224 research outputs found
Thermopower analysis of the electronic structure around metal-insulator transition in V1-xWxO2
Electronic structure across the metal-insulator (MI) transition of
electron-doped V1-xWxO2 epitaxial films (x = 0-0.06) grown on alfa-Al2O3
substrates was studied by means of thermopower (S) measurements. Significant
increase of |S|-values accompanied by MI transition was observed, and the
transition temperatures of S (TS) decreased with x in good linear relation with
MI transition temperatures. |S| values of V1-xWxO2 films at T > TS were
constant at low values of 23 microV K-1 independently of x, which reflects a
metallic electronic structure, whereas, those at T < TS almost linearly
decreased with logarithmic W-concentrations. The gradient of -213 microV K-1
agrees well with -kB/e*ln10 (-198 microV K-1), suggesting that V1-xWxO2 films
have insulating electronic structures with a parabolic density of state around
the conduction band bottom.Comment: Accepted for publication as a Rapid Commun. in Phys. Rev.
Infrared-transmittance tunable metal-insulator conversion device with thin-film-transistor-type structure on a glass substrate
Infrared (IR) transmittance tunable metal-insulator conversion was
demonstrated on glass substrate by using thermochromic vanadium dioxide (VO2)
as the active layer in three-terminal thin-film-transistor-type device with
water-infiltrated glass as the gate insulator. Alternative positive/negative
gate-voltage applications induce the reversible protonation/deprotonation of
VO2 channel, and two-orders of magnitude modulation of sheet-resistance and 49%
modulation of IR-transmittance were simultaneously demonstrated at room
temperature by the metal-insulator phase conversion of VO2 in a non-volatile
manner. The present device is operable by the room-temperature protonation in
all-solid-state structure, and thus it will provide a new gateway to future
energy-saving technology as advanced smart window.Comment: To appear in APL Mater. (2017
Leakage-free electrolytes with different conductivity for non-volatile memory device utilizing insulator/metal ferromagnet transition of SrCoOx
The electrochemical switching of SrCoOx-based non-volatile memory with
thin-film-transistor structure was examined by using liquid-leakage-free
electrolytes with different conductivity (s) as the gate insulator. We first
examined leakage-free water, which is incorporated in the amorphous (a-) 12CaO
7Al2O3 film with nanoporous structure (CAN), but the electrochemical
oxidation/reduction of SrCoOx layer required the application of high gate
voltage (Vg) up to 20 V for a very long retention-time (t) 40 minutes,
primarily due to the low s (2.0 x 10-8 S cm-1 at RT) of leakage-free water.We
then controlled the s of leakage-free electrolyte, infiltrated in the a-NaxTaO3
film with nanopillar array structure, from 8.0 x 10-8 S cm-1 to 2.5 x 10-6 S
cm-1 at RT by changing the x = 0.01-1.0. As the result, the t, required for the
metallization of SrCoOx layer under small Vg = -3 V, becomes two orders of
magnitude shorter with increase of the s of the a-NaxTaO3 leakage-free
electrolyte. These results indicate that the ion migration in the leakage-free
electrolyte is the rate-determining step for the electrochemical switching,
compared to the other electrochemical process, and the high s of the
leakage-free electrolyte is the key factor for the development of the
non-volatile SrCoOx-based electro-magnetic phase switching device
Experimental characterization of the electronic structure of anatase TiO2: Thermopower modulation
Thermopower (S) for anatase TiO2 epitaxial films (n3D: 1E17-1E21 /cm3) and
the gate voltage (Vg) dependence of S for thin film transistors (TFTs) based on
TiO2 films were investigated to clarify the electronic density of states (DOS)
around the conduction band bottom. The slope of the |S|-log n3D plots was -20
{\mu}V/K, which is an order magnitude smaller than that of semiconductors (-198
{\mu}V/K), and the |S| values for the TFTs increased with Vg in the low Vg
region, suggesting that the extra tail states are hybridized with the original
conduction band bottom.Comment: 11 pages, 4 figure
- …