64 research outputs found
Linear optical properties of Ge nanocrystals in silica
The absorption and extinctionspectra of Genanocrystals in silica formed by ion implantation are studied using photothermal deflection and transmission spectroscopies. It is found that scattering makes a significant contribution to the extinction spectrum, damping the spectral features and resulting in a Rayleigh scattering-likeω⁴ dependence. In contrast, the spectra measured by photothermal deflection clearly show features such as the E1/E1+Δ1 transitions. The Tauc gap is extracted to be ∼0.7±0.1 eV
Direct growth of nickel disilicide nanocrystals in silicon dioxide films
Nickel disilicide (NiS₂)nanocrystals (NCs) have been grown in silicon-rich oxide (SiOₓ)films ion implanted with nickel by annealing at 1100°C. It was found that NiS₂ NCs grew into well-defined single crystalline structures embedded in a SiOₓ matrix and were approximately spherical in shape. The size of NCs can be influenced by limiting either the Ni or excess Si concentration. It was found that the resulting NCs could be produced with diameters in the range from 5to40nm in the SiOₓ layers with excess Si concentrations of 4–8at.% implanted with Ni concentrations of 0.1–10at.%.This work was carried out under Scientists Exchange
Program between the Korea Science and Engineering
Foundation and the Australian Academy of Science, and
supported by the Research Grant from the Kangwon
National University
Formation of nickel-based nanocrystal monolayers for nonvolatile memory applications
A simple method for fabricating metal silicide nanocrystal layers with narrow spatial distributions is demonstrated and shown to produce structures suitable for nonvolatile memory applications. The method is based on high-temperature annealing of a sandwich structure comprised of a thin metal (Ni)film sandwiched between two silicon-rich oxide (SiOₓ) layers and has the feature in which the size of the NCs can be controlled by varying the silicon concentrations in the SiOₓ layers or the initial nickelfilm thickness. The typical nanocrystal diameters and densities are 3.6nm and 1.2×10¹²cm⁻², respectively. Capacitance-voltage (C-V) measurements on test structures with these characteristics are shown to have C-V characteristics suitable for nonvolatile memory applications, including a C-V memory window of 11.7V for sweep voltages between −12V and +12.This work was supported by the Korea Research Foundation
Grant funded by the Korean Government MOEHRD,
KRF-2007-313-C00269 and by the Australian Research
Council through its Discovery Grant Program
Rapid, substrate-independent thickness determination of large area graphene layers
Phase-shifting interferometric imaging is shown to be a powerful analytical tool for studying graphene films, providing quantitative analysis of large area samples with an optical thickness resolution of ≤0.05 nm. The technique is readily able to identify single sheets of graphene and to quantitatively distinguish between layers composed of multiple graphene sheets. The thickness resolution of the technique is shown to result from the phase shift produced by a graphene film as incident and reflected light pass through it, rather than from path-length differences produced by surface height variations. This is enhanced by the high refractive index of graphene, estimated in this work to be nG = 2.99 ± 0.18.The authors wish to acknowledge the Australian Research Council for financial support
Self-assembled nanoparticle spirals from two-dimensional compositional banding in thin films
A self-assembly process is reported in which spiral patterns of goldnanoparticles form on siliconsurfaces during the epitaxial crystallization of thin gold-silicon alloy layers. This behavior is observed only for gold concentrations above a critical value and is shown to result from two-dimensional compositional banding of a liquid alloy layer during the crystallization process. The compositional banding consists of alternate gold-rich and silicon-rich alloy bands, which are shown to be a direct consequence of free energy minimization, the band spacing being that which gives the maximum diffusive composition-separation rate. Goldnanoparticles subsequently form by Ostwald ripening on the surface of the gold-rich bands to give rise to the observed spiral patterns.We thank P. Evans and D. Button for MEVVA implantation
at Australian Nuclear Science Technology Organization
under an AINSE Grant No. AINGRA05155P. We thank
S.K. Bhargava at RMIT University for the financial support
to D.K.V. to carry out initial stages of this research
A high-energy electron scattering study of the electronic structure and elemental composition of O-implanted Ta films used for the fabrication of memristor devices
High-energy electron scattering is used to investigate Ta films implanted with 10 keV O ions. These
films are of interest as they have been used for the fabrication of memristors. High-energy electron
scattering is used with incoming electron energies ranging from 5 to 40 keV. The inelastic mean free
path, and hence the probing depth, is at these energies of the same order as the range of the implanted
ions. At the same time, we can distinguish the mass of the atom that scattered the electron elastically,
due to the dependence of the recoil energy on the mass of the scatterer. This allows us to determine
quantitatively the atomic composition near the surface from the signal of electrons that have
scattered elastically but not inelastically. Electrons that have scattered inelastically as well as
elastically provide us with information on the possible electronic excitations. Their signal is used to
monitor the presence of the Ta2O5 phase near the surface (characterised by a significant band gap of
’4:5 eV), and estimate at what depth below the surface pure Ta metal is present. In this way, we
obtain a fairly detailed picture of the elemental composition and electronic properties of these films.This research was made possible by funding of the
Australian Research Council. Oxygen-implanted Tantalum
films were provided by Dr. S. Ruffell and Dr. J. England of
Varian Semiconductor Equipment, a Division of Applied
Materials, as part of a broader collaboration funded by an
Australian Research Council Linkage Project Grant. The stay
of P.L.G. at the ANU was made possible by a Grant No.
10209/12-3 from CAPES (Brazil). S.K.N. gratefully acknowledges
RSAA for his Ph.D. scholarship
Effect of substrate proximity on luminescence yield from Si nanocrystals
The influence of the proximity of a high refractive index substrate on the luminescence of Si nanocrystals was investigated by time-integrated and time-resolved photoluminescence. The luminescence yield was found to be ∼2.5 times larger for emitters distanced from the substrate compared to those in proximity with the substrate, while luminescence decay measurements revealed only a slight increase in the luminescence lifetime (∼15%). Results are discussed in terms of local density of optical modes surrounding a pointlike light emitter with important implications for the collection efficiency of luminescence and the estimation of internal quantum efficiency for a quantum dot.Support for this work was provided by
the Swedish Research Council VR and the Australian Research
Council ARC
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