Transmission High-energy Electron Diffraction Research Articles

Quartz crystal microbalance sensor for NO2 detection based on electrospun amorphous titanium oxide fibers

The sensitivity to various concentrations of NO2 is studied of a 16-MHz quartz crystal microbalance (QCMs) coated by immobilized electrospun amorphous titanium oxide fibers. The morphology, phase and chemical composition of the sensing material are determined by scanning and high-resolution transmission electron microscopy (SEM, HRTEM), transmission high-energy electron diffraction (THEED) and X-ray photoelectron spectroscopy (XPS). Resonance frequency shifts are established of the QCM-TiO2 system within a broad interval of NO2 concentrations. Experimental evidence is found for a reversible gas sorption at the lowest tested gas concentration of 50 ppm. Additional sensor response is established to gradually increasing NO2 concentrations up to 5000 ppm. It is demonstrated that electrospun amorphous titanium oxide fibers are promising sensing materials for NO2 detection.

Inversion of Many-Beam Bragg Intensities for Phasing by Iterated Projections: Removal of Multiple Scattering Artifacts from Diffraction Data.

An iterated projection algorithm (N-Phaser) is developed that reconstructs a scattering potential from N-beam multiple Bragg scattered intensities. The method may be used to eliminate multiple scattering artifacts from electron diffraction data, solving the phase problem and increasing the thicknesses of samples used in materials science, solid-state chemistry, and small molecule crystallography. For high-energy transmission electron diffraction, we show that the algorithm recovers accurate complex structure factors from a wide range of thicknesses, orientations, and relativistic beam energies, and does not require known thickness or atomic-resolution data if sufficient multiple scattering occurs. Extensions to Cryo-electron microscopy and Micro-electron diffraction are suggested.

Preparation of Zn-Al2O3 and Zn-TiO2 Composite Films Plated from Non-Suspended Solution by Using Electrochmical Techniques

A composite plating film that contains particles in the plated films have been investigated. The coexistence of nonmetal particles in metallic matrix improve the mechanical and chemical properties such as wear resistance, self-lubrication, corrosion resistance and metal-polymer adhesion. The plating baths for composite plating usually contain codeposited powders. However the powders in the bath generally detriorate bath stability and make filtalization difficult. A composite plated film which is plated bath without powder, non-suspended solution, is strongly requested. Dr. S.Oue and his co-workers have reported that Zn-Al2O3 composite films were plated from non-suspended solution by using quaternary ammonium salt1). The zinc matrix with aluminum oxide particles composite films from non-suspended solution containing quaternary ammonium salts were also investigated. The plating bath contains 520 mol/m3 ZnSO4·7H2O and 79 mol/m3 Al2(SO4)3·14-18H2O as metal source. A quaternary ammonium salts of benzyldimethyltetradecylammonium chloride dehydrate (BDTAC, Wako Co.,Ltd.) was used in this