In-situ deposition of sparse vertically aligned carbon nanofibres on catalytically activated stainless steel mesh for field emission applications

We report on an inexpensive, facile and industry viable carbon nanofibre catalyst activation process achieved by exposing stainless steel mesh to an electrolyzed metal etchant. The surface evolution of the catalyst islands combines low-rate electroplating and substrate dissolution. The plasma enhanced chemical vapour deposited carbon nanofibres had aspect-ratios > 150 and demonstrated excellent height and crystallographic uniformity with localised coverage. The nanofibres were well-aligned with spacing consistent with the field emission nearest neighbour electrostatic shielding criteria, without the need of any post-growth processing. Nanofibre inclusion significantly reduced the emission threshold field from 4.5 V/μm (native mesh) to 2.5 V/μm and increased the field enhancement factor to approximately 7000. © 2011 Elsevier B.V. All rights reserved.

Precursor flow rate manipulation for the controlled fabrication of twin-free GaAs nanowires on silicon substrates

Vertically oriented GaAs nanowires (NWs) are grown on Si(111) substrates using metal-organic chemical vapor deposition. Controlled epitaxial growth along the 111 direction is demonstrated following the deposition of thin GaAs buffer layers and the elimination of structural defects, such as twin defects and stacking faults, is found for high growth rates. By systematically manipulating the AsH 3 (group-V) and TMGa (group-III) precursor flow rates, it is found that the TMGa flow rate has the most significant effect on the nanowire quality. After capping the minimal tapering and twin-free GaAs NWs with an AlGaAs shell, long exciton lifetimes (over 700ps) are obtained for high TMGa flow rate samples. It is observed that the Ga adatom concentration significantly affects the growth of GaAs NWs, with a high concentration and rapid growth leading to desirable characteristics for optoelectronic nanowire device applications including improved morphology, crystal structure and optical performance. © 2012 IOP Publishing Ltd.

Compensatory growth in the gibel carp following feed deprivation: temporal patterns in growth, nutrient deposition, feed intake and body composition

To investigate the nature of compenstory growth in fish, an 8 week study at 28 degreesC was performed on juvenile gibel carp Carassius auratus gibelio weighing 6.6 g. Fish were starved for 0 (control), 1 (Sl)or 2 (S2) weeks and then re-fed to satiation For 5 weeks. Weekly changes in weight gain, feed intake and body composition were monitored during re-feeding. No significant difference was found in final body weight between the three groups, indicating complete compensation in the deprived fish, The deprived groups caught up in body weight with that of the control after 2 weeks of re-feeding. Body fat:lean body mass ratio was restored to the control level within 1 week of re-feeding. In the re-feeding period, weekly gains in body weight, protein. lipid, ash and energy in the S1 group were significantly higher than in the controls for 1 week. For the S2 group, weekly gains in body weight. lipid. ash and energy were higher than in the controls for 2 weeks, and gain in protein was higher than in the controls for 3 weeks, though gain in body energy became elevated again during the last 2 weeks of the experiment. Feed intake remained higher than the control level for 3 weeks in the S1 group and 3 weeks in the SZ group. Growth efficiency was not significantly different among the three groups in any of the weeks during re-feeding. Compensatory responses in growth and especially feed intake tended to last longer than the recovery of body composition. (C) 2001 The Fisheries Society of the British Isles.

Growing 20 cm Long DWNTs/TWNTs at a Rapid Growth Rate of 80-90 mu m/s

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Photoluminescence and lasing properties of InAs/GaAs quantum dots grown by metal-organic chemical vapour deposition

Photoluminescence (PL) and lasing properties of InAs/GaAs quantum dots (QDs) with direrent growth procedures prepared by metalorganic chemical vapour deposition are studied. PL measurements show that the low growth rate QD sample has a larger PL intensity and a narrower PL line width than the high growth rate sample. During rapid thermal annealing, however, the lowgrowth rate sample shows a greater blue shift of PL peak wave length. This is caused by the larger InAs layer thickness which results from the larger 2-3 dimensional transition critical layer thickness for the QDs in the low-growth-rate sample. A growth technique including growth interruption and in-situ annealing, named indium flush method, is used during the growth of GaAs cap layer, which can flatten the GaAs surface effectively. Though the method results in a blue shift of PL peak wavelength and a broadening of PL line width, it is essential for the fabrication of room temperature working QD lasers.

