Growth of SiC nanowires and nanocones using mixture of oil palm fibres and rice husk ash

3C-SiC nanowires and nanocones were grown by pyrolysing mixture of acid-treated oil palm empty fruit bunch fibres and rice husk ash (RHA), which acted as carbon and silicon source, respectively. The effects of different RHA amounts and pyrolysis temperature were studied. When the amount of RHA was increased to 80 % of the mixture, there was a change in the morphology from nanowires to nanocones. Overall, it was found that 40 % of RHA in the mixture was the ideal amount in growing the nanowires with the maximum yield and with the least amount of impurities. When the pyrolysis temperature was raised, there was an increase in the amount, diameter and length of the nanowires. The proposed main growth mechanism for the SiC nanowires were combination of solid-state reaction and vapour–solid mechanisms, with some nanowires grown under vapour–liquid–solid (VLS) mechanism induced by trace metals as well. The growth of the nanocones could also be related to VLS mechanism.     

AlN晶须的形貌及取向

利用VLS法制备了AlN晶须,观察了诸如生长“小山”、堆垛等各种晶须形态．对AlN晶须的取向进行了研究,发现了一些不同于密排面的生长面,诸如{101n}（n＝1,2,3）．对AlN晶须的生长机制进行了初步探索,验证了螺旋位猪生长机制,并提出了斜生长机制,从而解释了VLS法制备的AlN晶须无[0001]取向的问题     

Formation of MgO whiskers on the surface of bulk MgB<Subscript>2</Subscript> superconductors during in situ sintering

Magnesium oxide (MgO) whiskers (with diameters of about 60–80 nm) formed on the surface of bulk polycrystalline MgB₂ superconductor at a relative low temperature (720 °C) during in situ sintering process. The reaction between Mg and B powders begins at a temperature below melting point of Mg and maintains till about 750 °C. The residual Mg powders evaporate and react with trace oxygen to form MgO vapor as the temperature exceeds the melting temperature of Mg and a low supersaturation is required for the growth of MgO whiskers. The preformed MgB₂ and MgO crystals act as substrates and the melted Mg powders on the surface of them serve as catalysts during the growth process of MgO whiskers. The growth process of MgO whiskers is dominated by a self-catalytic vapor–liquid–solid (VLS) mechanism.     

Synthesis and investigation of optical properties of ZnS nanostructures

Structural characterizations of wurtzite zinc sulfide (ZnS) nanostructures synthesized by vapour–liquid–solid technique (VLS) were carried out by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses. Spectral dependence of photoluminescence (PL) was also carried out for optical characterization. PL results indicate that the bandgap energy of bulk ZnS which is 3·68 eV at room temperature changes from 3·7 eV to 3·72 eV depending on the size of the structures. We also supported these results by calculating the bandgap energies theoretically with using the infinite potential well approximation for 1D structures.     

Combustion synthesis of AlN whiskers

Long and coarse AlN whiskers comprising more than 80 vol% of the combustion product have been successfully produced through combustion synthesis. Addition of ammonia halides can accelerate the vaporization of Al, and retard the deposition rate of AlN, with the result that the growth of AlN whiskers is markedly promoted. A growth model for a spiral whisker by a helical screw dislocation mechanism, or a combination mechanism of a helical screw dislocation and the VLS process, is proposed. Periodic interactions of vacancies and the tip of a screw dislocation cause the growth of a spiral whisker in the model. Under an atmosphere of supersaturated “AlN vapor,” the growth of whiskers along the axial direction slows down and gradually arrests, due to the limitation of the diffusion distance. A series of deposition sites are then produced at regular, isolated locations along the center line on the prismatic plane, and eventually cause the formation of dendritic whiskers.     

Cathodoluminescence study of Te-doped ZnO microstructures grown by a vapour–solid process

Sintering of a mixture of TeO₂ and ZnO powders under an Ar flux leads to the formation of elongated Te-doped ZnO nano- and microstructures on the sample surface. The growth of the structures occurs via a vapour–solid process. Cathodoluminescence (CL) and energy dispersive spectroscopy (EDS) measurements show an inhomogeneous incorporation of Te along the growth axis of the structures. An enhancement of the band edge emission upon Te doping is attributed to the passivation of oxygen vacancies by Te atoms, which reduces the deep energy level-related recombination path.     

