GaSb Nanoparticles Research Articles

Size- and shape-dependent phase diagram of Ga-Sb nanoparticles

It is well known that the phase diagrams calculated using bulk Gibbs energy alone is insufficient when the dimensions of alloy particles are less than 100 nm. This is due to the surface energy contribution to the Gibbs energy, which increases as surface-to-volume ratio of alloy particles increases. In this work, we have used the CALPHAD approach to calculate the phase diagram of the Ga-Sb system taking into account of the size and shape of alloy particles. To accomplish this, we have added size-dependent surface energy terms and optimized the Gibbs energy expressions of various phases in the Ga-Sb system using surface tension information. The surface tension of the liquid phase is calculated using the Butler equation. The surface energy contribution to the Gibbs energy of the terminal phases is approximated using the surface tension expressions of the elements. The surface energy of the line compound GaSb is computed using the slab model within the framework of Density Functional Theory (DFT). The calculations show that there is lowering of liquidus and eutectic temperatures when size decreases. Among the two shapes considered, the depression is more prominent in the nano-spheres than the nano-rods.

Enhanced thermoelectric properties of Ga and In Co-added CoSb3-based skutterudites with optimized chemical composition and microstructure

Skutterudite compounds such as Co antimonite (CoSb3) contain cage-like voids inside crystal structure, which can be completely or partially filled with various different atoms, including group 13 elements. The multiple filling approach is known as an effective way of reducing lattice thermal conductivity (κlat), which results in a high value of the thermoelectric dimensionless figure of merit (zT). In this work, enhanced zT was achieved for the Ga and In co-added CoSb3 samples with a preferable microstructure and the nominal composition (Ga0.8In0.2)xCo4Sb12 (x = 0.05−0.45). Although all added In atoms occupied exclusively the void sites, the Ga species filled both the void and Sb sites of CoSb3. Moreover, Ga atoms added in the quantities exceeding the solubility limit precipitated as GaSb nanoparticles. The sample with x = 0.45 was characterized by the largest filling factions of Ga and In as well as the unique microstructure, consisting of microscale grains of the skutterudite phase and corresponding amounts of the GaSb nanoparticles. The Ga and In co-added skutterudite samples with optimized chemical composition and microstructure maintained high carrier mobility and sufficiently low κlat values, resulting in zT > 1.1, one of the best values for the skutterudites filled with group 13 elements.

Electronic-Excitation-Induced Processing in GaSb Compound Nanoparticles

Temperature dependence of electronic-excitation-induced structural changes in nanoparticles has been studied by in situ transmission electron microscopy. When GaSb nanoparticles kept at 340 K were excited by 25 keV electrons, the compound transforms to the porous compound or the two-phase structure consisting of an antimony core and a gallium shell with increasing the total electron dose. On the other hand, in GaSb nanoparticles kept at 293 K the structure remains the original compound phase. It is suggested that such temperature dependence of the structural changes may arise from synergetic behaviors of point defects introduced athermally by the excitation and thermal mobility.

Process of phase separation induced by low energy electronic excitation in GaSb nanoparticles

The process of electronic-excitation-induced phase separation in GaSb nanoparticles has been studied by transmission electron microscopy from the viewpoint of the relationship between the atomic diffusion and the behaviour of the defects introduced by electronic excitation. When approximately 20 nm-sized GaSb particles kept at 430 K are excited by 25keV electrons, gallium atoms on the lattice points are displaced to form vacancies and gallium interstitials in the crystal. Two-phase separation takes place via the void formation and an increase in lattice constant of GaSb. It is suggested that the vacancy supersaturation near the particle core brings about the void formation and the diffusion of gallium interstitials to the particle surface causes the phase separation.

Electron Dose Rate Dependence of Phase Separation Induced by Electronic Excitation in GaSb Nanoparticles

The effect of electron dose rate on phase separation induced by electronic excitation in GaSb nanoparticles has been studied in order to see whether a nonlinear relation between density of excited states introduced and the efficiency of the phase separation is found or not. The phase separation to two phases consisting of an antimony core and a gallium shell proceeds after incubation time with increasing electron dose and does only at the dose rate above a threshold value. It is suggested that such nonlinear behaviors take place as a cooperative phenomenon among electronic-excitation effect, nano-size effect and temperature.

Effect of electron flux on electronic-excitation-induced phase separation in GaSb nanoparticles

We studied the effect of electron flux on phase separation induced by electronic excitation in GaSb nanoparticles, in order to see whether the phase separation is characterized as a cooperative phenomenon, in which a nonlinear relation may be found between density of excited states introduced and the efficiency of the phase separation or not. The phase separation to two phases consisting of an antimony core and a gallium shell proceeds abruptly after incubation time with increasing electron dose and does only at the flux above a threshold value. It is suggested that such nonlinear behaviors take place as a cooperative phenomenon among electronic-excitation effect, nano-size effect and temperature.

