Search results for "amorphous"
showing 10 items of 790 documents
Density functional/molecular dynamics simulations of phase-change materials
2013
Nucleus-driven crystallization of amorphous Ge2Sb2Te5: A density functional study
2012
Early stages of nucleus-driven crystallization of the prototype phase change material Ge2Sb2Te5 have been studied by density functional/molecular dynamics simulations for amorphous samples (460 and 648 atoms) at 500, 600, and 700 K. All systems assumed a fixed cubic seed of 58 atoms and 6 vacancies. Crystallization occurs within 600 ps for the 460-atom system at 600 and 700 K, and signs of crystallization (nucleus growth, percolation) are present in the others. Crystallization is accompanied by an increase in the number of “ABAB squares” (A: Ge, Sb, B: Te), and atoms of all elements move significantly. There is no evidence of cavity movement to the crystal-glass interface, as suggested rece…
Enhancing the luminescence efficiency of silicon-nanocrystals by interaction with H+ions
2018
The emission of silicon nanocrystals (Si-NCs), synthesized by pulsed laser ablation in water, was investigated on varying the pH of the solution. These samples emit μs decaying orange photoluminescence (PL) associated with radiative recombination of quantum-confined excitons. Time-resolved spectra reveal that both the PL intensity and the lifetime increase by a factor of ∼20 when the pH decreases from 10 to 1 thus indicating that the emission quantum efficiency increases by inhibiting nonradiative decay rates. Infrared (IR) absorption and electron paramagnetic resonance (EPR) experiments allow addressing the origin of defects on which the excitons nonradiatively recombine. The linear correl…
EPR investigation on the polyamorphic transformation induced by electron irradiation in SiO2 glass
2013
Investigation of photoluminescence and amplified spontaneous emission properties of cyanoacetic acid derivative (KTB) in PVK amorphous thin films
2018
This work was supported by European Regional Development Fund within the Project No. 1.1.1.1/16/A/046 and A.Riekstins SIA “Mikrotīkls” donation, administered by University of Latvia Foundation.
Revealing lattice disorder, oxygen incorporation and pore formation in laser induced two-photon oxidized graphene
2019
Abstract Laser induced two-photon oxidation has proven to be a reliable method to pattern and control the level of oxidation of single layer graphene, which in turn allows the development of graphene-based electronic and optoelectronic devices with an all-optical method. Here we provide a full structural and chemical description of modifications of air-suspended graphene during the oxidation process. By using different laser irradiation doses, we were able to show via transmission electron microscopy, electron energy loss spectroscopy, electron diffraction and Raman spectroscopy how graphene develops from its pristine form up to a completely oxidized, porous and amorphous carbon layer. Furt…
Cathodoluminescence and photoluminescence study of trap centers in amorphous silicon oxynitride
2002
Amorphous silicon oxynitride (a-SiO/sub x/N/sub y/) films with different compositions were prepared using low-pressure chemical vapor deposition (LPCVD) technique, The cathodoluminescence and photoluminescence of this samples were measured from the red band to the ultraviolet band to study the trap centers in silicon oxynitride. A 1.8-1.9 eV band was found and is attributed to the oxygen and nitrogen atoms with unpaired electrons whereas the 2.7 eV band is attributed to two-fold coordinated silicon atoms with two electrons. The 5.4 eV shoulder is due to the peroxy radicals and other ultraviolet bands are supposed to due due to the Si-Si bonds.
Anomalous and normal Hall effect in hydrogenated amorphous Si prepared by plasma enhanced chemical vapor deposition
2010
The double sign anomaly of the Hall coefficient has been studied in p -doped and n -doped hydrogenated amorphous silicon grown by plasma enhanced chemical vapor deposition and annealed up to 500 °C. Dark conductivity as a function of temperature has been measured, pointing out a conduction mechanism mostly through the extended states. Anomalous Hall effect has been observed only in the as-deposited n -doped film, disappearing after annealing at 500 °C, while p -doped samples exhibit normal Hall effect. When Hall anomaly is present, a larger optical band gap and a greater Raman peak associated with Si-H bond are measured in comparison with the cases of normal Hall effect. The Hall anomaly wi…
A neutron diffraction study of the glass transition in (KBr)0.47(KCN)0.53
1985
Abstract The molecular crystal (KBr) 0.47 (KCN) 0.53 has been investigated by elastic neutron diffraction at the transition from the paraelastic to the orientational glass state. The freezing temperature is characterized by the onset of a momentum transfer dependent broadening of the diffraction lines indicating the transition from a crystalline to an amorphous state.
Creation of glass-characteristic point defects in crystalline SiO2 by 2.5 MeV electrons and by fast neutrons
2019
The support from M -ERANET project “MyND” is acknowledged. K.K. was partially supported by the Collaborative Research Project of Laboratory for Materials and Structures, Tokyo Institute of Technology . Visiting researcher support from Ecole Polytechnique, Palaiseau is appreciated. Mr. Olivier Cavani is thanked for the expert help with irradiations.