Sintering of ZnO pressed powder under Ar flow at temperatures between 1250 and 1300 °C leads to the formation of elongated microstructures and nanostructures, with different morphologies, on the sample surface. Rods and needles with cross-sectional dimensions ranging from tens of nanometres to several tens of microns and up to hundreds of microns in length are obtained. In an advanced stage of growth, nanoneedles are frequently arranged in bundles, forming the walls of tubes with different cross-sectional dimensions. In addition, microcombs and microfeathers consisting of well oriented nanoneedles are observed. Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to characterize the structures grown. The formation of the elongated structures causes spectral changes, in particular an enhancement of the green–orange luminescence. High CL emission from the internal surface of the tubes has been observed.
A novel method of etching channels in glass microchips with the most tunable solvent, water, was tested as an alternative to common hydrogen fluoride-containing etchants. The etching properties of water strongly depend on temperature and pressure, especially in the vicinity of the water critical point. The chips were etched at the subcritical, supercritical and critical temperature of water, and the resulting channel shape, width, depth and surface morphology were studied by scanning electron microscopy and 3D laser profilometry. Channels etched with the hot water were compared with the chips etched with standard hydrogen fluoride-containing solution. Depending on the water pressure and temperature, the silicate dissolved from the glass could be re-deposited on the channel surface. This interesting phenomenon is described together with the conditions necessary for its utilization. The results illustrate the versatility of pure water as a glass etching and surface morphing agent.
photodiodes (Ho et al., 1995) or nuclear particle detector structures (Procházková et al., 2005a), where high electron and hole drift velocities are appreciated. Main ObjectivesRecently, we have performed a unique study of the impact of REs (Tb, Dy, Pr, Tm, Er, Gd, Nd, Lu, Ce) and their oxides (PrO x , TbO x , Tm 2 O 3 , Gd 2 O 3 , Eu 2 O 3 ) on the properties of InP layers (Procházková et al., 2002; Procházková et al., 2005a;Grym et al., 2009).This study was motivated by the lack of systematic research in the field of liquid phase epitaxy (LPE) grown III-V semiconductors from RE treated melts.REs open the door for the preparation of high purity III-V layers without extended baking of the melts or other complicated and time consuming methods.In this chapter we cover the following topics:-Short introduction to LPE.-Discussion of the behaviour of REs in the liquid and solid phase during LPE, their incorporation and gettering.-Comparison of the behaviour of different RE species in the growth process of InP layers, their structural, electrical, and optical properties.InP has been chosen as a simple binary system to perform this investigation.-Preparation of p-type InP layers, which have not been systematically investigated by other groups.Detailed description of the gettering phenomenon will be given together with the explanation of the conductivity conversion from n to p-type. www.intechopen.comRole of rare-earth elements in the technology of III-V semiconductors prepared by liquid phase epitaxy 297 beam epitaxy (MBE) or metal organic vapour phase deposition (MOVPE) (Capper & Mauk, 2007).LPE has nearly disappeared from universities so that the know-how exists in the industry only and papers on LPE are scarce.Still, lots of niches in semiconductor technology remain to be served by LPE.We believe that LPE growth from RE treated melts is one of them.LPE growth is typically carried out from supersaturated solutions composed of source materials in a graphite boat.The boat is placed in a quartz reactor tube in the atmosphere of high purity hydrogen.There are several sources of impurities that may be introduced into the grown layer (Dhar, 2005):-Source materials and chemicals to clean them.-Parts of the graphite boat being in contact with the growth solution.-Contaminants deposited on the inner wall of the quartz reactor tube.These contaminants can be transported to the solution by the ambient gas during high temperature growth.-The carrier hydrogen gas itself.