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Sample records for al codoped zno

  1. (Al, Er) co-doped ZnO nanoparticles for photodegradation of rhodamine blue

    NASA Astrophysics Data System (ADS)

    Ghomri, R.; Shaikh, M. Nasiruzzaman; Ahmed, M. I.; Bououdina, M.; Ghers, M.

    2016-10-01

    Pure and co-doped (Al, Er) ZnO nanoparticles (NPs) have been synthesized by hydrothermal method using (Zn, Er and Al) nitrates. X-ray diffraction patterns reveal the formation of single phase of ZnO würtzite-type structure. The crystallite size for pure ZnO is in the order of 26.5 nm which decreases up to the range 14.2-22.0 nm after (Al, Er) co-doping. SEM micrographs show that the specimen is composed of regular spherical particles in the nanoscale regime with homogeneous size distribution and high tendency to agglomeration. FTIR spectra exhibit absorption lines located at wavenumbers corresponding to vibration modes between the constituent atoms. Raman spectra recorded under excitation ( λ exc = 632.8 nm) reveal peaks related to modes of transverse and longitudinal optical phonons of the würtzite ZnO structure. The energy band gap E g of ZnO:(Al, Er) NPs ranges in 3.264-3.251 eV. The photocatalytic activity of pure and co-doped (Al, Er) ZnO NPs was evaluated by the photodegradation of rhodamine blue under an irradiation of wavelength 554 nm. It is found that a photodegradation rate above 90 % could be achieved for a period of time of 40 min for pure ZnO and 120 min for (Al, Er) co-doped ZnO. A photodegradation mechanism is proposed.

  2. Electron transport in Al-Cu co-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Serin, T.; Atilgan, A.; Kara, I.; Yildiz, A.

    2017-03-01

    To investigate the influence of varying Al content on structural, optical, and electrical properties of ZnO thin films, Al-Cu co-doped ZnO thin films with fixed Cu content at 1 wt. % and different Al contents (1, 3, and 5 wt. %) were successfully synthesized on glass substrates using a sol-gel process. The results indicated that the varying Al content affects not only the grain size and band gap but also the electrical conductivity of the films, and a linear relationship was found between the band gap and strain values of the films. The temperature-dependent electrical conductivity data of the films demonstrated that electron transport was mainly controlled by the grain boundaries at intermediate and high temperatures, whereas it was governed by Mott-variable range hopping at low temperatures. Additionally, 3 wt. % Al content improved the electrical conductivity of Al-Cu co-doped ZnO by lowering the trap density and enhancing the hopping probability.

  3. Thermoelectric Properties of ZnO Ceramics Co-Doped with Al and Transition Metals

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Hiroyuki; Chonan, Yasunori; Oda, Manabu; Komiyama, Takao; Aoyama, Takashi; Sugiyama, Shigeaki

    2011-05-01

    The effect of co-doping with transition metals (Fe, Ni, and Sm) on the thermoelectric properties of Al-doped ZnO (AZO) ceramics was studied. The electrical conductivity σ of AZO was significantly (12%) increased by Ni co-doping, while an unfavorable deterioration in σ was observed for Fe- or Sm-co-doped AZO. Hall-effect measurements indicated that the electron mobility of AZO decreased due to co-doping in all samples. Only the Ni-co-doped AZO sample showed significant enhancement in electron density, resulting in its black color. The thermal conductivity κ decreased drastically due to Ni or Sm co-doping of AZO, while only a small change was observed for Fe co-doping of AZO. The κ value at 1073 K for Ni-co-doped AZO was 77% of that for AZO. A dimensionless figure of merit ZT = 0.126 was attained at 1073 K for Ni-co-doped AZO, representing an improvement over that of conventional AZO by a factor of 1.50.

  4. Local structure analysis of diluted magnetic semiconductor Co and Al co-doped ZnO nanoparticles

    SciTech Connect

    Hyodo, K.; Morimoto, S.; Yamazaki, T.; Ishikawa, T.; Ichiyanagi, Y.; Utsumi, J.

    2016-02-01

    In this study, Co and Al ions co-doped ZnO nanoparticles (Zn(Al, Co)O NPs) were prepared by our original chemical preparation method. The obtained samples prepared by this method, were encapsulated in amorphous SiO{sub 2}. X-ray diffraction (XRD) results showed Zn(Al, Co)O NPs had a single-phase nature with hexagonal wurtzite structure. These particle sizes could be controlled to be approximately 30 nm. We investigate the effect that the increase in the carrier has on the magnetization by doping Al to Co-doped ZnO NPs. The local structures were qualitatively analyzed using X-ray absorption fine structure (XAFS) measurements.

  5. Sol-gel derived Al and Ga co-doped ZnO thin films: An optoelectronic study

    NASA Astrophysics Data System (ADS)

    Ebrahimifard, Reza; Golobostanfard, Mohammad Reza; Abdizadeh, Hossein

    2014-01-01

    Al and Ga co-doped ZnO (AGZO) thin films with different doping contents of 0.5-4 at.% were synthesized via sol-gel route using dip coating method and the results were compared to the single doped specimens Al:ZnO (AZO) and Ga:ZnO (GZO). All samples were highly transparent in visible region (T > 85%) with band gap values around 3.3 eV. Introduction of Al and Ga to the ZnO crystal structure decreased the crystallinity and reduced the particle size of the films. Electrical resistivity was investigated and engineered in this study as the main parameter. Single doped samples showed reduction of resistivity compared to the un-doped ZnO. In this regard, Ga was more efficient than Al in decreasing the electrical resistivity. Furthermore, samples with 1 at.% Al and 1 at.% Ga showed the minimum amount of electrical resistivity. Co-doping was performed with two different approaches including variable doping content (Al + Ga ≠ cte) and constant doping content (Al + Ga = 0.5, 1, and 2 at.%) for the sake of the comparison with single doped samples. Samples with Al = 1 at.% and Ga = 1 at.% showed the lowest electrical resistivity in AGZO samples of former approach. However, in latter approach the lowest resistivity was obtained in Al + Ga = 2 at.% sample. The results proved the capability of co-doped samples in optoelectronic industry regarding partially substitution of expensive Ga with Al and obtaining co-doped AGZO transparent conductive thin films with lower resistivity compared to conventional AZO thin films and also achieving commercial advantages compared to costly GZO thin films.

  6. Hydrothermal growth and conductivity enhancement of (Al, Cu) co-doped ZnO nanorods thin films

    NASA Astrophysics Data System (ADS)

    Chakraborty, Mohua; Mahapatra, Preetilata; Thangavel, R.

    2016-05-01

    The incorporation of Al, Cu co-doping in ZnO host lattice plays an important role in modification of structural, optical and electrical properties in optoelectronic devices. In the present work, we were grown one dimensional ZnO nanorods (NRs) doped with different concentration of Al (0%~5%) and Cu was kept 20 M% on ITO glass substrates using a facile hydrothermal method, and investigated the effect of the codoping on the surface morphology and the electrical and optical performances of the doped ZnO NRs as photo anodes for solar water splitting applications. The crystallite size of NRs shows tuning in the band gap between 3.194 (Zn0.79Al0.01Cu0.2O) to 3.212 eV (Zn0.75Al0.05Cu0.2O) with Aluminium doping concentration and a remarkable improvement in current density (J) from 0.05 mA/cm2 to 4.98 mA/cm2 was achieved by incorporating Al and Cu has a critical effect of ZnO nanorods.

  7. RETRACTED: Investigation of structural, optical and electronic properties in Al-Sn co-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Pan, Zhanchang; Tian, Xinlong; Wu, Shoukun; Yu, Xia; Li, Zhuliang; Deng, Jianfeng; Xiao, Chumin; Hu, Guanghui; Wei, Zhigang

    2013-01-01

    This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Figures 3 and 4 of this paper have also been presented as belonging to other materials in other publications. This observation is evidence of fraud and therefore it is not certain that the described research and conclusions of this paper belong to the presented images. Figures 3 and 4 of this paper can also be found in: Effect of annealing on the structures and properties of Al and F co-doped ZnO nanostructures, Materials Science in Semiconductor Processing, 2014, 17, 162-167, http://dx.doi.org/10.1016/j.mssp.2013.09.023 Highly transparent and conductive Sn/F and Al co-doped ZnO thin films prepared by sol-gel method, Journal of Alloys and Compounds, 2014,583, 32-38, http://dx.doi.org/10.1016/j.jallcom.2013.06.192 Properties of fluorine and tin co-doped ZnO thin films deposited by sol-gel method, Journal of Alloys and Compounds, 2013,576, 31-37, http://dx.doi.org/10.1016/j.jallcom.2013.04.132

  8. Characterization of Al-As codoped p-type ZnO films by magnetron cosputtering deposition

    SciTech Connect

    Yun, Eui-Jung; Park, Hyeong-Sik; Lee, Kyu H.; Nam, Hyoung G.; Jung, Myunghee

    2008-04-01

    We report the preparation of Al-As codoped p-type ZnO films by rf magnetron cosputtering deposition. The p-type conductivity of the films was revealed by Hall measurements, x-ray photoelectron spectroscopy (XPS), and photoluminescence measurements after being annealed in O{sub 2}. It was observed by XPS that Al content increased with increasing AlAs target power from 80 to 160 W and reached a maximum value at an AlAs target power of 160 W. Hole concentration decreased with increasing Al content. With increasing AlAs target power greater than 160 W, the samples exhibit increases in As and O contents and decreases in Al and Zn contents, which contribute to the increase in hole concentration. A high hole concentration of 2.354x10{sup 20} cm{sup -3}, a low resistivity of 2.122x10{sup -2} {omega} cm, and a Hall mobility of 0.13 cm{sup 2}/V s for the films with high As content of 16.59% were obtained. XPS has also been used to address the unresolved issues related to the p-type formation mechanism of As-doped ZnO, supporting that the acceptor is As{sub Zn}-2V{sub Zn}.

  9. Effect of annealing atmosphere on photoluminescence and gas sensing of solution-combustion-synthesized Al, Pd co-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Li, Yan; Liu, Min; Lv, Tan; Wang, Qiong; Zou, Yun-ling; Lian, Xiao-xue; Liu, Hong-peng

    2015-11-01

    Al, Pd co-doped ZnO nanoparticles (NPs) synthesized using a solution combustion method and subsequent annealing process under various atmospheres, including air, nitrogen, and hydrogen, were characterized using x-ray diffraction, energy-dispersive x-ray spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The gas-sensing properties of the sensors based on the NPs were also examined. The results indicated that the Al, Pd co-doped ZnO NPs, with an average crystallite size of 10 nm, exhibited enhanced gas-sensing performance compared with that of pure ZnO and Al-doped ZnO. The response of the Al, Pd co-doped ZnO NPs annealed in N2 to ethanol (49.22) was nearly 5.7 times higher than that to acetone (8.61) and approximately 20 - 27 times higher than that to benzene (2.38), carbon monoxide (2.23), and methane (1.78), which demonstrates their excellent selectivity to ethanol versus other gases. This high ethanol response can be attributed to the combined effects of the small size, Schottky barrier, lattice defects, and catalysis. [Figure not available: see fulltext.

  10. Origin of Ferromagnetism in Al and Ni Co-doped ZnO Based DMS Materials

    NASA Astrophysics Data System (ADS)

    Murtaza, Saleem; Saadat, A. Siddiqi; Shahid, M. Ramay; Shahid, Atiq; Shahzad, Naseem

    2012-10-01

    Zn0.95Ni0.05O and Zn0.90Ni0.05Al0.05O compositions of nanocrystallites are synthesised using the well recognised auto-combustion technique. The x-ray diffraction patterns demonstrate the phase pure characteristic wurtzite-type crystal structure with space group P63mc in both the compositions. The elemental incorporation of Ni and Al contents into the ZnO structure is confirmed by energy dispersive x-ray analysis. The micrographs of scanning electron microscopy show an approximate ordered morphology. The electrical resistivity is observed to decrease with the rising temperature, depicting the characteristic semiconductor behaviour of the samples. The lower values of resistivity and ferromagnetic interactions in the Al-doped sample correspond to an increase of carrier's density. It is observed that the carrier mediated mechanism is mainly responsible for ferromagnetism in ZnO-based diluted magnetic semiconductors.

  11. Transparent conducting Si-codoped Al-doped ZnO thin films prepared by magnetron sputtering using Al-doped ZnO powder targets containing SiC

    SciTech Connect

    Nomoto, Jun-ichi; Miyata, Toshihiro; Minami, Tadatsugu

    2009-07-15

    Transparent conducting Al-doped ZnO (AZO) thin films codoped with Si, or Si-codoped AZO (AZO:Si), were prepared by radio-frequency magnetron sputtering using a powder mixture of ZnO, Al{sub 2}O{sub 3}, and SiC as the target; the Si content (Si/[Si+Zn] atomic ratio) was varied from 0 to 1 at. %, but the Al content (Al/[Al+Zn] atomic ratio) was held constant. To investigate the effect of carbon on the electrical properties of AZO:Si thin films prepared using the powder targets containing SiC, the authors also prepared thin films using a mixture of ZnO, Al{sub 2}O{sub 3}, and SiO{sub 2} or SiO powders as the target. They found that when AZO:Si thin films were deposited on glass substrates at about 200 degree sign C, both Al and Si doped into ZnO acted as effective donors and the atomic carbon originating from the sputtered target acted as a reducing agent. As a result, sufficient improvement was obtained in the spatial distribution of resistivity on the substrate surface in AZO:Si thin films prepared with a Si content (Si/[Si+Zn] atomic ratio) of 0.75 at. % using powder targets containing SiC. The improvement in resistivity distribution was mainly attributed to increases in both carrier concentration and Hall mobility at locations on the substrate corresponding to the target erosion region. In addition, the resistivity stability of AZO: Si thin films exposed to air for 30 min at a high temperature was found to improve with increasing Si content.

  12. Preparation and characterization of n-type conductive (Al, Co) co-doped ZnO thin films deposited by sputtering from aerogel nanopowders

    NASA Astrophysics Data System (ADS)

    El Mir, L.; Ayadi, Z. Ben; Saadoun, M.; Djessas, K.; von Bardeleben, H. J.; Alaya, S.

    2007-11-01

    Highly transparent, n-type conducting ZnO thin films were obtained by low temperature magnetron sputtering of (Co, Al) co-doped ZnO nanocrystalline aerogels. The nanoparticles of ˜30 nm size were synthesized by a sol-gel method using supercritical drying in ethyl alcohol. The structural, optical and electrical properties of the films were investigated. The ZnO films were polycrystalline textured, preferentially oriented with the (0 0 2) crystallographic direction normal to the film plane. The films show within the visible wavelength region an optical transmittance of more than 90% and a low electrical resistivity of 3.5 × 10 -4 Ω cm at room temperature.

  13. N and Al co-doping as a way to p-type ZnO without post-growth annealing

    NASA Astrophysics Data System (ADS)

    Snigurenko, Dymitr; Guziewicz, Elzbieta; Krajewski, Tomasz A.; Jakiela, Rafal; Syryanyy, Yevgen; Kopalko, Krzysztof; Paszkowicz, Wojciech

    2016-12-01

    We demonstrate experimental results on p-type ZnO films grown by atomic layer deposition (ALD) and co-doped with aluminum and nitrogen (ANZO). The films were obtained at low temperature (100 °C) with different N to Al ratio and show conductivity type, which depends on the N and Al content. We applied the x-ray photoelectron spectroscopy in order to get insight into a chemical nature of dopants and we found three pronounced contributions of the N1s core level which appear at binding energies of 396.1, 397.4 and around 399 eV. Based on ANZO and undoped ZnO films, both grown by the ALD technique, the ZnO homojunction was obtained in one technological process without any post-growth high temperature processing. The rectification ratio as high as 4 × 104 at ± 2 V was achieved when an ultrathin Al2O3 layer was inserted between p- and n-type ZnO and a n-type ZnO buffer layer deposited on an insulating Si substrate was applied.

  14. Effect of substrate temperature on transparent conducting Al and F co-doped ZnO thin films prepared by rf magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Wang, Fang-Hsing; Chang, Chiao-Lu

    2016-05-01

    ZnO is a wide bandgap semiconductor that has many potential applications such as solar cells, thin film transistors, light emitting diodes, and gas/biological sensors. In this study, a composite ceramic ZnO target containing 1 wt% Al2O3 and 1.5 wt% ZnF2 was prepared and used to deposit transparent conducting Al and F co-doped zinc oxide (AFZO) thin films on glass substrates by radio frequency magnetron sputtering. The effect of substrate temperatures ranging from room temperature (RT) to 200 °C on structural, morphological, electrical, chemical, and optical properties of the deposited thin films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Hall effect measurement, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and UV-vis spectrophotometer. The XRD results showed that all the AFZO thin films had a (0 0 2) diffraction peak, indicating a typical wurtzite structure with a preferential orientation of the c-axis perpendicular to the substrate. The FE-SEM and AFM analyses indicated that the crystallinity and grain size of the films were enhanced while the surface roughness decreased as the substrate temperature increased. Results of Hall effect measurement showed that Al and F co-doping decreased the resistivity more effectively than single-doping (either Al or F doping) in ZnO thin films. The resistivity of the AFZO thin films decreased from 5.48 × 10-4 to 2.88 × 10-4 Ω-cm as the substrate temperature increased from RT to 200 °C due to the increased carrier concentration and Hall mobility. The optical transmittances of all the AFZO thin films were over 92% in the wavelength range of 400-800 nm regardless of substrate temperature. The blue-shift of absorption edge accompanied the rise of the optical band gap, which conformed to the Burstein-Moss effect. The developed AFZO thin films are suitable as transparent conducting electrodes for various optoelectronic

  15. Structural and optical properties of nanoparticles (V, Al) co-doped ZnO synthesized by sol-gel processes

    NASA Astrophysics Data System (ADS)

    El Ghoul, J.; Bouguila, N.; Gómez-Lopera, S. A.; El Mir, L.

    2013-12-01

    ZnO, Zn0.9V0.1O and Zn0.89V0.1Al0.01O nanoparticles have been prepared by a sol-gel method and their structural and optical properties have been investigated. The obtained nanopowder was characterised by various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. After thermal treatment at 500 °C in air, the powder of Zn0.89V0.1Al0.01O with an average particle size of 25 nm presents a strong luminescence band in the visible range. The PL band energy position presents a small blue shift with the increase of measurement temperature. Different possible attributions of this emission band will be discussed.

  16. Controlled fabrication of oriented co-doped ZnO clustered nanoassemblies.

    PubMed

    Barick, K C; Aslam, M; Dravid, Vinayak P; Bahadur, D

    2010-09-01

    Clustered nanoassemblies of Mn doped ZnO and co-doped ZnO (Mn, Sn co-doped ZnO; Mn, Sb co-doped ZnO; and Mn, Bi co-doped ZnO) were prepared by refluxing their respective precursors in diethylene glycol medium. The co-doping elements, Sn, Sb and Bi exist in multi oxidation states by forming Zn-O-M (M=Sb, Bi and Sn) bonds in hexagonal wurtzite nanostructure. The analyses of detailed structural characterization performed by XRD, X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), show that co-doping ions are successfully incorporated into the ZnO nanostructure and do not appear as precipitates or secondary phases. HRTEM analysis also confirmed the oriented attachment of nanocrystals as well as their defect structures. The formation/activation of higher amount of intrinsic host defects, for instance, oxygen vacancies in co-doped ZnO as compared to Mn doped ZnO sample is evident from Raman spectra. The doped and co-doped samples exhibit ferromagnetic like behavior at room temperature presumably due to the presence of defects. Specifically, it has been observed that the incorporation of dopant and co-dopants into ZnO structure can modulate the local electronic structure due to the formation/activation of defects and hence, cause significant changes in their structural, vibrational, optical and magnetic properties.

  17. Electrical and optical properties of p-type codoped ZnO thin films prepared by spin coating technique

    NASA Astrophysics Data System (ADS)

    Pathak, Trilok Kumar; Kumar, Vinod; Swart, H. C.; Purohit, L. P.

    2016-03-01

    Undoped, doped and codoped ZnO thin films were synthesized on glass substrates using a spin coating technique. Zinc acetate dihydrate, ammonium acetate and aluminum nitrate were used as precursor for zinc, nitrogen and aluminum, respectively. X-ray diffraction shows that the thin films have a hexagonal wurtzite structure for the undoped, doped and co-doped ZnO. The transmittance of the films was above 80% and the band gap of the film varied from 3.20 eV to 3.24 eV for undoped and doped ZnO. An energy band diagram to describe the photoluminescence from the thin films was also constructed. This diagram includes the various defect levels and possible quasi-Fermi levels. A minimum resistivity of 0.0834 Ω-cm was obtained for the N and Al codoped ZnO thin films with p-type carrier conductivity. These ZnO films can be used as a window layer in solar cells and in UV lasers.

  18. Preparation and structural properties of pure and codoped (Mg, Ag) ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Reddy, B. Sankara; Reddy, S. Venkatramana; Reddy, N. Koteeswara

    2013-06-01

    Pure and co-doped (Mg, Ag) ZnO nanoparticles (Zn0.90Mg0.05Ag0.05O) are synthesized by chemical co-precipitation method in the presence of capping agent Polyethylene glycol 600 (PEG 600) and annealed at 500°C in air ambient for 1h. The XRD measurements reveals that the pure and co-doped ZnO samples have hexagonal structure without any change and the size of ZnO nanoparicles were decreased from 17 nm to 13 nm. FESEM images indicates that they are flake like structures of the ZnO and co-doped ZnO samples and ED AX spectra reveals that the successful doping concentration of Mg and Ag. From the TEM results, the size of the ZnO nanoparticles which are in good agreement with the XRD results.

  19. Influence of defects on electrical properties of electrodeposited co-doped ZnO nanocoatings

    NASA Astrophysics Data System (ADS)

    Simimol, A.; Anappara, Aji A.; Barshilia, Harish C.

    2017-01-01

    We present a systematic investigation of the electrical properties of undoped and Co-doped ZnO nanostructures at room temperature as an extensive study of the role of defects in ZnO. The ZnO nanostructures were fabricated by the electrodeposition method at low bath temperature (80 °C) and the Co concentration was varied from 0.01 to 0.2 mM. Electrical properties of the undoped and Co-doped ZnO nanostructures were studied in detail. The carrier concentration increases while the mobility reduces with increase in Co-concentration. The resistivity increases with an increase in Co-concentration and the reason is correlated with the defects in ZnO. In order to understand more details of the role of defects in the present I-V characteristic behavior of the Co-doped ZnO, high temperature vacuum annealing of ZnO sample was carried out. Electrical, optical and magnetic properties of the high temperature vacuum annealed ZnO were studied in detail. Photoluminescence spectroscopy (PL) results revealed more information of the defect levels which act as scattering centers for the carriers. Co-doping as well as annealing at high temperature in vacuum environment tunes the defects in ZnO and which influence the optical, magnetic and electrical behavior of the ZnO nanostructures.

  20. Synthesis, structural and optical characterization of undoped, N-doped ZnO and co-doped ZnO thin films

    SciTech Connect

    Pathak, Trilok Kumar Kumar, R.; Purohit, L. P.

    2015-05-15

    ZnO, N-doped ZnO and Al-N co-doped ZnO thin films were deposited on ITO coated corning glass by spin coater using sol-gel method. The films were annealed in air at 450°C for one hour. The crystallographic structure and morphology of the films were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The X-ray diffraction results confirm that the thin films are of wurtzite hexagonal with a very small distortion. The optical properties were investigated by transmission spectra of different films using spectrophotometer (Shimadzu UV-VIS-NIR 3600). The results indicate that the N doped ZnO thin films have obviously enhanced transmittance in visible region. Moreover, the thickness of the films has strong influences on the optical constants.

  1. Ni, Fe Co-doped ZnO nanoparticles synthesized by solution combustion method

    SciTech Connect

    Dhiman, Pooja Chand, Jagdish Verma, S. Sarveena, Singh, M.

    2014-04-24

    This paper outlines the synthesis and characterization of Ni-Fe co-doped ZnO nanoparticles by facile solution combustion method. The structural characterization by XRD confirmed the phase purity of the samples. Surface morphology studied by scanning electron microscope revealed cubic type shape of grains. EDS analysis conformed the elemental composition. Higher value of DC electrical conductivity and less band gap for co-doped ZnO from UV-Vis studies confirmed the change in defect chemistry of ZnO Matrix.

  2. Ni, Fe Co-doped ZnO nanoparticles synthesized by solution combustion method

    NASA Astrophysics Data System (ADS)

    Dhiman, Pooja; Chand, Jagdish; Verma, S.; Sarveena, Singh, M.

    2014-04-01

    This paper outlines the synthesis and characterization of Ni-Fe co-doped ZnO nanoparticles by facile solution combustion method. The structural characterization by XRD confirmed the phase purity of the samples. Surface morphology studied by scanning electron microscope revealed cubic type shape of grains. EDS analysis conformed the elemental composition. Higher value of DC electrical conductivity and less band gap for co-doped ZnO from UV-Vis studies confirmed the change in defect chemistry of ZnO Matrix.

  3. Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: Optical and electrochemical properties

    NASA Astrophysics Data System (ADS)

    Romeiro, Fernanda C.; Marinho, Juliane Z.; Lemos, Samantha C. S.; de Moura, Ana P.; Freire, Poliana G.; da Silva, Luis F.; Longo, Elson; Munoz, Rodrigo A. A.; Lima, Renata C.

    2015-10-01

    We report for the first time a rapid preparation of Zn1-2xCoxNixO nanoparticles via a versatile and environmentally friendly route, microwave-assisted hydrothermal (MAH) method. The Co, Ni co-doped ZnO nanoparticles present an effect on photoluminescence and electrochemical properties, exhibiting excellent electrocatalytic performance compared to undoped ZnO sample. Photoluminescence spectroscopy measurements indicated the reduction of the green-orange-red visible emission region after adding Co and Ni ions, revealing the formation of alternative pathways for the generated recombination. The presence of these metallic ions into ZnO creates different defects, contributing to a local structural disorder, as revealed by Raman spectra. Electrochemical experiments revealed that the electrocatalytic oxidation of dopamine on ZnO attached to multi-walled carbon nanotubes improved significantly in the Co, Ni co-doped ZnO samples when compared to pure ZnO.

  4. Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: Optical and electrochemical properties

    SciTech Connect

    Romeiro, Fernanda C.; Marinho, Juliane Z.; Lemos, Samantha C.S.; Moura, Ana P. de; Freire, Poliana G.; Silva, Luis F. da; Longo, Elson; Munoz, Rodrigo A.A.; Lima, Renata C.

    2015-10-15

    We report for the first time a rapid preparation of Zn{sub 1−2x}Co{sub x}Ni{sub x}O nanoparticles via a versatile and environmentally friendly route, microwave-assisted hydrothermal (MAH) method. The Co, Ni co-doped ZnO nanoparticles present an effect on photoluminescence and electrochemical properties, exhibiting excellent electrocatalytic performance compared to undoped ZnO sample. Photoluminescence spectroscopy measurements indicated the reduction of the green–orange–red visible emission region after adding Co and Ni ions, revealing the formation of alternative pathways for the generated recombination. The presence of these metallic ions into ZnO creates different defects, contributing to a local structural disorder, as revealed by Raman spectra. Electrochemical experiments revealed that the electrocatalytic oxidation of dopamine on ZnO attached to multi-walled carbon nanotubes improved significantly in the Co, Ni co-doped ZnO samples when compared to pure ZnO. - Graphical abstract: Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: optical and electrochemical properties. Co, Ni co-doped ZnO hexagonal nanoparticles with optical and electrocatalytic properties were successfully prepared for the first time using a microwave hydrothermal method at mild conditions. - Highlights: • Co{sup 2+} and Ni{sup 2+} into ZnO lattice obtained a mild and environmentally friendly process. • The heating method strongly influences in the growth and shape of the particles. • Short-range defects generated by the ions insertion affects the photoluminescence. • Doped ZnO nanoparticles improve the electrocatalytic properties of pure oxide.

  5. Characterization of co-doped (In, N): ZnO by indigenous thermopower measurement system

    NASA Astrophysics Data System (ADS)

    Kedia, Sanjay Kumar; Singh, Anil; Chaudhary, Sujeet

    2016-05-01

    The thermopower measurement of (In, N) co-doped ZnO thin films have been carried out using indigenous high and low temperature thermopower measurement system. The compact thermopower measurement system has been designed, developed, tested in house. The sensitivity and accuracy of indigenous thermopower system have been investigated by measuring thermopower of standard samples like Cu, Ni, Sb etc. It has been also investigated by the comparison of carrier concentration using Hall Effect and Thermopower measurement of these (In, N) co-doped ZnO thin films. The constant temperature gradient between hot and cold junction has been maintained by using the temperature controller. The room temperature and low temperature Seebeck coefficient measurements were performed on these co-doped ZnO samples. A series of experiments have been performed to detect the p-type conductivity in co-doped ZnO thin films, particularly at low temperature. The negative Seebeck coefficient observed down to 40 K established the n-type behavior in these co-doped samples.

  6. Electronic structure of Co-doped ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Neffati, Ahmed; Souissi, Hajer; Kammoun, Souha

    2012-10-01

    The optical transmission spectra, the photoluminescence (PL), and the photoluminescence excitation (PLE) spectra of the cobalt doped zinc oxide nanorods Zn1-xCoxO (x = 0.01, 0.10) were measured by Loan et al. [J. Phys. D: Appl. Phys. 42, 065412 (2009)] in the region 1.5-4 eV. These spectra exhibit a group of ultraviolet narrow lines in the region of 3.0-3.4 eV related to the near-band-edge emission of the host ZnO materials and a group of emission lines in the red region of 1.8-1.9 eV assigned to the radiative transitions within the tetrahedral Co2+ ions in the ZnO host crystal. The group of lines in the visible region provides important information about the electronic structure of the cobalt doped zinc oxide nanorods. This work investigates a theoretical crystal-field analysis of the visible lines associated to the Co2+ ion transition occupying a Td site symmetry in ZnO host crystal. A satisfactory correlations were obtained between experimental and calculated energy levels. The electronic structure was compared with the reported for cobalt transition ion doped in ZnO nanoparticles and bulk crystals [Volbers et al., Appl. Phys. A 88, 153 (2007) and H. J. Schulz and M. Thiede, Phys. Rev. B 35, 18 (1987)]. In order to explain the existence of excitation peaks observed near the band edge of the ZnO host, an energy transfer mechanism is proposed.

  7. Physical study on Cobalt-Indium Co-doped ZnO nanofilms as hydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Mimouni, R.; Mahdhi, N.; Boubaker, K.; Madouri, A.; Amlouk, M.

    2016-03-01

    The present work reports some physical investigations on (Co,In) codoped zinc oxide nanofilms deposited on glass substrates at 460 °C by the spray pyrolysis technique. The effect of Co and In concentration on the structural, morphological, optical and surface wettability properties have been investigated using X-ray diffraction (XRD) patterns, Raman spectroscopy, SEM, optical measurement, photoluminescence spectroscopy as well as the measurement of hydrophobicity in terms of water contact angle. It is found that all films crystallized in würtzite ZnO phase, with a preferentially orientation towards (002) direction parallel to c-axis. The Raman spectra of the samples exhibit the presence of E2high characteristic mode of würtzite structure with high crystallinity as well as two dominant bands 1LO and 2LO. Also, no additional modes introduced by codopoing have been found. SEM micrographs show the uniform deposition of fine grains on surface films. Thicknesses of films are less than 100 nm. In addition, optical investigations indicate that the band gap narrowing of (Co,In) codoped ZnO thin films is due to the increase in the band tail width. Indeed, PL study indicates that (Co,In) codoped ZnO nanofilms exhibit a large decrease of the UV luminescence, which is assigned to the trapping of photo-generated electrons by both In3+ and Co2+ ions as well as an improvement of charge separation in the ZnO thin films. Finally, the (Co,In) codoping influences the surface wettability property and transform the ZnO character from hydrophilic (θ < 90°) for pure ZnO nanofilm to hydrophobic (θ > 90°) for (Co,In) codoped ZnO ones.

  8. Luminescence Properties of Sm3+/Eu3+ Co-Doped ZnO Quantum Dots.

    PubMed

    Liu, Fengyi; Li, Hong; Hu, Yajing; Na, Jin; Mou, Yun; Yang, Kun; Ye, Zuhu; Li, Mingyue; Xie, Ya-Hong

    2016-04-01

    In order to improve luminescence properties of semiconductor ZnO quantum dots (QDs), Sm3+/Eu3+ co-doped ZnO QDs have been controllably synthesized by sol-gel method in this paper. ZnO QDs have a spherical shape with mean diameter at about 5-6 nm, which was characterized by high-resolution transmission electron microscopy (HRTEM). ZnO QDs have hexagonal wurtzite structure with parts of Sm3+ and Eu3+ incorporated into the lattice, which was demonstrated by X-ray Diffraction (XRD). Luminescence properties at room temperature (RT) of different amount of Sm3+ and 2 mol% Eu3+ doped ZnO QDs were examined in-depth by optical spectra. In contrast to the Pr3+/Eu3+ co-doped fluorescent performance researched in our previous study, the photoluminescence (PL) spectra indicates the unique luminescence properties of Sm3+/Eu3+ co-doped ZnO QDs. In addition, fluorescence lifetimes were obtained to illustrate the luminous mechanism.

  9. Magnetization and Raman scattering studies of (Co,Mn) codoped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Duan, L. B.; Rao, G. H.; Wang, Y. C.; Yu, J.; Wang, T.

    2008-07-01

    Single-phase (Co,Mn) codoped ZnO nanoparticles were synthesized by an autocombustion method. Hysteresis loop was observed at 300 K for the sample Zn0.98Co0.01Mn0.01O with a low coercivity (40±5 Oe). Temperature dependence of magnetization rules out the possibility of superparamagnetism or spin-glass behavior. Raman scattering studies manifested that there might exist a defect annihilation arising from the (Co,Mn) codoped into ZnO host lattice. As the ferromagnetism of diluted magnetic semiconductors is closely related to the dopant-defect hybridization, the ferromagnetic ordering was significantly enhanced in the sample Zn0.98Co0.01Mn0.01O by the (Co,Mn) codoping, in comparison to the Zn0.99Co0.01O and Zn0.99Mn0.01O fabricated by the same method.

  10. Enhanced Visible-Light Photocatalytic Activity of C/Ce-Codoped ZnO Nanoellipsoids Synthesized by Hydrothermal Method

    NASA Astrophysics Data System (ADS)

    Ha, Luu Thi Viet; Dai, Luu Minh; Nhiem, Dao Ngoc; Van Cuong, Nguyen

    2016-08-01

    C/Ce-codoped ZnO nanomaterial has been synthesized by a hydrothermal method and its physical properties and characterization investigated using thermogravimetric and differential thermal analysis (TG-DTA), x-ray diffraction (XRD) analysis, Fourier-transform infrared (FTIR) spectroscopy, energy-dispersive x-ray (EDX) spectroscopy, UV-Vis diffuse reflectance spectroscopy, and scanning electron microscopy (SEM). The photocatalytic activity of the nanomaterial was examined using methylene blue as organic dye under visible-light source. The results show that the C/Ce-codoped ZnO nanomaterial exhibited higher photocatalytic activity under visible-light irradiation compared with undoped ZnO, Ce-doped ZnO or C-doped ZnO nanomaterials. Such enhancement of the photocatalytic activity of C/Ce-codoped ZnO under visible-light irradiation suggests that these nanoparticles might have good applications in optoelectronics and wastewater treatment.

  11. Structural and magnetic properties of Ni/Mn codoped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Vijayaprasath, G.; Murugan, R.; Asaithambi, S.; Sakthivel, P.; Mahalingam, T.; Ravi, G.

    2016-05-01

    We report systematic studies of the magnetic properties of Ni and Mn co-doped ZnO nanoparticles prepared by co-precipitation method. Structural characterization reveals that Ni and Mn ions substituted into ZnO lattices without any secondary phases formation. Photoluminescence and Raman spectra shows that the Ni/Mn were doped into the ZnO lattice resulting slight shift in near-band-edge emission. Moreover, the novel Raman peak at 586 cm-1 indicates two kinds of cations via doping that could affect the local polarizability. Magnetic measurements of the nanoparticles exhibits ferromagnetic behavior at room-temperature.

  12. First-principles study on the electronic and optical properties of Si and Al co-doped zinc oxide for solar cell devices

    NASA Astrophysics Data System (ADS)

    Abbassi, A.; El Amrani, A.; Ez-Zahraouy, H.; Benyoussef, A.; El Amraoui, Y.

    2016-06-01

    Electronic and optical properties of co-doped zinc oxide ZnO with silicon (Si) and aluminum (Al), in Zn1-2 x Si x Al x O (0 ≤ x ≤ 0.0625) original structure forms, are investigated by the first-principles calculations based on the density functional theory (DFT). The optical constants and dielectric functions are investigated with the full-potential linearized augmented plane wave (FP-LAPW) method and the generalized gradient approximation (GGA) by WIEN2k package. The complex dielectric functions, refractive index and band gap of the pure as well as doped and co-doped ZnO were investigated, which are in good agreement with the available experimental results for the undoped ZnO. Thus, the maximum optical transmittance of the co-doped ZnO of about 95 % was achieved; it is higher than that of pure ZnO. Thus, we showed for the Si-Al co-doped ZnO with x = 0.0315 that the optical transmittance can cover a larger range in the visible light region. In addition, an occurrence of important energy levels around Fermi levels was showed, which is mainly due to doping atoms that lead to an overlap between valence and conduction bands, and consequently to the significant conductor behavior of the Si-Al co-doped ZnO. The original Zn1-2 x Si x Al x O structure reveals promising optical and electronic properties, and it can be investigated as good candidates for practical uses as transparent and conducting electrodes in solar cell devices.

  13. EPR investigation of pure and Co-doped ZnO oriented nanocrystals

    NASA Astrophysics Data System (ADS)

    Savoyant, A.; Alnoor, H.; Bertaina, S.; Nur, O.; Willander, M.

    2017-01-01

    Pure and cobalt-doped zinc oxide aligned nanorods have been grown by the low-temperature (90 °C) aqueous chemical method on amorphous ZnO seed layer, deposited on a sapphire substrate. High crystallinity of these objects is demonstrated by the electron paramagnetic resonance investigation at liquid helium temperature. The successful incorporation of Co2+ ions in substitution of Zn2+ ones in the ZnO matrix has also been confirmed. A drastic reduction of intrinsic ZnO nanorods core defects is observed in the Co-doped samples, which enhances the structural quality of the NRs. The quantification of substitutional Co2+ ions in the ZnO matrix is achieved by comparison with a reference sample. The findings in this study indicate the potential of using the low-temperature aqueous chemical approach for synthesizing material for spintronics applications.

  14. Resistive switching: An investigation of the bipolar–unipolar transition in Co-doped ZnO thin films

    SciTech Connect

    Santos, Daniel A.A.; Zeng, Hao; Macêdo, Marcelo A.

    2015-06-15

    Highlights: • A purely bipolar behavior on a Co-doped ZnO thin film has been demonstrated. • We have shown what can happen if a unipolar test is performed in a purely bipolar device. • An explanation for how a sample can show a purely bipolar switching behavior was suggested. • An important open issue about resistive switching effect was put in debate. - Abstract: In order to investigate the resistive switching effect we built devices in a planar structure in which two Al contacts were deposited on the top of the film and separated by a small gap using a shadow mask. Therefore, two samples of 10% Co-doped ZnO thin films were sputtered on glass substrate. High resolution X-ray diffraction (HRXRD) revealed a highly c-axis oriented crystalline structure, without secondary phase. The high resolution scanning electron microscopy (HRSEM) showed a flat surface with good coverage and thickness about 300 nm. A Keithley 2425 semiconductor characterization system was used to perform the resistive switching tests in the bipolar and unipolar modes. Considering only the effect of compliance current (CC), the devices showed a purely bipolar behavior since an increase in CC did not induce a transition to unipolar behavior.

  15. Reversible ferromagnetic spin ordering governed by hydrogen in Co-doped ZnO semiconductor

    SciTech Connect

    Cho, Yong Chan; Kim, Sung-Jin; Lee, Seunghun; Kim, Su Jae; Cho, Chae Ryong; Nahm, Ho-Hyun; Park, Chul Hong; Jeong, Il Kyoung; Park, Sungkyun; Hong, Tae Eun; Kuroda, Shinji; Jeong, Se-Young

    2009-10-26

    We report a reversible manipulation of short-range spin ordering in Co-doped ZnO through hydrogenation and dehydrogenation processes. In both magnetic-circular dichroism and superconducting quantum interference device measurements, the ferromagnetism was clearly induced and removed by the injection and ejection of hydrogen, respectively. The x-ray photoelectron spectroscopy results and the first-principles electronic structure calculations consistently support the dependence of the ferromagnetism on the hydrogen position and the contribution of transition metal ions. The results suggest the ferromagnetic interaction between Co ions can be reversibly controlled by the hydrogen-mediated intrinsic spin ordering in Co doped ZnO.

  16. Observation of low field microwave absorption in co-doped ZnO system

    NASA Astrophysics Data System (ADS)

    Mahule, Tebogo S.; Srinivasu, Vijaya V.; Das, Jayashree

    2016-10-01

    Room temperature low field microwave absorption (LFMA) in magnetic materials find application in microwave absorbers and low field sensors. However not all the magnetic materials show LFMA and the phenomenon is not fully understood. We report on the observation of low field microwave absorption (LFMA) or the non-resonant microwave absorption (NRMA) in the transition metal (TM) co-doped ZnO samples of the composition Zn1-x(TM:TM)xO synthesized by solid state reaction technique. LFMA peaks and hysteresis matches very well with that of the magnetization hysteresis loop and the anisotropy fields at room temperature similar to the reports in the literature for other magnetic systems. However we show through our careful experiments that such a correlation between LFMA and the magnetization does not survive at low temperatures and particularly at 10 K the LFMA hysteresis collapses in our TM co-doped ZnO system; whereas the magnetization hysteresis loop becomes very big and anisotropy field becomes bigger in the range of kOe. We interpret the LFMA as field dependent surface impedance or eddy current losses, in terms of a possible role of anomalous hall resistivity that follows magnetization and the ordinary hall resistivity that only follows the applied field. We then argue that LFMA accordingly follows magnetization or applied field when AHE or OHE dominates respectively. Also we confirm the absence of LFMA signals in the rare earth co-doped ZnO system.

  17. Fabrication and photoelectric properties of Er3+ and Yb3+ co-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Feng, Wei; Wang, Xiangfu; Meng, Lan; Yan, Xiaohong

    2016-01-01

    In this paper, the Er3+ and Yb3+ co-doped ZnO films deposited by a novel thermal decomposition method under different annealing temperature process have been reported. The effects of annealing temperature on the morphology and properties of the films are systematically studied. The resulting spectra demonstrate that the Er3+ and Yb3+ co-doped ZnO films possessed the property of up-conversion, converting IR light into visible light that can be absorbed by amorphous silicon solar cell. After all, inner photoelectric effect of the Er3+ and Yb3+ co-doped ZnO films in the amorphous as a light scattering layer are also found with an infrared 980 nm laser as excitation source.

  18. Extrinsic origin of room-temperature ferromagnetism in Co-doped ZnO annealed in Zn vapor

    NASA Astrophysics Data System (ADS)

    Yan, Guoqing; Xuan, Haicheng

    2011-08-01

    Co-doped ZnO and CoO were prepared at 950 °C by the solid-state reaction method, then were annealed in N2 flow at 950 °C, and finally annealed in Zn vapor at 600 °C or 800 °C. The samples before annealing in Zn vapor have no ferromagnetism, but after annealing in Zn vapor, Co-doped ZnO and CoO both exhibit room-temperature ferromagnetism. Through x-ray diffraction and element composition measurements, it was found that the ferromagnetism of Co-doped ZnO annealed in Zn vapor is extrinsic and comes from cubic Co5Zn21 and/or cubic CoZn.

  19. Enhanced photocatalytic properties of quantum-sized ZnO induced by La3+-Nd3+ co-doping

    NASA Astrophysics Data System (ADS)

    Lu, S. X.; Zhu, T.; Xu, W. G.

    2009-09-01

    Nanoparticles of ZnO doped with La3+, Nd3+, co-doped with La3+ and Nd3+ were prepared using the sol-gel method. The samples were characterized by means of X-ray diffraction (XRD), UV-Vis spectroscopy (UV). The photocatalytic reactivities were evaluated by photodegradation of unsymmetrical dimethylhydrazine solution. Nanocrystalline ZnO co-doped with La3+ and Nd3+ at optimal concentration (2 at.% La3+ and 1.5 at.% Nd3+) shows a better synergistic effect, which significantly increases the photodegradation activity of nano-ZnO. The factors influencing photoreactivity of co-doped nanocrystalline ZnO have been discussed.

  20. Preparation and characterization of Mn and (Mn, Cu) co-doped ZnO nanostructures.

    PubMed

    Wang, H B; Wang, H; Zhang, C; Yang, F J; Duan, J X; Yang, C P; Gu, H S; Zhou, M J; Li, Q; Jiang, Y

    2009-05-01

    We report on the ferromagnetic characteristics of Zn(1-x)Mn(x)O nanorods synthesized by a seed-mediated solution method. The as-doped ZnO nanorods had a length about 200 nm and a diameter ranging from 20 to 30 nm. Magnetic property measurements revealed that the Zn(1-x)Mn(x)O nanorods exhibited weak ferromagnetism at 305 K. Similar solution method were also employed to fabricate the (Mn, Cu) co-doped nanostructures. The presence of Cu2+ was found to change the nanorod morphology (in the case of pure ZnO) to nanoparticle. On the other hand, not only the hysteresis curve saturated at lower magnetic field, but also the saturation magnetization was increased with the Cu doping. Transmission electron microscopy, X-ray photoelectron spectroscopy and Photoluminescence analysis suggested that the room temperature (RT) ferromagnetism could be originated from the Mn2+ doped into the ZnO lattice, and additional carriers due to the Cu co-doping may enhance the room temperature ferromagnetism in the Mn:ZnO system.

  1. Photoluminescence, ellipsometric, optical and morphological studies of sprayed Co-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Gençyılmaz, O.; Atay, F.; Akyüz, I.

    2016-06-01

    In this study, undoped and cobalt (Co)-doped zinc oxide (ZnO) films were successfully produced by ultrasonic spray pyrolysis (USP) technique at low temperature (350°C). The optical and surface properties were investigated as a function of Co content. The optical parameters (thickness, refractive index and extinction coefficient) were determined using spectroscopic ellipsometry (SE) and it was seen that the refractive index and extinction coefficient values of Co-doped ZnO films decreased slightly depending on the increasing of Co doping. For investigation, the transmittance and photoluminescence (PL) spectra of the films, UV-Vis spectrophotometer and PL spectroscopy were used at room temperature. The transmittance spectra show that transmittance values decreased and Co+2 ions substitute Zn+2 ions of ZnO lattice. The optical band gap values decreased from 3.26 eV to 2.85 eV with the changing of Co content. The results of PL spectra exhibit the position of the different emission peaks unchanged but the intensity of peaks increased with increasing Co doping. Also, the surface properties of the films were obtained by atomic force microscopy (AFM) and these results indicated that the surface morphology and roughness values were prominently changed with Co doping.

  2. Facile synthesis of highly uniform Mn/Co-codoped ZnO nanowires: optical, electrical, and magnetic properties.

    PubMed

    Li, Huifeng; Huang, Yunhua; Zhang, Qi; Qiao, Yi; Gu, Yousong; Liu, Jing; Zhang, Yue

    2011-02-01

    In this article, Co/Mn-codoped ZnO nanowires (NWs) were successfully synthesized on a silicon substrate by the thermal evaporation method with Au catalyst. The X-ray diffraction pattern indicated that the Co/Mn-codoped ZnO NWs are a hexagonal wurtzite structure without a second phase, and energy dispersive X-ray spectroscopy revealed that the Co and Mn ions were introduced into the ZnO NWs with the content of ∼0.8 at% and ∼1.2 at%, respectively. Photoluminescence spectra and Raman spectra showed that the Co/Mn were doped into the NWs and resulted in the shift of the near-band-edge emission. Moreover, the novel Raman peak at 519.3 cm(-1) has suggested that the two kinds of cations via doping could affect the local polarizability. Compared with the undoped ZnO NW, the electrical measurement showed that the Co/Mn-codoping enhanced the conductivity by an order of magnitude due to the presence of Co, Mn cations. The electron mobility and carrier concentration of a fabricated field effect transistor (FET) device is 679 cm2 V(-1) s(-1) and 2×10(18) cm(-3), respectively. Furthermore, the M-H curve demonstrated that the Co/Mn-codoped ZnO NWs have obvious ferromagnetic characteristics at room temperature. Our study enhances the understanding of the novel performances of transition-metal codoped ZnO NWs and also provides a potential way to fabricate optoelectronic devices.

  3. Color tunable ZnO nanorods by Eu and Tb co-doping for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Pal, Partha P.; Manam, J.

    2014-07-01

    Eu/Tb co-doped ZnO nanorods were prepared by co-precipitation method and the effect of Eu-Tb co-doping was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy, Fourier transform infrared spectroscopy (FTIR), UV-Vis-NIR diffuse reflectance (DR) and photoluminescence (PL) spectroscopy. The XRD pattern shows typical peak pattern for pure hexagonal wurtzite structure to match with the JCPDS data. The samples are found to be consisting of nanorods of diameter 20-30 nm as revealed by the TEM image. The FTIR pattern confirms the formation of the compounds. The DR study was carried to show the variation of absorption edge and the variation in band gap values, which showed the crystal size effect in the co-doped sample of different rare-earth ratios. The room temperature PL study shows bright emission spectra for the samples with different rare-earth ratios. It shows a very good energy transfer from Tb to Eu ions. The energy transfer mechanism and color tunability were discussed thoroughly.

  4. Reactive codoping of GaAlInP compound semiconductors

    DOEpatents

    Hanna, Mark Cooper; Reedy, Robert

    2008-02-12

    A GaAlInP compound semiconductor and a method of producing a GaAlInP compound semiconductor are provided. The apparatus and method comprises a GaAs crystal substrate in a metal organic vapor deposition reactor. Al, Ga, In vapors are prepared by thermally decomposing organometallic compounds. P vapors are prepared by thermally decomposing phospine gas, group II vapors are prepared by thermally decomposing an organometallic group IIA or IIB compound. Group VIB vapors are prepared by thermally decomposing a gaseous compound of group VIB. The Al, Ga, In, P, group II, and group VIB vapors grow a GaAlInP crystal doped with group IIA or IIB and group VIB elements on the substrate wherein the group IIA or IIB and a group VIB vapors produced a codoped GaAlInP compound semiconductor with a group IIA or IIB element serving as a p-type dopant having low group II atomic diffusion.

  5. Thermal ionization induced metal-semiconductor transition and room temperature ferromagnetism in trivalent doped ZnO codoped with lithium

    SciTech Connect

    Sivagamasundari, A.; Chandrasekar, S.; Pugaze, R.; Kannan, R.; Rajagopan, S.

    2014-03-07

    Thermal ionization induced metallic to semiconductor (MST) transition occurring at 460 K for Zn{sub 0.97}Al{sub 0.03}O, 463 K for Zn{sub 0.94}Al{sub 0.03}Li{sub 0.03}O, and 503 K for Zn{sub 0.91}Al{sub 0.03}Li{sub 0.03}Mn{sub 0.03}O has been found in the sol-gel synthesized (using hexamethylenetetramine), trivalent doped (Al, Mn) ZnO codoped with lithium. Increase in the thermally ionized carrier concentration due to Al doping is responsible for near band edge (NBE) peak shift causing Fermi level to move into conduction band making it metallic consistent with resistivity results. Free carrier (thermally activated) neutralization with ionized donor is responsible for semiconducting nature, which is supported from the free carrier screening produced energy shift in the NBE of photoluminescence peak. Furthermore, independently band gap shrinkage is also obtained from UV-Visible studies confirming localization induced MST. An anti-correlation is found between defect density (DLE) and room temperature ferromagnetism (RTFM) indicating intrinsic defects are not directly responsible for RTFM.

  6. Thermal ionization induced metal-semiconductor transition and room temperature ferromagnetism in trivalent doped ZnO codoped with lithium

    NASA Astrophysics Data System (ADS)

    Sivagamasundari, A.; Chandrasekar, S.; Pugaze, R.; Rajagopan, S.; Kannan, R.

    2014-03-01

    Thermal ionization induced metallic to semiconductor (MST) transition occurring at 460 K for Zn0.97Al0.03O, 463 K for Zn0.94Al0.03Li0.03O, and 503 K for Zn0.91Al0.03Li0.03Mn0.03O has been found in the sol-gel synthesized (using hexamethylenetetramine), trivalent doped (Al, Mn) ZnO codoped with lithium. Increase in the thermally ionized carrier concentration due to Al doping is responsible for near band edge (NBE) peak shift causing Fermi level to move into conduction band making it metallic consistent with resistivity results. Free carrier (thermally activated) neutralization with ionized donor is responsible for semiconducting nature, which is supported from the free carrier screening produced energy shift in the NBE of photoluminescence peak. Furthermore, independently band gap shrinkage is also obtained from UV-Visible studies confirming localization induced MST. An anti-correlation is found between defect density (DLE) and room temperature ferromagnetism (RTFM) indicating intrinsic defects are not directly responsible for RTFM.

  7. The effects of group-I elements co-doping with Mn in ZnO dilute magnetic semiconductor

    NASA Astrophysics Data System (ADS)

    Zhang, Liqiang; Zhang, Yinzhu; Ye, Zhizhen; Lu, Jianguo; Lu, Bin; He, Bo

    2012-06-01

    Mn-Li codoped ZnO (Zn(Mn,Li)O), Mn-Na codoped ZnO (Zn(Mn,Na)O), and Mn-K codoped ZnO (Zn(Mn,K)O) thin films were deposited on quartz substrates by pulsed laser deposition. The doping effects of group-I elements (e.g., Li, Na, and K) on the structural, magnetic, and optical properties of the Mn doped ZnO (ZnMnO) films were discussed. X-ray diffraction and K-edge x-ray absorption near-edge structure measurements revealed that all the films showed a hexagonal wurtzite ZnO structure, and no other clusters, precipitates, or second phases were detected. Zn(Mn,Na)O and Zn(Mn,Li)O films showed a weak p-type conductivity, while the Zn(Mn,K)O film appeared a highly resistivity. The saturation magnetization of Zn(Mn,Na)O and Zn(Mn,Li)O films was 1.2 and 0.18 μB/Mn, respectively. The hole-related defects, induced by doping with a low content of Li or Na, contributed to the room temperature ferromagnetism in the ZnMnO system.

  8. Effects on the optical properties and conductivity of Ag-N co-doped ZnO

    NASA Astrophysics Data System (ADS)

    Xu, Zhenchao; Hou, Qingyu; Qu, Lingfeng

    2017-01-01

    Nowadays, the studies of the effects on the optical bandgap, absorption spectrum, and electrical properties of Ag-N co-doped ZnO have been extensively investigated. However, Ag and N atoms in doped systems are randomly doped, and the asymmetric structure of ZnO is yet to be explored. In this paper, the geometric structure, stability, density of states, absorption spectra and conductivity of pure and Ag-N co-doped Zn1‑xAgxO1‑xNx(x=0.03125, 0.0417 and 0.0625) in different orientations are calculated by using plane-wave ultrasoft pseudopotential on the basis of density functional theory with GGA+U method. Results show that the volume, equivalent total energy and formation energy of the doped system increase as the concentration of Ag-N co-doped Zn1‑xAgxO1‑xNx increases at the same doping mode. The doped systems also become unstable, and difficulty in doping. At the same concentration of Ag-N co-doped Zn1‑xAgxO1‑xNx, the systems with Ag-N along the c-axis orientation is unstable, and doping is difficult. The optical bandgap of Ag-N co-doped systems is narrower than that of the pure ZnO. At the same doping mode, the optical bandgap of the systems with Ag-N perpendicular to the c-axis orientation becomes narrow as the concentration of Ag-N co-doped Zn1‑xAgxO1‑xNx increases. The absorption spectra of the doped systems exhibit a red shift, and this red shift becomes increasingly significant as the concentration of Ag-N co-doped Zn1‑xAgxO1‑xNx increases. Under the same condition, the relative hole concentrations of the doped systems increases, the hole effective mass in valence band maximum decreases, the hole mobility decreases, the ionization energy decreases, Bohr radius increases, the conductance increases and the conductivity become better. Our results may be used as a basis for the designing and preparation of new optical and electrical materials for Ag-N co-doped ZnO applied in low temperature end of temperature difference battery.

  9. Origins of shallow level and hole mobility in codoped p-type ZnO thin films

    NASA Astrophysics Data System (ADS)

    Ye, H. B.; Kong, J. F.; Shen, W. Z.; Zhao, J. L.; Li, X. M.

    2007-03-01

    A combination study of structural, optical, and electrical properties has been carried out on N-In codoped p-type ZnO thin films for the origins of shallow level and hole mobility. The observed small activation energy of ˜20meV for the hole concentration corresponds well to the results from photoluminescence and conductivity data, revealing the grain boundary trapping nature of the shallow level. The achieved hole mobility is mainly due to the lack of grain boundary barrier effect, and the codoping yielded weak ionized impurity scattering. The authors have also revealed the scattering and conduction mechanisms in these p-ZnO films.

  10. Self-consistent GW calculation of the electronic structure of co-doped ZnO

    NASA Astrophysics Data System (ADS)

    Kim, Maengsuk; Park, Chul Hong

    2012-01-01

    The electronic structure of Co-doped ZnO is presented using a first-principles self-consistent GW calculation based on the screened hybrid HSE06 functional and is compared to the structure calculated using the generalized gradient density approximation plus U (GGA+U) method. The obtained energy splittings between unoccupied Co t 2 and the occupied Co e states are about 3.0 eV and 5.1 eV for the GGA+U and the HSE06 calculations, respectively. Through a correction of the self-consistent GW calculations on the top of HSE06, the electronic energy levels of the occupied Co e band states are moved downward slightly while those at the unoccupied Co t 2 bands are shifted upward, and the occupied Co e and the empty Co t 2 levels of the minority spin are located, respectively, far below and far above the conduction band minimum.

  11. Local fields in Co and Mn Co-doped ZnO

    NASA Astrophysics Data System (ADS)

    Sato, W.; Kano, Y.; Suzuki, T.; Nakagawa, M.; Kobayashi, Y.

    2016-12-01

    The magnetic properties of ZnO co-doped with 5 at. % Co and 5 at. % Mn(Zn0.90Co0.05Mn0.05O) synthesized by a solid-state reaction were investigated by means of 57Co emission Mössbauer spectroscopy. The majority of the probe ions (80 %) residing in defect-free substitutional Zn sites take the oxidation state of 57Fe 2+, and the others presumably form local defects taking the state of 57Fe 3+ at room temperature. Both components show doublets, and RT ferromagnetism was thus absent in the sample. For the measurement at 10 K, spectral broadening was observed, implying a possible presence of a weak magnetic component.

  12. Fabrication and characterization of a diluted magnetic semiconducting TM co-doped Al:ZnO (TM=Co, Ni) thin films by sol-gel spin coating method.

    PubMed

    Siddheswaran, R; Mangalaraja, R V; Tijerina, Eduardo P; Menchaca, J-Luis; Meléndrez, M F; Avila, Ricardo E; Jeyanthi, C Esther; Gomez, M E

    2013-04-01

    Effect of transition metal oxides (TM=Co and Ni) co-doping on the crystallinity, surface morphology, grain growth and magnetic properties of nanostructure Al:ZnO thin films has been studied for diluted magnetic semiconductor applications. Al:ZnO thin films were fabricated by sol-gel spin coating on p-type Si (100) substrates. Fabrication of hexagonal wurtzite TM co-doped Al:ZnO thin films having thickness 2μm was successfully achieved. The Raman spectra of the TM co-doped Al:ZnO thin films showed a broad vibrational mode in the range 520-540cm(-1) due to crystal defects created co-doping elements in the ZnO host lattice. Scanning electron microscopy (SEM) revealed that the films are composed of uniform size, polycrystalline dense ZnO particles with defect free, smooth surfaces. The surface roughness was further verified with atomic force microscopy (AFM). The energy dispersive X-ray spectroscopic analysis (EDX) confirmed the stoichiometric compositions of the TM co-doped Al:ZnO films. The magnetic measurements exhibited that the Co, Al:ZnO and Ni, Al:ZnO thin films were ferromagnetic at room temperature.

  13. Physical structure and optical properties of Co-doped ZnO nanoparticles prepared by co-precipitation

    NASA Astrophysics Data System (ADS)

    He, Rongliang; Tang, Bin; Ton-That, Cuong; Phillips, Matthew; Tsuzuki, Takuya

    2013-11-01

    The structural and optical properties of cobalt-doped zinc oxide (Co-doped ZnO) nanoparticles have been investigated. The nanopowder with Co concentrations up to 5 at% was synthesized by a co-precipitation method. The physical structure and the chemical states of the Co-doped ZnO were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-Visible reflectance and cathodoluminescence (CL) spectroscopy. The results show that cobalt ions predominantly occupy Zn2+ sites in the wurtzite crystal lattice and possess a valence state of 2+. CL analysis revealed that the incorporation of Co2+ creates a new emission band at 1.85 eV, but quenched the near-band-edge luminescence.

