Resolution Transmission Electron Microscopy Results Research Articles

Boosting photocurrent density of 1D TiO2 based photoanodes by bismuth vanadium oxide enhancement for photoelectrochemical cell application

A photoelectrochemical cell (PEC) is a device that can convert light energy into hydrogen fuel. In the present work, a 1D TiO2 based photoanode was enhanced by BiVO4 (BVO). All TiO2 and BVO/TiO2 photoanodes were fabricated by a hydrothermal method. Structural and surface morphology of the thin films were characterized by various spectroscopies. The 1D TiO2 and BVO/TiO2 nanorods were well aligned perpendicular to the fluorine doped tin oxide (FTO) substrate. X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) revealed BVO formation on the TiO2 surface, which was in agreement with the energy dispersive X-ray spectroscopy (EDS) and high resolution transmission electron microscopy (HRTEM) results. The bandgap of the TiO2 photoanode was decreased due to the BVO enhancement. According to UV–visible spectroscopy and the valence band binding energy from XPS, the estimated bandgap of BVO/TiO2 was 2.8 eV, while pure TiO2 was 3.1 eV. Based on this result, the PEC comprised of a BVO/TiO2 photoanode can harvest visible light. Electrochemical impedance spectroscopy (EIS) was performed to reveal the underlying physical properties when the PEC was operated. Upon illumination with a solar simulator, most of the PECs comprised of a BVO/TiO2 photoanode exhibited greater performance than the PECs comprised of a pristine TiO2 photoanode. The significant increase in performance was due to the light absorption extension to the visible region and the BVO anchoring, which leads to a low internal charge carrier resistance of the TiO2 based photoanode.

ZnO nanoparticles doping with transition metal elements in polymeric and biomacromolecular matrix and their optical evolution

Abstract The 5% Cu doped zinc oxide nanoparticles in polyvinylpyrrolidone matrix and 5% Fe doped zinc oxide nanoparticles in biotin matrix were prepared and the effect of dopants and stabilizers on different properties were investigated. Surfactant controlled particle sizes and dopants induced changes in optical properties were reported as evident from X-ray diffraction data analysis and absorption measurements. High resolution transmission electron microscopy results of Cu doped ZnO nanoparticles are close to the XRD results. The reduced band gaps are estimated to be 2.90 eV and 2.37 eV for Cu and Fe doped ZnO respectively from absorption measurements. Photoluminescence measurements show how the dopants and surfactant can alter the excitonic and defect related emission in the doped ZnO nanoparticles. Raman spectroscopy of Cu doped ZnO nanoparticles shows characteristics of Cu in to ZnO lattice and new phonon scattering mode. The room temperature ferromagnetism in Fe doped ZnO and its correlation with defects were discussed.

Direct observation of ultra-rapid solid phase crystallization of amorphous silicon films irradiated by micro-thermal-plasma-jet

This paper presents a new method to directly observe the transient evolution of amorphous silicon temperature and the solid phase crystallization during micro-thermal-plasma-jet irradiation. Using the time-resolved reflectivity analysis, nucleation temperature and characteristic crystallization time were determined. When the heating rate increases from 4.45×105to 2.28×106K/s, the nucleation temperature increases from 985 to 1071 °C. The characteristic crystallization time decreases from 95 to 20 μs with an increase in heating rate. Crystallization time as a function of temperature corresponds to the activation energy of 2.9 eV. This energy relates to both the nucleation and growth process. Micro-Raman spectroscopy results indicate that the crystalline volume fraction of solid–phase crystallized Si film is higher than 65 %, and it increases to 80 % with decreasing scanning speed. Both high resolution transmission electron microscopy results and theoretical calculation indicate that there is a distribution of final crystal size. The average grain size is smaller than 50 nm and depends on the annealing conditions, namely the faster heating rate is, the smaller grain size is.