study. An observation by transmission electron microscopy (TEM). Two different deposits were observed, one is needle-shaped deposit and the other is closely packed fine particle area. Magnified photograph shows closely packed fine particle area and fine particles are clearly observed. From results of composition analyses, the A area, needle-shaped deposit, is composed of 82.6 at% zinc, 17.0 at% aluminum and 15.7at％ oxygen. As the same matter, the B area, closely packed fine particle area, is composed of 45.6 at% zinc, 29.2 at% aluminum, 20.6 at％ oxygen and 4.5 at% sulfur. The zinc content of area A, needle-shaped deposit, is much higher than that of area B, closely paced fine particle area. On the other hand, the aluminum content of area B is much higher than that of area A. It is concluded based on above results that the needle-shaped deposit is mainly composed of Zn or ZnO, and the fine particle is mainly composed of θ-Al2O3 from transmission high energy electron diffraction (THEED) observation. The origin of sulfur is not clear. Next, a composite Zn-TiO2 plated film from non-suspended solution has been investigated. The plating bath 390 mol/m3 ZnSO4·7H2O and 20 mol/m3 TiOSO4・1-2H2O as metal source. A quaternary ammonium salts of 1.0 mol/m3 benzyldimethylphenylammonium chloride was used in this study. Since a titanium easily changes to hydroxide, 9.0 mol/m3 sodium gluconate is added as a complexing agent. In the case of Zn-Al2O3 composite plating, galvanostatic method is effective to increase Al content. The aluminum content increased with increasing current density. On the other hand, in the case of Zn-TiO2 composite plating, a pulse plating method is effective for to increase Ti content in the films. A titanium content decreased abruptly with increasing duty cycle and reached minimum content at 0.5 duty cycle, and then increased with increasing duty cycle. The titanium content increased with increasing current density less than 500 A/m2 and reached at maximum titanium content, 35.9 at%, then the titanium content decreased with increasing current density. From X-ray photoelectron spectroscopy (XPS) measurement, Ti was confirmed as oxidic state, TiO2. Since titanium dioxide has two kinds of crystal structure, rutyl and anatase. Next, a crystal structure was investigated. Figure 1 shows TEM observation results of Zn-TiO2 plated films from non-suspended solution as the same method as Zn-Al2O3 plating using quaternary ammonium salts. Figure 1a shows bright image of TEM micrograph. A grain is clearly observed and its diameter is about 10nm. Figure 1b shows results of transmission high energy electron diffraction (THEED) and Fig.1c summarizes results of Fig.1b. Three different of crystals have been observed by THEED, anatase type TiO2, Zn and ZnO. Since the anatase type TiO2 shows photocatalytic properties. It is expected that the composite Zn-TiO2 plated films show photocatalytic properties. These results shows the composite film have been prepared from non-suspended solution by electrochemical techniques. Reference 1) S. Oue, H. Nakano, S. Kobayashi, T. Akiyama, H. Fukushima, and K. Okumura, J. Surf. Finish. Soc. Jpn. 53, pp.920-925(2002) [In Japanese] Figure 1

