Forming time of conducting channels in double-layer Pt/Ta2O5/TaOx/Pt and single-layer Pt/TaOx/Pt resistance memories

Oxide double-layer systems have recently attracted much attention, owing to their excellent performance as nonvolatile bipolar resistance memory. In this study, we measured the time required to form conducting channels (i.e., the forming time) in double-layer Pt/Ta2O5/TaOx/Pt cells and single-layer Pt/TaOx/Pt cells by applying a pulse-waveformvoltage signal. The voltage amplitude dependence of forming times in both samples revealed nonlinearities with nine orders of magnitude. By investigating their temperature dependence,we found that channel formation for both samples can be attributed to thermally assisted dielectric breakdown.© 2013 Published by Elsevier B.V.1441sciescopu

Polaron Transport and Thermoelectric Behavior in La-Doped SrTiO3 Thin Films with Elemental Vacancies

The electrodynamic properties of La-doped SrTiO 3 thin fi lms with controlled elemental vacancies are investigated using optical spectroscopy and thermopower measurement. In particular, a correlation between the polaron formation and thermoelectric properties of the transition metal oxide (TMO) thin fi lms is observed. With decreasing oxygen partial pressure during the fi lm growth ( P (O 2 )), a systematic lattice expansion is observed along with the increased elemental vacancy and carrier density, experimentally determined using optical spectroscopy. Moreover, an absorption in the mid-infrared photon energy range is found, which is attributed to the polaron formation in the doped SrTiO 3 system. Thermopower of the La-doped SrTiO 3 thin fi lms can be largely modulated from –120 to –260 μV K −1 , refl ecting an enhanced polaronic mass of ≈3 < m polron / m < ≈4. The elemental vacancies generated in the TMO fi lms grown at various P (O 2 ) infl uences the global polaronic transport, which governs the charge transport behavior, including the thermoelectric properties.114151sciescopu

Dynamic switching mechanism of conduction/set process in Cu/a-Si/Si memristive device

The conduction/set processes of resistive switching have been systemically investigated for Cu/a-Si/Si electrochemical memristive devices. Experimental results indicate that the set process was driven by two different mechanisms, depending on the programming pulse amplitude: a purely electrical dielectric breakdown and a thermally assisted dielectric breakdown. For the latter process, we observe that the set time decreased exponentially with the increase in the programming pulse amplitude, whereas the former process shows amplitude independence. Through the temperature-dependent set transition characteristics, we argue that the filament growth in set process could be dominated by cation transport in the dielectric film. The thermal activation energy of Cu hopping in a-Si is extracted to be 0.16 eV. © 2013 AIP Publishing LLC.1691sciescopu

Forming process of unipolar resistance switching in Ta2O5-x thin films

We investigated the film-thickness and ambient oxygen-pressure dependence of the electric field, EF, required to initiate unipolar resistance switching (URS) in Ta2O5x thin films. We measured the dependence of EF by applying a triangular-waveform voltage signal to the film over a wide sweep-rate range (v ¼ 20 mV s1 to 5 MV s1). Our results showed that the URS-EF was not influenced by the Ta2O5x film thickness nor ambient oxygen-pressure. This suggested that the URS-forming process in Ta2O5x thin films should be governed by thermally assisted dielectric breakdown in our measurement range. 2013 Elsevier B.V. All rights reserved.101sciescopuskc

Enhanced tunability of two-dimensional electron gas on SrTiO3 through heterostructuring

© 2020 Korean Physical Society. Two-dimensional electron gases (2DEGs) on the SrTiO3 (STO) surface or in STO-based heterostructures have exhibited many intriguing phenomena, which are strongly dependent on the 2DEG-carrier density. We report that the tunability of the 2DEG-carrier density is significantly enhanced by adding a monolayer LaTiO3 (LTO) onto the STO. Ultraviolet (UV) irradiation induced maximum carrier density of the 2DEG in LTO/STO is increased by a factor of similar to 4 times, compared to that of the bare STO. By oxygen gas exposure, it becomes 10 times smaller than that of the bare STO. This enhanced tunability is attributed to the drastic surface property change of a polar LTO layer by UV irradiation and O-2 exposure. This indicates that the 2DEG controllability in LTO/STO is more reliable than that on the bare STO driven by defects, such an oxygen vacancy11sciescopuskc