Effect of PMMA on the surface of exfoliated MoS2 nanosheets and their highly enhanced ammonia gas sensing properties at room temperature

Abstract Highly sensitive ammonia (NH3) gas sensors were fabricated through polymethyl-methacrylate (PMMA) assisted exfoliation of molybdenum disulfide (MoS2) based multilayered nanosheets. The PMMA-MoS2 nanocomposites were successfully prepared by facile ultra-sonication technique. The physical-chemical properties of PMMA assisted MoS2 nanocomposites were evaluated by various analytical methods. High resolution Transmission Electron Microscopy and AFM results were revealed the uniform and thin surface coating of PMMA on the MoS2 sheets. Most importantly, obtained PMMA-MoS2 nanocomposites were dropped on SiO2/Si substrates, subsequently fabricated lateral integrated Pt electrodes to measure the gas sensing properties. Remarkable sensing properties obtained for PMMA-MoS2 nanocomposite-based sensor with an excellent sensitivity of (54%), which is significantly higher than that of bulk MoS2 (15.2%). Moreover, the fabricated PMMA-MoS2 nanocomposites based gas sensor possesses excellent selectivity to H2, C3H6O, and CO2. The observed results exhibit that the exfoliation of MoS2 with PMMA using ultra sonication techniques are promising for enhanced NH3 gas monitoring. Compared to the pure MoS2, the adsorption ability of PMMA-MoS2 surface induces the oxygen functional groups strongly affect the sensing properties. The superior gas sensing properties of this present surface modified PMMA-MoS2 hybrid sensors are promising and sustainable compared with the existing MoS2 based NH3 sensors.

Gamma irradiation-induced phase transitions of boron nitride nanoparticles

Recently different methods are explored to synthesize suparhard orthorhombic boron nitride (o-BN) nanomaterials which have a wide range of industrial applications in the sensors, fiters, battery, biological applications and deep ultraviolet light emitting diodes. In this research work, a simple method is reported to synthesis of cubic boron nitride nanoparticles (c-BNNPs) via gamma irradiation induced phase transition of hexagonal boron nitride nanoparticles (h-BNNPs). X Ray Diffraction (XRD) and Raman Spectroscopy results confirmed the phase transition of h-BNNPs to o-BNNPs at the dose of 21 kGy. At the dose of 24 kGy, high resolution transmission electron microscopy (HRTEM) results showed that phase of hexagonal boron nitride nanoparticles (h-BNNPs) are transformed to B2O3 whereas at lower dose (18 kGy), coalescence of hexagonal boron nitride nanoparticles (h-BNNPs) is observed through high resolution transmission electron microscopy (HRTEM) results. X-rays diffractions (XRD) results showed that grain size of hexagonal boron nitride nanoparticles (h- BNNPs) is increased. Mechanism of phase transition and coalescence of hexagonal boron nitride nanoparticles (h-BNNPs) are explained via high energy and short wavelength gamma radiations act on B-N covalent bond isotopically.

Opto-Electronic Properties of Green Synthesized ZnS Nanostructures

ZnS nanostructures are synthesized by a wet chemical route using starch as green capping agent under nitrogen environment. The as-prepared nanostructures are characterized structurally, optically and electrically. X-ray diffraction (XRD) spectra confirm that the zinc sulfide (ZnS) nanoparticles have cubic phase (zinc blende). UV–Vis spectrum of the sample clearly shows that the absorption peak exhibits blue shift compared to their bulk counterpart, which confirms the quantum confinement effect of the nanostructures. Its photoluminescence (PL) spectrum shows near band gap emission at 392[Formula: see text]nm and extrinsic emission at 467[Formula: see text]nm. The particle sizes calculated from XRD and UV studies are in fair agreement with high resolution transmission electron microscopy (HRTEM) results. Starch is found to be a noble capping agent in bringing quantum confinement. The synthesis under nitrogen environment has been observed to produce quality products by reducing the oxide traces. Moreover, the I–V characteristics under dark and illumination show that ZnS can be more suitable as photodetector.

