Vapor-phase Transport Method Research Articles

On the synthesis of AlPO4-21 molecular sieve by vapor phase transport method and its phase transformation to AlPO4-15 molecular sieve

An experimental design was applied to the synthesis of AlPO4-21 molecular sieve (AWO structure) by vapor phase transport (VPT) method, using tetramethylguanidine (TMG) as the template. In this study, the effects of crystallization time, crystallization temperature, phosphor content, template content and water content in the synthesis gel were investigated. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy and fourier transform infrared spectroscopy (FT-IR). Microstructural analysis of the crystal growth in vapor synthetic conditions revealed a revised crystal growth route from zeolite AlPO4-21 to AlPO4-15 in the presence of the TMG. Homogenous hexagonal prism AlPO4-21 crystals with size of 7 × 3 μm were synthesized at a lower temperature (120 °C), which were completely different from the typical tabular parallelogram crystallization microstructure of AlPO4-21 phase. The crystals were transformed into AlPO4-21 phase with higher crystallization temperature, longer crystallization time, higher P2O5/Al2O3 ratio and higher TMG/Al2O3 ratio.

Room temperature H2S gas sensor based on rather aligned ZnO nanorods with flower-like structures

Rather vertically aligned ZnO rods with flower-like structures were grown on quartz substrates through vapor phase transport method. X-ray diffraction (XRD) analysis and photoluminescence (PL) measurement were performed to determine crystalline structure and defects, respectively. H2S gas sensing properties of the grown structure were investigated at both room temperature and 250°C for comparison. A remarkable increase in response and selectivity at room temperature compared to 250°C was observed. High response and selectivity to low concentrations of H2S at room temperature as well as good stability make the sensor a promising candidate for practical applications.

Doped ZnO 1D nanostructures: synthesis, properties, and photodetector application.

In the past decades, the doping of ZnO one-dimensional nanostructures has attracted a great deal of attention due to the variety of possible morphologies, large surface-to-volume ratios, simple and low cost processing, and excellent physical properties for fabricating high-performance electronic, magnetic, and optoelectronic devices. This article mainly concentrates on recent advances regarding the doping of ZnO one-dimensional nanostructures, including a brief overview of the vapor phase transport method and hydrothermal method, as well as the fabrication process for photodetectors. The dopant elements include B, Al, Ga, In, N, P, As, Sb, Ag, Cu, Ti, Na, K, Li, La, C, F, Cl, H, Mg, Mn, S, and Sn. The various dopants which act as acceptors or donors to realize either p-type or n-type are discussed. Doping to alter optical properties is also considered. Lastly, the perspectives and future research outlook of doped ZnO nanostructures are summarized.

Localized surface plasmon resonance enhanced ultraviolet emission and F-P lasing from single ZnO microflower

In this work, monodispersed ZnO microflowers are fabricated by a vapor phase transport method, and Au nanoparticles (NPs) are directly decorated on the surface of the ZnO microflowers. The micro-photoluminescence of a single ZnO microflower demonstrates that the near band-edge emission is tremendously enhanced while the defect-related emission is completely suppressed after Au decoration. The average enhancement factor reaches up to 65 fold. The enhancement mechanism is assumed to be the electron transfer from excited Au NPs to the ZnO microflower induced by the localized surface plasmon resonance based on the time-resolved photoluminescence. The enhanced F-P lasing from a single ZnO sample is further realized.

Microwave-Assisted Synthesis and Permeation Performance of NaA Zeolite Membrane by Secondary Growth Method

The highly intergrown NaA zeolite membranes on seeded α-Al2O3substrate were synthesized by microwave heating method. The preparation of seeds with the size of ca.120nm employed the vapor phase transport method (VPT). The XRD patterns indicated that the pure NaA zeolite membranes formed on the seeded α-Al2O3substrate for varied synthesis times. However, the peak intensity of NaA zeolite membrane with synthesis time of 50min obviously decreased, suggesting that the NaA membrane could take place the dissolution at that time. The SEM images indicated that the NaA zeolite membranes with synthesis time of 15-30min had a good integrity and consisted of highly intergrown zeolite crystals, but the NaA membrane with synthesis time of 50min appeared some large defects, further verifying the result of XRD pattern. The gas permeability showed that the maximum of H2/N2and H2/C3H8permselectivities attained 4.23 and 8.24, respectively, higher than those of the corresponding Knudsen diffusion. These results suggested that the diffusion of gases, at least in part, are affected by the pore size of zeolite and the function of molecular sieving can be embodied on the synthesized membrane.