Hopping Precession of Molecules in Crystalline Carbon Dioxide Films

We report a low-temperature transmission high-energy electron diffraction study of solid carbon dioxide films in the temperature range 15–87 K. The precise analysis of the experimental diffraction intensities shows that molecular axes noticeably deviate from the cubic space diagonals of the \(Pa\overline{3}\) structure. The molecular tips tend to be oriented toward the empty spaces between two molecules in the nearest basal planes. Nevertheless, the crystal structure is still identified as \(Pa\overline{3}\) but with 24 equivalent positions for oxygen atoms instead of 8 positions as it was thought before. We have shown that the relevant maximal angle deviations in the selected directions could be as big as \({\sim } 30^{\circ }\) at the lowest temperatures and they decrease at higher temperature. This results in hopping precession of molecules instead of simple librations.

Preparation of Composite Film from Non-Suspended Solution By Electrochemical Technique

A composite plating method is very useful to add new function in plated films. However, the composite plating method has serious problems due to particles in the bath, deterioration of bath stability and difficulty of filtering to maintain quality of plated films. Oue et. al.1) reported a composite films, Zn-Al2O3, plated from non-suspended solution bath without particles by using quaternary ammonium salts. In this study, two type composite films, Zn-Al2O3 and Zn-TiO2, have been prepared from non-suspended solution by electrochemical technique. First, results of Zn-Al2O3 composite films were reported. The zinc matrix with aluminum oxide particles composite films from non-suspended solution containing quaternary ammonium salts were investigated. The solution contains 520 mol/m3 ZnSO4·7H2O and 79 mol/m3 Al2(SO4)3·14-18H2O as metal source. A quaternary ammonium salts of Benzyldimethyltetradecylammonium chloride dehydrate (BDTAC, Wako Co.,Ltd.) was used in this study. Transmission electron microscopy (TEM) was used to evaluate the composite films. Bath pH at 2.5 is the best of all and high aluminum content ratio values, Al/(Al+Zn), more than 30at% are obtained. The aluminum content ratio values increase with increasing current density under the condition of bath pH at 2.5 and 3.0. However, the films plated bath whose bath pH adjusted at 2.0 showed almost no aluminum content. Since the codeposition mechanism is pH jump at the cathode electrodes, pH value of 2.0 is too low. From transmission electron microscopy (TEM) measurement, two different deposits were observed as shown in Fig.1, one is needle-shaped deposit and the other is closely packed fine particle area. Magnified photograph shows closely packed fine particle area and fine particles are clearly observed. From results of composition analyses, the D area, needle-shaped deposit, is composed of 82.6 at% zinc, 17.0 at% aluminum and 15.7at% oxygen. As the same matter, the E area, closely packed fine particle area, is composed of 45.6 at% zinc, 29.2 at% aluminum, 20.6 at% oxygen and 4.5 at% sulfur. The zinc content of area D, needle-shaped deposit, is much higher than that of area E, closely paced fine particle area. On the other hand, the aluminum content of area E is much higher than that of area D. It is concluded based on above results that the needle-shaped deposit is mainly composed of Zn or ZnO, and the fine particle is mainly composed of Al2O3 from electron diffraction measurement. From results of transmission high energy electron diffraction (THEED) measurement, the fine particles were determined as θ-Al2O3. Therefore, first, aluminum ion formed Al(OH)3 near the cathode electrode by increasing pH value. Then it was dehydrated and it changed to θ-Al2O3. From X-ray diffraction (XRD) measurement, no peaks due to θ-Al2O3 have been observed. The size of θ-Al2O3 particles, whose diameter is about 5nm, is too small to detect by XRD measurement. However, transmission high energy electron diffraction (THEED) measurement shows higher sensitivity and the crystal structure is determined as θ-Al2O3. The origin of sulfur is not clear. Second, the results of Zn-TiO2 composite films were reported. The solution contains 520 mol/m3 ZnSO4·7H2O and 79 mol/m3 TiSO4·1-2H2O as metal source. A quaternary ammonium salts of Benzyldimethyltetradecylammonium chloride dehydrate (BDTAC, Wako Co.,Ltd.) was also used in this study. The plating bath temperature was controlled at 40 oC. The titanium was difficult to plate because it is easy to precipitate as a hydroxide. A complexing agent was very important to prevent from precipitating. In this study, six kinds of complexing agents ethylenediamintetraacetic acid (EDTA), glycine, formic acid, trisodium citrate, ascorbic acid and gluconic acid, have been investigated. A critical pH value to precipitate was evaluated by changing complexing agent. The critical pH values by different complexing agents, ethylenediamintetraacetic acid (EDTA), glycine , formic acid, trisodium citrate, ascorbic acid and gluconic acid, were 1.65, 1.85, 2.06, 2.65, 2.67 and 5.50, respectively. The gluconic acid is one of the most promising candidates of theses 6 complexing reagent. The 0.5g or 1.0g gluconic acid added to the plating baths and bath pH was controlled at 0.5 or 1.0. A current density was controlled from 50 to 500 A/m2. The highest TiO2 content value, 1.53 at%, was obtained at following condition, gluconic acid concentration was 1.0 g/l, bath pH was 0.5, and current density was 100 A/m2. Therefore, the two types of composite films, Zn-Al2O3 and Zn-TiO2, have been prepared by using quaternary ammonium salts, BDTAC, from non-suspended solution. Acknowledgement: This work was partially aided by MEXT-supported Program for the Strategic Research Foundation at Private Universities. [1] S. Oue, H. Nakano, S. Kobayashi, T. Akiyama, and K. Okumura, J. Surface Finishing Soc. Jpn.,53 920 (2002) . Figure 1

