Surface Crystalline Structure Research Articles

Effect of titania polymorph on the properties of CuO/TiO2 catalysts for trace methane combustion

Anatase and rutile have the same chemical composition as TiO2 but different crystalline structures and surface structures, which draws effect on the properties of their supported catalysts. Additionally, titania mixture, e.g., Degussa P25, which consists of both anatase and rutile, presents different physicochemical properties with anatase and rutile. In this work, P25-, anatase- or rutile-supported copper oxide catalysts (signed as CuO/P25, CuO/A and CuO/R) were prepared and characterized to study the titania support effect on the physicochemical properties and catalytic properties for the trace CH4 combustion. It is found that the activity of CuO/R is better than the corresponding CuO/A sample when their pore size and specific surface area are comparable, which is attributed to the different chemical states of the copper oxide caused by the different TiO2 support polymorphs. The loading of CuO and subsequent calcination promotes more significant sintering and anatase to rutile transform for CuO/P25 than those for CuO/A. Thus, CuO/R shows better stability than CuO/P25.

Fabrication and characterization of ZnO nanorods on polished titanium substrate using electrochemical–hydrothermal methods

ZnO nanorods were deposited on the polished Ti substrate using electrochemical–hydrothermal methods. The titanium substrate was first electro-polished to remove the oxide and obtain an ideal flat surface. Subsequently, a seed layer of ZnO was electrochemically deposited in both Zn(NO3)2 and ZnCl2 solutions. On top of the seed layer, ZnO nanorods were hydrothermally deposited in Zn(NO3)2 and hexamethylenetetramine solution. To examine the polishing and growth conditions, atomic force microscope, X-ray diffraction analysis, and optical images under a microscope were used to measure the surface roughness, crystalline structure, and film morphology. Well-crystallized nanorods can be grown on top of the Ti substrate with a suitable polishing voltage and sufficient growth time.

Assessment of anodized titanium implants bioactivity

This study was conducted to create nanostructured surface titanium implants by anodic oxidation process aiming to bring out bioactivity and to assess the resultant bioactivity both in vitro and in vivo. An economic protocol was used to apply anodic spark discharge and create surface nanoporosities on grade II commercially pure titanium (cpTi). The in vitro investigation included morphology, surface chemical analysis, roughness and crystalline structure of titanium oxide (TiO₂) film prepared. Assessment of the bioactivity was carried out by immersing the specimens in simulate body fluid (SBF) and investigating the surface-deposited layer. The in vivo investigation was conducted by surgically placing the anodized implants into rabbits tibia for different healing periods. Then biomechanical evaluation was performed to verify the effect of treatments on the interface resistance to shear force. Routine histological analysis was performed to evaluate the bone tissue reactions to anodized implants. Anodization of titanium implants produced morphological changes, raised the percentage of oxygen in the TiO₂ layer, increased surface area and roughness of implants remarkably, and modified the crystallinity of the film. The in vitro assessments of bioactivity showed that a layer of calcium phosphate was precipitated on the titanium surfaces 7 days after soaking into SBF. The implant-bone interface resistance to shear force was enhanced at 2-week healing period. This was confirmed by histological findings. Nanostructured surface titanium implants could be prepared by anodic oxidation with resultant accelerated bioactivity that may be recommended for early loading.

Stability of Palladium-Polypyrrole-Foam Nickel Electrode and Its Electrocatalytic Hydrodechlorination for Dichlorophenol Isomers

Palladium-polypyrrole-foam nickel composite electrode (Pd/PPY(PTS)/Ni) was prepared through electrodeposited of palladium nanoparticles onto preformed electrodes (surface of electrodes was coated with potentiostatic electropolymerized polypyrrole). The stability of the fresh and used composite electrode was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It was found that the surface state, morphology, and crystalline structure of the composite electrode were stable after 5 recycle uses. Electrocatalytic activity of the composite electrode was evaluated for the hydrodechlorination (ECH) of six kinds of dichlorophenols (DCPs). Results indicated that 2,4-DCP showed higher hydrodechlorination rate. Further, the pathway of electrochemical hydrodechlorination of six kinds of dichlorophenol isomers was investigated.