Hollow SAPO-34 Cubes with Hierarchically Organized Internal Structure

We herein report novel hollow SAPO-34 cubes with a hierarchical internal structure. They are prepared from dry gels containing gelatin by a vapor-phase transport method. Microscopic characterization reveals that the cubes are constructed by symmetrically packed four two-top-point truncated octahedrons encapsulated by dense crystalline shells, exhibiting a structure-in-structure formation. The cubes show either +-shaped or the butterfly like X-shaped black spots on their faces under light. Investigation of the formation process of the hollow SAPO-34 cubes demonstrates a surface to core crystal growth route, which has not been found in vapor-phase transport synthesis of zeolites. A possible formation mechanism is proposed.

Photoluminescence and Two-Photon Lasing of ZnO:Sn Microdisks

ZnO:Sn microdisks were fabricated by a vapor phase transport method at different pressure conditions. The photoluminescence of the ZnO:Sn microdisks was measured, and the origination of defect emission was attributed to the oxygen vacancy defects. Under the excitation of the 532 nm line of a femtosecond pulsed laser, two-photon absorption induced UV amplified spontaneous emission and whispering-gallery mode lasing were observed from the ZnO:Sn microdisks. The electron–hole plasma induced red-shift and broadening of the amplified spontaneous emission and lasing emission were demonstrated when the excitation power was increased. In addition, the WGM lasing light distribution was simulated by a numerical method.

Comparative study of the grown ZnO nanostructures on quartz and alumina substrates by vapor phase transport method without catalyst: Synthesis and acetone sensing properties

Uniform layers of ZnO nanostructures were formed on quartz and alumina substrates through a simple vapor phase transport (VPT) method without any catalyst or buffer layer by making proper growth conditions. The effect of substrate on morphology, crystalline structure and photoluminescence spectra has been investigated. Scanning electron microscopy images revealed that morphlogical grwoth depends on used substrate, aligned rods with flower-like bundels and entangled rods are vertically aligned rods on the quartz and alumina substrates, respectively. X-ray diffraction studies showed that grown films on the quartz substrates possess stronger c-axis orientation compared to those on the alumina ones. Consequently, growth mechanism is discussed and illustrated schematically. Acetone sensing measurements indicated that the oriented rods on the quartz substrates have better sensing properties than entangled ones on the alumina substrates.

Ultraviolet microphotoluminescence resonance and lasing action in a single ZnO micro-tetrapod

ZnO micro-tetrapod microstructures were fabricated by a vapor phase transport method. Under the excitation of 325nm continuous wave He–Cd laser, the microphotoluminescence spectrum from a single ZnO micro-tetrapod presented a two-band structure with a series of optical resonance modes; a possible optical resonance loop formed in two adjacent legs of the tetrapod was suggested, and the two-band spectrum structure was attributed to the exciton–exciton scattering process. The lasing emission was obtained from single ZnO micro-tetrapod under intense excitation of 355nm nanosecond pulsed laser. The lasing spectrum shows clear mode structure with the lasing quality factor of 1300 and the lasing threshold of 150kW/cm2. The microphotoluminescence resonance and lasing results indicate that ZnO tetrapod can serve as a high-Q ultraviolet microcavity laser.

Highly Sensitive $\beta{-}{\rm Ga}_{2}{\rm O}_{3}$ Nanowire Nanowires Isopropyl Alcohol Sensor

We report the growth of β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanowires using a vapor phase transport method and the fabrication of β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanowire gas sensor. The β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanowire sensor shows reversible response to isopropyl alcohol (IPA) gas at temperature as low as 100 °C. With 300 ppm IPA gas introduced, it was found that measured responses were ~ 7.5%, 13.5%, and 23% when the sensor was operated at 100 °C, 200 °C, and 300 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C, respectively. It was also found that the responses measured at 300 °C were ~ 9%, 15.5%, 24%, and 33% when the injected IPA gas concentrations were 100, 200, 300, and 400 ppm, respectively.

Room-temperature blue–violet laser emission from individual ultra-long ZnO microbelts

Blue–violet lasing action in a single ZnO microbelt has been demonstrated at room temperature. The microbelts, with widths of about 0.65μm and lengths up to several millimeters, have been synthesized via the vapor-phase transport method with CuO catalyst at 900°C. Under a direct-current voltage excitation, surface-emitting lasing actions from the microbelts treated by hydrogen plasma were observed in hydrogen gas ambient. The luminescence spectrum exhibits a series of sharp peaks with a maximum at 481.2nm and the full-width at half-maximun of 0.3nm. The results strongly suggest that hydrogen is one of the primary origins of blue–violet laser. The facilitation of fabrication and the low dimensionality of these microbelts make them ideal miniaturized laser light sources for optoelectronic applications.