Fabrication of a Co(OH)2/ZnCr LDH "p-n" Heterojunction Photocatalyst with Enhanced Separation of Charge Carriers for Efficient Visible-Light-Driven H2 and O2 Evolution.

Photocatalytic generation of H2 and O2 by water splitting remains a great challenge for clean and sustainable energy. Taking into the consideration promising heterojunction photocatalysts, analogous energy issues have been mitigated to a meaningful extent. Herein, we have architectured a highly efficient bifunctional heterojunction material, i.e., p-type Co(OH)2 platelets with an n-type ZnCr layered double hydroxide (LDH) by an ultrasonication method. Primarily, the Mott-Schottky measurements confirmed the n- and p-type semiconductive properties of LDH and CH material, respectively, with the construction of a p-n heterojunction. The high resolution transmission electron microscopy results suggest that surface modification of ZnCr LDH by Co(OH)2 hexagonal platelets could form a fabulous p-n interfacial region that significantly decreases the energy barrier for O2 and H2 production by effectively separating and transporting photoinduced charge carriers, leading to enhanced photoreactivity. A deep investigation into the mechanism shows that a 30 wt % Co(OH)2-modified ZnCr LDH sample liberates maximum H2 and O2 production in 2 h, i.e., 1115 and 560 μmol, with apparent conversion efficiencies of H2 and O2 evolution of 13.12% and 6.25%, respectively. Remarkable photocatalytic activity with energetic charge pair transfer capability was illustrated by electrochemical impedance spectroscopy, linear sweep voltammetry, and photoluminescence spectra. The present study clearly suggests that low-cost Co(OH)2 platelets are the most crucial semiconductors to provide a new p-n heterojunction photocatalyst for photocatalytic H2 and O2 production on the platform of ZnCr LDH.

Facile one-step synthesis of Ag@CeO2core–shell nanospheres with efficient catalytic activity for the reduction of 4-nitrophenol

Ag@CeO2 core–shell nanospheres were synthesized by a facile one-step solvothermal route from Ce(NO3)3·6H2O, AgNO3, poly(N-vinylpyrrolidone) (PVP), and ethanol. The structure, composition, BET specific surface area and optical properties of Ag@CeO2 core–shell nanospheres were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, N2 adsorption–desorption isotherm analysis, and UV-vis diffuse reflectance spectroscopy. Field emission scanning, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy etching results of the as-synthesized Ag@CeO2 nanospheres revealed that the as-synthesized Ag@CeO2 nanospheres consist of a Ag core and a CeO2 shell. The catalytic results demonstrated that the as-synthesized Ag@CeO2 nanospheres possessed higher catalytic activity than pure Ag (which was synthesized by a similar solvothermal method) in the reduction of 4-nitrophenol. Their enhanced catalytic activity is found to be due to the unique oxidized Ag species induced by the strong interaction between the core surface of Ag nanospheres and surface defects (oxygen vacancies) of the CeO2 shell. The herein proposed Ag@CeO2 core–shell nanospheres are promising catalytic candidates for the reduction of p-nitrophenol because of their simple preparation route and high catalytic activity.

Effect of dislocation-twin boundary interaction on deformation by twin boundary migration

The effect of interaction between {101̅2} twin boundaries (TBs) and 〈a〉 dislocations on deformation behavior of TBs migration process was studied. This TB-dislocation interaction greatly enhances activation stress for TB motion and retards TB migration during reloading. Interestingly, a severe TB-dislocation interaction improves strain hardening at the early stage, while reduces the peak hardening rate at the latter stage. High resolution transmission electron microscopy results indicate that severe TB-dislocation interaction greatly damages the coherence of TBs and might induce curving of TBs. Migration of the TBs that intensively interact with dislocations leaves behind low angle boundaries at the initial TBs.