Effects of reaction parameters on solution combustion synthesis of lepidocrocite-like K0.80Ti1.733Li0.267O4: phase formation and morphology evolution

A lepidocrocite-like potassium lithium titanate K0.80Ti1.733Li0.267O4 (KLTO) with layered structure was synthesized by an auto-igniting solution combustion method using glycine and metal (Ti, K and Li) nitrate as reactants. The crystalline structure and morphology of the as-prepared product were examined using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Effects of reaction parameters such as ignition temperature and oxidizers to fuel ratio on the phase formation and morphology evolution are investigated in this paper. A pure phase of KTLO was obtained at a low temperature (650 °C) within several minutes. Excessive glycine added into the aqueous precursor solution facilitated the synthesis of a pure and well-crystallized product. As-prepared particles exhibited plate-like shape with a length of 5–20 μm and a thickness of about 2 μm. No residual organic compound existed in the product. After the as-prepared product was post solution combustion heat-treated (1100 °C for 2 h), the particles became uniform in size with smooth surface and well-defined crystalline structure. The product exhibited excellent ion-exchange, intercalation, and exfoliation properties. The exfoliated titania nanosheets are characterized by high two-dimensional anisotropy with a thickness of about 20 nm and a lateral size ranging from sub-micrometers to several tens of micrometers.

Effect of calcination temperature on the activity of solid Ca/Al composite oxide-based alkaline catalyst for biodiesel production

A solid Ca/Al composite oxide-based alkaline catalyst containing Ca12Al14O33 and CaO was prepared by chemical synthesis and thermal activation from sodium aluminate solution and calcium hydroxide emulsion. The effect of calcination temperatures ranging from 120°C to 1000°C on activity of the catalyst was investigated. The catalyst calcined at 600°C showed the highest activity with >94% yield of fatty acid methyl esters (i.e. biodiesel) when applied to the transesterification of rapeseed oil at a methanol:oil molar ratio of 15:1 at 65°C for 3h. Structure and properties of the catalyst were studied and the characterizations with XRD, TGA, FTIR, BET, and SEM demonstrated that the performance of the catalyst was closely related to its specific surface area and crystalline structure. In particular, the generation of crystalline Ca12Al14O33 improved the catalytic activity due its synergistic effect with CaO.

Advanced nanomechanics in the TEM: effects of thermal annealing on FIB prepared Cu samples

The effect of focused ion beam (FIB) fabrication on the mechanical properties of miniaturized mechanical tests has recently been realized, but is not well documented. In this study, the effect of post thermal annealing on the plastic properties of FIB fabricated micro- and nanometer-sized Cu samples was studied by means of advanced analytic and in situ transmission electron microscopy. In situ heating experiments on thin films and pillars revealed a reduction of the initially high dislocation density, but never a recovery of the bulk dislocation density. Aberration-corrected atomic imaging documented the recovery of a pristine crystalline surface structure upon annealing, while electron energy-loss spectroscopy showed that the remaining contamination layer consisted of amorphous carbon. These structural observations were combined with the mechanical data from in situ tests of annealed micro- and nanometer-sized tensile and compression samples. The thermal annealing in the micron regime mainly influences the initial yield point, as it reduces the number of suited dislocation sources, while the flow behavior is mostly unaffected. For the submicron samples, the annealed material sustains significantly higher stresses throughout the deformation. This is explained by the high stresses required for surface-mediated dislocation nucleation of the annealed material at the nanoscale. In the present case, the FIB affected the surface near defects and facilitated dislocation nucleation, thereby lowering the material strength.

Effect of growth temperature on surface morphology and structure of InAs/GaSb superlattices grown by metalorganic chemical vapor deposition

The effect of growth temperature on the surface morphology and crystalline structure of InAs/GaSb type-II superlattices (SLs) grown on (100) GaSb substrates by metalorganic chemical vapor deposition (MOCVD) was investigated by in-situ reflectance measurement, atomic force microscopy, high-resolution x-ray diffraction and Raman scattering spectroscopy. All the data show that the structural properties of the SL samples are very sensitive to the growth temperatures. The optimal SL growth temperature in our MOCVD is 520°C. Only 20°C lower of the temperature resulted in rough surfaces from the beginning of SL epitaxy and 20°C higher resulted in the composition of the mixing interfaces far from expected and consequently deteriorated structure. Room temperature absorption from 2 to 8μm has been realized by our samples.