Hierachical Zeolite-Zeolite Composite Prepared by a Vapor Phase Transport Method

A zeolite-zeolite composite composed of Y and ZSM-5 was successfully prepared by a vapor phase transport (VPT) method. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2 adsorption-desorption and FT-IR. The results display that the synthesis is influenced by the Y content, preparing condition of dry gel and transfering condition for VPT method. FT-IR spectra show the characteristic peaks of MFI framework on ZSM-5 precursor after hydrothermal pre-treatment for 16 h. The result can be attributed to the crystal nucleus or microcrystal of ZSM-5 zeolite, either of which may promote growth of ZSM-5 crystals during the VPT procedure, and depresse formation of ZSM-35 crystals. The mesopores structure, created in as-synthesized zeolite-zeolite composite, can be ascribed to the extracted aluminum from Y zeolite crystals by VPT procedure.

Enhancement of nonlinear optical phenomena from crown-like nanostructure zinc oxide based on whispering gallery mode

Whispering gallery mode (WGM)-enhanced nonlinear optical phenomena from crown-like nanostructure zinc oxide (ZnO) samples are observed. The samples are synthesized by vapor-phase transport method. The morphology and crystal structure are examined and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), and they are excited by femtosecond laser pulses with central wavelengths of 355 nm, 800 nm and 1150 nm, respectively. The typical stimulated emission presents a red shift compared with spontaneous emission, which is observed under the excitation of 355 nm with a relatively low threshold. The ultraviolet (UV) frequency up-conversion emission is obtained when the excitation pulse wavelengths are selected as 800 nm and 1150 nm, respectively. The peak position and the relationship between the emission intensity and excitation intensity demonstrate that the UV up-conversion photoluminescence (PL) is induced by two- and three-photon absorptions. The PL characteristics and their WGM-enhanced mechanism are investigated.

Synthesis of ZnO/Cu micro and nanostructures via a vapor phase transport method using different tube systems

ZnO micro and nanostructures were grown on copper coated silicon substrates using two different systems: an opened system (both ends opened tube) and a closed system (one closed end tube). The thermodynamic conditions of the systems made a significant difference in boundary layer and super-saturation between the systems. The results indicate that diffusion of the gaseous species through the boundary layers at low and high pressures controls the final formation of the morphologies. The ZnO nanostructures which have been grown in a restricted place have larger diameters and lengths. The structure of the products was analyzed by X-ray diffractometer (XRD) and it was found that the good crystalline quality of the samples was obtained in a closed system. To study the optical properties, photoluminescence (PL) and ultra violet–visible (UV–vis) spectroscopy were employed. It was observed that a decrease in the growth temperature of the opened system caused a broad and dominant visible emission covering the blue and green emission in the PL spectra.

Formation of and silicon incorporation in SAPO-5 synthesized via dry-gel conversion

Molecular sieves have been scientifically and industrially important materials since their discovery. These porous, crystalline networks of tetrahedrally coordinated atoms bridged by oxygen are known as excellent catalysts. The framework of the aluminophosphate family of molecular sieves is itself non-catalytic, but through heteroatomic substitution these materials can diversify into, for example, the silicoaluminophosphate (SAPO) family of heterogeneous acid catalysts. Research into the methods by which these substitutions occur, as discoveries can lead to refined control over material property and function. SAPO-5 was chosen as model system of study. 27Al, 29Si and 31P solid state NMR and PXRD were used as the primary methods of investigation. The SAPO-5 study determined that the dry gel conversion (DGC) methods of steam assisted conversion (SAC) and vapor phase transport (VPT) follow similar reaction pathways. After an initial difference caused by the lack of organic structure directing agent in the gel for the VPT method, crystallization is similar between methods, and silicon incorporation results in two populations of silicon sites. One represents isolated Si(OAl)4 species well incorporated into the framework, while the other represents silica islands within the framework. The initial core of the nuclei is AlPO4 in nature and the Si is gradually incorporated into the lattice as the crystals grow. The vapor phase silicon uptake (VPSU) method provides a contrast to this data, inducing nucleation that occurs concurrently with Si incorporation and producing only isolated Si(OAl)4 species.

