Enhancement of the imprinting effect in cholesterol-imprinted microporous silica

A sol-gel method has been used to fabricate a cholesterol MIP for application in polar solutions. In this study, (cholesteryl propylcarbamate)triethoxysilane and tetraethyl orthosilicate were used as the hydrophobic monomer and crosslinker, respectively. The MIP had a larger pore volume when formation of the polymer was catalyzed at a higher pH than when it was formed at lower pH values, with the pore diameters being 3.5 nm and 2 nm, respectively for materials formed at high and low pH values. Both of these pore volumes were greater than those found for the respective control polymers formed without template. However, only the polymers formed at low pH values showed an imprinting effect. Compared with other methods explored, the sol-gel procedure gave only a small amount of non-specific binding for both the MIP and NIP when synthesized at low pH values. The largest imprinting-induced promotion of binding (IPB) value of the MIP (13 650%) was obtained with [HCl] = 0.01 M in the sol-gel solution. The MIP showed high selectivity towards cholesterol in comparison with other steroid hormones, and also to a lesser extent recognized vitamin D3 in methanol solution containing 5 vol.% water.     

MOVPE growth of single-crystal hexagonal AlN on cubic diamond

We have obtained single-crystal aluminum nitride (AlN) layers on diamond (1 1 1) substrates by metalorganic vapor-phase epitaxy (MOVPE). When the thermal cleaning temperature of the substrate and growth temperature of the AlN layer were below 1100 °C, the AlN layer had multi-domain structures mainly consisting of rotated domains. An interface layer, consisting of amorphous carbon and poly-crystal AlN, was formed between the AlN layer and the diamond substrate. On the other hand, when the thermal cleaning temperature and growth temperature were above 1200 °C, a single-crystal AlN layer was grown and no interface layer was formed. Therefore, we attribute the multi-domain structures to the interface layer. Even at the growth temperature of 1100 °C, by performing the thermal cleaning at 1200 °C, the single-crystal AlN layer was obtained, indicating that the thermal cleaning temperature of the substrate is a critical factor for the formation of the interface layer. The epitaxial relationship between the single-crystal AlN layer and the diamond (1 1 1) substrate was determined to be [0 0 0 1]_AlN∥[1 1 1]_diamond and [1 0 1¯ 0]_AlN∥[1 1¯ 0]_diamond. The AlN surface had Al polarity and no inversion domains were observed in the AlN layer.     

AlGaN epitaxial lateral overgrowth on Ti-evaporated GaN/sapphire substrate

AlGaN growth using epitaxial lateral overgrowth (ELO) by metalorganic chemical vapor deposition on striped Ti, evaporated GaN on sapphire, has been investigated. AlGaN/AlN films growth on GaN/AlGaN superlattices (SLs) structure on the Ti masks, with various SLs growth temperature (1030, 1060 and 1090 °C) were grown. With increasing the growth temperature, AlGaN surface became flat. The AlGaN film had a cathodoluminescence peak around 345 nm. However, in secondary ion mass spectrometry (SIMS) measurement, Ti signal was detected on the top of AlGaN surface when GaN/AlGaN SLs was grown on Ti striped masks. By inserting the AlN blocking layer on SLs, Ti diffusion was stopped at the AlN layer, and the AlGaN crystalline quality was improved.     

MOVPE growth of InN buffer layers on sapphire

We report on the MOCVD growth of InN buffer layers on sapphire substrate for InN growth. The approach used assumes that an optimized InN buffer layer has to exhibit at least the same crystalline quality and sapphire surface coverage than the GaN buffer layers allowing to grow high crystalline quality GaN on sapphire. The buffer layers were characterized by AFM and GID measurements. Sapphire nitridation was investigated: it has a strong influence on in-plane crystalline quality. Two kinds of buffer layers were optimized according to the GaN buffer layer specifications: one of them only presented In droplets at its surface. It was shown that the small amount of In droplets increases the adatoms mobility of the main layer overgrown, leading to a 25% decrease of its in-plane mosaicity, compared to InN films directly grown on sapphire. To achieve a same improvement on InN buffer layer free of In droplets, the InN main layer growth temperature had to be increased from 550 °C. to 600 °C.     