In situ investigation of conducting interface formation in LaAlO3/SrTiO3 heterostructure

© 2021 Korean Physical SocietyThe high-mobility conducting interface (CI) between LaAlO3 (LAO) and SrTiO3 (STO) has revealed many fascinating phenomena, including exotic magnetism and superconductivity. But, the formation mechanism of the CI has not been conclusively explained. Here, using in situ angle-resolved photoemission spectroscopy, we elucidated the mechanisms for the CI formation. In as-grown samples, we observed a built-in potential (Vbi) proportional to the polar LAO thickness starting from the first unit cell (UC) with CI formation appearing above 3 UCs. However, we found that the Vbi is removed by synchrotron ultraviolet (UV)-irradiation; The built-in potential is recovered by oxygen gas (O2(g))-exposure. Furthermore, after UV-irradiation, the CI appears even below 3UC of LAO. Our results demonstrate not only the Vbi-driven CI formation in as-grown LAO/STO, but also a new route to control of the interface state by UV lithographic patterning or other surface modification.11Nsciescopuskc

Effect of epicatechin against radiation-induced oral mucositis: in vitro and in vivo study.

PURPOSE: Radiation-induced oral mucositis limits the delivery of high-dose radiation to head and neck cancer. This study investigated the effectiveness of epicatechin (EC), a component of green tea extracts, on radiation-induced oral mucositis in vitro and in vivo. EXPERIMENTAL DESIGN: The effect of EC on radiation-induced cytotoxicity was analyzed in the human keratinocyte line HaCaT. Radiation-induced apoptosis, change in mitochondrial membrane potential (MMP), reactive oxygen species (ROS) generation and changes in the signaling pathway were investigated. In vivo therapeutic effects of EC for oral mucositis were explored in a rat model. Rats were monitored by daily inspections of the oral cavity, amount of oral intake, weight change and survival rate. For histopathologic evaluation, hematoxylin-eosin staining and TUNEL staining were performed. RESULTS: EC significantly inhibited radiation-induced apoptosis, change of MMP, and intracellular ROS generation in HaCaT cells. EC treatment markedly attenuated the expression of p-JNK, p-38, and cleaved caspase-3 after irradiation in the HaCaT cells. Rats with radiation-induced oral mucositis showed decreased oral intake, weight and survival rate, but oral administration of EC significantly restored all three parameters. Histopathologic changes were significantly decreased in the EC-treated irradiated rats. TUNEL staining of rat oral mucosa revealed that EC treatment significantly decreased radiation-induced apoptotic cells. CONCLUSIONS: This study suggests that EC significantly inhibited radiation-induced apoptosis in keratinocytes and rat oral mucosa and may be a safe and effective candidate treatment for the prevention of radiation-induced mucositis

Direct visualization and control of SrOx segregation on semiconducting Nb doped SrTiO3 (100) surface

We investigated how SrOx segregates on a Nb doped SrTiO3 (100) surface by in air annealing. Using atomic force and photoemission electron microscopes, we can directly visualize the morphology and the electronic phase changes with SrOx segregation. SrOx islands less than 2 mu m in size and 1-5 unit cells thick nucleate first and grow in a labyrinth domain pattern. After prolonged annealing, SrOx forms a similar to 10 nm thick film. We show that the domain pattern can be controlled by introducing a surface miscut angle of SrTiO3. Additionally, the segregated SrOx has a lower work function, compared to that of SrTiO3. These results suggest that the control and tunability of SrOx segregation is applicable to the design of a new functional electronic devices in the semiconducting SrTiO3 based heterostructure.11Nsciescopuskc