Structure characteristics of AlN whiskers fabricated by the carbo-thermal reduction method

With Al2O3 and graphite as raw materials, CaF2 and B2O3 as additives, AlN whiskers were fabricated by a carbo-thermal reduction method. The fabrication mechanism and growth characteristics of AlN whiskers were investigated. At the beginning of the high-temperature fabrication, AlN whiskers grew by the vapour/liquid/solid (VLS) mechanism, and defects existed on the surfaces of the whiskers. In later stages, the VLS mechanism possibly changed to a vapour/solid (VS) mechanism, and the defects disappeared. The orientation of most AlN whiskers was normal to (n=0, 1, 2, 3), and normal to (n=0, 1, 2). The growth processes of both two-dimensional nucleation and screw dislocations existed at the same time. © 1998 Kluwer Academic Publishers     

Vapour–liquid–solid growth of TiB2 whiskers

Whiskers of TiB₂ have been synthesised via a carbothermal vapour–liquid–solid (VLS) growth mechanism. The whisker growth was investigated in the temperature region 1100–1800°C in argon. The best result was obtained with a starting mixture of TiO₂:B₂O₃:C:NaCl:Ni in the molar ratios 1:1:6:0.25:0.1 at 1500°C. Thermogravimetric analyses and mass-spectroscopy measurements were used in studying the whisker growth. The obtained TiB₂ whiskers are 0.5–2 m in diameter and 10–50 m in length. TEM studies of the whiskers showed that the dominating growth direction is temperature dependent.     

Growth mechanism and multiphoton-induced photoluminescence of crownlike zinc oxide

A crownlike zinc oxide crystal composed of a hexagonal cap and a towerlike shaft was synthesized by vapor-phase transport method. Based on vapor–liquid–solid and vapor–solid mechanism, the growth model of the crystal was proposed. Under the excitation of pulse laser with 1150-nm wavelength, strong ultraviolet emission at 388 nm was observed. The peak position and the relationship between the emission intensity and excitation intensity demonstrated that the ultraviolet photoluminescence was induced by three-photon absorption. The photoluminescence characteristic of the sample was investigated.     

Morphologies and growth mechanisms of aluminum nitride whiskers by SHS method—Part I

AlN whiskers grown by combustion of Al powder under high nitrogen pressure were investigated. Several types of whiskers' structures, such as wavy structure, crossed structure, stack structure, bead-necklace structure, branch structure, dendritic crystal, were found due to the variation of growth conditions. The causes of some structures were explained.     

Morphologies and growth mechanisms of aluminum nitride whiskers by SHS method—Part 2

The high resolution electron microscopy was used to investigate the microstructure of AlN whiskers. The growth mechanisms of AlN whiskers were VLS and VS mechanism. The phenomenon of stacking fault was analyzed. Moreover, the growth mechanism of dendritic crystal was proposed.     

Properties of a carbon woven fabric filter grown SiC whisker by chemical vapor infiltration

β-silicon carbide whiskers were synthesized on a carbon fabric using a vapor–solid (VS) mechanism. The morphologies of the SiC deposits changed as deposition time increased. Pore size distribution and mean pore size of the fabric filter was reduced by whisker growth. A particle-trapping test was conducted to examine the efficiency of the filter. Then, the size of the particles infiltrated within the filter was analyzed. The maximum increase rate of the particle trap rate was 136.6% by whisker growth. The fine particles ranged from 550 to 800 nm and could be trapped by forming whiskers on the carbon filaments of the fabric filter. The carbon fabric filter’s gas permeability is 6 times higher than conventional honeycomb filters.     

Synthesis of TiC Whiskers through Carbothermal Reduction of TiO2

TiC whiskers were produced through carbothermal reduction of TiO₂ in the presence of potassium (K₂CO₃) and nickel (NiCl₂). The effect of potassium, nickel, and heating rate on the formation of whiskers was studied. Potassium was found to be an essential constituent for whisker formation. Nickel acts as a catalyst for TiC whisker formation only in the presence of potassium. The yield of whiskers was maximum at 1000–1200°C. At higher temperatures, formation of particulates of TiC was the dominant process. An increase in K₂CO₃ concentration during fast heating and decrease in K₂CO₃ concentration during slow heating was found to be beneficial in increasing the formation of TiC whiskers. A vapor–liquid–solid growth mechanism of whisker formation was explained.     

Aluminum nitride on silicon: Role of silicon carbide interlayer and chloride vapor-phase epitaxy technology

A new approach to the deposition of aluminum nitride (AlN) layers with thicknesses ranging within ∼0.1–10 μm on silicon single crystal substrates by hydride-chloride vapor-phase epitaxy (HVPE) has been developed and implemented, which involves the formation of thin (∼100-nm-thick) intermediate silicon carbide (3C-SiC) interlayers. It is established that wavy convex bands with a height of about 40 nm are present on the surface of as-grown AlN layers, which are situated at the boundaries of blocks in the layer structure. It is suggested that the formation of these wavy structures is related to morphological instability that develops due to accelerated growth of AlN at the block boundaries. Experiments show that, at low deposition rates, AlN layers grow according to a layer (quasi-two-dimensional) mechanism, which allows AlN layers characterized by half-widths (FWHM) of the X-ray rocking curves of (0002) reflections about ω_θ = 2100 arc sec to be obtained.     