Synthesis Procedures for Silver Nanoparticles

This article gives some proposals on how to grow silver nanoparticles using different methods. Dilute silver salts are recommended as the metal precursor starting solutions. The formation of the silver nanoparticles is to be monitored using UV-Vis absorption spectroscopy so as to reveal the formation of silver nanoparticles and how they will exhibit surface plasmon absorption maxima at 418-420 nm from the UV–Vis spectrum. The Mie light scattering theory will be applied and the experimental results analyzed to show the diameter of silver nanoparticles in colloidal solution. Energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–Vis spectroscopy are proposed to be used to characterize the formed silver nanoparticles obtained. The energy-dispersive spectroscopy (EDX) of the nanoparticles dispersion will confirm the presence or absence of elemental silver signal peaks. The size and morphology of the formed silver nanoparticles will be determined by transmission electron microscopy. The synthesized silver nanoparticles will be structurally characterized by using X-ray diffraction and transmission high-energy electron diffraction (HEED) and the peaks in the XRD pattern will be compared to the standard values of the face-centeredcubic form of metallic silver (ICCD-JCPDS card no. 4-0787).

Comparing ultrafast surface and bulk heating using time-resolved electron diffraction

From measurements of the transient Debye-Waller effect in Bismuth, we determine the buildup time of the random atomic motion resulting from the electronic relaxation after short pulse laser excitation. The surface sensitive reflection high energy electron diffraction and transmission electron diffraction yield a time constant of about 12 ps and 3 ps, respectively. The different energy transfer rates indicate relatively weak coupling between bulk and surface vibrational modes.

Synthesis Procedures for Silver Nanoparticles

This article gives some proposals on how to grow silver nanoparticles using different methods. Dilute silver salts are recommended as the metal precursor starting solutions. The formation of the silver nanoparticles is to be monitored using UV-Vis absorption spectroscopy so as to reveal the formation of silver nanoparticles and how they will exhibit surface plasmon absorption maxima at 418-420 nm from the UV–Vis spectrum. The Mie light scattering theory will be applied and the experimental results analyzed to show the diameter of silver nanoparticles in colloidal solution. Energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–Vis spectroscopy are proposed to be used to characterize the formed silver nanoparticles obtained. The energy-dispersive spectroscopy (EDX) of the nanoparticles dispersion will confirm the presence or absence of elemental silver signal peaks. The size and morphology of the formed silver nanoparticles will be determined by transmission electron microscopy. The synthesized silver nanoparticles will be structurally characterized by using X-ray diffraction and transmission high-energy electron diffraction (HEED) and the peaks in the XRD pattern will be compared to the standard values of the face-centered-cubic form of metallic silver (ICCD-JCPDS card no. 4-0787).

Properties of Sb2S3 and Sb2Se3 thin films obtained by pulsed laser ablation

The properties of Sb2S3 and Sb2Se3 thin films of variable thickness deposited onto Al2O3, Si, and KCl substrates are investigated by the method of pulsed laser ablation. The samples are obtained at a substrate temperature of 180°C in a vacuum chamber with a residual pressure of 10−5 Torr. The thickness of the films amounted to 40–1500 nm. The structure of the bulk material of the targets and films is investigated by the methods of X-ray diffraction and transmission high-energy electron diffraction, respectively. The electrical properties of the films are investigated in the temperature range of 253–310 K. It is shown that the films have semiconductor properties. The structural features of the films determine their optical parameters.

Interface reconstruction in the Ga2Se3/GaAs(100) and In2Se3/InAs(100) nanoheterostructures

The surface of GaAs(100) and InAs(100) substrates thermally treated in selenium vapor has been investigated by transmission electron microscopy (TEM) and reflection high-energy electron diffraction. Transmission electron microscopy and high-energy electron diffraction data on these heterostructures confirms the epitaxial pseudomorphic growth of the gallium selenide Ga2Se3(100) and indium selenide In2Se3(100) phases with ordered stoichiometric cation vacancies. A model of the atomic structure of the Ga2Se3(100) and In2Se3(100) surfaces is proposed, and the 2 × 2 reconstruction of the GaAs(100) and InAs(100) surfaces after treatment in selenium vapor is discussed within this model.