Effect of ambient environment on excimer laser induced micro and nano-structuring of stainless steel

The effect of laser fluence and an ambient environment on the formation and development of the micro and nano-structures on the laser irradiated stainless steel (AISI-304) targets have been investigated. For this purpose KrF excimer laser (λ=248nm, t=20ns, repetition rate 20Hz) has been used. The targets are exposed for various laser fluences ranging from 0.72Jcm−2 to 1.27Jcm−2 under the vacuum condition and in the oxygen environment at a pressure of 133mbar. Various features of treated targets, such as surface morphology, chemical composition and crystalline structure are analyzed by scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction techniques, respectively. Scanning electron microscope analysis reveals the formation of laser-induced periodic surface structures (LIPSS), cavities, hillocks in both ambient environments (vacuum, oxygen). Cone-formation on the top of wave like ridges is observed under vacuum condition. In case of oxygen only redeposition is observed. Energy dispersive X-ray spectroscopy analysis exhibits that there is variation in chemical composition in both environments. When the target is treated in oxygen environment enhancement of the surface oxygen content is observed. X-ray diffraction exhibits that no new phases are formed under vacuum condition but a phase change in oxygen ambient is observed. For various fluences the variation in the peak intensity, crystallinity and d-spacing is observed under both ambient conditions.

Synthesis and characterization of CdSe/ZnS core‐shell quantum dots immobilized on solid substrates through laser irradiation

AbstractCdSe/ZnS core‐shell quantum dots (QDs) have been immobilized onto solid substrates by matrix assisted pulsed laser evaporation (MAPLE). An UV KrF* (λ = 248 nm, τFWHM ≅ 25 ns) excimer laser source was used for irradiations of the composite MAPLE targets. The targets were prepared by the dispersion of the CdSe/ZnS QDs in a solvent with high absorption at the incident laser radiation. The dependence of the surface morphology, crystalline structure, chemical composition, and functional properties of the laser transferred CdSe/ZnS QDs on the processing conditions as incident laser fluence value and ambient atmosphere inside the irradiation chamber was investigated. The possible physical mechanisms implied in the laser ablation process were identified.

Effect of laser irradiation on crystalline structure of enamel surface during whitening treatment with hydrogen peroxide

ObjectiveThis study is to evaluate the effect of laser activation on the whitening and crystalline structure of enamel surface during whitening treatment with hydrogen peroxide. MethodsBovine teeth were treated with whitening gel containing 35% hydrogen peroxide. A whitening gel was applied on the enamel surface for a period of 5min, and then irradiated using a diode laser (740nm) during whitening treatment for 0, 30, 60, 120 and 180s for the GL0-W, GL30-W, GL60-W, GL120-W and GL180-W groups, respectively. The total whitening application time was 30min for all groups. ResultsLaser-irradiated enamel groups showed a similar lightness compared to the GL0-W group. The thickness of porous layer observed on the enamel surface of GL0-W group was decreased by increasing the laser irradiation time. While the Ca and P contents of the GL0-W group were lower than those of the non-whitening treated group (GL0-C), the Ca and P contents of the GL180-W group were similar to those of the GL180-C group. The enamel crystallinity was dramatically decreased by whitening treatment without laser irradiation. However, the decrease of crystallinity was protected by laser irradiation during whitening treatment. Raman measurement verified that laser irradiation could prevent the loss of mineral compositions on enamel and maintain its crystalline structure. SignificanceThe professional whitening treatment with hydrogen peroxide and diode laser activation improves not only the whitening effect but also protects the change of enamel structure compared to the treatment with only gel.

Enhanced photocatalytic activity of CoO/TiO2 nanotube composite

Titania nanotube (TNT) array was fabricated by anodization of titanium in 0.2wt.% HF aqueous solution. The as-anodized TNT was crystallized to anatase phase with a heat treatment at 450°C. CoO/TNT nanocomposite was synthesized by cathodic deposition over the annealed TNT in 0.05M Co(NO3)2. The surface morphology and crystalline structure of the resultant CoO/TNT nanocomposite were characterized by X-ray diffraction (XRD), Raman spectrum and field emission scanning electron microscopy (FESEM). The influences of deposition time and current density on the surface morphology of CoO/TNT were studied. The photoelectrochemical response of CoO/TNT nanocomposite was investigated. All CoO/TNT exhibited higher photocurrent than bare annealed TNT did, which was caused by the enhanced photogenerated electron–hole pairs separation. However, the photocatalytic activity cannot be straightforwardly related to photocurrent response because it also depends on some other factors such as catalyst acidic properties, specific surface area and the adsorption of organic dye. Transient photocurrent measurement should not be used alone for the screening of photocatalytic materials.

