Crystal Surface Properties Research Articles

Electrodeposited ZnS Precursor Layer with Improved Electrooptical Properties for Efficient Cu2ZnSnS4 Thin-Film Solar Cells

Zinc sulfide (ZnS) thin films were prepared on indium tin oxide-coated glass by electrodeposition using aqueous zinc sulfate, thiourea, and ammonia solutions at 80°C. The effects of sulfurization at temperatures of 350°C, 400°C, 450°C, and 500°C on the morphological, structural, optical, and electrical properties of the ZnS thin films were investigated. X-ray diffraction analysis showed that the ZnS thin films exhibited cubic zincblende structure with preferred (111) orientation. The film crystallization improved with increasing annealing temperature. Field-emission scanning electron microscopy images showed that the film morphology became more compact and uniform with increasing annealing temperature. The percentage of sulfur in the ZnS thin films increased after sulfurization until a stoichiometric S/Zn ratio was achieved at 500°C. The annealed films showed good adhesion to the glass substrates, with moderate transmittance (85%) in the visible region. Based on absorption measurements, the direct bandgap increased from 3.71 eV to 3.79 eV with annealing temperature, which is attributed to the change of the buffer material composition and suitable crystal surface properties for effective p–n junction formation. The ZnS thin films were used as a buffer layer in thin-film solar cells with the structure of soda-lime glass/Mo/Cu2ZnSnS4/ZnS/ZnO/Al grid. The best solar cell efficiency was 1.86%.

The adsorption of fluorinated dopants at the surface of 5CB: a neutron reflection study

The adsorption of dopants at the surface of 5CB has been studied using neutron reflection. The dopants were versions of 11OCB with partly fluorinated chains, and the 5CB was interfaced with air or with silica treated with fluorocarbon or hydrocarbon coatings. At the air interface, the F17-11OCB adsorbed homeotropically, and the amount increased on cooling into the nematic phase of 5CB. At low temperatures, the adsorption from the nematic phase appeared to saturate at a bilayer. At the solid interfaces, there was some evidence for a thin planar layer at the surface, but most of the adsorbed dopant was in the form of diffuse layers. In both cases, an increase in dopant concentration caused higher adsorbed amounts. For F17-11OCB, the amount absorbed was much greater for a fluorinated coating as opposed to a hydrocarbon-coated surface. Also no adsorption of the F3-11OCB could be detected, suggesting that the adsorption process is driven by the oleophobic effect. The results demonstrate that it is possible to manipulate surface properties of liquid crystals using surfactant-like dopants.

Experimental Study on the Surface Cutting Mechanical Properties of Single Crystal Silicon in Micro-Nano Scale

The experiment of cutting mechanical properties of single crystal silicon surface in the micro-nanoscale is researched using nanoindenter and atomic force microscopy. The result of the experiment shows that: in the constant load, the impact of different scratching velocity for single crystal silicon surface scratch groove width and chip accumulation volume are not big; but the cutting force and friction coefficient are not increases with the scratching velocity increases; when the scratching speed is certain, the size of load has a greater impact on the cutting mechanical properties of single crystal silicon surface, with the increase of the load, the cutting force increases, but the cutting force is not linearly growth.

Effect of crystal chemistry and surface properties on ilmenite flotation behavior

The crystal chemistry, surface properties and flotation behavior of three ilmenite samples: IL-F (purchased from the mineral dealership of A. and F. Krantz), IL-Q (Qara-aghaj deposit, Iran) and IL-K (Kahnuj deposit, Iran) were investigated. The substitution of different amounts of Mg, Mn and V in the crystal structure of ilmenite was identified by microprobe analysis. Different amounts of hemoilmenite exsolution were observed inside all three ilmenite samples using SEM, electron microprobe and X-ray diffraction analyses. Using these analytical techniques, the titanite phase was found inside the IL-K ilmenite. The XPS analysis indicated that the contents of Fe3+ are 5.66, 5.33 and 3.72% for IL-F, IL-Q and IL-K, respectively which are in good agreement with the amounts of hemoilmenite exsolution.The IEP was determined to be 4.2, 5.4 and 6.3 for IL-F, IL-Q and IL-K, respectively. Using sodium oleate as a collector, the maximum flotation recovery was obtained at 78.4, 73.5 and 51.5% for IL-F, IL-Q and IL-K samples, respectively, at a pH range of 5 to 7 where iron cations are active ions. The IEP has a negative correlation with Fe3+ ions, collector adsorption density and ilmenite floatability. Mg and V have negative correlation with ilmenite flotation recovery. Si and Ca sourced mainly from the titanite phase affect the flotation recovery of ilmenite negatively.