Nonuniformity in lattice contraction of bismuth nanoclusters heated near its melting point

The structural properties of bismuth nanoclusters were investigated with transmission high-energy electron diffraction from room temperature up to 525 ± 6 K. The Bi nanoclusters were fabricated by thermal evaporation at room temperature on transmission electron microscope grids coated with an ultrathin carbon film, followed by thermal and femtosecond laser annealing. The annealed sample had an average cluster size of ∼14 nm along the minor axis and ∼16 nm along the major axis. The Debye temperature of the annealed nanoclusters was found to be 53 ± 6 K along the [012] direction and 86 ± 9 K along the [110] direction. At T = 464 ± 6 K, the diffraction intensity started to deviate from Debye–Waller behavior due to increased lattice anharmonicity. The onset of the melting of the Bi nanoclusters was T ∼ 500 ± 6 K, as measured by the reduction of the nanocluster size through the formation of a liquid shell detected by the width of the diffraction rings. The thermal expansion coefficient of the Bi (012) and (110) planes is positive up to ∼ 499 ± 11 K. However, the expansion coefficient of the Bi (012) planes showed a transition from a positive to a negative value that occurs over the temperature range Tc ∼ 499 ± 11 K to 511 ± 8 K. For the Bi (110) planes, the thermal expansion coefficient is positive up to their melting point, which is 525 ± 6 K.

Spin scattering asymmetric coefficients and enhanced specific interfacial resistance of fully epitaxial current-perpendicular-to-plane giant magnetoresistance spin valves using alternate monatomic layered [Fe/Co]n and a Ag spacer layer

Using current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) measurement, we have evaluated the bulk and interface spin scattering asymmetric coefficients, βF and γF/N and the specific interfacial resistance, AR*F/N, for exchange-biased spin-valves consisting of artificially ordered B2 structure Fe50Co50 and Ag spacer layer. Artificially epitaxial ordered Fe50Co50 superlattices have been successfully fabricated on MgO (001) substrate by alternate monatomic layer (AML) deposition at a substrate temperature of 75 °C. The structural properties of the full epitaxial trilayer, AML[Fe/Co]n/Ag/AML[Fe/Co]n, on the Ag electrode have been confirmed by in situ reflection high-energy electron diffraction and transmission electron diffraction microscopy. A considerably large resistance-area product change and MR ratio (ΔRA > 3 mΩμm2 and MR ratio ∼5%) were confirmed even at thin AML[Fe/Co]n layer at room temperature (RT) in our spin-valve elements. The estimated values of βF and γF/N were 0.80 and 0.84 ± 0.02, respectively, from the Valet–Fert theory analysis of ΔRA as a function of thickness of the ferromagnetic layer (3, 4, and 5 nm) on the basis of the two-current model.

Orientation and substructure of chemoepitaxial rutile films

The orientation and substructure of rutile films obtained by oxidation of oriented Ti films are investigated by transmission electron microscopy and high-energy electron diffraction. It is shown that the textures of the oxide are defined by the textures of the initial metal film. A set of orientation relations between the crystal lattices of titanium and rutile is established, and the optimal orientation relation is determined. The dislocation substructure of the high-angle 90° boundaries in TiO2 films is revealed. The size and orientation mismatch at this boundary is compensated by the grain boundary lattice dislocations.

ChemInform Abstract: Magnetic Nanopowders: Ultrasound-Assisted Electrochemical Preparation and Properties.

The development of cost-effective nanopowder production methods has been a major obstacle to the development and industrial utilization of nanostructured materials. This paper describes a new cost-effective production technology for these materials which combines both pulsed electrochemistry and pulsed ultrasound. This technique has been applied to the synthesis of pure and binary and ternary alloyed nanopowders containing iron, cobalt, and nickel. The resulting nanopowders have been characterized by transmission electron microscopy, X-ray fluorescence, transmission high-energy electron diffraction, X-ray diffraction, and Mossbauer spectroscopy. The results indicate that this new production method is ideal for the preparation of high performance nanocomposite powders and related high-density nanocomposite materials.

