39. Electronic structure and optical properties of silicon nanowires: A study using x-ray excited optical luminescence and x-ray emission spectroscopy (original) (raw)
Related papers
Optical Characterization of Oxide Encapsulated Silicon Nanowires of Various Morphologies
Journal of Nanoscience and Nanotechnology, 2008
The optical properties of four different silicon nanowire structures were investigated. Two of the samples consisted of spheres of nanocrystalline silicon en-capsulated by silicon oxide nanowires, with other two consisting of crystalline silicon nanowires coated by silicon oxide shells. The nanostructures produced by oxide assisted growth consisted of spheres of crystalline silicon encapsulated by silicon oxide shells. The absorption and photoluminescence of the different structures of the sample are investigated. The emitting species responsible for photoluminescence across the visible spectrum are discussed.
Physical Review B, 2007
Time-resolved photoluminescence spectroscopy and cathodoluminescence spectroscopy and imaging have been used to investigate the optical properties of oxygen-and hydrogen-terminated silicon nanowires. We have found that the red-and the blue-emission bands from these nanowires are characterized by homogeneous broadening and are due to interface states in the silicon core and oxygen-based defects at the oxide cladding layer, respectively. Our results exclude the possibility that quantum confinement effects are responsible for these emission bands.
Optical Characterization of Luminescent Silicon Nanowires
Journal of the Korean Physical Society, 2019
Visible photoluminescence (PL) at room temperature from silicon nanowires (Si NWs) prepared by using the metal-assisted chemical-etching (MACE) technique is reported. The morphology and the luminescence properties of Si NWs are characterized by using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), and luminescence spectroscopy. TEM images of the luminescent Si NWs reveal that the surfaces of the Si NWs are very rough, with a few nano-sized silicon particles being attached to the Si NWs. Luminescent Si NWs are optically characterized by PL and Raman measurements. Temperature-dependent PL measurements are measured at temperatures from 5 K to room temperature to determine the origin of the PL. The PL intensity decreases and the wavelength of the PL is blue-shifted as the temperature is increased. The Raman spectra of luminescent Si NWs reveal quantum confinement of the Si NWs.
Advances in Natural Sciences: Nanoscience and Nanotechnology, 2011
In the present work, silicon nanowires were prepared by a thermal evaporation method. The evaporating source was a mixture of silicon and carbon nanopowders. Surface morphology, structural characteristics and emission properties of the silicon nanowires were investigated by several techniques. The results showed that the obtained products have the shape of nanowires with diameters ranging from 30 to 120 nm and lengths from 300 to 400 nm. The x-ray diffraction (XRD) patterns confirmed the presence of crystalline silicon. Transmission electron microscope (TEM) images revealed the core-shell structure of the wires. In the photoluminescence (PL) spectra recorded at room temperature, only a broad emission band peaking at about 650 nm was observed. In addition to the red emission, two other bands centered at around 455 nm and 510 nm appeared when measured at low temperatures. The origin and emission mechanism of these bands are discussed.
Journal of Applied Physics, 2001
X-ray absorption fine structures XAFS and electron energy loss spectroscopy EELS at the Si L 3,2 edge have been used to investigate a series of Si nanowires as-prepared and HF refreshed. X-ray excited optical luminescence XEOL was also used to study the optical properties of these Si nanowires. Although no noticeable edge-jump blueshift widened band gap is observed in XAFS, a noticeable change in the edge jump a less steep rise and the blurring of spectral features is observed, indicating considerable degradation in the long-range order and size effects. However, EELS with a nanobeam exhibits a threshold blueshift and parabolic behavior for some selected wires indicating that there are grains smaller than the nominal diameter in these nanowires. Thus, XAFS probes the average of a distribution of wires of various sizes of which the majority is too large to exhibit detectable quantum confinement behavior blueshift observed and inferred in EELS and XEOL. The results and their implications are discussed.
