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Ramesh P. Sapkota,Peter D. Stahl,Urszula Norton 국립중앙과학관 2019 Journal of Asia-Pacific Biodiversity Vol.12 No.1
Assessing diameter distribution is an approach of observing regeneration strategies and impacts ofanthropogenic disturbances on forest structural attributes. In this study, we evaluated the differences indiameter distributions in highly disturbed, moderately disturbed, and undisturbed forest sites of BufferZone Community Forests (BZCFs), viz. Janajagaran BZCF, Musharni Mai BZCF, and Radha Krishna BZCF ofCentral Terai, Nepal. Weibull and gamma distributions were fitted to explain changes in frequency distribution of diameter data collected. We observed a significant decrease in species richness (overall:p < 0.001) and density of smallest diameter class (0e10 cm diameter at breast height) stems (overall:p < 0.001) with increasing disturbances. Similarly, increase in median diameters (p < 0.01) and parameters of Weibull’s and gamma distributions along gradients from undisturbed to highly disturbedforest sites (except between moderately disturbed and undisturbed sites of Musharni Mai BZCF) wereobserved. Bowley coefficient of skewness was lower in all highly disturbed sites of BZCFs showingreduction in right skewness of the distribution curves with disturbances. These results indicateanthropogenic disturbances shift diameter structure of forests stands, negatively affecting abundance ofsmall diameteresized woody species and shifting Shorea robusta mixed forests towards even-agedstands.
Measurement of band offsets in MgO/InGaZnO4 heterojunction by X-ray photoelectron spectroscopy
최병수,K. W. Kim,B. P Gila,D. P. NORTON,S. J. PEARTON,조현 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.9
Amorphous InGaZnO4 (α-IGZO) thin film transistors (TFTs) are one of the most promising candidates for switches in theactive-matrix and driver-integrated circuits of transparent liquid crystal displays and flexible displays. The stability andoverall performance of amorphous IGZO TFTs depend to a great extent on the band offsets in gate dielectric/α-IGZOheterojunction. The energy discontinuity in the valence band (ΔEV) and conduction band (ΔEC) in MgO/IGZO heterojunctionswere systematically examined by using X-ray photoelectron spectroscopy (XPS). The MgO gate dielectric was found to havea straddled type band offset alignment on the IGZO. The valence band offset value for the MgO/IGZO heterojunction wasdetermined as 0.81 ± 0.17 eV using the Ga 2p3/2, Zn 2p3/2 and In 3d5/2 energy levels as references. The bandgap energy differencebetween the MgO and IGZO led to a corresponding conduction band offset (ΔEC) of ~3.79 eV and a nested interface alignment.
Band Offsets in YSZ/InGaZnO<sub>4</sub> Heterostructure System
Kim, J.K.,Kim, K.-W.,Douglas, E.A.,Gila, B.P.,Craciun, V.,Lambers, E.S.,Norton, D.P.,Ren, F.,Pearton, S.J.,Cho, H. American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.5
The energy discontinuity in the valence band (Delta E-V) of Y2O3-stabilized ZrO2 (YSZ)/InGaZnO4 (IGZO) heterostructures was obtained from X-ray photoelectron spectroscopy (XPS) measurements. The YSZ exhibited a bandgap of 4.4 eV from absorption measurements. A value of Delta E-V = 0.57 +/- 0.12 eV was obtained by using Ga 2p(3/2), Zn 2p(3/2) and In 3d(5/2) energy levels as references. This implies a conduction band offset (Delta E-C) of 0.63 eV in YSZ/InGaZnO4 heterostructures and a nested interface band alignment.
Size-dependent electrical conductivity of indium zinc oxide deposited by RF magnetron sputtering.