Deposition of thin Bi2Te3 and Sb2Te3 films by pulsed laser ablation

Bi2Te3 and Sb2Te3 films were obtained by pulsed laser ablation. The films were deposited in vacuum (1 × 10−5 Torr) on single crystal substrates of Al2O3 (0001), BaF2 (111), and fresh cleavages of KCl or NaCl (001) heated to 453–523 K. The films were 10–1500 nm thick. The structures of the bulk material of targets and films were studied by X-ray diffractometry and transmission high-energy electron diffraction, respectively. Electrical properties of the films were measured in the temperature range of 77–300 K. It is shown that the films possess semiconductor properties. Several activation portions are observed in the temperature dependences of resistivity; the energies of activation portions depend on the film thickness and crystallite size.

Orientational order parameter in CO2-based alloys with rare gases from THEED data: pure CO2

Using the transmission high-energy electron diffraction technique, we study the temperature dependence of the diffraction reflection intensities from the solid phase of CO2. To deduce absolute values of the orientational order parameter, we modify the existing reconstruction method to take into account the triatomic shape of the molecule. It is shown that for triatomic solids a higher-rank order parameter, η4, is important and cannot be neglected. Application of the modified approach yield η and η4 values as a function of temperature over the range from 6 to 70K. Both orientational order parameters prove to be a nonmonotone function of temperature.

Self-selection in size and structure in argon clusters formed on amorphous carbon

Argon clusters formed on an amorphous carbon substrate as deposited from the vapor phase were studied by means of transmission high energy electron diffraction using the liquid helium cryostat. Electron diffractograms were analysed on the basis of assumption that there exist a cluster size distribution in samples formed on substrate and multi-shell structures such as icosahedra, decahedra, fcc and hcp were probed for different sizes up to ∼15 000 atoms. The experimental data were considered as a result of a superposition of diffracted intensities from clusters of different sizes and structures. The comparative analysis was based on the R-factor minimization that was found to be equal to 0.014 for the best fit between experiment and modelling. The total size and structure distribution function shows the presence of ‘non-crystallographic’ structures such as icosahedra and decahedra with five-fold symmetry that was found to prevail and a smaller amount of fcc and hcp structures. Possible growth mechanisms as well as observed general tendency to self-selection in sizes and structures are presumably governed by confined pore-like geometry in an amorphous carbon substrate.

Three-dimensional defects in CdTe films obtained by pulsed laser deposition

The quality of Cd chalcodenides epitaxial films can be enhanced seriously by applying a pulsed (electron beam or laser beam) method for ablation of targets. The structure of laser deposited CdTe layers was investigated by transmission high energy electron diffraction. This method is very useful for detection of two kinds of three-dimensional structural defects: (1) inclusions of a second crystallographic phase (2) twinnings. Layers investigated exhibit pure sphalerite phase and contain some amount of twins of the type {1 1 1}. The amount of defects depends strongly on the technological variables (like substrate temperature, crystallisation rate, etc.) of the deposition process.

Epitaxial silicon films deposited at high rates by gas-jet electron beam plasma CVD

We discuss a new method for low temperature epitaxial growth of silicon films by gas-jet electron beam plasma chemical vapor deposition in SiH 4–Ar mixture. The growth rate up to 0.8 μm/min becomes possible at the substrate temperature below 650 °C, without using ultra-high vacuum chamber. Epitaxial Si films were deposited with the thickness up to 2–10 μm. The structure of the films has been studied after deposition by transmission electron microscopy, transmission high energy electron diffraction and reflection high energy electron diffraction. All films were of epitaxial types, but they were characterized by a high density of threading dislocations (≈10 7 cm −2).

Magnetic Nanopowders: Ultrasound-Assisted Electrochemical Preparation and Properties

The development of cost-effective nanopowder production methods has been a major obstacle to the development and industrial utilization of nanostructured materials. This paper describes a new cost-effective production technology for these materials which combines both pulsed electrochemistry and pulsed ultrasound. This technique has been applied to the synthesis of pure and binary and ternary alloyed nanopowders containing iron, cobalt, and nickel. The resulting nanopowders have been characterized by transmission electron microscopy, X-ray fluorescence, transmission high-energy electron diffraction, X-ray diffraction, and Mossbauer spectroscopy. The results indicate that this new production method is ideal for the preparation of high performance nanocomposite powders and related high-density nanocomposite materials.