Synthesis of Pt Doped Bi2O3/RuO2 Photocatalysts for Hydrogen Production from Water Splitting Using Visible Light

This study was focused on the preparation of modified bismuth oxide photocatalysts, including Ru and Pt doped Bi2O3, using sonochemically assisted method to enhance their photocatalytic activity. The crystalline phase composition and surface structure of Bi2O3 photocatalysts were examined using SEM, XRD, UV-visible spectroscopy, and XPS. Optical characterizations have indicated that the Bi2O3 presents the photoabsorption properties shifting from UV light region into visible light which is approaching towards the edge of 470 nm. According to the experimental results, visible-light-driven photocatalysis for water splitting with the addition of 0.3 M Na2SO3 and 0.03 M H2C2O4 as sacrificing agents demonstrates that Pt/Bi2O3-RuO2 catalyst could increase the amount of hydrogen evolution, which is around 11.6 and 14.5 micromol g(-1) h(-1), respectively. Plausible formation mechanisms of modified bismuth oxide and reaction mechanisms of photocatalytic water splitting have been proposed.

EFFECT OF STRUCTURAL CHANGES ON ENZYMATIC HYDROLYSIS OF EUCALYPTUS, SWEET SORGHUM BAGASSE, AND SUGARCANE BAGASSE AFTER LIQUID HOT WATER PRETREATMENT

A woody (eucalyptus (Eu)) and two herbaceous materials (sweet sorghum bagasse (SSB) and sugarcane bagasse (SCB)) were used to evaluate the effect of liquid hot water (LHW) pretreatment on enzymatic hydrolysis of various lignocelluloses. The results showed that enzymatic hydrolysis efficiency of pretreated materials was SCB>SSB>Eu at 5% solids loading, while SSB>SCB>Eu was at 10% and 20% solids loadings. This indicated the enzymatic hydrolysis efficiency of SCB could be influenced by solids concentration. The differences in surface morphology, crystalline structure, and functional groups of pretreated samples were also examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. SEM photographs and crystallinity indexes (CrI) showed that the structural compactness was Eu>SSB>SCB for both of untreated and treated materials. FTIR spectra showed that the conspicuousness of physicochemical changes was SCB>SSB>Eu. The differences in enzymatic hydrolysis efficiency of pretreated materials can be ascribed mainly to the structural differences.

Structure and surface nanomechanics of poly(l-lactide) from thermally induced phase separation process

The surface morphology, crystalline structure and nanomechanical properties of poly(l-lactide) (PLLA) samples prepared via thermally induced phase separation (TIPS) process have been investigated by scanning electron microscopy (SEM), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), wide-angle X-ray diffraction (WAXD), atomic force microscopy (AFM), force spectroscopy and nanoindentation. Typical nanofibrous scaffold was obtained at −24°C (NF sample) while a denser matrix with some plateletlike structure was obtained at 15°C (PL sample). The NF sample has a higher crystallinity with α′-form crystals while the PL sample has α-form crystals embedded in a largely amorphous matrix. The two kinds of samples have differences in the chain conformation with a more restricted backbone vibration and stiffened segmental motion in NF samples. The NF samples have a higher adhesion force although both samples showed a heterogeneous distribution of adhesion force on the surface based on force spectroscopy analysis. The alternating distribution of domains with higher and lower adhesion force exhibited a banded pattern on PLLA nanofibre. This pattern is proposed to reflect the distribution of crystal-rich and amorphous-rich domains in the semicrystalline samples. AFM-based nanoindentation test indicated that the nanofibrous NF samples can have more significant plastic deformation and creep than the largely amorphous PL samples. The sliding of the crystal-rich domains along the fibrils would account for this increased plasticity of the nanofiber.

Initial stages of the ion-beam assisted epitaxial GaN film growth on 6H-SiC(0001)

Ultra-thin gallium nitride (GaN) films were deposited using the ion-beam assisted molecular-beam epitaxy technique. The influence of the nitrogen ion to gallium atom flux ratio (I/A ratio) during the early stages of GaN nucleation and thin film growth directly, without a buffer layer on super-polished 6H-SiC(0001) substrates was studied. The deposition process was performed at a constant substrate temperature of 700°C by evaporation of Ga and irradiation with hyperthermal nitrogen ions from a constricted glow-discharge ion source. The hyperthermal nitrogen ion flux was kept constant and the kinetic energy of the ions did not exceed 25eV. The selection of different I/A ratios in the range from 0.8 to 3.2 was done by varying the Ga deposition rate between 5×1013 and 2×1014at.cm−2s−1. The crystalline surface structure during the GaN growth was monitored in situ by reflection high-energy electron diffraction. The surface topography of the films as well as the morphology of separated GaN islands on the substrate surface was examined after film growth using a scanning tunneling microscope without interruption of ultra-high vacuum. The results show, that the I/A ratio has a major impact on the properties of the resulting ultra-thin GaN films. The growth mode, the surface roughness, the degree of GaN coverage of the substrate and the polytype mixture depend notably on the I/A ratio.