Synthesis of Ag2CO3/CeO2 microcomposite with visible light-driven photocatalytic activity

Ag2CO3/CeO2 microcomposite was synthesized via chemical precipitation from pure CeO2 microspheres, AgNO3, and NaHCO3. X-ray diffraction, inductively coupled plasma optical emission spectroscopy, field emission scanning electron microscope, and high resolution transmission electron microscopy results confirmed the forming of Ag2CO3/CeO2 microcomposite. Field emission scanning microscope and high resolution transmission electron microscopy results of the as-synthesized Ag2CO3/CeO2 microcomposite revealed that Ag2CO3 particles were uniformly deposited on the surface of CeO2 microspheres (core). UV–vis diffuse reflectance spectra of both pure CeO2 and Ag2CO3/CeO2 microcomposite displayed a band gap edge at about 360−390nm. However, compared with pure CeO2, an additional broad tail from approximately 400nm to 800nm appeared in the UV–vis diffuse reflectance spectrum of Ag2CO3/CeO2 microcomposite. The photocatalytic studies indicated that the as-synthesized Ag2CO3/CeO2 microcomposite was promising photocatalyst in remediation of water polluted by some chemically stable azo dyes under visible light irradiation.

Multi-layered Al2O3/LixV2O5/LiV3O8 nanoflakes with superior cycling stability as cathode material for Li-ion battery

Al2O3 coating is utilized in this work to further improve the cycling stability of LiV3O8 nanoflakes. Surprisingly, three layered Al2O3/LixV2O5/LiV3O8 nanostructure is well formed as confirmed by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) results. When used as a cathode for Li-ion battery, the hybrid demonstrates significantly improved cycling stability with a discharge capacity of 203mAhg−1 remaining after 200 cycles at 150mAg−1 and 87.5% of the initial capacity maintaining after 500 cycles at 300mAg−1. Such superior cycling performance should be attributed to the mutual protection of Al2O3 and LixV2O5 layer between Al2O3 and LiV3O8, which can well suppress the damage of LiV3O8 during the long-term cycling process. More importantly, the LixV2O5 middle layer could contribute to the improvement of interfacial electrochemical properties of the hybrid electrode.

Graphene oxide supported molybdenum cluster: first heterogenized homogeneous catalyst for the synthesis of dimethylcarbonate from CO2 and methanol.

The octahedral molybdenum cluster-based compound, Cs2 Mo6 Br(i) 8 Br(a) 6 was immobilized on graphene oxide (GO) by using a facile approach. High resolution transmission electron microscopy results revealed that molybdenum clusters were uniformly distributed on the GO nanosheets. Cs2 Mo6 Br(i) 8 Br(a) 6 was attached to the GO support via chemical interaction between apical ligands of Mo6 Br(i) 8 Br(a) 6 cluster units and oxygen functionalities of GO, as revealed by XPS studies. The developed material was used for the synthesis of dimethyl carbonate by reduction of carbon dioxide. The synthesized catalyst, that is, GO-Cs2 Mo6 Br(i) 8 Br(a) x , exhibited higher catalytic efficiency than its homogeneous analogue without using dehydrating agent. The catalyst was found to be efficiently recyclable without significant loss of catalytic activity.

Synthesis of Ag2CO3/ZnO nanocomposite with visible light-driven photocatalytic activity

Ag2CO3/ZnO nanocomposite was synthesized via a chemical precipitation from pure ZnO nanowires, AgNO3, and NaHCO3. X-ray diffraction, inductively coupled plasma optical emission spectroscopy, and high resolution transmission electron microscopy results confirmed the forming of Ag2CO3/ZnO nanocomposite. High resolution transmission electron microscopy results of the as-synthesized Ag2CO3/ZnO nanocomposite revealed that Ag2CO3 nanoparticles were attached to the surface of ZnO nanowires. UV–vis diffuse reflectance spectra of both pure ZnO and Ag2CO3/ZnO nanocomposite displayed a band gap edge at about 360−390nm. However, compared with pure ZnO, an additional broad tail from approximately 400nm–800nm appeared in the UV–vis diffuse reflectance spectrum of Ag2CO3/ZnO nanocomposite. The photocatalytic studies indicated that the as-synthesized Ag2CO3/ZnO nanocomposite was a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes under visible light.

