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Kim H.,Yeungnam University | Lee M.Y.,Yeungnam University | Kim S.-H.,Yeungnam University | Bae S.I.,Global Frontier R and nter for Hybrid Interface Materials | And 5 more authors.
Applied Surface Science

A highly-conformal and stoichiometric p-type cuprous copper(I) oxide (Cu2O) thin films were grown using atomic layer deposition (ALD) by a fluorine-free amino-alkoxide Cu precursor, bis(1-dimethylamino-2-methyl-2-butoxy)copper (C14H32N2O2Cu), and water vapor (H2O). Among tested deposition temperatures ranging from 120 to 240 °C, a self-limited film growth was clearly confirmed for both precursor and reactant pulsing times at 140 °C. Between 140 and 160 °C, the process exhibited an almost constant growth rate of ∼0.013 nm/cycle and a negligible number of incubation cycles (approximately 6 cycles). The Cu2O films deposited at the optimal temperature (e.g. 140 °C) showed better properties in view of their crystallinity and roughness compared to the films deposited at higher temperatures. Rutherford backscattering spectrometry showed that the film deposited at 140 °C was almost stoichiometric (a ratio of Cu and O ∼2: 1.1) with negligible C and N impurities. X-ray photoelectron spectroscopy further revealed that Cu and O in the film mostly formed Cu2O bonding rather than CuO bonding. Plan-view transmission electron microscopy analysis showed formation of densely packed crystal grains with a cubic crystal structure of cuprous Cu2O. The step coverage of ALD-Cu2O film was remarkable, approximately 100%, over 1.14-μm-high Si nanowires with an aspect ratio (AR) of 7.6:1 and onto nano-trenches (top opening width: 25 nm) with an AR of 4.5:1. Spectroscopic ellipsometry was employed to determine optical constants, giving optical direct band gap of 2.52 eV. Finally, Hall measurement confirmed that the ALD-Cu2O film had p-type carriers with a high Hall mobility of 8.05 cm2/V s. © 2015 Elsevier B.V. All rights reserved. Source

Lee S.-D.,Korea Institute of Materials Science | Lee Y.-J.,Korea Institute of Materials Science | Rha J.-J.,Korea Institute of Materials Science | Park W.I.,Global Frontier R and nter for Hybrid Interface Materials | And 2 more authors.
Current Applied Physics

Vanadium oxide (V2O5-x) thin films with a thickness of about 4 nm were prepared by atomic layer deposition (ALD) to be used as a hole-transporting layer in an amorphous silicon solar cell. The ALD growth characteristics (growth rate, crystallinity, and surface morphology) of the V2O5-x films were investigated while exposed to different pulse times of ozone (O3), which was used as an oxidant. The effect of the different ozone pulse times, used in the V2O5 layer, on the device performance was also investigated. At the ozone pulse time of 1 s, the maximum value of power conversion efficiency (PCE), i.e., 5.35%, was achieved, whereas at the ozone pulse time of 5 s, the PCE was 4.18%. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) analyses confirmed that increasing the proportion of crystalline phase in the V2O4 films with lower work function of V2O5 resulted in decreased open-circuit voltage and conversion efficiency as the ozone pulse time increased. © 2015 Elsevier B.V. All rights reserved. Source

Jung J.-H.,Yeungnam University | Lee S.-J.,Yeungnam University | Lee H.-J.,Yeungnam University | Lee M.Y.,Yeungnam University | And 12 more authors.
Journal of Nanoscience and Nanotechnology

Ruthenium (Ru) thin films were grown on thermally-grown SiO2 substrates by plasma enhanced atomic layer deposition (PEALD) using a sequential supply of a new betadiketonate Ru metallorganic precursor, dicarbonyl-bis(5-methyl-2,4-hexanediketonato) Ru(II) (C16H22O6Ru) with a high vapor pressure and NH3 plasma as a reactant at the substrate temperature ranging from 175 and 310 °C. A self-limited film growth was confirmed at the deposition temperature of 225 °C and the growth rate was 0.063 nm/cycle on the SiO2 substrate with very short number of incubation cycles (approximately 10 cycles). The resistivity of PEALD-Ru films was dependent on the microstructural features characterized by grain size and crystallinity which could be controlled by varying the deposition temperature. Ru film with the resistivity of ∼20 μΩ-cm and high density of 11.5 g/cm3 was obtained at the deposition temperature as low as 225 °C. It formed polycrystalline structure with hexagonal-close-packed phase that was confirmed by X-ray diffractometry and transmission electronic microscopy analysis. Step coverage of PEALD-Ru film deposited with the optimum condition was good (∼75%) at the very small-sized trench (aspect ratio: ∼4.5 and the top opening size of 25 nm). Copyright © 2015 American Scientific Publishers. Source

Lee J.Y.,Pusan National University | Lee J.Y.,Korea Institute of Machinery and Materials | Kang M.C.,Pusan National University | Kang M.C.,Global Frontier R and nter for Hybrid Interface Materials | And 4 more authors.
Advances in Applied Ceramics

The thresholds and depths of ablation of carbon [carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs)] reinforced Al2O3 composites were compared and correlated with those of monolithic Al2O3 using femtosecond pulsed laser irradiation (λ 1027 nm, τP = 380 fs). These composites were processed using a spark plasma sintering method (Ts = 1500°C, τs = 10 min and P = 40 MPa) through which highly densified (more than 97%) composites were fabricated. The optical absorbance of each composite improved in the wavelength range from ultraviolet to near infrared. Compared with the corresponding values for monolithic Al2O3, the ablation thresholds of CNT/Al2O3 and GNP/Al2O3 were 50 and 75% lower respectively, and their ablation depths were two to three times deeper. © 2016 Institute of Materials, Minerals and Mining. Source

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