  14. Room Temperature Ferromagnetism of FeCo-Codoped ZnO Nanorods Prepared by Chemical Vapor Deposition

    SciTech Connect

    Chen, J.; Liu, J.; West, A.; Yan, Y.; Yu, M.; Zhou, W.

    2008-11-01

    FeCo-codoped ZnO nanorods with room temperature ferromagnetic ordering have been synthesized by chemical vapor deposition. Detailed nanostructures were investigated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and nanoprobe X-ray energy dispersive spectroscopy (EDS). The ZnO nanorods were grown along c-axis of a single crystalline wurtzite structure and no second phase was observed by high resolution TEM. EDS analysis along the nanowires indicated that Co and Fe were successfully doped into the ZnO lattice with concentrations about 0.6-1.0 at.%. Magnetic measurement demonstrates a ferromagnetic ordering with Curie temperature higher than 300 K presents in the ZnO nanorods.

  15. CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES: First-Principle Studies on Conductive Behaviors of P-Type ZnO Codoped by N and B

    NASA Astrophysics Data System (ADS)

    Li, Ping; Deng, Sheng-Hua; Zhang, Xue-Yong; Zhang, Li; Liu, Guo-Hong; Yu, Jiang-Ying

    2010-10-01

    Using a first-principle method, the electronic structures and the impurity formation energy of ZnO, ZnO (N), ZnO (N+B), and ZnO (2N+B) have been calculated, based on which the feasibility to obtain p-type ZnO is discussed. According to the results, when ZnO is single doped by N, the acceptor level is deep, and the formation energy is negative, so the ideal p-type ZnO can not be obtained by this way. On the contrary, when 2N+B are codoped into ZnO, the acceptor level becomes much lower, and the formation energy is positive, so it is a better way to obtain p-type ZnO.

  16. Intense white light emission in Tm3+/Er3+/Yb3+ co-doped Y2O3-ZnO nano-composite

    NASA Astrophysics Data System (ADS)

    Yadav, R. S.; Verma, R. K.; Rai, S. B.

    2013-07-01

    The Tm3+/Er3+/Yb3+ co-doped Y2O3-ZnO nano-composite is synthesized using the solution combustion technique. The structural morphology is monitored using x-ray diffraction, transmission electron microscopy and scanning electron microscopy. The Yb3+/Tm3+ co-doped nano-phosphor emits intense blue as well as weak red emissions, while Yb3+/Er3+ co-doped nano-phosphor emits strong green along with red emissions on excitation with 976 nm laser. Joining these together (i.e. Tm3+/Er3+/Yb3+ co-doped phosphor) give very strong white light, which is further verified by CIE coordinates (0.32, 0.36). The addition of ZnO with Y2O3 phosphor gives further enhancement in the intensity of white light. The possible reason for this enhancement is the removal of optical quenching sites.

  17. Lanthanum and zirconium co-doped ZnO nanocomposites: synthesis, characterization and study of photocatalytic activity.

    PubMed

    Moafi, Hadi Fallah; Zanjanchi, Mohammad Ali; Shojaie, Abdollah Fallah

    2014-09-01

    Nanocomposits of zinc oxide co-doped with lanthanum and zirconium were prepared using the modified sol-gel method. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), and BET surface area measurement. For comparison, the La and Zr mono doped ZnO have also been prepared under the same conditions. The XRD results revealed that all the materials showed a hexagonal wurtzite crystal structure. It was found that the particle size of La-Zr-doped ZnO is much smaller as compared to that of pure ZnO. The effect of operational parameters such as, doping concentration, catalyst loading, pH and initial concentration of methylene blue on the extent of degradation was investigated. The photocatalytic activity of the undoped ZnO, mono-doped and La-Zr-ZnO photocatalysts was evaluated by the photocatalytic degradation of methylene blue in aqueous solution. The presence of lanthanium and/or zirconium causes a red shift in the absorption band of ZnO. The results show that the photocatalytic activity of the La-Zr-ZnO photocatalyst is much higher than that of undoped and mono-doped ZnO, resulting from the La and Zr synergistic effect. The co-operation of the lanthanum and zirconium ion leads to the narrowing of the band gap and greatly improves the photocatalytic activity. The photocatalyst co-doped with lanthanum and zirconium 4 mol% shows the best photoactivity and photodecomposition efficiencies were improved by 92% under UV-Vis irradiation at the end of 30 min, compared with the pure and mono doped samples.

  18. First-principle study on Ag-2N heavy codoped of p-type graphene-like ZnO nanosheet

    NASA Astrophysics Data System (ADS)

    Zhang, W. X.; Li, T.; He, C.; Wu, X. L.; Duan, L.; Li, H.; Xu, L.; Gong, S. B.

    2015-02-01

    In this article, two different Ag-2N heavy codoped of graphene-like ZnO nanosheets have been investigated based on first-principles density-functional theory. The geometric optimization, Density of States (DOS) and Band structure (BS) for all models are calculated, respectively. The results indicate that Ag substituted on the cation site (AgZn) exhibit a strong attractive interaction with a nitrogen acceptor located at the nearest-neighbor oxygen site, forming passive Ag-N complex. This study can be a theoretical guidance to improve the electrical conductivity of p-type graphene-like ZnO nanosheet by heavy codoping.

  19. A sensitive and label-free photoelectrochemical aptasensor using Co-doped ZnO diluted magnetic semiconductor nanoparticles.

    PubMed

    Li, Hongbo; Qiao, Yunfei; Li, Jing; Fang, Hailin; Fan, Dahe; Wang, Wei

    2016-03-15

    Co-doped ZnO diluted magnetic semiconductor as a novel photoelectric beacon was first constructed for photoelectrochemical (PEC) aptasensor of acetamiprid. The fabricated PEC sensing is based on the specific binding of acetamiprid and its aptamer, which induces the decreasement of enhanced photocurrent produced by the electron donor of quercetin. Co(2+) doping has a beneficial effect in extending the band width of light absorption of ZnO into the visible region and to promote the separation of the photoinduced carriers due to the sp-d exchange interactions existing between the band electrons and the localized d electrons of Co(2+). The fabricated aptasensor was linear with the concentration of acetamiprid in the range of 0.5-800 nmolL(-1) with the detection limit of 0.18 nmolL(-1). The presence of same concentration of other conventional pesticides did not interfere in the detection of acetamiprid and the recovery is between 96.2% and 103.7%. This novel PEC aptasensor has good performances with high sensitivity, good selectivity, low cost and portable features. The strategy of Co-doped ZnO diluted magnetic semiconductor paves a new way to improve the performances of PEC aptasensor.

  20. Structure and properties of Co-doped ZnO films prepared by thermal oxidization under a high magnetic field.

    PubMed

    Li, Guojian; Wang, Huimin; Wang, Qiang; Zhao, Yue; Wang, Zhen; Du, Jiaojiao; Ma, Yonghui

    2015-01-01

    The effect of a high magnetic field applied during oxidation on the structure, optical transmittance, resistivity, and magnetism of cobalt (Co)-doped zinc oxide (ZnO) thin films prepared by oxidizing evaporated Zn/Co bilayer thin films in open air was studied. The relationship between the structure and properties of films oxidized with and without an applied magnetic field was analyzed. The results show that the high magnetic field obviously changed the structure and properties of the Co-doped ZnO films. The Lorentz force of the high magnetic field suppressed the oxidation growth on nanowhiskers. As a result, ZnO nanowires were formed without a magnetic field, whereas polyhedral particles formed under a 6 T magnetic field. This morphology variation from dendrite to polyhedron caused the transmittance below 1,200 nm of the film oxidized under a magnetic field of 6 T to be much lower than that of the film oxidized without a magnetic field. X-ray photoemission spectroscopy indicated that the high magnetic field suppressed Co substitution in the ZnO lattice, increased the concentration of oxygen vacancies, and changed the chemical state of Co. The increased concentration of oxygen vacancies affected the temperature dependence of the resistivity of the film oxidized under a magnetic field of 6 T compared with that of the film oxidized without a magnetic field. The changes of oxygen vacancy concentration and Co state caused by the application of the high magnetic field also increase the ferromagnetism of the film at room temperature. All of these results indicate that a high magnetic field is an effective tool to modify the structure and properties of ZnO thin films.

  1. Twin grain boundary mediated ferromagnetic coupling in Co-doped ZnO: First-principles calculations

    NASA Astrophysics Data System (ADS)

    Wu, Jingjing; Tang, Xin; Pu, Chunying; Long, Fei; Tang, Biyu

    2017-01-01

    First principle calculation, based on density functional theory, is applied to study the electronic and magnetic properties of Co-doped ZnO ∑7 (12 3 ̅0) twin grain boundary. Co atoms substituting Zn at the threefold-coordination sites have the lowest formation energy, compared with other sites. More importantly, the configuration can result in the stable formation of ferromagnetic state (FM). Meanwhile, the strong Co-Co interaction is found to be responsible for the ferromagnetic state. Due to the structural character of the twin grain boundary, periodical defects can be offered, which favors the macroscopic FM ordering. The result also gives us a new thinking to understand the origin of FM in transition metal doped ZnO.

  2. Studies on the structural and optical properties of zinc oxide nanobushes and Co-doped ZnO self-aggregated nanorods synthesized by simple thermal decomposition route

    SciTech Connect

    Freedsman, Joseph J.; Kennedy, L. John; Kumar, R. Thinesh; Sekaran, G.; Vijaya, J. Judith

    2010-10-15

    Pure and Co-doped zinc oxide nanomaterials were prepared by a simple low temperature synthesis and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution-transmission electron microscopy (HR-TEM), diffused reflectance spectroscopy (DRS) and electron paramagnetic resonance (EPR) techniques. The results showed the formation of nanobushes that consists of several nanowires for pure ZnO and the nanorods formed by self-aggregation for Co-doped ZnO. The presence of Co{sup 2+} ions replacing some of the Zn{sup 2+} in the ZnO lattice was confirmed by EPR and DRS studies. The mechanism for the formation of self-aggregated and self-aligned ZnO rods after the incorporation of cobalt in the lattice by the building block units is discussed in this study. Morphological studies were carried out using SEM and HR-TEM, which supports the validity of the proposed mechanism for the formation of ZnO nanobushes and Co-doped ZnO nanorods. The synthesized nanomaterials were found to have good optoelectronic properties.

  3. Annealing in tellurium-nitrogen co-doped ZnO films: The roles of intrinsic zinc defects

    SciTech Connect

    Tang, Kun Gu, Ran; Gu, Shulin Ye, Jiandong; Zhu, Shunming; Yao, Zhengrong; Xu, Zhonghua; Zheng, Youdou

    2015-04-07

    In this article, the authors have conducted an extensive investigation on the roles of intrinsic zinc defects by annealing of a batch of Te-N co-doped ZnO films. The formation and annihilation of Zn interstitial (Zn{sub i}) clusters have been found in samples with different annealing temperatures. Electrical and Raman measurements have shown that the Zn{sub i} clusters are a significant compensation source to holes, and the Te co-doping has a notable effect on suppressing the Zn{sub i} clusters. Meanwhile, shallow acceptors have been identified in photoluminescence spectra. The N{sub O}-Zn-Te complex, zinc vacancy (V{sub Zn})-N{sub O} complex, and V{sub Zn} clusters are thought to be the candidates as the shallow acceptors. The evolution of shallow acceptors upon annealing temperature have been also studied. The clustering of V{sub Zn} at high annealing temperature is proposed to be a possible candidate as a stable acceptor in ZnO.

  4. EXAFS and XANES investigation of (Li, Ni) codoped ZnO thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Mino, Lorenzo; Gianolio, Diego; Bardelli, Fabrizio; Prestipino, Carmelo; Senthil Kumar, E.; Bellarmine, F.; Ramanjaneyulu, M.; Lamberti, Carlo; Ramachandra Rao, M. S.

    2013-09-01

    Ni doped, Li doped and (Li, Ni) codoped ZnO thin films were successfully grown using a pulsed laser deposition technique. Undoped and doped ZnO thin films were investigated using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES). Preliminary investigations on the Zn K-edge of the undoped and doped ZnO thin films revealed that doping has not influenced the average Zn-Zn bond length and Debye-Waller factor. This shows that both Ni and Li doping do not appreciably affect the average local environment of Zn. All the doped ZnO thin films exhibited more than 50% of substitutional Ni, with a maximum of 77% for 2% Ni and 2% Li doped ZnO thin film. The contribution of Ni metal to the EXAFS signal clearly reveals the presence of Ni clusters. The Ni-Ni distance in the Ni0 nanoclusters, which are formed in the film, is shorter with respect to the reference Ni metal foil and the Debye-Waller factor is higher. Both facts perfectly reflect what is expected for metal nanoparticles. At the highest doping concentration (5%), the presence of Li favors the growth of a secondary NiO phase. Indeed, 2% Ni and 5% Li doped ZnO thin film shows %Nisub = 75 ± 11, %Nimet = 10 ± 8, %NiO = 15 ± 8. XANES studies further confirm that the substitutional Ni is more than 50% in all the samples. These results explain the observed magnetic properties.

  5. Photoluminescence of transparent glass-ceramics based on ZnO nanocrystals and co-doped with Eu3+, Yb3+ ions

    NASA Astrophysics Data System (ADS)

    Arzumanyan, Grigory M.; Kuznetsov, Evgeny A.; Zhilin, Aleksandr A.; Dymshits, Olga S.; Shemchuk, Daria V.; Alekseeva, Irina P.; Mudryi, Alexandr V.; Zhivulko, Vadim D.; Borodavchenko, Olga M.

    2016-12-01

    Glasses of the K2Osbnd ZnOsbnd Al2O3sbnd SiO2 system co-doped with Eu2O3 and Yb2O3 were prepared by the melt-quenching technique. Transparent zincite (ZnO) glass-ceramics were obtained by secondary heat-treatments at 680-860 °C. At 860 °C, traces of Eu oxyapatite appeared in addition to ZnO nanocrystals. The average crystal size obtained from the X-ray diffraction data was found to range between 14 and 35 nm. Absorption spectra of the initial glasses are composed of an absorption edge and absorption bands due to electronic transitions of Eu3+ ions. With heat-treatment, the absorption edge pronouncedly shifts to the visible spectral range. The luminescence properties of the glass and glass-ceramics were studied by measuring their excitation and emission spectra at 300, 78, and 4.2 K. Strong red emission of Eu3+ ions dominated by the 5D0-7F2 (612 nm) electric dipole transition was detected. Changes in the luminescence properties of the Eu3+-related excitation and emission bands were observed after heat-treatments at 680 °C and 860 °C. The ZnO nanocrystals showed both broad luminescence (400-850 nm) and free-exciton emission near 3.3 eV at room temperature. The upconversion luminescence spectrum of the initial glass was obtained under excitation of the 976 nm laser source.

  6. Li and Ag Co-Doped ZnO Photocatalyst for Degradation of RO 4 Dye Under Solar Light Irradiation.

    PubMed

    Dhatshanamurthi, P; Shanthi, M

    2016-06-01

    The synthesis of Li doped Ag-ZnO (Li-Ag-ZnO) has been successfully achieved by a sonochemically assisted precipitation-decomposition method. The synthesized catalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), X-ray photoelectron spectra (XPS) and BET surface area measurements. The photocatalytic activity of Li-Ag-ZnO was investigated for the degradation of Reactive orange 4 (RO 4) dye in aqueous solution under solar light irradiation. Co-dopants shift the absorbance of ZnO to the visible region. Li-Ag-ZnO is found to be more efficient than Ag-ZnO, Li-ZnO, commercial ZnO and prepared ZnO at pH 7 for the mineralization of RO 4 dye under solar light irradiation. The influences of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photo-mineralization of RO 4 have been analyzed. The mineralization of RO 4 dye has been confirmed by COD measurements. A degradation mechanism is proposed for the degradation of RO 4 under solar light. The catalyst was found to be more stable and reusable.

  7. Crystal Structures of Al-Nd Codoped Zirconolite Derived from Glass Matrix and Powder Sintering.

    PubMed

    Liao, Chang-Zhong; Shih, Kaimin; Lee, William E

    2015-08-03

    Zirconolite is a candidate host for immobilizing long-lived radionuclides. Zirconolite-based glass-ceramics in the CaO-SiO2-Al2O3-TiO2-ZrO2-Nd2O3-Na2O matrix are a potential waste form for immobilizing actinide radionuclides and can offer double barriers to immobilize radioactive elements. However, the X-ray diffraction patterns of the zirconolite derived from the glass matrix (glass ceramic, GC) are significantly different from those prepared by powder sintering (PS). In this Article, the crystal structures of Al-Nd codoped zirconolite grown via the glass matrix route and the powder sintering route are investigated in detail. Two samples of Al-Nd codoped zirconolite were prepared: one was grown from a CaO-SiO2-Al2O3-TiO2-ZrO2-Nd2O3-Na2O glass matrix, and the other was prepared with a Ca0.75Nd0.25ZrTi1.75Al0.25O7 composition by powder sintering. The samples were then characterized using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX), and selected area electron diffraction (SAED). The chemical composition of the 100-500 nm zirconolite crystals grown from a glass matrix was determined by TEM-EDX to be Ca0.83Nd0.25Zr0.85Ti1.95Al0.11O7. PXRD and SAED results showed that these two Al-Nd codoped zirconolite phases were crystallized in space group C12/c1. The HRTEM images and SAED results showed that there were heavy stacking faults in the zirconolite crystals grown from the glass matrix. In contrast, far fewer defects were found in the zirconolite crystals prepared by powder sintering. The split-atom model was adopted for the first time to construct the Al-Nd codoped zirconolite structure grown from glass during the Rietveld refinement. The isostructural method assisted by Rietveld refinement was used to resolve the Al-Nd codoped zirconolite structures prepared by different methods. The occupancies of the cation sites were identified, and the distribution behavior of Nd

  8. Role of donor defects in stabilizing room temperature ferromagnetism in (Mn, Co) co-doped ZnO nanoparticles.

    PubMed

    Naeem, M; Hasanain, S K

    2012-06-20

    We report the effects of co-doping ZnO with Co and Mn in an n-type environment on ferromagnetism (FM). Two sets of samples, Zn(0.95-x)Co(0.04)Mn(x)O (0.000 ≤ x ≤ 0.02) and Zn(0.95-y)Co(y)Mn(0.04)O (0.000 ≤ y ≤ 0.02), were synthesized by the chemical route with oxygen vacancies introduced via annealing in a forming gas (reducing the atmosphere). In addition to the magnetization, the particles were characterized by x-ray diffraction, diffuse reflectance spectroscopy and x-ray absorption near-edge emission spectroscopy. The Co and Mn ions were determined to be in the + 2 state in a tetrahedral symmetry, with no evidence of metallic Co or Mn. We find that while a purely Mn-doped sample exhibits weak FM at room temperature, the general effect of Mn as a co-dopant with Co, in an n-type environment, is to decrease the moment strongly. All of our results can be systematically explained within the context of defect mediated FM in these wide bandgap semiconductors, where the coincidence of the spin-split-impurity (defect) band states and the 3d states leads to the development of a net moment alongside the formation of spin polarons.

  9. Morphological evolution and electronic alteration of ZnO nanomaterials induced by Ni/Fe co-doping

    NASA Astrophysics Data System (ADS)

    Fletcher, Cameron; Jiang, Yijiao; Sun, Chenghua; Amal, Rose

    2014-06-01

    Zinc oxide (ZnO) nanocrystals mono- and co-doped with nickel/iron were prepared using a facile solvothermal procedure. A significant change in the surface morphology from nanorods to plate-like nanoparticles was observed with an increase in the dopant concentration. The variations of their optical and electronic properties induced by metal dopants were investigated using a combination of characterization techniques and ab initio calculations. It is found that both nickel and iron atoms have been successfully incorporated into the crystal lattice rather than forming a secondary phase, suggesting good dispersion of dopants within the ZnO matrix. Doping with iron has red-shifted the absorption edges of ZnO towards the visible portion resulting in lower band gap energies with increasing dopant concentration. Evidenced by Raman and EPR spectroscopy, the addition of iron has been shown to promote the formation of more oxygen vacancy and crystal defects within the host lattice as well as increasing the free-electron density of the nanomaterial. The DFT plus Hubbard model calculations confirm that low concentration Ni-doping does not induce band gap narrowing but results in localized states. The calculations show that Fe-doping has the potential to greatly improve the optical absorption characteristics and lead to structural deformation, corroborating the UV-Vis, Raman, and EPR spectra.Zinc oxide (ZnO) nanocrystals mono- and co-doped with nickel/iron were prepared using a facile solvothermal procedure. A significant change in the surface morphology from nanorods to plate-like nanoparticles was observed with an increase in the dopant concentration. The variations of their optical and electronic properties induced by metal dopants were investigated using a combination of characterization techniques and ab initio calculations. It is found that both nickel and iron atoms have been successfully incorporated into the crystal lattice rather than forming a secondary phase

  10. White Light Emission and Luminescence Dynamics in Eu³⁺/Dy³⁺ Codoped ZnO Nanocrystals.

    PubMed

    Luo, L; Huang, F Y; Dong, G S; Wang, Y H; Hu, Z F; Chen, J

    2016-01-01

    In order to expand the use of ZnO in advanced display and lighting device applications, such as distinguishable emissive flat panel displays and liquid crystal display backlights, Eu³⁺/Dy³⁺-codoped ZnO nanocrystals were synthesized using a low temperature wet chemical doping technique and chemical surface modification. X-ray diffraction patterns revealed that co-doping Eu³⁺ and Dy³⁺ does not change the wurtzite structure of ZnO. A high-resolution TEM image showing obvious lattice fringes confirmed the high crystallinity of the nanosized sample. The luminescence and dynam- ics of Eu³⁺/Dy³⁺-codoped ZnO nanocrystals of various doping concentrations were studied under ultraviolet excitation. Excitation into the ZnO conduction band was also studied. ZnO doped with Eu³⁺ and Dy³⁺ ions exhibited a strong blue (483 nm) emission from the ⁴F₉/₂ --> ⁶H₁₅/₂ transition of Dy³⁺ ions, a yellowish-green (575 nm) emission from the ⁴F₉/₂ --> ⁶H₁₃/₂ transition of Dy³⁺ ions and a red (612 nm) emission from the ⁵D₀ --> ⁷F₂ transition of Eu³⁺ ions, without a defect background. Undoped ZnO emitted a broadband green light, demonstrating an efficient energy transfer from the ZnO host to the Eu³⁺ and Dy³⁺ ions. Moreover, energy transfer from the Eu³⁺ ions to the Dy³⁺ ions in the ZnO host was also observed by analyzing luminescence decay curves. The luminescence dynamics of the Eu³⁺/Dy³⁺-codped ZnO sample indicate that as the Eu³⁺ concentration increased, both the rise and the decay time constants of the ⁴H₉/₂ level of the Dy³⁺ ions became longer, while the decay time constants of the ⁵D₀ level of the Eu³⁺ ions became shorter, suggesting an energy transfer from the Eu³⁺ ions to the Dy³⁺ ions in the ZnO host. Furthermore, by adjusting the doping concentration ratio of Eu³⁺ and Dy³⁺ ions, the Eu³⁺/Dy³⁺-codoped ZnO phosphors emitted strong white luminescence with a high

  11. Visible upconversion in Er3+/Yb3+ co-doped LaAlO3 phosphors

    NASA Astrophysics Data System (ADS)

    Singh, Vijay; Rai, V. K.; Singh, N.; Pathak, M. S.; Rathaiah, M.; Venkatramu, V.; Patel, Rahul V.; Singh, Pramod K.; Dhoble, S. J.

    2017-01-01

    The Er3+ doped and Er3+/Yb3+ co-doped LaAlO3 phosphors have been synthesized by the combustion method and characterized their structural, morphological, elemental, vibrational and optical properties. The optical absorption and upconversion properties of the synthesized phosphors have been studied. Upon co-doping Yb3+ ions into Er3+:LaAlO3, the blue, green and red upconversion emissions of Er3+ ions have been enhanced about 20, 54 and 22 times, under 978 nm laser excitation. The observed upconversion emissions could be due to excited state absorption in Er3+:LaAlO3, whereas energy transfer is dominant mechanism in Er3+/Yb3+:LaAlO3 phosphors. The tuning in the color emitted from the synthesized phosphors towards the green region has been found due to incorporation of the Yb3+ ions. With increase in the pump power, the color emitted from the co-doped phosphor is not tuned significantly, showing its applicability in making the green display devices.

  12. Highly piezoelectric co-doped AlN thin films for wideband FBAR applications.

    PubMed

    Yokoyama, Tsuyoshi; Iwazaki, Yoshiki; Onda, Yosuke; Nishihara, Tokihiro; Sasajima, Yuichi; Ueda, Masanori

    2015-06-01

    We report piezoelectric materials composed of charge-compensated co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) thin films. The effect of the dopant element into AlN on the crystal structure, and piezoelectric properties of co-doped AlN was determined on the basis of a first-principles calculation, and the theoretical piezoelectric properties were confirmed by experimentally depositing thin films of magnesium (Mg) and zirconium (Zr) co-doped AlN (Mg-Zr-doped AlN). The Mg-Zrdoped AlN thin films were prepared on Si (100) substrates by using a triple-radio-frequency magnetron reactive co-sputtering system. The crystal structures and piezoelectric coefficients (d33) were investigated as a function of the concentrations, which were measured by X-ray diffraction and a piezometer. The results show that the d33 of Mg-Zr-doped AlN at total Mg and Zr concentrations (both expressed as β) of 0.35 was 280% larger than that of pure AlN. The experimentally measured parameter of the crystal structure and d33 of Mg-Zr-doped AlN (plotted as functions of total Mg and Zr concentrations) were in very close agreement with the corresponding values obtained by the first-principle calculations. Thin film bulk acoustic wave resonators (FBAR) employing (Mg,Zr)0.13Al0.87N and (Mg, Hf)0.13 Al0.87N as a piezoelectric thin film were fabricated, and their resonant characteristics were evaluated. The measured electromechanical coupling coefficient increased from 7.1% for pure AlN to 8.5% for Mg-Zr-doped AlN and 10.0% for Mg- Hf-doped AlN. These results indicate that co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) films have potential as piezoelectric thin films for wideband RF applications.

  13. Preparation, structural and optical characterization of ZnO, ZnO: Al nanopowder

    SciTech Connect

    Mohan, R. Raj; Rajendran, K.; Sambath, K.

    2014-01-28

    In this paper, ZnO and ZnO:Al nanopowders have been synthesized by low cost hydrothermal method. Zinc nitrate, hexamethylenetetramine (HMT) and aluminium nitrate are used as precursors for ZnO and AZO with different molar ratios. The structural and optical characterization of doped and un-doped ZnO powders have been investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDAX), photoluminescence (PL) and ultra violet visible (UV-Vis) absorption studies. The SEM results show that the hydrothermal synthesis can be used to obtain nanoparticles with different morphology. It is observed that the grain size of the AZO nanoparticles increased with increasing of Al concentration. The PL measurement of AZO shows that broad range of green emission around 550nm with high intensity. The green emission resulted mainly because of intrinsic defects.

  14. Preparation, structural and optical characterization of ZnO, ZnO: Al nanopowder

    NASA Astrophysics Data System (ADS)

    Mohan, R. Raj; Rajendran, K.; Sambath, K.

    2014-01-01

    In this paper, ZnO and ZnO:Al nanopowders have been synthesized by low cost hydrothermal method. Zinc nitrate, hexamethylenetetramine (HMT) and aluminium nitrate are used as precursors for ZnO and AZO with different molar ratios. The structural and optical characterization of doped and un-doped ZnO powders have been investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDAX), photoluminescence (PL) and ultra violet visible (UV-Vis) absorption studies. The SEM results show that the hydrothermal synthesis can be used to obtain nanoparticles with different morphology. It is observed that the grain size of the AZO nanoparticles increased with increasing of Al concentration. The PL measurement of AZO shows that broad range of green emission around 550nm with high intensity. The green emission resulted mainly because of intrinsic defects.

  15. Enhanced room temperature ferromagnetism in electrodeposited Co-doped ZnO nanostructured thin films by controlling the oxygen vacancy defects

    SciTech Connect

    Simimol, A.; Anappara, Aji A.; Greulich-Weber, S.; Chowdhury, Prasanta; Barshilia, Harish C.

    2015-06-07

    We report the growth of un-doped and cobalt doped ZnO nanostructures fabricated on FTO coated glass substrates using electrodeposition method. A detailed study on the effects of dopant concentration on morphology, structural, optical, and magnetic properties of the ZnO nanostructures has been carried out systematically by varying the Co concentration (c.{sub Co}) from 0.01 to 1 mM. For c.{sub Co }≤ 0.2 mM, h-wurtzite phase with no secondary phases of Co were present in the ZnO nanostructures. For c.{sub Co} ≤ 0.2 mM, the photoluminescence spectra exhibited a decrease in the intensity of ultraviolet emission as well as band-gap narrowing with an increase in dopant concentration. All the doped samples displayed a broad emission in the visible range and its intensity increased with an increase in Co concentration. It was found that the defect centers such as oxygen vacancies and zinc interstitials were the source of the visible emission. The X-ray photoelectron spectroscopy studies revealed, Co was primarily in the divalent state, replacing the Zn ion inside the tetrahedral crystal site of ZnO without forming any cluster or secondary phases of Co. The un-doped ZnO nanorods exhibited diamagnetic behavior and it remained up to a c.{sub Co} of 0.05 mM, while for c.{sub Co }> 0.05 mM, the ZnO nanostructures exhibited ferromagnetic behavior at room temperature. The coercivity increased to 695 G for 0.2 mM Co-doped sample and then it decreased for c.{sub Co }> 0.2 mM. Our results illustrate that up to a threshold concentration of 0.2 mM, the strong ferromagnetism is due to the oxygen vacancy defects centers, which exist in the Co-doped ZnO nanostructures. The origin of strong ferromagnetism at room temperature in Co-doped ZnO nanostructures is attributed to the s-d exchange interaction between the localized spin moments resulting from the oxygen vacancies and d electrons of Co{sup 2+} ions. Our findings provide a new insight for tuning the

  16. Synergistic effect of Indium and Gallium co-doping on growth behavior and physical properties of hydrothermally grown ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Lim, Jun Hyung; Lee, Seung Muk; Kim, Hyun-Suk; Kim, Hyun You; Park, Jozeph; Jung, Seung-Boo; Park, Geun Chul; Kim, Jungho; Joo, Jinho

    2017-02-01

    We synthesized ZnO nanorods (NRs) using simple hydrothermal method, with the simultaneous incorporation of gallium (Ga) and indium (In), in addition, investigated the co-doping effect on the morphology, microstructure, electronic structure, and electrical/optical properties. The growth behavior of the doped NRs was affected by the nuclei density and polarity of the (001) plane. The c-axis parameter of the co-doped NRs was similar to that of undoped NRs due to the compensated lattice distortion caused by the presence of dopants that are both larger (In3+) and smaller (Ga3+) than the host Zn2+ cations. Red shifts in the ultraviolet emission peaks were observed in all doped NRs, owing to the combined effects of NR size, band gap renormalization, and the presence of stacking faults created by the dopant-induced lattice distortions. In addition, the NR/p-GaN diodes using co-doped NRs exhibited superior electrical conductivity compared to the other specimens due to the increase in the charge carrier density of NRs and the relatively large effective contact area of (001) planes. The simultaneous doping of In and Ga is therefore anticipated to provide a broader range of optical, physical, and electrical properties of ZnO NRs for a variety of opto-electronic applications.

  17. Synergistic effect of Indium and Gallium co-doping on growth behavior and physical properties of hydrothermally grown ZnO nanorods

    PubMed Central

    Lim, Jun Hyung; Lee, Seung Muk; Kim, Hyun-Suk; Kim, Hyun You; Park, Jozeph; Jung, Seung-Boo; Park, Geun Chul; Kim, Jungho; Joo, Jinho

    2017-01-01

    We synthesized ZnO nanorods (NRs) using simple hydrothermal method, with the simultaneous incorporation of gallium (Ga) and indium (In), in addition, investigated the co-doping effect on the morphology, microstructure, electronic structure, and electrical/optical properties. The growth behavior of the doped NRs was affected by the nuclei density and polarity of the (001) plane. The c-axis parameter of the co-doped NRs was similar to that of undoped NRs due to the compensated lattice distortion caused by the presence of dopants that are both larger (In3+) and smaller (Ga3+) than the host Zn2+ cations. Red shifts in the ultraviolet emission peaks were observed in all doped NRs, owing to the combined effects of NR size, band gap renormalization, and the presence of stacking faults created by the dopant-induced lattice distortions. In addition, the NR/p-GaN diodes using co-doped NRs exhibited superior electrical conductivity compared to the other specimens due to the increase in the charge carrier density of NRs and the relatively large effective contact area of (001) planes. The simultaneous doping of In and Ga is therefore anticipated to provide a broader range of optical, physical, and electrical properties of ZnO NRs for a variety of opto-electronic applications. PMID:28155879

  18. Study on Co-doped ZnO comparatively by first-principles calculations and relevant experiments

    NASA Astrophysics Data System (ADS)

    Su, Y. L.; Zhang, Q. Y.; Zhou, N.; Ma, C. Y.; Liu, X. Z.; Zhao, J. J.

    2017-01-01

    Co-doped ZnO was studied using first-principles methods with comparison to experimental results taken from epitaxial Zn1-xCoxO (x 0.05) films. Density of Co2+ ions was determined using absorption spectra for the first time, and then a definite correlation between metallic Co clusters and the magnetism of the ZnCoO films was proved and the average number of Co atoms in the metallic Co clusters was estimated to be less than 200 using a superparamagnetic model. First-principles calculations of ZnCoO alloys and the relevant problems were discussed by comparing the electronic structures with absorption spectra and the results calculated by Tanabe-Sugano theory. U correction was proved to be necessary for calculating the band-gap energy of ZnCoO alloys, but other optical properties related to Co2+ ions are incorrect and the conclusion for magnetic properties is ambiguous due to uncertainty of the calculated highly localized states, which are in pressing for solution in study of material properties relevant to electronic structure.

  19. Enhanced room temperature ferromagnetism and photoluminescence behavior of Cu-doped ZnO co-doped with Mn

    NASA Astrophysics Data System (ADS)

    Ashokkumar, M.; Muthukumaran, S.

    2015-05-01

    Cu, Mn co-doped ZnO nanoparticles were successfully synthesized by the sol-gel technique. XRD pattern described that Mn-doping did not affect the hexagonal wurtzite structure of the samples and no secondary phases were found. The reduced crystallite size at Mn=2% is due to the suppression of grain surface growth by foreign impurity. The enhancement of crystal size after Mn=2% is due to the expansion of lattice volume produced by the distortion around the dopant ion. The better dielectric constant and conductivity noticed at Mn=2% are explained by charge carrier density and crystallite size. The suppression of broad UV band by Mn-doping is discussed based on the generation of non-radiative recombination centers. Hysteresis loop showed the clear room temperature ferromagnetism in all the samples and the magnetization increased with Mn-doping. Better electrical and magnetic behavior of Zn0.94Cu0.04Mn0.02O sample is suggested for effective opto-magnetic devices.

  20. SiO2 substrate and Mo,In codoping effect on crystalline and vibrational characteristics of ZnO sprayed thin films

    NASA Astrophysics Data System (ADS)

    Souissi, A.; Mimouni, R.; Amlouk, M.; Guermazi, S.

    2015-09-01

    Undoped ZnO and codoped ZnO:Mo:In thin films were deposited on an amorphous SiO2 substrate at 460 °C using a (Mo/Zn) molar ratio of 1% and (In/Zn) ratios of 1%, 2%, 3% and 10%. The thin films were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Raman spectroscopy (RS). The results revealed that the average crystallite sizes ranged from 36.2 to 18.97 nm, decreasing uniformly with the increase of co-doping. They were also lower than the grain size values of 48.29, 51.38, 60.59, 36.76, and 54.52 nm and dependent on the evolution of the residual compressive stress values, namely 0.358, 0.314, 0.569, 0.278 and 0.108 GPa, without and with the co-doping, respectively. The non-uniformities recorded at In 2% could presumably be attributed to the variable effect of the SiO2 substrate and dopants on the formation of ZnO:Mo:In thin films. Raman spectroscopy confirmed the findings from structural analysis, showing that all samples crystallized following the hexagonal Wurtzite single phase. It highlighted the presence of two dominant bands, 1LO and 2LO, whose ∼71 and 137 meV energies were comparable and above the ZnO exciton binding energy of 60 meV. The 2LO band showed marked dependencies on the physicochemical parameters mentioned above. The strong bands noted for optimal co-doping at Mo 1% and In 3% can be used (tested) in various electrical and optoelectronic applications.

  1. Yb/Al-codoped fused-silica planar-waveguide amplifier

    NASA Astrophysics Data System (ADS)

    Atar, Gil; Eger, David; Bruner, Ariel; Sfez, Bruno; Ruschin, Shlomo

    2016-05-01

    We report an Yb/Al-codoped fused silica planar waveguide amplifier with <0.2 dB/cm passive loss and 0.6 dB/cm gain, featuring a high damage threshold (>0.1 GW/cm2) and a relatively large core (20 μm thick). Waveguide fabrication is based on a novel silica-on-silica technology combining modified-chemical-vapor deposition and a high temperature CO2 laser treatment for making high-power photonic devices.

  2. Structural, optical and magnetic properties of Cu and V co-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Huilian; Cheng, Xin; Liu, Hongbo; Yang, Jinghai; Liu, Yang; Liu, Xiaoyan; Gao, Ming; Wei, Maobin; Zhang, Xu; Jiang, Yuhong

    2013-01-01

    Zn0.98-xCuxV0.02O (x=0, 0.01, 0.02 and 0.03) samples were synthesized by the sol-gel technology to dope up to 3% Cu in ZnO. Investigations of structural, optical and magnetic properties of the samples have been done. The results of X-ray diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) indicated that the V and Cu ions were incorporated into the crystal lattices of ZnO. With Cu doping concentration increasing up to 2 at%, the XRD results showed that all diffraction peaks corresponded to the wurtzite structure of ZnO. Photoluminescence (PL) measurements showed that Zn0.98-xCuxV0.02O powders exhibited that the position of the ultraviolet (UV) emission peak of the samples showed an obvious red-shift and the green emission peak enhanced significantly with Cu doping in ZnVO nanoparticle. Magnetic measurements indicated that room temperature ferromagnetism (RTFM) of Zn0.98-xCuxV0.02O was an intrinsic property when Cu concentration was less than 3 at%. The saturation magnetization (Ms) of Zn0.98-xCuxV0.02O (x=0, 0.01 and 0.02) increased with the increase of the Cu concentration.

  3. Characteristic coordination structure around Nd Ions in sol-gel-derived Nd-Al-codoped silica glasses.

    PubMed

    Funabiki, Fuji; Kajihara, Koichi; Kaneko, Ken; Kanamura, Kiyoshi; Hosono, Hideo

    2014-07-24

    Al codoping can improve the poor solubility of rare-earth ions in silica glasses. However, the mechanism is not well understood. The coordination structure around Nd ions in sol-gel-derived Nd-Al-codoped silica glasses with different Al content was investigated by optical and pulsed electron paramagnetic resonance spectroscopies. Both tetrahedral AlO4 and octahedral AlO6 units were observed around Nd ions as ligands. The average total number of these two types of ligands for each Nd(3+) ion was ∼ 2 irrespective of Al content and was larger by 1-2 orders of magnitude than that calculated for a uniform distribution of codopant ions (∼ 0.08-0.25). With increasing Al content, AlO4 units disappeared and AlO6 units became dominant. The preferential coordination of AlOx (x = 4, 6) units to Nd ions enabled the amount of Al necessary to dissolve Nd ions uniformly in silica glass at a relatively low temperature of 1150-1200 °C to be minimized, and the conversion of AlO4 units to AlO6 units around Nd ions caused the asymmetry of the crystal field at the Nd sites to increase and the site-to-site distribution to decrease.

  4. Effect of Al and Fe doping in ZnO on magnetic and magneto-transport properties

    NASA Astrophysics Data System (ADS)

    Kumar, Santosh; Deepika; Tripathi, Malvika; Vaibhav, Pratyush; Kumar, Aman; Kumar, Ritesh; Choudhary, R. J.; Phase, D. M.

    2016-12-01

    The structural, magnetic and magneto-transport of undoped ZnO, Zn0.97Al0.03O, Zn0.95Fe0.05O and Zn0.92Al0.03Fe0.05O thin films grown on Si(100) substrate using pulsed laser deposition were investigated. The single phase nature of the films is confirmed by X-ray diffraction and Raman spectroscopy measurements. The possibility of Fe metal cluster in Fe doped/co-doped films is ruled out by Fe 2p core level photoelectron spectra. From O 1s core level spectra it is observed that oxygen vacancy is present in all the films. The undoped ZnO film shows magnetic ordering below ∼175 K, whereas Fe doped/codoped samples show magnetic ordering even at 300 K. The Al doped sample reveals paramagnetic behavior. The magneto-transport measurements suggest that the mobile carriers undergo exchange interaction with local magnetic moments.

  5. Structure and Properties of Al and Ga- Doped ZnO

    NASA Astrophysics Data System (ADS)

    Temizer, Namik Kemal

    Recently there is tremendous interest in Transparent conducting oxide (TCO) research due to the unlimited and exciting application areas. Current research is mostly focused on finding alternative low cost and sustainable materials in order to replace indium tin oxide (ITO), which caused serious concern due to the increasing cost of indium and chemical stability issues of ITO. The primary aim of this research is to develop alternative TCO materials with superior properties in order to increase the efficiency in optoelectronic applications, as well as to study the properties of these materials to fully characterize them. We have grown Al and Ga-doped ZnO films with an optimized composition under different deposition conditions in order to understand the effect of processing parameters on the film properties. We report a detailed investigation on the structure-property correlations in Ga and Al codoped ZnO films on c-sapphire substrates where the thin film microstructure varies from nanocrystalline to single crystal. We have achieved highly epitaxial films with very high optical transmittance (close to 90%) and low resistivity (˜110muO-cm) values. The films grown in an ambient oxygen partial pressure (PO2 ) of 50 mTorr and at growth temperatures from room temperature to 600°C showed semiconducting behavior, whereas samples grown at a Po2 of 1 mTorr showed metallic nature. The most striking feature is the occurrence of resistivity minima at relatively high temperatures around 110 K in films deposited at high temperatures. The structure-property correlations reveal that point defects play an important role in modifying the structural, optical, electrical and magnetic properties and such changes in physical properties are controlled predominantly by the defect content. To gain a better understanding of the conduction processes in doped ZnO thin films, we have studied the temperature variation of resistivity of some selected samples that showed some interesting behavior

  6. Co-doping effects on luminescence and scintillation properties of Ce doped (Lu,Gd)3(Ga,Al)5O12 scintillator

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Hiroaki; Kamada, Kei; Kurosawa, Shunsuke; Pejchal, Jan; Shoji, Yasuhiro; Yokota, Yuui; Ohashi, Yuji; Yoshikawa, Akira

    2016-11-01

    Mg co-doping effects on scintillation properties of Ce:Lu1Gd2(Ga,Al)5O12 (LGGAG) were investigated. Mg 200 ppm co-doped Ce:LGGAG single crystals were prepared by micro pulling down method. Absorption and luminescence spectra were measured together with several other scintillation characteristics, namely the scintillation decay and light yield to reveal the effect of Mg co-doping. Ce4+ charge transfer absorption was observed below 300 nm in Mg,Ce:LGGAG which is in good agreement with previous reports. The scintillation decay times were accelerated by Mg co-doping.

  7. Structural, linear and nonlinear optical properties of co-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Shaaban, E. R.; El-Hagary, M.; Moustafa, El Sayed; Hassan, H. Shokry; Ismail, Yasser A. M.; Emam-Ismail, M.; Ali, A. S.

    2016-01-01

    Different compositions of Co-doped zinc oxide [(Zn(1- x)Co x O) ( x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10)] thin films were evaporated onto highly clean glass substrates by thermal evaporation technique using a modified source. The structural properties investigated by X-ray diffraction revealed hexagonal wurtzite ZnO-type structure. The crystallite size of the films was found to decrease with increasing Co content. The optical characterization of the films has been carried out using spectral transmittance and reflectance obtained in the wavelength range from 300 to 2500 nm. The refractive index has been found to increase with increasing Co content. It was further found that optical energy gap decreases from 3.28 to 3.03 eV with increasing Co content from x = 0 to x = 0.10, respectively. The dispersion of refractive index has been analyzed in terms of Wemple-DiDomenico (WDD) single-oscillator model. The oscillator parameters, the single-oscillator energy ( E o), the dispersion energy ( E d), and the static refractive index ( n 0), were determined. The nonlinear refractive index of the Zn(1- x)Co x O thin films was calculated and revealed well correlation with the linear refractive index and WDD parameters which in turn depend on the density and molar volume of the system.

  8. Semiconducting properties of Al doped ZnO thin films.

    PubMed

    Al-Ghamdi, Ahmed A; Al-Hartomy, Omar A; El Okr, M; Nawar, A M; El-Gazzar, S; El-Tantawy, Farid; Yakuphanoglu, F

    2014-10-15

    Aluminum doped ZnO (AZO) thin films were successfully deposited via spin coating technique onto glass substrates. Structural properties of the films were analyzed by X-ray diffraction, atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy. X-ray diffraction results reveal that all the films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction (002) plane. The crystallite size of ZnO and AZO films was determined from Scherrer's formula and Williamson-Hall analysis. The lattice parameters of the AZO films were found to decrease with increasing Al content. Energy dispersive spectroscopy (EDX) results indicate that Zn, Al and O elements are present in the AZO thin films. The electrical conductivity, mobility carriers and carrier concentration of the films are increased with increasing Al doping concentration. The optical band gap (Eg) of the films is increased with increasing Al concentration. The AZO thin films indicate a high transparency in the visible region with an average value of 86%. These transparent AZO films may be open a new avenue for optoelectronic and photonic devices applications in near future.

  9. Fabrication and laser performance of Yb3+/Al3+ co-doped photonic crystal fiber synthesized by plasma nonchemical vapor deposition method

    NASA Astrophysics Data System (ADS)

    Xia, Changming; Zhou, Guiyao; Liu, Jiantao; Wang, Chao; Han, Ying; Zhang, Wei; Yuan, Jinhui

    2015-10-01

    In this paper, the bulk Yb3+/Al3+ co-doped silica glass with 1.3 Yb2O3-2.5Al2O3-96.2SiO2 (wt%) are synthesized by plasma nonchemical vapor deposition method combining solution doping technology, where the inductively coupled plasma is used as the heat source. The influence of different O2/N2 ratios on the fluorescence properties of Yb3+/Al3+ co-doped silica glass are investigated. The large mode area photonic crystal fiber (PCF) is fabricated by using the bulk Yb3+/Al3+ co-doped silica glass as fiber core. The laser performance of Yb3+/Al3+ co-doped photonic crystal fiber is studied.

  10. Synthesis and characterization of Mn and Co codoped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Abdullahi, Sabiu Said; Köseoğlu, Yuksel; Güner, Sadik; Kazan, Sinan; Kocaman, Bayram; Ndikilar, Chifu E.

    2015-07-01

    MnxCo0.1Zn0.9-xO nanoparticles with different doping concentration (x = 0.0, 0.05, 0.1, 0.15, and 0.2) has been successfully synthesized by microwave assisted combustion synthesis method using urea as a fuel. The structural, morphological, compositional, magnetic and optical properties of these nanoparticles were investigated by X-ray diffraction (XRD), Scanning electron microscopes (FE-SEM JEOL-7001), Energy-dispersive X-ray spectroscopy (EDX), Quantum Design Physical Property Measurement System (PPMS) and UV-visible spectroscopy, respectively. The structural properties showed the formation of single phase Wurtzite structure of ZnO, with the strong diffraction peaks appear in (1 0 0), (0 0 2) and (1 0 1) respectively. The average size of the nanoparticles decreases from 32.65 to 23.69 nm as dopant concentration is increase. Scanning electron microscope (SEM) pictures showed that smaller crystallites have sizes smaller than 100 nm, no phase separation and agglomeration was observed. Moreover, Energy-dispersive X-ray spectroscopy (EDX) confirmed the synthesis results. The magnetic characterization of the samples reveals that the samples showed paramagnetic and ferromagnetic behavior, meanwhile there is no linear variation of magnetic moment with concentration of Mn ion whereby at x = 0.15 the samples show room temperature ferromagnetic behavior with coercive field and remanent magnetization of 47.70 Oe and 1.8 × 10-1 emu/g, respectively. UV-vis spectroscopy results show that the optical band gap of the nanoparticles varies between 3.24 eV and 3.02 eV.

  11. Effects of hydrogen annealing and codoping (Mn, Fe, Ni, Ga, Y) of nanocrystalline Cu-doped ZnO dilute magnetic semiconductor

    NASA Astrophysics Data System (ADS)

    Bououdina, Mohamed; Aziz Dakhel, Aqeel

    2015-01-01

    Zinc oxide (ZnO) codoped with Cu and M ions (M = Mn, Fe, Ni, Ga, Y) powders were synthesised by simultaneous thermal co-decomposition of a mixture of zinc and metal complexes. The synthesised chemical formula for the prepared solid solution is Zn0.97Cu0.01M0.02O. X-ray diffraction (XRD) analysis confirms the formation of single nanocrystalline structure of the as-prepared powders, thus, both Cu and M ions were incorporated into ZnO lattice forming solid solutions. Magnetic measurements reveal that all the as-synthesised doped ZnO powders gained partial (RT-FM) properties but with different strength and BH-behaviour depends on the nature of the doping (M). Furthermore, H2 post-treatment was subsequently carried out and it was found that the observed RT-FM is enhanced. Very interestingly, in case of Ni dopant, the whole powder becomes completely ferromagnetic with coercivity (Hc), remanence (Mr) and saturation magnetisation (Ms) of 133.6 Oe, 1.086 memu/g and 4.959 memu/g, respectively. The value of Ms was increased by ~ 95% in comparison with as-prepared.

  12. Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

    SciTech Connect

    Kovacs, Andras; Ney, A.; Duchamp, Martial; Ney, V.; Boothroyd, Chris; Galindo, Pedro L.; Kaspar, Tiffany C.; Chambers, Scott A.; Dunin-Borkowski, Rafal

    2013-12-23

    We have studied planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al2O3) and the Co:ZnO/Al2O3 interface structure at atomic resolution using aberration-corrected transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). Comparing Co:ZnO samples deposited by pulsed laser deposition and reactive magnetron sputtering, both exhibit extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3-4 Co:ZnO layers at the interface.. In addition, we have measured the local strain which reveals the lattice distortion around the stacking faults.

  13. Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

    SciTech Connect

    Kovács, A.; Duchamp, M.; Boothroyd, C. B.; Dunin-Borkowski, R. E.; Ney, A.; Ney, V.; Galindo, P. L.; Kaspar, T. C.; Chambers, S. A.

    2013-12-28

    We study planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al{sub 2}O{sub 3}), as well as the Co:ZnO/Al{sub 2}O{sub 3} interface, using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy. Co:ZnO samples that were deposited using pulsed laser deposition and reactive magnetron sputtering are both found to contain extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3–4 Co:ZnO layers next to the Al{sub 2}O{sub 3} substrate. The stacking fault density is in the range of 10{sup 17} cm{sup −3}. We also measure the local lattice distortions around the stacking faults. It is shown that despite the relatively high density of planar defects, lattice distortions, and small compositional variation, the Co:ZnO films retain paramagnetic properties.

  14. A Density Functional Theory Study of Codoping Characteristics of Sulfur with Alkaline Earth in Delafossite CuAlO2

    NASA Astrophysics Data System (ADS)

    Liu, Qi-Jun; Qin, Han; Liu, Zheng-Tang

    2016-04-01

    The structural, electronic properties and formation energies of sulfur and alkaline earth codoped delafossite CuAlO2 have been investigated using the first-principles density functional theory calculations. Our results reveal that the volume of codoping systems increases with the increasing atomic radius of metal atoms. The formation energies under different growth conditions have been calculated, showing that the codoping systems are formed easily under O-rich growth conditions. Electronic band structures and density of states have been obtained. The decreased bandgaps, enhanced covalence and appearance of electron acceptors after codoping are all good for p-type conductivity. Supported by the National Natural Science Foundation of China under Grant Nos. 11347199, 51402244, and 11547311, the Specialized Research Fund for Doctoral Program of Higher Education of China under Grant No. 20130184120028, the Fundamental Research Fund for the Central Universities, China under Grant Nos. 2682014CX084, 2682014ZT30, and 2682014ZT31, and the fund of the State Key Laboratory of Solidification Processing in NWPU under Grant No. SKLSP201511

  15. Reversible p-type conductivity in H passivated nitrogen and phosphorous codoped ZnO thin films using rapid thermal annealing

    NASA Astrophysics Data System (ADS)

    Mannam, Ramanjaneyulu; Kumar, E. Senthil; DasGupta, Nandita; Ramachandra Rao, M. S.

    2017-04-01

    We demonstrate reversible p-type nature of pulsed laser deposited (P, N) codoped ZnO thin films using rapid thermal annealing process. As grown thin films exhibited change in conductivity from p to n-type over a span of 120 days. Non-annealed n-type thin films contain unintentional donor impurities such as hydrogen and carbon. X-ray photoelectron spectroscopy and Raman measurements conclusively show that hydrogen passivates nitrogen acceptors by forming Nsbnd H complex. Carbon can be annealed out at 600 °C, whereas, the dissociation of Nsbnd H complex takes place at 800 °C. The films revert its p-type nature at an annealing temperature of 800 °C.

  16. Co-doped ZnO epitaxial films: from a Brillouin-like paramagnet to a phase-separated superparamagnetic ensemble.

    PubMed

    Ney, V; Ye, S; Ollefs, K; Kammermeier, T; Wilhelm, F; Rogalev, A; Ney, A

    2010-09-01

    Co-doped ZnO films are epitaxially grown on sapphire by reactive magnetron sputtering. The preparation conditions such as temperature and the composition of the sputtering gas are systematically varied. For optimized growth conditions virtually all Co dopant atoms are located on substitutional Zn lattice sites as revealed by X-ray linear dichroism (XLD). The material behaves as a Brillouin-like paramagnet with S = 3/2 and L = 1 as revealed by integral and element specific magnetometry. Reducing the oxygen content during preparation leads to the onset of phase separation as revealed by X-ray diffraction, and more clearly by a strong reduction of the XLD signal. Such samples behave like a blocked superparamagnetic ensemble. In the entire range of preparation conditions no signs of intrinsic ferromagnetism are found.

  17. Interplay of dopant, defects and electronic structure in driving ferromagnetism in Co-doped oxides: TiO2, CeO2 and ZnO

    NASA Astrophysics Data System (ADS)

    Ali, Bakhtyar; Shah, Lubna R.; Ni, C.; Xiao, J. Q.; Shah, S. Ismat

    2009-11-01

    A comprehensive study of the defects and impurity (Co)-driven ferromagnetism is undertaken in the oxide semiconductors: TiO2, ZnO and CeO2. The effect of magnetic (Co2+) and non-magnetic (Cu2+) impurities in conjunction with defects, such as oxygen vacancies (Vo), have been thoroughly investigated. Analyses of the x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) data reveal the incorporation of cobalt in the lattice, with no signature of cobalt segregation. It is shown that oxygen vacancies are necessary for the ferromagnetic coupling in the Co-doped oxides mentioned above. The possible exchange mechanisms responsible for the ferromagnetism are discussed in light of the energy levels of dopants in the host oxides. In addition, Co and Cu co-doped TiO2 samples are studied in order to understand the role of point defects in establishing room temperature ferromagnetism. The parameters calculated from the bound magnetic polaron (BMP) and Jorgensen's optical electronegativity models offer a satisfactory explanation of the defect-driven ferromagnetism in the doped/co-doped samples.

  18. Effects of F- on the optical and spectroscopic properties of Yb3+/Al3+-co-doped silica glass

    NASA Astrophysics Data System (ADS)

    Xu, Wenbin; Yu, Chunlei; Wang, Shikai; Lou, Fengguang; Feng, Suya; Wang, Meng; Zhou, Qinling; Chen, Danping; Hu, Lili; Guzik, Malgorzata; Boulon, Georges

    2015-04-01

    Yb3+/Al3+-co-doped silica glasses with different F- content were prepared in this work by sol-gel method combined with high temperature sintering. XRF, FTIR and XPS methods were used to confirm the presence of F-. The effects of F- on the optical and spectroscopic properties of these glasses have been investigated. It is worth to notice that the F-/Si4+ mass ratio equal to 9% is a significant value showing a real change in the variation trends of numerous following parameters: refractive index, UV absorption edge, absorption and emission cross sections, scalar crystal-field NJ and fluorescent lifetimes. Furthermore, introduction of F- can adjust the refractive index of Yb3+/Al3+-co-doped silica glass and it is useful for large mode area (LMA) fibers.

  19. Structural, optical and electronic structure studies of Al doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Devi, Vanita; Kumar, Manish; Shukla, D. K.; Choudhary, R. J.; Phase, D. M.; Kumar, Ravindra; Joshi, B. C.

    2015-07-01

    Structural, optical and electronic structure of Al doped ZnO thin films grown using pulsed laser deposition on glass substrate are investigated. X-ray diffraction measurements reveal that all the films are textured along the c-axis and have wurtzite structure. Al doping in ZnO films leads to increase in grain size due to relaxation in compressive stress. Enhancement in band gap of ZnO films with the Al doping is also noticed which can be ascribed to the Brustein-Moss shift. The changes in the electronic structure caused by Al in the doped thin film samples are understood through X-ray absorption measurements.

  20. Atomic layer deposition of Al-doped ZnO thin films

    SciTech Connect

    Tynell, Tommi; Yamauchi, Hisao; Karppinen, Maarit; Okazaki, Ryuji; Terasaki, Ichiro

    2013-01-15

    Atomic layer deposition has been used to fabricate thin films of aluminum-doped ZnO by depositing interspersed layers of ZnO and Al{sub 2}O{sub 3} on borosilicate glass substrates. The growth characteristics of the films have been investigated through x-ray diffraction, x-ray reflection, and x-ray fluorescence measurements, and the efficacy of the Al doping has been evaluated through optical reflectivity and Seebeck coefficient measurements. The Al doping is found to affect the carrier density of ZnO up to a nominal Al dopant content of 5 at. %. At nominal Al doping levels of 10 at. % and higher, the structure of the films is found to be strongly affected by the Al{sub 2}O{sub 3} phase and no further carrier doping of ZnO is observed.

  1. Role of Ce4+ in the scintillation mechanism of codoped Gd3Ga3Al2O12:Ce

    DOE PAGES

    Wu, Yuntao; Meng, Fang; Li, Qi; ...

    2014-10-17

    To control the time-response performance of widely used cerium-activated scintillators in cutting-edge medical-imaging devices, such as time-of-flight positron-emission tomography, a comprehensive understanding of the role of Ce valence states, especially stable Ce4+, in the scintillation mechanism is essential. However, despite some progress made recently, an understanding of the physical processes involving Ce4+ is still lacking. The aim of this work is to clarify the role of Ce4+ in scintillators by studying Ca2+ codoped Gd3Ga3Al2O12∶Ce (GGAG∶Ce). By using a combination of optical absorption spectra and x-ray absorption near-edge spectroscopies, the correlation between Ca2+codoping content and the Ce4+ fraction is seen. The energy-levelmore » diagrams of Ce3+ and Ce4+ in the Gd3Ga3Al2O12 host are established by using theoretical and experimental methods, which indicate a higher position of the 5d1 state of Ce4+ in the forbidden gap in comparison to that of Ce3+. Underlying reasons for the decay-time acceleration resulting from Ca2+ codoping are revealed, and the physical processes of the Ce4+-emission model are proposed and further demonstrated by temperature-dependent radioluminescence spectra under x-ray excitation.« less

  2. Al-doped ZnO seed layer-dependent crystallographic control of ZnO nanorods by using electrochemical deposition

    SciTech Connect

    Son, Hyo-Soo; Choi, Nak-Jung; Kim, Kyoung-Bo; Kim, Moojin; Lee, Sung-Nam

    2016-10-15

    Highlights: • Polar and semipolar ZnO NRs were successfully achieved by hydrothermal synthesis. • Semipolar and polar ZnO NRs were grown on ZnO and AZO/m-sapphire, respectively. • Al % of AZO/m-sapphire enhanced the lateral growth rate of polar ZnO NRs. - Abstract: We investigated the effect of an Al-doped ZnO film on the crystallographic direction of ZnO nanorods (NRs) using electrochemical deposition. From high-solution X-ray diffraction measurements, the crystallographic plane of ZnO NRs grown on (1 0 0) ZnO/m-plane sapphire was (1 0 1). The surface grain size of the (100) Al-doped ZnO (AZO) film decreased with increasing Al content in the ZnO seed layer, implying that the Al dopant accelerated the three-dimensional (3D) growth of the AZO film. In addition, it was found that with increasing Al doping concentration of the AZO seed layer, the crystal orientation of the ZnO NRs grown on the AZO seed layer changed from [1 0 1] to [0 0 1]. With increasing Al content of the nonpolar (1 0 0) AZO seed layer, the small surface grains with a few crystallographic planes of the AZO film changed from semipolar (1 0 1) ZnO NRs to polar (0 0 1) ZnO NRs due to the increase of the vertical [0 0 1] growth rate of the ZnO NRs owing to excellent electrical properties.