Effect of Electron Flux on the Electronic-excitation-induced Phase Separation in GaSb Nanoparticles

Effect of Electron Flux on the Electronic-excitation-induced Phase Separation in GaSb Nanoparticles

Electron-irradiation-induced phase separation in GaSb nanoparticles

Electron irradiation effects in GaSb compound nanoparticles have been studied by transmission electron microscopy, in order to examine structural stability under electron irradiation in a nanometer-sized system. It is revealed that when 75 keV electron irradiation was carried out in approximately (10--25)-nm-sized GaSb particles kept at 423 K, a phase separation of the GaSb compound was induced to form a two-phase structure consisting of a crystalline antimony core and a liquid gallium shell. The phase separation was induced neither by 75 keV electron irradiation in GaSb nanoparticles kept at more than 443 K or less than 363 K nor by 200 keV electron irradiation in particles kept from 363 to 443 K. It is suggested that the phase separation in GaSb nanoparticles may be induced by electronic excitations rather than knock-on displacements.

Sonochemical preparation of GaSb nanoparticles.

A room temperature sonochemical method for the preparation of GaSb nanoparticles using less hazardous Ga and antimony chloride (SbCl(3)) as the precursors has been described. The formation of GaSb has been confirmed by means of XRD, EDAX, and XPS characterization. TEM and SAED results show that the as-prepared solid consists of nanosized GaSb crystals with sizes in the range 20-30 nm. The photoacoustic spectrum result reveals that the GaSb nanoparticles have a direct band gap of about 1.21 eV. On the basis of the control experiments and the extreme conditions produced by ultrasound, an ultrasound-assisted in-situ reduction/combination mechanism has been proposed to explain the reaction.

Preparation and optical properties of GaSb nanoparticles embedded in SiO2 composite films

The composite films of GaSb nanoparticles embedded in SiO 2 matrices were fabricated by radio-frequency magnetron co-sputtering. Transmission electron microscope and X-ray diffraction pattern indicate that the GaSb nanoparticles were uniformly dispersed in SiO 2 matrices. Room temperature transmission spectra exhibit a blue shift of about 2.73 eV. The blue shift increases with decreasing size of GaSb nanoparticles, suggesting the existence of quantum size effects. Room temperature Raman spectra show that there is a larger Raman peak red shift and broadening of the composite films than that of bulk GaSb. This phenomenon is explained by photon confinement effect and tensile stress effect.

Optical diffuse reflectance spectra of GaSb nanocrystals embedded in SiO 2 matrix by radio-frequency magnetron co-sputtering

Nanocrystalline GaSb embedded in SiO2 films was grown by radio-frequency magnetron co-sputtering. X-ray diffraction pattern and transmission electron microscopy (TEM) confirm the existence of GaSb nanocrystals in the SiO2 matrix. The average size of GaSb nanoparticles is in the range of 3 to 11 nm. Diffuse reflectance spectra were used to characterize the small change of the band gap of the semiconductor. The diffuse reflectance spectra shows that the absorption peaks have a large blueshift of about 4.0 eV of the absorption relative to that of bulk GaSb. It has been explained by quantum confinement effects. Room temperature optical transmission spectra show that the absorption edge exhibits a very large blueshift of about 2.1 eV with respect to that of bulk GaSb in agreement with quantum confinement.

Temperature-controlled synthesis of gallium antimonide nanoparticles in solution

Reactions of GaCl 3 and Sb(SiMe 3) 3 in a 1:1 molar ratio in different solvents (pentane, hexane, toluene, and xylene) are described. The resulting GaSb was characterized by electron and X-ray diffraction studies, energy-dispersive X-ray (EDS) analysis, and transmission electron micrography (TEM) studies. The particle size and chemical composition was controlled by the solvent. The size of the GaSb nanoparticles varied between 10 and 50 nm.

X-ray photoelectron spectroscopy of GaSb nanoparticles embedded in SiO2 matrices by radio-frequency magnetron co-sputtering

GaSb-SiO2 composite films were fabricated by radio-frequency magnetron co-sputtering. Transmission electron microscope (TEM) results exhibit that the GaSb nanoparticles were uniformly dispersed in SiO2 matrices. The sizes of nanoparticles are in the range of 4-10 nm. X-ray photoelectron spectroscopy (XPS) analysis confirms the high purity of GaSb nanoparticles contained in the SiO2 matrices and shows that the GaSb and SiO2 exist in nonstoichiometry in the composite films due to the strong affinity of Sb and Si with oxygen. Room temperature optical transmission spectra show a very large blue shift of about 2.76 eV with respect to that of bulk GaSb, suggesting the existence of quantum size effects.