Formulation pre-screening of inhalation powders using computational atom-atom systematic search method.

The synthonic modeling approach provides a molecule-centered understanding of the surface properties of crystals. It has been applied extensively to understand crystallization processes. This study aimed to investigate the functional relevance of synthonic modeling to the formulation of inhalation powders by assessing cohesivity of three active pharmaceutical ingredients (APIs, fluticasone propionate (FP), budesonide (Bud), and salbutamol base (SB)) and the commonly used excipient, α-lactose monohydrate (LMH). It is found that FP (-11.5 kcal/mol) has a higher cohesive strength than Bud (-9.9 kcal/mol) or SB (-7.8 kcal/mol). The prediction correlated directly to cohesive strength measurements using laser diffraction, where the airflow pressure required for complete dispersion (CPP) was 3.5, 2.0, and 1.0 bar for FP, Bud, and SB, respectively. The highest cohesive strength was predicted for LMH (-15.9 kcal/mol), which did not correlate with the CPP value of 2.0 bar (i.e., ranking lower than FP). High FP-LMH adhesive forces (-11.7 kcal/mol) were predicted. However, aerosolization studies revealed that the FP-LMH blends consisted of agglomerated FP particles with a large median diameter (∼4-5 μm) that were not disrupted by LMH. Modeling of the crystal and surface chemistry of LMH identified high electrostatic and H-bond components of its cohesive energy due to the presence of water and hydroxyl groups in lactose, unlike the APIs. A direct comparison of the predicted and measured cohesive balance of LMH with APIs will require a more in-depth understanding of highly hydrogen-bonded systems with respect to the synthonic engineering modeling tool, as well as the influence of agglomerate structure on surface-surface contact geometry. Overall, this research has demonstrated the possible application and relevance of synthonic engineering tools for rapid pre-screening in drug formulation and design.

Thermoelectric, electronic, optical and chemical bonding properties of Ba2PrRuO6: At temperature 7 K and 150 K

We present first principles calculations of the band structure, density of states, electronic charge density, Fermi surface and optical properties of Ba2PrRuO6 single crystals at two different temperatures. The atomic positions were optimized by minimizing the forces acting on the atoms. We have employed the full potential linear augmented plane wave method within local density approximation, generalized gradient approximation and Engel–Vosko generalized gradient approximation to treat the exchange correlation potential. The calculation shows that the compound is superconductor with strong hybridization near the Fermi energy level. Fermi surface is composed of two sheets. The calculated electronic specific heat capacities indicate, very close agreement with the experimental one. The bonding features of the compounds are analyzed using the electronic charge density in the (100) and (0–10) crystallographic planes. The dispersion of the optical constants was calculated and discussed. The thermoelectric properties are also calculated using the BoltzTrap code.

Study of the effects of surface modification by thermal shock method on photocatalytic activity of TiO2 P25

In this study, we have modified TiO2 P25 photocatalyst by thermal shock method at different temperatures in order to study the effects of thermal shock process on the crystal structure, surface properties and photocatalytic activity. The thermal-shock-modified catalysts were respectively characterized by X ray diffraction (XRD), scanning electronic microscopy (SEM), X ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectra and compared with thermal-shock-fluorinated TiO2 catalysts. The photocatalytic activity was evaluated via the degradation of methylene blue under UV and visible light irradiation. The results show that the deficiency of oxygen on the surface of catalysts created by thermal shock at 500°C can enhance the photocatalysis under both UV and visible light. Moreover, when the thermal shock was combined with the fluorination of TiO2, the photocatalytic performance was further improved. However, the thermal shock from 700°C promoted the growth of particles and the phase transition from anatase to rutile, which resulted in two different effects: inhibit the photocatalysis under UV irradiation but improve it under visible irradiation.

Modification of electronic properties of the surface of (100) silicon crystals under microwave plasma micromachining

The behavior of the effect of microwave plasma micromachining on electronic properties of (100) silicon crystal surfaces at weak adsorption was investigated. Model process mechanisms and factors providing stable modification of the electronic properties of the silicon surface by the formation of built-in surface potentials determined by chemical reactivity of the used working gases and modes of microwave plasma treatment were considered. The possibility in principle of the active formation of electronic properties of the surface of semiconductor crystals to extend their electrophysical and functional properties was shown.

