Browsing by Author "Mimura, Hidenori"

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EFFECT OF CARRIER GAS AND VACUUM ANNEALING ON THE PHYSICAL PROPERTIES OF ZnO THIN FILMS DOPED WITH GALLIUM BY CHEMICAL SPRAY PYROLYSIS
(Editura "Tehnica-UTM", 2018-05-24) Potlog, Tamara; Lungu, Ion; Botnariuc, Vasile; Raevschi, Simion; Worasawat, Suchada; Mimura, Hidenori; Gorceac, Leonid
Structural, optical and electrical properties of zinc oxide thin films doped with 2% Ga, annealed in the vacuum at the same temperature and obtained onto glass substrates by the chemical spray pyrolysis method in the different gas atmospheres were investigated by X-ray Diffraction (XRD), UV-VIS spectrophotometry and Hall measurements, respectively. XRD studies revealed that all films were polycrystalline in nature, with a hexagonal wurtzite crystal structure and a predominant (002) c-axis orientation. All ZnO:Ga thin films had higher than 80 % transmittances in the visible region. Doping with 2% Ga led to a decrease in the optical band gap indifferent of the nature of the carrier gas. The synthesis of ZnO thin films with 2% Ga doping and annealing in the same conditions in Ar and O2 atmospheres led to the lower conductivity with electron concentration of 1016 cm−3.
ELECTRICAL PROPERTIES OF THERMAL ANNEALED IN VACUUM SPRAY DEPOSITED AL-DOPED ZnO THIN FILMS
(Springer Nature, 2020) Potlog, Tamara; Lungu, Ion; Raevschi, Simion; Botnariuc, Vasile; Robu, Stephan; Worasawat, Suchada; Mimura, Hidenori
Al-doped ZnO thin films have been prepared by spray pyrolysis, which facilitates the incorporation of a higher percentage of dopant atoms. The vacuum thermally annealed at 420 °C temperature thin films have been characterized by X-ray diffraction (XRD), optical spectroscopy. Electrical conductivity and the Hall effect are investigated in the temperature interval (77–300) K. X-ray analysis results reveal that all the films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction (002) plane. Different characters of the temperature dependence of conductibility are observed in the Al-doped ZnO films vacuum thermally annealed at 420 °C temperature. In all cases, the conductivity, mobility carriers and carriers’ concentration of ZnO thin films obtained under Ar are higher than under O2 atmosphere, unless they are not doped. of your paper no longer than 300 words.
MATERIAL PROPERTIES OF ZINC PHTHALOCYANINE FROM FA SOLUTION AND APPLICATION IN ORGANIC SOLAR CELLS
(IJIEEE, 2018) Potlog, Tamara; Furtuna, Vadim; Rusnac, Roman; Rotaru, Cornel; Masuzawa, Tomoaki; Mimura, Hidenori; Robu, Stefan
This paper presents for a first time asolution-processableZnPc thin films from formic acid (FA) solution by drop casting method and the photovoltaic parameters of the Organic Solar Cells (OPV) based on ZnPc-diode Schottky.Structural and optical propertiesof ZnPc thin films were investigated by X-raydiffraction (XRD),Fourier transform infrared spectroscopy (FTIR) and UV-VIS spectroscopy.XRD analysis show phase transformation of the alpha-beta phases of ZnPc thin films to beta phase due to the annealing in H 2 atmosphere at 400 o C for 30 min. FTIR analysis show that the formate ion (HCOO −) is attached to Zn(II)Pc. Further on, ITO/PEDOT: PSS/ZnPc(I 2)/Al Schottkyphotovoltaic devices with efficiency of 0.3 % were prepared and their characteristics 'enhancement is discussed. The values for the opencircuit voltage (1.03 V) and the current density (8.2 µA/cm 2) are higher than in the case of Schottky diode devices obtained by thermal vacuum evaporation.
THE PHOTOPHYSICAL PROPERTIES OF Ga DOPED ZnO THIN FILMS GROWN BY SPRAY PYROLYSIS METHOD
(Springer Nature, 2020) Worasawat, Suchada; Taku, Miyake; Potlog, Tamara; Mimura, Hidenori
In this paper we report nanocrystalline ZnO thin films deposited by varying the Ga concentrations and atmosphere gas, onto the glass substrates using spray pyrolysis technique at 450 °C substrate temperature. After deposition Ga-doped ZnO thin films were annealed at temperature 420 °C in vacuum. The morphological, structural, optical and spectral properties of synthetized thin films have been characterized by scanning electron microscopy, X-ray diffraction, Raman analysis, UV–Vis spectrophotometry and spectrofluorimetry. The XRD result shows hexagonal structure with preferential orientation along the (0002) plane and the dependence of the values of the full-width at half-maximum of this peak on the nature of the gas used in the synthesis. Also, it is found that the optical bandgap can be increased by increasing the doping level. The fluorescence spectra of ZnO thin films with 1%, 2%, 3% and 5% concentrations of Ga demonstrate that these nanostructured thin films can produce reactive oxygen species (ROS) such as singlet oxygen under ultraviolet light. Nanocrystalline ZnO thin films in function of the Ga concentration provide the phosphorescence lifetime of the charge separated states up to 102 ms.
SELF-PROPELLED AERO-GaN BASED LIQUID MARBLES EXHIBITING PULSED ROTATION ON THE WATER SURFACE
(2021) Braniște, Tudor; Ciobanu, Vladimir; Schűtt, Fabian; Mimura, Hidenori; Raevschi, Simion; Adelung, Rainer; Pugno, Nicola M.; Tighineanu, Ion
We report on self-propelled rotating liquid marbles fabricated using droplets of alcoholic solution encapsulated in hollow microtetrapods of GaN with hydrophilic free ends of their arms and hydrophobic lateral walls. Apart from stationary rotation, elongated-spheroid-like liquid marbles were found, for the first time, to exhibit pulsed rotation on water surfaces characterized by a threshold speed of rotation, which increased with the weight of the liquid marble while the frequency of pulses proved to decrease. To throw light upon the unusual behavior of the developed self-propelled liquid marbles, we propose a model which takes into account skimming of the liquid marbles over the water surface similar to that inherent to flying water lily beetle and the so-called helicopter effect, causing a liquid marble to rise above the level of the water surface when rotating.
SYNTHESIS AND PROPERTIES OF AL-DOPED ZnO THIN FILMS FOR PHOTOVOLTAICS
(Institute of Electrical and Electronics Engineers Inc., 2018-11-27) Potlog, Tamara; Lungu, Ion; Botnariuc, Vasile; Gorceac, Leonid; Raevschi, Simion; Taku, Miyake; Worasawat, Suchada; Mimura, Hidenori
Polycrystalline undoped and Al-doped ZnO thin films were deposited by spray pyrolysis using oxygen and argon atmospheres. The influence of postdeposition vacuum annealing on the structure, morphology and optical properties was studied by X-ray diffraction, atomic force microscopy and UV–VIS spectroscopy. The thermal vacuum annealing induces structural and morphological changes, especially in Al-doped ZnO thin films synthetized in oxygen atmosphere. Further on, the electrical conductivity in dependence of the nature of gas atmosphere and Al concentration is discussed.