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Facile Route to the Controlled Synthesis of Tetragonal and Orthorhombic SnO2 Films by Mist Chemical Vapor Deposition
No full textTwo types of tin dioxide (SnO2) films were grown by mist chemical vapor deposition (Mist-CVD), and their electrical properties were studied. A tetragonal phase is obtained when methanol is used as the solvent, while an orthorhombic structure is formed with acetone. The two phases of SnO2 exhibit different electrical properties. Tetragonal SnO2 behaves as a semiconductor, and thin-film transistors (TFTs) incorporating this material as the active layer exhibit n-type characteristics with typical field-effect mobility (mu(FE)) values of approximately 3-4 cm(2)/(V s). On the other hand, orthorhombic SnO2 is found to behave as a metal-like transparent conductive oxide. Density functional theory calculations reveal that orthorhombic SnO2 is more stable under oxygen-rich conditions, which correlates well with the experimentally observed solvent effects. The present study paves the way for the controlled synthesis of functional materials by atmospheric pressure growth techniques
A Study on the Degradation of In-Ga-Zn-O Thin-Film Transistors Under Current Stress by Local Variations in Density of States and Trapped Charge Distribution
No full textThin-film transistors using In-Ga-Zn-O (IGZO) semiconductors were evaluated under current stress by applying positive voltages to the gate and drain electrodes. Initially, the transfer characteristics exhibit identical threshold voltages (V-T) when the source and drain electrodes are interchanged during measurement (forward and reverse V-DS sweep). However, as stress time increases, larger shifts in V-T are observed under forward V-DS sweep than under reverse V-DS sweep conditions. Subgap states analyses based on the photoresponse of capacitance-voltage (C-V) curves suggest that local annihilation of donor-like traps occurs near the drain electrode. Hump-like features are clearly observed in the C-V curves collected between the drain and gate electrodes, while they do not appear in the C-V data obtained between the source and the gate. Based on the above, a local charge trapping model is introduced in order to interpret the device degradation. In this model, the major carrier electrons are trapped more abundantly near the source electrode due to the presence of a Schottky junction between IGZO and the source/drain electrodes
Wrinkle-free graphene electrodes in zinc tin oxide thin-film transistors for large area applications
No full textWrinkle-free graphene was used to form the source-drain electrodes in thin film transistors based on a zinc tin oxide (ZTO) semiconductor. A 10 nm thick titanium adhesion layer was applied prior to transferring a conductive graphene film on top of it by chemical detachment. The formation of an interlayer oxide between titanium and graphene allows the achievement of uniform surface roughness over the entire substrate area. The resulting devices were thermally treated in ambient air, and a substantial decrease in field effect mobility is observed with increasing annealing temperature. The increase in electrical resistivity of the graphene film at higher annealing temperatures may have some influence, however the growth of the oxide interlayer at the ZTO/Ti boundary is suggested to be most influential, thereby inducing relatively high contact resistance.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effect of Annealing Temperature on the Interfacial Interaction of LiNi0.5Mn1.5O4 Thin Film Cathode with Stainless-Steel Substrate
No full textLiNi0.5Mn1.5O4 thin films were coated on stainless steel substrates by radio-frequency sputtering at room temperature for a lithium-ion battery. The cathode films were post-annealed at 500, 600 and 700 °C to study (i) the impact of annealing temperature on the crystallization of the cathode film and (ii) the reactivity between the cathode film and the stainless steel substrate. X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy were adopted to characterize the thin films. The electrochemical properties of the LiNi0.5Mn1.5O4 cathodes were investigated with cyclic voltammetry and galvanostatic charge/discharge tests. As the annealing temperature increased from 500 to 600 °C, the crystallinity and electrochemical characteristics of LiNi0.5Mn1.5O4 both improved. However, as the annealing temperature further increased to 700 °C, the phase purity and the electrochemical performance were greatly deteriorated. Combined chemical analyses with time-of-flight secondary ion mass spectrometry depth profiling and energy-dispersive X-ray spectroscopy in scanning transmission electron microscopy mapping have indicated that the cross-diffusion of metal ions between LiNi0.5Mn1.5O4 and the stainless steel substrate takes place at a temperature higher than 600 °C, which was attributed as a main origin of the phase change in the LiNi0.5Mn1.5O4 cathode layer and electrochemistry degradations of lithium-ion battery.
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A Study on the Transition of Copper Oxide by the Incorporation of Nitrogen
No full textIn the present study, the effects of nitrogen incorporation on the transition of a p-type copper oxide semiconductor are investigated. The properties of sputtered copper oxide and nitrogen-incorporated copper oxide are evaluated and compared at various nitrogen gas flow rates. The results indicate that the addition of nitrogen results in an increased optical bandgap, accompanied by significantly reduced tail states compared to pristine copper oxide. In addition, X-ray diffraction and X-ray photoelectron spectroscopy reveal that the incorporation of nitrogen stimulates the transition from copper (II) oxide to copper (I) oxide
The resonant interaction between anions or vacancies in ZnON semiconductors and their effects on thin film device properties
Get PDFAbstractZinc oxynitride (ZnON) semiconductors are suitable for high performance thin-film transistors (TFTs) with excellent device stability under negative bias illumination stress (NBIS). The present work provides a first approach on the optimization of electrical performance and stability of the TFTs via studying the resonant interaction between anions or vacancies in ZnON. It is found that the incorporation of nitrogen increases the concentration of nitrogen vacancies (VN+s), which generate larger concentrations of free electrons with increased mobility. However, a critical amount of nitrogen exists, above which electrically inactive divacancy (VN-VN)0 forms, thus reducing the number of carriers and their mobility. The presence of nitrogen anions also reduces the relative content of oxygen anions, therefore diminishing the probability of forming O-O dimers (peroxides). The latter is well known to accelerate device degradation under NBIS. Calculations indicate that a balance between device performance and NBIS stability may be achieved by optimizing the nitrogen to oxygen anion ratio. Experimental results confirm that the degradation of the TFTs with respect to NBIS becomes less severe as the nitrogen content in the film increases, while the device performance reaches an intermediate peak, with field effect mobility exceeding 50 cm2/Vs.</jats:p
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