Heo, Young-Woo,Pearton, S J,Norton, D P American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.4
<P>We investigated the size-dependent electrical conductivities of indium zinc oxide stripes with different widths from 50 nm to 4 microm and with the same thickness of 50 nm deposited by RF magnetron sputtering. The size of the indium zinc oxide stripes was controlled by e-beam lithography. The distance of the two Ti/Au Ohmic electrodes along the indium zinc oxide stripes was kept constant at 25 microm. The electrical conductivity decreased as the size of the indium zinc oxide stripes decreased below a critical width (80 nm). The activation energy, derived from the electric conductivity versus temperature measurement, was dependent on the dimensions of indium zinc oxide stripes. These results can be understood as stemming from surface charge trapping from the absorption of oxygen and/or water vapor, which leads to an increase in the energy difference between the conduction energy band and the Fermi energy.</P>
Low Temperature Growth and Optical Properties of ZnO Nanowires Using an Aqueous Solution Method
Chu, Manh-Hung,Lee, Joon-Hyung,Kim, Jeong-Joo,Kim, Kyeong-Won,Norton, D. P.,Heo, Young-Woo American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.2
<P>ZnO nanowires were grown on indium tin oxide (ITO) coated glass substrates at a low temperature of 90 degrees C using an aqueous solution method. The ZnO seeds were coated on the ITO thin films by using a spin coater. ZnO nanowires were formed in an aqueous solution containing zinc nitrate hexahydrate (Zn(NO3)(2)center dot 6H(2)O) and hexamethylenetetramine (C6H12N4). The pH value and concentration of the solution play an important role in the growth and morphologies of ZnO nanowires. The size of ZnO naonowires increased as the concentration of the solution increased. It was formed with a top surface of hexagonal and tapered shape at low and high pH values respectively. Additionally, the single crystalline structure and optical property of the ZnO nanowires were investigated using high-resolution transmission electron microscopy and photoluminescence spectroscopy.</P>
Effects of Codoping with Fluorine on the Properties of ZnO Thin Films
허영우,D. P. Norton 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.11
We report on the effects of co-doping with fluorine on properties of ZnO thin films grown by pulsed-laser deposition. The transport characteristics of Ag-F and Li-F codoped ZnO films were determined by Hall-effect measurements at room temperature. Ag-F codoped ZnO films showed n-type semiconducting behaviors. An ambiguous carrier type was observed in Li-F codoped ZnO films grown at a temperature of 500oC with the oxygen pressures of 20 and 200 mTorr. The qualities of the codoped ZnO films were studied by X-ray diffraction, atomic force microscopy, X-ray photoemission spectroscopy, and photoluminescence.
Effects of Codoping with Fluorine on the Properties of ZnO Thin Films
Heo, Young-Woo,Norton, D.P. The Korean Ceramic Society 2006 한국세라믹학회지 Vol.43 No.11
We report on the effects of co-doping with fluorine on properties of ZnO thin films grown by pulsed-laser deposition. The transport characteristics of Ag-F and Li-F codoped ZnO films were determined by Hall-effect measurements at room temperature. Ag-F codoped ZnO films showed n-type semiconducting behaviors. An ambiguous carrier type was observed in Li-F codoped ZnO films grown at a temperature of 500$^{\circ}C$ with the oxygen pressures of 20 and 200 mTorr. The qualities of the codoped ZnO films were studied by X-ray diffraction, atomic force microscopy, X-ray photoemission spectroscopy, and photoluminescence.
Heo, Y.W.,Kelly, J.,Norton, D.P.,Hebard, A.F.,Pearton, S.J.,Zavada, J.M.,Park, Y.D. The Institute of Electronics and Information Engin 2004 Journal of semiconductor technology and science Vol.4 No.4
High dose ($3{\times}10^{16}cm^{-2}$) implantation of Fe or Ni ions into bulk, single-crystal ZnO substrates was carried out at substrate temperature of ${\sim}350^{\circ}C$ to avoid amorphization of the implanted region. The samples were subsequently annealed at $700^{\circ}C$ to repair some of the residual implant damage. X-Ray Diffraction did not show any evidence of secondary phase formation in the ZnO. The Ni implanted samples remained paramagnetic but the Fe-implanted ZnO showed evidence of ferromagnetism with an approximate Curie temperature of ${\sim}$240K. Preliminary X-Ray Photoelectron Spectroscopy measurements showed the Fe to be ill the 2+ oxidation state. The earrler density in the implanted region still appears to be too low to support carrier-meditated origin of the ferromagnetism and formation of bound magnetic polarons may be one potential explanation for the observed magnetic properties, No evidence of the Anomalous Hall Effect could be found in the Fe-implanted ZnO, but its transport properties were dominated by the conventional or ordinary Hall effect.
Y.W.Heo,J.Kelly,D.P.Norton,A.F.Hebard,S.J.Pearton,J.M.Zavada,Y.D.Park 대한전자공학회 2004 Journal of semiconductor technology and science Vol.4 No.4
High dose (3×lO^(16)cm^(-2)) implantation of Fe or Ni ions into bulk, single-crystal ZnO substrates was carried out at substrate temperature of ~350℃ to avoid amorphization of the implanted region. The samples were subsequently annealed at 700℃ to repair some of the residual implant damage. X-Ray Diffraction did not show any evidence of secondary phase formation in the ZnO. The Ni implanted samples remained paramagnetic but the Fe-implanted ZnO showed evidence of ferromagnetism with an approximate Curie temperature of ~240K.Preliminary X-Ray Photoelectron Spectroscopy measurements showed the Fe to be in the 2+ oxidation state. The carrier density in the implanted region still appears to be too low to support carrier-meditated origin of the ferromagnetism and formation of bound magnetic polarons may be one potential explanation for the observed magnetic properties. No evidence of the Anomalous Hall Effect could be found in the Fe-implanted ZnO, but its transport properties were dominated by the conventional or ordinary Hall effect.