  3. Effects of Mg-codoping on luminescence and scintillation properties of Ce doped Lu3(Ga,Al)5O12 single crystals

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Hiroaki; Kamada, Kei; Pejchal, Jan; Kurosawa, Shunsuke; Shoji, Yasuhiro; Yokota, Yuui; Ohashi, Yuji; Yoshikawa, Akira

    2017-03-01

    Effects of Mg co-doping on scintillation properties of Ce:Lu3(Ga,Al)5O12 (LGAG) were investigated. Mg 200 ppm co-doped Ce:LGAG single crystals were prepared by micro pulling down method. Absorption and radioluminescence spectra were measured together with several other scintillation characteristics, namely the scintillation decay and light yield to reveal the effect of Mg co-doping. Ce4+ charge transfer absorption was observed below 340 nm in Mg,Ce:LGAG which is in good agreement with previous reports for other garnet-based crystals. The scintillation decay time showed the tendency to be accelerated and the light yield was enhanced by Mg co-doping.

  4. Influence Al doped ZnO nanostructure on structural and optical properties

    NASA Astrophysics Data System (ADS)

    Ramelan, Ari Handono; Wahyuningsih, Sayekti; Chasanah, Uswatul; Munawaroh, Hanik

    2016-04-01

    The preparation of Al-doped ZnO (AZO) thin films prepared by the spin-coating method was reported. Preparation of AZO was conducted by annealing treatment at a temperature of 700°C. While the spin-coating process of AZO thin films were done at 2000 and 3000 rpm respectively. The structural properties of ZnO were determined by X- ray diffraction (XRD) analysis. ZnOnanostructure was formed after annealed at atemperature of 400°C.The morphology of ZnO was determined by Scanning Electron Microscopy (SEM) showed the irregular morphology about 30-50µm in size. Al doped on ZnO influenced the optical properties of those material. Increasing Al contain on ZnO cause of shifting to the lower wavelength. The optical properties of the ZnO as well as AZO films showed that higher reflectance on the ultraviolet region so those materials were used as anti-reflecting agent.Al addition significantly enhance the optical transparency and induce the blue-shift in optical bandgap of ZnO films.

  5. Effects of Codoping with Ga and P on Thermoelectric Properties of Ba8Al16Si30 Clathrate System

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Ueda, Takahiro; Okamoto, Kazuya

    2017-01-01

    We have investigated the effects of Codoping With Ga and P on the thermoelectric properties of the Ba8Al16Si30 clathrate system, attempting to optimize the carrier concentration. The elastic properties, which are important for design of thermoelectric devices, were investigated by ultrasonic testing. Ga/P-codoped specimens with nominal compositions Ba8Al16Ga x Si30-2x P x (x = 1.0, 1.5, 2.0) were prepared by arc melting and spark plasma sintering and their Seebeck coefficient, electrical conductivity, and thermal conductivity were measured. Analytical studies revealed that the total content of Al and Ga, expressed as atoms per formula unit, increased to 15.65 at nominal x = 2.0, exceeding the maximum content (y = 15.16) of Al for the Ba8Al y Si46-y clathrate system. Ultrasonic tests determined the Young's modulus, shear modulus, bulk modulus, and Poisson's ratio to be 102.55 GPa, 40.14 GPa, 76.85 GPa, and 0.2775, respectively, for Ba8Al16Ga x Si30-2x P x (x = 2.0). The Hall carrier concentration decreased from ˜1.0 × 1021 cm-3 for Ba8Al y Si46-y to ˜6.3 × 1020 cm-3 for Ba8Al16Ga x Si30-2x P x (x = 2.0), suggesting that Ga/P codoping may be useful for tuning the carrier concentration. The value of the Seebeck coefficient at ˜320 K increased from -46 μV K-1 for Ba8Al y Si46-y to -67 μV K-1 for Ba8Al16Ga x Si30-2x P x (x = 2.0). The dimensionless thermoelectric figure␣of merit ZT at 900 K improved from ˜0.4 for Ba8Al y Si46-y to ˜0.47 for Ba8Al16Ga x Si30-2x P x (x = 2.0).

  6. Effects of Codoping with Ga and P on Thermoelectric Properties of Ba8Al16Si30 Clathrate System

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Ueda, Takahiro; Okamoto, Kazuya

    2017-03-01

    We have investigated the effects of Codoping With Ga and P on the thermoelectric properties of the Ba8Al16Si30 clathrate system, attempting to optimize the carrier concentration. The elastic properties, which are important for design of thermoelectric devices, were investigated by ultrasonic testing. Ga/P-codoped specimens with nominal compositions Ba8Al16Ga x Si30-2 x P x ( x = 1.0, 1.5, 2.0) were prepared by arc melting and spark plasma sintering and their Seebeck coefficient, electrical conductivity, and thermal conductivity were measured. Analytical studies revealed that the total content of Al and Ga, expressed as atoms per formula unit, increased to 15.65 at nominal x = 2.0, exceeding the maximum content ( y = 15.16) of Al for the Ba8Al y Si46- y clathrate system. Ultrasonic tests determined the Young's modulus, shear modulus, bulk modulus, and Poisson's ratio to be 102.55 GPa, 40.14 GPa, 76.85 GPa, and 0.2775, respectively, for Ba8Al16Ga x Si30-2 x P x ( x = 2.0). The Hall carrier concentration decreased from ˜1.0 × 1021 cm-3 for Ba8Al y Si46- y to ˜6.3 × 1020 cm-3 for Ba8Al16Ga x Si30-2 x P x ( x = 2.0), suggesting that Ga/P codoping may be useful for tuning the carrier concentration. The value of the Seebeck coefficient at ˜320 K increased from -46 μV K-1 for Ba8Al y Si46- y to -67 μV K-1 for Ba8Al16Ga x Si30-2 x P x ( x = 2.0). The dimensionless thermoelectric figure of merit ZT at 900 K improved from ˜0.4 for Ba8Al y Si46- y to ˜0.47 for Ba8Al16Ga x Si30-2 x P x ( x = 2.0).

  7. 2 inch size Czochralski growth and scintillation properties of Li+ co-doped Ce:Gd3Ga3Al2O12

    NASA Astrophysics Data System (ADS)

    Kamada, Kei; Shoji, Yasuhiro; Kochurikhin, Vladimir V.; Yoshino, Masao; Okumura, Satoshi; Yamamoto, Seiichi; Yeom, Jung Yeol; Kurosawa, Shunsuke; Yokota, Yuui; Ohashi, Yuji; Nikl, Martin; Yoshino, Masao; Yoshikawa, Akira

    2017-03-01

    The 2 inch size Li 0.15 and 1.35 mol% co-doped Ce:Gd3Al2Ga3O12 single crystals were prepared by the Czochralski (Cz) method. Absorption and luminescence spectra were measured together with several other scintillation characteristics, namely the scintillation decay and light yield to reveal the effect of Li co-doping. Ce4+ CT absorption below 350 nm is clearly enhanced by Li co-doping as same as divalent ions co-doping. By 1.35 at.% Li co-doping, light yield was decrease to 88% of the Ce: GAGG standard and decay time was accelerated to 34.3ns 21.0%, 84.6ns 68.7%, 480ns 10.3%. The timing resolution measurement for a pair of 3 × 3 × 3mm3 size Li,Ce:GAGG scintillator crystals was performed using Si-PMs and the timing resolution of the 1.35 at.% Li co-doped Ce:GAGG was 218ps.

  8. Structural defects and photoluminescence studies of sol-gel prepared ZnO and Al-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Sandeep, K. M.; Bhat, Shreesha; Dharmaprakash, S. M.

    2016-11-01

    ZnO and Al-doped ZnO (AZO) films were synthesized using sol-gel spin-coating method. The powder XRD analysis revealed the stress relaxation mechanism upon Al doping in ZnO film. The reduction in the imaginary part of the dielectric constant and suppression of deep level acceptor type octahedral oxygen interstitial defects account for the reduction in carrier concentration in AZO with respect to ZnO. Electrical conductivity measurements and grain boundary conduction model are used to quantify the carrier concentration. From the Commission Internationale d'Eclairge diagram of ZnO and AZO, color parameters like dominant wavelength, color purity and luminosity are determined and reported for the first time. The prepared ZnO and AZO films show considerable blue emission. These films can be used for white light generation.

  9. Coherent effect of Er 3+-Yb 3+ co-doping on enhanced photoluminescence properties of Al 2O 3 powders by the sol-gel method

    NASA Astrophysics Data System (ADS)

    Wang, X. J.; Lei, M. K.; Yang, T.; Cao, B. S.

    2004-08-01

    The Er 3+-Yb 3+ co-doped Al 2O 3 powders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC 3H 7) 3]-derived Al 2O 3 sols with the addition of erbium nitrate [Er(NO 3) 3 · 5H 2O] and ytterbium nitrate [Yb(NO 3) 3 · 5H 2O]. The phase structure, including only two crystalline types of Al 2O 3 phases, γ and θ, was obtained for the 0-1 mol% Er 3+ and 0-2 mol% Yb 3+ co-doped Al 2O 3 powders at the different sintering temperature of 800-1000 °C. The evidence for indirect pumping of Er 3+ through transfer of energy from Yb 3+ was found in the Al 2O 3 matrix material. For the 0.5 mol% Er 3+ and 0.5 mol% Yb 3+, the 1.0 mol% Er 3+ and 1.0 mol% Yb 3+ co-doped Al 2O 3 powders, the photoluminescence (PL) peak intensity at 1.533 μm in the spectra increased by a factor of about 2, and the corresponding full widths at half maximum (FWHM) was increased to about 59 nm, compared with that of the 0.5 and 1 mol% Er 3+-doped Al 2O 3 powders, respectively. At the same Er 3+-Yb 3+ co-doping concentration, the PL intensity increased with increasing the sintering temperature from 800 to 1000 °C. Coherent effect of Er 3+-Yb 3+ co-doping on enhanced PL properties of Al 2O 3 powders was observed. A proper molar ratio of 1:1 for Yb 3+ and Er 3+ led to the maximum PL intensity at the same sintering temperature.

  10. Thermoelectric properties of Al-doped ZnO: experiment and simulation

    NASA Astrophysics Data System (ADS)

    Jantrasee, S.; Moontragoon, P.; Pinitsoontorn, S.

    2016-09-01

    Advancement in doping other elements, such as Ce, Dy, Ni, Sb, In and Ga in ZnO[1], have stimulated great interest for high-temperature thermoelectric application. In this work, the effects of Al-doping in a ZnO system on the electronic structure and thermoelectric properties are presented, by experiment and calculation. Nanosized powders of Zn1-x Al x O (x = 0,0.01, 0.02, 0.03 and 0.06) were synthesized by hydrothermal method. From XRD results, all samples contain ZnO as the main phase and ZnAl2O4 (spinel phase) peaks were visible when Al additive concentrations were just 6 at%. The shape of the samples changed and the particle size decreased with increasing Al concentration. Seebeck coefficients, on the other hand, did not vary significantly. They were negative and the absolute values increased with temperature. However, the electrical resistivity decreased significantly for higher Al content. The electronic structure calculations were carried out using the open-source software package ABINIT[2], which is based on DFT. The energy band gap, density of states of Al-doped ZnO were investigated using PAW pseudopotential method within the LDA + U. The calculated density of states was then used in combination with the Boltzmann transport equation[3] to calculate the thermoelectric parameters of Al-doped ZnO. The electronic band structures showed that the position of the Fermi level of the doped sample was shifted upwards in comparison to the undoped one. After doping Al in ZnO, the energy band gap was decreased, Seebeck coefficient and electrical conductivity were increased. Finally, the calculated results were compared with the experimental results. The good agreement of thermoelectric properties between the calculation and the experimental results were obtained.

  11. Defect assisted saturable absorption characteristics in Al and Li doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    K. M., Sandeep; Bhat, Shreesha; S. M., Dharmaprakash; P. S., Patil; Byrappa, K.

    2016-09-01

    The influence of different doping ratios of Al and Li on the nonlinear optical properties, namely, a two-photon absorption and a nonlinear refraction using single beam Z-scan technique, of nano-crystalline ZnO thin films has been investigated in the present study. A sol-gel spin-coated pure ZnO, Al-doped ZnO (AZO), and Li-doped ZnO (LZO) thin films have been prepared. The stoichiometric deviations induced by the occupancy of Al3+ and Li+ ions at the interstitial sites injects the compressive stress in the AZO and LZO thin films, respectively, while the extended defect states below the conduction band leads to a redshift of energy band gap in the corresponding films as compared to pure ZnO thin film. Switching from an induced absorption in ZnO and 1 at. wt. % doped AZO and LZO films to a saturable absorption (SA) in 2 at. wt. % doped AZO and LZO films has been observed, and it is attributed to the saturation of a linear absorption of the defect states. The closed aperture Z-scan technique revealed the self-focusing (a positive nonlinear refractive index) in all the films, which emerge out of the thermo-optical effects due to the continuous illumination of laser pulses. A higher third-order nonlinear optical susceptibility χ(3) of the order 10-3 esu has been observed in all the films.

  12. Synthesis and conductivity enhancement of Al-doped ZnO nanorod array thin films.

    PubMed

    Hsu, Chih-Hsiung; Chen, Dong-Hwang

    2010-07-16

    Al-doped ZnO (AZO) nanorod array thin films with various Al/Zn molar ratios were synthesized by chemical bath deposition. The resultant AZO nanorods were well-aligned at the glass substrate, growing vertically along the c-axis [001] direction. In addition, they had an average diameter of 64.7 +/- 16.8 nm and an average length of about 1.0 microm with the structure of wurtzite-type ZnO. Analyses of energy dispersive x-ray spectra and x-ray photoelectron spectra indicated that Al atoms had been doped into the ZnO crystal lattice. The doping of Al atoms did not result in significant changes in the structure and crystal orientation, but the electrical resistivity was found to increase first and then decrease with increasing Al content owing to the increase of carrier concentration and the decrease of mobility. In addition, the transmission in the visible region increased but the increase was reduced at higher Al doping levels. After hydrogen treatment, the morphology of the AZO nanorod array thin films remained unchanged. However, the electrical resistivity decreased significantly due to the formation of oxygen vacancies and interstitial hydrogen atoms. When the real Al/Zn molar ratio was about 3.7%, the conductivity was enhanced about 1000 times and a minimum electrical resistivity of 6.4 x 10( - 4) Omega cm was obtained. In addition, the transmission of the ZnO nanorod array thin film in the visible region was significantly increased but the increase was less significant for the AZO nanorod array thin film, particularly at higher Al doping levels. In addition, the current-voltage curves of the thin film devices with ZnO or AZO nanorod arrays revealed that AZO had a higher current response than ZnO and hydrogen treatment led to a more significant enhancement of current responses (about 100-fold).

  13. Using the hydrothermal method to grow p-type ZnO nanowires on Al-doped ZnO thin film to fabricate a homojunction diode.

    PubMed

    Tseng, Yung-Kuan; Hung, Meng-Chun; Su, Shun-Lung; Li, Sheng-Kai

    2014-10-01

    In this study, the hydrothermal method is used to grow phosphorus-doped ZnO nanowires on Si/SiO2 substrates deposited with Al-doped ZnO thin film. This structure forms a homogeneous p-n junction. In this study, we are the pioneers to use ammonium hypophosphite (NH4H2PO2) as a source of phosphorus to prepare the precursor solution. Ammonium hypophosphite of different concentration levels is used to observe its effects on the growth of nanowires. The results show that the precursor solution prepared from ammonium hypophosphite can produce good crystalline ZnO nanowires while there is no linear relationship between the amounts and concentration levels of phosphorus doped into the nanowires. Whether the phosphorus-doped ZnO nanowires have the characteristics of a p-type semiconductor is indirectly verified by measuring whether the p-n junction made up of Al-doped ZnO thin film and phosphorus-doped ZnO nanowires shows rectifying behavior. I-V measurements are made on the specimens. The results show good rectifying behavior, proving that the phosphorus-doped ZnO nanowires and Al-doped AZO films have p-type and n-type semiconductor properties, constituting a good p-n junction. This result also proves that ammonium hypophosphite is a better source of phosphorus in the hydrothermal method to synthesize phosphorus-doped ZnO nanowires.

  14. Investigation of Co-Doped ZnO Nanowires by X-ray Absorption Spectroscopy and Ab Initio Simulation

    NASA Astrophysics Data System (ADS)

    Chu, Manh Hung; Nguyen, Van Duy; Nguyen, Duc Hoa; Nguyen, Van Hieu

    2017-01-01

    The local structure of single room- and high-temperature Co-implanted ZnO nanowires with subsequent thermal annealing has been studied using hard-x-ray techniques in combination with ab initio Zn K-edge x-ray absorption near-edge structure (XANES) simulations. X-ray fluorescence data reveal a homogeneous distribution of Co atoms/ions with concentration of about 0.1 at.% to 0.3 at.% in the nanowires. XANES data indicate substitutional incorporation of Co2+ ions at Zn sites in both types of nanowire. Improved structural order around Co atoms is obtained in nanowires with high-temperature ion implantation followed by thermal annealing. The ab initio Zn K-edge simulations not only confirm recovery of implantation-induced damage in the ZnO host lattice by the thermal annealing process, but also assist in studying the effect of oxygen vacancies in the Zn K-edge XANES spectra. Microphotoluminescence data certify that high-temperature ion implantation with subsequent thermal annealing is an effective approach to achieve the strongest optical activation of Co ions and good energy transfer to Co ions from the ZnO host matrix.

  15. Photoluminescence enhancement of ZnO via coupling with surface plasmons on Al thin films

    NASA Astrophysics Data System (ADS)

    Dellis, S.; Kalfagiannis, N.; Kassavetis, S.; Bazioti, C.; Dimitrakopulos, G. P.; Koutsogeorgis, D. C.; Patsalas, P.

    2017-03-01

    We present that the ultra-violet emission of ZnO can be enhanced, as much as six-times its integral intensity, using an Al thin interlayer film between the Si substrate and ZnO thin film and a post-fabrication laser annealing process. The laser annealing is a cold process that preserves the chemical state and integrity of the underlying aluminum layer, while it is essential for the improvement of the ZnO performance as a light emitter and leads to enhanced emission in the visible and in the ultraviolet spectral ranges. In all cases, the metal interlayer enhances the intensity of the emitted light, either through coupling of the surface plasmon that is excited at the Al/ZnO interface, in the case of light-emitting ZnO in the ultraviolet region, or by the increased back reflection from the Al layer, in the case of the visible emission. In order to evaluate the process and develop a solid understanding of the relevant physical phenomena, we investigated the effects of various metals as interlayers (Al, Ag, and Au), the metal interlayer thickness, and the incorporation of a dielectric spacer layer between Al and ZnO. Based on these experiments, Al emerged as the undisputable best choice of metal interlayers because of its compatibility with the laser annealing process, as well as due to its high optical reflectivity at 380 and 248 nm, which leads to the effective coupling with surface plasmons at the Al/ZnO interfaces at 380 nm and the secondary annealing of ZnO by the back-reflected 248 nm laser beam.

  16. Fabrication of highly transparent Al-ion-implanted ZnO thin films by metal vapor vacuum arc method

    NASA Astrophysics Data System (ADS)

    Lee, Han; Sivashanmugan, Kundan; Kao, Chi-Yuan; Liao, Jiunn-Der

    2017-03-01

    In this study, we utilized the metal vapor vacuum arc technique to implant vaporized aluminum (Al) ions in zinc oxide (ZnO) thin films. By adjusting the ion implantation dose and operational parameters, the conductivity and optical properties of the ZnO thin film can be controlled. The electrical sheet resistance of Al-ion-implanted ZnO decreased from 3.02 × 107 to 3.03 × 104 Ω/sq, while the transparency of the film was mostly preserved (91.5% at a wavelength of 550 nm). The ZnO thin-film Young’s modulus significantly increased with increasing Al ion dose.

  17. Electron transport in Al-doped ZnO nanolayers obtained by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Blagoev, B. S.; Dimitrov, D. Z.; Mehandzhiev, V. B.; Kovacheva, D.; Terziyska, P.; Pavlic, J.; Lovchinov, K.; Mateev, E.; Leclercq, J.; Sveshtarov, P.

    2016-03-01

    Al-doped ZnO thin films with different Al content were prepared by atomic layer deposition (ALD). To carry out thermal ALD, diethyl zinc (DEZ) and tri-methyl aluminium (TMA) were used as Zn and Al precursors, respectively, and water vapor as oxidant. Various numbers n of DEZ and m TMA cycles was used to obtain different [ZnO] n [Al2O3] m films, where n = 100 - 95, m = 1 - 5. The X-ray diffraction analysis showed a predominantly (100) oriented polycrystalline phase for the ZnO:Al films with a low Al content (m = 1 - 3) and an amorphous structure for pure Al2O3. In ZnO:Al with a higher Al content (m = 4 - 6) the (100) reflection disappeared and the (002) peak increased. The resistivity of the films decreased with the increase in the Al content, reaching a minimum of 3.3×10-3 Ω cm at about 1.1 % Al2O3 for the [ZnO]99[Al2O3]2 sample; for higher dopant concentrations, the resistivity increased because of the increased crystal inhomogeneity due to axis reorientation.

  18. Photoluminescence lifetime of Al-doped ZnO films in visible region

    NASA Astrophysics Data System (ADS)

    Sharma, Bhupendra K.; Khare, Neeraj; Haranath, D.

    2010-12-01

    ZnO and Al-doped ZnO films have been deposited on quartz substrates by ultrasonically assisted chemical vapor deposition technique. Photoluminescence (PL) spectra of the films reveal that Al doping leads to suppression of defect related visible band. Time resolved photoluminescence studies have been carried out for the measurement of lifetime of deep level luminescence. The decay of PL intensity with time has been found to follow biexponential behavior. The relative contributions of fast decay component (τ1) and slow decay component (τ2) in total decay process are found to be ˜99% and ˜1% respectively. The values of τ1 and τ2 are found to decrease with Al doping in ZnO film. The decrease of both τ1 and τ2 is attributed to increase in non-radiative recombination due to reduction in grain sizes and the decrease in radiative recombination due to suppression of defects.

  19. Gas sensing properties of Al-doped ZnO for UV-activated CO detection

    NASA Astrophysics Data System (ADS)

    Dhahri, R.; Hjiri, M.; El Mir, L.; Bonavita, A.; Iannazzo, D.; Latino, M.; Donato, N.; Leonardi, S. G.; Neri, G.

    2016-04-01

    Al-doped ZnO (AZO) samples were prepared using a modified sol-gel route and charaterized by means of trasmission electron microscopy, x-ray diffraction and photoluminescence analysis. Resistive planar devices based on thick films of AZO deposited on interdigitated alumina substrates were fabricated and investigated as UV light activated CO sensors. CO sensing tests were performed in both dark and illumination condition by exposing the samples to UV radiation (λ  =  400 nm).Under UV light, Al-doped ZnO gas sensors operated at lower temperature than in dark. Furthermore, by photoactivation we also promoted CO sensitivity and made signal recovery of AZO sensors faster. Results demonstrate that Al-doped ZnO might be a promising sensing material for the detection of CO under UV illumination.

  20. Tailoring Energy Bandgap of Al Doped ZnO Thin Films Grown by Vacuum Thermal Evaporation Method.

    PubMed

    Vyas, Sumit; Singh, Shaivalini; Chakrabarti, P

    2015-12-01

    The paper presents the results of our experimental investigation pertaining to tailoring of energy bandgap and other associated characteristics of undoped and Al doped ZnO (AZO) thin film by varying the atomic concentration of Al in ZnO. Thin films of ZnO and ZnO doped with Al (1, 3, and 5 atomic percent (at.%)) were deposited on silicon substrate for structural characterization and on glass substrate for optical characterization. The dependence of structural and optical properties of Al doped ZnO on the atomic concentration of Al added to ZnO has been reported. On the basis of the experimental results an empirical formula has been proposed to calculate the energy bandgap of AZO theoretically in the range of 1 to 5 at.% of Al. The study revealed that AZO films are composed of smaller and larger number of grains as compared to pure ZnO counterpart and density of the grains was found to increase as the Al concentration increased (from 1 to 5 at.%). The transmittance in the visible region was greater than 90% and found to increase with increasing Al concentration up to 5 at.%. The optical bandgap was found to increase initially with increase in atomic concentration of Al concentration up to 3 at.% and decrease thereafter with increasing concentration of Al.

  1. Antiferromagnetic half metallicity in codoped chalcopyrite semiconductors Cu(Al 1 - 2 xAxBx)Se2 (A and B are 3d transition-metal atoms)

    NASA Astrophysics Data System (ADS)

    Shahjahan, M.; Oguchi, T.

    2016-06-01

    Electronic structures and magnetic properties of group I-III-VI2 chalcopyrite-type compounds Cu(Al 1 - 2 xAxBx)Se2 are calculated using the Korringa-Kohn-Rostoker Green's function method, where A (Ti, V, Cr, Mn) and B (Fe, Co, Ni) are 3d transition metal atoms, and x is atomic concentration. We found that codoping of Cr-Co and V-Ni pairs at Al site of host CuAlSe2 exhibit antiferromagnetic (AF) half metallicity with low Curie temperature (TC). The AF half metallic property is supported by nullified net magnetic moment and compensated density of states in the minority spin direction. On the other hand, codoping of Cr-Ni, Mn-Co, V-Co, and Ti-Co pairs at Al site of host CuAlSe2 manifest ferrimagnetic half metallicity with a small net magnetization and keeping antiparallel local spin moments. In Mn-Co case TC is close to room temperature. Besides, Cr-Fe, V-Fe, and Ti-Ni codoping cases lead to an instable magnetic ordering and therefore obtain a disordered local moment (spin-glass like) state.

  2. Properties of transparent (Gd,Lu)3(Al,Ga)5O12:Ce ceramic with Mg, Ca and Ce co-dopants

    NASA Astrophysics Data System (ADS)

    Wang, Yimin; Baldoni, Gary; Brecher, Charles; Rhodes, William H.; Shirwadkar, Urmila; Glodo, Jarek; Shah, Ishaan; Ji, Chuncheng

    2015-08-01

    Cerium activated mixed lutetium/gadolinium- and aluminum/gallium-based garnets have great potential as host scintillators for medical imaging applications. (Gd,Lu)3(Al,Ga)5O12:Ce and denoted as GLuGAG feature high effective atomic number and good light yield, which make it particularly attractive for Positron Emission Tomography (PET) and other γ-ray detection applications. For PET application, rapid decay and good timing resolution are extremely important. Most Ce-doped mixed garnet materials such as GLuGAG:Ce, have their main decay component at around 80 ns. However, it has been reported that the decays of some single crystal scintillators (e.g., LSO and GGAG) can be effectively accelerated by codoping with selected additives such as Ca, Mg and B. In this study, transparent polycrystalline (Gd,Lu)3(Al,Ga)5O12:Ce ceramics codoped with Ca or Mg or additional Ce, were fabricated by the sinter-HIP approach. It was found the transmission of the ceramics are closely related to the microstructure of the ceramics. As the co-dopant levels increase, 2nd phase occurs in the ceramic and thus transparency of the ceramic decreases. Ca and Mg co-doping in GLuGAG:Ce ceramic effectively accelerate decays of GLuGAG:Ce ceramics at a cost of light output. However, additional Ce doping in the GLuGAG:Ce has no benefit on improving decay time but, on the other hand, reduces transmission, light output. The mechanism under the different scintillation behaviors with Mg, Ca and Ce dopants are discussed. The results suggest that decay time of GLuGAG:Ce ceramics can be effectively tailored by co-doping GLuGAG:Ce ceramic with Mg and Ca for applications with optimal timing resolution.

  3. Combinatorial approach to MgHf co-doped AlN thin films for Vibrational Energy Harvesters

    NASA Astrophysics Data System (ADS)

    Nguyen, H. H.; Oguchi, H.; Kuwano, H.

    2016-11-01

    In this report, we studied MgHf co-doped AlN ((Mg,Hf)xA11-xN) aiming for developing an AlN-based dielectric material with the large piezoelectric coefficient. To rapidly screen the wide range of composition, we applied combinatorial film growth approach. To get continuous composition gradient on a single substrate, films were deposited on Si (100) substrates by sputtering AlN and Mg-Hf targets simultaneously. Crystal structure was investigated by X-ray diffractometer equipped with a two-dimensional detector (2D-XRD). Composition was determined by Energy Dispersive Spectroscopy (EDS). These studies revealed that we successfully covered the widest ever composition range of 0 < x < 0.24 for this material. In addition, these studies found that we succeeded in realizing largest ever c-axis expansion of 2.7% at x = 0.24, which will lead to the highest enhancement in the piezoelectric coefficient. The results of this study opened the way for high-throughput development of the dielectric materials.

  4. Growth of Polarity-Controlled ZnO Films on (0001) Al2O3

    NASA Astrophysics Data System (ADS)

    Park, J. S.; Chang, J. H.; Minegishi, T.; Lee, H. J.; Park, S. H.; Im, I. H.; Hanada, T.; Hong, S. K.; Cho, M. W.; Yao, T.

    2008-05-01

    The polarity control of ZnO films grown on (0001) Al2O3 substrates by plasma-assisted molecular-beam epitaxy (P-MBE) was achieved by using a novel CrN buffer layer. Zn-polar ZnO films were obtained by using a Zn-terminated CrN buffer layer, while O-polar ZnO films were achieved by using a Cr2O3 layer formed by O-plasma exposure of a CrN layer. The mechanism of polarity control was proposed. Optical and structural quality of ZnO films was characterized by high-resolution X-ray diffraction and photoluminescence (PL) spectroscopy. Low-temperature PL spectra of Zn-polar and O-polar samples show dominant bound exciton (I8) and strong free exciton emissions. Finally, one-dimensional periodic structures consisting of Zn-polar and O-polar ZnO films were simultaneously grown on the same substrate. The periodic inversion of polarity was confirmed in terms of growth rate, surface morphology, and piezo response microscopy (PRM) measurement.

  5. Ferromagnetic behavior due to Al3+ doping into ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Yingsamphancharoen, T.; Nakarungsee, P.; Herng, T. S.; Ding, J.; Tang, I. M.; Thongmee, S.

    2016-12-01

    Al doped ZnO nanorods (NR's) having Al concentration up to 10 mol% were grown by the hydrothermal method. XRD measurements showed that the Al substituted ZnO NR's maintained the hexagonal wurtzite structure for all levels of Al substitution. EDX measurements of the ZnO:Al NR's indicated that the Al substitution created additional Zn vacancies in the wurtzite structure which is reflected in the enhanced photoluminescence emission in the visible light spectra between 450 and 550 nm of the more heavily doped ZnO:Al NR's. SEM images of the heavier doped ZnO:Al nanorods showed nano nodules being formed on the surface of the hexagonal shaped NR's. The saturation magnetizations of the ZnO:Al NR's as measured by a SQUID magnetometer increased to 10.66×10-4 emu/g as more Al was substituted in. The hysteresis loops for the ZnO:Al NR's began to exhibit novel effects, such as horizontal shift (exchange bias field 0.0382 kOe for the 9 mol% NR) and butterfly shapes.

  6. Synthesis and Characterization of Al doped ZnO (AZO) by Sol-gel Method

    NASA Astrophysics Data System (ADS)

    Munawaroh, H.; Wahyuningsih, S.; Ramelan, A. H.

    2017-02-01

    Al doped ZnO (AZO) nanoparticles have been successfully synthesized by the simple sol-gel method. The starting materials of Al doped ZnO were Zn(CH3COO)2·2H2O and Al(OH)(CH3COO)2. Preparation of AZO using polyethylene glycol as a surfactant. The solution of precursors was stirred at 60 °C for 2 hour in the conditions of Al contents are 0%, 2%, 3% and 4% (g/mL), respectivelly. In the last step reaction, gelation occurred from solution to sol gel. The sol gel then were dried at 60 °C following by annealing process for crystalization. By this simple sol gel method, the nanoparticles have been produced. The characterizations were conducted X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourrier Transform Infra-Red (FTIR) and X-Ray Fluorescence (XRF). XRD analysis reveals that all samples has crystallizes in polycrystalline nature and exhibit no other impurity phase. The variation of Al doped ZnO slighly affect the crystallinity and crystal size. Both crystallinity and crystal size decrease with increasing of Al content in AZO. Morphology of AZO shown the particle distribution more equitable with increased Al content. The synthesized AZO gaved shift peak absorption of asymetric and symetric vibrations of Zn-O-Zn around wavelengths of 680 cm-1 and 1630 cm-1 atributed of the uptake of the Al-O-Al bond instead Zn-O-Zn. XRF analysis shown that the increase ratio of Al entering into Zn influenced the Al dopant concentration.

  7. Characterization and Fabrication of ZnO Nanowires Grown on AlN Thin Film

    SciTech Connect

    Yousefi, Ramin; Kamaluddin, Burhanuddin; Ghoranneviss, Mahmood; Hajakbari, Fatemeh

    2009-07-07

    In this paper, we report ZnO nanowires grown on AlN thin film deposited on glass as substrate by physical vapour deposition. The temperature of substrates was kept between 600 deg. C and 500 deg. C during the growth. The typical average diameters of the obtained nanowires on substrate at 600 deg. C and 500 deg. C was about 57 nm and 22 nm, respectively with several micrometers in lengths. X-ray diffraction and Auger spectroscopy results showed Al diffused from AlN thin film into ZnO nanowires for sample at high temperature zone. In the photoluminescence spectra two emission bands appeared, one related to ultraviolet emission with a strong peak at 380-382 nm, and another related to deep level emission with a weak peak at 510 nm.

  8. Structural and optical properties of pure and Al doped ZnO nanocrystals

    NASA Astrophysics Data System (ADS)

    Ghosh, A.; Kumari, N.; Tewari, S.; Bhattacharjee, A.

    2013-11-01

    Pure and Al doped zinc oxide (ZnO) were prepared by co-precipitation method. The dopant concentration [Al/Zn in atomic percentage (wt%)] was varied from 0 to 3 wt%. Structural characterisation of the samples performed with XRD and SEM-EDAX confirmed that polycrystalline nature of samples containing ZnO nanoparticles of size in the range of 97-47 nm. UV-Vis studies showed that the absorbance peaks, observed in the wavelength range of 800-250 nm, decreased with the increase in dopant concentration indicating widening of the band gap. The calculations of band gap (analyzed in terms of Burstein-Moss shift) from the reflectance showed an increase from 3.37 to 3.49 eV with increasing Al concentration.

  9. Effect of Mg2+ ions co-doping on timing performance and radiation tolerance of Cerium doped Gd3Al2Ga3O12 crystals

    NASA Astrophysics Data System (ADS)

    Lucchini, M. T.; Babin, V.; Bohacek, P.; Gundacker, S.; Kamada, K.; Nikl, M.; Petrosyan, A.; Yoshikawa, A.; Auffray, E.

    2016-04-01

    Inorganic scintillators with high density and high light yield are of major interest for applications in medical imaging and high energy physics detectors. In this work, the optical and scintillation properties of Mg co-doped Ce:Gd3Al2Ga3O12 crystals, grown using Czochralski technique, have been investigated and compared with Ce:Gd3Al2Ga3O12 ones prepared with identical technology. Improvements in the timing performance of the Mg co-doped samples with respect to Ce:Gd3Al2Ga3O12 ones have been measured, namely a substantial shortening of the rise time and scintillation decay components and lower afterglow were achieved. In particular, a significantly better coincidence time resolution of 233 ps FWHM, being a fundamental parameter for TOF-PET devices, has been observed in Mg co-doped crystals. The samples have also shown a good radiation tolerance under high doses of γ-rays, making them suitable candidates for applications in harsh radiation environments, such as detectors at future collider experiments.

  10. Origins of low resistivity in Al ion-implanted ZnO bulk single crystals

    SciTech Connect

    Oga, T.; Izawa, Y.; Kuriyama, K.; Kushida, K.; Kinomura, A.

    2011-06-15

    The origins of low resistivity in Al ion-implanted ZnO bulk single crystals are studied by combining Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), photoluminescence (PL), and Van der Pauw methods. The Al-ion implantation (peak concentration: 2.6 x 10{sup 20}cm{sup -3}) into ZnO is performed using a multiple-step energy. The resistivity decreases from {approx}10{sup 4{Omega}} cm for un-implanted ZnO to 1.4 x 10{sup -1{Omega}} cm for as-implanted, and reaches 6.0 x 10{sup -4{Omega}} cm for samples annealed at 1000 deg. C. RBS and NRA measurements for as-implanted ZnO suggest the existence of the lattice displacement of Zn (Zn{sub i}) and O (O{sub i}), respectively. After annealing at 1000 deg. C, the Zn{sub i} related defects remain and the O{sub i} related defects disappear. The origin of the low resistivity in the as-implanted sample is attributed to the Zn{sub i} ({approx}30 meV [Look et al., Phys. Rev. Lett. 82, 2552 (1999)]). In contrast, the origin of the low resistivity in the sample annealed at 1000 deg. C is assigned to both of the Zn{sub i} related defects and the electrically activated Al donor. A new PL emission appears at around 3.32 eV after annealing at 1000 deg. C, suggesting electrically activated Al donors.

  11. A clear effect of charge compensation through Na+ co-doping on the luminescence spectra and decay kinetics of Nd3+-doped CaAl4O7

    NASA Astrophysics Data System (ADS)

    Puchalska, M.; Watras, A.

    2016-06-01

    We present a detailed analysis of luminescence behavior of singly Nd3+ doped and Nd3+, Na+ co-doped calcium aluminates powders: Ca1-xNdxAl4O7 and Ca1-2xNdxNaxAl4O7 (x=0.001-0.1). Relatively intense Nd3+ luminescence in IR region corresponding to typical 4F3/2→4IJ (J=9/2-13/2) transitions with maximum located at about 1079 nm was obtained in all samples on direct excitation into f-f levels. The effect of dopant concentration and charge compensation by co-doping with Na+ ions on morphology and optical properties were studied. The results show that both, the Nd3+ concentration and the alkali metal co-doping affected the optical properties but had no influence on the powders morphology. The studies of luminescence spectra (298 and 77 K) in a function of dopant concentration showed an increasing distortion of the local symmetry of Nd3+with raising activator content due to certain defects created in the crystal lattice. On the other hand Na+ addition led to significant narrowing of absorption and luminescence bands and also a reduction of the number of their components, showing smaller disturbance of Nd3+ ions local symmetries. Consequently, charge compensated by Na+ co-doping materials showed significantly enhanced Nd3+ luminescence. The decrease of emission intensity and luminescence lifetimes with increase of activator concentration was attributed mainly to phonon-assisted cross-relaxation processes between Nd3+ ions. Analysis with Inokuti-Hirayama model indicated dipole-dipole mechanism of ion-ion interaction. Na+ addition led to much smaller concentration quenching due to smaller clustering of dopant ions in CaAl4O7 lattice.

  12. Plasmonic enhancement of UV emission from ZnO thin films induced by Al nano-concave arrays

    NASA Astrophysics Data System (ADS)

    Norek, Małgorzata; Łuka, Grzegorz; Włodarski, Maksymilian

    2016-10-01

    Surface plasmons (SPs) supported by Al nano-concave arrays with increasing interpore distance (Dc) were used to enhance the ultraviolet light emission from ZnO thin films. Two sets of samples were prepared: in the first set the thin ZnO films were deposited directly on Al nanoconcaves (the Al/ZnO samples) and in the second set a 10 nm - Al2O3 spacer was placed between the textured Al and the ZnO films (the Al/Al2O3-ALD/ZnO samples). In the Al/ZnO samples the enhancement was limited by a nonradiative energy dissipation due to the Ohmic loss in the Al metal. However, for the ZnO layer deposited directly on Al nanopits synthesized at 150 V (Dc = 333 ± 18 nm), the largest 9-fold enhancement was obtained by achieving the best energy fit between the near band-edge (NBE) emission from ZnO and the λ(0,1) SPP resonance mode. In the Al/Al2O3-ALD/ZnO samples the amplification of the UV emission was smaller than in the Al/ZnO samples due to a big energy mismatch between the NBE emission and the λ(0,1) plasmonic mode. The results obtained in this work indicate that better tuning of the NBE - λ(0,1) SPP resonance mode coupling is possible through a proper modification of geometrical parameters in the Al/Al2O3-ALD/ZnO system such as Al nano-concave spacing and the thickness of the corresponding layer. This approach will reduce the negative influence of the non-radiative plasmonic modes and most likely will lead to further enhancement of the SP-modulated UV emission from ZnO thin films.

  13. Control of mean ionic radius at Ca site by Sr co-doping for Ce doped LiCaAlF6 single crystals and the effects on optical and scintillation properties

    NASA Astrophysics Data System (ADS)

    Yokota, Yuui; Yamaji, Akihiro; Kurosawa, Shunsuke; Kamada, Kei; Yoshikawa, Akira

    2014-10-01

    Sr co-doped Ce:LiCaAlF6 [Ce:Li(Ca,Sr)AlF6] crystals with various Ca/Sr ratios were grown by a micro-pulling-down (μ-PD) method and effects of Sr co-doping on crystal structure, chemical composition, optical and scintillation properties for Ce:LiCaAlF6 crystals were investigated as a neutron scintillator. High transparent Ce2%:Li(Ca,Sr)AlF6 crystals with 2% and 5% Sr contents were obtained while Ce2%:Li(Ca,Sr)AlF6 crystals with 10% and 20% Sr contents included milky parts in the crystals. a- and c-axis lengths of Ce:Li(Ca,Sr)AlF6 phase systematically increased with an increase of Sr content. In addition to the emission at 284 and 308 nm from Ce3+ ion, emission peaks at 367 nm appeared by Sr co-doping.

  14. Role of Ce4+ in the Scintillation Mechanism of Codoped Gd3Ga3Al2O12∶Ce

    NASA Astrophysics Data System (ADS)

    Wu, Yuntao; Meng, Fang; Li, Qi; Koschan, Merry; Melcher, Charles L.

    2014-10-01

    To control the time-response performance of widely used cerium-activated scintillators in cutting-edge medical-imaging devices, such as time-of-flight positron-emission tomography, a comprehensive understanding of the role of Ce valence states, especially stable Ce44, in the scintillation mechanism is essential. However, despite some progress made recently, an understanding of the physical processes involving Ce4+ is still lacking. The aim of this work is to clarify the role of Ce4+ in scintillators by studying Ca2+ codoped Gd3Ga3Al2O12∶Ce (GGAG ∶Ce). By using a combination of optical absorption spectra and x-ray absorption near-edge spectroscopies, the correlation between Ca2+ codoping content and the Ce4+ fraction is seen. The energy-level diagrams of Ce3+ and Ce4+ in the Gd3Ga3Al2O12 host are established by using theoretical and experimental methods, which indicate a higher position of the 5d1 state of Ce4+ in the forbidden gap in comparison to that of Ce3+. Underlying reasons for the decay-time acceleration resulting from Ca2+ codoping are revealed, and the physical processes of the Ce4+-emission model are proposed and further demonstrated by temperature-dependent radioluminescence spectra under x-ray excitation.

  15. Enhanced photocatalytic degradation of humic acids using Al and Fe co-doped TiO2 nanotubes under UV/ozonation for drinking water purification.

    PubMed

    Yuan, Rongfang; Zhou, Beihai; Hua, Duo; Shi, Chunhong

    2013-11-15

    O3/UV/TiO2 was used to effectively decompose humic acids (HAs) in drinking water. To obtain a large specific surface area and low band gap energy, Al and Fe co-doped TiO2 nanotubes were successfully synthesized using the hydrothermal method. The effect of the optimal co-doped TiO2 nanotubes catalyst on the HAs removal efficiency through O3/UV/co-doped TiO2 process was investigated. The highest HAs removal efficiency (79.4%) that exhibited a pseudo-first-order rate constant of 0.172 min(-1) was achieved, in the presence of 550 °C calcined 1.0% co-doped TiO2 nanotubes with an Al:Fe ratio of 0.25:0.75. The effects of calcination temperature and doping concentration on anatase phase weight fractions, average crystallite sizes, Brunauer-Emmett-Teller surface area, catalyst band gap energy, and catalyst photocatalytic activity were also discussed. The inorganic anions also affected the catalyst photocatalytic ability. In a neutral solution, SO4(2-) slightly promoted HAs removal. However, HCO3(-) was found to significantly inhibit the catalyst activity, whereas Cl(-) had negligible effect on photocatalytic ability.

  16. Up-conversion luminescence in Yb(3+)-Er(3+)/Tm(3+) co-doped Al2O3-TiO2 nano-composites.

    PubMed

    Mokoena, Teboho Patrick; Linganiso, Ella Cebisa; Kumar, Vinod; Swart, Hendrik C; Cho, So-Hye; Ntwaeaborwa, Odireleng Martin

    2017-06-15

    The sol gel method was used to prepare rare-earths (Yb(3+)-Er(3+) and Yb(3+)-Tm(3+)) co-doped Al2O3-TiO2 nano-composite powder phosphors and their up-conversion luminescence properties were investigated. Mixed oxides of titania (TiO2) rutile phase and an early stage crystallization of alumina (Al2O3) phase were confirmed from the X-ray diffraction data with the average crystallite size of ∼36nm. The rutile phase TiO2 was further confirmed by selected area diffraction analysis of the composites. Microscopy analysis showed interesting rod-like morphologies with rough surfaces indicating that a spherulitic growth process took place during the crystal growth. Photoluminescence characterization of the phosphors was carried out under near infra-red excitation at 980nm and the prominent emission bands were observed in the visible region at 523, 548 and 658nm for the Yb(3+)-Er(3+) co-doped systems. Emission in bands extending from the visible to near infra-red regions were observed at 480, 650, 693 and 800nm for the Yb(3+)-Tm(3+) co-doped systems. These upconverted emissions and energy transfer mechanisms taking place are discussed in detail.

  17. Trap depth and color variation of Ce3+-Cr3+ co-doped Gd3(Al,Ga)5O12 garnet persistent phosphors

    NASA Astrophysics Data System (ADS)

    Asami, Kazuki; Ueda, Jumpei; Tanabe, Setsuhisa

    2016-12-01

    Persistent luminescent properties in Ce3+-Cr3+ codoped Gd3Al5-xGaxO12 garnet (GAGG:Ce-Cr) solid solution have been investigated. The persistent luminescent color is shifted from orange to yellowish green with increasing Ga content because Ce3+: 5d level splitting becomes much weaker. The depth of electron trap introduced by Cr codoping was estimated from the intense thermoluminescence glow peak by the initial rise method. The trap depth decreases from 0.56 eV to 0.29 eV with increasing Ga content. The shift can be explained by downshift of bottom of conduction band. From the persistent luminescence decay curve measurement after ceasing 450 nm blue illumination, the samples with x = 2.5 exhibited the longest persistent luminescence for 405 min until the luminance becomes 2 mcd/m2 in GAGG:Ce-Cr phosphors.

  18. Fabrication and characterization of silicon wire solar cells having ZnO nanorod antireflection coating on Al-doped ZnO seed layer

    PubMed Central

    2012-01-01

    In this study, we have fabricated and characterized the silicon [Si] wire solar cells with conformal ZnO nanorod antireflection coating [ARC] grown on a Al-doped ZnO [AZO] seed layer. Vertically aligned Si wire arrays were fabricated by electrochemical etching and, the p-n junction was prepared by spin-on dopant diffusion method. Hydrothermal growth of the ZnO nanorods was followed by AZO film deposition on high aspect ratio Si microwire arrays by atomic layer deposition [ALD]. The introduction of an ALD-deposited AZO film on Si wire arrays not only helps to create the ZnO nanorod arrays, but also has a strong impact on the reduction of surface recombination. The reflectance spectra show that ZnO nanorods were used as an efficient ARC to enhance light absorption by multiple scattering. Also, from the current-voltage results, we found that the combination of the AZO film and ZnO nanorods on Si wire solar cells leads to an increased power conversion efficiency by more than 27% compared to the cells without it. PMID:22222067

  19. Fabrication and characterization of silicon wire solar cells having ZnO nanorod antireflection coating on Al-doped ZnO seed layer.

    PubMed

    Baek, Seong-Ho; Noh, Bum-Young; Park, Il-Kyu; Kim, Jae Hyun

    2012-01-05

    In this study, we have fabricated and characterized the silicon [Si] wire solar cells with conformal ZnO nanorod antireflection coating [ARC] grown on a Al-doped ZnO [AZO] seed layer. Vertically aligned Si wire arrays were fabricated by electrochemical etching and, the p-n junction was prepared by spin-on dopant diffusion method. Hydrothermal growth of the ZnO nanorods was followed by AZO film deposition on high aspect ratio Si microwire arrays by atomic layer deposition [ALD]. The introduction of an ALD-deposited AZO film on Si wire arrays not only helps to create the ZnO nanorod arrays, but also has a strong impact on the reduction of surface recombination. The reflectance spectra show that ZnO nanorods were used as an efficient ARC to enhance light absorption by multiple scattering. Also, from the current-voltage results, we found that the combination of the AZO film and ZnO nanorods on Si wire solar cells leads to an increased power conversion efficiency by more than 27% compared to the cells without it.

  20. Plasma versus thermal annealing for the Au-catalyst growth of ZnO nanocones and nanowires on Al-doped ZnO buffer layers

    NASA Astrophysics Data System (ADS)

    Güell, Frank; Martínez-Alanis, Paulina R.; Roso, Sergio; Salas-Pérez, Carlos I.; García-Sánchez, Mario F.; Santana, Guillermo; Marel Monroy, B.

    2016-06-01

    We successfully synthesized ZnO nanocones and nanowires over polycrystalline Al-doped ZnO (AZO) buffer layers on fused silica substrates by a vapor-transport process using Au-catalyst thin films. Different Au film thicknesses were thermal or plasma annealed in order to analyze their influence on the ZnO nanostructure growth morphology. Striking differences have been observed. Thermal annealing generates a distribution of Au nanoclusters and plasma annealing induces a fragmentation of the Au thin films. While ZnO nanowires are found in the thermal-annealed samples, ZnO nanocones and nanowires have been obtained on the plasma-annealed samples. Enhancement of the preferred c-axis (0001) growth orientation was demonstrated by x-ray diffraction when the ZnO nanocones and nanowires have been grown over the AZO buffer layer. The transmittance spectra of the ZnO nanocones and nanowires show a gradual increase from 375 to 900 nm, and photoluminescence characterization pointed out high concentration of defects leading to observation of a broad emission band in the visible range from 420 to 800 nm. The maximum emission intensity peak position of the broad visible band is related to the thickness of the Au-catalyst for the thermal-annealed samples and to the plasma power for the plasma-annealed samples. Finally, we proposed a model for the plasma versus thermal annealing of the Au-catalyst for the growth of the ZnO nanocones and nanowires. These results are promising for renewable energy applications, in particular for its potential application in solar cells.

  1. Enhanced 2 μm broad-band emission and NIR to visible frequency up-conversion from Ho3+/Yb3+ co-doped Bi2O3-GeO2-ZnO glasses.

    PubMed

    Biswas, Kaushik; Sontakke, Atul D; Sen, R; Annapurna, K

    2013-08-01

    In this work, a new and non-conventional oxide glass composition based on Bi2O3-GeO2-ZnO system has been formulated with an aim to realize low phonon oxide glass and elucidate its performance when co-doped with Ho(3+)/Yb(3+) for the energy transfer based NIR emission at 2 μm from Ho(3+) ions under Yb(3+) excitation. The glass with 1.0 mol% Ho2O3 and 0.5 mol% Yb2O3 has exhibited maximum energy transfer rate (3602 s(-1)) and energy transfer efficiency (65.92%). Important radiative properties have been predicted for emission transitions of Ho(3+) ions using intensity parameters derived from measured absorption spectra using standard Judd-Ofelt theory. At lower acceptor ion concentration (0.1 mol%), an efficient NIR to visible up-conversion emission has been observed based on two photon absorption process which has found to be reduced significantly at higher Ho(3+) concentrations with simultaneous enhancement in 2 μm emission. Hence, this newly developed glass codoped with Yb(3+)/Ho(3+) is promising glass for sensitized 2 μm emission applications as broad band tunable lasers because of the combination of low phonon energy (707 cm(-1)), high energy transfer efficiency, moderately high emission cross-section (5.33×10(-21) cm(2)) and larger effective half-width of the emission band value of 169 nm.

  2. Electrical and optical properties of Al-doped ZnO and ZnAl2O4 films prepared by atomic layer deposition

    PubMed Central

    2013-01-01

    ZnO/Al2O3 multilayers were prepared by alternating atomic layer deposition (ALD) at 150°C using diethylzinc, trimethylaluminum, and water. The growth process, crystallinity, and electrical and optical properties of the multilayers were studied with a variety of the cycle ratios of ZnO and Al2O3 sublayers. Transparent conductive Al-doped ZnO films were prepared with the minimum resistivity of 2.4 × 10−3 Ω·cm at a low Al doping concentration of 2.26%. Photoluminescence spectroscopy in conjunction with X-ray diffraction analysis revealed that the thickness of ZnO sublayers plays an important role on the priority for selective crystallization of ZnAl2O4 and ZnO phases during high-temperature annealing ZnO/Al2O3 multilayers. It was found that pure ZnAl2O4 film was synthesized by annealing the specific composite film containing alternative monocycle of ZnO and Al2O3 sublayers, which could only be deposited precisely by utilizing ALD technology. PMID:23537274

  3. Atomic scattering spectroscopy for determination of the polarity of semipolar AlN grown on ZnO

    SciTech Connect

    Kobayashi, Atsushi; Ohta, Jitsuo; Ueno, Kohei; Oshima, Masaharu; Fujioka, Hiroshi

    2013-11-04

    Determination of the polarity of insulating semipolar AlN layers was achieved via atomic scattering spectroscopy. The back scattering of neutralized He atoms on AlN surfaces revealed the atomic alignment of the topmost layers of semipolar AlN and the ZnO substrate. Pole figures of the scattering intensity were used to readily determine the polarity of these wurtzite-type semipolar materials. In addition, we found that +R-plane AlN epitaxially grows on −R-plane ZnO, indicating that the polarity flips at the semipolar AlN/ZnO interface. This polarity flipping is possibly explained by the appearance of −c and m-faces on the −R ZnO surfaces, which was also revealed by atomic scattering spectroscopy.

  4. Spectroscopic characterization of the plasmas formed during the deposition of ZnO and Al-doped ZnO films by plasma-assisted pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Liang, Peipei; Cai, Hua; Yang, Xu; Li, Hui; Zhang, Wu; Xu, Ning; Sun, Jian; Wu, Jiada

    2016-11-01

    An oxygen-zinc plasma and an oxygen-zinc-aluminum plasma are formed by pulsed laser ablation of a Zn target or pulsed laser co-ablation of a Zn target and an Al target in an electron cyclotron resonance (ECR) discharge-generated oxygen plasma for the deposition of ZnO and Al-doped ZnO (AZO) films. The plasmas are characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy. Both the oxygen-zinc plasma and the oxygen-zinc-aluminum plasma contain excited species originally present in the working O2 gas and energetic species ablated from the targets. The optical emission of the oxygen-zinc-aluminum plasma is abundant in the emission bands of oxygen molecular ions and the emission lines of mono-atomic oxygen, zinc and aluminum atoms and atomic ions. The time-integrated spectra as well as the time-resolved spectra of the plasma emission indicate that the oxygen species in the ECR oxygen plasma experience additional excitation by the expanding ablation plumes, and the ablated species are excited frequently when traveling accompanying the plume expansion in the oxygen plasma, making the formed plasma highly excited and very reactive, which plays an important role in the reactive growth of ZnO matrix and the in-situ doping of Al into the growing ZnO matrix. The deposited ZnO and AZO films were evaluated for composition analysis by energy dispersive X-ray spectroscopy, structure characterization by X-ray diffraction and optical transmission measurement. The deposited ZnO is slightly rich in O. The Al concentration of the AZO films can be controlled and varied simply by changing the repetition rate of the laser used for Al target ablation. Both the ZnO and the AZO films are featured with hexagonal wurtzite crystal structure and exhibit high optical transparency in a wide spectral region. Al doping results in an improvement in the ultraviolet transparency, a blue shift in the absorption edge and a widening of the band gap.

  5. Microstructure and property of diamond-like carbon films with Al and Cr co-doping deposited using a hybrid beams system

    NASA Astrophysics Data System (ADS)

    Dai, Wei; Liu, Jingmao; Geng, Dongsen; Guo, Peng; Zheng, Jun; Wang, Qimin

    2016-12-01

    DLC films with weak carbide former Al and carbide former Cr co-doping (Al:Cr-DLC) were deposited by a hybrid beams system comprising an anode-layer linear ion beam source (LIS) and high power impulse magnetron sputtering using a gas mixture of C2H2 and Ar as the precursor. The doped Al and Cr contents were controlled via adjusting the C2H2 fraction in the gas mixture. The composition, microstructure, compressive stress, mechanical properties and tribological behaviors of the Al:Cr-DLC films were researched carefully using X-ray photoelectron spectroscopy, transmission electron microscopy, Raman spectroscopy, stress-tester, nanoindentation and ball-on-plate tribometer as function of the C2H2 fraction. The results show that the Al and Cr contents in the films increased continuously as the C2H2 fraction decreased. The doped Cr atoms preferred to bond with the carbon while the Al atoms mainly existed in metallic state. Structure modulation with alternate multilayer consisted of Al-poor DLC layer and Al-rich DLC layer was found in the films. Those periodic Al-rich DLC layers can effectively release the residual stress of the films. On the other hand, the formation of the carbide component due to Cr incorporation can help to increase the film hardness. Accordingly, the residual stress of the DLC films can be reduced without sacrificing the film hardness though co-doping Al and Cr atoms. Furthermore, it was found that the periodic Al-rich layer can greatly improve the elastic resilience of the DLC films and thus decreases the film friction coefficient and wear rate significantly. However, the existence of the carbide component would cause abrasive wear and thus deteriorate the wear performance of the films.

  6. Effect of annealing on structural and electrical properties of ZnO and In2S3:Al thin layers

    NASA Astrophysics Data System (ADS)

    Jebbari, N.; Ajili, M.; Guasch, C.; Kamoun, N.; Bennaceur, R.

    2010-11-01

    Thin films of ZnO and In2S3:Al are deposited on Pyrex substrates by spray technique. Structural and electrical properties of ZnO and β-In2S3:Al compounds were studied using X Ray Diffraction (XRD), (MEB) and the Vander Pauw method before and after annealing. The X-rays revealed that, ZnO and In2S3:Al were well crystallized respectively in the hexagonal and cubic structure. The main orientations of ZnO were (101), (100) and (110). The (101) direction is the preferentially one. The annealing favors the preferential peak crystallization with a reduction of the grains size and the thickness layer. The β-In2S3 contain Aluminum inclusion by introducing the ratio x= [Al3+]/[In3+] in sprayed solution. X-ray diffraction spectra of In2-xAlxS3 thin layer, realized for the value of z equal to 20%, show well-defined peaks of (311), (400), (511), and (440) principal orientations corresponding to cubic structure of β-In2S3. For In2S3:Al, we note that the annealing increase the intensity of all peaks with an increase of the grains size and the thickness layer. Besides, thanks to the determination of the resistance from which we calculated resistivity, we note that the annealing increase conductivity of β-In2S3:Al and decrease it for ZnO.

  7. Substrate temperature effects on the electrical properties of sputtered Al doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Kim, Deok-Kyu; Kim, Hong-Bae

    2015-09-01

    Al doped ZnO (AZO) thin films were deposited on glass substrate by RF magnetron sputtering system. The dependence of structural, electrical, and optical properties on the substrate temperature variations in the range of 0-400 °C was investigated. The structural results reveal that the AZO films are (0 0 2) oriented and at 400 °C a considerable crystallinity enhancement of the films is observed. With increasing the substrate temperature, the resistivity is increased by decreasing of the mobility and carrier concentration. X-ray photoelectron spectroscopy (XPS) results show that the mobility and the carrier concentration are decreased by increasing the surface bonding and decreasing the Al content, respectively. In our case, the increase in substrate temperature suppressed the incorporation of Al atoms together with the decrease of oxygen vacancy. The improvement of Al doping efficiency is a very important factor to obtain better electrical properties at high substrate temperatures.

  8. Electrochemical Synthesis of Highly Oriented, Transparent, and Pinhole-Free ZnO and Al-Doped ZnO Films and Their Use in Heterojunction Solar Cells.

