ScAlN nanowires: A cathodoluminescence study (original) (raw)
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Photoluminescence Studies of Aluminum Nitride Nanowires
Aluminium nitride (AlN) is a promising material for application in electronics and optoelectronics [1]. In recent years, several researchers have reported the photoluminescence (PL) properties of nanocrystalline AlN and suggested that the efficient visible luminescence of nanocrystalline wurtzite AlN in the 2–4 eV region makes it promising materials for light-emitting applications [2, 3]. However, there has been rare report on the properties and associated mechanisms of PL emission.
Growth of scandium aluminum nitride nanowires on ScN(111) films on 6H-SiC substrates by HVPE
physica status solidi (a), 2009
The formation of ScAlN nanowires on ScN/6H-SiC(0001) by hydride vapor phase epitaxy (HVPE) was analyzed. The diameters and lengths of the nanowires were 50 to 150 nm and 1 m, respectively. The nanowires had a Al/Sc metal ratio of 95/5 as measured by energy dispersive analysis of Xrays (EDX). The 4.84Å unit cell periodicity along the length of the ScAlN nanowires was similar to that of pure AlN (4.98Å), as measured by Fourier transforms of high resolution transmission electron microscopy images of a single nanowire. Only the and peaks of the ScN continuous film and the (0006) of the 6H-SiC substrate were detected by θ-2θ X-ray diffraction. A tentative model, based on catalystinduced growth, is proposed to explain the unintentional formation of nanowires on the ScN film. This model is based on the production of volatile Al (possibly AlCl) by the reaction of the scandium metal source with the alumina reactor tube and subsequent reaction with hydrogen chloride. This reacts with ammonia in the deposition zone to create ScAlN nanowires, catalyzed by small ScAl clusters, which are spontaneously formed on the ScN film before the nanowire growth.
The Effects of Substrates on the Geometry and Optical Properties of Aluminum Nitride Nanowires
Journal of Nanoscience and Nanotechnology, 2012
Based on a Chemical Vapor Deposition (CVD) process, an alumina tube electric furnace was assembled to synthesize different one dimensional aluminum nitride (AlN) nanostructures via aluminum powder and nitrogen gas flow. The products obtained where nanowires, nanorods, a unique chain-linked nanocage structure made from an entanglement of AlN nanowires and an interesting micro-sized spherical architecture. The different growth parameters dictated to the system result the product variety, making structure tuning possible. The incorporation of different substrates (silicon and alumina) not only leads to the formation of different shaped structures, but also results different optical emissions ranging from 450 nm (blue) to 650 nm (red), indicating the high potential of AlN nanostructures in LED fabrication. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selective Area Electron Diffraction (SAED), X-ray Diffraction (XRD), Photoluminescence (PL) and Energy Dispersive X-ray (EDX) analysis results are discussed and a Vapor-Liquid-Solid (VLS)/Vapor-Solid (VS) based growth mechanism is proposed for the mentioned structures.
Self-assembled AlN nanowires (NWs) are grown by plasma-assisted molecular beam epitaxy (PAMBE) on SiO 2 /Si (111) substrates. Using a combination of in situ reflective high energy electron diffraction and ex situ x-ray diffraction (XRD), we show that the NWs grow nearly strainfree, preferentially perpendicular to the amorphous SiO 2 interlayer and without epitaxial relationship to Si(111) substrate, as expected. Scanning electron microscopy investigation reveals significant NWs coalescence, which results in their progressively increasing diameter and formation of columnar structures with non-hexagonal cross-section. Making use of scanning transmission electron microscopy (STEM), the NWs initial diameters are found in the 20-30 nm range. In addition, the formation of a thin (≈30 nm) polycrystalline AlN layer is observed on the substrate surface. Regarding the structural quality of the AlN NWs, STEM measurements reveal the formation of extended columnar regions, which grow with a virtually perfect metal-polarity wurtzite arrangement and with extended defects only sporadically observed. Combination of STEM and electron energy loss spectroscopy reveals the formation of continuous aluminum oxide (1-2 nm) on the NW surface. Low temperature photoluminescence measurements reveal a single near-band-edge (NBE) emission peak, positioned at 6.03 eV (at 2 K), a value consistent with nearly zero NW strain evidenced by XRD and in agreement with the values obtained on AlN bulk layers synthesized by other growth techniques. The significant full-width-at-half-maximum of NBE emission, found at ≈20 meV (at 2 K), suggests that free and bound excitons are mixed together within this single emission band. Finally, the optical properties of the hereby reported AlN NWs grown by PAMBE are comprehensively compared to optical properties of bulk, epitaxial and/or columnar AlN grown by various techniques such as: physical vapor transport, metal organic vapor phase epitaxy, metal organic chemical vapor deposition and molecular beam epitaxy.
Synthesis of aluminum nitride nanowires
Physica B-condensed Matter, 2002
Aluminum nitride (AlN) nanowires were synthesized by co-heating a mixture of Al and AlN nanopowders produced by nitrogen plasma-molten Al reaction in N 2 atmosphere at 750-8501C for 1 h. The morphology and structure of AlN nanowires were investigated using transmission electron microscopy (TEM) and X-ray diffraction techniques (XRD). The obtained AlN nanowires are either surface-smooth stick or bamboo-like structured. TEM observations showed that the AlN nanowires have a diameter of approximately 10-50 nm and a length of 500 nm-500 mm. r
Formation of AlN nanowires using Al powder
Materials Chemistry and Physics, 2008
Using direct nitridation method of Al powder, single crystalline AlN nanowires were synthesized. The morphology of synthesized AlN nanowires depending on the nitridation temperature and atmosphere was investigated using XRD, SEM and TEM techniques. At 1100 • C in N 2 atmosphere, the diameter of the synthesized AlN nanowires was about 60-75 nm having a high aspect ratio. However, at 1000 • C in N 2 + 10% H 2 atmosphere, the diameter of the AlN nanowires was about 80-120 nm having high yield and minimum agglomeration. The synthesized AlN nanowires had hexagonal single crystal structure, covered with a thin (∼1.5 nm) amorphous layer and large number of stacking faults along the (0 0 2) plane.
Ab Initio Study of Confinement and Surface Effects in AlN Nanowires
The Journal of Physical Chemistry C, 2010
Thickness dependence of electronic and optical properties of AlN nanotubes is studied using density functional theory. It is found that the surface atoms induce their electronic states near the upper valence band edge as well as the lower conduction band edge. Moreover, the absorption spectrum of AlN nanotubes is shown to be dependent on the ratio of surface to bulk atoms. The effect of piezoelectric field on the optical properties of AlN nanotubes is also computed. We showed that in addition to the shifts towards higher energies, as it is usual in bulk AlN, one can also obtain shifts towards lower energies according to frequencies.
Optical properties of strain-free AlN nanowires grown by molecular beam epitaxy on Si substrates
Applied Physics Letters, 2014
The optical properties of catalyst-free AlN nanowires grown on Si substrates by molecular beam epitaxy were investigated. Such nanowires are nearly free of strain, with strong free exciton emission measured at room temperature. The photoluminescence intensity is significantly enhanced, compared to previously reported AlN epilayer. Moreover, the presence of phonon replicas with an energy separation of ∼100 meV was identified to be associated with the surface-optical phonon rather than the commonly reported longitudinal-optical phonon, which is further supported by the micro-Raman scattering experiments.