Liquid–solid interfacial reactions of Sn–Ag and Sn–Ag–In solders with Cu under bump metallization

Intermetallic compounds formed during the liquid–solid interfacial reaction of Sn–Ag and Sn–Ag–In solder bumps on Cu under bump metallization at temperatures ranging from 240 to 300 °C were investigated. Two types of intermetallic compounds layer, η Cu₆Sn₅ type and ε Cu₃Sn type, were formed between solder and Cu. It was found that indium addition was effective in suppressing the formation of large Ag₃Sn plate in Sn–Ag solder. During interfacial reaction, Cu consumption rate was mainly influenced by superheat of solder, contact area between solder and Cu and morphology of intermetallic compounds. The growth of η intermetallic compounds was governed by a kinetic relation: ΔX = tⁿ, where the exponent n values for Sn–Ag/Cu and Sn–Ag–In/Cu samples at 240 °C were 0.35 ± 0.01 and 0.34 ± 0.02, respectively. The n values increased with reaction temperature, and it was higher for Sn–Ag/Cu than that for Sn–Ag–In/Cu sample at the same temperature. After Cu was exhausted, ε intermetallic compound was converted to η intermetallic compound. The mechanisms for such growth of interfacial intermetallic compounds during the liquid–solid reaction were investigated.     

Plasma-plasmonics synergy in the Ga-catalyzed growth of Si-nanowires

This paper reports on the growth of Si nanowires (NWs) by SiH₄/H₂ plasmas using the non-noble Ga-nanoparticles (NPs) catalysts. A comparative investigation of conventional Si-NWs vapour–liquid–solid (VLS) growth catalyzed by Au NPs is also reported. We investigate the use of a hydrogen plasma and of a SiH₄/H₂ plasma for removing Ga oxide shell and for enhancing the Si dissolution into the catalyst, respectively. By exploiting the Ga NPs surface plasmon resonance (SPR) sensitivity to their surface chemistry, the SPR characteristic of Ga NPs has been monitored by real time spectroscopic ellipsometry in order to control the hydrogen plasma/Ga NPs interaction and the involved processes (oxide removal and NPs dissolution by volatile gallium hydride). Using in situ laser reflectance interferometry the metal catalyzed Si NWs growth process has been investigated to find the effect of the plasma activation on the growth kinetics. The role of atomic hydrogen in the NWs growth mechanism and, in particular, in the SiH₄ dissolution into the catalysts, is discussed. We show that while Au catalysts because of the re-aggregation of NPs yields NWs that do not correspond to the original size of the Au NPs catalyst, the NWs grown by the Ga catalyst retains the diameter dictated by the size of the Ga NPs. Therefore, the advantage of Ga NPs as catalysts for controlling NWs diameter is demonstrated.     

On the growth mechanism of silicon carbide whiskers

The microstructure of SiC whiskers has been studied through analytical electron microscopy. The whiskers were found to contain discrete regions of high and low planar defect density. These regions of low defect density were identified as 3C beta-SiC, whereas the regions of high defect density were consistent with a mixture of SiC polytypes, with the 3C and the 6H polytypes being the most predominant as a result of the formation of a high density of microtwins on the (1 1 1) planes perpendicular to the 〈1 1 1〉 growth direction. A growth mechanism is suggested based on observations of (a) outer layers of SiC on vapour-liquid-solid catalysts and (b) C∶Si variations between the regions of high and low densities of planar defects. It appears that there is some degree of stoichiometric control over the microstructure of the SiC whiskers in that slight carbon enrichments seem to promote the growth of relatively defect-free regions of beta-SiC whiskers.     

Role of Surface Energy in the Vapor–Liquid–Solid Growth of Silicon

The conditions of vapor-phase Si whisker growth are examined, and the role of the surface Gibbs energy in the vapor–liquid–solid process is evaluated. The mechanism responsible for the catalytic activity of the liquid phase on the tip of Si whiskers is elucidated. Experimental surface tension data are used to estimate the driving force acting on the three-phase line of contact upon a displacement of the liquid droplet in the course of whisker growth.     

Synthesis and formation of alumina whiskers from hydrothermal solution

Al₂O₃ whiskers with an average length of 5 μm have been synthesized from hydrothermal solution. Al(NO₃)₃ and urea were mixed and put into a Teflon-lined stainless steel autoclave and then treated at 120 °C to fabricate precursor whiskers NH₄Al(OH)₂CO₃ (AACH). AACH whiskers were heated at 1200 °C in a furnace to obtain Al₂O₃ whiskers. The time-dependent examinations revealed that the formation process of AACH whiskers involves two sequential processes: a short liquid–solid deposition process in the initial stage and a long Ostwald ripening process. During calcinations, AACH transforms to amorphism then to α-Al₂O₃. The escape of NH₃ and CO₂ induced the distortion and toothlike morphology on the surface of the Al₂O₃ whiskers.     

Ultra-sharp pointed tip Si nanowires produced by very high frequency plasma enhanced chemical vapor deposition via VLS mechanism

Needle-like silicon nanowires have been grown using gold colloid as the catalyst and silane (SiH₄) as the precursor by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Si nanowires produced by this method were unique with sharpness below 3 nm. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction technique (XRD) confirmed the single crystalline growth of the Si nanowires with (111) crystalline structure. Raman spectroscopy also has revealed the presence of crystalline Si in the grown Si nanowire body. In this research, presence of a gold nanoparticle on tip of the nanowires proved vapor–liquid–solid growth mechanism.