    PubMed

    Kang, Donghyeon; Lee, Dongho; Choi, Kyoung-Shin

    2016-10-04

    Electrochemical synthesis conditions using nonaqueous solutions were developed to prepare highly transparent (T > 90%) and crystalline ZnO and Al-doped ZnO (AZO) films for use in solar energy conversion devices. A focused effort was made to produce pinhole-free films in a reproducible manner by identifying a key condition to prevent the formation of cracks during deposition. The polycrystalline domains in the resulting films had a uniform orientation (i.e., the c-axis perpendicular to the substrate), which enhanced the electron transport properties of the films. Furthermore, electrochemical Al doping of ZnO using nonaqueous media, which was demonstrated for the first time in this study, effectively increased the carrier density and raised the Fermi level of ZnO. These films were coupled with an electrodeposited p-type Cu2O to construct p-n heterojunction solar cells to demonstrate the utilization of these films for solar energy conversion. The resulting n-ZnO/p-Cu2O and n-AZO/p-Cu2O cells showed excellent performance compared with previously reported n-ZnO/p-Cu2O cells prepared by electrodeposition. In particular, replacing ZnO with AZO resulted in simultaneous enhancements in short circuit current and open circuit potential, and the n-AZO/p-Cu2O cell achieved an average power conversion efficiency (η) of 0.92 ± 0.09%. The electrodeposition condition reported here will offer a practical and versatile way to produce ZnO or AZO films, which play key roles in various solar energy conversion devices, with qualities comparable to those prepared by vacuum-based techniques.

  9. Structure and thermoelectric properties of Al-doped ZnO films prepared by thermal oxidization under high magnetic field

    NASA Astrophysics Data System (ADS)

    Liu, Shiying; Peng, Sunjuan; Ma, Jun; Li, Guojian; Qin, Xuesi; Li, Mengmeng; Wang, Qiang

    2017-04-01

    This paper studies the effects of high magnetic field (HMF) on the structure, optical and thermoelectric properties of the doped ZnO thin films. The results show that both Al dopant and application of HMF can affect the crystal structure, surface morphology, elemental distribution and so on. The particles of the thin films become small and regular by doping Al. The ZnO films oxidized from the Au/Zn bilayer have needle structure. The ZnO films oxidized from the Au/Zn-Al bilayer transform to spherical from hexagonal due to the application of HMF. The transmittance decreases with doping Al because of the opaque of Al element and decreases with the application of HMF due to the dense structure obtained under HMF. Electrical resistivity (ρ) of the ZnO films without Al decreases with increasing measurement temperature (T) and is about 1.5 × 10-3 Ω·m at 210 °C. However, the ρ of the Al-doped ZnO films is less than 10-5 Ω·m. The Seebeck coefficient (S) of the films oxidized from the Au/Zn-Al films reduces with increasing T. The S values oxidized under 0 T and 12 T conditions are 2.439 μV/K and -3.415 μV/K at 210 °C, respectively. Power factor reaches the maximum value (3.198 × 10-4 W/m·K2) at 210 °C for the film oxidized under 12 T condition. These results indicate that the Al dopant and the application of HMF can be used to control structure and thermoelectric properties of doped ZnO films.

  10. Effects of Al Doping on the Properties of ZnO Thin Films Deposited by Atomic Layer Deposition

    NASA Astrophysics Data System (ADS)

    Zhai, Chen-Hui; Zhang, Rong-Jun; Chen, Xin; Zheng, Yu-Xiang; Wang, Song-You; Liu, Juan; Dai, Ning; Chen, Liang-Yao

    2016-09-01

    The tuning of structural, optical, and electrical properties of Al-doped ZnO films deposited by atomic layer deposition technique is reported in this work. With the increasing Al doping level, the evolution from (002) to (100) diffraction peaks indicates the change in growth mode of ZnO films. Spectroscopic ellipsometry has been applied to study the thickness, optical constants, and band gap of AZO films. Due to the increasing carrier concentration after Al doping, a blue shift of band gap and absorption edge can be observed, which can be interpreted by Burstein-Moss effect. The carrier concentration and resistivity are found to vary significantly among different doping concentration, and the optimum value is also discussed. The modulations and improvements of properties are important for Al-doped ZnO films to apply as transparent conductor in various applications.

  11. Effects of Al Doping on the Properties of ZnO Thin Films Deposited by Atomic Layer Deposition.

    PubMed

    Zhai, Chen-Hui; Zhang, Rong-Jun; Chen, Xin; Zheng, Yu-Xiang; Wang, Song-You; Liu, Juan; Dai, Ning; Chen, Liang-Yao

    2016-12-01

    The tuning of structural, optical, and electrical properties of Al-doped ZnO films deposited by atomic layer deposition technique is reported in this work. With the increasing Al doping level, the evolution from (002) to (100) diffraction peaks indicates the change in growth mode of ZnO films. Spectroscopic ellipsometry has been applied to study the thickness, optical constants, and band gap of AZO films. Due to the increasing carrier concentration after Al doping, a blue shift of band gap and absorption edge can be observed, which can be interpreted by Burstein-Moss effect. The carrier concentration and resistivity are found to vary significantly among different doping concentration, and the optimum value is also discussed. The modulations and improvements of properties are important for Al-doped ZnO films to apply as transparent conductor in various applications.

  12. Transparent conductive Al-doped ZnO thin films grown at room temperature

    SciTech Connect

    Wang Yuping; Lu Jianguo; Bie Xun; Gong Li; Li Xiang; Song Da; Zhao Xuyang; Ye Wenyi; Ye Zhizhen

    2011-05-15

    Aluminum-doped ZnO (ZnO:Al, AZO) thin films were prepared on glass substrates by dc reactive magnetron sputtering from a Zn-Al alloy target at room temperature. The effects of the Ar-to-O{sub 2} partial pressure ratios on the structural, electrical, and optical properties of AZO films were studied in detail. AZO films grown using 100:4 to 100:8 Ar-to-O{sub 2} ratio result in acceptable quality films with c-axis orientated crystals, uniform grains, 10{sup -3} {Omega} cm resistivity, greater than 10{sup 20} cm{sup -3} electron concentration, and high transmittance, 90%, in the visible region. The lowest resistivity of 4.11x10{sup -3} {Omega} cm was obtained under the Ar-to-O{sub 2} partial pressure ratio of 100:4. A relatively strong UV emission at {approx}3.26 eV was observed in the room-temperature photoluminescence spectrum. X-ray photoelectron spectroscopy analysis confirmed that Al was introduced into ZnO and substitutes for Zn and doped the film n-type.

  13. Sol-gel synthesis and characterization of undoped and Al-doped ZnO thin films for memristive application

    NASA Astrophysics Data System (ADS)

    Ayana, Dawit G.; Prusakova, Valentina; Collini, Cristian; Nardi, Marco V.; Tatti, Roberta; Bortolotti, Mauro; Lorenzelli, Leandro; Chiappini, Andrea; Chiasera, Alessandro; Ferrari, Maurizio; Lunelli, Lorenzo; Dirè, Sandra

    2016-11-01

    The Sol-gel route is a versatile method to fabricate multi-layer, dense and homogeneous ZnO thin films with a controlled thickness and defects for a memristive application. In this work, sol-gel derived multi-layer undoped and Al-doped ZnO thin films were prepared by a spin-coating technique on SiO2/Ti/Pt and silica glass substrates. The effect of both Al doping and curing conditions on the structural and morphological features of ZnO films was investigated by complementary techniques, including electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, micro-Raman spectroscopy, and X-ray diffraction analysis. Electrical measurements were performed on SiO2/Ti/Pt/ZnO/Pt(dishes) and SiO2/Ti/Pt/ZnO(Al)/Pt(dishes) fabricated memristive cells and preliminary current-voltage curves were acquired.

  14. Bi-layer channel structure-based oxide thin-film transistors consisting of ZnO and Al-doped ZnO with different Al compositions and stacking sequences

    NASA Astrophysics Data System (ADS)

    Cho, Sung Woon; Yun, Myeong Gu; Ahn, Cheol Hyoun; Kim, So Hee; Cho, Hyung Koun

    2015-03-01

    Zinc oxide (ZnO)-based bi-layers, consisting of ZnO and Al-doped ZnO (AZO) layers grown by atomic layer deposition, were utilized as the channels of oxide thin-film transistors (TFTs). Thin AZO layers (5 nm) with different Al compositions (5 and 14 at. %) were deposited on top of and beneath the ZnO layers in a bi-layer channel structure. All of the bi-layer channel TFTs that included the AZO layers showed enhanced stability (Δ V Th ≤ 3.2 V) under a positive bias stress compared to the ZnO single-layer channel TFT (Δ V Th = 4.0 V). However, the AZO/ZnO bi-layer channel TFTs with an AZO interlayer between the gate dielectric and the ZnO showed a degraded field effect mobility (0.3 cm2/V·s for 5 at. % and 1.8 cm2/V·s for 14 at. %) compared to the ZnO single-layer channel TFT (5.5 cm2/V·s) due to increased scattering caused by Al-related impurities near the gate dielectric/channel interface. In contrast, the ZnO/AZO bi-layer channel TFTs with an AZO layer on top of the ZnO layer exhibited an improved field effect mobility (7.8 cm2/V·s for 14 at. %) and better stability. [Figure not available: see fulltext.

  15. Temperature dependent dual hydrogen sensor response of Pd nanoparticle decorated Al doped ZnO surfaces

    SciTech Connect

    Gupta, D.; Barman, P. B.; Hazra, S. K.; Dutta, D.; Kumar, M.; Som, T.

    2015-10-28

    Sputter deposited Al doped ZnO (AZO) thin films exhibit a dual hydrogen sensing response in the temperature range 40 °C–150 °C after surface modifications with palladium nanoparticles. The unmodified AZO films showed no response in hydrogen in the temperature range 40 °C–150 °C. The operational temperature windows on the low and high temperature sides have been estimated by isolating the semiconductor-to-metal transition temperature zone of the sensor device. The gas response pattern was modeled by considering various adsorption isotherms, which revealed the dominance of heterogeneous adsorption characteristics. The Arrhenius adsorption barrier showed dual variation with change in hydrogen gas concentration on either side of the semiconductor-to-metal transition. A detailed analysis of the hydrogen gas response pattern by considering the changes in nano palladium due to hydrogen adsorption, and semiconductor-to-metal transition of nanocrystalline Al doped ZnO layer due to temperature, along with material characterization studies by glancing incidence X-ray diffraction, atomic force microscopy, and transmission electron microscopy, are presented.

  16. Exploration of Al-Doped ZnO in Photovoltaic Thin Films

    NASA Astrophysics Data System (ADS)

    Ciccarino, Christopher; Sahiner, M. Alper

    The electrical properties of Al doped ZnO-based thin films represent a potential advancement in the push for increasing solar cell efficiency. Doping with Aluminum will theoretically decrease resistivity of the film and therefore achieve this potential as a viable option in the P-N junction phase of photovoltaic cells. The n-type semi-conductive characteristics of the ZnO layer will theoretically be optimized with the addition of Aluminum carriers. In this study, Aluminum doping concentrations ranging from 1-3% by mass were produced, analyzed, and compared. Films were developed onto ITO coated glass using the Pulsed Laser Deposition technique. Target thickness was 250 nm and ellipsometry measurements showed uniformity and accuracy in this regard. Active dopant concentrations were determined using Hall Effect measurements. Efficiency measurements showed possible applications of this doped compound, with upwards of 7% efficiency measured, using a Keithley 2602 SourceMeter set-up. XRD scans showed highly crystalline structures, with effective Al intertwining of the hexagonal wurtzile ZnO molecular structure. This alone indicates a promising future of collaboration between these two materials.

  17. Temperature dependent dual hydrogen sensor response of Pd nanoparticle decorated Al doped ZnO surfaces

    NASA Astrophysics Data System (ADS)

    Gupta, D.; Dutta, D.; Kumar, M.; Barman, P. B.; Som, T.; Hazra, S. K.

    2015-10-01

    Sputter deposited Al doped ZnO (AZO) thin films exhibit a dual hydrogen sensing response in the temperature range 40 °C-150 °C after surface modifications with palladium nanoparticles. The unmodified AZO films showed no response in hydrogen in the temperature range 40 °C-150 °C. The operational temperature windows on the low and high temperature sides have been estimated by isolating the semiconductor-to-metal transition temperature zone of the sensor device. The gas response pattern was modeled by considering various adsorption isotherms, which revealed the dominance of heterogeneous adsorption characteristics. The Arrhenius adsorption barrier showed dual variation with change in hydrogen gas concentration on either side of the semiconductor-to-metal transition. A detailed analysis of the hydrogen gas response pattern by considering the changes in nano palladium due to hydrogen adsorption, and semiconductor-to-metal transition of nanocrystalline Al doped ZnO layer due to temperature, along with material characterization studies by glancing incidence X-ray diffraction, atomic force microscopy, and transmission electron microscopy, are presented.

  18. Enhancing the Photocatalytic Activity of Sr4 Al14 O25 :Eu(2+) ,Dy(3+) Persistent Phosphors by Codoping with Bi(3+) ions.

    PubMed

    García, Carlos R; Oliva, Jorge; Romero, Maria Teresa; Diaz-Torres, Luis A

    2016-01-20

    The photocatalytic activity of Bismuth codoped Sr4 Al14 O25 : Eu(2+) ,Dy(3+) persistent phosphors is studied by monitoring the degradation of the blue methylene dye UV light irradiation. Powder phosphors are obtained by a combustion synthesis method and a post-annealing process in reductive atmosphere. The XRD patterns show a single orthorhombic phase of Sr4 Al14 O25 : Eu(2+) ,Dy(3+) ,Bi(3+) phosphors even at high Bismuth dopant concentrations of 12 mol%, suggesting that Bi ions are well incorporated into the host lattice. SEM micrographs show irregular micro grains with sizes in the range of 0.5-20 μm. The samples present an intense greenish-blue fluorescence and persistent emissions at 495 nm, attributed to the 5d-4f allowed transitions of Eu(2+) . The fluorescence decreases as Bi concentration increases; that suggest bismuth induced traps formation that in turn quench the luminescence. The photocatalytic evaluation of the powders was studied under both 365 nm UV and solar irradiations. Sample with 12 mol% of Bi presented the best MB degradation activity; 310 min of solar irradiation allow 100% MB degradation whereas only 62.49% MB degradation is achieved under UV irradiation. Our Results suggest that codoping the persistent phosphors with Bi(3+) can be an alternative to enhance their photocatalytic activity. This article is protected by copyright. All rights reserved.

  19. Electrical and optical properties of Al doped Zno film prepared by spray pyrolysis technique

    NASA Astrophysics Data System (ADS)

    Shrestha, Shankar Prasad; Basnet, Pradeep

    2008-04-01

    Transparent conducting thin films of zinc oxides and aluminum doped zinc oxide (AZO) were prepared by the spray pyrolysis technique using an aqueous solution of dehydrate zinc acetate (CH 3COOH. 2H IIO, pure- Merck A. R. grade) and hex hydrate aluminum chloride (AlCl 3 .6H IIO) on the micro glass slides. The prepared thin films are found to be highly adherent to the substrate and possess uniform conduction. The optical and electrical properties of the film were investigated in terms of different Al concentration in the starting solution and different substrate temperature. Four probe method in Van der pauw configuration was used for electrical resistivity measurements. The resistivity of Al doped film is observed to vary with doping concentration. The lowest resistivity is observed in the film doping with 2 at % [Al/Zn]. The Hall coefficient measurements show that both ZnO and AZO show the n-type conduction. The carrier concentration was observed to be highest at 2 at% of Al doping. The optical measurements of all the samples with aluminum concentrations was found to be >85 % showing the film to be highly transparent in nature. With increase in Al concentration, the optical band gap was observed increase from 3.27 eV to 3.41 eV.

  20. Optical parameters of Al-doped ZnO nanorod array thin films grown via the hydrothermal method.

    PubMed

    Kim, Soaram; Kim, Min Su; Nam, Giwoong; Park, Hyunggil; Yoon, Hyunsik; Leem, Jae-Young

    2013-09-01

    ZnO seed layers were deposited onto a quartz substrate using the sol--gel method, and Al-doped ZnO (AZO) nanorod array thin films with different Al concentrations that ranged from 0 to 2.0 at. % were grown on the ZnO seed layers via the hydrothermal method. Optical parameters, including the optical band gap, the absorption coefficient, the Urbach energy, the refractive index, the dispersion parameter, and the optical conductivity, were studied to investigate the effects of Al doping on the optical properties of AZO nanorod array thin films. The optical band gaps of the ZnO and AZO nanorod array thin films were 3.206 at 0 at.%, 3.214 at 0.5 at.%, 3.226 at 1.5 at.%, and 3.268 at 2.0 at.%. The Urbach energy gradually decreased from 126 meV (0 at.%) to 70 meV (2.0 at.%) as the Al concentration was increased. The dispersion energy, the single-oscillator energy, the average oscillator wavelength, the average oscillator strength, the refractive index, and the optical conductivity of the AZO nanorod array thin films were all affected by Al doping.

  1. Structural, electrical, and optical properties of atomic layer deposition Al-doped ZnO films

    SciTech Connect

    Banerjee, P; Lee, W. J.; Bae, K. R.; Lee, Sang Bok; Rubloff, Gary W

    2010-01-01

    Al-doped ZnO (AZO) films of ~100nm thickness with various Aldoping were prepared at 150°C by atomic layer deposition on quartz substrates. At low Aldoping, the films were strongly textured along the [100] direction, while at higher Aldoping the films remained amorphous. Atomic force microscopy results showed that Al–O cycles when inserted in a ZnOfilm, corresponding to a few atomic percent Al, could remarkably reduce the surface roughness of the films. Hall measurements revealed a maximum mobility of 17.7cm{sup 2} /Vs . Film resistivity reached a minima of 4.4×10{sup -3} Ωcm whereas the carrier concentration reached a maxima of 1.7×10{sup 20} cm{sup -3} , at 3 at.% Al. The band gap of AZO films varied from 3.23 eV for undoped ZnOfilms to 3.73 eV for AZO films with 24.6 at.% Al. Optical transmittance over 80% was obtained in the visible region. The detrimental impact of increased Al resulting in decreased conductivity due to doping past 3.0 at.% is evident in the x-ray diffraction data, as an abrupt increase in the optical band gap and as a deviation from the Burstein–Moss effect.

  2. Enhanced photoluminescence and Raman properties of Al-Doped ZnO nanostructures prepared using thermal chemical vapor deposition of methanol assisted with heated brass.

    PubMed

    Thandavan, Tamil Many K; Gani, Siti Meriam Abdul; San Wong, Chiow; Md Nor, Roslan

    2015-01-01

    Vapor phase transport (VPT) assisted by mixture of methanol and acetone via thermal evaporation of brass (CuZn) was used to prepare un-doped and Al-doped zinc oxide (ZnO) nanostructures (NSs). The structure and morphology were characterized by field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD). Photoluminescence (PL) properties of un-doped and Al-doped ZnO showed significant changes in the optical properties providing evidence for several types of defects such as zinc interstitials (Zni), oxygen interstitials (Oi), zinc vacancy (Vzn), singly charged zinc vacancy (VZn-), oxygen vacancy (Vo), singly charged oxygen vacancy (Vo+) and oxygen anti-site defects (OZn) in the grown NSs. The Al-doped ZnO NSs have exhibited shifted PL peaks at near band edge (NBE) and red luminescence compared to the un-doped ZnO. The Raman scattering results provided evidence of Al doping into the ZnO NSs due to peak shift from 145 cm-1 to an anomalous peak at 138 cm-1. Presence of enhanced Raman signal at around 274 and 743 cm-1 further confirmed Al in ZnO NSs. The enhanced D and G band in all Al-doped ZnO NSs shows possible functionalization and doping process in ZnO NSs.

  3. Enhanced Photoluminescence and Raman Properties of Al-Doped ZnO Nanostructures Prepared Using Thermal Chemical Vapor Deposition of Methanol Assisted with Heated Brass

    PubMed Central

    Thandavan, Tamil Many K.; Gani, Siti Meriam Abdul; San Wong, Chiow; Md. Nor, Roslan

    2015-01-01

    Vapor phase transport (VPT) assisted by mixture of methanol and acetone via thermal evaporation of brass (CuZn) was used to prepare un-doped and Al-doped zinc oxide (ZnO) nanostructures (NSs). The structure and morphology were characterized by field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD). Photoluminescence (PL) properties of un-doped and Al-doped ZnO showed significant changes in the optical properties providing evidence for several types of defects such as zinc interstitials (Zni), oxygen interstitials (Oi), zinc vacancy (Vzn), singly charged zinc vacancy (VZn-), oxygen vacancy (Vo), singly charged oxygen vacancy (Vo+) and oxygen anti-site defects (OZn) in the grown NSs. The Al-doped ZnO NSs have exhibited shifted PL peaks at near band edge (NBE) and red luminescence compared to the un-doped ZnO. The Raman scattering results provided evidence of Al doping into the ZnO NSs due to peak shift from 145 cm-1 to an anomalous peak at 138 cm-1. Presence of enhanced Raman signal at around 274 and 743 cm-1 further confirmed Al in ZnO NSs. The enhanced D and G band in all Al-doped ZnO NSs shows possible functionalization and doping process in ZnO NSs. PMID:25756598

  4. Efficiency enhancement of regular-type perovskite solar cells based on Al-doped ZnO nanorods as electron transporting layers

    NASA Astrophysics Data System (ADS)

    Huang, Zheng-Lun; Chen, Chih-Ming; Lin, Zheng-Kun; Yang, Sheng-Hsiung

    2017-02-01

    In this paper, we first incorporated Al(NO3)3·9H2O as the Al source into ZnO nanorods (NRs) lattice via the hydrothermal method to modify nature properties of ZnO NRs for the fabrication of perovskite solar cells (PSCs). The X-ray diffraction (XRD) pattern of Al-doped ZnO NRs exhibits higher 2θ values and stronger intensity of (002) plane. Larger optical band gap and higher electrical conductivity of Al-doped ZnO NRs are also observed relative to non-doped ZnO ones. The steady-state photoluminescence shows effective charge extraction and collection at the interface between Al-doped ZnO NRs and perovskite layer. The optimized PSC based on Al-doped ZnO NRs showed an open-circuit voltage of 0.84 V, a short-circuit current density of 21.93 mA/cm2, a fill factor of 57%, and a power conversion efficiency of 10.45% that was 23% higher than the non-doped ZnO ones.

  5. Effect of Mg2+ ions co-doping on luminescence and defects formation processes in Gd3(Ga,Al)5O12:Ce single crystals

    NASA Astrophysics Data System (ADS)

    Babin, V.; Bohacek, P.; Grigorjeva, L.; Kučera, M.; Nikl, M.; Zazubovich, S.; Zolotarjovs, A.

    2017-04-01

    Photo- and radioluminescence and thermally stimulated luminescence characteristics of Ce3+ - doped and Ce3+, Mg2+ co-doped Gd3(Ga,Al)5O12 (GAGG) single crystals of similar composition are investigated in the 9-500 K temperature range. The Ce3+ - related luminescence spectra and the photoluminescence decay kinetics in these crystals are found to be similar. Under photoexcitation in the Ce3+ - and Gd3+ - related absorption bands, no prominent rise of the photoluminescence intensity in time is observed neither in GAGG:Ce,Mg nor in GAGG:Ce crystals. The afterglow is strongly reduced in GAGG:Ce,Mg as compared to GAGG:Ce, and the afterglow decay kinetics is much faster. Co-doping with Mg2+ results in a drastic decrease of the thermally stimulated luminescence (TSL) intensity in the whole investigated temperature range and in the appearance of a new complex Mg2+ - related TSL glow curve peak around 285 K. After irradiation in the Ce3+ - related 3.6 eV absorption band, the TSL intensity in GAGG:Ce,Mg is found to be comparable with that in the GAGG:Ce epitaxial film of similar composition. The Mg2+ - induced changes in the concentration, origin and structure of the crystal lattice defects and their influence on the scintillation characteristics of GAGG:Ce,Mg are discussed.

  6. Effects of Al concentration on microstructural characteristics and electrical properties of Al-doped ZnO thin films on Si substrates by atomic layer deposition.

    PubMed

    Lee, Ju Ho; Lee, Jae-Won; Hwang, Sooyeon; Kim, Sang Yun; Cho, Hyung Koun; Lee, Jeong Yong; Park, Jin-Seong

    2012-07-01

    Al-doped ZnO (AZO) thin films with various Al concentrations were synthesized on Si(001) substrates with native oxide layers by atomic layer deposition process. The effects of the Al concentration on the microstructural characteristics of the AZO thin films grown at 250 degrees C and the correlation between their microstructural characteristics and electrical properties of the AZO thin films were investigated by AFM, XRD, HRTEM and Hall measurements. The XRD and HRTEM results revealed that the crystallinity and electrical properties of the undoped ZnO thin films were enhanced by 2.48 at% Al doping. However, 12.62 at% Al doping induced the deterioration of their crystallinity and electrical properties due to the formation of nano-sized metallic Al clusters and randomly oriented ZnO-based nano-crystals. To enhance the electrical properties of the AZO thin films while maintaining their crystallinity and electrical properties, a moderate Al concentration has to be chosen under the solubility limit of Al in ZnO.

  7. Work function increase of Al-doped ZnO thin films by B+ ion implantation.

    PubMed

    Hong, Sang-Jin; Heo, Gi-Seok; Park, Jong-Woon; Lee, In-Hwan; Choi, Bum-Ho; Lee, Jong-Ho; Park, Se-Yeon; Shin, Dong-Chan

    2007-11-01

    The work function of an Al-doped ZnO (AZO) thin film can be increased via B+ ion implantation from 3.92 eV up to 4.22 eV. The ion implantation has been carried out with the ion dose of 1 x 10(16) cm(-2) and ion energy of 5 keV. The resistance of the B+ implanted AZO films has been a bit raised, while their transmittance is slightly lowered, compared to those of un-implanted AZO films. These behaviors can be explained by the doping profile and the resultant band diagram. It is concluded that the coupling between the B+ ions and oxygen vacancies would be the main reason for an increase in the work function and a change in the other properties. We also address that the work function is more effectively alterable if the defect density of the top transparent conducting oxide layer can be controlled.

  8. Sputter deposition of Al-doped ZnO films with various incident angles

    SciTech Connect

    Sato, Yasushi; Yanagisawa, Kei; Oka, Nobuto; Nakamura, Shin-ichi; Shigesato, Yuzo

    2009-09-15

    Al-doped ZnO (AZO) films were sputter deposited on glass substrates heated at 200 degree sign C under incident angles of sputtered particles at 0 degree sign (incidence normal to substrate), 20 deg., 40 deg., 60 deg., and 80 deg. In the case of normal incidence, x-ray diffraction pole figures show a strong [001] preferred orientation normal to the film surface. In contrast, in the case wherein the incident angles were higher than 60 degree sign , the [001] orientation inclined by 25 deg. - 35 deg. toward the direction of sputtered particles. Transmission electron microscopy revealed that the tilt angle of the [001] orientation increased with increasing angle of the incident sputtered particles, whereas the columnar structure did not show any sign of inclination with respect to the substrate plane.

  9. Quality-enhanced AlN epitaxial films grown on c-sapphire using ZnO buffer layer for SAW applications

    NASA Astrophysics Data System (ADS)

    Fu, Sulei; Li, Qi; Gao, Shuang; Wang, Guangyue; Zeng, Fei; Pan, Feng

    2017-04-01

    AlN epitaxial films with a thin ZnO buffer layer were successfully deposited on c-sapphire by DC magnetron sputtering for surface acoustic wave (SAW) applications. The effect of ZnO buffer layer thickness on structural properties of AlN epitaxial films and the related SAW properties were investigated systematically. The results revealed that a thin ZnO buffer layer can significantly enhance the crystalline quality of AlN films and release the strain in AlN films. The AlN films were epitaxially grown on ZnO buffered-substrate with orientation relationship of (0001) [ 10 1 bar 0 ] AlN//(0001) [ 10 1 bar 0 ] ZnO//(0001) [2 bar 110 ] Al2O3. High frequency SAW devices with a center frequency of 1.4 GHz, a phase velocity of 5600 m/s were achieved on the obtained AlN films. The optimum ZnO buffer layer thickness was found to be 10 nm, resulting in high-quality epitaxial AlN films with a FWHM value of the rocking curve of 0.84°, nearly zero stress and low insertion loss of SAW devices. This work offers an effective approach to achieve high-quality AlN epitaxial films on sapphire substrates for the applications of AlN-based SAW devices.

  10. Enhanced mechanism investigation on violet-blue emission of ZnO films by incorporating Al and Zn to form ZnO-Al-Zn films

    NASA Astrophysics Data System (ADS)

    Chen, Haixia; Ding, Jijun; Wang, Xiaomeng; Wang, Xiaojun; Chen, Guoxiang; Ma, Li

    2016-12-01

    ZnO, ZnO-Zn, ZnO-Al0.10-Zn and ZnO-Al0.15-Zn are deposited on glass substrates by radio frequency and direct current magnetron co-sputtering. Photoluminescence (PL) measurements show that the optical performances of samples are strongly dependent on both Al and Zn incoprations. The origin of the defect-related PL emission has been investigated for a long time. Several different hypotheses have been proposed, however, they are still under investigation. Especially for the blue emissions, its origins have been debated intensely for more than thirty years because of its sparsity and instability. In this paper, both violet and blue emissions are observed in all the samples. PL emission decreases sharply as Zn is doped in ZnO to form ZnO-Zn film. However, as both Al and Zn are simultaneously doped in ZnO to form ZnO-Al0.10-Zn film, PL emission conversely increases and attains the maxima. In addition, PL emission decreases again with the increase of Al target power to form ZnO-Al0.15-Zn film. We concluded that violet-blue emission is ascribed to defect types in reverse change trend with interstitial Zn, such as Zn vacancies. This is different from previous universal hypothesis that violet-blue emission is from interstitial Zn defects.

  11. Mechanisms of lighting enhancement of Al nanoclusters-embedded Al-doped ZnO film in GaN-based light-emitting diodes

    SciTech Connect

    Lee, Hsin-Ying; Chou, Ying-Hung; Lee, Ching-Ting

    2010-01-15

    Aluminum (Al)-doped ZnO (AZO) films with embedded Al nanoclusters were proposed and utilized to enhance the light output power and maximum operation current of GaN-based light-emitting diodes (LEDs). The AZO films were sputtered using ZnO and Al targets in a magnetron cosputtering system. With Al dc power of 7 W and ZnO 100 W ac power, the electron concentration of 4.1x10{sup 20} cm{sup -3}, electron mobility of 16.2 cm{sup 2}/V s, and resistivity of 7.2x10{sup -4} {Omega} cm were obtained for the deposited AZO film annealed at 600 deg. C for 1 min in a N{sub 2} ambient. As verified by a high resolution transmission electron microscopy, the deposited AZO films with embedded Al nanoclusters were clearly observed. A 35% increase in light output power of the GaN-based LEDs with Al nanoclusters-embedded AZO films was realized compared with the conventional LEDs operated at 500 mA. It was verified experimentally that the various characteristics of GaN-based LEDs including the antireflection, light scattering, current spreading, and the light extraction efficiency in light emission could be significantly enhanced with the use of Al nanoclusters-embedded AZO films.

  12. Optical characterization of pure and Al-doped ZnO prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Belka, Radosław; Keczkowska, Justyna; Kasińska, Justyna

    2016-09-01

    In this paper the preparation process and optical characterization of pure and Al3+ doped zinc oxide (Al:ZnO) coatings will be presented. ZnO based materials have been studied extensively due to their potential applications in optoelectronic devices as conductive gas sensors, transparent conductive, electrodes, solar cell windows, varistors, UVfilters or photovoltaic cells. It is II-VI semiconductor with wide-band gap of 3.37 eV and large exciton binding energy of 60meV. It is possible to improve the conductivity of ZnO coating by intentionally doping ZnO with aluminium ions during preparation process. Such transparent and conducting thin films, known as AZO (Aluminium Zinc Oxide) films, are very good candidate for application as transparent conducting materials in many optoelectronic devices. The well-known sol-gel method is used for preparation of solution, coated on glass substrates by dip coating process. Prepared samples were investigated by Raman and UV-VIS spectroscopy. Transmittance as well as specular and diffuse reflectance spectroscopy methods were used for studies of optical parameters. We found that Al admixture influences on optical bandgap of ZnO.

  13. Enhanced Performance in Al-Doped ZnO Based Transparent Flexible Transparent Thin-Film Transistors Due to Oxygen Vacancy in ZnO Film with Zn-Al-O Interfaces Fabricated by Atomic Layer Deposition.

    PubMed

    Li, Yang; Yao, Rui; Wang, Huanhuan; Wu, Xiaoming; Wu, Jinzhu; Wu, Xiaohong; Qin, Wei

    2017-04-05

    Highly conductive and optical transparent Al-doped ZnO (AZO) thin film composed of ZnO with a Zn-Al-O interface was fabricated by thermal atomic layer deposition (ALD) method. The as-prepared AZO thin film exhibits excellent electrical and optical properties with high stability and compatibility with temperature-sensitive flexible photoelectronic devices; film resistivity is as low as 5.7 × 10(-4) Ω·cm, the carrier concentration is high up to 2.2 × 10(21) cm(-3). optical transparency is greater than 80% in a visible range, and the growth temperature is below 150 °C on the PEN substrate. Compared with the conventional AZO film containing by a ZnO-Al2O3 interface, we propose that the underlying mechanism of the enhanced electrical conductivity for the current AZO thin film is attributed to the oxygen vacancies deficiency derived from the free competitive growth mode of Zn-O and Al-O bonds in the Zn-Al-O interface. The flexible transparent transistor based on this AZO electrode exhibits a favorable threshold voltage and Ion/Ioff ratio, showing promising for use in high-resolution, fully transparent, and flexible display applications.

  14. Photoluminescence and energy transfer in Tb{sup 3+}/Mn{sup 2+} co-doped ZnAl{sub 2}O{sub 4} glass ceramics

    SciTech Connect

    Lakshminarayana, Gandham; Wondraczek, Lothar

    2011-08-15

    We report on Tb{sup 3+} as efficient sensitizer for red photoemission from Mn{sup 2+}-centers in ZnO-B{sub 2}O{sub 3}-Al{sub 2}O{sub 3}-Si{sub 2}O-Na{sub 2}O-SrO glasses and corresponding gahnite glass ceramics. In comparison to singly or co-doped glasses, the glass ceramics exhibit significantly increased emission intensity. Structural considerations, ESR, and dynamic luminescence spectroscopy indicate partial incorporation of Mn{sup 2+} as well as Tb{sup 3+} into the crystalline phase, the former on octahedral Zn{sup 2+}-sites. Interionic distance and charge transfer probability between both species depend on crystallization conditions. This enables control of the energy transfer process and, hence, tunability of the color of photoemission by simultaneous emission from Tb{sup 3+} and Mn{sup 2+} centers. Concentration quenching in Mn{sup 2+}-singly doped materials was found at a critical dopant concentration of about 1.0 mol%. The energy transfer process was studied in detail by dynamic as well as static luminescence spectroscopy. Spectroscopic results suggest the application of the studied materials as single or dual-mode emitting phosphor for luminescent lighting. - Graphical abstract: In the prepared Tb{sup 3+}/Mn{sup 2+} codoped glass ceramics containing gahnite (ZnAl{sub 2}O{sub 4}) nanocrystals, the luminescence color is changed from green light to yellowish-red light with an increase in Mn{sup 2+} concentration due to enhanced energy transfer from Tb{sup 3+} to Mn{sup 2+} ions. This tunability should have potential applications in solid state lighting to produce white light, which can be obtained by appropriately optimizing the ratio of Tb{sup 3+}/Mn{sup 2+} ions under UV(350 nm) excitation. Highlights: > Photoluminescence from Mn{sup 2+} and Tb{sup 3+} singly and co-doped glasses and gahnite glass ceramics was studied. > Occurrence of energy transfer from Tb{sup 3+} to Mn{sup 2+} was confirmed. > Luminescence color tunability is achieved by varying dopant

  15. White luminescence and energy transfer process in Bi3+,Sm3+ co-doped Ca3Al2O6 phosphors

    NASA Astrophysics Data System (ADS)

    Wang, LongJun; Guo, Hai; Wei, YunLe; Noh, Hyeon Mi; Jeong, Jung Hyun

    2015-04-01

    Ca3Al2O6:Bi3+,Sm3+ phosphors were synthesized by conventional solid state reaction method and their luminescent properties were systemically investigated by excitation, emission spectra and decay curves measurement. Through an efficient energy transfer process from Bi3+ to Sm3+, the obtained phosphors exhibit emission from Bi3+ and Sm3+ with considerable intensity under near-ultraviolet excitation (300 nm). Tuning the content of Sm3+ can generate the varied hues from blue green to white. Our research will extend the understanding of interactions between Bi3+ and rare earth ions and show the potential application of Bi3+,Sm3+ co-doped phosphors in W-LEDs field.

  16. Enhancement of optical properties of hydrothermally synthesized TiO{sub 2}/ZrO{sub 2} nanoparticles by Al, Ce Co-doping

    SciTech Connect

    Tomar, Laxmi J.; Bhatt, Piyush J. Desai, Rahul K.; Chakrabarty, Bishwajit S.

    2015-06-24

    Al, Ce co-doped TiO{sub 2}/ZrO{sub 2} (TZ) nano composites have been prepared by hydrothermal method. The structural and optical properties of the obtained samples were investigated by X –ray diffraction (XRD) and UV-Visible spectroscopy respectively. It has been found that the crystallite size of all the samples was distributed in the range 9.19 to 17.41 nm. The content of anatase phase varied in the range 48.71 to 100% depending on doping. The dopant produced lattice strain in material and it was found between 0.027 - 0.069. A clear shift of absorption edge for different dopant has been observed from UV-Visible absorption spectra. The change in optical bandgap, refractive index, absorption co efficient and optical conductivity was also evaluated from absorption spectra.

  17. Structural and Magnetic Studies of Zn0.95Co0.05O and Zn0.90Co0.05Al0.05O

    NASA Astrophysics Data System (ADS)

    Murtaza, Saleem; Saadat, A. Siddiqi; Shahid, Atiq; M. Sabieh, Anwar

    2011-11-01

    Single-phase Zn0.95Co0.05O and Zn0.90Co0.05Al0.05O samples were prepared by a novel combustion method. X-ray diffraction studies exhibit the pure phase wurtzite structure of doped ZnO. Energy dispersive x-ray analysis confirms the incorporation of dopants into the host material. Scanning electron microscopy shows the ordered morphology in both of the samples. Temperature-dependent resistivity analysis describes the expected semiconducting behavior that is similar to the parent ZnO materials. Room-temperature magnetic measurements reveal the absence of ferromagnetism in Co-doped ZnO, while the Co and Al co-doped sample displays apparent room-temperature ferromagnetic behavior. The decrease of resistivity and presence of ferromagnetic behavior in Al-doped ZnCoO system corroborate the significant role of free carriers.

  18. RETRACTED: P-type Zno thin films fabricated by Al-N co-doping method at different substrate temperature

    NASA Astrophysics Data System (ADS)

    Yuan, Guodong; Ye, Zhizhen; Qian, Qing; Zhu, Liping; Huang, Jingyun; Zhao, Binghui

    2005-01-01

    This article has been retracted at the request of the Editor-in-Chief. Please see Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy). The editors and publisher would like to confirm the retraction of this paper at the request of the author Guodong Yuan. Reason: The SIMS profile published in this paper had already been included in articles published in Mater. Lett., 58 (2004) 3741-3744, and Thin Solid Films, 484 (2005) 420-425 describing a sample prepared under different conditions. The author did not notify either the Journal of Crystal Growth Editors or the coauthors of this fact. The author apologizes sincerely to the readers, referees, and Editors for violating the guidelines of ethical publication.Also the author apologizes to the coauthors for mishandling of the manuscript.

  19. Alternative Dielectric Films for rf MEMS Capacitive Switches Deposited using Atomic Layer Deposited Al2O3/ZnO Alloys

    DTIC Science & Technology

    2006-07-02

    switches deposited using atomic layer deposited Al2O3/ZnO alloys Cari F. Herrmann a,b, Frank W. DelRio a, David C. Miller a, Steven M. George b,c, Victor...The layer is an alloy mixture of Al2O3 and ZnO and is proposed for use as charge dissipative layers in which the dielectric onstant is significant...investigates Al2O3/ZnO ALD alloys deposited at 100 and 177 ◦C and compares their material properties. Auger electron pectroscopy was used to determine the

  20. The effect of sol aging time on Structural and Optical properties of sol gel ZnO doped Al

    NASA Astrophysics Data System (ADS)

    El Hallani, G.; Fazouan, N.; Liba, A.; Khuili, M.

    2016-10-01

    Currently the doped or undoped ZnO semiconductor is of great importance in the field of electronic and optoelectronic devices such as transparent conductors and optical windows of solar cells based on silicon. ZnO thin films are produced by several techniques such as sol-gel method which is a chemical technique usually dependent on solution conditions. However, the sol gel aging time is an important parameter, which can have a significant impact on the properties of thin films. In this work we studied the effect of aging times (0h, 24h, 48h, 72h, 1 week) of the precursor solution on the structural and optical properties of ZnO doped Al (3 at.%). Thin films prepared by spin coating on glass substrates were investigated. The X-ray diffraction (XRD) analysis shows that the ZnO doped Al (3 at.%) exhibit the hexagonal wurtzite structure with a preferential orientation along [002] direction. The shift of (002) peaks towards higher diffraction angles is observed with sol aging time and also, a variation of crystallite sizes and thickness of thin films are shown with increasing sol aging time. All films present an average optical transmittance around 90% in the visible range with some interference fringes indicating a relative smoothness of films. We note an increasing in transmittance level with sol aging time from 0h to 48h. We can conclude that the aging times of the precursor solution influences the structural and optical properties of studied thin films.

  1. Effects of annealing pressure and Ar+ sputtering cleaning on Al-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Wang, Jiwei; Mei, Yong; Lu, Xuemei; Fan, Xiaoxing; Kang, Dawei; Xu, Panfeng; Tan, Tianya

    2016-11-01

    Post-treatments of Al-doped ZnO films fabricated by sol-gel method were studied in condition of annealing in air, vacuum and protective ambient, as well as the follow-up Ar+ sputtering cleaning. The effect of annealing pressure on resistivity of AZO films was investigated from 105 to 10-4 Pa, where the resistivity decreased four orders of magnitude as the pressure decreased and approached to its minimum at 10 Pa. It was observed that the main decreasing of resistivity occurred in a very narrow range of middle vacuum (between 100 and 10 Pa) and high vacuum was dispensable. The XRD and XPS characterizations demonstrated that the radical increasing of oxygen vacancy, Zn interstitial and substitution of Al3+ for Zn2+ under middle vacuum were responsible for the significant enhancement of conductivity. The follow-up Ar+ sputtering cleaning can further decrease the resistivity through removing the chemisorbed oxygen on film surface and grain boundaries, meanwhile fulfil the surface texture process, and thus improve both electrical and optical performances for applications.

  2. Synthesis Al complex and investigating effect of doped ZnO nanoparticles in the electrical and optical efficiency of OLEDS

    NASA Astrophysics Data System (ADS)

    Shahedi, Zahra; Jafari, Mohammad Reza

    2017-01-01

    In this study, an organometallic complex based on aluminum ions is synthesized. And it is utilized as fluorescent material in the organic light-emitting diodes (OLEDs). The synthesized complex was characterized using XRD, UV-Vis, FT-IR as well as PL spectroscopy analyses. The energy levels of Al complex were determined by cyclic voltammetry measurements. Then, the effects of ZnO nanoparticles (NPs) of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS, on the electrical and optical performance of the organic light-emitting diodes have been investigated. For this purpose, two samples containing ITO/PEDOT:PSS/PVK/Alq3/PBD/Al with two different concentration and two samples containing ITO/PEDOT:PSS:ZnO/PVK/Alq3/PBD/Al with two different concentration were prepared. Then, hole transport, electron transport and emissive layers were deposited by the spin coating method and the cathode layer (Al) was deposited by the thermal evaporation method. The OLED simulation was also done by constructing the model and choosing appropriate parameters. Then, the experimental data were collected and the results interpreted both qualitatively and quantitatively. The results of the simulations were compared with experimental data of the J-V spectra. Comparing experimental data and simulation results showed that the electrical and optical efficiency of the samples with ZnO NPs is appreciably higher than the samples without ZnO NPs.

  3. Effects of In, Al and Sn dopants on the structural and optical properties of ZnO thin films.

    PubMed

    Caglar, Yasemin; Ilican, Saliha; Caglar, Mujdat; Yakuphanoglu, Fahrettin

    2007-07-01

    Effect of In, Al and Sn dopants on the optical and structural properties of ZnO thin films have been investigated by X-ray diffraction technique and optical characterization method. X-ray diffraction patterns confirm that the films have polycrystalline nature. The thin films have (002) as the preferred orientation. This (002) preferred orientation is due to the minimal surface energy which the hexagonal structure, c-plane to the ZnO crystallites, corresponds to the densest packed plane. The grain size values of the films are found to be 29.0, 35.2 and 39.5 nm for In, Al and Sn doped ZnO thin films, respectively. The optical band gaps of the films were calculated. The absorption edge shifts to the lower wavelengths with In, Al and Sn dopants. The inclusion of dopant into films expands also width of localized states as E(UIn)>E(UAl)>E(USn). The refractive index dispersion curves obey the single oscillator model. The dispersion parameters and optical constants of the films were determined. These parameters changed with In, Al and Sn dopants.

  4. A facile cost-effective method for preparing poinsettia-inspired superhydrophobic ZnO nanoplate surface on Al substrate with corrosion resistance

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Han, Huilong; Li, Junfeng; Fan, Xiaoliang; Ding, Haimin; Wang, Jinfeng

    2016-02-01

    This paper reports an easy method to imitate the "poinsettia leaves" by constructing ZnO nanoplates on Al substrate. Using ammonium hydroxide as the reactant, together with zinc nitrate hexahydrate, randomly distributed ZnO nanoplates can be fabricated on the Al substrate directly. The morphology of the ZnO nanoplates can be controlled by the growth time, and the nanoplate growth mechanism is discussed in detail. After modification with stearic acid, the nanoplate surface shows a stable superhydrophobicity. Moreover, the superhydrophobic ZnO nanoplate surface showed much smaller corrosion current density, reduced 23,088-fold from the bare Al 6061 substrate. This facile and low-cost method may open a new avenue in the design and fabrication of superhydrophobic surfaces on Al materials with anticorrosive property.

  5. Temperature-dependence on the structural, optical, and magnetic properties of Al-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Lu, Xiaofei; Liu, Yongsheng; Si, Xiaodong; Shen, Yulong; Yu, Wenying; Wang, Wenli; Luo, Xiaojing; Zhou, Tao

    2016-12-01

    Al-doped ZnO nanoparticles synthesized by a hydrothermal method at relatively low temperature synthesis and anneal were reported in this paper. The XRD results reveal that all the samples have a hexagonal wurtzite structure. A higher synthesis temperature leads to a slight increase in the grain size and improvement of the crystal quality. Different morphologies evolved from acicular closely-packed morphology to dandelion-like 3D nanostructures can be obtained by controlling the synthesis temperatures. Moreover, the influence of synthesis temperature on optical property indicates that the absorption ability in ultraviolet region declines with increasing the synthesis temperature. In addition, the annealed nanoparticles have an enhancement of the room temperature ferromagnetism (RT-FM) and the saturation magnetization (MS). Those results suggest that Al-doped ZnO nanoparticles synthesized at relatively low temperature could be a promising candidate for photosensitive and room temperature nanolasers applications.

  6. Energy transfer based photoluminescence spectra of co-doped (Dy3+ + Sm3+): Li2O-LiF-B2O3-ZnO glasses for orange emission

    NASA Astrophysics Data System (ADS)

    Vijayalakshmi, L.; Naveen Kumar, K.; Vijayalakshmi, R. P.

    2016-07-01

    The present paper brings out the results concerning the preparation and optical properties of Sm3+ and Dy3+ each ion separately in different concentrations (0.3, 0.5, 1.0 and 1.5 mol.%) and also together doped (x mol.% Dy3+ + 1.5 mol.% Sm3+): Li2O-LiF-B2O3-ZnO (where x = 0.5, 1.0 and 1.5 mol.%) glasses by a melt quenching method. Structural and thermal properties have been extensively studied for those glasses by XRD and TG/DTA. The compositional analysis has been carried out from FTIR spectral profile. Optical absorption spectral studies were also carried out. Sm3+: LBZ glasses have displayed an intense orange emission at 603 nm (4G5/2 → 6H7/2) with an excitation wavelength at 403 nm and Dy3+: LBZ glasses have shown two emissions located at 485 nm (4F9/2 → 6H15/2; blue) and 574 nm (4F9/2 → 6H13/2; yellow) with an excitation wavelength at 385 nm. Remarkably, it has been identified that the significant increase in the reddish orange emission of Sm3+ ions and diminished yellow emission pertaining to Dy3+ ions in the co-doped LBZ glass system under the excitation of 385 nm which relates to Dy3+ ions. This could be due energy transfer from Dy3+ to Sm3+. The non-radiative energy transfer from Dy3+ to Sm3+ is explained in terms of their emission spectra, donor lifetime, energy level diagram and energy transfer characteristic factors. These significantly enhanced orange emission exhibited glasses could be suggested as potential optical glasses for orange luminescence photonic devices.

  7. Genesis of flake-like morphology and dye-sensitized solar cell performance of Al-doped ZnO particles: a study

    NASA Astrophysics Data System (ADS)

    Sengupta, D.; Mondal, B.; Mukherjee, K.

    2017-03-01

    In dye-sensitized solar cell (DSSC) application, the particulate morphologies of photo-anode facilitate efficient dye loading and thus lead to better photo-conversion efficiency than their thin film counterpart. However, till date, the electronic and optical properties as well as the DSSC application of Al-doped ZnO (AZO) particles as photo-anode material is studied less than thin films. Herein, phase formation behavior, morphology evolution, optical properties, and dye-sensitized solar cell performance of wet chemically prepared ZnO and AZO (dopant level: 1-4 mol%) particles are studied. It is found that Al doping modulates significantly the ZnO morphology which in turn results the maximum dye adsorption as well as best photo-conversion efficiency at optimum dopant concentration. Specifically, the nanoparticle of ZnO turns predominantly to flake-like morphology with a higher surface area when 2 mol% Al is doped. Such morphology modulation is expected, since the crystallinity, lattice parameters, and lattice strain of ZnO changes appreciably with Al doping. The variations of optical properties (absorbance, diffused reflectance, and band gap) of AZO materials as compared to primitive ZnO are also identified through UV-vis studies. An attempt is made here to correlate the structural features with the photovoltaic performances of ZnO and AZO.

  8. Competition between (001) and (111) MgO thin film growth on Al-doped ZnO by oxygen plasma assisted pulsed laser deposition

    SciTech Connect

    Xiao, Bo; Yang, Qiguang; Walker, Brandon; Gonder, Casey A.; Romain, Gari C.; Mundle, Rajeh; Bahoura, Messaoud; Pradhan, A. K.

    2013-06-07

    We report on the study of epitaxial MgO thin films on (0001) Al-doped ZnO (Al: ZnO) underlayers, grown by oxygen plasma assisted pulsed laser deposition technique. A systematic investigation of the MgO thin films was performed by X-ray diffraction and atomic force microscopy, along with the current-voltage characteristics. A distinguished behavior was observed that the preferred MgO orientation changes from (111) to (001) in the films as the growth temperature increases. Two completely different in-plane epitaxial relationships were also determined from X-ray diffraction as: [110]MgO//[1120]Al: ZnO and [110]MgO//[1100]Al: ZnO for (001) MgO with 60 Degree-Sign rotated triplet domains, and [110]MgO//[1120]Al: ZnO for (111) MgO with 180 Degree-Sign rotated twin. The pronounced temperature dependence indicates a reconciliation of the nucleation driving forces among surface, interfacial, and strain energy for heteroepitaxy of cubic MgO on hexagonal Al: ZnO. The related interfacial atomic registry is considered to be important to the formation of unusual (001) MgO on hexagonal crystals. In addition, the electrical characterization revealed a dramatic reduction of the leakage current in (001) MgO thin films, whereas the small grain size of (111) MgO is identified by atomic force microscopy as a main cause of large leakage current.

  9. High carrier concentration ZnO nanowire arrays for binder-free conductive support of supercapacitors electrodes by Al doping.

    PubMed

    Zheng, Xin; Sun, Yihui; Yan, Xiaoqin; Sun, Xu; Zhang, Guangjie; Zhang, Qian; Jiang, Yaru; Gao, Wenchao; Zhang, Yue

    2016-12-15

    Doping semiconductor nanowires (NWs) for altering their electrical and optical properties is a critical strategy for tailoring the performance of nanodevices. Here, we prepared in situ Al-doped ZnO nanowire arrays by using continuous flow injection (CFI) hydrothermal method to promote the conductivity. This reasonable method offers highly stable precursor concentration for doping that effectively avoid the appearance of the low conductivity ZnO nanosheets. Benefit from this, three orders of magnitude rise of the carrier concentration from 10(16)cm(-3) to 10(19)cm(-3) can be achieved compared with the common hydrothermal (CH) mothed in Mott-Schottky measurement. Possible effect of Al-doping was discussed by first-principle theory. On this basis, Al-doped ZnO nanowire arrays was developed as a binder-free conductive support for supercapacitor electrodes and high capacitance was triggered. It is owing to the dramatically decreased transfer resistance induced by the growing free-moving electrons and holes. Our results have a profound significance not merely in the controlled synthesis of other doping nanomaterials by co-precipitation method but also in the application of binder-free energy materials or other materials.

  10. The formation of tungsten doped Al2O3/ZnO coatings on aluminum by plasma electrolytic oxidation and their application in photocatalysis

    NASA Astrophysics Data System (ADS)

    Stojadinović, Stevan; Vasilić, Rastko; Radić, Nenad; Tadić, Nenad; Stefanov, Plamen; Grbić, Boško

    2016-07-01

    Tungsten doped Al2O3/ZnO coatings are formed by plasma electrolytic oxidation of aluminum substrate in supporting electrolyte (0.1 M boric acid + 0.05 M borax + 2 g/L ZnO) with addition of different concentrations of Na2WO4·2H2O. The morphology, crystal structure, chemical composition, and light absorption characteristics of formed surface coatings are investigated. The X-ray diffraction and X-ray photoelectron spectroscopy results indicate that formed surface coatings consist of alpha and gamma phase of Al2O3, ZnO, metallic tungsten and WO3. Obtained results showed that incorporated tungsten does not have any influence on the absorption spectra of Al2O3/ZnO coatings, which showed invariable band edge at about 385 nm. The photocatalytic activity of undoped and tungsten doped Al2O3/ZnO coatings is estimated by the photodegradation of methyl orange. The photocatalytic activity of tungsten doped Al2O3/ZnO coatings is higher thanof undoped Al2O3/ZnO coatings; the best photocatalytic activity is ascribed to coatings formed in supporting electrolyte with addition of 0.3 g/L Na2WO4·2H2O. Tungsten in Al2O3/ZnO coatings acts as a charge trap, thus reducing the recombination rate of photogenerated electron-hole pairs. The results of PL measurements are in agreement with photocatalytic activity. Declining PL intensity corresponds to increasing photocatalytic activity of the coatings, indicating slower recombination of electron-hole pairs.

  11. Chemo-sensors development based on low-dimensional codoped Mn2O3-ZnO nanoparticles using flat-silver electrodes

    PubMed Central

    2013-01-01

    Background Semiconductor doped nanostructure materials have attained considerable attention owing to their electronic, opto-electronic, para-magnetic, photo-catalysis, electro-chemical, mechanical behaviors and their potential applications in different research areas. Doped nanomaterials might be a promising owing to their high-specific surface-area, low-resistances, high-catalytic activity, attractive electro-chemical and optical properties. Nanomaterials are also scientifically significant transition metal-doped nanostructure materials owing to their extraordinary mechanical, optical, electrical, electronic, thermal, and magnetic characteristics. Recently, it has gained significant interest in manganese oxide doped-semiconductor materials in order to develop their physico-chemical behaviors and extend their efficient applications. It has not only investigated the basic of magnetism, but also has huge potential in scientific features such as magnetic materials, bio- & chemi-sensors, photo-catalysts, and absorbent nanomaterials. Results The chemical sensor also displays the higher-sensitivity, reproducibility, long-term stability, and enhanced electrochemical responses. The calibration plot is linear (r2 = 0.977) over the 0.1 nM to 50.0 μM 4-nitrophenol concentration ranges. The sensitivity and detection limit is ~4.6667 μA cm-2 μM-1 and ~0.83 ± 0.2 nM (at a Signal-to-Noise-Ratio, SNR of 3) respectively. To best of our knowledge, this is the first report for detection of 4-nitrophenol chemical with doped Mn2O3-ZnO NPs using easy and reliable I-V technique in short response time. Conclusions As for the doped nanostructures, NPs are introduced a route to a new generation of toxic chemo-sensors, but a premeditate effort has to be applied for doped Mn2O3-ZnO NPs to be taken comprehensively for large-scale applications, and to achieve higher-potential density with accessible to individual chemo-sensors. In this report, it is also discussed the prospective

  12. Structural and electronic properties of ZnO nanoparticles grown on p-Si and Al2O3 substrates by using spin coating and thermal treatment.

    PubMed

    No, Young Soo; Son, Dong Ick; Leem, Jae Hyeon; Kim, Su Youn; Oh, Do Hyun; Kim, Tae Whan

    2008-10-01

    ZnO nanoparticles were formed on p-Si and Al2O3 substrates by using spin coating and thermal treatment method. Scanning electron microscopy images and X-ray energy dispersive spectrometry profiles showed that ZnO nanoparticles were formed on p-Si and Al2O3 substrates. X-ray diffraction patterns showed that ZnO nanoparticles formed on the p-Si substrates had polycrystalline hexagonal wurtzite structures and that those formed on the Al2O3 substrates had a c-axis preferential orientation. X-ray photoelectron spectroscopy profiles showed that the O 1s and the Zn 2p peaks corresponding to the ZnO nanoparticles were observed.

  13. Influence of (Co-Mn) co-doping on the microstructures, optical properties of sol-gel derived ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Neena, D.; Shah, A. H.; Deshmukh, K.; Ahmad, H.; Fu, D. J.; Kondamareddy, K. K.; Kumar, P.; Dwivedi, R. K.; Sing, V.

    2016-03-01

    A systematic investigation on the synthesis, characterization, optical and magnetic properties of (Co-Mn) co doped ZnO nanoparticles synthesized by sol-gel method is reported. Structural, Optical and magnetic properties of present sample have been characterized by X-ray diffraction (XRD), UV-VIS-NIR spectroscopy and VSM techniques. The single- phased wurtzite structure has been confirmed by XRD analysis. The nanoparticles nature of the samples and their crystallinity has been investigated by TEM measurements. Optical studies revealed red shift (3.315-3.289 eV) with increasing Mn doping concentration in the absorbance spectrum. Magnetization studies showed that Zn0.7Co0.2Mn0.1O exhibits ferromagnetic behavior.

  14. Fabrication of nanostructured Al-doped ZnO thin film for methane sensing applications

    NASA Astrophysics Data System (ADS)

    Shafura, A. K.; Sin, N. D. Md.; Azhar, N. E. I.; Saurdi, I.; Uzer, M.; Mamat, M. H.; Shuhaimi, A.; Alrokayan, Salman A. H.; Khan, Haseeb A.; Rusop, M.

    2016-07-01

    CH4 gas sensor was fabricated using spin-coating method of the nanostructured ZnO thin film. Effect of annealing temperature on the electrical and structural properties of the film was investigated. Dense nanostructured ZnO film are obtained at higher annealing temperature. The optimal condition of annealing temperature is 500°C which has conductivity and sensitivity value of 3.3 × 10-3 S/cm and 11.5%, respectively.

  15. Enhancement ZnO nanofiber as semiconductor for dye-sensitized solar cells by using Al doped

    NASA Astrophysics Data System (ADS)

    Sutanto, Bayu; Arifin, Zainal; Suyitno, Hadi, Syamsul; Pranoto, Lia Muliani; Agustia, Yuda Virgantara

    2016-03-01

    The purpose of this research is to produce Al-doped ZnO (AZO) nanofibers in order to enhance the performance of Dye-Sensitized Solar Cell (DSSC). AZO nanofiber semiconductor was manufactured by electrospinning process of Zinc Acetate Dehydrate (Zn(CH3COO)2) solution and precursor of Polyvinyl Acetate (PVA). The doping process of Al was built by dissolving 0-4 wt% in concentrations of AlCl3 to Zinc Acetate. AZO green fiber was sintered at temperature 500°C for an hour. The result shows that Al doped ZnO had capability to increase the electrical conductivity of semiconductor for doping 0, 1, 2, 3, and 4 wt% for 2,07×10-3; 3,71×10-3; 3,59 ×10-3; 3,10 ×10-3 and 2,74 ×10-3 S/m. The best performance of DSSC with 3 cm2 active area was obtained at 1 wt% Al-ZnO which the value of VOC, ISC, FF, and efficiency were 508,43 mV, 3,125 mA, 38,76%, and 0,411% respectively. These coincide with the electrical conductivity of semiconductor and the crystal size of XRD result that has the smallest size as compared to other doping variations.