Controlled Preparation of Co3O4@porous-SiO2 Nanocomposites for Fischer–Tropsch Synthesis

Monodispersible Co3O4 nanoparticles were prepared via a facile solvothermal route using polyvinylpyrrolidone (PVP) as capping agent and the porous silica shell was then coated by means of the Stöber process to fabricate Co3O4@porous-SiO2 (Co3O4@p-SiO2) nanocomposites. The particle size of Co3O4 and porous silica shell thickness of Co3O4@p-SiO2 nanocomposites could be easily controlled through changing the amount of PVP and tetraethoxysilane, respectively. The high resolution transmission electron microscopy results, together with the X-ray diffraction results, indicated that monodispersible Co3O4 nanoparticles were successfully prepared and uniformly encapsulated by porous silica. During the growth of silica shell, the PVP was trapped and dispersed in the silica shell. As a result, the porous silica shell was obtained after burning off the PVP and a positive correlation existed between the Brunauer–Emmett–Teller surface area of the porous silica shell and quantity of PVP in the original Co3O4 nanoparticles. Compared with the Co/SiO2 reference catalyst, CO conversion of the Co@p-SiO2 model catalyst was more stable and higher in a period of 240 h, and hydrocarbon selectivity towards C5–C18 fraction was also higher than that of the Co/SiO2 catalyst. The results of analysis for the Co@p-SiO2 catalyst showed that core@shell structure could maintain high dispersion of Co particles so as to provide higher number of Co active sites, and enhance selectivity towards C5–C18 fraction due to confined structure of porous channel in the silica shell. Schematic diagram of the procedure for synthesizing Co3O4@p-SiO2 nanocomposites.

Solvothermal synthesis of Ag/ZnO nanocomposite with enhanced photocatalytic activity

Ag/ZnO nanocomposite was fabricated by a solvothermal route from Zn(NO3)2·6H2O, AgNO3, ethanol, and NaOH. Inductively coupled plasma optical emission spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy results confirmed the forming of Ag/ZnO nanocomposite. High resolution transmission electron microscopy results of the as-synthesized Ag/ZnO nanocomposite revealed that Ag nanoparticles were attached to the surface of ZnO. Moreover, the PL results of the as-synthesized Ag/ZnO nanocomposite indicated that the separation efficiency of photogenerated carriers and the photostability of ZnO improved after ZnO is coupled with Ag. The photocatalytic studies indicated that the as-synthesized Ag/ZnO nanocomposite was a promising photocatalyst in remediation of water polluted by some chemically stable azo dyes.

Facile synthesis of two-dimensional highly branched gold nanostructures in aqueous solutions of cationic gemini surfactant

Snowflake-like two-dimensional highly branched gold nanostructures (2DHBNs) have been constructed in the presence of hexamethylene-1,6-bis (dodecyl dimethylammonium bromide) (C12C6C12Br2) through the reduction of HAuCl4 by ascorbic acid. High resolution transmission electron microscopy results indicate that the 2DHBNs are uniform in crystallographic orientation, where the branched nanostructures grow along the <211> direction and present multiple twin planes stacked along the <111> direction. An ex situ kinetic study, followed by TEM observations, shows that the 2DHBNs are evolved from triangular nanoprisms through overgrowth along the <211> direction. The gemini surfactant C12C6C12Br2 is found to be the most essential factor for the formation of the 2DHBNs. C12C6C12Br2 may selectively absorb onto the (111) planes, which promotes the construction of 2D nanostructures. Moreover, C12C6C12Br2 can act as an excellent kinetic modifier to control the growth of the nanostructures, which also affects the generation of branched nanostructures. The as-prepared 2DHBNs exhibit an efficient surface-enhanced Raman scattering (SERS) property which has potential application in constructing sensitive SERS substrates.