Development and properties of a glass made from MSWI bottom ash

A uniform shiny black-coloured glass was obtained using bottom ash produced by a Portuguese municipal solid waste incinerator (MSWI). The bottom ash was the single batch material used in the formation of the glass, which was obtained by vitrification of the solid waste at 1400 °C for 2 h. Under these conditions, a homogeneous melt with an appropriate viscosity to be shaped was obtained, indicating the suitability of this waste material to be employed in the development of vitreous products. The characterization of the resulting glass was performed in order to assess its structural, physical, mechanical, thermal and chemical features. The glass had a density of 2.69 g cm⁻³, a hardness of 5.5 GPa, a fracture strength of 75 MPa, a thermal expansion coefficient of 9.5 × 10⁻⁶ °C⁻¹ and it exhibited a very good chemical stability. In summary, the MSWI bottom ash glass has good mechanical and chemical properties and may, therefore, be used in several applications, particularly as a construction material.     

Synthesis and characterization of monolithic Gd2O3 aerogels

In this thesis, we will elaborate on the synthesis and characterization of monolithic Gd₂O₃ aerogel. We conducted the experiment in the following procedure. Use gadolinium nitrate or gadolinium chloride, a kind of inorganic gadolinium salt as raw material, and polymerize it in ethanol with propylene oxide as gelation initiator in the way of sol-gel. After this step, we can obtain the wet gel. Then, dry the wet gel by supercritical CO₂, at last we will get aerogel. The product has strong transparency and also shows some thermal stability. XRD characterization shows that it is amorphous. Nitrogen adsorption/desorption analysis tells clearly its surface area (223 m²/g), average pore diameters (42 nm) and large pore volume (1.83 ml/g). It is also characterized by transmission electron microscopy and high-resolution transmission electron microscopy.     

Mg segregation in a (1 1¯ 0 1) GaN grown on a 7° off-axis (0 0 1) Si substrate by MOVPE

Redistribution behavior of magnesium (Mg) in the N-terminated (1 1¯ 0 1) gallium nitride (GaN) has been investigated. A nominally undoped GaN layer was grown on a heavily Mg-doped GaN template by metalorganic vapor-phase epitaxy (MOVPE). Mg dopant profiles were measured by secondary ion mass spectrometry (SIMS) analysis. A slow decay of the Mg concentration was observed in the nominally undoped GaN layer due to the surface segregation. The calculated decay lengths of the (1 1¯ 0 1) GaN are ∼75–85 nm/decade. These values are shorter than the decay length determined in the sample grown on the Ga-terminated (0 0 0 1) GaN. This result indicates that Mg exhibited weak surface segregation in the (1 1¯ 0 1) GaN as compared to the (0 0 0 1) GaN. The weak surface segregation is in agreement with the high efficiency of Mg incorporation on the (1 1¯ 0 1) face. The high density of hydrogen was obtained in the (1 1¯ 0 1) GaN, which might enhance the Mg incorporation.     

Effects of temperature and carrier gas flow amount on the formation of GaN nanorods by the HVPE method

We fabricated one-dimensional GaN nanorods on AlN/Si (1 1 1) substrates at various temperatures, and carrier gas flow amount, using the hydride vapor phase epitaxy (HVPE) method. An AlN buffer layer of 50 nm thickness was deposited by RF sputtering for 25 min. Stalagmite-like GaN nanorods formed at a growth temperature of 650 °C. The diameters and lengths of GaN nanorods increase with growth time, whereas the density of nanorods decreases. And we performed the experiments by changing the carrier gas flow amount at a growth temperature of 650 °C and HCl:NH₃ flow ratio of 1:40. GaN nanorods, with an average diameter of 50 nm, were obtained at a carrier gas flow amount of 1340 sccm. The shape, structures, and optical characteristics of the nanorods were investigated by field-emission scanning electron microscopy, X-ray diffraction, and photoluminescence.     