  16. Plasmonic enhancement of blue emission from ZnO nanorods grown on the anodic aluminum oxide (AAO) template

    NASA Astrophysics Data System (ADS)

    Norek, Małgorzata; Łuka, Grzegorz; Godlewski, Marek; Płociński, Tomasz; Michalska-Domańska, Marta; Stępniowski, Wojciech J.

    2013-04-01

    Luminescent properties of ZnO nanorods covered with Ag nanoparticles are examined. Nanorods were synthesized on AAO templates using Atomic Layer Deposition (ALD) technique. Two types of the samples were prepared with different arrangement of ZnO nanorods and doping conditions. Nanorods of the second type were codoped with Al, to stimulate defect-related emissions. The ZnO material fills heterogeneously the interior of the AAO nanopores and has hexagonal, wurtzite structure. Both types of structures exhibit a broad defect-related emission at about 440 nm, most probably related to recombination at zinc interstitial (Zni) defects. This emission in samples with a random distribution of ZnO:Al nanorods and finer Ag nanoparticles is enhanced by factor of ˜2.5 upon Ag deposition. The so-obtained material is interesting from the point of view of its application in blue range emitting diodes.

  17. Synthesis of nano ZnO thin film on Al foil by rf glow discharge plasma and its effect on E. coli and P. aeruginosa

    NASA Astrophysics Data System (ADS)

    Panigrahi, Jagannath; Nayak, Bijan B.; Behera, Debadhyan; Subudhi, Umakanta; Acharya, Bhabani S.

    2012-09-01

    Nano ZnO thin films were deposited on thin Al foils by a rf glow discharge plasma method in which sublimed zinc acetate vapor (precursor) reacted with oxygen plasma inside a low-pressure reactor. The films were microstructurally characterized using XRD, TEM, FESEM, optical reflectance and micro-Raman spectroscopy methods. In view of the good scope of ZnO coating in food packaging, the antibacterial activity in the ZnO thin films was studied by exposing the films to E. coli and P. aeruginosa for up to 8 h. Bacterial cell inhibition of up to 98-99 % was observed in the thin films.

  18. Computational discovery of lanthanide doped and Co-doped Y{sub 3}Al{sub 5}O{sub 12} for optoelectronic applications

    SciTech Connect

    Choudhary, Kamal; Chernatynskiy, Aleksandr; Phillpot, Simon R.; Sinnott, Susan B.; Mathew, Kiran; Bucholz, Eric W.; Hennig, Richard G.

    2015-09-14

    We systematically elucidate the optoelectronic properties of rare-earth doped and Ce co-doped yttrium aluminum garnet (YAG) using hybrid exchange-correlation functional based density functional theory. The predicted optical transitions agree with the experimental observations for single doped Ce:YAG, Pr:YAG, and co-doped Er,Ce:YAG. We find that co-doping of Ce-doped YAG with any lanthanide except Eu and Lu lowers the transition energies; we attribute this behavior to the lanthanide-induced change in bonding environment of the dopant atoms. Furthermore, we find infrared transitions only in case of the Er, Tb, and Tm co-doped Ce:YAG and suggest Tm,Ce:YAG and Tb,Ce:YAG as possible functional materials for efficient spectral up-conversion devices.

  19. Characteristics of Al-doped ZnO films grown by atomic layer deposition for silicon nanowire photovoltaic device.

    PubMed

    Oh, Byeong-Yun; Han, Jin-Woo; Seo, Dae-Shik; Kim, Kwang-Young; Baek, Seong-Ho; Jang, Hwan Soo; Kim, Jae Hyun

    2012-07-01

    We report the structural, electrical, and optical characteristics of Al-doped ZnO (ZnO:Al) films deposited on glass by atomic layer deposition (ALD) with various Al2O3 film contents for use as transparent electrodes. Unlike films fabricated by a sputtering method, the diffraction peak position of the films deposited by ALD progressively moved to a higher angle with increasing Al2O3 film content. This indicates that Zn sites were effectively replaced by Al, due to layer-by-layer growth mechanism of ALD process which is based on alternate self-limiting surface chemical reactions. By adjusting the Al2O3 film content, a ZnO:Al film with low electrical resistivity (9.84 x 10(-4) Omega cm) was obtained at an Al2O3 film content of 3.17%, where the Al concentration, carrier mobility, optical transmittance, and bandgap energy were 2.8 wt%, 11.20 cm2 V(-1) s(-1), 94.23%, and 3.6 eV, respectively. Moreover, the estimated figure of merit value of our best sample was 8.2 m7Omega(-1). These results suggest that ZnO:Al films deposited by ALD could be useful for electronic devices in which especially require 3-dimensional conformal deposition of the transparent electrode and surface passivation.

  20. Structural and photoluminescence properties of Cd and Cu co-doped zinc oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Samuel, T.; Sujatha, K.; Rao, K. Ramachandra; Rao, M. C.

    2016-05-01

    Cd and Cu co-doped ZnO nanoparticles were synthesized by Polyol method and subsequently have been characterized by their structure, optical and photoluminescence studies. XRD and PSA results revealed the formation of Cd and Cu co-doped ZnO nanoparticles with an average crystallite size of 50 nm and average particle size of 246 nm. From Zeta Potential measurements the Zeta Potential was found to be - 29.2 eV indicating the stability of prepared nanoparticles. From Uv-Vis studies, it is found that the absorption of undoped ZnO is less compared with Cd and Cu co-doped ZnO and the absorbance increases with increase in dopant concentration. Photoluminescence studies revealed that the samples are with high structural and optical quality.

  1. Al-doped ZnO contact to CdZnTe for x- and gamma-ray detector applications

    NASA Astrophysics Data System (ADS)

    Roy, U. N.; Camarda, G. S.; Cui, Y.; Gul, R.; Hossain, A.; Yang, G.; Mundle, R. M.; Pradhan, A. K.; James, R. B.

    2016-06-01

    The poor adhesion of common metals to CdZnTe (CZT)/CdTe surfaces has been a long-standing challenge for radiation detector applications. In this present work, we explored the use of an alternative electrode, viz., Al-doped ZnO (AZO) as a replacement to common metallic contacts. ZnO offers several advantages over the latter, such as having a higher hardness, a close match of the coefficients of thermal expansion for CZT and ZnO, and better adhesion to the surface of CZT due to the contact layer being an oxide. The AZO/CZT contact was investigated via high spatial-resolution X-ray response mapping for a planar detector at the micron level. The durability of the device was investigated by acquiring I-V measurements over an 18-month period, and good long-term stability was observed. We have demonstrated that the AZO/CZT/AZO virtual-Frisch-grid device performs fairly well, with comparable or better characteristics than that for the same detector fabricated with gold contacts.

  2. Dependence on pressure of the refractive indices of wurtzite ZnO, GaN, and AlN

    SciTech Connect

    Goni, AR; Kaess, F; Reparaz, JS; Alonso, MI; Garriga, M; Callsen, G; Wagner, MR; Hoffmann, A; Sitar, Z

    2014-07-25

    We have measured both the ordinary and extraordinary refractive index of m-plane cuts of wurtzite ZnO, GaN, and AlN single crystals at room temperature and as a function of hydrostatic pressure up to 8 GPa. For that purpose we have developed an alternative optical interference method, called bisected-beam method, which leads, in general, to high contrast interference fringes. Its main feature, however, is to be particularly suitable for high pressure experiments with the diamond anvil cell, when the refractive index of the sample is low and similar to that of diamond and/or the pressure transmitting medium, as is the case here. For all three wide-gap materials we observe a monotonous decrease of the ordinary and extraordinary refractive indices with increasing pressure, being most pronounced for GaN, less marked for ZnO, and the smallest for AlN. The frequency dependence of the refractive indices was extrapolated to zero energy using a critical-point-plus-Lorentz-oscillator model of the ordinary and extraordinary dielectric function. In this way, we determined the variation with pressure of the electronic part (no-phonon contribution) of the static dielectric constant epsilon(infinity). Its volume derivative, r = d ln epsilon(infinity)/d ln V, serves as single scaling coefficient for comparison with experimental and/or theoretical results for other semiconductors, regarding the pressure effects on the dielectric properties. We have obtained an ordinary/extraordinary average value (r) over bar of 0.49(15) for ZnO, 1.22(9) for GaN, and 0.32(4) for AlN. With the values for the ordinary and extraordinary case being within experimental uncertainty, there is thus no apparent change in dielectric anisotropy under pressure for these wurtzite semiconductors. Results are discussed in terms of the pressure-dependent electronic band structure of the materials.

  3. Properties of atomic-layer-deposited Al2O3/ZnO dielectric films grown at low temperature for RF MEMS

    NASA Astrophysics Data System (ADS)

    Herrmann, Cari F.; Del Rio, Frank W.; George, Steven M.; Bright, Victor M.

    2005-01-01

    Al2O3/ZnO alloy films were grown at 100°C using atomic layer deposition (ALD) techniques. It has been previously established that the resistivity of these films can be tuned over a wide range by varying the amount of Zn in the film. Al2O3/ZnO ALD alloy films can therefore be designed with a dielectric constant high enough to provide a large down-state capacitance and a resistivity low enough to promote the dissipation of trapped charges. The material and electrical properties of the Al2O3/ZnO ALD films were investigated using Auger electron spectroscopy (AES), nanoindentation, and mercury probe measurements. Chemical analysis using AES confirmed the presence of both Al and Zn in the alloys. The nanoindentation measurements were used to calculate the Young's modulus and hardness of the films. Pure Al2O3 ALD was determined to have a modulus between 150 and 155 GPa and a hardness of ~8 GPa, while the results for pure ZnO ALD indicated a modulus between 120 and 140 GPa and a hardness of ~5 GPa. An Al2O3/ZnO ALD alloy displayed a modulus of 140-145 GPa, which falls between the two pure films, and a hardness of ~8 GPa, which is similar to the pure Al2O3 film. The dielectric constants of the ALD films were calculated from the mercury probe measurements and were determined to be around 6.8. These properties indicate that the Al2O3/ZnO ALD films can be engineered as a property specific dielectric layer for RF MEMS devices.

  4. Origin of the Phase Transition of AlN, GaN, and ZnO Nanowires

    SciTech Connect

    Wu, Y.; Chen, G.; Ye, H.; Zhu, Y.; Wei, S. H.

    2009-06-01

    The stabilities of AlN, GaN, and ZnO nanowires/nanorods with different structures and sizes are investigated using first-principles calculations. We found a structure transformation from the graphitelike phase to wurtzite phase as the diameter and length of the nanowire increases. We show that this is due to the competition between the bond energy, the Coulomb energy, and the energy originating from the dipole field of the wurtzite structure. A mechanism of growing uniform nanowires using a graphitelike structure as a precursor is proposed through analyzing the phase diagram of these materials.

  5. CdS/CdSe-sensitized solar cell based on Al-doped ZnO nanoparticles prepared by the decomposition of zinc acetate solid solution

    NASA Astrophysics Data System (ADS)

    Deng, Jianping; Wang, Minqiang; Ye, Wei; Fang, Junfei; Zhang, Pengchao; Yang, Yongping; Yang, Zhi

    2017-01-01

    In the study, Al-doped ZnO nanoparticles (Al-ZnO NPs) were prepared by the decomposition of zinc acetate solid solution. The X-ray diffraction results showed that Al3+ was successfully doped without the formation of Al and Al2O3 impurity phases. The less Al-doping did not change the hexagonal wurtzite crystal structure of ZnO. The ratio of Al to Al + Zn (9.05%) measured by the energy dispersive X-ray also confirmed the formation of Al-ZnO. The Al-ZnO NPs were used as the photoanode material to prepare CdS/CdSe-sensitized solar cell. Compared with the cell based on commercial ZnO NPs (C-ZnO), the short-circuit current density and the fill factor of the cell were increased from 5.8 mA/cm2 and 34.1% (C-ZnO) to 7.78 mA/cm2 and 48.7% (Al-ZnO), respectively. The cell efficiency was increased from 1.01% (C-ZnO) to (1.9%) (Al-ZnO) and the increase percentage reached 88.1%. The results of electrochemical impedance spectroscopy and open-circuit voltage-decay suggested the lower carrier transport resistance and the longer electron lifetime of Al-ZnO-based cell.

  6. Optical and electrical properties of ZnO nanocrystal thin films passivated by atomic layer deposited Al2O3

    NASA Astrophysics Data System (ADS)

    Choi, Ji-Hyuk; Kim, Jungwoo; Oh, Soong Ju; Kim, Daekyoung; Kim, Yong-Hoon; Chae, Heeyeop; Kim, Hyoungsub

    2016-07-01

    While colloidal semiconductor nanocrystal (NC) is preferred for use in solution-based optoelectronic devices, the large number of surface defects associated with its high surface-to-volume ratio degrades the optimal performance of NC-based devices due to the extensive trapping of free carriers available for charge transport. Here, we studied a simple and effective strategy to control the degree of passivation and doping level of solution-deposited ZnO NC films by infilling with ultra-thin Al2O3 using an atomic layer deposition (ALD) technique. According to various spectroscopic, microstructural, and electrical analyses, the ALD-Al2O3 treatment dramatically reduced the number of surface trap states with high ambient stability while simultaneously supplied excess carriers probably via a remote doping mechanism. As a consequence, the field-effect transistors built using the ZnO NC films with ALD-Al2O3 treatment for an optimal number of cycles exhibited significantly enhanced charge transport.

  7. Facile synthesis of yellow-emitting CaAlSiN3:Ce3+ phosphors and the enhancement of red-component by co-doping Eu2+ ions

    NASA Astrophysics Data System (ADS)

    Chen, Jingjing; Zhao, Yang; Li, Guanghao; Mao, Zhiyong; Wang, Dajian; Bie, Lijian

    2017-04-01

    In this paper, facile synthesis of CaAlSiN3:Ce3+ yellow-emitting phosphors under atmospheric pressure at a moderate temperature and their photoluminescent properties are reported. The prepared CaAlSiN3:Ce3+ phosphors exhibit a broad yellow emission band positioned at 580 nm and covering a bandwidth of 150 nm. The thermal stability of CaAlSiN3:Ce3+ phosphors shows obvious superiority than the commercial YAG: Ce3+ phosphor, indicating its promising application prospect in power LEDs. In addition, the enhancement of red-light component for CaAlSiN3:Ce3+ phosphor is demonstrated by co-doping Eu2+ ions. This study offers a facile route to prepare CaAlSiN3:Ce3+ yellow-emitting phosphors, which may be used as a promising candidate for high performance white LEDs.

  8. Codoped direct-gap semiconductor scintillators

    DOEpatents

    Derenzo, Stephen E.; Bourret-Courchesne, Edith; Weber, Marvin J.; Klintenberg, Mattias K.

    2006-05-23

    Fast, bright inorganic scintillators at room temperature are based on radiative electron-hole recombination in direct-gap semiconductors, e.g. CdS and ZnO. The direct-gap semiconductor is codoped with two different impurity atoms to convert the semiconductor to a fast, high luminosity scintillator. The codopant scheme is based on dopant band to dopant trap recombination. One dopant provides a significant concentration of carriers of one type (electrons or holes) and the other dopant traps carriers of the other type. Examples include CdS:In,Te; CdS:In,Ag; CdS:In,Na; ZnO:Ga,P; ZnO:Ga,N; ZnO:Ga,S; and GaN:Ge,Mg.

  9. Codoped direct-gap semiconductor scintillators

    DOEpatents

    Derenzo, Stephen Edward; Bourret-Courchesne, Edith; Weber, Marvin J.; Klintenberg, Mattias K.

    2008-07-29

    Fast, bright inorganic scintillators at room temperature are based on radiative electron-hole recombination in direct-gap semiconductors, e.g. CdS and ZnO. The direct-gap semiconductor is codoped with two different impurity atoms to convert the semiconductor to a fast, high luminosity scintillator. The codopant scheme is based on dopant band to dopant trap recombination. One dopant provides a significant concentration of carriers of one type (electrons or holes) and the other dopant traps carriers of the other type. Examples include CdS:In,Te; CdS:In,Ag; CdS:In,Na; ZnO:Ga,P; ZnO:Ga,N; ZnO:Ga,S; and GaN:Ge,Mg.

  10. The effect of sulfur and zirconium Co-doping on the oxidation of NiCrAl

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1987-01-01

    The adhesion behavior of Al2O3 scales formed on NiCrAl+Zr alloys was examined as a function of both sulfur and zirconium doping levels. In general, very high levels of zirconium were required to counteract the detrimental effects of sulfur. A sulfur-zirconium adherence map was constructed, as determined from the oxidation and spalling behavior in 1100 C cyclic tests. For low sulfur alloys, the amount of zirconium required for adherence at any given sulfur level can be described by Zr greater than 600 S sup 0.2 (in ppma). These results underscore the importance of sulfur to adhesion mechanisms and suggests that sulfur gettering is a first order effect of reactive element additions to MCrAl alloys.

  11. The effect of sulfur and zirconium co-doping on the oxidation of NiCrAl

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1988-01-01

    The adhesion behavior of Al2O3 scales formed on NiCrAl+Zr alloys was examined as a function of both sulfur and zirconium doping levels. In general, very high levels of zirconium were required to counteract the detrimental effects of sulfur. A sulfur-zirconium adherence map was constructed, as determined from the oxidation and spalling behavior in 1100 C cyclic tests. For low sulfur alloys (less than 500 ppma), the amount of zirconium required for adherence at any given sulfur level can be described by Zr greater than 600 S(0.2) (in ppma). These results underscore the importance of sulfur to adhesion mechanisms and suggest that sulfur gettering is a first order effect of reactive element additions to MCrAl alloys.

  12. High rate reactive magnetron sputter deposition of Al-doped ZnO with unipolar pulsing and impedance control system

    SciTech Connect

    Nishi, Yasutaka; Hirohata, Kento; Tsukamoto, Naoki; Sato, Yasushi; Oka, Nobuto; Shigesato, Yuzo

    2010-07-15

    Al-doped ZnO (AZO) films were deposited on quartz glass substrates, unheated and heated to 200 deg. C, using reactive sputtering with a special feedback system of discharge impedance combined with midfrequency pulsing. A planar Zn-Al alloy target was connected to the switching unit, which was operated in a unipolar pulse mode. The oxidation of the target surface was precisely controlled by a feedback system for the entire O{sub 2} flow ratio including ''the transition region''. The deposition rate was about 10-20 times higher than that for films deposited by conventional sputtering using an oxide target. A deposition rate of AZO films of 390 nm/min with a resistivity of 3.8x10{sup -4} {Omega} cm and a transmittance in the visible region of 85% was obtained when the films were deposited on glass substrates heated to 200 deg. C with a discharge power of 4 kW.

  13. Electronic structure of Al- and Ga-doped ZnO films studied by hard X-ray photoelectron spectroscopy

    SciTech Connect

    Gabás, M.; Ramos Barrado, José R.; Torelli, P.; Barrett, N. T.

    2014-01-01

    Al- and Ga-doped sputtered ZnO films (AZO, GZO) are semiconducting and metallic, respectively, despite the same electronic valence structure of the dopants. Using hard X-ray photoelectron spectroscopy we observe that both dopants induce a band in the electronic structure near the Fermi level, accompanied by a narrowing of the Zn 3d/O 2p gap in the valence band and, in the case of GZO, a substantial shift in the Zn 3d. Ga occupies substitutional sites, whereas Al dopants are in both substitutional and interstitial sites. The latter could induce O and Zn defects, which act as acceptors explaining the semiconducting character of AZO and the lack of variation in the optical gap. By contrast, mainly substitutional doping is consistent with the metallic-like behavior of GZO.

  14. Effect of Al and Ca co-doping, in the presence of Te, in superconducting YBCO whiskers growth.

    PubMed

    Pascale, Lise; Truccato, Marco; Operti, Lorenza; Agostino, Angelo

    2016-10-01

    High-Tc superconducting cuprates (HTSC) such as YBa2Cu3O7 - x (YBCO) are promising candidates for solid-state THz applications based on stacks of intrinsic Josephson junctions (IJJs) with atomic thickness. In view of future exploitation of IJJs, high-quality superconducting YBCO tape-like single crystals (whiskers) have been synthesized from Ca-Al-doped precursors in the presence of Te. The main aim of this paper is to determine the importance of the simultaneous use of Al, Te and Ca in promoting YBCO whiskers growth with good superconducting properties (Tc = 79-84 K). Further, single-crystal X-ray diffraction (SC-XRD) refinements of tetragonal YBCO whiskers (P4/mmm) are reported to fill the literature lack of YBCO structure investigations. All the as-grown whiskers have also been investigated by means of X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Our results demonstrate that the interplay of Ca, Te and Al elements is clearly necessary in order to obtain superconducting YBCO whiskers. The data obtained from SC-XRD analyses confirm the highly crystalline nature of the whiskers grown. Ca and Al enter the structure by replacing the Y and the octahedral coordinated Cu1 site, respectively, as in other similar orthorhombic compounds, while Te does not enter the structure of whiskers but its presence in the precursor is essential to the growth of the crystals.

  15. Direct ultraviolet excitation of an amorphous AlN:praseodymium phosphor by codoped Gd{sup 3+} cathodoluminescence

    SciTech Connect

    Maqbool, Muhammad; Ahmad, I.; Richardson, H. H.; Kordesch, M. E.

    2007-11-05

    Sputter deposited thin film amorphous AlN:Pr (1 at. %) emits in the blue-green (490-530 nm) and red ({approx}650 nm) regions of the visible spectrum under electron excitation. The addition of Gd 1 at. % in the film enhances the blue emission by an order of magnitude. The enhancement in the blue region is a result of cathodoluminescence from Gd{sup 3+} at 313 nm. The optical bandgap of amorphous AlN is about 210 nm, so that the film is transparent in the ultraviolet, allowing the Gd emission to excite the Pr{sup 3+} ions. No significant quenching of the Gd emission is observed when the Gd and Pr ions are mixed. The blue enhancement is observed even with the two films containing each of the ions that are separated by a 500 {mu}m thick quartz spacer, showing that the enhancement is due entirely to UV radiation.

  16. On the variations of optical property and electronic structure in heavily Al-doped ZnO films during double-step growth process

    SciTech Connect

    Hu, Q. C.; Ding, K. Zhang, J. Y.; Yan, F. P.; Pan, D. M.; Huang, F.; Chiou, J. W.

    2014-01-13

    We have investigated the variations of optical property and electronic structure in heavily Al-doped ZnO (AZO) films during the growth process, which were formed by first creating Zn vacancies in O{sub 2}-rich atmosphere and second filling the vacancies with Zn atoms in Zn-vapor atmosphere. After the first step, the high-resistance AZO films have the same optical bandgap with nominally undoped ZnO, indicating that negligible variations in the fundamental bandgap happened to the AZO films although Al atom was incorporated into the ZnO lattice. After the second step, once free electrons were brought into the lattice by Zn-filling, the optical transition energy blueshifts due to the band-filling effect. X-ray absorption fine structure measurements suggest that Zn-filling process decreased the unoccupied states of the conduction band, but not raised the conduction band minimum.

  17. Structural and superconducting properties of co-doped YBa2-xLaxCu3-xMxOz and La-free YBa2Cu3-xMxOz (M = Al, Zn) high-TC superconductors

    NASA Astrophysics Data System (ADS)

    Hao, S. J.; Jin, W. T.; Guo, C. Q.; Zhang, H.

    2012-05-01

    Two co-doped high-Tc superconducting systems, YBa2-xLaxCu3-xAlxOz and YBa2-xLaxCu3-xZnxOz (0 ⩽ x ⩽ 0.3), both of which have not been reported up to the present, were synthesized. The structural and superconducting properties have been investigated by X-ray diffraction (XRD) and DC magnetization measurement. Comparing the properties of these co-doped systems with single-doped systems YBa2Cu3-xAlxOz and YBa2Cu3-xZnxOz, it shows that in the Al-single-doped YBCO system, the depression of the critical temperature (Tc) with doping is stronger than that in (La, Al)-co-doped system, however, in the Zn-single-doped system, the Tc descends slower than that in (La, Zn)-co-doped system. This is possibly due to the opposite change of the distance between the Ba site and the CuO2 plane induced by the La doping. Besides, the La doping has another effect of improving the solid solubility compared with the Al- or Zn-single-doped system.

  18. Mg co-doping effects on Ce doped Y3(Ga,Al)5O12 scintillator

    NASA Astrophysics Data System (ADS)

    Kamada, Kei; Yamaji, Akihiro; Kurosawa, Shunsuke; Yokota, Yuui; Ohashi, Yuji; Yoshikawa, Akira

    2017-02-01

    Nonstoichiometric Lu3Al5+xO12 (x= 0.05, 0.15, 0.35, 0, -0.05, -0.15, -0.35) crystals were grown by the μ-PD method. Luminescence and scintillation properties such as absorption, excitation and emission spectra, light yield and decay time were evaluated. Expected anti-site defect related host emission have been observed in 250-420nm. Emission intensity was increased by increasing the nonstochiometry. The x=-0.35 sample showed the highest light yield of around 12000 photons/MeV and slowest scintillation decay time of 1.96μs.

  19. Investigation of the interrelation between the chemical state and the electric properties in Al-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Wang, Jinzhao; Ni, Dongfang; Zhang, Tianjin; Wang, Duofa; Liang, Kun

    2015-09-01

    Transparent conducting Al-doped ZnO (AZO) thin films were prepared on glass substrates by radio frequency magnetron sputtering in pure Ar. The influence of the annealing atmosphere on the microstructure, chemical state, electric and optical properties of the AZO films was investigated with X-ray diffraction, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy and Hall measurements. The AZO thin films annealed under vacuum had the highest carrier concentration of 2.488 × 1020 cm-3 and a Hall mobility of 16.35 cm2 V-1 s-1, while the AZO thin films annealed in air had the lowest carrier concentration of 4.182 × 1017 cm-3 and a Hall mobility of 2.375 cm2 V-1 s-1. The fitted narrow-scan O1 s spectra revealed that O1 s was composed of three components. The AZO thin films annealed under vacuum appeared to have a higher proportion of medium binding energy which correspond to O2- ions in the oxygen-deficient regions within the ZnO matrix, and have a lower proportion of high binding energy component which correspond to loosely bound chemisorbed oxygen. It believed that the oxygen vacancies and chemisorbed oxygen of the films played an important role in the electrical conductance. The carrier concentration increased with the formation of oxygen vacancies. The Hall mobility increased with desorption of the loosely bound oxygen.

  20. A clear effect of charge compensation through Na{sup +} co-doping on the luminescence spectra and decay kinetics of Nd{sup 3+}-doped CaAl{sub 4}O{sub 7}

    SciTech Connect

    Puchalska, M.; Watras, A.

    2016-06-15

    We present a detailed analysis of luminescence behavior of singly Nd{sup 3+} doped and Nd{sup 3+}, Na{sup +} co-doped calcium aluminates powders: Ca{sub 1−x}Nd{sub x}Al{sub 4}O{sub 7} and Ca{sub 1−2x}Nd{sub x}Na{sub x}Al{sub 4}O{sub 7} (x=0.001–0.1). Relatively intense Nd{sup 3+} luminescence in IR region corresponding to typical {sup 4}F{sub 3/2}→{sup 4}I{sub J} (J=9/2–13/2) transitions with maximum located at about 1079 nm was obtained in all samples on direct excitation into f–f levels. The effect of dopant concentration and charge compensation by co-doping with Na{sup +} ions on morphology and optical properties were studied. The results show that both, the Nd{sup 3+} concentration and the alkali metal co-doping affected the optical properties but had no influence on the powders morphology. The studies of luminescence spectra (298 and 77 K) in a function of dopant concentration showed an increasing distortion of the local symmetry of Nd{sup 3+}with raising activator content due to certain defects created in the crystal lattice. On the other hand Na{sup +} addition led to significant narrowing of absorption and luminescence bands and also a reduction of the number of their components, showing smaller disturbance of Nd{sup 3+} ions local symmetries. Consequently, charge compensated by Na{sup +} co-doping materials showed significantly enhanced Nd{sup 3+} luminescence. The decrease of emission intensity and luminescence lifetimes with increase of activator concentration was attributed mainly to phonon-assisted cross-relaxation processes between Nd{sup 3+} ions. Analysis with Inokuti–Hirayama model indicated dipole–dipole mechanism of ion-ion interaction. Na{sup +} addition led to much smaller concentration quenching due to smaller clustering of dopant ions in CaAl{sub 4}O{sub 7} lattice.

  1. Eu2+,Dy3+ codoped SrAl2O4 nanocrystalline phosphor for latent fingerprint detection in forensic applications

    NASA Astrophysics Data System (ADS)

    Sharma, Vishal; Das, Amrita; Kumar, Vinay

    2016-01-01

    In this work, europium and dysprosium doped strontium aluminate (SrAl2O4:Eu2+,Dy3+) nanophosphor is synthesized and its novel application for the detection of latent fingerprints on various contact surfaces is reported. The SrAl2O4:Eu2+,Dy3+ is synthesized using a combustion method and shows long-lasting afterglow luminescence. The powder particles are characterized using field emission scanning electron microscopy (FE-SEM), SEM-energy dispersive x-ray analysis, x-ray diffraction and photoluminescence spectrophotometry. The FE-SEM image analysis reveals that the nanoparticles are mostly 8-15 nm in size with an irregular spherical shape. This nano-structured powder was applied to fresh and aged fingerprints deposited on porous, semi-porous and non-porous contact surfaces, such as ordinary colored paper, glossy paper, glass, aluminum foil, a yellow foil chocolate wrapper, a soft drink can, a PET bottle, a compact disc and a computer mouse. The results are reproducible and show great sensitivity and high contrast in the developed fingermark regions on these surfaces. These nanophosphor particles also show a strong and long-lasting afterglow property, making them a suitable candidate for use as a fingerprint developing agent on luminescent and highly patterned surfaces. These kinds of powders have shown that they can remove the interference from background luminescence, which is not possible using ordinary luminescent fingerprinting powders.

  2. Room Temperature Growth of Al-Doped ZnO Thin Films by Reactive DC Sputtering Technique with Metallic Target

    NASA Astrophysics Data System (ADS)

    Hasuike, Noriyuki; Nishio, Koji; Kisoda, Kenji; Harima, Hiroshi

    2013-01-01

    We prepared Al-deopd ZnO (AZO) films by reactive DC sputtering method using metallic target at room temperature. All the tested AZO films (0<[Al]<8.9%) with the transmittance above 85% in visible region were successfully grown on quartz substrate. All the AZO films have wurtzite structure with no impurity phase. The AZO films with [Al]<2.9% have the preferential orientation in c-axis direction, and the orientation became indistinct as increasing in Al content. In the optical measurement, the absorption edge was shifted from 3.30 to 3.66 eV due to Burstein-Moss effect, and the electron densities were roughly estimated at 2.5×1019 to 1.5×1021 cm-3, respectively. On the other hand, the high transmittance in infrared region suggested low electron mobility. Since this gives rise to the high electric resistivity, the further improvements and optimization of the growth conditions are required for the realization of AZO based transparent conductive.

  3. Dopant-induced bandgap shift in Al-doped ZnO thin films prepared by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Hung-Chun Lai, Henry; Basheer, Tahseen; Kuznetsov, Vladimir L.; Egdell, Russell G.; Jacobs, Robert M. J.; Pepper, Michael; Edwards, Peter P.

    2012-10-01

    A series of 1 at. % Al-doped ZnO (AZO) films were deposited onto glass substrates by a spray pyrolysis technique. We find that the observed blue shift in the optical bandgap of 1% AZO films is dominated by the Burstein Moss effect. The Fermi level for an 807 nm thick AZO film rose by some 0.16 eV with respect to the edge of the conduction band. By controlling the film thickness, all AZO films exhibit the same lattice strain values. The influence of strain-induced bandgap shift was excluded by selecting films with nearly the same level of bandgap volume-deformation potentials, and the differences in out-plain strain and in-plain stress remained effectively constant.

  4. Structural, optical, morphological and electrical properties of undoped and Al-doped ZnO thin films prepared using sol—gel dip coating process

    NASA Astrophysics Data System (ADS)

    Boukhenoufa, N.; Mahamdi, R.; Rechem, D.

    2016-11-01

    In this work, sol—gel dip-coating technique was used to elaborate ZnO pure and ZnO/Al films. The impact of Al-doped concentration on the structural, optical, surface morphological and electrical properties of the elaborated samples was investigated. It was found that better electrical and optical performances have been obtained for an Al concentration equal to 5%, where the ZnO thin films exhibit a resistivity value equal to 1.64104 Ω·cm. Moreover, highest transparency has been recorded for the same Al concentration value. The obtained results from this investigation make the developed thin film structure a potential candidate for high optoelectronic performance applications.

  5. Isoelectronic co-doping

    DOEpatents

    Mascarenhas, Angelo

    2004-11-09

    Isoelectronic co-doping of semiconductor compounds and alloys with deep acceptors and deep donors is used to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, N and Bi, to customize solar cells, thermal voltaic cells, light emitting diodes, photodetectors, and lasers on GaP, InP, GaAs, Ge, and Si substrates. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  6. Near infrared ray annealing effects on the properties of Al-doped ZnO thin films prepared by spin-coating method.

    PubMed

    Jun, Min-Chul; Park, Sang-Uk; Chae, Moon-Soon; Shin, Dong-Jin; Ha, Jae-Geun; Koo, Sang-Mo; Lee, Kyung-Ju; Moon, Byung-Moo; Song, Chi-Young; Koh, Jung-Hyuk

    2013-09-01

    In this research, we will present Al doped ZnO thin films for transparent conducting oxide applications. Aluminum doped zinc oxide (AZO) thin films have been deposited on the glass substrates by sol-gel spin-coating method using zinc acetate dehydrate (Zn(CH3COO)2 2H2O) and aluminum chloride hexahydrate (AlCl3 x 6H2O) as cation sources. In this study, we investigated the effects of near infrared ray (NIR) annealing on the structural, optical and electrical characteristics of the AZO thin films. The experimental results showed that AZO thin films have a hexagonal wurtzite crystal structure and had a good transmittance higher than 85% within the visible wavelength region. It was also found that the additional energy of NIR helps to improve the electrical properties of Al doped ZnO transparent conducting oxides.

  7. Effect of aging under ambient conditions on the optical properties of Al-doped ZnO thin films deposited by direct current sputtering

    NASA Astrophysics Data System (ADS)

    Barhoumi, A.; Leroy, G.; Duponchel, B.; Gest, J.; Guermazi, S.

    2017-01-01

    Transparent and conductive Al-doped ZnO (AZO) thin films were deposited on a glass substrate by direct current sputtering. In a previous study, we noted the influence of time on structural and electrical characteristics of films. In the present paper, the effect of a two-year aging under ambient conditions on the optical properties was investigated. A global improvement of the optical properties of AZO thin films was observed. The optical transmittance spectra revealed a high transmittance more than 90% in the Vis-NIR regions and a high absorption in the ultraviolet range. It is assumed that the crystallinity segregation leads to the decrease of optical scattering. The results from the optical measurements showed a reorganization of the structure leading to the degradation of the structural homogeneity. Nevertheless, the evolution of the figure of merit shows that Al-doped ZnO is a good candidate for the manufacturing and the commercialization of transparent conducting oxide devices.

  8. Selective growth of catalyst-free ZnO nanowire arrays on Al:ZnO for device application

    SciTech Connect

    Chung, T. F.; Luo, L. B.; He, Z. B.; Leung, Y. H.; Shafiq, I.; Yao, Z. Q.; Lee, S. T.

    2007-12-03

    Vertically aligned ZnO nanowire (NW) arrays have been synthesized selectively on patterned aluminum-doped zinc oxide (AZO) layer deposited on silicon substrates without using any metal catalysts. The growth region was defined by conventional photolithography with an insulating template. Careful control of the types of template materials and growth conditions allows good alignment and growth selectivity for ZnO NW arrays. Sharp ultraviolet band-edge peak observed in the photoluminescence spectra of the patterned ZnO NW arrays reveals good optical qualities. The current-voltage characteristics of ZnO NWs/AZO/p-Si device suggest that patterned and aligned ZnO NW arrays on AZO may be used in optoelectronic devices.

  9. Influence of electron beam irradiation on nonlinear optical properties of Al doped ZnO thin films for optoelectronic device applications in the cw laser regime

    NASA Astrophysics Data System (ADS)

    Antony, Albin; Pramodini, S.; Poornesh, P.; Kityk, I. V.; Fedorchuk, A. O.; Sanjeev, Ganesh

    2016-12-01

    We present the studies on third-order nonlinear optical properties of Al doped ZnO thin films irradiated with electron beam at different dose rate. Al doped ZnO thin films were deposited on a glass substrate by spray pyrolysis deposition technique. The thin films were irradiated using the 8 MeV electron beam from microtron ranging from 1 kG y to 5 kG y. Nonlinear optical studies were carried out by employing the single beam Z-scan technique to determine the sign and magnitude of absorptive and refractive nonlinearities of the irradiated thin films. Continuous wave He-Ne laser operating at 633 nm was used as source of excitation. The open aperture Z-scan measurements indicated the sample displays reverse saturable absorption (RSA) process. The negative sign of the nonlinear refractive index n2 was noted from the closed aperture Z-scan measurements indicates, the films exhibit self-defocusing property due to thermal nonlinearity. The third-order nonlinear optical susceptibility χ(3) varies from 8.17 × 10-5 esu to 1.39 × 10-3 esu with increase in electron beam irradiation. The present study reveals that the irradiation of electron beam leads to significant changes in the third-order optical nonlinearity. Al doped ZnO displays good optical power handling capability with optical clamping of about ∼5 mW. The irradiation study endorses that the Al doped ZnO under investigation is a promising candidate photonic device applications such as all-optical power limiting.

  10. Recombination luminescence and trap levels in undoped and Al-doped ZnO thin films on quartz and GaSe (0 0 0 1) substrates

    SciTech Connect

    Evtodiev, I.; Caraman, I.; Leontie, L.; Rusu, D.-I.; Dafinei, A.; Nedeff, V.; Lazar, G.

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer ZnO films on GaSe create electron trapping states and PL recombination levels. Black-Right-Pointing-Pointer Zn and Al diffusion in GaSe produces low-energy widening of its PL emission. Black-Right-Pointing-Pointer ZnO:Al films on GaSe lamellas are suitable for gas-discharge lamp applications. -- Abstract: Photoluminescence spectra of ZnO and ZnO:Al (1.00, 2.00 and 5.00 at.%) films on GaSe (0 0 0 1) lamellas and amorphous quartz substrates, obtained by annealing, at 700 K, of undoped and Al-doped metal films, are investigated. For all samples, the nonequilibrium charge carriers recombine by radiative band-to-band transitions with energy of 3.27 eV, via recombination levels created by the monoionized oxygen atoms, forming the impurity band laying in the region 2.00 - 2.70 eV. Al doping induces an additional recombination level at 1.13 eV above the top of the valence band of ZnO films on GaSe substrates. As a result of thermal diffusion of Zn and Al into the GaSe interface layer from ZnO:Al/GaSe heterojunction, electron trap levels located at 0.22 eV and 0.26 eV below the conduction band edge of GaSe, as well as a deep recombination level, responsible for the luminescent emission in the region 1.10 - 1.40 eV, are created.

  11. Evolution of Metallic Conductivity in Epitaxial ZnO Thin Films on Systematic Al Doping

    NASA Astrophysics Data System (ADS)

    Chinta, P. V.; Lozano, O.; Wadekar, P. V.; Hsieh, W. C.; Seo, H. W.; Yeh, S. W.; Liao, C. H.; Tu, L. W.; Ho, N. J.; Zhang, Y. S.; Pang, W. Y.; Lo, Ikai; Chen, Q. Y.; Chu, W. K.

    2017-04-01

    The metal-like behaviors and metal-semiconductor transition (MST) of highly conducting Zn1- x Al x O ( x = 1 at.% to 10 at.%) thin films deposited by cosputtering on a-Al2O3 have been investigated. The temperature-dependent transport properties reveal that the Zn1- x Al x O films were highly degenerate. The MST temperature ( T MST) varied from 190 K to 260 K with Al doping from x = 2 at.% to 10 at.%. A simple degenerate band model is used to explain the observed shift in the metal-like behaviors upon Al doping. An empirical approach is used to analyze the resistivity functional below TMST, taking into account the contributions from both the weak localization and Coulomb interactions in explaining the MST. Analysis by least-square fittings of measured data shows excellent agreement. The optical bandgap increases with carrier concentration as n Hall 2/3 , which is interpreted as the Burstein-Moss shift for a nonparabolic effective mass. Such nonparabolicity is scrutinized by quantitative comparisons of the plasma edge values n optical versus the n Hall values.

  12. Evolution of Metallic Conductivity in Epitaxial ZnO Thin Films on Systematic Al Doping

    NASA Astrophysics Data System (ADS)

    Chinta, P. V.; Lozano, O.; Wadekar, P. V.; Hsieh, W. C.; Seo, H. W.; Yeh, S. W.; Liao, C. H.; Tu, L. W.; Ho, N. J.; Zhang, Y. S.; Pang, W. Y.; Lo, Ikai; Chen, Q. Y.; Chu, W. K.

    2016-11-01

    The metal-like behaviors and metal-semiconductor transition (MST) of highly conducting Zn1-x Al x O (x = 1 at.% to 10 at.%) thin films deposited by cosputtering on a-Al2O3 have been investigated. The temperature-dependent transport properties reveal that the Zn1-x Al x O films were highly degenerate. The MST temperature (T MST) varied from 190 K to 260 K with Al doping from x = 2 at.% to 10 at.%. A simple degenerate band model is used to explain the observed shift in the metal-like behaviors upon Al doping. An empirical approach is used to analyze the resistivity functional below TMST, taking into account the contributions from both the weak localization and Coulomb interactions in explaining the MST. Analysis by least-square fittings of measured data shows excellent agreement. The optical bandgap increases with carrier concentration as n {Hall/2/3}, which is interpreted as the Burstein-Moss shift for a nonparabolic effective mass. Such nonparabolicity is scrutinized by quantitative comparisons of the plasma edge values n optical versus the n Hall values.

  13. Synthesis and down-conversion luminescence properties of Er3+/Yb3+ co-doped AlF3-PbF2-CaF2 powders

    NASA Astrophysics Data System (ADS)

    Liu, Fangchao; Han, Qun; Liu, Tiegen; Chen, Yaofei; Du, Yang; Yao, Yunzhi

    2015-08-01

    Er3+/Yb3+ co-doped oxy-fluoride powders with varying Er/Yb concentration were prepared by a melt quenching method at various sintering temperature. The effect of the Er/Yb doped concentration and sintering temperature were analyzed by using optical absorption and emission techniques. The Judd-Ofelt theory has been used to evaluate the three intensity parameters (Ωλ, where λ = 2, 4 and 6) and calculate the oscillator strengths (fc). Ultraviolet-to-visible emissions were observed under the excitation of a 325 nm CW laser. It was found that the down-conversion fluorescence intensity changes with the sintering temperature and Er/Yb content ratio, the results were explained with the level transitions in Er3+/Yb3+ co-doped systems. The intensity ratios (intensity of 437 nm as reference) of the luminescence spectra that the samples sintered at various temperature are relevant to Ω6 parameter which indicates the vibration amplitude of the Er-O distance. The sintering temperature also has an influence on the intensity ratios via affecting the thermalization of the excited 4I15/2 level.

  14. Nonequilibrium-Plasma-Synthesized ZnO Nanocrystals with Plasmon Resonance Tunable via Al Doping and Quantum Confinement.

    PubMed

    Greenberg, Benjamin L; Ganguly, Shreyashi; Held, Jacob T; Kramer, Nicolaas J; Mkhoyan, K Andre; Aydil, Eray S; Kortshagen, Uwe R

    2015-12-09

    Metal oxide semiconductor nanocrystals (NCs) exhibit localized surface plasmon resonances (LSPRs) tunable within the infrared (IR) region of the electromagnetic spectrum by vacancy or impurity doping. Although a variety of these NCs have been produced using colloidal synthesis methods, incorporation and activation of dopants in the liquid phase has often been challenging. Herein, using Al-doped ZnO (AZO) NCs as an example, we demonstrate the potential of nonthermal plasma synthesis as an alternative strategy for the production of doped metal oxide NCs. Exploiting unique, thoroughly nonequilibrium synthesis conditions, we obtain NCs in which dopants are not segregated to the NC surfaces and local doping levels are high near the NC centers. Thus, we achieve overall doping levels as high as 2 × 10(20) cm(-3) in NCs with diameters ranging from 12.6 to 3.6 nm, and for the first time experimentally demonstrate a clear quantum confinement blue shift of the LSPR energy in vacancy- and impurity-doped semiconductor NCs. We propose that doping of central cores and heavy doping of small NCs are achievable via nonthermal plasma synthesis, because chemical potential differences between dopant and host atoms-which hinder dopant incorporation in colloidal synthesis-are irrelevant when NC nucleation and growth proceed via irreversible interactions among highly reactive gas-phase ions and radicals and ligand-free NC surfaces. We explore how the distinctive nucleation and growth kinetics occurring in the plasma influences dopant distribution and activation, defect structure, and impurity phase formation.

  15. Local probe microscopic studies on Al-doped ZnO: Pseudoferroelectricity and band bending at grain boundaries

    SciTech Connect

    Kumar, Mohit; Basu, Tanmoy; Som, Tapobrata

    2016-01-07

    In this paper, based on piezoforce measurements, we show the presence of opposite polarization at grains and grain boundaries of Al-doped ZnO (AZO). The polarization can be flipped by 180° in phase by switching the polarity of the applied electric field, revealing the existence of nanoscale pseudoferroelectricity in AZO grown on Pt/TiO{sub 2}/SiO{sub 2}/Si substrate. We also demonstrate an experimental evidence on local band bending at grain boundaries of AZO films using conductive atomic force microscopy and Kelvin probe force microscopy. The presence of an opposite polarization at grains and grain boundaries gives rise to a polarization-driven barrier formation at grain boundaries. With the help of conductive atomic force microscopy, we show that the polarization-driven barrier along with the defect-induced electrostatic potential barrier account for the measured local band bending at grain boundaries. The present study opens a new avenue to understand the charge transport in light of both polarization and electrostatic effects.

  16. Fabrication of deep-profile Al-doped ZnO one- and two-dimensional lattices as plasmonic elements

    NASA Astrophysics Data System (ADS)

    Jensen, Flemming; Shkondin, Evgeniy; Takayama, Osamu; Larsen, Pernille V.; Mar, Mikkel D.; Malureanu, Radu; Lavrinenko, Andrei V.

    2016-09-01

    In this work, we report on fabrication of deep-profile one- and two-dimensional lattices made from Al-doped ZnO (AZO). AZO is considered as an alternative plasmonic material having the real part of the permittivity negative in the near infrared range. The exact position of the plasma frequency of AZO is doping concentration dependent, allowing for tuning possibilities. In addition, the thickness of the AZO film also affects its material properties. Physical vapor deposition techniques typically applied for AZO coating do not enable deep profiling of a plasmonic structure. Using the atomic layer deposition technique, a highly conformal deposition method, allows us to fabricate high-aspect ratio structures such as one-dimensional lattices with a period of 400 nm and size of the lamina of 200 nm in width and 3 μm in depth. Thus, our structures have an aspect ratio of 1:15 and are homogeneous on areas of 2×2 cm2 and more. We also produce two-dimensional arrays of circular nanopillars with similar dimensions. Instead of nanopillars hollow tubes with a wall thickness on demand from 20 nm up to a complete fill can be fabricated.

  17. Local probe microscopic studies on Al-doped ZnO: Pseudoferroelectricity and band bending at grain boundaries

    NASA Astrophysics Data System (ADS)

    Kumar, Mohit; Basu, Tanmoy; Som, Tapobrata

    2016-01-01

    In this paper, based on piezoforce measurements, we show the presence of opposite polarization at grains and grain boundaries of Al-doped ZnO (AZO). The polarization can be flipped by 180° in phase by switching the polarity of the applied electric field, revealing the existence of nanoscale pseudoferroelectricity in AZO grown on Pt/TiO2/SiO2/Si substrate. We also demonstrate an experimental evidence on local band bending at grain boundaries of AZO films using conductive atomic force microscopy and Kelvin probe force microscopy. The presence of an opposite polarization at grains and grain boundaries gives rise to a polarization-driven barrier formation at grain boundaries. With the help of conductive atomic force microscopy, we show that the polarization-driven barrier along with the defect-induced electrostatic potential barrier account for the measured local band bending at grain boundaries. The present study opens a new avenue to understand the charge transport in light of both polarization and electrostatic effects.

  18. Highly transparent and conductive Al-doped ZnO nanoparticulate thin films using direct write processing.

    PubMed

    Vunnam, S; Ankireddy, K; Kellar, J; Cross, W

    2014-05-16

    Solution processable Al-doped ZnO (AZO) thin films are attractive candidates for low cost transparent electrodes. We demonstrate here an optimized nanoparticulate ink for the fabrication of AZO thin films using scalable, low-cost direct write processing (ultrasonic spray deposition) in air at atmospheric pressure. The thin films were made via thermal processing of as-deposited films. AZO films deposited using the proposed nanoparticulate ink with further reducing in vacuum and rf plasma of forming gas exhibited optical transparency greater than 95% across the visible spectrum, and electrical resistivity of 0.5 Ω cm and it drops down to 7.0 × 10(-2) Ω cm after illuminating with UV light, which is comparable to commercially available tin doped indium oxide colloidal coatings. Various structural analyses were performed to investigate the influence of ink chemistry, deposition parameters, and annealing temperatures on the structural, optical, and electrical characteristics of the spray deposited AZO thin films. Optical micrographs confirmed the presence of surface defects and cracks using the AZO NPs ink without any additives. After adding N-(2-Aminoethyl)-3-aminopropylmethyldimethoxy silane to the ink, AZO films exhibited an optical transparency which was virtually identical to that of the plain glass substrate.

  19. Evolution of dielectric function of Al-doped ZnO thin films with thermal annealing: effect of band gap expansion and free-electron absorption.

    PubMed

    Li, X D; Chen, T P; Liu, Y; Leong, K C

    2014-09-22

    Evolution of dielectric function of Al-doped ZnO (AZO) thin films with annealing temperature is observed. It is shown that the evolution is due to the changes in both the band gap and the free-electron absorption as a result of the change of free-electron concentration of the AZO thin films. The change of the electron concentration could be attributed to the activation of Al dopant and the creation/annihilation of the donor-like defects like oxygen vacancy in the thin films caused by annealing.

  20. Interfacially Al-doped ZnO nanowires: greatly enhanced near band edge emission through suppressed electron-phonon coupling and confined optical field.

    PubMed

    Wu, Yiming; Dai, Yanmeng; Jiang, Shenlong; Ma, Chao; Lin, Yue; Du, Dongxue; Wu, Yukun; Ding, Huaiyi; Zhang, Qun; Pan, Nan; Wang, Xiaoping

    2017-04-05

    Aluminium (Al)-doped zinc oxide (ZnO) nanowires (NWs) with a unique core-shell structure and a Δ-doping profile at the interface were successfully grown using a combination of chemical vapor deposition re-growth and few-layer AlxOy atomic layer deposition. Unlike the conventional heavy doping which degrades the near-band-edge (NBE) luminescence and increases the electron-phonon coupling (EPC), it was found that there was an over 20-fold enhanced NBE emission and a notably-weakened EPC in this type of interfacially Al-doped ZnO NWs. Further experiments revealed a greatly suppressed nonradiative decay process and a much enhanced radiative recombination rate. By comparing the finite-difference time-domain simulation with the experimental results from intentionally designed different NWs, this enhanced radiative decay rate was attributed to the Purcell effect induced by the confined and intensified optical field within the interfacial layer. The ability to manipulate the confinement, transport and relaxation dynamics of ZnO excitons can be naturally guaranteed with this unique interfacial Δ-doping strategy, which is certainly desirable for the applications using ZnO-based nano-photonic and nano-optoelectronic devices.

  1. The Influence of Spark Plasma Sintering Temperature on the Microstructure and Thermoelectric Properties of Al,Ga Dual-Doped ZnO

    NASA Astrophysics Data System (ADS)

    Han, Li; Hung, Le Thanh; van Nong, Ngo; Pryds, Nini; Linderoth, Søren

    2013-07-01

    ZnO dual-doped with Al and Ga was prepared by spark plasma sintering using different sintering temperatures. The microstructural evolution and thermoelectric properties of the samples were investigated in detail. The samples obtained with sintering temperature above 1223 K had higher relative densities and higher electronic conductivity than the sample sintered at 1073 K. These results were supported by the solid-state reaction completion rate, which suggested that sintering temperature above 1223 K would be preferable for complete solid-state reaction of the samples. The sintering mechanism of ZnO particles and microstructure evolution at different sintering temperatures were investigated by simulation of the self-Joule-heating effect of the individual particles.

  2. WITHDRAWN: p-Type ZnO thin films fabricated by Al-N co-doping method at different substrate temperature

    NASA Astrophysics Data System (ADS)

    Yuan, Guodong; Ye, Zhizhen; Qian, Qing; Zhu, Liping; Huang, Jingyun; Zhao, Binghui

    2009-07-01

    This article has been retracted at the request of the Editor-in-Chief of the Journal of Crystal Growth. This article has been retracted; please see Elsevier Policy on Article Withdrawal: http://www.elsevier.com/locate/withdrawalpolicy.

  3. Electrically tunable diffraction efficiency from gratings in Al-doped ZnO

    NASA Astrophysics Data System (ADS)

    George, David; Li, Li; Lowell, David; Ding, Jun; Cui, Jingbiao; Zhang, Hualiang; Philipose, Usha; Lin, Yuankun

    2017-02-01

    Transparent conducting aluminum-doped zinc oxide (AZO) can be used as part of an active plasmonic device due to its electrically tunable permittivity, which is accomplished by changing the carrier concentration with electrical biasing. In this letter, we report a continuous electrical tuning of diffraction efficiency from AZO gratings in the visible range (specifically 532 nm) when the AZO is under bias voltages between -1 V and -3.5 V. The carrier concentration in AZO under negative bias has been measured and simulated. The diffraction efficiency changes have been explained by the carrier concentration variation and induced complex refractive index change at the Al2O3 and AZO interface. The reported results can lead toward the application of post-fabrication tuning of optoelectronic devices using AZO.

  4. Strong Energy-Transfer-Induced Enhancement of Luminescence Efficiency of Eu(2+)- and Mn(2+)-Codoped Gamma-AlON for Near-UV-LED-Pumped Solid State Lighting.

    PubMed

    Liu, Lihong; Wang, Le; Zhang, Chenning; Cho, Yujin; Dierre, Benjamin; Hirosaki, Naoto; Sekiguchi, Takashi; Xie, Rong-Jun

    2015-06-01

    A series of Eu(2+)- and Mn(2+)-codoped γ-AlON (Al1.7O2.1N0.3) phosphors was synthesized at 1800 °C under 0.5 MPa N2 by using the gas-pressure sintering method (GPS). Eu(2+) and Mn(2+) ions were proved to enter into γ-AlON host lattice by means of XRD, CL, and EDS measurements. Under 365 nm excitation, two emission peaks located at 472 and 517 nm, resulting from 4f(6)5d(1) → 4f(7) and (4)T1(4G) → (6)A1 electron transitions of Eu(2+) and Mn(2+), respectively, can be observed. Energy transfer from Eu(2+) to Mn(2+) was evidenced by directly observing appreciable overlap between the excitation spectrum of Mn(2+) and the emission spectrum of Eu(2+) as well as by the decreased decay time of Eu(2+) with increasing Mn(2+) concentration. The critical energy-transfer distance between Eu(2+) and Mn(2+) and the energy-transfer efficiency were also calculated. The mechanism of energy transfer was identified as a resonant type via a dipole-dipole mechanism. The external quantum efficiency was increased 7 times (from 7% for γ-AlON:Mn(2+) to 49% for γ-AlON:Mn(2+),Eu(2+) under 365 nm excitation), and color-tunable emissions from blue-green to green-yellow were also realized with the Eu(2+) → Mn(2+) energy transfer in γ-AlON.

  5. Thickness Effect of Al-Doped ZnO Window Layer on Damp Heat Stability of CuInGaSe2 Solar Cells: Preprint

    SciTech Connect

    Pern, F. J.; Mansfield, L.; DeHart, C.; Glick, S. H.; Yan, F.; Noufi, R.

    2011-07-01

    We investigated the damp heat (DH) stability of CuInGaSe2 (CIGS) solar cells as a function of thickness of the Al-doped ZnO (AZO) window layer from the 'standard' 0.12 μm to a modest 0.50 μm over an underlying 0.10-μm intrinsic ZnO buffer layer. The CIGS cells were prepared with external electrical contact using fine Au wire to the tiny 'standard' Ni/Al (0.05 μm/3 μm) metal grid contact pads. Bare cell coupons and sample sets encapsulated in a specially designed, Al-frame test structure with an opening for moisture ingress control using a TPT backsheet were exposed to DH at 85oC and 85% relative humidity, and characterized by current-voltage (I-V), quantum efficiency (QE), and (electrochemical) impedance spectroscopy (ECIS). The results show that bare cells exhibited rapid degradation within 50-100 h, accompanied by film wrinkling and delamination and corrosion of Mo and AlNi grid, regardless of AZO thickness. In contrast, the encapsulated cells did not show film wrinkling, delamination, and Mo corrosion after 168 h DH exposure; but the trend of efficiency degradation rate showed a weak correlation to the AZO thickness.

  6. Highly (0001)-oriented Al-doped ZnO polycrystalline films on amorphous glass substrates

    NASA Astrophysics Data System (ADS)

    Nomoto, Junichi; Inaba, Katsuhiko; Osada, Minoru; Kobayashi, Shintaro; Makino, Hisao; Yamamoto, Tetsuya

    2016-09-01

    Very thin aluminum-doped zinc oxide (AZO) films with a well-defined (0001) orientation and a surface roughness of 0.357 nm were deposited on amorphous glass substrates at a temperature of 200 °C by radio frequency magnetron sputtering, which are promising, particularly in terms of orientation evolution, surface roughness, and carrier transport, as buffer layers for the subsequent deposition of highly (0001)-oriented AZO polycrystalline films of 490 nm thickness by direct current (DC) magnetron sputtering. Sintered AZO targets with an Al2O3 content of 2.0 wt. % were used. DC magnetron sputtered AZO films on bare glass substrates showed a mixed (0001) and the others crystallographic orientation, and exhibited a high contribution of grain boundary scattering to carrier transport, resulting in reduced Hall mobility. Optimizing the thickness of the AZO buffer layers to 10 nm led to highly (0001)-oriented bulk AZO films with a marked reduction in the above contribution, resulting in AZO films with improved Hall mobility together with enhanced carrier concentration. The surface morphology and point defect density were also improved by applying the buffer layers, as shown by atomic force microscopy and Raman spectroscopy, respectively.

  7. Single and combined effects of aluminum (Al2O3) and zinc (ZnO) oxide nanoparticles in a freshwater fish, Carassius auratus.

    PubMed

    Benavides, María; Fernández-Lodeiro, Javier; Coelho, Pedro; Lodeiro, Carlos; Diniz, Mário S

    2016-12-01

    The increasing use of nanoparticles (NPs) worldwide has raised some concerns about their impact on the environment. The aim of the study was to assess the toxicity of metal oxide nanoparticles, singly or combined, in a freshwater fish (Carassius auratus). The fish were exposed for 7, 14, and 21 days to different concentrations of NPs (10 μg Al2O3.L(-1), 10 μg ZnO.L(-1), 10 μg Al2O3.L(-1) plus 10 μg ZnO.L(-1), 100 μg Al2O3.L(-1), 100 μg ZnO.L(-1), and 100 μg Al2O3.L(-1) plus 100 μg ZnO.L(-1)). At the end of each exposure period, antioxidant enzyme activity (catalase, glutathione-S-transferase, and superoxide dismutase), lipid peroxidation, and histopathology were assessed in the gills and livers of C. auratus. The results show an increase in catalase (CAT) and superoxide dismutase (SOD) activity in the gills and livers of fish, especially after 14 days of exposure to single and combined NPs, followed by a reduction at 21 days. An increase in glutathione S-transferase (GST) was observed in gills after 7 days for all tested NP concentrations (single and combined); while in livers, a significant increase was determined after 14 days of exposure to 100 μg.L(-1) of both single ZnO and Al2O3 NPs. Lipid peroxidation (LPO) significantly increased in gills after 7 days of exposure to 100 μg.L(-1) Al2O3 NPs (single or combined). In livers, LPO increased significantly after 7 days of exposure to all tested concentrations of both single ZnO and Al2O3 (except for 10 μg Al2O3.L(-1)), and after 14 days of exposure to ZnO (10 and 100 μg.L(-1)) and Al2O3 (100 μg.L(-1)). The results from histological observations suggest that exposure to metal oxide NPs affected both livers and gills, presenting alterations such as gill hyperplasia and liver degeneration. However, the most pronounced effects were found in gills. In general, this study shows that the tested NPs, single or combined, are capable of causing sub-lethal effects on C. auratus, but when

  8. Improving p-type doping efficiency in Al{sub 0.83}Ga{sub 0.17}N alloy substituted by nanoscale (AlN){sub 5}/(GaN){sub 1} superlattice with Mg{sub Ga}-O{sub N} δ-codoping: Role of O-atom in GaN monolayer

    SciTech Connect

    Zhong, Hong-xia; Shi, Jun-jie Jiang, Xin-he; Huang, Pu; Ding, Yi-min; Zhang, Min

    2015-01-15

    We calculate Mg-acceptor activation energy E{sub A} and investigate the influence of O-atom, occupied the Mg nearest-neighbor, on E{sub A} in nanoscale (AlN){sub 5}/(GaN){sub 1} superlattice (SL), a substitution for Al{sub 0.83}Ga{sub 0.17}N disorder alloy, using first-principles calculations. We find that the N-atom bonded with Ga-atom is more easily substituted by O-atom and nMg{sub Ga}-O{sub N} (n = 1-3) complexes are favorable and stable in the SL. The O-atom plays a dominant role in reducing E{sub A}. The shorter the Mg-O bond is, the smaller the E{sub A} is. The Mg-acceptor activation energy can be reduced significantly by nMg{sub Ga}-O{sub N} δ-codoping. Our calculated E{sub A} for 2Mg{sub Ga}-O{sub N} is 0.21 eV, and can be further reduced to 0.13 eV for 3Mg{sub Ga}-O{sub N}, which results in a high hole concentration in the order of 10{sup 20} cm{sup −3} at room temperature in (AlN){sub 5}/(GaN){sub 1} SL. Our results prove that nMg{sub Ga}-O{sub N} (n = 2,3) δ-codoping in AlN/GaN SL with ultrathin GaN-layer is an effective way to improve p-type doping efficiency in Al-rich AlGaN.

