Thin film deposition and characterization of pure and iron-doped electron-beam evaporated tungsten oxide for gas sensors

Pure Tungsten Oxide (WO3) and Iron-doped (10 at%) Tungsten Oxide (WO3:Fe) nanostructured thin films were prepared using a dual crucible Electron Beam Evaporation techniques. The films were deposited at room temperature in high vacuum condition on glass substrate and post-heat treated at 300 oC for 1 hour. From the study of X-ray diffraction and Raman the characteristics of the as-deposited WO3 and WO3:Fe films indicated non-crystalline nature. The surface roughness of all the films showed in the order of 2.5 nm as observed using Atomic Force Microscopy (AFM). X-Ray Photoelectron Spectroscopy (XPS) analysis revealed tungsten oxide films with stoichiometry close to WO3. The addition of Fe to WO3 produced a smaller particle size and lower porosity as observed using Transmission Electron Microscopy (TEM). A slight difference in optical band gap energies of 3.22 eV and 3.12 eV were found between the as-deposited WO3 and WO3:Fe films, respectively. However, the difference in the band gap energies of the annealed films were significantly higher having values of 3.12 eV and 2.61 eV for the WO3 and WO3:Fe films, respectively. The heat treated samples were investigated for gas sensing applications using noise spectroscopy and doping of Fe to WO3 reduced the sensitivity to certain gasses. Detailed study of the WO3 and WO3:Fe films gas sensing properties is the subject of another paper

Operation analysis of resistive switching of CBRAM using in-situ TEM

Resistive random access memories (ReRAMs) have great potential as a candidate for next-generation nonvolatile memories for the high speed, high density storage per cost [1] and their ability to the neural network devices. In order to analyze the reliability of ReRAMs and to find out the origin of the failures, it indispensable to understand the resistive switching mechanism. Since the transmission electron microscopy (TEM) provides a high resolution images of the nanostructure, in-situ TEM should be a powerful tool for the analysis. In our in-situ TEM system [2, 3], repeatable switching characteristics, are achieved together with clear images of formation and rupture of conductive filaments corresponding to the low and high resistance states. In this work, we used several kinds of Cu-based ReRAM (CBRAM: Conductive Bridge RAM). TEM samples are fabricated by two methods. One is an ion-shadow method [4, 5], which is an ion milling technique with carbon mask particles. The other is FIB that is a conventional technique to make a sample observable in TEM. Almost the same characteristics as those measured at the outside of TEM by the use of real ReRAM cells are achieved in TEM by the both method. Fig. 1 shows an example of I-V switching characteristics of Cu-Te based ReRAM [6, 7] and the corresponding TEM images [2, 3]. It was clearly shown that a dark spot corresponding to a conductive filament appeared by SET and erased after RESET. These resistive switching characteristics by I-V sweep were reproducible at least 60 cycles in TEM. In addition, SET/RESET pulse operation more than 100k times are confirmed during TEM observation as shown in Fig. 2. These results clearly indicate that the in-situ TEM will be a powerful tool to guarantee the reliability of ReRAMs. Please click Additional Files below to see the full abstract

Nanoscale Switching and Degradation of Resistive Random Access Memory Studied by In Situ Electron Microscopy

The metal-filament-type resistive random access memories (ReRAMs) with copper were investigated from the point of view of dynamical microstructure evolution in the repetitive switching operations using in situ transmission electron microscopy (in situ TEM). Through a series of experiments for uncovered solid electrolyte films, stacked devices, and nanofabricated cells, formation and erasure of the copper filaments and deposits were confirmed. The behavior of the filament and deposit depended on the switching condition and history. Based on these in situ TEM results, the switching schematics and the degradation process were discussed

In Situ Transmission Electron Microscopy for Electronics

Electronic devices are strongly influenced by their microstructures. In situ transmission electron microscopy (in situ TEM) with capability to measure electrical properties is an effective method to dynamically correlate electric properties with microstructures. We have developed tools and in situ TEM experimental procedures for measuring electronic devices, including TEM sample holders and sample preparation methods. The method was used to study metallic nanowire by electromigration, magnetoresistance of a ferromagnetic device, conductance quantization of a metallic nanowire, single electron tunnelling, and operation details of resistive random access memories (ReRAM)

Changing Pattern of Deiminated Proteins in Developing Human Epidermis

Peptidylarginine deiminases are widely distributed, calcium-ion-dependent enzymes that convert arginine residues of proteins into citrulline residues. This reaction, deimination, is thought to be an important event during the final stage of epidermal differentiation, possibly associated with integration and disintegration of keratin filaments. To elucidate the possible roles of protein deimination during human epidermal development we investigated localization of deiminated proteins using anti-citrulline peptide antibody, which preferentially recognizes citrulline residues in the V subdomains of keratin 1, and anti-chemically modified citrulline antibody, which enables detection of citrulline residues independent of amino acid sequences. Anti-chemically modified citrulline antibody, but not anti-citrulline peptide antibody stained the periderm in two-layered epidermis of 49 d and 57 d estimated gestational age. In the stratified epidermis of 88 d, 96 d, and 108 d estimated gestational age fetal skin, anti-citrulline peptide antibody and anti-chemically modified citrulline antibody staining was seen in the periderm and intermediate cell layers. After periderm cells regressed and keratinization began in the interfollicular epidermis, anti-citrulline peptide antibody and anti-chemically modified citrulline antibody were restricted to the cornified cell layers of the interfollicular epidermis, similar to the distribution patterns of that in adult epidermis. Postembedding immunoelectron microscopy showed anti-citrulline peptide antibody immunogold labeling over the cytoplasmic intermediate filament network in the periderm and the intermediate cell layers. These results demonstrate an orderly formation of deiminated proteins in different layers of embryonic epidermis and suggest important roles for peptidylarginine deiminases in human epidermal morphogenesis

Multifunctional Logic Gate by Means of Nanodot Array with Different Arrangements

Multifunctional logic gate devices consisting of a nanodot array are studied from the viewpoint of single electronics. In a nanodot array, the dots come in a random variety of sizes, which sometimes has a negative effect on the performance of electrical device applications. Here, this feature is used in a positive sense to achieve higher functionality in the form of flexible logic gates with low power consumption in which the variability of logic functions is guaranteed. Nanodot arrays with two input gates and one control gate in a variety of arrangements are considered, in which the two-input logic functions (such as NAND, NOR, or exclusive-OR (XOR) gates) are selected by changing the voltage applied to the control gate. To ensure the flexibility of the device, it is important to guarantee the performance with any one of the six important logic functions: NAND, AND, NOR, OR, XOR, and XNOR. We ran a selection simulation using a nanodot array consisting of six nanodots with different dot arrangements to clarify the relation between the variability of the logic functions and the dot arrangements