The effect of growth temperature on structural quality of GaN/AlN quantum wells by metal-organic chemical vapour deposition

The effect of the growth temperature on the surface and interface quality for the GaN/AlN multiquantum well (MQW) layer grown by metal-organic vapour chemical deposition is investigated. The obtained GaN/AlN MQW structure is almost coherent to the underlying AlGaN layer at improved growth conditions. With a relatively low growth temperature, the GaN/AlN MQW growth rate increases, the surface roughness reduces considerably and no macro steps are observed, resulting in a better periodicity of MQW.

Suppression of indium droplet formation by adding CCl4 during metalorganic chemical vapor deposition growth of InN films

In this work, the influences of CCl4 on the metalorganic chemical vapor deposition (MOCVD) growth of InN were studied for the first time. It was found that the addition of CCl4 can effectively suppress the formation of metal indium (In) droplets during InN growth, which was ascribed to the etching effect of Cl to In. However, with increasing of CCl4 flow, the InN growth rate decreased but the lateral growth of InN islands was enhanced. This provides a possibility of promoting islands coalescence toward a smooth surface of the InN film by MOCVD. The influence of addition of CCl4 on the electrical properties was also investigated.

Synthesis and characterization of well-aligned Zn1-xMgxO nanorods and film by metal organic chemical vapor deposition

Well-aligned Zn1-xMgxO nanorods and film with Mg-content x from 0 to 0.051 have been successfully synthesized by metal organic chemical vapor deposition (MOCVD) without any catalysts. The characterization results showed that the diameters and lengths of the nanorods were in the range of 20-80 nm and 330-360 nm, which possessed wurtzite structure with a c-axis growth direction. As the increase of Mg precursor flows into the growth chamber, the morphology of Zn1-xMgxO evolves from nanorods to a film with scale-like surface and the height of the nanorods and the film was almost identical, it is suggested that the growth rate along the c-axis was hardly changed while the growth of six equivalent facets of the type {1 0 (1) over bar 0} of the Zn1-xMgxO has been improved. Photoluminescence and Raman spectra show that the products have a good crystal quality with few oxygen vacancies. With the Mg incorporation, multiple-phonon scattering become weak and broad, and the intensities of all observed vibrational modes decrease. And the ultraviolet near-band-edge emission shows a clear blueshift (x=0.051, as much as 90 meV) and slightly broadening compared with that of pure ZnO nanorods. (C) 2008 Elsevier B.V. All rights reserved.

Defect evolution and accompanied change of electrical properties during the GaN growth by metalorganic chemical vapor deposition

The defect evolution and its correlation with electrical properties of GaN films grown by metalorganic chemical vapor deposition are investigated. It is found that the dislocation density decreases gradually during the growth process, and the dislocation reduction rate in the island coalescence process is especially rapid. The changes in electron mobility of GaN with the increase of growth time are mainly dependent on the dislocations acting as scattering centers. Furthermore, the variation of carrier concentration in GaN may be related with the point defects and their clusters. The quality of GaN could be improved by suitably increasing the film thickness. (C) 2009 Elsevier B.V. All rights reserved.

Phase-separation suppression in GaN-rich side of GaNP alloys grown by metal-organic chemical vapor deposition

The GaN-rich side of GaNP ternary alloys has been successfully synthesized by light-radiation heating and low-pressure metal-organic chemical vapor deposition. X-ray diffraction (XRD) rocking curves show that the ( 0002) peak of GaNP shifts to a smaller angle with increasing P content. From the GaNP photoluminescence (PL) spectra, the red shifts from the band-edge emission of GaN are determined to be 73, 78 and 100 meV, respectively, in the GaNP alloys with the P contents of 1.5%, 5.5% and 7.5%. No PL peak or XRD peak related to GaP is observed, indicating that phase separation induced by the short-range distribution of GaP-rich regions in the GaNP layer has been effectively suppressed. The phase-separation suppression in the GaNP layer is associated with the high growth rate and the quick cooling rate under the given growth conditions, which can efficiently restrain the accumulation of P atoms in the GaNP layer.