  9. Arrays of ZnO/AZO (Al-doped ZnO) nanocables: a higher open circuit voltage and remarkable improvement of efficiency for CdS-sensitized solar cells.

    PubMed

    Deng, Jianping; Wang, Minqiang; Liu, Jing; Song, Xiaohui; Yang, Zhi

    2014-03-15

    Photoelectrode of nanocables (NCs) structure of ZnO nanowires (NWs) coated with Al-doped ZnO (AZO) shells was investigated for CdS quantum dots sensitized solar cells (QDSSCs). ZnO NWs serve as the frame for the preparation of AZO shells, in which electron transport more rapidly due to the more higher electron mobility of AZO (n-ZnO) than that of i-ZnO. AZO shells were assembled onto the surface of ZnO NWs via a spin-coating method. Optical band-gap of the ZnO/AZO films varies from 3.19 eV for pure ZnO to 3.25 eV for AZO (15%) depending on the Al-doping concentration. The PL intensity of AZO/ZnO, V(oc), J(sc) and η of the cells first increased and then decreased with the increase in the Al-doping (from 0% to 20%) and post-annealed temperature. Remarkably, the value of V(oc) can achieve above 0.8 V after Al-doping. The dark current and absorption spectrum provided direct evidence of the increase in J(sc) and V(oc), respectively. Moreover, we discussed the effect of Al-doping on optical band-gap of the samples and the transfer of electron.

  10. The role of Al, Ba, and Cd dopant elements in tailoring the properties of c-axis oriented ZnO thin films

    NASA Astrophysics Data System (ADS)

    Ali, Dilawar; Butt, M. Z.; Arif, Bilal; Al-Ghamdi, Ahmed A.; Yakuphanoglu, Fahrettin

    2017-02-01

    Highly c-axis oriented un-doped ZnO and Al-, Ba-, and Cd-doped ZnO thin films were successfully deposited on glass substrate employing sol-gel spin coating method. XRD analysis showed that all thin films possess hexagonal wurtzite structure with preferred orientation along c-axis. Field emission scanning electron microscope (FESEM) was used to study the morphology of thin films. The morphology consists of spherical and non-spherical shape grains. EDX analysis confirms the presence of O, Zn, Al, Ba, and Cd in the relevant thin films. The optical properties of thin films were studied using UV-Vis spectrometer. All thin films possess more than 85% optical transmittance in the visible region. Blue shift in optical band gap Eg has been observed on doping with Al, whereas doping with Ba and Cd resulted in red shift of Eg. Urbach energy Eu of all doped ZnO thin films was found to have excellent correlation with their band gap energy Eg. Moreover, Eg increases while Eu decreases on the increase in crystallite size D. Optical parameters Eg and Eu as well as structural parameters lattice strain and stacking fault probability also show excellent correlation with the B-factor or the mean-square amplitude of atomic vibrations of the dopant elements. Electrical conductivity measurement of the thin films was carried out using two-point probe method. The electrical conductivity was found to increase with the increase in crystallite orientation along c-axis.

  11. Electronic structure of Al-doped ZnO transparent conductive thin films studied by x-ray absorption and emission spectroscopies

    SciTech Connect

    Huang, W. H.; Sun, S. J.; Chiou, J. W.; Chou, H.; Chan, T. S.; Lin, H.-J.; Kumar, Krishna; Guo, J.-H.

    2011-11-15

    This study used O K-, Zn L{sub 3}-, Zn K-, and Al K-edges x-ray absorption near-edge structure (XANES) and O K-edge x-ray emission spectroscopy (XES) measurements to investigate the electronic structure of transparent Al-doped ZnO (AZO) thin film conductors. The samples were prepared on glass substrates at a low temperature near 77 K by using a standard RF sputtering method. High-purity Ne (5N) was used as the sputtering gas. The crystallography of AZO thin films gradually transformed from the ZnO wurtize structure to an amorphous structure during sample deposition, which suggests the suitability to grow on flexible substrates, eliminating the severe degradation due to fragmentation by repeated bending. The O K- and Zn L{sub 3}-edges XANES spectra of AZO thin films revealed a decrease in the number of both O 2p and Zn 3d unoccupied states when the pressure of Ne was increased from 5 to 100 mTorr. In contrast, Al K-edges XANES spectra showed that the number of unoccupied states of Al 3p increased in conjunction with the pressure of Ne, indicating an electron transfer from Al to O atoms, and suggesting that Al doping increases the negative effective charge of oxygen ions. XES and XANES spectra of O 2p states at the O K-edge also revealed that Al doping not only raised the conduction-band-minimum, but also increased the valence-band-maximum and the band-gap. The results indicate that the reduction in conductivity of AZO thin films is due to the generation of ionic characters, the increase in band-gap, and the decrease in density of unoccupied states of oxygen.

  12. Amplified spontaneous emission from ZnO in n-ZnO/ZnO nanodots-SiO(2) composite/p-AlGaN heterojunction light-emitting diodes.

    PubMed

    Shih, Ying Tsang; Wu, Mong Kai; Li, Wei Chih; Kuan, Hon; Yang, Jer Ren; Shiojiri, Makoto; Chen, Miin Jang

    2009-04-22

    This study demonstrates amplified spontaneous emission (ASE) of the ultraviolet (UV) electroluminescence (EL) from ZnO at lambda~380 nm in the n-ZnO/ZnO nanodots-SiO(2) composite/p- Al(0.12)Ga(0.88)N heterojunction light-emitting diode. A SiO(2) layer embedded with ZnO nanodots was prepared on the p-type Al(0.12)Ga(0.88)N using spin-on coating of SiO(2) nanoparticles followed by atomic layer deposition (ALD) of ZnO. An n-type Al-doped ZnO layer was deposited upon the ZnO nanodots-SiO(2) composite layer also by the ALD technique. High-resolution transmission electron microscopy (HRTEM) reveals that the ZnO nanodots embedded in the SiO(2) matrix have diameters of 3-8 nm and the wurtzite crystal structure, which allows the transport of carriers through the thick ZnO nanodots-SiO(2) composite layer. The high quality of the n-ZnO layer was manifested by the well crystallized lattice image in the HRTEM picture and the low-threshold optically pumped stimulated emission. The low refractive index of the ZnO nanodots-SiO(2) composite layer results in the increase in the light extraction efficiency from n-ZnO and the internal optical feedback of UV EL into n-ZnO layer. Consequently, significant enhancement of the UV EL intensity and super-linear increase in the EL intensity, as well as the spectral narrowing, with injection current were observed owing to ASE in the n-ZnO layer.

  13. Field-induced doping-mediated tunability in work function of Al-doped ZnO: Kelvin probe force microscopy and first-principle theory

    NASA Astrophysics Data System (ADS)

    Kumar, Mohit; Mookerjee, Sumit; Som, Tapobrata

    2016-09-01

    We demonstrate that the work function of Al-doped ZnO (AZO) can be tuned externally by applying an electric field. Our experimental investigations using Kelvin probe force microscopy show that by applying a positive or negative tip bias, the work function of AZO film can be enhanced or reduced, which corroborates well with the observed charge transport using conductive atomic force microscopy. These findings are further confirmed by calculations based on first-principles theory. Tuning the work function of AZO by applying an external electric field is not only important to control the charge transport across it, but also to design an Ohmic contact for advanced functional devices.

  14. Improved optical and electrical properties of rf sputtered Al doped ZnO films on polymer substrates by low-damage processes

    SciTech Connect

    Min, Hyung Seob; Yang, Min Kyu; Lee, Jeon-Kook

    2009-03-15

    Three types of low-damage radio-frequency (rf) magnetron sputtering processes--an interruptive process, a rotating cylindrical holder method, and an off-axis sputtering method--were designed and studied to reduce the film surface temperature during deposition. Low-damage sputtering processes were investigated to improve the resistivity and optical transmittance in the visible range of Al doped ZnO (AZO) thin films deposited on polymer substrates. In the case of the polyethersulfone substrate, AZO films with a resistivity of 1.0x10{sup -3} {omega} cm and an optical transmittance of 75% were obtained by the rotating repeat holder method during rf sputtering.

  15. Field-induced doping-mediated tunability in work function of Al-doped ZnO: Kelvin probe force microscopy and first-principle theory.

    PubMed

    Kumar, Mohit; Mookerjee, Sumit; Som, Tapobrata

    2016-09-16

    We demonstrate that the work function of Al-doped ZnO (AZO) can be tuned externally by applying an electric field. Our experimental investigations using Kelvin probe force microscopy show that by applying a positive or negative tip bias, the work function of AZO film can be enhanced or reduced, which corroborates well with the observed charge transport using conductive atomic force microscopy. These findings are further confirmed by calculations based on first-principles theory. Tuning the work function of AZO by applying an external electric field is not only important to control the charge transport across it, but also to design an Ohmic contact for advanced functional devices.

  16. Synthesis of flower-like Al doped ZnO microstructures by hydrothermal process and analysis of their gas sensing properties

    NASA Astrophysics Data System (ADS)

    Li, Zan; Qin, Wei; Zhao, Wenjie; Wu, Xiaohong

    2014-04-01

    Al-doped ZnO (AZO) powders with flower-like microstructures were successfully synthesized through a simple and efficient hydrothermal approach, and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy diffraction spectrum (EDS). All the samples presented high crystallinity with a hexagonal wurtzite structure. The heater gas sensors based on AZO were fabricated and investigation of gas sensing properties was conducted. The sensors showed high response values and reproducible response-recovery for 50-1800 ppm ethanol at 332°C, comparing with NH3, SO2, CO, and HCHO. The underlying mechanism was discussed.

  17. Atomic layer deposition of Al-doped ZnO films using ozone as the oxygen source: A comparison of two methods to deliver aluminum

    SciTech Connect

    Yuan Hai; Luo Bing; Yu Dan; Cheng, An-jen; Campbell, Stephen A.; Gladfelter, Wayne L.

    2012-01-15

    Aluminum-doped ZnO films were prepared by atomic layer deposition at 250 deg. C using diethylzinc (DEZ), trimethylaluminum (TMA), and ozone as the precursors. Two deposition methods were compared to assess their impact on the composition, structural, electrical, and optical properties as a function of Al concentration. The first method controlled the Al concentration by changing the relative number of Al to Zn deposition cycles; a process reported in the literature where water was used as the oxygen source. The second method involved coinjection of the DEZ and TMA during each cycle where the partial pressures of the precursors control the aluminum concentration. Depth profiles of the film composition using Auger electron spectroscopy confirmed a layered microstructure for the films prepared by the first method, whereas the second method led to a homogeneous distribution of the aluminum throughout the ZnO film. Beneath the surface layer the carbon concentrations for all of the films were below the detection limit. Comparison of their electrical and optical properties established that films deposited by coinjection of the precursors were superior.

  18. Comparison of heterojunction device parameters for pure and doped ZnO thin films with IIIA (Al or In) elements grown on silicon at room ambient

    NASA Astrophysics Data System (ADS)

    Kaya, Ahmet; Cansizoglu, Hilal; Mamtaz, Hasina H.; Mayet, Ahmed S.; Islam, M. Saif

    2016-09-01

    In this work, pure and IIIA element doped ZnO thin films were grown on p type silicon (Si) with (100) orientated surface by sol-gel method, and were characterized for comparing their electrical characteristics. The heterojunction parameters were obtained from the current-voltage (I-V) and capacitance-voltage (C-V) characteristics at room temperature. The ideality factor (n), saturation current (Io) and junction resistance of ZnO/p-Si heterojunction for both pure and doped (with Al or In) cases were determined by using different methods at room ambient. Other electrical parameters such as Fermi energy level (EF), barrier height (ΦB), acceptor concentration (Na), built-in potential (Φi) and voltage dependence of surface states (Nss) profile were obtained from the C-V measurements. The results reveal that doping ZnO with IIIA (Al or In) elements to fabricate n-ZnO/p-Si heterojunction can result in high performance diode characteristics.

  19. Thickness effect on the optical and morphological properties in Al2O3/ZnO nanolaminate thin films prepared by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    López, J.; Martínez, J.; Abundiz, N.; Domínguez, D.; Murillo, E.; Castillón, F. F.; Machorro, R.; Farías, M. H.; Tiznado, H.

    2016-02-01

    In this work, we studied the optical and morphological properties of ultrathin nanolaminate films based on Al2O3/ZnO (AZ) bilayers stack. The films were deposited on Si (100) by means of thermal atomic layer deposition (ALD) technique. The bilayer thicknesses (ratio = 1:1) were 0.2, 1, 2, 4, 10 and 20 nm. Refractive index (n) and band gap (Eg) of each nanolaminate were studied via spectroscopic ellipsometry (SE), and spectral reflectance ultraviolet-visible spectroscopy (UV-vis). Surface morphology and roughness parameters of the nanolaminates were measured by Atomic Force Microscopy (AFM). The optical and morphological properties were shown highly dependent on the bilayer thickness. Ellipsometric data treated through the Cody-Lorentz optical model revealed that the refractive index decreases for thinner bilayers. A sharp intensity decay of refractive index and peaks at the UV region (200-400 nm) indicated increased transparency for thinner bilayers. It is also shown that the band gap is tunable. The maximum band gap value was 4.8 eV. These results reveal that ZnO combined with Al2O3 as bilayers stack can be converted into a dielectric material with enhanced band gap, opening the possibility for new optical and dielectric applications.

  20. Doping effect of Ag+, Mn2+ ions on Structural and Optical Properties of ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Sankara Reddy, B.; Venkatramana Reddy, S.; Venkateswara Reddy, P.; Koteeswara Reddy, N.; Vijayalakshmi, R. P.

    2015-02-01

    Pure ZnO and co-doped (Mn, Ag) ZnO nanoparticles have been successfully prepared by chemical co-precipitation method without using a capping agent. X-ray diffraction (XRD) studies confirms the presence of wurtzite (hexagonal) crystal structure similar to undoped ZnO, suggesting that doped Mn, Ag ions are substituted to the regular Zn sites. The morphology of the samples were studied by scanning electron microscopy (SEM). The chemical composition of pure and co-doped ZnO nanoparticles were characterized by energy dispersive X-ray analysis spectroscopy (EDAX). Optical absorption properties were determined by UV-vis Diffuse Reflectance Spectrophotometer. The incorporation of Ag+, Mn2+ in the place of Zn2+ provoked to decrease the size of nanocrystals as compared to pure ZnO. Optical absorption measurements indicates blue shift in the absorption band edge upon Ag, Mn ions doped ZnO nanoparticles.

  1. Investigations on the roles of position controlled Al layers incorporated into an Al-doped ZnO active channel during atomic layer deposition for thin film transistor applications

    NASA Astrophysics Data System (ADS)

    Kim, Eom-Ji; Lee, Won-Ho; Yoon, Sung-Min

    2016-03-01

    We investigated the effects of the distance between incorporated Al layers on the characteristics of thin-film transistors (TFTs) using Al-doped ZnO (AZO) as the active channels. The intervals between the Al layers were controlled by designing the sequences of Al cycles during the atomic-layer deposition. Two configurations were designed as “scatter” or “focus”, in which the incorporated Al layers were dispersed to bottom and top sides or concentrated on the center region. Electrical conductivities of “scatter” and “focus” films were observed to be different. While the dispersed Al layers could work as dopants, a too-close interval between the Al layers suppressed carrier transport, even with the same incorporated Al amounts. These differences were reflected on the device characteristics. The TFT performance of the “scatter” device was better than that of the “focus” device. Consequently, adequately dispersed Al layers in the AZO channel are very important for improving device performance.

  2. Broadband down-conversion based near infrared quantum cutting in Eu{sup 2+}–Yb{sup 3+} co-doped SrAl{sub 2}O{sub 4} for crystalline silicon solar cells

    SciTech Connect

    Tai, Yuping; Zheng, Guojun; Wang, Hui; Bai, Jintao

    2015-03-15

    Near infrared (NIR) quantum cutting involving the down conversion of an absorbed visible photon to emission of two NIR photons was achieved in SrAl{sub 2}O{sub 4}:0.01Eu{sup 2+}, xYb{sup 3+} (x=0, 1, 2, 5, 10, 20, 30 mol%) samples. The photoluminescence properties of samples in visible and NIR regions were measured to verify the energy transfer (ET) from Eu{sup 2+} to Yb{sup 3+}. The results demonstrated that Eu{sup 2+} was an efficient sensitizer for Yb{sup 3+} in the SrAl{sub 2}O{sub 4} host lattice. According to Gaussian fitting analysis and temperature-dependent luminescence experiments, the conclusion was drawn that the cooperative energy transfer (CET) process dominated the ET process and the influence of charge transfer state (CTS) of Yb{sup 3+} could be negligible. As a result, the high energy transfer efficiency (ETE) and quantum yield (QY) have been acquired, the maximum value approached 73.68% and 147.36%, respectively. Therefore, this down-conversion material has potential application in crystalline silicon solar cells to improve conversion efficiency. - Graphical abstract: Near infrared quantum cutting was achieved in Eu{sup 2+}–Yb{sup 3+} co-doped SrAl{sub 2}O{sub 4} samples. The cooperative energy transfer process dominated energy transfer process and high energy transfer efficiency was acquired. - Highlights: • The absorption spectrum of Eu{sup 2+} ion is strong in intensity and broad in bandwidth. • The spectra of Eu{sup 2+} in SrAl{sub 2}O{sub 4} lies in the strongest region of solar spectrum. • The cooperative energy transfer (CET) dominated the energy transfer process. • The domination of CET is confirmed by experimental analysis. • SrAl{sub 2}O{sub 4}:Eu{sup 2+},Yb{sup 3+} show high energy transfer efficiency and long lifetime.

  3. Polymer solar cells with efficiency >10% enabled via a facile solution-processed Al-doped ZnO electron transporting layer (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Jagadamma, Lethy K.; Al-Senani, Mohammed; Amassian, Aram

    2015-10-01

    The present work details a facile and low-temperature (125C) solution-processed Al-doped ZnO (AZO) buffer layer functioning very effectively as electron accepting/hole blocking layer for a wide range of polymer:fullerene bulk heterojunction systems, and yielding power conversion efficiency in excess of 10% (8%) on glass (plastic) substrates. We show that ammonia addition to the aqueous AZO nanoparticle solution is a critically important step toward producing compact and smooth thin films which partially retain the aluminum doping and crystalline order of the starting AZO nanocrystals. The ammonia treatment appears to reduce the native defects via nitrogen incorporation, making the AZO film a very good electron transporter and energetically matched with the fullerene acceptor. Importantly, highly efficient solar cells are achieved without the need for additional surface chemical passivation or modification, which has become an increasingly common route to improving the performance of evaporated or solution-processed ZnO ETLs in solar cells.

  4. High-Hall-Mobility Al-Doped ZnO Films Having Textured Polycrystalline Structure with a Well-Defined (0001) Orientation.

    PubMed

    Nomoto, Junichi; Makino, Hisao; Yamamoto, Tetsuya

    2016-12-01

    Five hundred-nanometer-thick ZnO-based textured polycrystalline films consisting of 490-nm-thick Al-doped ZnO (AZO) films deposited on 10-nm-thick Ga-doped ZnO (GZO) films exhibited a high Hall mobility (μ H) of 50.1 cm(2)/Vs with a carrier concentration (N) of 2.55 × 10(20) cm(-3). Firstly, the GZO films were prepared on glass substrates by ion plating with dc arc discharge, and the AZO films were then deposited on the GZO films by direct current magnetron sputtering (DC-MS). The GZO interface layers with a preferential c-axis orientation play a critical role in producing AZO films with texture development of a well-defined (0001) orientation, whereas 500-nm-thick AZO films deposited by only DC-MS showed a mixture of the c-plane and the other plane orientation, to exhibit a μ H of 38.7 cm(2)/Vs with an N of 2.22 × 10(20) cm(-3).

  5. Biaxial stress and optoelectronic properties of Al-doped ZnO thin films deposited on flexible substrates by radio frequency magnetron sputtering.

    PubMed

    Chen, Hsi-Chao; Cheng, Po-Wei; Huang, Kuo-Ting

    2017-02-01

    Transparent conductive Al-doped ZnO (AZO) thin films were deposited on polyethylene terephthalate (PET) and polycarbonate (PC) substrates using radio frequency (RF) magnetron sputtering. The biaxial stress was measured with a double beam shadow moiré interferometer, and x-ray diffraction (XRD) was used to investigate the crystal orientation of ZnO. The substrate temperature was varied from room temperature to 150°C in steps of 25°C. The experimental results showed that the residual and shearing stresses increased with the increase in substrate temperature. The residual stress can be separated into principle and shearing stresses by Mohr's circle rule, and the shearing stress (tensile stress) was different from the compressive stress of the residual stress. However, the optimal substrate temperatures for PET and PC were 75°C and 100°C, and the shearing stresses were 424.82 and 543.68 MPa, respectively. AZO/PET and AZO/PC thin films cracked at substrate temperatures of 75°C and 100°C, respectively. AZO/PET thin film at a substrate temperature of 100°C had a resistivity low to the order of 10-3  Ω-cm.

  6. High-Hall-Mobility Al-Doped ZnO Films Having Textured Polycrystalline Structure with a Well-Defined (0001) Orientation

    NASA Astrophysics Data System (ADS)

    Nomoto, Junichi; Makino, Hisao; Yamamoto, Tetsuya

    2016-06-01

    Five hundred-nanometer-thick ZnO-based textured polycrystalline films consisting of 490-nm-thick Al-doped ZnO (AZO) films deposited on 10-nm-thick Ga-doped ZnO (GZO) films exhibited a high Hall mobility ( μ H) of 50.1 cm2/Vs with a carrier concentration ( N) of 2.55 × 1020 cm-3. Firstly, the GZO films were prepared on glass substrates by ion plating with dc arc discharge, and the AZO films were then deposited on the GZO films by direct current magnetron sputtering (DC-MS). The GZO interface layers with a preferential c-axis orientation play a critical role in producing AZO films with texture development of a well-defined (0001) orientation, whereas 500-nm-thick AZO films deposited by only DC-MS showed a mixture of the c-plane and the other plane orientation, to exhibit a μ H of 38.7 cm2/Vs with an N of 2.22 × 1020 cm-3.

  7. Micro/Nano hierarchical peony-like Al doped ZnO superhydrophobic film: The guiding effect of (100) preferred seed layer

    PubMed Central

    Li, Yang; Wang, Jingfeng; Kong, Yi; Zhou, Jia; Wu, Jinzhu; Wang, Gang; Bi, Hai; Wu, Xiaohong; Qin, Wei; Li, Qingkun

    2016-01-01

    In this communication, we present a versatile and controllable strategy for formation of superhydrophobic micro/nano hierarchical Al doped ZnO (AZO) films with a water contact angle (CA) of 170 ± 4°. This strategy involves a two-step layer-by-layer process employing an atomic layer deposition (ALD) technique followed by a hydrothermal method, and the resulting novel AZO surface layer consists of (100) dominant nano-rice-like AZO seed layer (the water CA of 110 ± 4°) covered with micro-peony-like AZO top. The growth mechanisms and superhydrophobic properties of the hierarchical AZO layer are discussed. It is believed that the present route holds promise for future success in the design and development of practical superhydrophobic materials. PMID:26753877

  8. Investigation of the biaxial stress of Al-doped ZnO thin films on a flexible substrate with RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Huang, Kuo-Ting; Chen, Hsi-Chao; Cheng, Po-Wei; Chang, Jhe-Ming

    2016-01-01

    Transparent conductive Al-doped ZnO (AZO) thin films were deposited onto poly(ethylene terephthalate) (PET) substrate, using the radio frequency (RF) magnetron sputtering method. The residual stress of flexible electronics was investigated by a double beam shadow moiré interferometer with phase shifting interferometry (PSI). Moreover, the biaxial stress of AZO thin films can be graphically represented by using Mohr’s circle of stress. The residual stress of AZO thin films becomes more compressive with the increase in sputtering power. The maximum residual stress is -1115.74 MPa, and the shearing stress is 490.57 MPa at a sputtering power of 200 W. The trends of residual stress were evidenced by the X-ray diffraction (XRD) patterns and optical properties of AZO thin films. According to the evaluation results of the refractive index and the extinction coefficient, the AZO thin films have better quality when the sputtering power less than 100 W.

  9. Spatial distribution of electrical properties for Al-doped ZnO films deposited by dc magnetron sputtering using various inert gases

    SciTech Connect

    Sato, Yasushi; Ishihara, Keita; Oka, Nobuto; Shigesato, Yuzo

    2010-07-15

    Spatial distribution of electrical properties of Al-doped ZnO (AZO) films deposited by magnetron sputtering was investigated. To adjust the intensity of bombardment by high-energy particles, the AZO films were deposited using Ar, Kr, or Xe gas with varying plasma impedance. The spatial distribution of the electrical properties clearly depends on the sputtering gas. In the case of using Kr or Xe, the resistivity of the films in front of the target center and erosion areas was significantly enhanced, in contrast with Ar. This was attributed to an enhancement in bombardment damage due to the increased sputtering voltages required for Kr or Xe discharges. The increase in plasma impedance was due to the smaller coefficients for secondary-electron emission of the target surface by Kr or Xe impingements, which leads to the larger sputtering voltage.

  10. Micro/Nano hierarchical peony-like Al doped ZnO superhydrophobic film: The guiding effect of (100) preferred seed layer

    NASA Astrophysics Data System (ADS)

    Li, Yang; Wang, Jingfeng; Kong, Yi; Zhou, Jia; Wu, Jinzhu; Wang, Gang; Bi, Hai; Wu, Xiaohong; Qin, Wei; Li, Qingkun

    2016-01-01

    In this communication, we present a versatile and controllable strategy for formation of superhydrophobic micro/nano hierarchical Al doped ZnO (AZO) films with a water contact angle (CA) of 170 ± 4°. This strategy involves a two-step layer-by-layer process employing an atomic layer deposition (ALD) technique followed by a hydrothermal method, and the resulting novel AZO surface layer consists of (100) dominant nano-rice-like AZO seed layer (the water CA of 110 ± 4°) covered with micro-peony-like AZO top. The growth mechanisms and superhydrophobic properties of the hierarchical AZO layer are discussed. It is believed that the present route holds promise for future success in the design and development of practical superhydrophobic materials.

  11. Novel red phosphors LaBSiO5 co-doped with Eu3+, Al3+ for near-UV light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Wang, Zhengliang; Cheng, Ping; Liu, Yong; Zhou, Yayun; Zhou, Qiang; Guo, Junmin

    2014-11-01

    Red-emitting phosphors LaBSiO5:Eu3+ and LaBSiO5:Eu3+, Al3+ were synthesized by the conventional solid state method at 1100 °C. The structure and luminescent properties of these phosphors are investigated. LaBSiO5:Eu3+ and LaBSiO5:Eu3+, Al3+ could be efficiently excited by near ultraviolet light with the strongest excitation peak at 395 nm. The main emission peak is located at around 616 nm, which corresponds to the transition of 5D0 → 7F2 of Eu3+ ions. The emission intensity of LaBSiO5:Eu3+ was enhanced by introducing Al3+ ions. Compared with Y2O2S:0.05Eu3+, the sample La0.70B0.75SiO5:0.30Eu3+, 0.25Al3+ shares the intense red emission, and its emission intensity is about 3.8 times as strong as that of Y2O2S:0.05Eu3+ under 395 nm light excitation. Bright red light can be observed from the red LED based on La0.70B0.75SiO5:0.30Eu3+, 0.25Al3+, hence La0.70B0.75SiO5:0.30Eu3+, 0.25Al3+ maybe find application on near-UV InGaN-based white LEDs.

  12. Realizing a facile and environmental-friendly fabrication of high-performance multi-crystalline silicon solar cells by employing ZnO nanostructures and an Al2O3 passivation layer

    PubMed Central

    Chen, Hong-Yan; Lu, Hong-Liang; Sun, Long; Ren, Qing-Hua; Zhang, Hao; Ji, Xin-Ming; Liu, Wen-Jun; Ding, Shi-Jin; Yang, Xiao-Feng; Zhang, David Wei

    2016-01-01

    Nowadays, the multi-crystalline silicon (mc-Si) solar cells dominate the photovoltaic industry. However, the current acid etching method on mc-Si surface used by firms can hardly suppress the average reflectance value below 25% in the visible light spectrum. Meanwhile, the nitric acid and the hydrofluoric contained in the etching solution is both environmental unfriendly and highly toxic to human. Here, a mc-Si solar cell based on ZnO nanostructures and an Al2O3 spacer layer is demonstrated. The eco-friendly fabrication is realized by low temperature atomic layer deposition of Al2O3 layer as well as ZnO seed layer. Moreover, the ZnO nanostructures are prepared by nontoxic and low cost hydro-thermal growth process. Results show that the best passivation quality of the n+ -type mc-Si surface can be achieved by balancing the Si dangling bond saturation level and the negative charge concentration in the Al2O3 film. Moreover, the average reflectance on cell surface can be suppressed to 8.2% in 400–900 nm range by controlling the thickness of ZnO seed layer. With these two combined refinements, a maximum solar cell efficiency of 15.8% is obtained eventually. This work offer a facile way to realize the environmental friendly fabrication of high performance mc-Si solar cells. PMID:27924911

  13. Realizing a facile and environmental-friendly fabrication of high-performance multi-crystalline silicon solar cells by employing ZnO nanostructures and an Al2O3 passivation layer

    NASA Astrophysics Data System (ADS)

    Chen, Hong-Yan; Lu, Hong-Liang; Sun, Long; Ren, Qing-Hua; Zhang, Hao; Ji, Xin-Ming; Liu, Wen-Jun; Ding, Shi-Jin; Yang, Xiao-Feng; Zhang, David Wei

    2016-12-01

    Nowadays, the multi-crystalline silicon (mc-Si) solar cells dominate the photovoltaic industry. However, the current acid etching method on mc-Si surface used by firms can hardly suppress the average reflectance value below 25% in the visible light spectrum. Meanwhile, the nitric acid and the hydrofluoric contained in the etching solution is both environmental unfriendly and highly toxic to human. Here, a mc-Si solar cell based on ZnO nanostructures and an Al2O3 spacer layer is demonstrated. The eco-friendly fabrication is realized by low temperature atomic layer deposition of Al2O3 layer as well as ZnO seed layer. Moreover, the ZnO nanostructures are prepared by nontoxic and low cost hydro-thermal growth process. Results show that the best passivation quality of the n+ -type mc-Si surface can be achieved by balancing the Si dangling bond saturation level and the negative charge concentration in the Al2O3 film. Moreover, the average reflectance on cell surface can be suppressed to 8.2% in 400–900 nm range by controlling the thickness of ZnO seed layer. With these two combined refinements, a maximum solar cell efficiency of 15.8% is obtained eventually. This work offer a facile way to realize the environmental friendly fabrication of high performance mc-Si solar cells.

  14. Structural and optical characterization of indium-antimony complexes in ZnO

    NASA Astrophysics Data System (ADS)

    Türker, M.; Deicher, M.; Johnston, K.; Wolf, H.; Wichert, Th.

    2015-04-01

    One of the main obstacles to the technical application of the wide-gap semiconductor ZnO represents the difficulty to achieve reliable p-type doping of ZnO with group V elements (N, P, As, Sb) acting as acceptors located on O lattice sites. The theoretically proposed concepts of cluster-doping or codoping may lead to an enhanced and stable p-type conductivity of ZnO. We report on PAC results obtained by codoping experiments of ZnO by ion implantation using the donor 111In and the group-V acceptor Sb. The formation of In-Sb pairs has been observed. Based on these PAC results, there is no evidence for the formation of In-acceptor complexes involving more than one Sb acceptor. These results has been complemented by photoluminescence measurements.

  15. Electrical transport in hydrogen-aluminium Co-doped ZnO and Zn{sub 1-x}Mg{sub x}O films: Relation to film structure and composition

    SciTech Connect

    Bikowski, A.; Ellmer, K.

    2013-02-07

    ZnO:Al and Zn{sub 1-x}Mg{sub x}O:Al films have been deposited in Ar/H{sub 2} atmospheres by magnetron sputtering from oxidic targets at two substrate temperatures: room temperature and 300 Degree-Sign C. The electrical transport parameters-carrier concentration, resistivity, and Hall mobility-have been measured and related to the structural properties and the chemical composition. The resistivity {rho} both of ZnO:Al as well as Zn{sub 1-x}Mg{sub x}O:Al films decreases with increasing hydrogen flow for the films deposited at room temperature. The decrease is up to 2 orders of magnitude and in both cases due to an increase of the electron concentration and the Hall mobility and occurred despite the fact, that the films became almost X-ray amorphous with increasing hydrogen content. In contrast to these results, for depositions at 300 Degree-Sign C, the resistivity increases with increasing hydrogen portion in the sputtering atmosphere, more strongly for the Zn{sub 1-x}Mg{sub x}O:Al films (3 orders of magnitude). Based on literature data, it is concluded that the built-in atomic hydrogen acts as a shallow donor at low deposition temperatures, while it becomes deactivated at T{sub sub}= 300 Degree-Sign C by the formation of molecular H{sub 2}.

  16. Polymer-assisted deposition of co-doped zinc oxide thin films for the detection of aromatic organic compounds.

    PubMed

    Li, Wei; Kim, Dojin

    2011-12-01

    Co-doped Zinc oxide thin films are deposited onto SiO2/Si substrate by polymer-assisted deposition method. The surface morphology, structures and chemical states of the thin films are examined by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The gas-sensing properties of the thin films upon exposure to aromatic organic compound vapors are also investigated. Co-doping is shown to be very effective in enhancing the response of ZnO thin film to aromatic organic compound.

  17. Reversible Change in Electrical and Optical Properties in Epitaxially Grown Al-Doped ZnO Thin Films

    SciTech Connect

    Noh, J. H.; Jung, H. S.; Lee, J. K.; Kim, J. Y; Cho, C. M.; An, J.; Hong, K. S.

    2008-01-01

    Aluminum-doped ZnO (AZO) films were epitaxially grown on sapphire (0001) substrates using pulsed laser deposition. As-deposited AZO films had a low resistivity of 8.01 x 10{sup -4} {Omega} cm. However, after annealing at 450 C in air, the electrical resistivity of the AZO films increased to 1.97 x 10{sup -1} {Omega} cm because of a decrease in the carrier concentration. Subsequent annealing of the air-annealed AZO films in H{sub 2} recovered the electrical conductivity of the AZO films. In addition, the conductivity change was reversible upon repeated air and H{sub 2} annealing. A photoluminescence study showed that oxygen interstitial (O{sub i}) is a critical material parameter allowing for the reversible control of the electrical conducting properties of AZO films.

  18. Homoepitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C-H; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; McCarty, P.; George, M. A.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    ZnO films have high potential for many applications, such as surface acoustic wave filters, UV detectors, and light emitting devices due to its structural, electrical, and optical properties. High quality epitaxial films are required for these applications. The Al2O3 substrate is commonly used for ZnO heteroepitaxial growth. Recently, high quality ZnO single crystals are available for grow homoepitaxial films. Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films were also deposited on (0001) Al2O3 substrates. It was found that the two polar ZnO surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which strongly influence the epitaxial film growth. The morphology and structure of homoepitaxial films grown on the ZnO substrates were different from heteroepitaxial films grown on the Al2O3. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

  19. Single and couple doping ZnO nanocrystals characterized by positron techniques

    NASA Astrophysics Data System (ADS)

    Pasang, Tenzin; Namratha, Keerthiraj; Guagliardo, Paul; Byrappa, Kullaiah; Ranganathaiah, Chikkakuntappa; Samarin, S.; Williams, J. F.

    2015-04-01

    Zinc oxide (ZnO) nanocrystals have been synthesized using a mild hydrothermal process using low temperatures and pressures with the advantages of free growth catalyst, low cost and alternative technology. Positron annihilation lifetime spectroscopy and coincidence Doppler broadening (CDB) spectroscopic methods have been used to investigate the roles of single- and co-dopants and native defects of the ZnO nanocrystals controlled by the synthesis process. It is shown that single Ag1+ and Pd2+ dopants occupy interstitial sites of the ZnO lattice and single Ru3+ doping replaces Zn vacancies substitutionally with a significant effect on the CDB momentum ratio curves when compared using ZnO as the reference spectrum. The co-doping of the ZnO lattice with (Sn4+ + Co2+) shows similar CDB ratios as Ru3+ single-doping. Also co-doping with (Ag1+ + Pd2+) or (Ag1+ + W6+) shows significant decreases in the band gap energy up to about 12.6% compared to single doping. The momentum ratio curves, referenced to undoped ZnO, indicate dopants in interstitial and substitutional sites. The presence of transition metal ions interstitially will trap electrons which resist the recombination of electrons and in turn affect the conductivity of the material.

  20. Corrosion Protection of Copper Using Al2O3, TiO2, ZnO, HfO2, and ZrO2 Atomic Layer Deposition.

    PubMed

    Daubert, James S; Hill, Grant T; Gotsch, Hannah N; Gremaud, Antoine P; Ovental, Jennifer S; Williams, Philip S; Oldham, Christopher J; Parsons, Gregory N

    2017-02-01

    Atomic layer deposition (ALD) is a viable means to add corrosion protection to copper metal. Ultrathin films of Al2O3, TiO2, ZnO, HfO2, and ZrO2 were deposited on copper metal using ALD, and their corrosion protection properties were measured using electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). Analysis of ∼50 nm thick films of each metal oxide demonstrated low electrochemical porosity and provided enhanced corrosion protection from aqueous NaCl solution. The surface pretreatment and roughness was found to affect the extent of the corrosion protection. Films of Al2O3 or HfO2 provided the highest level of initial corrosion protection, but films of HfO2 exhibited the best coating quality after extended exposure. This is the first reported instance of using ultrathin films of HfO2 or ZrO2 produced with ALD for corrosion protection, and both are promising materials for corrosion protection.

  1. Enhanced Visible Light Photocatalytic Activity of ZnO Nanowires Doped with Mn2+ and Co2+ Ions

    PubMed Central

    Li, Wei; Wang, Guojing; Chen, Chienhua; Liao, Jiecui; Li, Zhengcao

    2017-01-01

    In this research, ZnO nanowires doped with Mn2+ and Co2+ ions were synthesized through a facile and inexpensive hydrothermal approach, in which Mn2+ and Co2+ ions successfully substituted Zn2+ in the ZnO crystal lattice without changing the morphology and crystalline structure of ZnO. The atomic percentages of Mn and Co were 6.29% and 1.68%, respectively, in the doped ZnO nanowires. The photocatalytic results showed that Mn-doped and Co-doped ZnO nanowires both exhibited higher photocatalytic activities than undoped ZnO nanowires. Among the doped ZnO nanowires, Co-doped ZnO, which owns a twice active visible-light photocatalytic performance compared to pure ZnO, is considered a more efficient photocatalyst material. The enhancement of its photocatalytic performance originates from the doped metal ions, which enhance the light absorption ability and inhibit the recombination of photo-generated electron-hole pairs as well. The effect of the doped ion types on the morphology, crystal lattice and other properties of ZnO was also investigated. PMID:28336854

  2. Enhanced Visible Light Photocatalytic Activity of ZnO Nanowires Doped with Mn(2+) and Co(2+) Ions.

    PubMed

    Li, Wei; Wang, Guojing; Chen, Chienhua; Liao, Jiecui; Li, Zhengcao

    2017-01-19

    In this research, ZnO nanowires doped with Mn(2+) and Co(2+) ions were synthesized through a facile and inexpensive hydrothermal approach, in which Mn(2+) and Co(2+) ions successfully substituted Zn(2+) in the ZnO crystal lattice without changing the morphology and crystalline structure of ZnO. The atomic percentages of Mn and Co were 6.29% and 1.68%, respectively, in the doped ZnO nanowires. The photocatalytic results showed that Mn-doped and Co-doped ZnO nanowires both exhibited higher photocatalytic activities than undoped ZnO nanowires. Among the doped ZnO nanowires, Co-doped ZnO, which owns a twice active visible-light photocatalytic performance compared to pure ZnO, is considered a more efficient photocatalyst material. The enhancement of its photocatalytic performance originates from the doped metal ions, which enhance the light absorption ability and inhibit the recombination of photo-generated electron-hole pairs as well. The effect of the doped ion types on the morphology, crystal lattice and other properties of ZnO was also investigated.

  3. Transparent conducting impurity-doped ZnO thin films prepared using oxide targets sintered by millimeter-wave heating

    SciTech Connect

    Minami, Tadatsugu; Okada, Kenji; Miyata, Toshihiro; Nomoto, Juni-chi; Hara, Youhei; Abe, Hiroshi

    2009-07-15

    The preparation of transparent conducting impurity-doped ZnO thin films by both pulsed laser deposition (PLD) and magnetron sputtering deposition (MSD) using impurity-doped ZnO targets sintered with a newly developed energy saving millimeter-wave (28 GHz) heating technique is described. Al-doped ZnO (AZO) and V-co-doped AZO (AZO:V) targets were prepared by sintering with various impurity contents for 30 min at a temperature of approximately 1250 degree sign C in an air or Ar gas atmosphere using the millimeter-wave heating technique. The resulting resistivity and its thickness dependence obtainable in thin films prepared by PLD using millimeter-wave-sintered AZO targets were comparable to those obtained in thin films prepared by PLD using conventional furnace-sintered AZO targets; a low resistivity on the order of 3x10{sup -4} {Omega} cm was obtained in AZO thin films prepared with an Al content [Al/(Al+Zn) atomic ratio] of 3.2 at. % and a thickness of 100 nm. In addition, the resulting resistivity and its spatial distribution on the substrate surface obtainable in thin films prepared by rf-MSD using a millimeter-wave-sintered AZO target were almost the same as those obtained in thin films prepared by rf-MSD using a conventional powder AZO target. Thin films prepared by PLD using millimeter-wave-sintered AZO:V targets exhibited an improved resistivity stability in a high humidity environment. Thin films deposited with a thickness of approximately 100 nm using an AZO:V target codoped with an Al content of 4 at. % and a V content [V/(V+Zn) atomic ratio] of 0.2 at. % were sufficiently stable when long-term tested in air at 90% relative humidity and 60 degree sign C.

  4. Photocatalytic oxidation of organic dyes with visible-light-driven codoped TiO2 photocatalysts

    NASA Astrophysics Data System (ADS)

    Zhang, Dongfang; Zeng, Fanbin

    2011-06-01

    A novel copper (II) and zinc (II) codoped TiO2 photocatalyst was synthesized by a modified sol-gel method using titanium (IV) isopropoxide, Zn(NO3)2 · 6H2O and copper(Il) nitrate as precursors. The samples were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and photo-luminescence spectra (PL). The XRD results showed undoped and Zn, Cu-codoped TiO2 nanoparticles mainly including anatase phase and a tiny amount of Zn- and Cu-oxides exist in the mixed system, which is attributed to the decomposition of copper and zinc nitrates in the TiO2 gel to form CuO and ZnO and randomly dispersed on the TiO2 surface. On the basis of the optical characterization results, we found that the codoping of copper (II) and zinc (II) resulted a red shift of adsorption and lower recombination probability between electrons and holes, which were the reasons for high photocatalytic activity of Zn, Cu-codoped TiO2 nanoparticles under visible light (λ > 400 nm). The photocatalytic activity of samples was tested for degradation of methyl orange (MO) in solutions. The results indicated that the visible-light driven capability of the codoped catalyst were much higher than that of the pure TiO2 catalyst under visible irradiation. Because of the synergetic effect of copper (II) and zinc (II) element, the Zn, Cu-codoped TiO2 catalyst will show higher quantum yield and enhance absorption of visible light. In the end, a key mechanism was proposed in order to account for the enhanced activity.

  5. Effect of sputtering power on crystallinity, intrinsic defects, and optical and electrical properties of Al-doped ZnO transparent conducting thin films for optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Hu, Yu Min; Li, Jung Yu; Chen, Nai Yun; Chen, Chih Yu; Han, Tai Chun; Yu, Chin Chung

    2017-02-01

    The crystallinity and intrinsic defects of transparent conducting oxide (TCO) films have a high impact on their optical and electrical properties and therefore on the performance of devices incorporating such films, including flat panel displays, electro-optical devices, and solar cells. The optical and electrical properties of TCO films can be modified by tailoring their deposition parameters, which makes proper understanding of these parameters crucial. Magnetron sputtering is the most adaptable method for preparing TCO films used in industrial applications. In this study, we investigate the direct and inter-property correlation effects of sputtering power (PW) on the crystallinity, intrinsic defects, and optical and electrical properties of Al-doped ZnO (AZO) TCO films. All of the films were preferentially c-axis-oriented with a wurtzite structure and had an average transmittance of over 80% in the visible wavelength region. Scanning electron microscopy images revealed significantly increased AZO film grain sizes for PW ≥ 150 W, which may lead to increased conductivity, carrier concentration, and optical band gaps but decreased carrier mobility and in-plane compressive stress in AZO films. Photoluminescence results showed that, with increasing PW, the near band edge emission gradually dominates the defect-related emissions in which zinc interstitial (Zni), oxygen vacancy (VO), and oxygen interstitial (Oi) are possibly responsible for emissions at 3.08, 2.8, and 2.0 eV, respectively. The presence of Zni- and Oi-related emissions at PW ≥ 150 W indicates a slight increase in the presence of Al atoms substituted at Zn sites (AlZn). The presence of Oi at PW ≥ 150 W was also confirmed by X-ray photoelectron spectroscopy results. These results clearly show that the crystallinity and intrinsic-defect type of AZO films, which dominate their optical and electrical properties, may be controlled by PW. This understanding may facilitate the development of TCO

  6. Optimized structure stability and electrochemical performance of LiNi0.8Co0.15Al0.05O2 by sputtering nanoscale ZnO film

    NASA Astrophysics Data System (ADS)

    Lai, Yan-Qing; Xu, Ming; Zhang, Zhi-An; Gao, Chun-Hui; Wang, Peng; Yu, Zi-Yang

    2016-03-01

    LiNi0.8Co0.15Al0.05O2 (NCA) is one of the most promising cathode material for lithium-ion batteries (LIBs) in electric vehicles, which is successfully adopted in Tesla. However, the dissolution of the cation into the electrolyte is still a one of the major challenges (fading capacity and poor cyclability, etc.) presented in pristine NCA. Herein, a homogeneous nanoscale ZnO film is directly sputtered on the surface of NCA electrode via the magnetron sputtering (MS). This ZnO film is evidenced by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results clearly demonstrate that ZnO film is fully and uniformly covered on the NCA electrodes. After 90 cycles at 1.0C, the optimized MS-2min coated NCA electrode delivers much higher discharge capacity with 169 mAh g-1 than that of the pristine NCA electrode with 127 mAh g-1. In addition, the discharge capacity also reaches 166 mAh g-1 at 3.0C, as compared to that of 125 mAh g-1 for the pristine electrode. The improved electrochemical performance can be ascribed to the superiority of the MS ZnO film that reduce charge transfer resistance and protect the NCA electrode from cation dissolution.

  7. Nitrogen and cobalt co-doped zinc oxide nanowires - Viable photoanodes for hydrogen generation via photoelectrochemical water splitting

    NASA Astrophysics Data System (ADS)

    Patel, Prasad Prakash; Hanumantha, Prashanth Jampani; Velikokhatnyi, Oleg I.; Datta, Moni Kanchan; Hong, Daeho; Gattu, Bharat; Poston, James A.; Manivannan, Ayyakkannu; Kumta, Prashant N.

    2015-12-01

    Photoelectrochemical (PEC) water splitting has been considered as a promising and environmentally benign approach for efficient and economic hydrogen generation by utilization of solar energy. Development of semiconductor materials with low band gap, high photoelectrochemical activity and stability has been of particular interest for a viable PEC water splitting system. In this study, Co doped ZnO, .i.e., (Zn0.95Co0.05)O nanowires (NWs) was selected as the composition for further co-doping with nitrogen by comparing solar to hydrogen efficiency (SHE) of ZnO NWs with that of various compositions of (Zn1-xCox)O NWs (x = 0, 0.05, 0.1). Furthermore, nanostructured vertically aligned Co and N-doped ZnO, .i.e., (Zn1-xCox)O:N NWs (x = 0.05) have been studied as photoanodes for PEC water splitting. An optimal SHE of 1.39% the highest reported so far to the best of our knowledge for ZnO based photoanodes was obtained for the co-doped NWs, (Zn0.95Co0.05)O:N - 600 NWs generated at 600 °C in ammonia atmosphere. Further, (Zn0.95Co0.05)O:N-600 NWs exhibited excellent photoelectrochemical stability under illumination compared to pure ZnO NWs. These promising results suggest the potential of (Zn0.95Co0.05)O:N-600 NWs as a viable photoanode in PEC water splitting cell. Additionally, theoretical first principles study conducted explains the beneficial effects of Co and N co-doping on both, the electronic structure and the band gap of ZnO.

  8. ZnO based light emitting diodes growth and fabrication

    NASA Astrophysics Data System (ADS)

    Pan, M.; Rondon, R.; Cloud, J.; Rengarajan, V.; Nemeth, W.; Valencia, A.; Gomez, J.; Spencer, N.; Nause, J.

    2006-02-01

    ZnO and N-doped ZnO thin films were grown by MOCVD on sapphire and ZnO substrates. Diethyl zinc and O II were used as sources for Zn and O, respectively. A specially designed plasma system was employed to produce atomic N dopant for in-situ doping. Proper disk rotation speeds were found for ZnO growth on different size wafers. High crystal quality N-doped ZnO films were grown based on optimized growth conditions. Wet chemical etch of ZnO was investigated by using NH 4Cl, and etch activation energy was calculated to be 463meV. Ohmic contact on N-doped ZnO film was achieved by using Ni/Au/Al multiple layers. ZnO based p-n junction has demonstrated rectification. Electroluminescence at about 384nm was obtained from ZnO based LED.

  9. Origins of Highly Stable Al-evaporated Solution-processed ZnO Thin Film Transistors: Insights from Low Frequency and Random Telegraph Signal Noise

    PubMed Central

    Kim, Joo Hyung; Kang, Tae Sung; Yang, Jung Yup; Hong, Jin Pyo

    2015-01-01

    One long-standing goal in the emerging field of flexible and transparent electronic devices is to meet the demand of key markets, such as enhanced output performance for metal oxide semiconductor thin film transistors (TFTs) prepared by a solution process. While solution-based fabrication techniques are cost-effective and ensure large-area coverage at low temperature, their utilization has the disadvantage of introducing large trap states into TFTs. Such states, the formation of which is induced by intrinsic defects initially produced during preparation, have a significant impact on electrical performance. Therefore, the ability to enhance the electrical characteristics of solution-processed TFTs, along with attaining a firm understanding of their physical nature, remains a key step towards extending their use. In this study, measurements of low-frequency noise and random telegraph signal noise are employed as generic alternative tools to examine the origins of enhanced output performance for solution-processed ZnO TFTs through the control of defect sites by Al evaporation. PMID:26525284

  10. Photo-luminescent properties and synthesis of Ca3Al4ZnO10:Mn4+ deep red-emitting phosphor

    NASA Astrophysics Data System (ADS)

    Cao, Renping; Zhang, Jinlong; Wang, Wudi; Chen, Ting; Gou, Qingdong; Wen, Yufeng; Xiao, Fen; Luo, Zhiyang

    2017-04-01

    Novel deep red-emitting Ca3Al4ZnO10:Mn4+ (CAZO:Mn4+) phosphor is synthesized by high-temperature solid-state reaction method in air. The crystal structures and optical characterizations of the phosphors are described. X-ray diffraction patterns indicate that all samples are a pure phase. CAZO:Mn4+ phosphor with excitation 330 and 465 nm exhibits strong deep red emission in the range of 650-790 nm. CAZO:Mn4+ phosphor can be efficiently excited by near-ultraviolet and blue light from 300 to 500 nm. The optimal Mn4+ ion concentration in CAZO:Mn4+ phosphor is ∼0.6 mol%. Lifetimes of CAZO:xMn4+ (0.3 ≤ x ≤ 1.8 mol%) phosphors decrease from 1.95 to 1.56 ms with increasing Mn4+ ion concentration in the range of 0.3-1.8 mol%. The paper content is help to develop other Mn4+ ion doped luminescence materials.

  11. Characteristics of Ga-Al doped ZnO thin films with plasma treatment prepared by using facing target sputtering method.

    PubMed

    Kim, Ki Hyun; Choi, Hyung Wook; Kim, Kyung Hwan

    2013-09-01

    Ga-Al-doped ZnO (GAZO) thin films were prepared on glass substrates using facing targets sputtering at room temperature. GAZO thin films have been treated in O2 plasma to modify surface roughness in order to enhance the efficiency of OLED anodes made from the films. After deposition of the thin films, the substrate was subjected to plasma surface treatment. The electrical, optical, and surface properties of the deposited thin films were investigated by hall-effect measurement, UV/Vis spectrometry, and atomic force microscopy (AFM), respectively. As a result of increasing the plasma treatment time from 0 to 45 sec, the surface roughness of films after plasma treatment was improved, but their electrical, optical, and structural properties were slightly changed. The lowest values of the surface roughness were 1.409 nm for the as-deposited GAZO thin films for an O2 plasma treatment time of 40 sec. All GAZO thin films have an average transmittance of 90% in the visible range (400-800 nm).

  12. Raman study of TiO2 role in SiO2-Al2O3-MgO-TiO2-ZnO glass crystallization.

    PubMed

    Furić, Kresimir; Stoch, Leszek; Dutkiewicz, Jan

    2005-05-01

    Tough glass-ceramic material of special mechanical properties with nanosize crystal phases formed by appropriately controlled crystallization was studied by Raman spectroscopy. It was obtained by TiO2 activated crystallization of Mg-aluminosilicate glass of SiO2-Al2O3-MgO-TiO2-ZnO composition. Crystallization was preceded by a change in the TiO2 structural position and state, which is manifested by a changed color of glass from yellow into blue shortly before the glass transformation (Tg) temperature. Raman spectroscopy was applied to explain the mechanism of this process and to establish the role of TiO2 in the early stage of glass crystallization that precedes a complete crystal phase formation. The starting glasses were found in almost complete disorder, since all bands were weak, broad and dominated by a Bose band at about 90 cm-1. After the sample annealing all bands turned out better resolved and the Bose band practically disappeared, both confirming the amorphous structure reorganization process. A multiplet observed in the vicinity of 150 cm-1 we assigned to the anatase and other titania structures that can be considered prime centers of crystallization. Finally, in the closest neighborhood of the Rayleigh line the low frequency mode characterizing nanoparticles was observed. According to this band theory, the mean size of initial titania crystallites is about 10nm for all samples, but the size distribution varies within factor two among them.

  13. Photoluminescence of Ga-doped ZnO film grown on c-Al2O3 (0001) by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Park, H. C.; Byun, D.; Angadi, B.; Hee Park, D.; Choi, W. K.; Choi, J. W.; Jung, Y. S.

    2007-10-01

    High quality gallium doped ZnO (Ga:ZnO) thin films were grown on c-Al2O3(1000) by plasma-assisted molecular beam epitaxy, and Ga concentration NGa was controlled in the range of 1×1018-2.5×1020/cm3 by adjusting/changing the Ga cell temperature. From the low-temperature photoluminescence at 10K, the donor bound exciton I8 related to Ga impurity was clearly observed and confirmed by comparing the calculated activation energy of 16.8meV of the emission peak intensity with the known localization energy, 16.1meV. Observed asymmetric broadening with a long tail on the lower energy side in the photoluminescence (PL) emission line shape could be fitted by the Stark effect and the compensation ratio was approximately 14-17% at NGa⩾1×1020/cm3. The measured broadening of photoluminescence PL emission is in good agreement with the total thermal broadening and potential fluctuations caused by random distribution of impurity at NGa lower than the Mott critical density.

  14. Transparent conducting Al-doped ZnO thin films prepared by magnetron sputtering with dc and rf powers applied in combination

    SciTech Connect

    Minami, Tadatsugu; Ohtani, Yuusuke; Miyata, Toshihiro; Kuboi, Takeshi

    2007-07-15

    A newly developed Al-doped ZnO (AZO) thin-film magnetron-sputtering deposition technique that decreases resistivity, improves resistivity distribution, and produces high-rate depositions has been demonstrated by dc magnetron-sputtering depositions that incorporate rf power (dc+rf-MS), either with or without the introduction of H{sub 2} gas into the deposition chamber. The dc+rf-MS preparations were carried out in a pure Ar or an Ar+H{sub 2} (0%-2%) gas atmosphere at a pressure of 0.4 Pa by adding a rf component (13.56 MHz) to a constant dc power of 80 W. The deposition rate in a dc+rf-MS deposition incorporating a rf power of 150 W was approximately 62 nm/min, an increase from the approximately 35 nm/min observed in dc magnetron sputtering with a dc power of 80 W. A resistivity as low as 3x10{sup -4} {omega} cm and an improved resistivity distribution could be obtained in AZO thin films deposited on substrates at a low temperature of 150 deg. C by dc+rf-MS with the introduction of hydrogen gas with a content of 1.5%. This article describes the effects of adding a rf power component (i.e., dc+rf-MS deposition) as well as introducing H{sub 2} gas into dc magnetron-sputtering preparations of transparent conducting AZO thin films.

  15. In situ spectroscopic ellipsometry growth studies on the Al-doped ZnO films deposited by remote plasma-enhanced metalorganic chemical vapor deposition

    SciTech Connect

    Volintiru, I.; Creatore, M.; Sanden, M. C. M. van de

    2008-02-01

    In situ spectroscopic ellipsometry (SE) was applied to study the pyramidlike and pillarlike growth of Al doped ZnO (AZO) films deposited by means of remote plasma-enhanced metalorganic chemical vapor deposition for transparent conductive oxide applications. Real time SE studies in the visible region allowed discerning between the two growth modes by addressing the time evolution of the bulk and surface roughness layer thickness. While the pillarlike mode is characterized by a constant growth rate, a slower rate in the initial stage (up to 150-200 nm film thickness), compared to the bulk, is observed for the growth of pyramidlike AZO films. The two modes differ also in terms of surface roughness development: a saturation behavior is observed for film thickness above 150-200 nm in the case of the pyramidlike films, while a slow linear increase with film thickness characterizes the pillarlike mode. By extending the SE analysis of the AZO films to the near infrared region, valuable information about the in grain properties could be extracted: excellent in grain mobility values, i.e., larger than 100 and 50 cm{sup 2}/V s, are determined for the pyramidlike and pillarlike AZO layers, respectively. The comparison between the outcome of the in situ real time SE studies and the ex situ electrical and chemical characterization highlights the limitations in the electron transport occurring in both types of films and allows one to address routes toward further improvement in AZO conductivity.

  16. Origins of Highly Stable Al-evaporated Solution-processed ZnO Thin Film Transistors: Insights from Low Frequency and Random Telegraph Signal Noise

    NASA Astrophysics Data System (ADS)

    Kim, Joo Hyung; Kang, Tae Sung; Yang, Jung Yup; Hong, Jin Pyo

    2015-11-01

    One long-standing goal in the emerging field of flexible and transparent electronic devices is to meet the demand of key markets, such as enhanced output performance for metal oxide semiconductor thin film transistors (TFTs) prepared by a solution process. While solution-based fabrication techniques are cost-effective and ensure large-area coverage at low temperature, their utilization has the disadvantage of introducing large trap states into TFTs. Such states, the formation of which is induced by intrinsic defects initially produced during preparation, have a significant impact on electrical performance. Therefore, the ability to enhance the electrical characteristics of solution-processed TFTs, along with attaining a firm understanding of their physical nature, remains a key step towards extending their use. In this study, measurements of low-frequency noise and random telegraph signal noise are employed as generic alternative tools to examine the origins of enhanced output performance for solution-processed ZnO TFTs through the control of defect sites by Al evaporation.