Photoluminescence of silicon nanowires obtained by epitaxial chemical vapor deposition
Physica E: Low-dimensional Systems and Nanostructures, 2009
We study by low temperature photoluminescence measurements the electronic states of silicon nanowires obtained by copper catalyzed chemical vapor deposition and compare them with those of wires made by etching silicon on the insulator structure. Thermal oxidation of nanowires appears to be absolutely necessary to passivate surface states and to enhance radiative recombinations at the silicon band gap. The study of the behavior of this transition as a function of temperature and pump power demonstrates that it involves the phonon assisted recombination of free carriers. The recombination energy appears at the silicon band gap, renormalized by exchange and correlation interactions favored by spatial confinement.
Investigation of optical properties of core–shell silicon nanowires
Materials Chemistry and Physics, 2011
The ability to control the size, orientation, composition and morphology of silicon nanowires (SiNWs) presents an ideal platform for exploring a wide range of potential technological applications. In this work, we demonstrated the detail study of optical properties of highly disordered core-shell SiNWs that were grown by atmospheric pressure chemical vapor deposition. The microstructure of SiNWs was characterized by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The TEM study shows that the SiNWs consists of crystalline core silicon surrounded by thick amorphous silicon oxide. The total diameter including the outer SiO 2 sheath was 60-80 nm. The reflection and absorption of a-SiO 2 /c-SiNWs were affected by process parameter like silane flow rate and hydrogen dilution. The optical reflection of SiNWs decreased with increasing photon energy across the visible and near the ultraviolet range, approaching moth's eye antireflection. Specifically, a minimum reflection of 2-3% was observed at 400 nm. The band gap is estimated at ∼1.32 eV by quasi-direct band Tauc's plot. The sum of localized states at the band edge is ∼0.53 eV. Straight SiNWs have lower reflection than those of nanoparticles mixed SiNWs and coil mixed SiNWs. The reflection and absorption of SiO 2 /SiNWs were confirmed to respond strongly to infrared with increasing H 2 flow rate.
Spatial delocalization of absorption and emission process in silicon nanowires
Journal of Luminescence, 2019
Dependence of optical properties of porous silicon nanowires on their size has been investigated here. Based on the experimental evidence, a new model to explain the process of absorption and photoluminescence in these Si nanowire samples has been proposed. Three different samples, with different nanowire diameters, have been prepared using metal-induced etching of silicon wafers. These wafers have different doping type and doping concentration which results in silicon nanowires of different diameters embedded with Si nanostructures of sizes around the Bohr's exciton radius. The absorption properties of these different types of Si nanostructures show a strong size dependence. However, the photoluminescence spectrum does not show any direct dependence on the size of the nanostructures, doping levels and type of silicon wafer used for fabrication of silicon nanostructures. It is also observed that the photoluminescence life time from these structures inversely depends on the size of the nanostructures whereas directly depends on the porosity, thus defects, in the samples. Based on these results it has been shown that the absorption of photons in these porous silicon nanowires happens in the silicon nanostructures embedded in the nanowires while the photoluminescence emission originates due to the surrounding porous SiO x .
ACS Nano, 2011
We study the structural, electronic and magnetic properties of Co-based LiMgPdSn-types of quaternary Heusler compounds (CoFeCrAl, CoFeTiAs, CoFeCrGa, and CoMnVAS) using Density Functional Theory (DFT) implemented on Tight Binding Linear Muffin-Tin Orbital within Atomic Sphere Approximation (TB-LMTO-ASA) Code. The optimized value of lattice parameter for CoFeCrAl, CoFeTiAs, CoFeCrGa and CoMnVAs are found to be 5.61A˚, 5.76 A˚, 5.61A˚ and 5.71A˚ , respectively. From the calculation of electronic band structure and spin polarized total density of states (DOS), we found that CoFeCrAl and CoFeCrGa are spin-gapless semiconductors with halfmetallic gap of 0.82eV and 0.25eV respectively. CoFeTiAs half-metal (Nearly spin-gapless semiconductor) with half-metallic gap of 0.38 eV, and CoMnVAs is found to be nearly gapless halfmetal. Magnetic moment of these compounds almost obey the Slater-Pauling rules. All these compounds expected to have high curie temperature which makes them significant for spintroincs/magnetoelectroincs applications.