Chemical liquid phase deposition of thin aluminum oxide films

Thin aluminum oxide films were deposited by a new and simple physicochemical method called chemical liquid phase deposition (CLD) on semiconductor materials. Aluminum sulfate with crystallized water and sodium bicarbonate were used as precursors for film growth, and the control of the system's pH value played an important role in this experiment. The growth rate is 12 nm/h with the deposition at [Al-2(SO4)(3)]=0.0837 mol.L-1, [NaHCO3]=0.214 mol.L-1, 15 degreesC. Post-growth annealing not only densifies and purifies the films, but results in film crystallization as well. Excellent quality of Al2O3 films in this work is supported by electron dispersion spectroscopy, Fourier transform infrared spectrum, X-ray diffraction spectrum and scanning electron microscopy photograph.

Synthesis of GaN nanowires and nano-pyramids in a two-hot-boat chemical vapor deposition system via an in-doping technique

A two-hot-boat chemical vapor deposition system was modified from a thermal evaporation equipment. This system has the advantage of high vacuum, rapid heating rate and temperature separately controlled boats for the source and samples. These are in favor of synthesizing compound semiconducting nano-materials. By the system, we have synthesized high-quality wurtzite single crystal GaN nanowires and nanotip triangle pyramids via an in-situ doping indium surfactant technique on Si and 3C-SiC epilayer/Si substrates. The products were analyzed by x-ray diffraction, field emission scanning electron microscopy, highresolution transmission electron microscopy, energy- dispersive x-ray spectroscopy, and photoluminescence measurements. The GaN nanotip triangle pyramids, synthesized with this novel method, have potential application in electronic/ photonic devices for field-emission and laser.

Effect of Al incorporation on the AlGaN growth by metalorganic chemical vapor deposition

The effect of Al incorporation on the AlGaN growth by metalorganic chemical vapor deposition is investigated. With the increase of trimethylalluminum (TMAl) flux, the crystal quality becomes worse, and the epilayer surface becomes rougher. An interesting phenomenon is that the growth rate of AlGaN decrease with increasing TMAl flux, which is opposite to the AlN growth rate dependence on the TMAl flux. All these effects are attributed to the different properties of At atoms due to the higher bond strength of Al-N compared with Ga-N, which lead to lower surface mobility and stronger competitive ability of Al atoms during the growth. The enhancement of the surface mobility of Al is especially important for improving the quality of AlGaN. (c) 2006 Elsevier B.V. All rights reserved.

Crack control in GaN grown on silicon (111) using In doped low-temperature AlGaN interlayer by metalorganic chemical vapor deposition

The effects of In doped low-temperature (LT) AlGaN interlayer on the properties of GaN/Si(111) by MOCVD have been investigated. Using In doping LT-interlayer can decrease the stress sufficiently for avoiding crack formation in a thick (2.0 mu m) GaN layer. Significant improvement in the crystal and optical properties of GaN layer is also achieved. In doping is observed to reduce the stress in AlGaN interlayer measured by high-resolution X-ray diffraction (HRXRD). It can provide more compressive stress to counteract tensile stress and reduce crack density in subsequent GaN layer. Moreover, as a surfactant, indium is observed to cause an enhanced PL intensity and the narrowed linewidths of PL and XRD spectra for the LT-interlayer. Additionally, the crystal quality of GaN layer is found to be dependent on the growth parameters of underneath In-doped LT-AlGaN interlayer. The optimal parameters, such as TMIn flow rate, TMAl flow rates and thickness, are achieved to obtain nearly 2.0 mu m thick crack free GaN film with advanced optical and crystal properties. (c) 2005 Elsevier B.V. All rights reserved.

A passively mode-locked diode-end-pumped Nd : YAG laser with a semiconductor saturable absorber mirror grown by metal organic chemical vapour deposition

We report the experimental results of a mode-locked diode-end-pumped Nd:YAG laser with a semiconductor saturable absorber mirror (SESAM) from which we achieved a 10 ps pulse duration at 150 MHz repetition rate. The SESAM was grown by metal organic chemical vapour deposition at low temperature. The recovery time was measured to be 0.5 ps, indicating the potential pulse compression to sub-picoseconds.