  17. Band alignment at the interface between Ni-doped Cr2O3 and Al-doped ZnO: implications for transparent p-n junctions

    NASA Astrophysics Data System (ADS)

    Arca, Elisabetta; McInerney, Michael A.; Shvets, Igor V.

    2016-06-01

    The realization of transparent electronic and optoelectronic devices requires the use of transparent p-n junctions. In this context, understanding the band alignment at the interface between the p- and n-components represents a fundamental step towards the realization of high performance devices. In this work, the band alignment at the interface between Al-doped ZnO (AZO) and Ni-doped Cr2O3 has been analysed. The formation and evolution of the core levels as the interface progressively forms have been followed by means of x-ray Photoelectron Spectroscopy, x-ray diffraction and x-ray reflectivity. A type two (staggered) band alignment was identified, with the valence band offset and conduction band offset found to be 2.6 eV and 2.5 eV, respectively. The electrical behaviour will be discussed in terms of the position of the bands, the presence of band bending and the expected built-in potential and how these can be engineered in order to achieve the maximum performance for this hetero-structure.

  18. Correlations between 1/f noise and thermal treatment of Al-doped ZnO thin films deposited by direct current sputtering

    SciTech Connect

    Barhoumi, A. Guermazi, S.; Leroy, G.; Gest, J.; Carru, J. C.; Yang, L.; Boughzala, H.; Duponchel, B.

    2014-05-28

    Al-doped ZnO thin films (AZO) have been deposited on amorphous glass substrates by DC sputtering at different substrate temperatures T{sub s}. X-Ray diffraction results reveal that AZO thin films have a hexagonal wurtzite structure with (002) preferred orientation. (002) peaks indicate that the crystalline structure of the films is oriented with c-axis perpendicular to the substrate. Three-dimensional (3D) atomic force microscopy images of AZO thin films deposited on glass substrate at 200 °C, 300 °C, and 400 °C, respectively, shows the improvement of the crystallinity and the homogeneity of AZO thin films with T{sub s} which is in agreement with the noise measurements. The noise was characterized between 1 Hz and 100 kHz and we have obtained 1/f spectra. The noise is very sensitive to the crystal structure especially to the orientation of the crystallites which is perpendicular to the substrate and to the grain boundaries which generate a high current flow and a sharp increase in noise. Through time, R{sub sh} and [αμ]{sub eff} increase with the modification of the crystallinity of AZO thin films. Study of noise aging shows that the noise is more sensitive than resistivity for all AZO thin films.

  19. A brief review of co-doping

    NASA Astrophysics Data System (ADS)

    Zhang, Jingzhao; Tse, Kinfai; Wong, Manhoi; Zhang, Yiou; Zhu, Junyi

    2016-12-01

    Dopants and defects are important in semiconductor and magnetic devices. Strategies for controlling doping and defects have been the focus of semiconductor physics research during the past decades and remain critical even today. Co-doping is a promising strategy that can be used for effectively tuning the dopant populations, electronic properties, and magnetic properties. It can enhance the solubility of dopants and improve the stability of desired defects. During the past 20 years, significant experimental and theoretical efforts have been devoted to studying the characteristics of co-doping. In this article, we first review the historical development of co-doping. Then, we review a variety of research performed on co-doping, based on the compensating nature of co-dopants. Finally, we review the effects of contamination and surfactants that can explain the general mechanisms of co-doping.

  20. Magnetic properties of Co-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Franco, A.; Pessoni, H. V. S.; Ribeiro, P. R. T.; Machado, F. L. A.

    2017-03-01

    The magnetism in nanoparticulate powders of Zn1-xCoxO with 0 ≤ x ≤ 0.09 synthesized by a combustion reaction technique is investigated in a broad range of temperatures (5 ≤T ≤ 750K) for applied magnetic fields up to 85 kOe. The hysteresis loops indicated the presence of both ferromagnetic and paramagnetic ordering at room temperature. An additional antiferromagnetic phase was observed for temperatures below 260 K . A particle model that can account for the results is that the some of doping Co2+ ions are not interagent among themselves, a small quantity form clusters, leading to the ferromagnetic ordering with some of the particles in the superparamagnetic state, and few others Co2+ ions form CoO at the grain boundary yielding the antiferromagnetic phase. It was also found that a modified Langevin function can be used for describing the H - dependence for magnetization data.

  1. Optical and structural properties of Al-doped ZnO thin films by sol gel process.

    PubMed

    Jun, Min-Chul; Koh, Jung-Hyuk

    2013-05-01

    Transparent conducting oxide (TCO) materials with high transmittance and good electrical conductivity have been attracted much attention due to the development of electronic display and devices such as organic light emitting diodes (OLEDs), and dye-sensitized solar cells (DSSCs). Aluminum doped zinc oxide thin films (AZO) have been well known for their use as TCO materials due to its stability, cost-effectiveness, good optical transmittance and electrical properties. Especially, AZO thin film, which have low resistivity of 2-4 x 10(-4) omega x cm which is similar to that of ITO films with wide band gap semiconductors. The AZO thin films were deposited on glass substrates by sol-gel spin-coating process. As a starting material, zinc acetate dihydrate (Zn(CH3COO)2 x 2H2O) and aluminum chloride hexahydrate (AlCl3 6H2O) were used. 2-methoxyethanol and monoethanolamine (MEA) were used as solvent and stabilizer, respectively. After deposited, the films were preheated at 300 degrees C on a hotplate and post-heated at 650 degrees C for 1.5 hrs in the furnace. We have studied the structural and optical properties as a function of Al concentration (0-2.5 mol.%).

  2. Effects of NIR annealing on the characteristics of al-doped ZnO thin films prepared by RF sputtering.

    PubMed

    Jun, Min-Chul; Koh, Jung-Hyuk

    2012-06-06

    Aluminum-doped zinc oxide (AZO) thin films have been deposited on glass substrates by employing radio frequency (RF) sputtering method for transparent conducting oxide applications. For the RF sputtering process, a ZnO:Al2O3 (2 wt.%) target was employed. In this paper, the effects of near infrared ray (NIR) annealing technique on the structural, optical, and electrical properties of the AZO thin films have been researched. Experimental results showed that NIR annealing affected the microstructure, electrical resistance, and optical transmittance of the AZO thin films. X-ray diffraction analysis revealed that all films have a hexagonal wurtzite crystal structure with the preferentially c-axis oriented normal to the substrate surface. Optical transmittance spectra of the AZO thin films exhibited transmittance higher than about 80% within the visible wavelength region, and the optical direct bandgap (Eg) of the AZO films was increased with increasing the NIR energy efficiency.

  3. Electrical stability of Al-doped ZnO transparent electrode prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Tabassum, Samia; Yamasue, Eiji; Okumura, Hideyuki; Ishihara, Keiichi N.

    2016-07-01

    Al-doped zinc oxide (AZO) thin films have been considered as a promising alternative to tin doped indium oxide (ITO), which is currently used in various optoelectronic applications. However, the environmental stability of AZO film is not satisfactory, in that the resistivity is significantly increases in air. Here, we investigate the resistivity stability of AZO thin films prepared by sol-gel method using various annealing temperatures and durations. The degradation of resistivity property was observed for AZO films stored in ambient or damp heat environment, where the degradation rate was influenced by annealing temperature. A significant improvement of electrical stability was attained in AZO films that were prepared at high annealing temperature. The films, which showed the highest and the lowest increasing rate of resistivity, were further characterized in detail to shed light on the possible mechanisms explaining the improved stability through crystallinity, surface morphology and elemental state of the thin film.

  4. Stable and high-quality Al-doped ZnO films with ICP-assisted facing targets sputtering at low temperature

    NASA Astrophysics Data System (ADS)

    Choi, Yoon S.; Kim, Hye R.; Han, Jeon G.

    2014-04-01

    FTS (facing targets sputtering) has been studied intensively for high-quality TCO films in low-temperature processes. In this study, we designed ICP-assisted FTS process for high-quality Al-doped ZnO film synthesis in a low temperature process. A one-turn ICP coil was installed a few cm above the upper target edge through which hydrogen was introduced and fully dissociated to the atomic radicals. The increase of ICP power caused heating and rarefaction of Ar gas and generated abundant hydrogen atoms and hydrogenated molecules. In FESEM analysis, the films synthesized with high ICP power showed high crystallinity. XPS was used to analyze the film structure. In O1s spectra, the low binding energy component located at ˜530.3 ± 0.4 eV corresponding to O2- ions on the wurtzite structure of the hexagonal Zn2+ ion array increased with the ICP power, indicating good crystal quality. With increasing ICP power fixing while fixing the RF power at the cathode, the resistivity was observed to decrease to 5 × 10-4 Ω-cm. For thermal reliability tests, films were stored in an air-based chamber at 200 °C. The films synthesized without ICP showed rapid degradation in the electrical properties, while the films synthesized with high ICP power showed good stabilities with little change in the electrical properties after 30 h of storage in an oven. By adding hydrogen, the carrier concentration of the films increased, while the mobility did not change much. From these results, it is expected that hydrogen was incorporated into the film as a stable n-dopant by using an auxiliary ICP plasma source.

  5. In situ analyses on negative ions in the sputtering process to deposit Al-doped ZnO films

    SciTech Connect

    Tsukamoto, Naoki; Watanabe, Daisuke; Saito, Motoaki; Sato, Yasushi; Oka, Nobuto; Shigesato, Yuzo

    2010-07-15

    The origin of high energy negative ions during deposition of aluminum doped zinc oxide (AZO) films by dc magnetron sputtering of an AZO (Al{sub 2}O{sub 3}: 2.0 wt %) target was investigated by in situ analyses using the quadrupole mass spectrometer combined with the electrostatic energy analyzer. High energy negative oxygen (O{sup -}) ions which possessed the kinetic energy corresponding to the cathode sheath voltage were detected. The maximum flux of the O{sup -} ions was clearly observed at the location opposite to the erosion track area on the target. The flux of the O{sup -} ions changed hardly with increasing O{sub 2} flow ratio [O{sub 2}/(Ar+O{sub 2})] from 0% to 5%. The kinetic energy of the O{sup -} ions decreased with decreasing cathode sheath voltage from 403 to 337 V due to the enhancement of the vertical maximum magnetic field strength at the cathode surface from 0.025 to 0.100 T. The AZO films deposited with the lower O{sup -} bombardment energy showed the higher crystallinity and improved the electrical conductivity.

  6. Doped ZnO nanowires obtained by thermal annealing.

    PubMed

    Shan, C X; Liu, Z; Wong, C C; Hark, S K

    2007-02-01

    Doped ZnO nanowires were prepared in a very simple and inexpensive thermal annealing method using ZnSe nanowires as a precursor. As doped, P doped, and As/P codoped ZnO nanowires were obtained in this method. X-ray diffraction shows that the zincblende ZnSe nanowires were converted to doped wurtzite ZnO nanowires. The incorporation of the dopants was confirmed by energy dispersive X-ray spectroscopy. The doping concentration could be adjusted by changing the annealing temperature and duration. Scanning electron microscopy indicated that the morphology of the ZnSe nanowires was essentially retained after the annealing and doping process. Photoluminescence spectroscopy also verified the incorporation of the dopants into the nanowires.

  7. Anisotropic temperature-dependent thermal conductivity by an Al2O3 interlayer in Al2O3/ZnO superlattice films

    NASA Astrophysics Data System (ADS)

    Lee, Won-Yong; Lee, Jung-Hoon; Ahn, Jae-Young; Park, Tae-Hyun; Park, No-Won; Kim, Gil-Sung; Park, Jin-Seong; Lee, Sang-Kwon

    2017-03-01

    The thermal conductivity of superlattice films is generally anisotropic and should be studied separately in the in-plane and cross-plane directions of the films. However, previous works have mostly focused on the cross-plane thermal conductivity because the electrons and phonons in the cross-plane direction of superlattice films may result in much stronger interface scattering than that in the in-plane direction. Nevertheless, it is highly desirable to perform systematic studies on the effect of interface formation in semiconducting superlattice films on both in-plane and cross-plane thermal conductivities. In this study, we determine both the in-plane and cross-plane thermal conductivities of Al2O3 (AO)/ZnO superlattice films grown by atomic layer deposition (ALD) on SiO2/Si substrates in the temperature range of 50–300 K by the four-point-probe 3-ω method. Our experimental results indicate that the formation of an atomic AO layer (0.82 nm) significantly contributes to the decrease of the cross-plane thermal conductivity of the AO/ZnO superlattice films compared with that of AO/ZnO thin films. The cross-plane thermal conductivity (0.26–0.63 W m‑1 K‑1 of the AO/ZnO superlattice films (with an AO layer of ∼0.82 nm thickness) is approximately ∼150%–370% less than the in-plane thermal conductivity (0.96–1.19 W m‑1 K‑1) of the corresponding film, implying significant anisotropy. This indicates that the suppression of the cross-plane thermal conductivity is mainly attributed to the superlattice, rather than the nanograin columnar structure in the films. In addition, we theoretically analyzed strong anisotropic behavior of the in-plane and cross-plane thermal conductivities of the AO/ZnO superlattice films in terms of temperature dependence.

  8. Anisotropic temperature-dependent thermal conductivity by an Al2O3 interlayer in Al2O3/ZnO superlattice films.

    PubMed

    Lee, Won-Yong; Lee, Jung-Hoon; Ahn, Jae-Young; Park, Tae-Hyun; Park, No-Won; Kim, Gil-Sung; Park, Jin-Seong; Lee, Sang-Kwon

    2017-03-10

    The thermal conductivity of superlattice films is generally anisotropic and should be studied separately in the in-plane and cross-plane directions of the films. However, previous works have mostly focused on the cross-plane thermal conductivity because the electrons and phonons in the cross-plane direction of superlattice films may result in much stronger interface scattering than that in the in-plane direction. Nevertheless, it is highly desirable to perform systematic studies on the effect of interface formation in semiconducting superlattice films on both in-plane and cross-plane thermal conductivities. In this study, we determine both the in-plane and cross-plane thermal conductivities of Al2O3 (AO)/ZnO superlattice films grown by atomic layer deposition (ALD) on SiO2/Si substrates in the temperature range of 50-300 K by the four-point-probe 3-ω method. Our experimental results indicate that the formation of an atomic AO layer (0.82 nm) significantly contributes to the decrease of the cross-plane thermal conductivity of the AO/ZnO superlattice films compared with that of AO/ZnO thin films. The cross-plane thermal conductivity (0.26-0.63 W m(-1) K(-1) of the AO/ZnO superlattice films (with an AO layer of ∼0.82 nm thickness) is approximately ∼150%-370% less than the in-plane thermal conductivity (0.96-1.19 W m(-1) K(-1)) of the corresponding film, implying significant anisotropy. This indicates that the suppression of the cross-plane thermal conductivity is mainly attributed to the superlattice, rather than the nanograin columnar structure in the films. In addition, we theoretically analyzed strong anisotropic behavior of the in-plane and cross-plane thermal conductivities of the AO/ZnO superlattice films in terms of temperature dependence.

  9. Transition-metal-doped ZnO nanoparticles: synthesis, characterization and photocatalytic activity under UV light.

    PubMed

    Saleh, Rosari; Djaja, Nadia Febiana

    2014-09-15

    ZnO nanoparticles doped with transition metals (Mn and Co) were prepared by a co-precipitation method. The synthesized nanoparticles were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-rays, Fourier transform infrared spectroscopy, electron spin resonance spectroscopy and diffuse reflectance spectroscopy. The photocatalytic activities of the transition-metal-doped ZnO nanoparticles were evaluated in the degradation of methyl orange under UV irradiation. ZnO nanoparticles doped with 12 at.% of Mn and Co ions exhibited the maximum photodegradation efficiency. The experiment also demonstrated that the photodegradation efficiency of Mn-doped ZnO nanoparticles was higher than that of Co-doped ZnO nanoparticles. These results indicate that charge trapping states due to the doping were the decisive factor rather than the average particle size and energy gap. Moreover the effect of pH values on the degradation efficiency was discussed in the photocatalytic experiments using 12 at.% Mn- and Co-doped ZnO nanoparticles.

  10. Transition-metal-doped ZnO nanoparticles: Synthesis, characterization and photocatalytic activity under UV light

    NASA Astrophysics Data System (ADS)

    Saleh, Rosari; Djaja, Nadia Febiana

    2014-09-01

    ZnO nanoparticles doped with transition metals (Mn and Co) were prepared by a co-precipitation method. The synthesized nanoparticles were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-rays, Fourier transform infrared spectroscopy, electron spin resonance spectroscopy and diffuse reflectance spectroscopy. The photocatalytic activities of the transition-metal-doped ZnO nanoparticles were evaluated in the degradation of methyl orange under UV irradiation. ZnO nanoparticles doped with 12 at.% of Mn and Co ions exhibited the maximum photodegradation efficiency. The experiment also demonstrated that the photodegradation efficiency of Mn-doped ZnO nanoparticles was higher than that of Co-doped ZnO nanoparticles. These results indicate that charge trapping states due to the doping were the decisive factor rather than the average particle size and energy gap. Moreover the effect of pH values on the degradation efficiency was discussed in the photocatalytic experiments using 12 at.% Mn- and Co-doped ZnO nanoparticles.

  11. Poole-Frenkel effect on electrical characterization of Al-doped ZnO films deposited on p-type GaN

    SciTech Connect

    Huang, Bohr-Ran; Liao, Chung-Chi; Ke, Wen-Cheng Chang, Yuan-Ching; Huang, Hao-Ping; Chen, Nai-Chuan

    2014-03-21

    This paper presents the electrical properties of Al-doped ZnO (AZO) films directly grown on two types of p-type GaN thin films. The low-pressure p-GaN thin films (LP-p-GaN) exhibited structural properties of high-density edge-type threading dislocations (TDs) and compensated defects (i.e., nitrogen vacancy). Compared with high-pressure p-GaN thin films (HP-p-GaN), X-ray photoemission spectroscopy of Ga 3d core levels indicated that the surface Fermi-level shifted toward the higher binding-energy side by approximately 0.7 eV. The high-density edge-type TDs and compensated defects enabled surface Fermi-level shifting above the intrinsic Fermi-level, causing the surface of LP-p-GaN thin films to invert to n-type semiconductor. A highly nonlinear increase in leakage current regarding reverse-bias voltage was observed for AZO/LP-p-GaN. The theoretical fits for the reverse-bias voltage region indicated that the field-assisted thermal ionization of carriers from defect associated traps, which is known as the Poole-Frenkel effect, dominated the I-V behavior of AZO/LP-p-GaN. The fitting result estimated the trap energy level at 0.62 eV below the conduction band edge. In addition, the optical band gap increased from 3.50 eV for as-deposited AZO films to 3.62 eV for 300 °C annealed AZO films because of the increased carrier concentration. The increasing Fermi-level of the 300 °C annealed AZO films enabled the carrier transport to move across the interface into the LP-p-GaN thin films without any thermal activated energy. Thus, the Ohmic behavior of AZO contact can be achieved directly on the low-pressure p-GaN films at room temperature.

  12. Characteristics of Al-doped ZnO thin films prepared in Ar + H{sub 2} atmosphere and their vacuum annealing behavior

    SciTech Connect

    Zhu, Bailin; Lü, Kun; Wang, Jun; Li, Taotao; Wu, Jun; Zeng, Dawen; Xie, Changsheng

    2013-11-15

    The microstructure and electrical–optical properties of Al-doped ZnO (AZO) films have been studied as a function of H{sub 2} flux in the magnetron sputtering process at 150 °C and postannealing temperature in vacuum. As H{sub 2} flux increases in the sputtering gas, the AZO films deposited have a (002) preferred orientation rather than the mixed (100) and (002) orientations, the grain size shows a tendency to first increase then decrease, and (002) diffraction peak position is inclined to shift to higher angles first then to lower angles. The resistivity of the films first decreases then increases with H{sub 2} flux, and the lowest resistivity of 4.02 × 10{sup −4}Ω cm is obtained at a H{sub 2} flux of 10 sccm. The average transmittance in the visible region shows little dependence on H{sub 2} flux. As a whole, the AZO films with higher values of figure of merit are obtained when the H{sub 2} flux is in the range of 6–12 sccm. The AZO films deposited in Ar and Ar + H{sub 2} exhibit different annealing behaviors. For the AZO film deposited in Ar, the grain size gradually increases, the stresses are relaxed, the resistivity first decreases then increases, and the average transmittance in the visible region is unchanged initially then somewhat decreased as annealing temperature is increased. The optimum annealing temperature for improving properties of AZO films deposited in Ar is 300 °C. For the AZO films deposited in Ar + H{sub 2}, annealing does not significantly change the microstructure but increases the resistivity of the films; the average transmittance in the visible region remains unchanged initially but greatly reduced with further increase in annealing temperature. The carrier transport in the as-deposited and annealed films appears to be controlled by a mechanism of grain boundary scattering, and the value of E{sub g} increases with the increase in carrier concentration due to Burstein–Moss effect.

  13. Mediator-free interaction of glucose oxidase, as model enzyme for immobilization, with Al-doped and undoped ZnO thin films laser-deposited on polycarbonate supports.

    PubMed

    V T K P, Fidal; Inguva, Saikumar; Krishnamurthy, Satheesh; Marsili, Enrico; Mosnier, Jean-Paul; T S, Chandra

    2017-01-01

    Al doped and undoped ZnO thin films were deposited by pulsed-laser deposition on polycarbonate sheets. The films were characterized by optical transmission, Hall effect measurement, XRD and SEM. Optical transmission and surface reflectometry studies showed good transparency with thicknesses ∼100nm and surface roughness of 10nm. Hall effect measurements showed that the sheet carrier concentration was -1.44×10(15)cm(-2) for AZO and -6×10(14)cm(-2) for ZnO. The films were then modified by drop-casting glucose oxidase (GOx) without the use of any mediators. Higher protein concentration was observed on ZnO as compared to AZO with higher specific activity for ZnO (0.042Umg(-1)) compared to AZO (0.032Umg(-1)), and was in agreement with cyclic voltemmetry (CV). X-ray photoelectron spectroscopy (XPS) suggested that the protein was bound by dipole interactions between AZO lattice oxygen and the amino group of the enzyme. Chronoamperometry showed sensitivity of 5.5μAmM(-1)cm(-2) towards glucose for GOx/AZO and 2.2μAmM(-1)cm(-2) for GOx/ZnO. The limit of detection (LoD) was 167μM of glucose for GOx/AZO, as compared to 360μM for GOx/ZnO. The linearity was 0.28-28mM for GOx/AZO whereas it was 0.6-28mM for GOx/ZnO with a response time of 10s. Possibly due to higher enzyme loading, the decrease of impedance in presence of glucose was larger for GOx/ZnO as compared to GOx/AZO in electrochemical impedance spectroscopy (EIS). Analyses with clinical blood serum samples showed that the systems had good reproducibility and accuracy. The characteristics of novel ZnO and AZO thin films with GOx as a model enzyme, should prove useful for the future fabrication of inexpensive, highly sensitive, disposable electrochemical biosensors for high throughput diagnostics.

  14. Low-Temperature PLD-Growth of Ultrathin ZnO Nanowires by Using Zn x Al1- x O and Zn x Ga1- x O Seed Layers

    NASA Astrophysics Data System (ADS)

    Shkurmanov, Alexander; Sturm, Chris; Franke, Helena; Lenzner, Jörg; Grundmann, Marius

    2017-02-01

    ZnO nanowires (NWs) are used as building blocks for a wide range of different devices, e.g. light emitters, resonators, and sensors. Integration of the NWs into such structures requires a high level of NWs' diameter control. Here, we present that the doping concentration of Zn x Al1- x O and Zn x Ga1- x O seed layers has a strong impact on the NW growth and allows to tune the diameter of the NWs by two orders of magnitude down to less than 7 nm. These ultrathin NWs exhibit a well-oriented vertical growth and thus are promising for the investigation of quantum effects. The doping of the ZnO seed layers has also an impact on the deposition temperature which can be reduced down to T≈400∘C. This temperature is much smaller than those typically used for the fabrication of NWs by pulsed laser deposition. A comparison of the NWs indicates a stronger impact of the Ga doping on the NW growth than for the Al doping which we attribute to an impact of the size of the dopants. The optical properties of the NWs were investigated by cathodoluminescence spectroscopy which revealed a high crystalline quality. For the thin nanowires, the emission characteristic is mainly determined by the properties of the surface near region.

  15. Low-Temperature PLD-Growth of Ultrathin ZnO Nanowires by Using Zn x Al1-x O and Zn x Ga1-x O Seed Layers.

    PubMed

    Shkurmanov, Alexander; Sturm, Chris; Franke, Helena; Lenzner, Jörg; Grundmann, Marius

    2017-12-01

    ZnO nanowires (NWs) are used as building blocks for a wide range of different devices, e.g. light emitters, resonators, and sensors. Integration of the NWs into such structures requires a high level of NWs' diameter control. Here, we present that the doping concentration of Zn x Al1-x O and Zn x Ga1-x O seed layers has a strong impact on the NW growth and allows to tune the diameter of the NWs by two orders of magnitude down to less than 7 nm. These ultrathin NWs exhibit a well-oriented vertical growth and thus are promising for the investigation of quantum effects. The doping of the ZnO seed layers has also an impact on the deposition temperature which can be reduced down to T≈400(∘)C. This temperature is much smaller than those typically used for the fabrication of NWs by pulsed laser deposition. A comparison of the NWs indicates a stronger impact of the Ga doping on the NW growth than for the Al doping which we attribute to an impact of the size of the dopants. The optical properties of the NWs were investigated by cathodoluminescence spectroscopy which revealed a high crystalline quality. For the thin nanowires, the emission characteristic is mainly determined by the properties of the surface near region.

  16. Control of phonon transport by the formation of the Al2O3 interlayer in Al2O3-ZnO superlattice thin films and their in-plane thermoelectric energy generator performance.

    PubMed

    Park, No-Won; Ahn, Jay-Young; Park, Tae-Hyun; Lee, Jung-Hun; Lee, Won-Yong; Cho, Kwanghee; Yoon, Young-Gui; Choi, Chel-Jong; Park, Jin-Seong; Lee, Sang-Kwon

    2017-04-03

    Recently, significant progress has been made in increasing the figure-of-merit (ZT) of various nanostructured materials, including thin-film and quantum dot superlattice structures. Studies have focused on the size reduction and control of the surface or interface of nanostructured materials since these approaches enhance the thermopower and phonon scattering in quantum and superlattice structures. Currently, bismuth-tellurium-based semiconductor materials are widely employed for thermoelectric (TE) devices such as TE energy generators and coolers, in addition to other sensors, for use at temperatures under 400 K. However, new and promising TE materials with enhanced TE performance, including doped zinc oxide (ZnO) multilayer or superlattice thin films, are also required for designing solid-state TE power generating devices with the maximum output power density and for investigating the physics of in-plane TE generators. Herein, we report the growth of Al2O3/ZnO (AO/ZnO) superlattice thin films, which were prepared by atomic layer deposition (ALD), and the evaluation of their electrical and TE properties. All the in-plane TE properties, including the Seebeck coefficient (S), electrical conductivity (σ), and thermal conductivity (κ), of the AO/ZnO superlattice (with a 0.82 nm-thick AO layer) and AO/ZnO films (with a 0.13 nm-thick AO layer) were evaluated in the temperature range 40-300 K, and the measured S, σ, and κ were -62.4 and -17.5 μV K(-1), 113 and 847 (Ω cm)(-1), and 0.96 and 1.04 W m(-1) K(-1), respectively, at 300 K. Consequently, the in-plane TE ZT factor of AO/ZnO superlattice films was found to be ∼0.014, which is approximately two times more than that of AO/ZnO films (ZT of ∼0.007) at 300 K. Furthermore, the electrical power generation efficiency of the TE energy generator consisting of four couples of n-AO/ZnO superlattice films and p-Bi0.5Sb1.5Te3 (p-BST) thin-film legs on the substrate was demonstrated. Surprisingly, the output power of

  17. Structural characterization and magnetic properties of Co co-doped Ni/ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Vijayaprasath, G.; Murugan, R.; Asaithambi, S.; Babu, G. Anandha; Sakthivel, P.; Mahalingam, T.; Hayakawa, Y.; Ravi, G.

    2016-02-01

    In this paper, we present the structural, morphological, optical and magnetic properties of Zn1- x A x O ( A = Ni, Co and x = 0.20 mol%) and Zn0.80Ni0.10Co0.10O nanoparticles synthesized by a chemical co-precipitation method. Powder X-ray diffraction data confirm the formation of a single-phase wurtzite-type ZnO structure for all the samples. FTIR and EDS measurements ensure that the divalent Ni and Co ions are incorporated in the wurtzite host matrix without any impurity phase. Photoluminescence and Raman spectra indicate the presence of donor defects and oxygen vacancies in the prepared samples. In VSM analysis, undoped ZnO nanoparticles exhibit diamagnetic behavior at room temperature. A systematic increase in ferromagnetic moment (~0.70 emu/g) is observed for Ni-, Co-doped and Co co-doped Ni/ZnO at 300 K. The exchange interaction between delocalized carriers and the localized `d' spins of Ni and Co ions is predicted as the cause of the room temperature ferromagnetism.

  18. Synergistic effects of carboxymethyl cellulose and ZnO as alkaline electrolyte additives for aluminium anodes with a view towards Al-air batteries

    NASA Astrophysics Data System (ADS)

    Liu, Jie; Wang, Dapeng; Zhang, Daquan; Gao, Lixin; Lin, Tong

    2016-12-01

    The synergistic effects of carboxymethyl cellulose (CMC) and zinc oxide (ZnO) have been investigated as alkaline electrolyte additives for the AA5052 aluminium alloy anode in aluminium-air battery by the hydrogen evolution test, the electrochemical measurements and the surface analysis method. The combination of CMC and ZnO effectively retards the self-corrosion of AA5052 alloy in 4 M NaOH solution. A complex film is formed via the interaction between CMC and Zn2+ ions on the alloy surface. The carboxyl groups adsorbed on the surface of aluminium make the protective film more stable. The cathodic reaction process is mainly suppressed significantly. AA5052 alloy electrode has a good discharge performance in the applied electrolyte containing the composite CMC/ZnO additives.

  19. Synthesis and characterization of doped and undoped ZnO nanostructures.

    PubMed

    McBean, Katie E; Phillips, Matthew R; Goldys, Ewa M

    2006-08-01

    Zinc oxide (ZnO) nanoparticles have been produced using precipitation methods from ethanolic solution. Rare-earth metal doping was performed, and the effect of lithium codoping on the luminescence properties of the rare-earth doped products was assessed. The resulting particles were characterized using cathodoluminescence and scanning electron microscopy. It was found that lithium significantly enhanced the cathodoluminescence signal from the rare-earth ions, which has been attributed to the increased integration of the rare-earth ions into the ZnO structure. The nanophase ZnO products were also annealed in argon, hydrogen, and oxygen, with hydrogen being the most successful for removing the broad defect emission present in as-grown samples and enhancing the ZnO near band edge emission.

  20. Room-temperature ferromagnetism in lightly Cr-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Duan, L. B.; Zhao, X. R.; Liu, J. M.; Wang, T.; Rao, G. H.

    2010-06-01

    Zn1- x Cr x O (0≤ x≤0.15) nanoparticles were synthesized by an auto-combustion method and characterized by x-ray diffraction and Raman scattering techniques. The solubility limit for Cr in ZnO was determined as x≈0.03. Room-temperature ferromagnetism (RT-FM) was observed in lightly Cr-doped ZnO nanoparticles with x=0.01 and 0.02. Raman scattering spectra of the lightly Cr-doped and Co-doped ZnO were studied and compared. The enhancement of both the magnetization and the intensity of Raman scattering peak associated with donor defects (Zni and/or VO) and carriers indicates that light Cr doping in ZnO could be an effective way to achieve pronounced RT-FM and the ferromagnetism is closely related to the dopant-donor hybridization besides the ferromagnetic Cr-O-Cr superexchange interactions.

  1. Spatial atomic layer deposition on flexible porous substrates: ZnO on anodic aluminum oxide films and Al{sub 2}O{sub 3} on Li ion battery electrodes

    SciTech Connect

    Sharma, Kashish; Routkevitch, Dmitri; Varaksa, Natalia; George, Steven M.

    2016-01-15

    Spatial atomic layer deposition (S-ALD) was examined on flexible porous substrates utilizing a rotating cylinder reactor to perform the S-ALD. S-ALD was first explored on flexible polyethylene terephthalate polymer substrates to obtain S-ALD growth rates on flat surfaces. ZnO ALD with diethylzinc and ozone as the reactants at 50 °C was the model S-ALD system. ZnO S-ALD was then performed on nanoporous flexible anodic aluminum oxide (AAO) films. ZnO S-ALD in porous substrates depends on the pore diameter, pore aspect ratio, and reactant exposure time that define the gas transport. To evaluate these parameters, the Zn coverage profiles in the pores of the AAO films were measured using energy dispersive spectroscopy (EDS). EDS measurements were conducted for different reaction conditions and AAO pore geometries. Substrate speeds and reactant pulse durations were defined by rotating cylinder rates of 10, 100, and 200 revolutions per minute (RPM). AAO pore diameters of 10, 25, 50, and 100 nm were utilized with a pore length of 25 μm. Uniform Zn coverage profiles were obtained at 10 RPM and pore diameters of 100 nm. The Zn coverage was less uniform at higher RPM values and smaller pore diameters. These results indicate that S-ALD into porous substrates is feasible under certain reaction conditions. S-ALD was then performed on porous Li ion battery electrodes to test S-ALD on a technologically important porous substrate. Li{sub 0.20}Mn{sub 0.54}Ni{sub 0.13}Co{sub 0.13}O{sub 2} electrodes on flexible metal foil were coated with Al{sub 2}O{sub 3} using 2–5 Al{sub 2}O{sub 3} ALD cycles. The Al{sub 2}O{sub 3} ALD was performed in the S-ALD reactor at a rotating cylinder rate of 10 RPM using trimethylaluminum and ozone as the reactants at 50 °C. The capacity of the electrodes was then tested versus number of charge–discharge cycles. These measurements revealed that the Al{sub 2}O{sub 3} S-ALD coating on the electrodes enhanced the capacity stability. This S

  2. Codoping of zinc and tungsten for practical high-performance amorphous indium-based oxide thin film transistors

    SciTech Connect

    Kizu, Takio E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Mitoma, Nobuhiko; Tsukagoshi, Kazuhito E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Miyanaga, Miki; Awata, Hideaki; Nabatame, Toshihide

    2015-09-28

    Using practical high-density sputtering targets, we investigated the effect of Zn and W codoping on the thermal stability of the amorphous film and the electrical characteristics in thin film transistors. zinc oxide is a potentially conductive component while W oxide is an oxygen vacancy suppressor in oxide films. The oxygen vacancy from In-O and Zn-O was suppressed by the W additive because of the high oxygen bond dissociation energy. With controlled codoping of W and Zn, we demonstrated a high mobility with a maximum mobility of 40 cm{sup 2}/V s with good stability under a negative bias stress in InWZnO thin film transistors.

  3. Low temperature synthesis of radio frequency magnetron sputtered gallium and aluminium co-doped zinc oxide thin films for transparent electrode fabrication

    NASA Astrophysics Data System (ADS)

    Muchuweni, E.; Sathiaraj, T. S.; Nyakotyo, H.

    2016-12-01

    Gallium and aluminium co-doped zinc oxide (GAZO) thin films were prepared on glass substrates at low temperatures by radio frequency (rf) magnetron sputtering and their physical properties were investigated. All films possessed a hexagonal wurtzite crystal structure with a strong growth orientation along the (0 0 2) c-axis. The (0 0 2) peak intensity and mean crystallite size increased with substrate temperature from room temperature (RT) to 75 °C and then decreased at 100 °C, indicating an improvement in crystallinity up to 75 °C and its deterioration at 100 °C. Scanning electron microscopy (SEM) micrographs revealed the strong dependency of surface morphology on substrate temperature and energy dispersive spectroscopy (EDS) confirmed the incorporation of Ga and Al into the ZnO films. All films exhibited excellent transmittances between 85 and 90% in the visible region and their optical band gap increased from 3.22 eV to 3.28 eV with substrate temperature. The Urbach energy decreased from 194 meV to 168 meV with increasing substrate temperature, indicating a decrease in structural disorders which was consistent with X-ray Diffraction (XRD) analysis. Films deposited at 75 °C exhibited the lowest electrical resistivity (2.4 Ωcm) and highest figure of merit (7.5 × 10-5 Ω-1), proving their potential as candidates for transparent electrode fabrication.

  4. Effect of Er3+ and Yb3+ co-doping on the performance of a ZnO-based DSSC

    NASA Astrophysics Data System (ADS)

    Tsege, Ermias Libnedengel; Vu, Hong Ha Thi; Atabaev, Timur Sh.; Kim, Hyung-Kook; Hwang, Yoon-Hwae

    2016-06-01

    Zinc-oxide (ZnO) nanoparticles (NPs) co-doped with different concentrations of rare-earth ions of erbium and ytterbium, (ZnO: Er3+, Yb3+) were synthesized for applications to ZnO-based dye sensitized solar cells (DSSC). The composite NPs used for the photoelectrode (PE) were synthesized using a simple co-precipitation technique. X-ray diffraction and scanning electron microscopy measurements on the prepared samples revealed a single phase wurzite ZnO powder with approximate sizes in the range from 15 to 20 nm. Photoluminescence (PL) measurements confirmed that the synthesized composite NPs had a good up-conversion (UPC) property. The prepared powders were directly used to make PEs for DSSCs. The photovoltaic efficiency of the DSSCs was enhanced compared to that of pure ZnO-based DSSCs. Particularly, the PE made up of ZnO: Er3+, Yb3+ NPs with 4 wt% of Er3+ and Yb3+ generates a short-circuit current density ( J sc ) of 4.794 mA·cm -2 and an open circuit voltage ( V oc ) of 0.602 V with an efficiency ( η) of 1.58%. The result indicates a 48.4% J sc improvement compared to a pure ZnO PE-based DSSC. The photocurrent improvement is due to an increase in the light-harvesting capacity of the PEs attained through the UPC property of ZnO: Er3+, Yb3+ NPs. As confirmed by PL and electrochemical impedance spectra (EIS), the use of ZnO: Er3+,Yb3+ NPs as PEs for DSSCs enhances charge concentration and transport as a result of n-type doping. However, all ZnO: Er3+, Yb3+ NP based PEs exhibited a lower V oc as a result of a down shift in the Fermi energy, which affects the overall efficiency of the cell.

  5. First-principles study for ferromagnetism of Cu-doped ZnO with carrier doping

    SciTech Connect

    Kang, Byung-Sub; Kim, Kyeong-Sup; Yu, Seong-Cho; Chae, Heejoon

    2013-02-15

    We studied the effects on the ferromagnetism of carrier doping in Zn{sub 1-x}Cu{sub x}O with x=0.0277-0.0833 by using the first-principles calculations. The total magnetic moment of Cu is about 1, 2, and 3 {mu}{sub B}/cell at the concentration of 2.77%, 5.55%, and 8.33%, respectively. For Zn{sub 1-x}Cu{sub x}O{sub 1-y}N{sub y}, we obtained the ferromagnetic and half-metallic ground state. The Cu magnetic moment in low Cu concentration is increased by the N-doping. However, for the F-doping it decreases. The ferromagnetism in Cu-doped ZnO is controllable by changing the carrier density. The N 2p states hybridize well with Cu 3d states instead of the O 2p states. Due to the hybridization between N 2p and Cu 3d states, the holes are itinerant with keeping its 3d states. For (Cu,N)-codoped ZnO, it is recognized that the width of 3d states is larger than that of (Cu,F)-codoped ZnO. - Graphical abstract: Considered clean wurtzite ZnO structure, the Cu magnetic moments for Zn{sub 1-x}Cu{sub x}O{sub 1-y}N{sub y} or Zn{sub 1-x}Cu{sub x}O{sub 1-y}F{sub y} of the ferromagnetic state (left), and the charge density difference of Zn{sub 1-x}Cu{sub x}O (x=0.0277) (right). Highlights: Black-Right-Pointing-Pointer The ferromagnetism of Cu-doped ZnO is controllable by N or F carrier density. Black-Right-Pointing-Pointer The Cu magnetic moment in low Cu concentration is increased by hole doping. Black-Right-Pointing-Pointer The N 2p states hybridize well with the Cu 3d states instead of the O 2p states. Black-Right-Pointing-Pointer For (Cu,F)-codoped ZnO, the Cu 3d band is narrower than that for (Cu,N)-codoped ZnO.

  6. Enhanced light extraction of GaN-based light-emitting diodes with periodic textured SiO2 on Al-doped ZnO transparent conductive layer

    NASA Astrophysics Data System (ADS)

    Yu, Zhao; Bingfeng, Fan; Yiting, Chen; Yi, Zhuo; Zhoujun, Pang; Zhen, Liu; Gang, Wang

    2016-07-01

    We report an effective enhancement in light extraction of GaN-based light-emitting diodes (LEDs) with an Al-doped ZnO (AZO) transparent conductive layer by incorporating a top regular textured SiO2 layer. The 2 inch transparent through-pore anodic aluminum oxide (AAO) membrane was fabricated and used as the etching mask. The periodic pore with a pitch of about 410 nm was successfully transferred to the surface of the SiO2 layer without any etching damages to the AZO layer and the electrodes. The light output power was enhanced by 19% at 20 mA and 56% at 100 mA compared to that of the planar LEDs without a patterned surface. This approach offers a technique to fabricate a low-cost and large-area regular pattern on the LED chip for achieving enhanced light extraction without an obvious increase of the forward voltage. ).

  7. CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Effect of Annealing Conditions on Properties of Sol-Gel Derived Al-Doped ZnO Thin Films

    NASA Astrophysics Data System (ADS)

    Gao, Mei-Zhen; Zhang, Feng; Liu, Jing; Sun, Hui-Na

    2009-08-01

    Transparent conductive Al-doped ZnO (AZO) thin films are prepared on normal glass substrates by the sol-gel spin coating method. The effects of drying conditions, annealing temperature and cooling rate on the structural, electrical and optical properties of AZO films are investigated by x-ray diffraction, scanning electron microscopy, the four-point probe method and UV-VIS spectrophotometry, respectively. The deposited films show a hexagonal wurtzite structure and high preferential c-axis orientation. As the drying temperature increases from 100°C to 300°C the resistivity of AZO films decreases dramatically. In contrast to the annealed films cooled in a furnace and in air, the resistivity of the annealed film which is cooled at -15°C is greatly reduced. Increasing the cooling rate dramatically increases the electrical conductivity of AZO films.

  8. Domain matched epitaxial growth of (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} thin films on (0001) Al{sub 2}O{sub 3} with ZnO buffer layer

    SciTech Connect

    Krishnaprasad, P. S. E-mail: mkj@cusat.ac.in; Jayaraj, M. K. E-mail: mkj@cusat.ac.in; Antony, Aldrin; Rojas, Fredy

    2015-03-28

    Epitaxial (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) thin films have been grown by pulsed laser deposition on (0001) Al{sub 2}O{sub 3} substrate with ZnO as buffer layer. The x-ray ω-2θ, Φ-scan and reciprocal space mapping indicate epitaxial nature of BST thin films. The domain matched epitaxial growth of BST thin films over ZnO buffer layer was confirmed using Fourier filtered high resolution transmission electron microscope images of the film-buffer interface. The incorporation of ZnO buffer layer effectively suppressed the lattice mismatch and promoted domain matched epitaxial growth of BST thin films. Coplanar inter digital capacitors fabricated on epitaxial (111) BST thin films show significantly improved tunable performance over polycrystalline thin films.

  9. Origins of electronic band gap reduction in Cr/N codoped TiO2.

    PubMed

    Parks Cheney, C; Vilmercati, P; Martin, E W; Chiodi, M; Gavioli, L; Regmi, M; Eres, G; Callcott, T A; Weitering, H H; Mannella, N

    2014-01-24

    Recent studies indicated that noncompensated cation-anion codoping of wide-band-gap oxide semiconductors such as anatase TiO2 significantly reduces the optical band gap and thus strongly enhances the absorption of visible light [W. Zhu et al., Phys. Rev. Lett. 103, 226401 (2009)]. We used soft x-ray spectroscopy to fully determine the location and nature of the impurity levels responsible for the extraordinarily large (∼1 eV) band gap reduction of noncompensated codoped rutile TiO2. It is shown that Cr/N codoping strongly enhances the substitutional N content, compared to single element doping. The band gap reduction is due to the formation of Cr 3d3 levels in the lower half of the gap while the conduction band minimum is comprised of localized Cr 3d and delocalized N 2p states. Band gap reduction and carrier delocalization are critical elements for efficient light-to-current conversion in oxide semiconductors. These findings thus raise the prospect of using codoped oxide semiconductors with specifically engineered electronic properties in a variety of photovoltaic and photocatalytic applications.

  10. The effect of dopant concentration on properties of transparent conducting Al-doped ZnO thin films for efficient Cu2ZnSnS4 thin-film solar cells prepared by electrodeposition method

    NASA Astrophysics Data System (ADS)

    Mkawi, E. M.; Ibrahim, K.; Ali, M. K. M.; Farrukh, M. A.; Mohamed, A. S.

    2015-11-01

    Al-doped ZnO (AZO) thin films were potentiostatically deposited on indium tin oxide substrates. The influence of the doping level of the ZnO:Al films was investigated. The results of the X-ray diffraction and scanning electron microscopy analysis revealed that the structural properties of the AZO films were found polycrystalline with a hexagonal wurtzite-type structure along the (002) plane. The grain size of the AZO films was observed as approximately 3 μm in the film doping with 4 mol% ZnO:Al concentration. The thin films also exhibited an optical transmittance as high as 90 % in the wavelength range of 100-1,000 nm. The optical band gap increased from 3.33 to 3.45 eV. Based on the Hall studies, the lowest resistivity (4.78 × 10-3 Ω cm) was observed in the film doping with 3 mol% ZnO:Al concentration. The sheet resistant, carrier concentration and Hall mobility values were found as 10.78 Ω/ square, 9.03 × 1018 cm-3 and 22.01 cm2/v s, respectively, which showed improvements in the properties of AZO thin films. The ZnO:Al thin films were used as a buffer layer in thin-film solar cells with the structure of soda-lime glass/Mo/Cu2ZnSnS4/ZnS/ZnO/Al grid. The best solar cell efficiency was 2.3 % with V OC of 0.430 V, J SC of 8.24 mA cm-2 and FF of 68.1 %.

  11. Synthesis and optical properties of turquoise- and green-colored brownmillerite-type Ba2In2- x- y Mn x Al y O5+ x codoped with manganese and aluminum

    NASA Astrophysics Data System (ADS)

    Jiang, Peng; Yang, Wen-hui; Zhou, Yun-cheng; Kuang, Jian-lei; Li, Yong; Xiao, Ting

    2016-11-01

    Brownmillerite-type oxides Ba2In2- x- y Mn x Al y O5+ x (0 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.5) were prepared at 1300°C through solid-state reaction. X-ray diffraction (XRD) analysis showed that the structure symmetry evolved from orthorhombic to cubic with increasing Mn and Al contents. When y was greater than 0.3, peaks associated with small amounts of BaAl2O4 and Ba2InAlO5 impurities were observed in the XRD patterns. When substituted with a small amount of Mn ( x ≤ 0.3), the Ba2In2- x- y Mn x Al y O5+ x samples exhibited an intense turquoise color. The color changed to green and dark-green with increasing Mn concentration. UV-vis absorbance spectra revealed that the color changed only slightly upon Al doping. The valence state of Mn ions in Ba2In2- x- y Mn x Al y O5+ x was confirmed to be +5 on the basis of X-ray photoelectron spectroscopic analysis. According to this analysis, the intense turquoise color of the Ba2In2- x- y Mn x Al y O5+ x samples is rooted in the existence of Mn5+; thus, the introduction of Al does not affect the optical properties of the compounds.

  12. Efficiency and Color Coordinate Improvement Using Codopants in Blue Organic Light-Emitting Diode

    NASA Astrophysics Data System (ADS)

    Wang, Xiu Ru; Chen, Jiang Shan; You, Han; Ma, Dong Ge; Sun, Run Guang

    2005-12-01

    The codoping method is applied to fabricate efficient blue organic light-emitting diodes (OLEDs). With the same structure of indium-tin oxide (ITO)/N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'diamine (NPB)(80 nm)/light-emitting layer (30 nm)/tris-(8-hydroxy-quinoline)aluminum (Alq3) (20 nm)/LiF (1 nm)/Al (120 nm), a set of three devices was manufactured for comparison. For Devices 1, 2, and 3, the light-emitting layers are 9,10-di(2-naphthyl)anthracene (ADN):4,4'-(1,4-phenylenedi-2,1-ethene diyl)bis[N,N-bis(4-methylphenyl)-benzenamine] (DPAVB) (1 wt %), ADN:2,5,8,11-tetra-(t-butyl)-perylene (TBPE) (1 wt %), and ADN:DPAVB (0.3 wt %):TBPE (0.7 wt %), respectively. It is found that the codoped Device 3 has the highest maximum luminance, Electroluminescence (EL) quantum efficiency and color saturation. Further study on the effect of the codopants was through a relative photoluminescence (PL) quantum efficiency measurement. The result shows that the relative PL efficiencies of Devices 1, 2, and 3 are 15.6, 19.3, and 24%, respectively, as determined using an integrating sphere system excited at 375 nm. The codoping method improves the EL efficiency intrinsically. Codopants of the heterogeneous light-emitting molecules may decrease the possibility of self-quenching from the interaction of the homogenous molecules at the same total doping concentration. Furthermore, the decrease in the interaction of homogenous molecules suppresses the light emission from the aggregations thus narrowing the emission spectrum, and results in saturated blue light emission.

  13. Impacts of Co doping on ZnO transparent switching memory device characteristics

    NASA Astrophysics Data System (ADS)

    Simanjuntak, Firman Mangasa; Prasad, Om Kumar; Panda, Debashis; Lin, Chun-An; Tsai, Tsung-Ling; Wei, Kung-Hwa; Tseng, Tseung-Yuen

    2016-05-01

    The resistive switching characteristics of indium tin oxide (ITO)/Zn1-xCoxO/ITO transparent resistive memory devices were investigated. An appropriate amount of cobalt dopant in ZnO resistive layer demonstrated sufficient memory window and switching stability. In contrast, pure ZnO devices demonstrated a poor memory window, and using an excessive dopant concentration led to switching instability. To achieve suitable memory performance, relying only on controlling defect concentrations is insufficient; the grain growth orientation of the resistive layer must also be considered. Stable endurance with an ON/OFF ratio of more than one order of magnitude during 5000 cycles confirmed that the Co-doped ZnO device is a suitable candidate for resistive random access memory application. Additionally, fully transparent devices with a high transmittance of up to 90% at wavelength of 550 nm have been fabricated.

  14. Fundamental understanding of the growth, doping and characterization of aligned ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Shen, Gang

    Zinc oxide (ZnO) is a II-VI semiconductor whose wide direct bandgap (3.37 eV) and large exciton binding energy (60 meV) make it compelling for optoelectronic devices such as light emitting diodes, lasers, photodetectors, solar cells, and mechanical energy harvesting devices. One dimensional structures of ZnO (nanowires) have become significant due to their unique physical properties arising from quantum confinement, and they are ideal for studying transport mechanisms in one-dimensional systems. In this doctoral research work, ZnO nanowire (NW) arrays were synthesized on sapphire substrates through carbo-thermal reduction of ZnO powders, and the effects of growth parameters on the properties of ZnO NW arrays were studied by scanning and transmission electron microscopy, X-ray diffraction, photoluminescence and Raman spectroscopy. Based on the phonon mode selection rules in wurtzite ZnO, confocal Raman spectroscopy was used to assess the alignment of ZnO NWs in an array, thereby complementing X-ray diffraction. Al doped ZnO NW arrays were achieved by mixing Al powder into the ZnO and graphite source mixture, and the presence of Al was confirmed by Energy-dispersive X-ray spectroscopy. The incorporation of Al had the effects of lowering the electrical resistivity, slightly deteriorating crystal quality and suppressing defect related green emission. Two models of ZnO NW growth were developed by establishing the relationship between NW length and diameter for undoped and Al doped ZnO NWs separately. The growth of undoped ZnO NWs followed the diffusion-induced model which was characterized by thin wires being longer than thick wires, while the growth of Al doped ZnO was controlled by Gibbs-Thomson effect which was characterized by thin wires being shorter than thin wires. Local electrode atom probe analysis of ZnO NWs was carried out to study the crystal stoichiometry and Al incorporation. Undoped ZnO NWs were found to be high purity with no detectable impurities

  15. Conductivity and touch-sensor application for atomic layer deposition ZnO and Al:ZnO on nylon nonwoven fiber mats

    SciTech Connect

    Sweet, William J.; Oldham, Christopher J.; Parsons, Gregory N.

    2015-01-15

    Flexible electronics and wearable technology represent a novel and growing market for next generation devices. In this work, the authors deposit conductive zinc oxide films by atomic layer deposition onto nylon-6 nonwoven fiber mats and spun-cast films, and quantify the impact that deposition temperature, coating thickness, and aluminum doping have on the conductivity of the coated substrates. The authors produce aluminum doped zinc oxide (AZO) coated fibers with conductivity of 230 S/cm, which is ∼6× more conductive than ZnO coated fibers. Furthermore, the authors demonstrate AZO coated fibers maintain 62% of their conductivity after being bent around a 3 mm radius cylinder. As an example application, the authors fabricate an “all-fiber” pressure sensor using AZO coated nylon-6 electrodes. The sensor signal scales exponentially under small applied force (<50 g/cm{sup 2}), yielding a ∼10{sup 6}× current change under 200 g/cm{sup 2}. This lightweight, flexible, and breathable touch/force sensor could function, for example, as an electronically active nonwoven for personal or engineered system analysis and diagnostics.

  16. Influence of the P2O5/Al2O3 co-doping on the local environment of erbium ions and on the 1.5 μm quantum efficiency of Er3+-borosilicate glasses

    NASA Astrophysics Data System (ADS)

    Bourhis, Kevin; Boetti, Nadia G.; Koponen, Joona; Milanese, Daniel; Petit, Laetica

    2014-03-01

    In this paper, the absorption properties of Er3+-doped borosilicate glasses with various P2O5 and Al2O3 content are measured for different silica concentrations. The Judd-Ofelt parameters (Ω2, Ω4 and Ω6) have been calculated in order to investigate the local environment of the rare-earth cations. The compositional changes of Ω2 and Ω6 are attributed to changes in the bonding between Er3+ and surrounding ligand groups due to structural modifications occurring with the introduction of P2O5 and Al2O3. The luminescence quantum efficiency of the 4I13/2 → 4I15/2 transition slightly increases with the addition of P2O5 whereas it decreases with the progressive replacement of P2O5 by Al2O3. We noticed that it also increases when the silica content is higher.

  17. Design and development of a new generation of UV-visible-light-driven nanosized codoped titanium dioxide photocatalysts and biocides/sporocides, and environmental applications

    NASA Astrophysics Data System (ADS)

    Hamal, Dambar B.

    For solar environmental remediation, a new generation of nanosized (< 10 nm) titanium dioxide photocatalysts codoped with metals and nonmetals, or metals only were prepared by the xero-gel and aero-gel methods. For silver or cobalt-based xero-gel titanium dioxide photocatalysts, photoactivities tests revealed that codoping of titanium dioxide with a metal (1% Ag or 2% Co) and nonmetals (carbon and sulfur) is necessary to achieve high-activities for acetaldehyde degradation under visible light (wavelength > 420 nm). It was concluded that high visible-light-activities for acetaldehyde degradation over codoped titanium dioxide were attributed to an interplay of anatase crystallinity, high-surface area, reduced band-gap (< 3.0 eV), uniform dispersion of doped metal ions, and suppressed recombination rate of photogenerated electronhole pairs. Moreover, the nature and amount of codoped metals play a significant role in visible-light-induced photocatalysis. Metals (Al, Ga, and In) doped/codoped titanium dioxide photocatalysts were prepared by the aero-gel method. The photocatalytic studies showed that activities of metal doped/codoped photocatalysts under UV light (wavelength < 400 nm) were found to be dependent on pollutants. Indium demonstrated beneficial effects in both textural and photocatalytic properties. Gallium and indium codoped titanium dioxide photocatalysts displayed even better performance in the CO oxidation reaction under UV light. Notably, titanium dioxide codoped with Ga, In, and Pt, exhibited unique photoactivities for the CO oxidation under both UV and visible light irradiation, indicating that this system could have promise for the water-gas shift reaction for hydrogen production. Silver-based nanostructured titanium dioxide samples were developed for killing human pathogens (Escherichia coli cells and Bacillus subtilis spores). Biocidal tests revealed that silver, carbon, and sulfur codoped titanium dioxide nanoparticles (< 10 nm) possess very strong

  18. Growth and characterization of periodically polarity-inverted ZnO structures on sapphire substrates

    SciTech Connect

    Park, Jinsub; Yao, Takafumi

    2012-10-15

    We report on the fabrication and characterization of periodically polarity inverted (PPI) ZnO heterostructures on (0 0 0 1) Al{sub 2}O{sub 3} substrates. For the periodically inverted array of ZnO polarity, CrN and Cr{sub 2}O{sub 3} polarity selection buffer layers are used for the Zn- and O-polar ZnO films, respectively. The change of polarity and period in fabricated ZnO structures is evaluated by diffraction patterns and polarity sensitive piezo-response microscopy. Finally, PPI ZnO structures with subnanometer scale period are demonstrated by using holographic lithography and regrowth techniques.

  19. Enhanced broadband near-infrared luminescence from transparent Yb3+/Ni2+ codoped silicate glass ceramics.

    PubMed

    Wu, Botao; Zhou, Shifeng; Ruan, Jian; Qiao, Yanbo; Chen, Danping; Zhu, Congshan; Qiu, Jianrong

    2008-02-04

    The near-infrared emission intensity of Ni(2+) in Yb(3+)/Ni(2+) codoped transparent MgO-Al(2)O(3)-Ga(2)O(3)-SiO(2)-TiO(2) glass ceramics could be enhanced up to 4.4 times via energy transfer from Yb(3+) to Ni(2+) in nanocrystals. The best Yb(2)O(3) concentration was about 1.00 mol%. For the Yb(3+)/Ni(2+) codoped glass ceramic with 1.00 mol% Yb(2)O(3), a broadband near-infrared emission centered at 1265 nm with full width at half maximum of about 300 nm and lifetime of about 220 mus was observed. The energy transfer mechanism was also discussed.

  20. Intrinsic and extrinsic doping of ZnO and ZnO alloys

    NASA Astrophysics Data System (ADS)

    Ellmer, Klaus; Bikowski, André

    2016-10-01

    In this article the doping of the oxidic compound semiconductor ZnO is reviewed with special emphasis on n-type doping. ZnO naturally exhibits n-type conductivity, which is used in the application of highly doped n-type ZnO as a transparent electrode, for instance in thin film solar cells. For prospective application of ZnO in other electronic devices (LEDs, UV photodetectors or power devices) p-type doping is required, which has been reported only minimally. Highly n-type doped ZnO can be prepared by doping with the group IIIB elements B, Al, Ga, and In, which act as shallow donors according to the simple hydrogen-like substitutional donor model of Bethe (1942 Theory of the Boundary Layer of Crystal Rectifiers (Boston, MA: MIT Rad Lab.)). Group IIIA elements (Sc, Y, La etc) are also known to act as shallow donors in ZnO, similarly explainable by the shallow donor model of Bethe. Some reports showed that even group IVA (Ti, Zr, Hf) and IVB (Si, Ge) elements can be used to prepare highly doped ZnO films—which, however, can no longer be explained by the simple hydrogen-like substitutional donor model. More probably, these elements form defect complexes that act as shallow donors in ZnO. On the other hand, group V elements on oxygen lattice sites (N, P, As, and Sb), which were viewed for a long time as typical shallow acceptors, behave instead as deep acceptors, preventing high hole concentrations in ZnO at room temperature. Also, ‘self’-compensation, i.e. the formation of a large number of intrinsic donors at high acceptor concentrations seems to counteract the p-type doping of ZnO. At donor concentrations above about 1020 cm-3, the electrical activation of the dopant elements is often less than 100%, especially in polycrystalline thin films. Reasons for the electrical deactivation of the dopant atoms are (i) the formation of dopant-defect complexes, (ii) the compensation of the electrons by acceptors (Oi, VZn) or (iii) the formation of secondary phases, for

  1. Role of Ce4+ in the scintillation mechanism of codoped Gd3Ga3Al2O12:Ce

    SciTech Connect

    Wu, Yuntao; Meng, Fang; Li, Qi; Koschan, Merry; Melcher, Charles L.

