Engineering the composition, morphology, and optical properties of InAsSb nanostructures via graded growth technique

Graded growth technique is utilized to realize the control over the composition, morphology, and optical properties of self-assembled InAsSb/InGaAs/InP nanostructures. By increasing the initial mole fraction of the Sb precursor during the graded growth of InAsSb, more Sb atoms can be incorporated into the InAsSb nanostructures despite the same Sb mole fraction averaged over the graded growth. This leads to a shape change from dots to dashes/wires for the InAsSb nanostructures. As a result of the composition and morphology change, photoluminescence from the InAsSb nanostructures shows different polarization and temperature characteristics. This work demonstrates a technologically important technique—graded growth, to control the growth and the resultant physical properties of self-assembled semiconductor nanostructures.Financial support from Australian Research Council is gratefully acknowledged

Antiferromagnetism in semiconducting KFe0.85Ag1.15Te2 single crystals

We have synthesized single crystals of K1.00(3)Fe0.85(2)Ag1.15(2)Te2.0(1). The materials crystallizes in the ThCr2Si2 structure with I4/mmm symmetry and without K and Fe/Ag deficiencies, unlike in KxFe2-ySe2 and KxFe2-yS2. In contrast to theoretical prediction for higher Tc in KFe2Te2, KFe0.85Ag1.15Te2 is a semiconductor with long-range antiferromagnetic transition at TN = 35 K.Comment: 4 pages, 4 figure

Glassy Dynamics in a Frustrated Spin System: Role of Defects

In an effort to understand the glass transition, the kinetics of a spin model with frustration but no quenched randomness has been analyzed. The phenomenology of the spin model is remarkably similiar to that of structural glasses. Analysis of the model suggests that defects play a major role in dictating the dynamics as the glass transition is approached.Comment: 9 pages, 5 figures, accepted in J. Phys.: Condensed Matter, proceedings of the Trieste workshop on "Unifying Concepts in Glass Physics

Development of hot drawing process for nitinol tube

In recent years, Nitinol, near-equiatomic nickel-titanium alloys, have found growing applications in medical technology and joining technology, due to their special characteristics such as shape memory, superplasticity and biocompatibility. The production of Nitinol tube cost-effectively remains a technical challenge. In this paper, we describe a hot drawing process for Nitinol tube production. A Nitinol tube blank and a metal core are assembled together. The assembly is hot drawn for several passes to a final diameter. The metal core is then plastically stretched to reduce its diameter and removed from the tube. Hot drawing process has been applied to Ni50.7Ti and Ni47Ti44Nb9 alloys. Nitinol tubes of 13.6 mm outer diameter and 1 mm wall thickness have been successfully produced from a tube blank of 20 mm outer diameter and 3.5 mm thickness

Controlling the morphology and optical properties of self-assembled InAsSb/InGaAs/InP nanostructures via Sb exposure

Engineering the surface energy, interface energy, and elastic strain energy in the system viaSb exposure is used to realize the control on the morphology and optical properties of self-assembled InP-based InAsSb/InGaAs nanostructures. By flowing trimethylantimony precursor over the surface of InGaAs buffer layer before the growth of InAsSbnanostructures, the surface/interface energy in the system is reduced, while the strain energy in the system is enhanced, which lead to a shape transition from dot to dash, and to wire for the InAsSbnanostructures. As a result of their morphology changes, the InAsSbnanostructures show different polarization characteristics in their photoluminescence emission.Financial support from Australian Research Council is gratefully acknowledged

Formation and shape control of InAsSb/InP (001) nanostructures

This paper presents a study on the formation and shape control of InAsSb/InP nanostructures on InP (001) substrates. For the formation of InAsSbnanostructures, incorporation of Sb atoms into InAs islands results in significant morphology change in the islands due to the surfactant effect of Sb atoms and the large strain in the system. And, shape control of InAsSb/InP nanostructures is achieved by optimizing their growth parameters. Low growth temperature and high growth rate will induce the formation of InAsSb elongated quantum dots, while high growth temperature and low growth rate will promote the formation of InAsSbquantum wires or dashes.Financial support from the Australian Research Council is gratefully acknowledged

Enhanced photoluminescence efficiency of mid-infrared InAsSb nanostructures using a carrier blocking layer

This paper presents a study on the emission efficiency enhancement of InAsSbnanostructures using a carrier blocking layer. InP is proposed to serve as the carrier blocking layer to suppress the thermal escape of carriers in InAsSbnanostructures and significantly enhance their emission efficiency at high temperature (good photoluminescence signal even at 330 K). However, this leads to a blueshift in their emission wavelength due to the significantly increased quantum confinement of the nanostructures. By inserting a thin InGaAs layer between InP blocking layer and InAsSbnanostructures, longer emission wavelength can be maintained. This provides an approach to achieve InAsSbnanostructures with both good high-temperature optical characteristics and long emission wavelength, which is very useful for fabricating mid-infrared emitters operating at room temperature.Financial support from Australian Research Council No. DP0774366 is gratefully acknowledged

Effect of matrix material on the morphology and optical properties of InP-based InAsSb nanostructures

This paper presents a study on the effect of matrix material on the morphology and optical properties of self-assembled InP-based InAsSbnanostructures. Due to the differences in surface roughness of the growth front, In 0.53 Ga 0.47 As matrix layer induces the formation of short quantum dashes (QDashes) and elongated quantum dots, while InP and In 0.52 Al 0.48 As matrix layers promote the formation of long QDashes and quantum wires, respectively. The shape anisotropy of InAsSbnanostructures on In 0.53 Ga 0.47 As , InP, and In 0.52 Al 0.48 As layers is further investigated with polarized photoluminescence measurements. The InAsSbnanostructures show a luminescence polarization degree of 8.5%, 14.3%, and 29% for In 0.53 Ga 0.47 As , InP, and In 0.52 Al 0.48 As matrixes, which corresponds well with the shape anisotropy observed with atomic force microscope. Furthermore, InAsSb/In 0.53 Ga 0.47 As nanostructures also show the longest, thermally stable emission wavelength, which serves as a promising material system for fabricating midinfrared emitters.Financial support from Australian Research Council is gratefully acknowledged. Facilities used in this work are supported by the Australian National Fabrication Facility

Nano-porosity in GaSb induced by swift heavy ion irradiation

Nano-porous structures form in GaSb after ion irradiation with 185 MeV Au ions. The porous layer formation is governed by the dominant electronic energy loss at this energy regime. The porous layer morphology differs significantly from that previously reported for low-energy, ion-irradiated GaSb. Prior to the onset of porosity, positron annihilation lifetime spectroscopy indicates the formation of small vacancy clusters in single ion impacts, while transmission electron microscopy reveals fragmentation of the GaSb into nanocrystallites embedded in an amorphous matrix. Following this fragmentation process, macroscopic porosity forms, presumably within the amorphous phase.The authors thank the Australian Research Council for support and the staff at the ANU Heavy Ion Accelerator Facility for their continued technical assistance. R.C.E. acknowledges the support from the Office of Basic Energy Sciences of the U.S. DOE (Grant No. DE-FG02-97ER45656)