Investigation of void formation beneath thin AlN layers by decomposition of sapphire substrates for self-separation of thick AlN layers grown by HVPE

Void formation at the interface between thick AlN layers and (0 0 0 1) sapphire substrates was investigated to form a predefined separation point of the thick AlN layers for the preparation of freestanding AlN substrates by hydride vapor phase epitaxy (HVPE). By heating 50–200 nm thick intermediate AlN layers above 1400 °C in a gas flow containing H₂ and NH₃, voids were formed beneath the AlN layers by the decomposition reaction of sapphire with hydrogen diffusing to the interface. The volume of the sapphire decomposed at the interface increased as the temperature and time of the heat treatment was increased and as the thickness of the AlN layer decreased. Thick AlN layers subsequently grown at 1450 °C after the formation of voids beneath the intermediate AlN layer with a thickness of 100 nm or above self-separated from the sapphire substrates during post-growth cooling with the aid of voids. The 79 μm thick freestanding AlN substrate obtained using a 200 nm thick intermediate AlN layer had a flat surface with no pits, high optical transparency at wavelengths above 208.1 nm, and a dislocation density of 1.5×10⁸ cm⁻².     

Synthesis and growth mechanism of rough PbTe polycrystalline thermoelectric nanorods

Rough PbTe polycrystalline one-dimensional nanostructure is expected to exhibit improved thermoelectric properties, compared to single-crystal one. In this article, polycrystalline PbTe thermoelectric nanorods with rough surfaces are successfully synthesized with or without surfactants by a simple alkaline reducing chemical route. Microstructural analyses show that these nanorods range from 50 to 200 nm in diameter with lengths up to 1 μm, and are composed of PbTe nanoparticles of about 30–50 nm. The formation mechanism of PbTe nanorods can be reasonably explained by tellurium template-based process from the time-dependent experiments.     

Preparation of a crack-free AlN template layer on sapphire substrate by hydride vapor-phase epitaxy at 1450 °C

A crack-free aluminum nitride (AlN) template layer was grown on a (0 0 0 1) sapphire substrate at 1450 °C using a thin (100 nm) protective AlN layer grown at 1065 °C by hydride vapor-phase epitaxy (HVPE). Full-width at half-maximum (FWHM) values of X-ray rocking curves (XRCs) for (0 0 0 2) and (1 0 1¯ 0) planes of the AlN layer were 378 and 580 arcsec, respectively. The formation of voids was observed at the interface between the thin protective AlN layer and the sapphire substrate due to decomposition reaction of sapphire during heating up to 1450 °C. The voids relaxed the tensile stress in the AlN layer, which resulted in the suppression of cracks.     

Influence of annealing on the physical properties of filtered vacuum arc deposited tin oxide thin films

Tin oxide (SnO₂) thin films were deposited on UV fused silica (UVFS) substrates using filtered vacuum arc deposition (FVAD). During deposition, the substrates were at room temperature (RT). As-deposited films were annealed at 400 and 600 °C in Ar for 30 min. The film structure, composition, and surface morphology were determined as function of the annealing temperature using X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The XRD patterns of the SnO₂ thin films deposited on substrates at RT indicated that the films were amorphous, however, after the annealing the film structure became polycrystalline. The grain size of the annealed films, obtained from the XRD analysis, increased with the annealing temperature, and it was in the range 8-34 nm. The AFM analysis of the surface revealed an increase in the film surface average grain size from 15 nm to 46 nm, and the surface roughness from 0.2 to 1.8 nm, as function of the annealing temperature. The average optical transmission of the films in the visible spectrum was >80%, and increased by the annealing ∼10%. The films’ optical constants in the 250-989 nm wavelength range were determined by variable angle spectroscopic ellipsometry (VASE). The refractive indexes of as-deposited and annealed films were in the range 1.83-2.23 and 1.85-2.3, respectively. The extinction coefficients, k(λ), of as-deposited and annealed films were in the range same range ∼0-0.5. The optical energy band gap (E_g), as determined by the dependence of the absorption coefficient on the photon energy at short wavelengths, increased with the annealing temperature from 3.90 to 4.35 eV. The lowest electrical resistivity of the as-deposited tin oxide films was 7.8 × 10⁻³ Ω cm, however, film annealing resulted in highly resistive films.     

