameter. Defect introduction has been studied by microscopic photoluminescence.
Authors: Björn Magnusson, Alexsandre Ellison, F.H.C. Carlsson, Nguyen Tien Son, Erik Janzén
Authors: M. Godlewski, M. Surma, A.J. Zakrzewski, T. Wojtowicz, G. Karczewski, Jacek Kossut, Peder Bergman, Bo Monemar
Authors: N.Y. Garces, E.R. Glaser, W.E. Carlos, Mark A. Fanton
Abstract: We have recently explored the nature and stability of native defects in high-purity semi-insulating 4H-SiC bulk substrates grown by PVT and HTCVD methods after post-growth anneal treatments up to 2400oC using electron paramagnetic resonance (EPR) and low-temperature photoluminescence (PL) experiments. In the present study we have extended these investigations to SI 4H-SiC subjected to the same post-growth high-temperature anneal treatments, where significantly enhanced carrier lifetimes have been reported for such conditions, but cooled at different rates ranging from ~2-25oC/min. Previously, the intensities of the native defects decreased monotonically with anneals from 1200–1800oC; however, it was recently observed that several of these defects reappear after annealing at 2100oC and above. Our results illustrate the effects of the post-growth anneal treatments and cool-down rates on the concentrations of native defects.
Authors: Li Kun Pan, Ming Xia Gu, Gang Ouyang, Chang Q. Sun
Abstract: Shrinking the size of a solid down to nanometer scale is indeed fascinating, which makes all the otherwise constant physical quantities to be tunable such as the Young’s modulus, dielectric constant, melting point, etc. The variation of size also generates novel properties that can hardly be seen in the bulk such as the conductor-insulator and nonmagnetic-magnetic transition of noble metals at the nanoscale. Although the physics of materials at the nanoscale has been extensively investigated, the laws governing the energetic and dynamic behavior of electrons at such a scale and their consequences on the tunable physical properties of nanostructures have not been well understood [C. Q. Sun, Prog Solid State Chem 35, 1-159 (2007); Prog Mater Sci 54, 179-307 (2009)]. The objective of the contribution is to update the recent progress in dealing with the coordination-resolved energetic and dynamic behavior of bonds in the low-dimensional systems with consideration of the joint effect of temperature and pressure. It is shown that the broken-bond-induced local strain and the associated charge and energy quantum trapping at the defect sites perturbs the atomic cohesive energy, electroaffinity, the Hamiltonian and the associated properties of entities ranging from point defects, surfaces, nanocavities and nanostructures. Application of the theories to observations has led to consistent understanding of the behavior of nanometer-sized materials and the interdependence of these entities as well as the means of determining the bond energy through the temperature-dependent measurements.
Authors: Ruggero Micheletto, Kotaro Oikawa, Christian Feldmeier
Abstract: The photoluminescence from III-V wide band-gap semiconductors as InGaN is characterized by localized large intensity fluctuations, known as blinking, that, despite decades of research, is not yet completely understood. In structures where there is a three-dimensional confinement, as for example semiconductors nanocrystals, the phenomena is supposed to be related to temporary quenching due to highly efficient non-radiative recombination processes (for example, Auger). Nevertheless, in typical InGaN devices, the band structure is an infinitely wide quantum well, so the understanding of the blinking phenomenon remains elusive. We present experimental data and a model that suggests that the discussed optical fluctuations are a general phenomena caused by the slow beating between THz thermal vibrations of the Quantum Well. These minuscule displacements are occurring naturally all over the device, the displacements along the growth direction induce a modulation of the matrix elements that drives the optical emission process; this have measurable effect on the device photo-luminescence. In presence of impurities or gradient of concentration, the vibrations have locally slight frequency differences on adjacent domains, this give rise to a band of beats, and we observe the lower frequency tail of this band.
Authors: Bao Gai Zhai, Yuan Ming Huang
Abstract: A rod-like liquid crystal 4-butoxybenzylidene-4'-octylphenylamine was synthesized. The molecular structure and the liquid crystalline phases of the synthesized compound were characterized with the nuclear magnetic resonance spectroscopy, the differential scanning calorimetry, and the polarizing optical microscopy, respectively. The absorption measurement shows that the dilute tetrahydrofuran solutions of the rod-like liquid crystal absorb photons at about 290 and 330 nm, respectively; while the luminescence measurements indicate that this rod-like liquid crystal can give off intense blue photoluminescence with its dominant peak located at about 430 nm. Using Hückel tight-binding program, we have calculated the electronic structures of the liquid crystal, and the origin of the blue photoluminescence is discussed. Introduction
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