Boron-doped silicon carbide supported Pt catalyst for methanol electrooxidation

Boron-doped silicon carbide (B0.1SiC) synthesized by the carbothermal reduction method was used as support to prepare Pt/B0.1SiC catalyst by cyclic voltammtric deposition of Pt nanoparticles. The crystal structure, surface property and morphology of the catalysts were studied with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy techniques and N2 adsorption-desorption experiment. It is shown that B atoms have been incorporated into the SiC lattice sites by substituting Si, which increases the electrical conductivity of SiC. Pt nanoparticles uniformly dispersed on the B0.1SiC support with an average size of 2.7 nm. The prepared Pt/B0.1SiC had a larger electrochemically active area and exhibited higher electrocatalytic activity and stability for methanol oxidation than the Pt/SiC synthesized by the same method. This shows that B-doped SiC is a promising support for preparing high-performance methanol oxidation electrocatalysts.

Elongated titania nanostructures as efficient photocatalysts for degradation of selected herbicides

Titanium dioxide nanotubes (TNT) were synthesized via hydrothermal method and calcined at various temperatures. The obtained calcined TiO2 nanomaterials with specific elongation orientation were characterized by transmission and scanning electron microscopy (TEM, SEM), X-ray diffraction (XRD), UV/Vis diffuse reflection spectroscopy (DRS), Laser Doppler electrophoresis (LDE) and their textural properties were evaluated. The photocatalytic activity of obtained nanopowders was evaluated considering photodegradation rate of herbicide clomazone, rarely studied herbicide. The influence of calcination temperature of catalysts with elongated morphology on their photocatalytic activity was evaluated. The best results were obtained with TNT annealed at 700°C, which can be assigned to the best balance between crystal structure, morphology and surface properties of nanoparticles induced by annealing. Also, the photocatalytic degradation rates of another two herbicides (picloram, and mecoprop) were compared, due to possibility that the efficiency of photocatalytic degradation is greatly influenced by the molecular structure. The mineralization degree of selected herbicides in the presence of TiO2 based photocatalysts was evaluated applying total organic carbon (TOC) measurements.

Formulation Design Facilitates Magnetic Nanoparticle Delivery to Diseased Cells and Tissues

Magnetic nanoparticles (MNPs) accumulate at disease sites with the aid of magnetic fields; biodegradable MNPs can be designed to facilitate drug delivery, influence disease diagnostics, facilitate tissue regeneration and permit protein purification. Because of their limited toxicity, MNPs are widely used in theranostics, simultaneously facilitating diagnostics and therapeutics. To realize therapeutic end points, iron oxide nanoparticle cores (5-30 nm) are encapsulated in a biocompatible polymer shell with drug cargos. Although limited, the toxic potential of MNPs parallels magnetite composition, along with shape, size and surface chemistry. Clearance is hastened by the reticuloendothelial system. To surmount translational barriers, the crystal structure, particle surface and magnetic properties of MNPs need to be optimized. With this in mind, we provide a comprehensive evaluation of advancements in MNP synthesis, functionalization and design, with an eye towards bench-to-bedside translation.

Benzene hydrogenation over oxide-modified MCM-41 supported ruthenium–lanthanum catalyst: The influence of zirconia crystal form and surface hydrophilicity

The effects of the preparation conditions on the crystal form and surface properties of zirconia were studied. Mesoporous MCM-41 modified by tetragonal and monoclinic zirconia were synthesized by hydrothermal and precipitation methods. Then MCM-41 and zirconia-modified MCM-41 supported ruthenium–lanthanum catalysts were prepared via cyclohexane–water double solvent impregnation method. The obtained supports and catalysts were characterized by powder X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, N2 adsorption–desorption, thermogravimetric and differential scanning calorimetry, temperature programmed desorption of NH3, static water/benzene adsorption techniques. It has been found that MCM-41 modified by tetragonal zirconia with exclusive Lewis-acidic sites exhibits more surface hydroxyl groups and higher hydrophilicity than MCM-41 modified by monoclinic and amorphous zirconia. Tetragonal zirconia-modified MCM-41 supported ruthenium–lanthanum catalyst shows better catalytic performance in benzene hydrogenation to cyclohexene with benzene conversion of 54.4% and cyclohexene selectivity of 84.7%.