-Tools and containers for storing, handling, and cleaning the substrate and source materials.Several procedures help to prevent these impurities to be incorporated into the layer being grown.The materials for growth are of a high purity level.At present, indium is available at 6N or even 7N purity, REs typically at 3N but recently some of their oxides up to 4N+ purity.These materials, before loading into the growth boat, are thoroughly cleaned to remove the contaminated surface.The graphite boat is made of ultra high purity graphite with low porosity.The reactor tube is made of high quality quartz and the inside wall is periodically cleaned and baked-out at high temperatures.High-purity hydrogen generator or palladium diffusion cell is used to guarantee high purity hydrogen flow.Typical LPE InP layers grown under these conditions posses electron concentrations above 10 17 cm -3 at room temperature.In addition to the above self-evident precautions, there are several methods to suppress residual impurity concentrations (Rhee & Bhattacharya, 1983;Kumar et al., 1995):-Prolonged baking of the growth solution above the growth temperature.A long bake-out under the dry hydrogen atmosphere leads to the removal of volatile impurities such as Zn, Mg, Cd, Te, and Se from the In melt by the evaporation.However, S is only partly removed due to the formation of In-S compounds and Si remains due to its low vapour pressure.-Introduction of controlled amounts of H 2 O in the growth ambient.Si is oxidized and thus prevented from being incorporated into the epitaxial layer in the electrically active form.However, this method can lead to inferior surface morphology and creation of oxygen-related traps.-Extended prebaking of the melt can be alternatively realized in high vacuum generally leading to suppressed S concentrations.-Other improvements including growth in PH 3 atmosphere or use of dummy substrates as the source material.-And finally, the addition of REs acting as effective gettering agents.www.intechopen.
A new concept for electrospray coupling of microfluidic devices with mass spectrometry was developed. The sampling orifice of the time-of-flight mass spectrometer was modified with an external adapter assisting in formation and transport of the electrosprayed plume from the multichannel polycarbonate microdevice. The compact disk sized microdevice was designed with radial channels extending to the circumference of the disk. The electrospray exit ports were formed by the channel openings on the surface of the disk rim. No additional tips at the channel exits were used. Electrospray was initiated directly from the channel openings by applying high voltage between sample wells and the entrance of the external adapter. The formation of the spatially unstable droplet at the electrospray openings was eliminated by air suction provided by a pump connected to the external adapter. Compared with the air intake through the original mass spectrometer sampling orifice, more than an order of magnitude higher flow rate was achieved for efficient transport of the electrospray plume into the mass spectrometer. Additional experiments with electric potentials applied between the entrance sections of the external adapter and the mass spectrometer indicated that the air flow was the dominant transport mechanism. Basic properties of the system were tested using mathematical modeling and characterized using ESI/TOF-MS measurements of peptide and protein samples.
One of the important questions about understanding the principle mechanisms of electrophoretic deposition in nonpolar systems is to identify the origin of electric charge carried by nanoparticles. We developed a simple model of nanoparticle charging and we explained how the amount of the charge carried by nanoparticles can affect the quality of deposited monolayers. We used the centrifugation of Pt nanoparticles in water-AOT-isooctane reverse micellar system for controlling the charge carried by Pt nanoparticles.
Current–voltage characteristics of rectifying graphite/SiC junctions are investigated in a wide temperature range. The main parameters of the diodes, the ideality factor, and the Schottky barrier height show strong temperature dependence. Such behavior is interpreted on the basis of standard thermionic emission theory assuming Gaussian distribution of the barrier heights due to inhomogeneity at the graphite/SiC interface.
The influence of Yb and Yb 2 O 3 addition on the properties of InP epitaxial layers is reported. We concentrated on the investigation of gettering and/or doping efficiency of Yb added in various forms. Layers prepared by Liquid Phase Epitaxy were examined by using SEM, SIMS, low temperature PL spectroscopy, C-V and temperature dependent Hall measurements. The efficient gettering was confirmed for both Yb and Yb 2 O 3 addition into the growth melt; doping effect, i.e. incorporation of Yb 3+ into InP lattice was confirmed only for Yb addition. Dominant acceptor, responsible for n→p conductivity conversion was identified as isoelectronic Yb impurity on the In site.