A Rhombic Dodecahedral Honeycomb Structure with Cation Vacancy Ordering in a γ-Ga2O3 Crystal

The crystal structure of a γ-Ga2O3 layer grown epitaxially on an MgO substrate by a vapor phase transport method was investigated by transmission electron microscopy, electron diffraction, and scanning transmission electron microscopy with aberration correctors. Some forbidden reflections were excited in electron diffraction patterns by double reflection from the vicinity of the substrate interface. Phase boundaries are observed in atomic column images using high-angle annular dark field images. A structure model is proposed to explain the experimental results. Cation vacancy ordering is introduced in the structure model to distort the γ-Ga2O3 crystal lattice along one axis and reduce the lattice mismatch with the substrate. Some grains are formed and alter the directions to reduce the distortion for the other axis. The grains are stacked with {110} phase boundaries and form a rhombic dodecahedral honeycomb. The rhombic dodecahedral honeycomb structure model with cation vacancy ordering is stabilized by the lattice mismatch between the γ-Ga2O3 crystal and the MgO substrate, and it disappears at a depth of 170 nm from the interface.

Synthesis of tin-doped zinc oxide microrods for gas sensor application

Sn-doped ZnO microrods have been fabricated via the vapor-phase transport method. The as-synthsized samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The gas sensors based on the Sn-doped ZnO microrods are very sensitive to ethanol gas, and the sensitivity is about 52.4 against 100ppm ethanol at working temperature of 300°C. The synthesized microrods have high surface-to-volume ratio and large quantity of oxygen vacancy which might be the origin of the high sensitivity for ethanol gas. The results suggest that the Sn-doped ZnO microrods are good candidates for fabricating effective and high performance gas sensors.

${\rm Ga}_{2}{\rm O}_{3}$ Nanowire Photodetector Prepared on ${\rm SiO}_{2}/{\rm Si}$ Template

The authors report the growth of β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanowires using a vapor phase transport method on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si template. It is found that average diameter, average length, and density of the nanowires all increased as we increase the growth temperature. β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanowire solar-blind photodetectors with a sharp cutoff at 255 nm are also fabricated. With an incident light wavelength of 255 nm and an applied bias of 5 V, it is found that measured responsivity of the photodetector prepared at 950°C is 3.43×10 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> A/W.

Differential pathogen loads affecting quality of life during Lapita colonisation of the Pacific: Skeletal pathology in the SAC Watom and Teouma samples

Molecular sieves have been scientifically and industrially important materials since their discovery. These porous, crystalline networks of tetrahedrally coordinated atoms bridged by oxygen are known as excellent catalysts. The framework of the aluminophosphate family of molecular sieves is itself non-catalytic, but through heteroatomic substitution these materials can diversify into, for example, the silicoaluminophosphate (SAPO) family of heterogeneous acid catalysts. Research into the methods by which these substitutions occur, as discoveries can lead to refined control over material property and function. SAPO-5 was chosen as model system of study. 27Al, 29Si and 31P solid state NMR and PXRD were used as the primary methods of investigation. The SAPO-5 study determined that the dry gel conversion (DGC) methods of steam assisted conversion (SAC) and vapor phase transport (VPT) follow similar reaction pathways. After an initial difference caused by the lack of organic structure directing agent in the gel for the VPT method, crystallization is similar between methods, and silicon incorporation results in two populations of silicon sites. One represents isolated Si(OAl)4 species well incorporated into the framework, while the other represents silica islands within the framework. The initial core of the nuclei is AlPO4 in nature and the Si is gradually incorporated into the lattice as the crystals grow. The vapor phase silicon uptake (VPSU) method provides a contrast to this data, inducing nucleation that occurs concurrently with Si incorporation and producing only isolated Si(OAl)4 species.

Non-layered wurtzite-type extralarge-area flexible ZnO (011̄0) paper-like nanostructures grown by electrostatically induced vapor-phase transport

We report the synthesis of transparent, curling, extra large-area non-layered wurtzite-type low-defect-concentration ZnO (010) nanopapers with a maximum area of over 2000 μm2 and 30–60 nm in thickness via an indium-assisted vapor-phase transport (VPT) method. The ZnO nanopapers exhibit an intense ultraviolet emission band centered at about 382 nm. On reducing the substrate temperature, the morphological evolution of VPT-grown ZnO nanostructures from nanopapers to nanobelts and then to nanowires was sequentially observed, suggesting that the “one-dimensional branching and subsequent two-dimensional interspace filling” process was not necessary. Finally, based on the ZnO and Zn supersaturation state, a possible electrostatic interaction induced nanobricks alternatively interconnecting self-assembled growth mechanism of high-quality single-crystalline ZnO nanopapers is discussed.