蓝紫光氮化镓光子晶体面射型激光器

We experimentally and theoretically investigate the optical properties of GaN-based photonic crystal surface emitting lasers( PCSELs). We discuss the effects of lattice constant,boundary shape,and lattice type of photonic crystal( PC) on lasing characteristics. The PCSEL structures are fabricated using the metal-organic chemical vapor deposition,the electron beam lithography,and inductively coupled plasma reactive ion etching technique. The optical properties of PCSEL which include the diffraction pattern,emission spectrum,divergence angle and so on are measured by the angular-resolved photoluminescence system. Meanwhile,the plane wave expansion and multiple scattering method( MSM) are used to calculate the band diagram and threshold gain of PCSELs,respectively. The results reveal that the lattice constant plays an important role in selection of lasing mode. Despite the lasing wavelength and linewidth of circular and hexagonal shapes PCSELs are almost the same,the threshold excitation energy density of circular shape PCSEL is 0. 3 mJ /cm2 smaller than that ofhexagonal PCSEL. The PCSEL with honeycomb lattice shows the lower excitation energy density of1. 6 mJ /cm2 and divergence angle of 1. 3°. In case of square lattice,the excitation energy density is twice as large as that of honeycomb lattice. The overall results show that the single-mode emission,low divergence angle,and so on can be produced from GaN-based PCSEL. On the other hand,the numerical results calculated using the MSM are in good agreement with experimental results. The MSM could be a fast and cost-effective approach for predicting the lasing characteristic. We believe that these contributions provide guidance for the development of GaN-based PCSEL.

Synthesis and Characterization of Boron-Doped SiC for Visible Light Driven Hydrogen Production

Boron-doped β-SiC (BxSiC) photocatalysts were prepared by in-situ carbothermal reduction, and their photocatalytic performances for H2 evolution under visible light irradiation were investigated. The crystal structure, surface property, morphology, and band gap structure of the BxSiC photocatalysts were studied using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and ultraviolet-visible absorption spectroscopy. The characterization results indicate that B atoms have doped into the SiC lattice and substituted Si sites, leading to the formation of a shallow acceptor level above the valence band of SiC, resulting in a narrowed band gap energy. The shallow acceptor level acts as a hole trap, preventing the recombination of photo-excited electrons and holes. Therefore, the photocatalytic H2 evolution activity of B-doped SiC was greatly improved compared with that of SiC. The highest hydrogen evolution rate was obtained when the B/Si molar ratio was 0.05.

Nano-hydroxyapatite formation via co-precipitation with chitosan-g-poly(N-isopropylacrylamide) in coil and globule states for tissue engineering application

With the excellent biocompatibility and osteoconductivity, nano-hydroxyapatite (nHA) has shown significant prospect in the biomedical applications. Controlling the size, crystallinity and surface properties of nHA crystals is a critical challenge in the design of HA based biomaterials. With the graft copolymer of chitosan and poly(N-isopropylacrylamide) in coil and globule states as a template respectively, a novel composite from chitosan-g-poly(N-isopropylacrylamide) and nano-hydroxyapatite (CS-g-PNIPAM/nHA) was prepared via coprecipitation. Zeta potential analysis, thermogravimetric analysis and X-ray diffraction were used to identify the formation mechanism of the CS-g-PNIPAM/nHA composite and its morphology was observed by transmission electron microscopy. The results suggested that the physical aggregation states of the template polymer could induce or control the size, crystallinity and morphology of HA crystals in the CS-g-PNIPAM/nHA composite. The CS-g-PNIPAM/nHA composite was then introduced to chitosan-gelatin (CS-Gel) polyelectronic complex and the cytocompatibility of the resulting CSGel/composite hybrid film was evaluated. This hybrid film was proved to be favorable for the proliferation of MC 3T3-E1 cells. Therefore, the CS-g-PNIPAM/nHA composite is a potential biomaterial in bone tissue engineering.

The anti-adherence and bactericidal activity of sol–gel derived nickel oxide nanostructure films: solvent effect

This study presents the characterization and antibacterial activity of nanostructure NiO films synthesized by sol–gel dip coating method using solvents of different polarities and viscosities without any catalysts, templates or surfactants. Methanol, 1,4-butanediol, ethanol, and 2-propanol were used as solvent. The antibacterial activity was tested against two common foodborne pathogenic bacteria Staphylococcus aureus (ATCC 25922) and Escherichia coli (ATCC 29213) using the so-called antibacterial drop test. X-ray diffraction, scanning electron microscopy, atomic force microscopy, UV–vis spectroscopy and static contact angles test were used to analysis the structure and morphology character, surface topography, optical property and surface wettability of different coatings, respectively. The characterization results showed different preferred crystallographic orientations, particle sizes, surface properties and optical band gap of NiO films according to the solvent physicochemical properties. The antibacterial efficiencies were affected by the physiological status of the bacterial cells and degree of bacteria adherence, morphologies and crystal growth habits, surface and optical properties of NiO samples.