Effect of Serine and Arginine on the Phase Transition from Amorphous CaCO<sub>3</sub> and CaCO<sub>3</sub>·6H<sub>2</sub>O to Calcite Film

Calcium carbonate, ubiquitous throughout nature, is one of the most biologically significant minerals. It is known that the organic matrix of biological materials controls the phase transition of CaCO3, but much remains undiscovered regarding its pathway from an amorphous to crystalline solid. In this study, examination of the initial formation of CaCO3 films has been proposed as a new methodology to identify the phase transition of CaCO3. We have identified a significant role for both serine and arginine in the synthesis of CaCO3 and have found them to be important for the stabilization of amorphous calcium carbonate and CaCO3·6H2O. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy have been used for the identification of crystalline phase and surface structure. This study presents information useful for understanding the phase transition of CaCO3 and the function of organic molecules in the formation of biological materials. [doi:10.2320/matertrans.M2012164]

Cathodic Deposition of TiO2: Effects of H2O2 and Deposition Modes

Cathodic deposition of titanium dioxide (TiO2) from two plating solutions with H2O2 and NaNO3 as their respective oxidants for converting Ti(III) into Ti(IV) are systematically compared. From the electrochemical quartz crystal microbalance (EQCM) and mass loading studies, the deposition solution containing H2O2, denoted as bath A, exhibits a higher rate of TiO2 deposition in comparison with the solution containing NaNO3, denoted as bath B, probably due to the formation of Ti(IV) oxy-hydroxyl species in bath A. However, the surface morphology and crystalline structure of annealed TiO2 deposits are not significantly affected by using different deposition baths. TiO2 deposits have been successfully electroplated onto Ti substrates from both baths under the dual-electrode deposition mode. The surface morphology of TiO2 is significantly influenced by the deposition methods including galvanostatic, potentiostatic, and pulse-rest modes. Finally, uniform porous morphologies of TiO2 in cm2 scale are controllable by varying the pulse-rest deposition variables (e.g., pulse frequency and duty percentage) due to its unique advantages such as excellent adhesion, good uniformity, and controllable particle size of TiO2.

Structural Characterizations and Optical Properties of CeO2 Thin Films Prepared by Laser Molecular-Beam Epitaxy

Epitaxial CeO2 thin films were deposited on Si (111) substrates by laser molecular-beam epitaxy (LMBE). Surface roughness, crystalline structure and optical constants were characterized by in situ reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), Raman spectroscopy and spectroscopic ellipsometry. AFM showed that the epitaxial CeO2 film has a quite smooth surface with a root mean square roughness of 0.563 nm over a 2 μm × 2 μm area. Raman spectroscopy results indicated good crystallinity of the thin film. Refractive index n and extinction coefficient k of the thin films were calculated in the wavelength region of 370–1000 nm and the values were found to gradually decrease from 2.90 and 0.0321 at 370 nm to 2.35 and 0.0017 at 1000 nm, respectively. The direct and indirect optical band gaps of the film were estimated to be around 3.17 and 2.64 eV, respectively.

Influence of Substrate Temperature on Structural, Electrical and Optical Properties of ZnO:Al Thin Films

Transparent and conductive aluminium-doped zinc oxide thin films have been prepared by dc magnetron sputtering technique using targets composed of ZnO and aluminium. Polycrystalline ZnO:Al films were deposited onto a heated glass substrate. Surface morphology and crystalline structure as well as optical and electrical properties of the deposited films were found to depend directly on substrate temperature. From optical and electrical analysis it was observed that optical transmittance and conductivity of the ZnO:Al transparent conductive oxide films increased when the deposition temperature was raised from 200 to 400 o C. Films grown on substrates heated at 300 o C showed a high conductivity value of 0.2 x 10 2 Ω -1 cm -1 and a visible transmission of about 80%. The growth of ZnO:Al thin films on the surface of glass substrate at temperatures of 300 o C and aluminium doping levels of 0.9 at.% were the best to attain ZnO:Al films with optical and structural qualities as required for solar cell applications, as a window material in antireflection coatings or optical filters. Received: 17 March 2009; Revised: 22 November 2009 ; Accepted: 23 November 2009