The kinematics of hydrogen diffusion in nontransparent metallic materials is crucial to the hydrogen-sensing and-storage technology and remains a challenge. Alongside the conventional optical investigations, the hydrogen absorption-induced reversible changes of magnetic properties in ferromagnetic thin films provides a new method for visualization of hydrogen in solids. Here we monitor real-time hydrogen diffusion in a cobalt-palladium alloy (Co 25 Pd 75) film using a magneto-optical Kerr microscope. The spatially resolved magneto-optical contrasted images provide a noninvasive method of monitoring hydrogen movement. Hydrogen diffusion follows Fick's diffusion law, and a diffusion coefficient of 3 ± 2 × 10 −12 m 2 /s is obtained. The diffusion velocity of the 2-4% hydrogen concentration fronts reaches 30 ± 15 nm/s in the uniform film area and increases to 50 ± 20 nm/s near a defect site. These results can be applied in detecting hydrogen diffusion in other spintronic materials, such as magnetic palladium-alloy thin films.

We have investigated the gate-voltage dependence and the temperature dependence of the magnetoconductivity of amorphous indium-gallium-zinc-oxide thin-film transistors. A weak-localization feature is observed at small magnetic fields on top of an overall negative magnetoconductivity at higher fields. An intriguing controllable competition between weak localization and weak antilocalization is observed by tuning the gate voltage or varying the temperature. Our findings reflect controllable quantum interference competition in the electron systems in amorphous indiumgallium-zinc-oxide thin-film transistors.Amorphous metal-oxide semiconductors have recently been studied for applications in thin-film transistors (TFTs) for large-area flexible electronics because of their electrical uniformity and fabrication advantage of roomtemperature deposition and patterning [1][2][3][4]. In particular, zinc oxide (ZnO) has recently attracted intense experimental and theoretical attention owing to its potential use in the emerging nanoelectronics and optoelectronics [5][6][7]. ZnO-based semiconductors can incorporate indium oxide as a carrier-mobility enhancer and gallium oxide or hafnium oxide as a columnar-structure suppressor for the amorphous phase in order to achieve high field-effect mobility and low off-state current of the channel [8][9][10]. They have become promising candidates of transparent and flexible nonvolatile memories to be integrated in system-on-panel displays [11][12][13].Aside from practical studies to achieve higher quality of amorphous indium-gallium-zinc-oxide (InGaZnO 4 ) TFTs, investigations of their fundamental electrical properties at low temperatures are necessary for studying quantum corrections to the conductivities of these carrier systems with disorders. Quantum interference and weak localization have been explored in three-dimensional and low-dimensional electron systems in various materials [14][15][16][17][18][19][20][21]. Indium zinc oxide (IZO) films and nanowires [22][23][24][25][26][27] in particular have raised special interest because of their potential applications in modern technologies. However, a comprehensive, in-depth study of lowtemperature electrical transport in IZO is still missing, and the underlying mesoscopic and microscopic mechanisms remain largely unclear. Moreover, there are few detailed studies of low-temperature transport properties of practical IZO transistor devices. Measurements of IZO * E-mail: pjiang@ntnu.edu.tw transistors at low temperatures may reveal interesting quantum-mechanical phenomena.In this work, we present a study of the drain-source channel magnetoconductivity (MC) of an amorphous InGaZnO 4 (a-IGZO) TFT measured at cryogenic temperatures. Manipulated via electric gating, the MC reveals a competition between weak localization (WL) and weak antilocalization (WAL) at small magnetic fields, where the WL component stays small but steady, while the WAL component lessens drastically with decreasing gate voltage. On the other hand, the temperature dependence...

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We investigate the gate-voltage dependence of the magnetoconductivity of several amorphous InGaZnO4 (a-IGZO) thin-film transistors (TFTs). The magnetoconductivity exhibits gate-voltagecontrolled competitions between weak localization (WL) and weak antilocalization (WAL), and the respective weights of WL and WAL contributions demonstrate an intriguing universal dependence on the channel conductivity regardless of the difference in the electrical characteristics of the a-IGZO TFTs. Our findings help build a theoretical interpretation of the competing WL and WAL observed in the electron systems in a-IGZO TFTs.Extensive use of integrated circuits with low power consumption [1] is required in the fabrication of modern electronic devices. Among these consumer products, thin-film-transistor (TFT) nonvolatile memory devices based on oxide semiconductors have recently attracted great attention owing to their potential application in flexible system-on-panel displays [2][3][4][5]. Amorphous InGaZnO 4 (a-IGZO) TFTs, in particular, have several advantages over other transparent conducting oxides, such as high field-effect mobilities [6][7][8][9][10][11], small subthreshold swings with low off-state currents [12], good uniformity, and tunable carrier concentrations even when deposited at room temperature [13,14]. Therefore, they are a promising alternative to amorphous silicon TFTs as switching and driving devices for application in activematrix liquid-crystal displays and organic light-emitting diode displays.Apart from the investigation of a few quality issues of a-IGZO TFTs for practical applications conducted so far [15][16][17], research on their fundamental electrical properties at low temperatures is necessary for exploring quantum corrections to the conductivity of these carrier systems with disorders. Quantum interference and weak localization have been studied in electron systems in various materials [18][19][20][21][22][23][24][25] . InZnO semiconductor films and nanowires, in particular, have raised special interest because of their intricate physical properties and potential applications in nanoelectronic and spintronic devices [26][27][28][29][30][31][32][33]. However, few comprehensive in-depth studies of the low-temperature electrical transports in InZnO and similar multicomponent oxide semiconductors were condected. Recently, we reported an intriguing observation of controllable competition between weak localization (WL) and weak antilocalization (WAL) in the electron systems in a-IGZO TFTs under variation of the gate voltage or the temperature [34], but the underlying mechanism remains undetermined. More studies are re- * These authors contributed equally to this work. † quired to further understand the quantum interference in these systems.In this work, we extend our study of the competing WL and WAL observed in a-IGZO TFTs by examining the low-temperature channel magnetoconductivity (MC) of a series of a-IGZO TFTs with various channel dimensions. Manipulated via electric gating, the MC of all the samples r...