Low-temperature/high-temperature AlN superlattice buffer layers for high-quality AlxGa1−xN on Si (1 1 1)

We present MOVPE-grown, high-quality Al_xGa_1−x N layers with Al content up to x=0.65 on Si (1 1 1) substrates. Crack-free layers with smooth surface and low defect density are obtained with optimized AlN-based seeding and buffer layers. High-temperature AlN seeding layers and (low temperature (LT)/high temperature (HT)) AlN-based superlattices (SLs) as buffer layers are efficient in reducing the dislocation density and in-plane residual strain. The crystalline quality of Al_xGa_1−xN was characterized by high-resolution X-ray diffraction (XRD). With optimized AlN-based seeding and SL buffer layers, best ω-FWHMs of the (0 0 0 2) reflection of 540 and 1400 arcsec for the (1 0 1¯ 0) reflection were achieved for a ∼1-μm-thick Al_0.1Ga_0.9N layer and 1010 and 1560 arcsec for the (0 0 0 2) and (1 0 1¯ 0) reflection of a ∼500-nm-thick Al_0.65Ga_0.35N layer. AFM and FE-SEM measurements were used to study the surface morphology and TEM cross-section measurements to determine the dislocation behaviour. With a high crystalline quality and good optical properties, Al_xGa_1−x N layers can be applied to grow electronic and optoelectronic device structures on silicon substrates in further investigations.     

Heteroepitaxial growth of InN layers on (1 1 1) silicon substrates

Indium nitride (InN) layers were grown on (1 1 1) silicon substrates by reactive magnetron sputtering using an indium target. Atomic force microscope, X-ray diffraction, and Raman spectroscopy analysis revealed that highly c-axis preferred wurtzite InN layers with very smooth surface can be obtained on (1 1 1) silicon substrates at a substrate temperature as low as 100 °C. The results indicate that the reactive sputtering is a promising growth technique for obtaining InN layers on silicon substrates at low substrate temperature with low cost and good compatibility with microelectronic silicon-based devices.     

Preparation of amorphous composites with polymer-derived silicon nitride matrix reinforced by three-dimensional silica fiber

Perhydropolysilazane, a low viscosity preceramic polymer with good infiltration efficiency and high char yield, was used to prepare amorphous composites with polymer-derived silicon nitride matrix reinforced by three-dimensional silica fiber, and the mechanical properties and microstructures were investigated. The composites without fiber coating showed a typical brittle fracture behavior with a smooth fracture surface, and a flexural strength of just 33.5 MPa. While the composites with fiber coating exhibited a non-brittle fracture behavior with distinct fiber pull-out in the fracture surface, and a high flexural strength of 144.9 MPa. It was the controlled fiber/matrix interface by precoating treatment that contributed to the high mechanical property of the composites.     

Growth and characterization of GaAs layers on polished Ge/Si by selective aspect ratio trapping

Epitaxial GaAs layers have been deposited on polished Ge film grown on exactly (0 0 1) oriented Si substrate by metal-organic chemical vapor deposition (MOCVD) via aspect ratio trapping (ART) method. Double-crystal X-ray diffraction shows that the full-width at half-maximum (FWHM) of the (4 0 0) reflection obtained from 1 μm GaAs is 140 arcsec. Scanning electron microscopy (SEM) of the GaAs layer surface shows that the amount of antiphase domain defects (APD) raised from GaAs/Ge interface using Ge ART on Si is dramatically reduced compared to GaAs layers grown on exact (0 0 1) Ge substrate. Defect reduction and Ge diffusion at vicinal GaAs/Ge interface were investigated via cross-section transmission electron microscopy (X-TEM) and secondary ion mass spectrometry (SIMS). Film morphology and optical properties were evaluated via SEM and room temperature photoluminescence (PL).     