Synthesis of AgBr/ZnO nanocomposite with visible light-driven photocatalytic activity

AgBr/ZnO nanocomposite was synthesized via chemical precipitation from pure ZnO nanowires, AgNO 3, and NaBr. Inductively coupled plasma optical emission spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy results confirmed the forming of AgBr/ZnO nanocomposite. High resolution transmission electron microscopy results of the as-synthesized AgBr/ZnO nanocomposite revealed that AgBr nanoparticles were attached to the surface of ZnO nanowires. UV–vis diffuse reflectance spectra of both pure ZnO and AgBr/ZnO nanocomposite displayed a band gap edge at about 350–380 nm. However, compared with pure ZnO, an additional broad tail from approximately 400 nm to 700 nm appeared in the UV–vis diffuse reflectance spectrum of AgBr/ZnO nanocomposite. The photocatalytic studies indicated that the as-synthesized AgBr/ZnO nanocomposite was a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes under visible light.

Hydrothermal deposition of single crystalline germanium nanorods

Abstract Single crystalline germanium nanorods have been prepared via a simple hydrothermal deposition process using Ge and GeO2 as the starting materials under the hydrothermal conditions of 400 °C and 7.1 – 8 MPa. Scanning electron microscopy and transmission electron microscopy observations show the diameter of the nanorods ranging from 70 nm to 500 nm and the length greater than 10 μm. X-ray diffraction and high resolution transmission electron microscopy results indicate that the nanorods are mainly composed of single crystalline Ge with cubic diamond structure. The growth process has been proposed as the CuGeO3-assisted growth mechanism.

Structural and optical properties of RF magnetron sputtered aluminum nitride films without external substrate heating

We report structural and optical properties of aluminum nitride (AlN) thin films prepared by RF magnetron sputtering. A ceramic AlN target was used to sputter deposit AlN films without external substrate heating in Ar–N 2 (1:1) ambient. The X-ray diffraction and high resolution transmission electron microscopy results revealed that the films were preferentially oriented along c-axis. Cross-sectional imaging revealed columnar growth perpendicular to the substrate. The secondary ion mass spectroscopy analysis confirmed that aluminum and nitrogen distribution was uniform within the thickness of the film. The optical band gap of 5.3 eV was evaluated by UV–vis spectroscopy. Photo-luminescence broad band was observed in the range of 420–600 nm with two maxima, centered at 433 nm and 466 nm wavelengths related to the energy states originated during the film growth. A structural property correlation has been carried out to explore the possible application of such important well oriented nano-structured two-dimensional semiconducting objects.

Influence of the Cd/S Molar Ratio on the Optical and Structural Properties of Nanocrystalline CdS Thin Films

Nanocrystalline CdS thin films have been deposited using precursors with different thiourea concentration onto glass substrates by sol-gel spin coating method. The crystalline nature of the films has been observed to be strongly dependent on thiourea concentration and annealing temperature. The CdS films are found to be nanocrystalline in nature with hexagonal structure. The grain size is found to be in the range of 7.6 to 11.5 nm depending on the thiourea concentration and annealing temperature. The high resolution transmission electron microscopy (HRTEM) results of the CdS films prepared using cadmium to thiourea molar ratio of 0.3:0.3 indicate the formation of nanocrystalline CdS with grain size of 5 nm. Fourier transform infrared (FTIR) analysis shows the absorption bands corresponding to Cd and S. The optical study carried out to determine the band gap of the nanostructured CdS thin films shows a strong blue shift. The band gap energy has been observed to lie in the range of 3.97 to 3.62 eV following closely the quantum confinement dependence of energy on crystallite radius. The dependence of band gap of the CdS films on the annealing temperature and thiourea concentration has also been studied. The photoluminescence (PL) spectra display two main emission peaks corresponding to the blue and green emissions of CdS.