Structure and electronic properties of oxyanionic crystal surfaces

The atomic and electronic structures of the surfaces of alkali-metal nitrates, chlorates, and perchlorates are determined in the gradient approximation of density functional theory via the linear combination of atomic orbitals using the CRYSTAL09 program package. The geometric parameters, surface energies, densities of states, overlap populations, and atomic charges are calculated. It is established that the upper layer is formed by oxygen atoms for the most stable surfaces. For oxygen atoms of the upper layer, the intra-anionic bond length decreases with respect to that in the bulk, the overlap populations increase, and the charges decrease. Changes in the atomic and electronic structures of the surface decrease with respect to those of the bulk as the cation atomic number increases.

Adsorption Removal of Ni(II) from Aqueous Solution by Raw and Acid-Activated Kaolinite

X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen physical adsorption, potentiometric titrations and batch adsorption experiments were employed to characterize the crystal structure, micromorphologies and surface properties of raw kaolinite (RKao) and acid-activated kaolinite (AAKao). Compared to RKao, the particle size of AAKao became smaller, but the specific surface area (SSA), cation exchange capacity (CEC) and surface negative charge at pH 5.5 increased. The adsorption capacity (qmax) for Ni (II) of RKao and AAKao was 3.25 mg/g and 5.09 mg/g, respectively. The adsorption data for Ni (II) by RKao and AAKao could be fitted by Langmuir model (R2 =0.991 and 0.989, respectively).

Optical, luminescence and thermal properties of radiopure ZnMoO4 crystals used in scintillating bolometers for double beta decay search

Zinc molybdate (ZnMoO4) crystals are an excellent candidate material to fabricate scintillating bolometers for the study of neutrinoless double beta decay of 100Mo, provided that the crystal quality meets strict optical, thermal and radiopurity requirements. This paper addresses the characterization of improved crystalline samples grown by the low-thermal-gradient Czochralski technique. Transmittance measurements confirm significant improvement of the material with respect to previously developed samples. Luminescence properties (emission spectra, dependence of intensity on temperature, thermally stimulated luminescence and phosphorescence) have been studied under X-ray excitation from liquid-helium to room temperature. The index of refraction was measured in the wavelength interval 406–655nm. Samples of ZnMoO4 crystals with masses of 5.07g and 23.8g were operated as scintillating bolometers at temperatures below 30mK, with simultaneous detection of scintillation and heat signals, confirming an excellent alpha/beta rejection power. Background measurements allowed encouraging radiopurity level estimations. The light collection from ZnMoO4 scintillators was Monte Carlo simulated, analysing different crystal size, shape and surface properties and different photodetector sizes.

Sorption and transport of aqueous FeII in a goethite-coated sand column under anoxic conditions

Experiments were conducted under static batch and dynamic flow conditions to evaluate the sorption of FeII onto three goethites (G1, G2 and G3) having different crystal habits, morphologies and surface properties. Results reveal that G1 exhibited the highest FeII sorption extent and lowest kinetic rate constant, which may result from higher surface site density, surface roughness and edge surface faces. Surface complexation modeling parameters derived from batch experiments were combined with hydrodynamic parameters to simulate breakthrough curves in goethite-coated sand packed columns. The total sorbed amount of FeII at complete breakthrough was in agreement with that expected from the batch experiments, except for G1. Sorption breakthrough predictions that make use of surface complexation parameters accurately predicted FeII mobility in G2 and G3 columns, but poorly in G1 column. Experiments at various flow rates in G1 columns represented different amounts of FeII sorbed at complete breakthrough, thereby underscoring the impact of kinetic sorption. Moreover, Fe dissolution/re-precipitation or FeII-induced transformation of goethite was suspected at the lowest flow rate in the G1 column. The influence of goethite phase specific reactivity on FeII sorption under batch versus advective–dispersive flow is herein demonstrated. These findings have strong implications to assess transport of FeII and environmental contaminants both in natural and engineered systems.