Ordered arrays of high-quality single-crystalline α-Si3N4 nanowires: Synthesis,properties and applications

Ordered arrays of high-quality single-crystalline α-Si₃N₄ nanowires (NWs) have been synthesized via thermal evaporation and detailed characteristics of the NWs have been analyzed by employing scanning electron microscope (SEM) along with energy dispersive spectroscopy (EDS), high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photospectroscopy (XPS), infrared (IR), photoluminescence (PL) and in situ I–V measurements by STM/TEM holder. The microscopic results revealed that the NWs having diameter in the range of ~30–100 nm and length in microns. Furthermore, the NWs are found to be single crystalline grown along [0 0 1] direction. The elemental composition and valence states of elements are analyzed by EDS and XPS. The room temperature PL spectra exhibit a broad range visible emission band. The electron transport property of a single NW illustrates the symmetric I–V curve of a semiconductor. The possible growth mechanism is also briefly discussed.     

Synthesis and characterization of SiO2-PEG hybrid materials

Sol-gel is a promising technique for the synthesis of organic-inorganic hybrid materials both of class I and II. In materials of class I organic molecules are physically entrapped in an inorganic matrix, while in those of class II organic and inorganic parts are connected by covalent bonds. In this paper a sol-gel procedure to obtain SiO₂-PEG hybrids of class I, in which PEG is simply mixed at the sol stage, is compared to a sol-gel procedure to obtain SiO₂-PEG hybrid materials of class II, where a particular sol-gel Si-C precursor is synthesized. XPS analyses showed the different distribution of the organic phase in the SiO₂ matrix and the bond between PEG and SiO₂ for hybrids of class II. The PEG molecule in hybrid of class II showed an enhanced thermal stability up to 350 °C. Doping with a lithium salt was performed on hybrids of class II, and the ionic conductivity was measured.     

Growth and characterization of c-plane AlGaN on γ-LiAlO2

This study demonstrates a pure c-plane AlGaN epilayer grown on a γ-LiAlO₂ (1 0 0) (LAO) substrate with an AlN nucleation layer grown at a relatively low temperature (LT-AlN) by metal-organic chemical vapor deposition (MOCVD). The AlGaN film forms polycrystalline film with m- and c-plane when the nucleation layer grows at a temperature ranging from 660 to 680 °C. However, a pure c-plane AlGaN film with an Al content of approximately 20% can be obtained by increasing the LT-AlN nucleation layer growth temperature to 700 °C. This is because the nuclei density of AlN increases as the growth temperature increases, and a higher nuclei density of AlN deposited on LAO substrate helps prevent the deposition of m-plane AlGaN. Therefore, high-quality and crack-free AlGaN films can be obtained with a (0 0 0 2) ω-rocking curve FWHM of 547 arcsec and surface roughness of 0.79 nm (root-mean-square) using a 700-°C-grown LT-AlN nucleation layer.     

Fluorinated nanoporous SiO2 films with ultra-low dielectric constant

Fluorinated nanoporous silica (denoted as SiO₂:F) thin films with low dielectric constant were prepared by a sol-gel method and spin coating technique. The leakage current densities of the SiO₂:F thin films were 10⁻⁸ and 3 × 10⁻⁶ A/cm² respectively for the as-deposited films and for those subjected to annealing at a temperature of 450 °C. These currents are more than one order of magnitude lower than those of the common SiO₂ films. Photoluminescent results showed strong blue-light emission and a small blue shift in the SiO₂:F films that were related to the increment of the porosity. The dielectric properties were also characterized and the k value of the annealed SiO₂:F film was found to be about 1.67. The hole size in the films is small and the size distribution is uniform for the annealed SiO₂:F samples due to the effects of fluorination. The underlying mechanism for fluorination is discussed in this paper.