    2014-10-17

    To control the time-response performance of widely used cerium-activated scintillators in cutting-edge medical-imaging devices, such as time-of-flight positron-emission tomography, a comprehensive understanding of the role of Ce valence states, especially stable Ce4+, in the scintillation mechanism is essential. However, despite some progress made recently, an understanding of the physical processes involving Ce4+ is still lacking. The aim of this work is to clarify the role of Ce4+ in scintillators by studying Ca2+ codoped Gd3Ga3Al2O12∶Ce (GGAG∶Ce). By using a combination of optical absorption spectra and x-ray absorption near-edge spectroscopies, the correlation between Ca2+codoping content and the Ce4+ fraction is seen. The energy-level diagrams of Ce3+ and Ce4+ in the Gd3Ga3Al2O12 host are established by using theoretical and experimental methods, which indicate a higher position of the 5d1 state of Ce4+ in the forbidden gap in comparison to that of Ce3+. Underlying reasons for the decay-time acceleration resulting from Ca2+ codoping are revealed, and the physical processes of the Ce4+-emission model are proposed and further demonstrated by temperature-dependent radioluminescence spectra under x-ray excitation.

  2. High-quality ZnO growth, doping, and polarization effect

    NASA Astrophysics Data System (ADS)

    Kun, Tang; Shulin, Gu; Jiandong, Ye; Shunming, Zhu; Rong, Zhang; Youdou, Zheng

    2016-03-01

    The authors have reported their recent progress in the research field of ZnO materials as well as the corresponding global advance. Recent results regarding (1) the development of high-quality epitaxy techniques, (2) the defect physics and the Te/N co-doping mechanism for p-type conduction, and (3) the design, realization, and properties of the ZnMgO/ZnO hetero-structures have been shown and discussed. A complete technology of the growth of high-quality ZnO epi-films and nano-crystals has been developed. The co-doping of N plus an iso-valent element to oxygen has been found to be the most hopeful path to overcome the notorious p-type hurdle. High mobility electrons have been observed in low-dimensional structures utilizing the polarization of ZnMgO and ZnO. Very different properties as well as new physics of the electrons in 2DEG and 3DES have been found as compared to the electrons in the bulk. Project supported by the National Natural Science Foundation of China (Nos. 61025020, 61274058, 61322403, 61504057, 61574075), the Natural Science Foundation of Jiangsu Province (Nos. BK2011437, BK20130013, BK20150585), the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the Fundamental Research Funds for the Central Universities.

  3. Synthesis and optical properties of ZnO and carbon nanotube based coaxial heterostructures

    NASA Astrophysics Data System (ADS)

    Kim, D. S.; Lee, S.-M.; Scholz, R.; Knez, M.; Gösele, U.; Fallert, J.; Kalt, H.; Zacharias, M.

    2008-09-01

    Carbon nanotubes and ZnO based functional coaxial heterostructured nanotubes have been fabricated by using atomic layer deposition. An irregular structured shell composed of ZnO nanocrystals was deposited on pristine nanotubes, while a highly defined ZnO shell was deposited on the tubes after its functionalization with Al2O3. Photoluminescence measurements of the ZnO shell on Al2O3/nanotube show a broad green band emission, whereas the shell grown on the bare nanotube shows a band shifted to the orange spectral range.

  4. Dual Mode Thin Film Bulk Acoustic Resonators (FBARs) Based on AlN, ZnO and GaN Films with Tilted c-Axis Orientation

    DTIC Science & Technology

    2010-01-01

    FBARs fabri - cation, and their thickness usually ranges from several mi- crometers down to tenth of micrometers, which results in high resonant...mentioned be- fore. Films with in-plane polarization have also been fabri - cated on certain substrate crystal such as tetragonal LiAlO2 100 for...dynamics, and cerebral aneurysm diseases ; his research work is also related to experimental and medical device design. Hongbin Cheng received his

  5. Improved photovoltaic performance of inverted polymer solar cells through a sol-gel processed Al-doped ZnO electron extraction layer.

    PubMed

    Kim, Jun Young; Cho, Eunae; Kim, Jaehoon; Shin, Hyeonwoo; Roh, Jeongkyun; Thambidurai, Mariyappan; Kang, Chan-mo; Song, Hyung-Jun; Kim, SeongMin; Kim, Hyeok; Lee, Changhee

    2015-09-21

    We demonstrate that nanocrystalline Al-doped zinc oxide (n-AZO) thin film used as an electron-extraction layer can significantly enhance the performance of inverted polymer solar cells based on the bulk heterojunction of poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT) and [6,6]-phenyl C(71)-butyric acid methyl ester (PC(70)BM). A synergistic study with both simulation and experiment on n-AZO was carried out to offer a rational guidance for the efficiency improvement. As a result, An n-AZO film with an average grain size of 13 to 22 nm was prepared by a sol-gel spin-coating method, and a minimum resistivity of 2.1 × 10(-3) Ω·cm was obtained for an Al-doping concentration of 5.83 at.%. When an n-AZO film with a 5.83 at.% Al concentration was inserted between the ITO electrode and the active layer (PCDTBT:PC(70)BM), the power conversion efficiency increased from 3.7 to 5.6%.

  6. Enhanced ultraviolet upconversion luminescence of Tm and Yb codoped ZrF4-BaF2-LaF3-AlF3-NaF glass.

    PubMed

    He, Chunfeng; Zhao, Dan; Qin, Guanshi; Zheng, Kezhi; Qin, Weiping

    2011-11-01

    Ultraviolet (UV) upconversion (UC) luminescence properties of Tm3+ ions sensitized by Yb3+ ions in ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) glass were studied in detail. Under the excitation from a 980 nm continuous wave (CW) diode laser, red, blue, and even UV emissions were observed in the fluorozirconate glass. Several fluorescence bands appeared in the UC emission spectrum from 292.8 nm to 805.8 nm. The UC emission peaks at 291 nm, 347 nm, 363 nm, 454 nm, 475 nm, 647 nm, 687 nm, and 804 nm correspond to the transitions of 1I6 --> 3H6, 1I6 --> 3F4, 1D2 --> 3H6, 1D2 --> 3F4, 1G4 --> 3H6, 1G4 --> 3F4, 3F3 --> 3H6, and 3H4 --> 3H6, respectively. Experimental results of intensity dependence of the up-converted fluorescence on the pump power indicate a five-photon excitation scheme of 1I6 energy level.

  7. Effect of Li+ ions co-doping on luminescence, scintillation properties and defects characteristics of LuAG:Ce ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Shuping; Feng, Xiqi; Mares, Jiri A.; Babin, Vladimir; Hu, Chen; Kou, Huamin; D'Ambrosio, Carmelo; Li, Jiang; Pan, Yubai; Nikl, Martin

    2017-02-01

    Monovalent Li+ codoped Lu3Al5O12:Ce (LuAG:Ce) optical ceramics were fabricated by solid state reaction method and further optimized by an air-annealing process. Optical absorption, radioluminescence spectra and scintillation properties such as light yield, scintillation decay times and afterglow were measured and compared with those of the Li+ free LuAG:Ce ceramic and the commercial LuAG:Ce single crystal samples. Positive effect of Li+ codopant consists mainly in the significant increase of scintillation light yield, acceleration of scintillation decay as well as the decrease of afterglow intensity. With 0.3% Li codoping, the obtained LuAG:Ce,Li ceramic displays a light yield of ∼29200 ph/MeV at 10 μs shaping time, higher than that of the LuAG:Ce single crystal and optical ceramic scintillators ever reported. The partial conversion of the stable Ce3+ to Ce4+ centers and the shallow and deep traps effect suppression by the Li+ codoping are discussed.

  8. AlGaN/GaN HEMT And ZnO nanorod-based sensors for chemical and bio-applications

    NASA Astrophysics Data System (ADS)

    Chu, B. H.; Kang, B. S.; Wang, H. T.; Chang, C. Y.; Lele, T.,; Tseng, Y.; Goh, A.; Sciullo, A.; Wu, W. S.; Lin, J. N.; Gila, B. P.; Pearton, S. J.; Johnson, J. W.; Piner, E. L.; Linthicum, K. J.; Ren, F.

    2009-02-01

    Chemical sensors can be used to analyze a wide variety of environmental and biological gases and liquids and may need to be able to selectively detect a target analyte. Different methods, including gas chromatography (GC), chemiluminescence, selected ion flow tube (SIFT), and mass spectroscopy (MS) have been used to measure biomarkers. These methods show variable results in terms of sensitivity for some applications and may not meet the requirements for a handheld biosensor. A promising sensing technology utilizes AlGaN/GaN high electron mobility transistors (HEMTs). HEMT structures have been developed for use in microwave power amplifiers due to their high two dimensional electron gas (2DEG) mobility and saturation velocity. The conducting 2DEG channel of GaN/AlGaN HEMTs is very close to the surface and extremely sensitive to adsorption of analytes. HEMT sensors can be used for detecting gases, ions, pH values, proteins, and DNA. In this paper we review recent progress on functionalizing the surface of HEMTs for specific detection of glucose, kidney marker injury molecules, prostate cancer and other common substances of interest in the biomedical field.

  9. Influence of doping Co to characterization of ZnO nanostructures

    NASA Astrophysics Data System (ADS)

    Thuy Doan, Minh; Ho, Xuan Vinh; Nguyen, Tu; Nghia Nguyen, Van

    2014-06-01

    Cobalt doped zinc oxide nanoparticles were successfully synthesized using the hydrothermal method. The structure of these nanoparticles studied using x-ray diffraction clearly presented the existence of Co3O4 phase in the 4% Co-doped ZnO samples. Field-emission electron scanning microscopy (FESEM) was used to examine the morphologies of products. Optical absorption measurements confirm the presence of a strong ultraviolet peak at 374 nm. The room temperature photoluminescence spectra investigated under the excitation at 325 nm by a neon laser exhibit both the ultraviolet and visible emission bands.

  10. Ultra-violet absorption induced modifications in bulk and nanoscale electrical transport properties of Al-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Kumar, Mohit; Basu, Tanmoy; Som, Tapobrata

    2015-08-01

    Using conductive atomic force microscopy and Kelvin probe force microscopy, we study local electrical transport properties in aluminum-doped zinc oxide (ZnO:Al or AZO) thin films. Current mapping shows a spatial variation in conductivity which corroborates well with the local mapping of donor concentration (˜1020 cm-3). In addition, a strong enhancement in the local current at grains is observed after exposing the film to ultra-violet (UV) light which is attributed to persistent photocurrent. Further, it is shown that UV absorption gives a smooth conduction in AZO film which in turn gives rise to an improvement in the bulk photoresponsivity of an n-AZO/p-Si heterojunction diode. This finding is in contrast to the belief that UV absorption in an AZO layer leads to an optical loss for the underneath absorbing layer of a heterojunction solar cell.

  11. An enzymatic biosensor based on three-dimensional ZnO nanotetrapods spatial net modified AlGaAs/GaAs high electron mobility transistors

    SciTech Connect

    Song, Yu; Zhang, Xiaohui; Yan, Xiaoqin; Liao, Qingliang; Wang, Zengze; Zhang, Yue

    2014-11-24

    We designed and constructed three dimensional (3D) zinc oxide Nanotetrapods (T-ZnOs) modified AlGaAs/GaAs high electron mobility transistors (HEMTs) for enzymatic uric acid (UA) detection. The chemical vapor deposition synthesized T-ZnOs was distributed on the gate areas of HEMTs in order to immobilize uricase and improve the sensitivity of the HEMTs. Combining with the high efficiency of enzyme immobilization by T-ZnOs and high sensitivity from HEMT, the as-constructed uricase/T-ZnOs/HEMTs biosensor showed fast response towards UA at ∼1 s, wide linear range from 0.2 nM to 0.2 mM and the low detect limit at 0.2 nM. The results point out an avenue to design electronic device as miniaturized lab-on-chip device for high sensitive and specific in biomedical and clinical diagnosis applications.

  12. Ultraviolet band-pass Schottky barrier photodetectors formed by Al-doped ZnO contacts to n-GaN

    SciTech Connect

    Sheu, J.K.; Lee, M.L.; Tun, C.J.; Lin, S.W.

    2006-01-23

    This work prepared Al-doped ZnO(AZO) films using dc sputtering to form Schottky contacts onto GaN films with low-temperature-grown GaN cap layer. Application of ultraviolet photodetector showed that spectral responsivity exhibits a narrow bandpass characteristic ranging from 345 to 375 nm. Moreover, unbiased peak responsivity was estimated to be around 0.12 A/W at 365 nm, which corresponds to a quantum efficiency of around 40%. In our study, relatively low responsivity can be explained by the marked absorption of the AZO contact layer. When the reverse biases were below 5 V, the study revealed that dark currents were well below 5x10{sup -12} A even though the samples were annealed at increased temperatures.

  13. Ultra-violet absorption induced modifications in bulk and nanoscale electrical transport properties of Al-doped ZnO thin films

    SciTech Connect

    Kumar, Mohit; Basu, Tanmoy; Som, Tapobrata

    2015-08-07

    Using conductive atomic force microscopy and Kelvin probe force microscopy, we study local electrical transport properties in aluminum-doped zinc oxide (ZnO:Al or AZO) thin films. Current mapping shows a spatial variation in conductivity which corroborates well with the local mapping of donor concentration (∼10{sup 20 }cm{sup −3}). In addition, a strong enhancement in the local current at grains is observed after exposing the film to ultra-violet (UV) light which is attributed to persistent photocurrent. Further, it is shown that UV absorption gives a smooth conduction in AZO film which in turn gives rise to an improvement in the bulk photoresponsivity of an n-AZO/p-Si heterojunction diode. This finding is in contrast to the belief that UV absorption in an AZO layer leads to an optical loss for the underneath absorbing layer of a heterojunction solar cell.

  14. Evolution of the electrical and structural properties during the growth of Al doped ZnO films by remote plasma-enhanced metalorganic chemical vapor deposition

    SciTech Connect

    Volintiru, I.; Creatore, M.; Kniknie, B. J.; Spee, C. I. M. A.; Sanden, M. C. M. van de

    2007-08-15

    Al-doped zinc oxide (AZO) films were deposited by means of remote plasma-enhanced metalorganic chemical vapor deposition from oxygen/diethylzinc/trimethylaluminum mixtures. The electrical, structural (crystallinity and morphology), and chemical properties of the deposited films were investigated using Hall, four point probe, x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), electron recoil detection (ERD), Rutherford backscattering (RBS), and time of flight secondary ion mass spectrometry (TOF-SIMS), respectively. We found that the working pressure plays an important role in controlling the sheet resistance R{sub s} and roughness development during film growth. At 1.5 mbar the AZO films are highly conductive (R{sub s}<6 {omega}/{open_square} for a film thickness above 1200 nm) and very rough (>4% of the film thickness), however, they are characterized by a large sheet resistance gradient with increasing film thickness. By decreasing the pressure from 1.5 to 0.38 mbar, the gradient is significantly reduced and the films become smoother, but the sheet resistance increases (R{sub s}{approx_equal}100 {omega}/{open_square} for a film thickness of 1000 nm). The sheet resistance gradient and the surface roughness development correlate with the grain size evolution, as determined from the AFM and SEM analyses, indicating the transition from pyramid-like at 1.5 mbar to pillar-like growth mode at 0.38 mbar. The change in plasma chemistry/growth precursors caused by the variation in pressure leads to different concentration and activation efficiency of Al dopant in the zinc oxide films. On the basis of the experimental evidence, a valid route for further improving the conductivity of the AZO film is found, i.e., increasing the grain size at the initial stage of film growth.

  15. High-performance InGaN/GaN MQW LEDs with Al-doped ZnO transparent conductive layers grown by MOCVD using H2O as an oxidizer

    NASA Astrophysics Data System (ADS)

    Lin, Jia-Yong; Pei, Yan-Li; Zhuo, Yi; Chen, Zi-Min; Hu, Rui-Qin; Cai, Guang-Shuo; Wang, Gang

    2016-11-01

    In this study, the high performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs) with Al-doped ZnO (AZO) transparent conductive layers (TCLs) has been demonstrated. The AZO-TCLs were fabricated on the n+-InGaN contact layer by metal organic chemical vapor deposition (MOCVD) using H2O as an oxidizer at temperatures as low as 400 °C without any post-deposition annealing. It shows a high transparency (98%), low resistivity (510-4 Ω·cm), and an epitaxial-like excellent interface on p-GaN with an n+-InGaN contact layer. A forward voltage of 2.82 V @ 20 mA was obtained. Most importantly, the power efficiencies can be markedly improved by 53.8%@20 mA current injection and 39.6%@350 mA current injection compared with conventional LEDs with indium tin oxide TCL (LED-III), and by 28.8%@20 mA current injection and 4.92%@350 mA current injection compared with LEDs with AZO-TCL prepared by MOCVD using O2 as an oxidizer (LED-II), respectively. The results indicate that the AZO-TCL grown by MOCVD using H2O as an oxidizer is a promising TCL for a low-cost and high-efficiency GaN-based LED application. Project supported by the National Natural Science Foundation of China (Grant Nos. 61204091, 61404177, 51402366, and U1201254) and the Science and Technology Planning Project of Guangdong Province, China (Grant No. 2015B010132006).

  16. Comparative study on beryllium and magnesium as a co-doping element for ZnO:N

    NASA Astrophysics Data System (ADS)

    Yu-Quan, Su; Ming-Ming, Chen; Long-Xing, Su; Yuan, Zhu; Zi-Kang, Tang

    2016-06-01

    Stable nitrogen doping is an important issue in p-type ZnO research for device applications. In this paper, beryllium and magnesium are systematically compared as a dopant in ZnO to reveal their nitrogen-stabilizing ability. Secondary ion mass spectrum shows that Be and Mg can both enhance the stability of nitrogen in ZnO while Be has a better performance. Zn 2p and O 1s electron binding energies change in both MgZnO and BeZnO thin films. Donor-acceptor luminescence is observed in the BeZnO samples. We conclude that Be is a better co-doping element than Mg for p-type ZnO:N. Project supported by the National Key Basic Research Program of China (Grant No. 2011CB302000), the National Natural Science Foundation of China (Grant Nos. 51232009 and 51202299), the Fundamental Research Funds for the Central Universities, China (Grant No. 11lgpy16), the Natural Science Foundation for Jiangsu Provincial Higher Education, Institutions of China (Grant No. 15KJB510005), and the Talent Fund of Jiangsu University, China (Grant No. 15JDG042).

  17. Effect of the Molar Ratio of B2O3 to Bi2O3 in Al Paste with Bi2O3-B2O3-ZnO Glass on Screen Printed Contact Formation and Si Solar Cell Performance

    NASA Astrophysics Data System (ADS)

    Kim, Bit-Na; Kim, Hyeong Jun; Chang, Hyo Sik; Hong, Hyun Seon; Ryu, Sung-Soo; Lee, Heon

    2013-10-01

    In this study, eco-friendly Pb-free Bi2O3-B2O3-ZnO glass frits were chosen as an inorganic additive for the Al paste used in Si solar cells. The effects of the molar ratio of Bi2O3 to B2O3 in the glass composition on the electrical resistance of the Al electrode and on the cell performance were investigated. The results showed that as the molar ratio of Bi2O3 to B2O3 increased, the glass transition temperature and softening temperature decreased because of the reduced glass viscosity. In Al screen-printed Si solar cells, as the molar ratio of Bi2O3 to B2O3 increased, the sheet electrical resistance of the Al electrode decreased and the cell efficiency increased. The uniformity and thickness of the back-surface field was significantly influenced by the glass composition.

  18. (Indium, Aluminum) co-doped Zinc Oxide as a Novel Material System for Quantum-Well Multilayer Thermoelectrics

    NASA Astrophysics Data System (ADS)

    Teehan, Sean

    Waste heat recovery from low efficiency industrial processes requires high performance thermoelectric materials to meet challenging requirements. The efficiency such a device is quantified by the dimensionless figure of merit ZT=S2sigmaT/kappa, where S is the Seebeck coefficient, sigma is the electrical conductivity, T is the absolute temperature and kappa is the thermal conductivity. For practical applications these devices are only cost-effective if the ZT is higher than 2. Theoretically it has been proven that by engineering nanostructures with lower dimensionality one can significantly increase ZT. A superlattice, or a system of 2-dimensional multilayer quantum wells has previously shown the potential to be used for thermoelectric structures. However, the use of conventional materials within these structures has only allowed this at low temperatures and has utilized cross-plane transport. This study focuses on both high temperature range operation and the in-plane transport properties of such structures, which benefit from both quantum confinement and an enhancement in density of states near EF. The n-type structures are fabricated by alternately sputtering barrier and well materials of Al-doped ZnO (AZO) and indium co-doped AZO, respectively. Samples investigated consist of 50 periods with targeted layer thicknesses of 10nm, which results in sufficient sampling material as well as quantum well effects. The indium doping level within the quantum well was controlled by varying the target power, and ultimately results in a 3x improvement in power factor (S 2sigma) over the parent bulk materials. The film characterization was determined by X-ray reflectometry, transmission electron microscopy, X-ray diffraction, auger electron spectroscopy, as well as other relevant techniques. In addition, process optimization was performed on material parameters such as layer thickness, interface roughness, and band-gap offset which all play a major role in determining the

  19. Evaluation of the optoelectronic properties and corrosion behavior of Al2O3-doped ZnO films prepared by dc pulsed magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Zubizarreta, C.; Berasategui, E. G.; Bayón, R.; Escobar Galindo, R.; Barros, R.; Gaspar, D.; Nunes, D.; Calmeiro, T.; Martins, R.; Fortunato, E.; Barriga, J.

    2014-12-01

    The main requirements for transparent conducting oxide (TCO) films acting as electrodes are a high transmission rate in the visible spectral region and low resistivity. However, in many cases, tolerance to temperature and humidity exposure is also an important requirement to be fulfilled by the TCOs to assure proper operation and durability. Besides improving current encapsulation methods, the corrosion resistance of the developed TCOs must also be enhanced to warrant the performance of optoelectronic devices. In this paper the performance of aluminum-doped zinc oxide (AZO) films deposited by pulsed dc magnetron sputtering has been studied. Structure, optical transmittance/reflectance, electrical properties (resistivity, carrier concentration and mobility) and corrosion resistance of the developed coatings have been analyzed as a function of the doping of the target and the coating thickness. Films grown from a 2.0 wt% Al2O3 target with a thickness of approximately 1 µm showed a very low resistivity of 6.54  ×  10-4 Ωcm and a high optical transmittance in the visible range of 84%. Corrosion studies of the developed samples have shown very low corrosion currents (nanoamperes), very high corrosion resistances (in the order of 107 Ω) and very high electrochemical stability, indicating no tendency for electrochemical corrosion degradation.

  20. Robustly Single-mode Polarization Maintaining Er/Yb co-doped LMA Fiber for High Power Applications

    DTIC Science & Technology

    2007-05-08

    the fabrication of highly efficient, polarization maintaining ( PM ) LMA fibers. A PM - LMA Er/Yb co-doped fiber suitable for nanosecond pulsed...associated with fabricating LMA Er/Yb and Tm-doped fibers have previously been discussed in detail by Tankala et. al. [6]. In the case of a PM - LMA ...demonstrate a large core diameter PM Er/Yb fiber incorporating a unique raised inner-cladding which facilitates the use of conventional LMA mode selection

  1. Effect of internal stress on the electro-optical behaviour of Al-doped ZnO transparent conductive thin films

    NASA Astrophysics Data System (ADS)

    Proost, J.; Henry, F.; Tuyaerts, R.; Michotte, S.

    2016-08-01

    In this work, we will report on scientific efforts aimed at unraveling the quantitative effect of elastic strain on the electro-optical behaviour of Al-doped zinc oxide (AZO). AZO thin films have been deposited by reactive magnetron sputtering to thicknesses from 300 to 500 nm, both on extra-clear glass substrates as well as on oxidised Si wafers. This resulted in both cases in polycrystalline, strongly textured (002) films. During deposition, the internal stress evolution in the growing film was monitored in-situ using high resolution curvature measurements. The resulting growth-induced elastic strain, which was found to depend heavily on the oxygen partial pressure, could further be modulated by appropriately choosing the deposition temperature. The latter also induces an additional extrinsic thermal stress component, whose sign depends on the substrate used. As such, a wide range of biaxial internal stresses could be achieved, from -600 MPa in compression up to 800 MPa in tension. The resulting charge carrier mobilities, obtained independently from room temperature Hall measurements, were found to range between 5 and 25 cm2/V s. Interestingly, the maximum mobility occurred at the zero-stress condition, and together with a charge carrier concentration of about 8 × 1020 cm-3, this gave rise to a resistivity of only 300 μΩ cm. From the stress-dependent optical transmission spectra in the range of 200-1000 nm, the pressure coefficient of the optical bandgap was estimated from the corresponding Tauc plots to be 31 meV/GPa, indicating a very high strain-sensitivity as well.

  2. Fabrication of Vertical Organic Light-Emitting Transistor Using ZnO Thin Film

    NASA Astrophysics Data System (ADS)

    Yamauchi, Hiroshi; Iizuka, Masaaki; Kudo, Kazuhiro

    2007-04-01

    Organic light-emitting diodes (OLEDs) combined with thin film transistor (TFT) are well suitable elements for low-cost, large-area active matrix displays. On the other hand, zinc oxide (ZnO) is a transparent material and its electrical conductivity is controlled from conductive to insulating by growth conditions. The drain current of ZnO FET is 180 μA. The OLED uses ZnO thin film (Al-doped) for the electron injection layer and is controlled by radio frequency (rf) and direct current (dc) sputtering conditions, such as Al concentration and gas pressure. Al concentration in the ZnO film and deposition rate have strong effects on electron injection. Furthermore, the OLED driven by ZnO FET shows a luminance of 13 cd/m2, a luminance efficiency of 0.7 cd/A, and an on-off ratio of 650.

  3. Properties of (Ga,Mn)As codoped with Li

    SciTech Connect

    Miyakozawa, Shohei; Chen, Lin; Matsukura, Fumihiro; Ohno, Hideo

    2014-06-02

    We grow Li codoped (Ga,Mn)As layers with nominal Mn composition up to 0.15 by molecular beam epitaxy. The layers before and after annealing are characterized by x-ray diffraction, transport, magnetization, and ferromagnetic resonance measurements. The codoping with Li reduces the lattice constant and electrical resistivity of (Ga,Mn)As after annealing. We find that (Ga,Mn)As:Li takes similar Curie temperature to that of (Ga,Mn)As, but with pronounced magnetic moments and in-plane magnetic anisotropy, indicating that the Li codoping has nontrivial effects on the magnetic properties of (Ga,Mn)As.

  4. Highly piezoelectric MgZr co-doped aluminum nitride-based vibrational energy harvesters.

    PubMed

    Minh, Le Van; Hara, Motoaki; Yokoyama, Tsuyoshi; Nishihara, Tokihiro; Ueda, Masanori; Kuwano, Hiroki

    2015-11-01

    The first MgZr co-doped AlN-based vibrational energy harvester (VEH) is presented. (MgZr)AlN, which is a new class of doped AlN, provides high piezoelectricity and cost advantage. Using 13%-(MgZr)-doped AlN for micromachined VEHs, maximum output power of 1.3 μW was achieved with a Q-factor of 400 when resonant frequency, vibration acceleration, load resistance were 792 Hz, 8 m/s(2), and 1.1 MΩ, respectively. Normalized power density was 8.1 kW·g(-2)·m(-3). This was one of the highest values among the currently available piezoelectric VEHs.

  5. Improved conversion efficiency of amorphous Si solar cells using a mesoporous ZnO pattern

    PubMed Central

    2014-01-01

    To provide a front transparent electrode for use in highly efficient hydrogenated amorphous silicon (a-Si:H) thin-film solar cells, porous flat layer and micro-patterns of zinc oxide (ZnO) nanoparticle (NP) layers were prepared through ultraviolet nanoimprint lithography (UV-NIL) and deposited on Al-doped ZnO (AZO) layers. Through this, it was found that a porous micro-pattern of ZnO NPs dispersed in resin can optimize the light-trapping pattern, with the efficiency of solar cells based on patterned or flat mesoporous ZnO layers increased by 27% and 12%, respectively. PMID:25276101

  6. Spectroscopy and visible frequency upconversion in Er3+-Yb3+: TeO2-ZnO glass.

    PubMed

    Mohanty, Deepak Kumar; Rai, Vineet Kumar

    2014-01-01

    The UV-Vis-NIR absorption studies of the Er(3+)/Er(3+)-Yb(3+) doped/codoped TeO2-ZnO (TZO) glasses fabricated by the melting and quenching method has been performed. The spectroscopic radiative parameters viz. radiative transition probabilities, branching ratios and lifetimes have been determined from the absorption spectrum by using Judd-Ofelt theory. The near infrared (NIR) to visible frequency upconversion (UC) have been monitored by using an excitation of 976 nm wavelength radiation from a CW diode laser. The effect of codoping with Yb(3+) ions on the intensity of the UC emission bands from the Er(3+) ions throughout visible region has been studied. The mechanism responsible for the observed upconversion emissions in the prepared samples have been explained on the basis of excited state absorption and efficient energy transfer processes.

  7. Spectroscopy and visible frequency upconversion in Er3+-Yb3+: TeO2-ZnO glass

    NASA Astrophysics Data System (ADS)

    Mohanty, Deepak Kumar; Rai, Vineet Kumar

    2014-03-01

    The UV-Vis-NIR absorption studies of the Er3+/Er3+-Yb3+ doped/codoped TeO2-ZnO (TZO) glasses fabricated by the melting and quenching method has been performed. The spectroscopic radiative parameters viz. radiative transition probabilities, branching ratios and lifetimes have been determined from the absorption spectrum by using Judd-Ofelt theory. The near infrared (NIR) to visible frequency upconversion (UC) have been monitored by using an excitation of 976 nm wavelength radiation from a CW diode laser. The effect of codoping with Yb3+ ions on the intensity of the UC emission bands from the Er3+ ions throughout visible region has been studied. The mechanism responsible for the observed upconversion emissions in the prepared samples have been explained on the basis of excited state absorption and efficient energy transfer processes.

  8. Niobia and tantala codoped orthorhombic zirconia ceramics

    SciTech Connect

    Hoeftberger, M.; Gritzner, G.

    1995-04-15

    During recent studies it was found that codoping of zirconia with niobia and tantala yielded very corrosion resistant, orthorhombic zirconia ceramics. The powders for those novel ceramics were made via the sol-gel technique by hydrolysis of the respective metal propoxides; a method which required dry-box techniques during the preparation of the alkoxides. In these studies the authors investigated the fabrication of precursor material from aqueous solutions. The preparation of aqueous solutions of salts of zirconium, niobium and tantalum is hampered by rapid hydrolysis. Premature hydrolysis of the chlorides and oxichlorides of niobium, tantalum and zirconium can be, however, prevented in aqueous solutions of oxalic acid. Thus the authors investigated the coprecipitation of hydroxides as precursors by reacting oxalic acid solutions of the respective cations with aqueous ammonia. In addition they studied the effects of calcination and of hydrothermal conversion of the hydroxides to oxides on the powder characteristics and on the mechanical properties of the niobia and tantala codoped zirconia ceramics.

  9. Synthesis and properties of novel liquid-medicine-filter shaped ZnO nanostructures

    NASA Astrophysics Data System (ADS)

    Zhuang, Huizhao; Xu, Peng; Li, Junlin

    2013-06-01

    Liquid-medicine-filter shaped ZnO nanostructures have been synthesized on Al2O3-coated Si (1 1 1) substrates by chemical vapor deposition method (CVD) at 1050 °C. Every liquid-medicine-filter shaped ZnO nanostructure is made up of one nanorod and two nanowires at the ends. The liquid-medicine-filter shaped ZnO nanostructures are characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectrometer (EDS) photoluminescence (PL). The results indicate that the liquid-medicine-filter shaped ZnO nanostructures are wurtzite hexagonal structure and the growth direction is [0 0 0 1]. The liquid-medicine-filter shaped ZnO nanostructures became the new member of ZnO nanostructures for the novel configuration. PL reveals ultraviolet (UV) emission at 384 nm and a broad emission peak at 540 nm. These novel liquid-medicine-filter shaped ZnO nanostructures will provide an improvement for electronic and optical devices. The pre-prepared Al2O3 film on the Si (1 1 1) substrate solves the troublesome lattice mismatch problem between the Si substrate and ZnO, and makes the growth of liquid-medicine-filter shaped ZnO nanostructures more effective. In addition, the effect of screw dislocation and polar surfaces in understanding crystal growth mechanisms in nanometer scale were also provided.

  10. Synthesis and properties of novel liquid-medicine-filter shaped ZnO nanostructures.

    PubMed

    Zhuang, Huizhao; Xu, Peng; Li, Junlin

    2013-06-01

    Liquid-medicine-filter shaped ZnO nanostructures have been synthesized on Al2O3-coated Si (111) substrates by chemical vapor deposition method (CVD) at 1050 °C. Every liquid-medicine-filter shaped ZnO nanostructure is made up of one nanorod and two nanowires at the ends. The liquid-medicine-filter shaped ZnO nanostructures are characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectrometer (EDS) photoluminescence (PL). The results indicate that the liquid-medicine-filter shaped ZnO nanostructures are wurtzite hexagonal structure and the growth direction is [0001]. The liquid-medicine-filter shaped ZnO nanostructures became the new member of ZnO nanostructures for the novel configuration. PL reveals ultraviolet (UV) emission at 384 nm and a broad emission peak at 540 nm. These novel liquid-medicine-filter shaped ZnO nanostructures will provide an improvement for electronic and optical devices. The pre-prepared Al2O3 film on the Si (111) substrate solves the troublesome lattice mismatch problem between the Si substrate and ZnO, and makes the growth of liquid-medicine-filter shaped ZnO nanostructures more effective. In addition, the effect of screw dislocation and polar surfaces in understanding crystal growth mechanisms in nanometer scale were also provided.

  11. Valency configuration of transition metal impurities in ZnO

    SciTech Connect

    Petit, Leon; Schulthess, Thomas C; Svane, Axel; Temmerman, Walter M; Szotek, Zdzislawa; Janotti, Anderson

    2006-01-01

    We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM=Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn{sub 1-x}TM{sub x}O, the localized TM{sup 2+} configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy {epsilon}F close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with {epsilon}F close to the valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.

  12. A dual-colored bio-marker made of doped ZnO nanocrystals

    NASA Astrophysics Data System (ADS)

    Wu, Y. L.; Fu, S.; Tok, A. I. Y.; Zeng, X. T.; Lim, C. S.; Kwek, L. C.; Boey, F. C. Y.

    2008-08-01

    Bio-compatible ZnO nanocrystals doped with Co, Cu and Ni cations, surface capped with two types of aminosilanes and titania are synthesized by a soft chemical process. Due to the small particle size (2-5 nm), surface functional groups and the high photoluminescence emissions at the UV and blue-violet wavelength ranges, bio-imaging on human osteosarcoma (Mg-63) cells and histiocytic lymphoma U-937 monocyte cells showed blue emission at the nucleus and bright turquoise emission at the cytoplasm simultaneously. This is the first report on dual-color bio-images labeled by one semiconductor nanocrystal colloidal solution. Bright green emission was detected on mung bean seedlings labeled by all the synthesized ZnO nanocrystals. Cytotoxicity tests showed that the aminosilanes capped nanoparticles are non-toxic. Quantum yields of the nanocrystals varied from 79% to 95%. The results showed the potential of the pure ZnO and Co-doped ZnO nanocrystals for live imaging of both human cells and plant systems.

  13. Effects of co-doping on ferromagnetism in (Zn,Cr)Te.

    NASA Astrophysics Data System (ADS)

    Kuroda, Shinji

    2007-03-01

    Room-temperature ferromagnetism in semiconductors has emerged as one of the most challenging topics in today's materials science and technology. Indeed, enormous research activities have so far been directed towards developing ferromagnetic semiconductors with high transition temperatures. Despite many reports claiming high-temperature ferromagnetism for a broad class of diluted magnetic semiconductors, their intrinsic nature has sometimes been controversial[1], with a lack of elaborated analysis of structural and electronic properties. Among them, Cr-doped ZnTe has been regarded as one of the promising materials of room-temperature ferromagnetism because its intrinsic nature was confirmed through magnetic circular dichroism (MCD) measurement[2]. In this presentation, we report the effect of co-doping of charge impurities on ferromagnetic properties in this material. It was found that ferromagnetism was suppressed in (Zn,Cr)Te co-doped with nitrogen (N) as an acceptor impurity[3] and was enhanced in a crystal co-doped with iodine (I) as a donor impurity[4]. In particular, the apparent Curie temperature TC of Zn1-xCrxTe with a Cr composition of x = 0.05 increased up to 300K at maximum due to I-doping, compared to TC˜30K in the undoped crystal. In the structural and compositional analysis using TEM/EDS, it was revealed that the origin of this remarkable effect of the co-doping was the variation of Cr distribution in the crystals; the Cr distribution was strongly inhomogeneous in I-doped crystals with higher TC, in contrast to an almost uniform distribution in undoped or N-doped crystals with lower TC or being paramagnetic. In the crystals of inhomogeneous distribution, Cr-rich regions with a typical size of several ten nanometers formed in the Cr-poor matrix act as ferromagnetic nanoclusters, resulting in an apparent ferromagnetic behavior of the whole crystal. These variation of the Cr uniformity can be linked to a change in the Cr charge state due to the co-doping

  14. Theoretical investigation of ZnO and its doping clusters.

    PubMed

    Wang, Chunlei; Xu, Shuhong; Ye, Lihua; Lei, Wei; Cui, Yiping

    2011-05-01

    Four clusters of ZnO, O-Zn-SR (-SR = ligand) and doping ZnO structures (with Cr, Cu, Al atoms) were investigated using density functional theory at theB3LYP/Lanl2dz level. The characteristics of Zn(3)O(3) and Zn(4)O(4) structures, which are the units of experimental wurtzite and zinc blende structures, were found to be similar to those of experimental ZnO nanocrystals. Moreover, the calculated Raman and IR spectra of ZnO clusters were almost consistent with experimental results. Raman spectra were observed to shift to higher frequencies with decreasing numbers of atoms. Both ligands and solvent make the wavelength of absorption peaks shift to blue. All transitions of absorption peaks for these pure clusters were from d to p orbitals. Finally, doping clusters and experimental doping nanocrystals were similar in character. The doping of metal changed the orbital of ZnO nanocrystals. The transitions in doping clusters (Cr-ZnO, Cu-ZnO) are from d to d orbitals, while Al-ZnO clusters have s-p transitions.

  15. Photocurrent detection of chemically tuned hierarchical ZnO nanostructures grown on seed layers formed by atomic layer deposition

    PubMed Central

    2012-01-01

    We demonstrate the morphological control method of ZnO nanostructures by atomic layer deposition (ALD) on an Al2O3/ZnO seed layer surface and the application of a hierarchical ZnO nanostructure for a photodetector. Two layers of ZnO and Al2O3 prepared using ALD with different pH values in solution coexisted on the alloy film surface, leading to deactivation of the surface hydroxyl groups. This surface complex decreased the ZnO nucleation on the seed layer surface, and thereby effectively screened the inherent surface polarity of ZnO. As a result, a 2-D zinc hydroxyl compound nanosheet was produced. With increasing ALD cycles of ZnO in the seed layer, the nanostructure morphology changes from 2-D nanosheet to 1-D nanorod due to the recovery of the natural crystallinity and polarity of ZnO. The thin ALD ZnO seed layer conformally covers the complex nanosheet structure to produce a nanorod, then a 3-D, hierarchical ZnO nanostructure was synthesized using a combined hydrothermal and ALD method. During the deposition of the ALD ZnO seed layer, the zinc hydroxyl compound nanosheets underwent a self-annealing process at 150 °C, resulting in structural transformation to pure ZnO 3-D nanosheets without collapse of the intrinsic morphology. The investigation on band electronic properties of ZnO 2-D nanosheet and 3-D hierarchical structure revealed noticeable variations depending on the richness of Zn-OH in each morphology. The improved visible and ultraviolet photocurrent characteristics of a photodetector with the active region using 3-D hierarchical structure against those of 2-D nanosheet structure were achieved. PMID:22672780

  16. Aluminum doping tunes band gap energy level as well as oxidative stress-mediated cytotoxicity of ZnO nanoparticles in MCF-7 cells.

    PubMed

    Akhtar, Mohd Javed; Alhadlaq, Hisham A; Alshamsan, Aws; Majeed Khan, M A; Ahamed, Maqusood

    2015-09-08

    We investigated whether Aluminum (Al) doping tunes band gap energy level as well as selective cytotoxicity of ZnO nanoparticles in human breast cancer cells (MCF-7). Pure and Al-doped ZnO nanoparticles were prepared by a simple sol-gel method. Characterization study confirmed the formation of single phase of Al(x)Zn(1-x)O nanocrystals with the size range of 33-55 nm. Al-doping increased the band gap energy of ZnO nanoparticles (from 3.51 eV for pure to 3.87 eV for Al-doped ZnO). Al-doping also enhanced the cytotoxicity and oxidative stress response of ZnO nanoparticles in MCF-7 cells. The IC50 for undoped ZnO nanoparticles was 44 μg/ml while for the Al-doped ZnO counterparts was 31 μg/ml. Up-regulation of apoptotic genes (e.g. p53, bax/bcl2 ratio, caspase-3 &caspase-9) along with loss of mitochondrial membrane potential suggested that Al-doped ZnO nanoparticles induced apoptosis in MCF-7 cells through mitochondrial pathway. Importantly, Al-doping did not change the benign nature of ZnO nanoparticles towards normal cells suggesting that Al-doping improves the selective cytotoxicity of ZnO nanoparticles toward MCF-7 cells without affecting the normal cells. Our results indicated a novel approach through which the inherent selective cytotoxicity of ZnO nanoparticles against cancer cells can be further improved.

  17. Ab initio studies of magnetic anisotropy energy in highly Co-doped ZnO

    NASA Astrophysics Data System (ADS)

    Łusakowski, A.; Szuszkiewicz, W.

    2017-03-01

    Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted magnetic semiconductor (Zn,Co)O were performed using OpenMX package with fully relativistic pseudopotentials. The analysis of the band spin-orbit interaction and the magnetic ion's surrounding on magnetic anisotropy have been provided. As a result, the calculations show that the magnetic anisotropy in (Zn,Co)O solid solution, mainly of the single ion anisotropy type has been caused by Co ions.

  18. Optical properties of ZnO nanoparticles on the porous structure of mordenites and ZSM-5.

    PubMed

    Susarrey-Arce, A; Petranovskii, V; Hernández-Espinosa, M A; Portillo, R; de la Cruz, W

    2011-06-01

    ZnO nanoparticles ranging from 2 to 10 nm were grown on ZSM-5 and mordenite zeolite hosts with different SiO2/Al2O3 molar ratios (MR). Formation of ZnO nanoparticles in the samples was confirmed by TEM. XRD and nitrogen adsorption measurements revealed that the zeolite structure is not destroyed. Surface Zn concentration was calculated from XPS data. ZnO nanoparticles in the zeolite matrix were studied by UV-Vis, diffuse reflectance and cathodoluminescence (CL) spectroscopies. CL revealed three different emissions from ZnO nanoparticles, approximately 3.1, 2.8 and 2.5 eV. The ZnO band-edge emission was associated with blue defects-related and oxygen vacancies emissions. The generation of the point defects at the interface explains the presence of this blue band.

  19. Zn(O, S) layers for chalcoyprite solar cells sputtered from a single target

    NASA Astrophysics Data System (ADS)

    Grimm, A.; Kieven, D.; Lauermann, I.; Lux-Steiner, M. Ch.; Hergert, F.; Schwieger, R.; Klenk, R.

    2012-09-01

    A simplified Cu(In, Ga)(S, Se)2/Zn(O, S)/ZnO:Al stack for chalcopyrite thin-film solar cells is proposed. In this stack the Zn(O, S) layer combines the roles of the traditional CdS buffer and undoped ZnO layers. It will be shown that Zn(O, S) films can be sputtered in argon atmosphere from a single mixed target without substrate heating. The photovoltaic performance of the simplified stack matches that of the conventional approach. Replacing the ZnO target with a ZnO/ZnS target may therefore be sufficient to omit the CdS buffer layer and avoid the associated complexity, safety and recycling issues, and to lower production cost.

  20. Strong Enhancement of Near-Band-Edge Photoluminescence of ZnO Nanowires Decorated with Sputtered Metallic Nanoparticles

    NASA Astrophysics Data System (ADS)

    Purahmad, Mohsen; Stroscio, Michael A.; Dutta, Mitra

    2013-12-01

    The effect of the Ar plasma during metal deposition on the photoluminescence (PL) of metal-coated ZnO nanowires (NWs) has been investigated. Strong enhancement of near-band-edge emission (NBE) is observed for ZnO NWs coated with Al and Ni nanoparticles (NPs) by radiofrequency magnetron sputtering, while the samples coated with NPs by e-beam evaporation show quenching of the PL intensity. A model is proposed that satisfies the observed experimental results and assigns the strong enhancement of the NBE PL of ZnO NWs to excitons bound to structural defects in the surface layer of the ZnO NWs.

  1. Aluminum doping tunes band gap energy level as well as oxidative stress-mediated cytotoxicity of ZnO nanoparticles in MCF-7 cells

    PubMed Central

    Akhtar, Mohd Javed; Alhadlaq, Hisham A.; Alshamsan, Aws; Majeed Khan, M.A.; Ahamed, Maqusood

    2015-01-01

    We investigated whether Aluminum (Al) doping tunes band gap energy level as well as selective cytotoxicity of ZnO nanoparticles in human breast cancer cells (MCF-7). Pure and Al-doped ZnO nanoparticles were prepared by a simple sol-gel method. Characterization study confirmed the formation of single phase of AlxZn1-xO nanocrystals with the size range of 33–55 nm. Al-doping increased the band gap energy of ZnO nanoparticles (from 3.51 eV for pure to 3.87 eV for Al-doped ZnO). Al-doping also enhanced the cytotoxicity and oxidative stress response of ZnO nanoparticles in MCF-7 cells. The IC50 for undoped ZnO nanoparticles was 44 μg/ml while for the Al-doped ZnO counterparts was 31 μg/ml. Up-regulation of apoptotic genes (e.g. p53, bax/bcl2 ratio, caspase-3 & caspase-9) along with loss of mitochondrial membrane potential suggested that Al-doped ZnO nanoparticles induced apoptosis in MCF-7 cells through mitochondrial pathway. Importantly, Al-doping did not change the benign nature of ZnO nanoparticles towards normal cells suggesting that Al-doping improves the selective cytotoxicity of ZnO nanoparticles toward MCF-7 cells without affecting the normal cells. Our results indicated a novel approach through which the inherent selective cytotoxicity of ZnO nanoparticles against cancer cells can be further improved. PMID:26347142

  2. Aluminum doping tunes band gap energy level as well as oxidative stress-mediated cytotoxicity of ZnO nanoparticles in MCF-7 cells

    NASA Astrophysics Data System (ADS)

    Akhtar, Mohd Javed; Alhadlaq, Hisham A.; Alshamsan, Aws; Majeed Khan, M. A.; Ahamed, Maqusood

    2015-09-01

    We investigated whether Aluminum (Al) doping tunes band gap energy level as well as selective cytotoxicity of ZnO nanoparticles in human breast cancer cells (MCF-7). Pure and Al-doped ZnO nanoparticles were prepared by a simple sol-gel method. Characterization study confirmed the formation of single phase of AlxZn1-xO nanocrystals with the size range of 33-55 nm. Al-doping increased the band gap energy of ZnO nanoparticles (from 3.51 eV for pure to 3.87 eV for Al-doped ZnO). Al-doping also enhanced the cytotoxicity and oxidative stress response of ZnO nanoparticles in MCF-7 cells. The IC50 for undoped ZnO nanoparticles was 44 μg/ml while for the Al-doped ZnO counterparts was 31 μg/ml. Up-regulation of apoptotic genes (e.g. p53, bax/bcl2 ratio, caspase-3 & caspase-9) along with loss of mitochondrial membrane potential suggested that Al-doped ZnO nanoparticles induced apoptosis in MCF-7 cells through mitochondrial pathway. Importantly, Al-doping did not change the benign nature of ZnO nanoparticles towards normal cells suggesting that Al-doping improves the selective cytotoxicity of ZnO nanoparticles toward MCF-7 cells without affecting the normal cells. Our results indicated a novel approach through which the inherent selective cytotoxicity of ZnO nanoparticles against cancer cells can be further improved.

  3. Pulsed laser deposited cobalt-doped ZnO thin film

    NASA Astrophysics Data System (ADS)

    Wang, Li; Su, Xue-qiong; Lu, Yi; Chen, Jiang-bo

    2013-09-01

    To realize the room-temperature ferromagnetism (RTFM) in diluted magnetic semiconductors (DMS), we prepared a series of Cobalt-doped ZnO thin films using pulsed laser deposition (PLD) at deposition temperatures 500°C under oxygen pressure from 2.5×10-4 Pa to 15 Pa. To elucidate the physical origin of RTFM, Co 2p spectra of cobalt-doped ZnO thin films was measured by X-ray photoelectron spectroscopy (XPS). The magnetic properties of films were measured by an alternating gradient magnetometer (AGM), and the electrical properties were detected by a Hall Effect instrument using the Van der Pauw method. XPS analysis shows that the Co2+ exists and Co clusters and elemental content change greatly in samples under various deposition oxygen pressures. Not only the valence state and elemental content but also the electrical and magnetic properties were changed. In the case of oxygen pressure 10 Pa, an improvement of saturation magnetic moment about one order of magnitude over other oxygen pressure experiments, and the film exhibits ferromagnetism with a curie temperature above room temperature. It was found that the value of carrier concentration in the Co-doped ZnO film under oxygen pressure 10Pa increases about one order of magnitude than the values of other samples under different oxygen pressure. Combining XPS with AGM measurements, we found that the ferromagnetic signals in cobalt-doped ZnO thin film deposited at 500 °C under oxygen pressure 10 Pa only appear with the detectable Co2+ spectra from incompletely oxidized Co metal or Co cluster. So oxygen pressure 10 Pa can be thought the best condition to obtain room-temperature dilute magnetic semiconductor about cobalt-doped ZnO thin films.

  4. Identification of hydrogen molecules in ZnO.

    PubMed

    Lavrov, E V; Herklotz, F; Weber, J

    2009-05-08

    Hydrogen molecules in ZnO are identified by their local vibrational modes. In a Raman study, interstitial H2, HD, and D2 species were found to exhibit local vibrational modes at frequencies 4145, 3628, and 2985 cm-1, respectively. After thermal treatment of vapor phase grown ZnO samples in hydrogen atmosphere, most hydrogen forms shallow donors at the bond-centered site (HBC). Subsequently, HBC migrates through the crystal and forms electrically inactive H2. These results imply that the "hidden" hydrogen in ZnO [G. A. Shi et al., Appl. Phys. Lett. 85, 5601 (2004)10.1063/1.1832736] occurs in the form of interstitial H2.

  5. In situ codoping of a CuO absorber layer with aluminum and titanium: the impact of codoping and interface engineering on the performance of a CuO-based heterojunction solar cell

    NASA Astrophysics Data System (ADS)

    Masudy-Panah, Saeid; Radhakrishnan, K.; Ru, Tan Hui; Yi, Ren; Wong, Ten It; Dalapati, Goutam Kumar

    2016-09-01

    Aluminum-doped cupric oxide (CuO:Al) was prepared via an out-diffusion process of Al from an Al-coated substrate into the deposited CuO thin film upon thermal treatment. The effect of the annealing temperature on the structural and optical properties of CuO:Al was investigated in detail. The influence of Al incorporation on the photovoltaic properties was then investigated by preparing a p-CuO:Al/n-Si heterojunction solar cell. A significant improvement in the performance of the solar cell was achieved by controlling the out-diffusion of Al. A novel in situ method to co-dope CuO with Al and titanium (Ti) has been proposed to demonstrate CuO-based solar cells with the front surface field (FSF) design. The FSF design was created by depositing a CuO:Al layer followed by a Ti-doped CuO (CuO:Ti) layer. This is the first successful experimental demonstration of the codoping of a CuO thin film and CuO thin film solar cells with the FSF design. The open circuit voltage (V oc), short circuit current density (J sc) and fill factor (FF) of the fabricated solar cells were significantly higher for the FSF device compared to devices without FSF. The FF of this device improved by 68% through the FSF design and a record efficiency ɳ of 2% was achieved. The improvement of the solar cell properties is mainly attributed to the reduction of surface recombination, which influences the charge carrier collection.

  6. Synergistic effects of Mo and F doping on the quality factor of ZnO thin films prepared by a fully automated home-made nebulizer spray technique

    NASA Astrophysics Data System (ADS)

    Ravichandran, K.; Dineshbabu, N.; Arun, T.; Manivasaham, A.; Sindhuja, E.

    2017-01-01

    Transparent conducting oxide films of undoped, Mo doped, Mo + F co-doped ZnO were deposited using a facile homemade nebulizer spray pyrolysis technique. The effects of Mo and F doping on the structural, optical, electrical and surface morphological properties were investigated using XRD, UV-vis-NIR spectroscopy, I-V and Hall probe techniques, FESEM and AFM, and XPS, respectively. The XRD analysis confirms that all the films are well crystallized with hexagonal wurtzite structure. All the synthesized samples exhibit high transmittance (above 85%) in the visible region. The current-voltage (I-V) characteristics show the ohmic conduction nature of the films. The Hall probe measurements show that the synergistic effects of Mo and F doping cause desirable improvements in the quality factor of the ZnO films. A minimum resistivity of 5.12 × 10-3 Ω cm with remarkably higher values of mobility and carrier concentration is achieved for Mo (2 at.%) + F (15 at.%) co-doped ZnO films. A considerable variation in the intensity of deep level emission caused by Mo and F doping is observed in the photoluminescence (PL) studies. The presence of the constituent elements in the samples is confirmed by XPS analysis.

  7. Non-linear Electrical Characteristics of ZnO Modified by Trioxides Sb2O3, Bi2O3, Fe2O3, Al2O3 and La2O3

    NASA Astrophysics Data System (ADS)

    Mekap, Anita; Das, Piyush R.; Choudhary, R. N. P.

    2016-08-01

    The non-linear behavior of polycrystalline-ZnO-based voltage-dependent resistors is considered in the present study. A high-temperature solid-state reaction route was used to synthesize polycrystalline samples of ZnO modified by small amounts of the trioxides Sb2O3, Bi2O3, Fe2O3, etc. in various proportions. X-ray diffraction and scanning electron microscopy techniques were used to study the structural and microstructural characteristics of modified ZnO. Detailed studies of non-linear phenomena of the I-V characteristics, dielectric permittivity ( ɛ r), impedance ( Z), etc. of the samples have provided many interesting results. All the samples exhibited dielectric anomaly. Non-linear variation in polarization with electric field for all the samples was observed. Moreover, significant non-linearity in the I-V characteristics was observed in the breakdown region of all the samples at room temperature. The non-linear coefficient ( α) in different cases, i.e. for I- V, ɛ r- f, ɛ r- T, and ɛ r- Z, was calculated and found to be appreciable. The frequency dependence of ac conductivity suggests that the material obeys Jonscher's universal power law.

  8. Photocatalytic degradation of organic dyes by Er3+: YAlO3/Co- and Fe-doped ZnO coated composites under solar irradiation

    NASA Astrophysics Data System (ADS)

    Chen, Yang; Lu, Chunxiao; Tang, Liang; Song, Yahui; Wei, Shengnan; Rong, Yang; Zhang, Zhaohong; Wang, Jun

    2016-12-01

    In this work, the Er3+: YAlO3/Co- and Fe-doped ZnO coated composites were prepared by the sol-gel method. Then, they were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). Photo-degradation of azo fuchsine (AF) as a model dye under solar light irradiation was studied to evaluate the photocatalytic activity of the Er3+: YAlO3/Co- and Fe-doped ZnO coated composites. It was found that the photocatalytic activity of Co- and Fe-doped ZnO composites can be obviously enhanced by upconversion luminescence agent (Er3+: YAlO3). Besides, the photocatalytic activity of Er3+: YAlO3/Fe-doped ZnO is better than that of Er3+: YAlO3/Co-doped ZnO. The influence of experiment conditions, such as the concentration of Er3+: YAlO3, heat-treatment temperature and time on the photocatalytic activity of the Er3+: YAlO3/Co- and Fe-doped ZnO coated composites was studied. In addition, the effects of solar light irradiation time, dye initial concentration, Er3+: YAlO3/Co- and Fe-doped ZnO amount on the photocatalytic degradation of azo fuchsine in aqueous solution were investigated in detail. Simultaneously, some other organic dyes, such as Methyl Orange (MO), Rhodamine B (RM-B), Acid Red B (AR-B), Congo Red (CR), and Methyl Blue (MB) were also studied. The possible excitation principle of Er3+: YAlO3/Co- and Fe-doped ZnO coated composites under solar light irradiation and the photocatalytic degradation mechanism of organic dyes were discussed.

  9. Assessment of structural, optical and conduction properties of ZnO thin films in the presence of acceptor impurities

    NASA Astrophysics Data System (ADS)

    Plugaru, R.; Plugaru, N.

    2016-06-01

    The structural, optical and electrical conduction properties of (Li/Cu,N):ZnO codoped thin films synthesized by the sol-gel method were investigated by field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), transmission and absorption, photoluminescence (PL) and I-V measurements in order to bring evidence of the formation of acceptor centers by dual-acceptor codoping processes. The (Li 3%,N 5%):ZnO films consist of crystallites with average size of 15 nm, show 95% transmission in the visible region, and an optical band gap of 3.22 eV. The PL spectra show emission maxima at 3.21 and 2.96 eV which are related to the emission of acceptor centers and the presence of defects, respectively. Li occupies interstitial sites and may form Lii-N(O) defect complexes that act as acceptor centers. The (Cu 3%,N 5%):ZnO films consist of crystallites with average size of 12 nm, and exhibit 90% transmission in the visible region. The PL spectra reveal band edge emission at 3.23 eV and defect related emission at 2.74 eV. In the (Cu,N) codoped films, copper substitutes zinc and adopts mainly the Cu1+ state. A possible defect complex involving Cu and N determines the transition from n- to p-type conductivity. These findings are in agreement with results of electronic structure calculations at the GGA-PBE level.

  10. Transparent Conducting Oxides for Infrared Plasmonic Waveguides: ZnO (Preprint)

    DTIC Science & Technology

    2014-01-15

    ZnO (AZO) layers grown by RF sputtering on quartz glass that employ a unique, 20-nm-thick, ZnON buffer layer, which minimizes the strong thickness...ZnON buffer layer, which minimizes the strong thickness dependence of mobility (µ) on thickness (d). The values of mobility and carrier...inserting a thin ZnON buffer layer between the substrate and ZnO layer. For example, in undoped ZnO grown on c-plane Al2O3, the rocking-curve FWHM of the

  11. Ho3+-Yb3+ codoped tellurite based glasses in visible lasers and optical devices: Judd-Ofelt analysis and frequency upconversion

    NASA Astrophysics Data System (ADS)

    Azam, Mohd; Rai, Vineet Kumar

    2017-04-01

    The optical absorption and frequency upconversion emission in the Ho3+/Yb3+ codoped TeO2-ZnO (TZ), TeO2-ZnO-WO3 (TZW) and TeO2-ZnO-WO3-TiO2 (TZWTi) glasses prepared by melting and quenching method has been studied. Judd-Ofelt theory has been used to calculate the Judd-Ofelt intensity parameters (Ω2, Ω4 and Ω6), transition probabilities, radiative lifetimes, absorption cross sections and the branching ratios. Upconversion (UC) emission bands centered at ∼ 549 nm, ∼658 nm and ∼754 nm are observed upon 980 nm excitation. On codoping with the Yb3+ ions at 3.0 mol% the upconversion emission intensity enhancement of about ∼57 times, ∼342 times and ∼480 times for the green band whereas for the red band arising from the Ho3+ ions it is about ∼71 times, ∼438 times and ∼707 times respectively have been observed. The enhancement observed in the UC emission intensity is explained on the basis of efficient energy transfer from Yb3+ to Ho3+, larger absorption cross section, larger oscillator strengths and increase in the local field corrections factor. The spectroscopic quality factor Ω4/Ω6 has been calculated to get the information about the developed materials for laser applications. The upconversion emission cross section determined on the basis of Judd-Ofelt analysis is found to be maximum for Ho-Yb-TZWTi glass. The nephelauxetic ratio, bonding and covalency parameters have been calculated to know the nature of bonding between the rare earth ions and neighbouring oxygen atoms. The high color purity 83.8% has been reported in the codoped glasses at ∼81.2 W/cm2 pump power density.

  12. ZnO nanowire lasers.

    PubMed

    Vanmaekelbergh, Daniël; van Vugt, Lambert K

    2011-07-01

    The pathway towards the realization of optical solid-state lasers was gradual and slow. After Einstein's paper on absorption and stimulated emission of light in 1917 it took until 1960 for the first solid state laser device to see the light. Not much later, the first semiconductor laser was demonstrated and lasing in the near UV spectral range from ZnO was reported as early as 1966. The research on the optical properties of ZnO showed a remarkable revival since 1995 with the demonstration of room temperature lasing, which was further enhanced by the first report of lasing by a single nanowire in 2001. Since then, the research focussed increasingly on one-dimensional nanowires of ZnO. We start this review with a brief description of the opto-electronic properties of ZnO that are related to the wurtzite crystal structure. How these properties are modified by the nanowire geometry is discussed in the subsequent sections, in which we present the confined photon and/or polariton modes and how these can be investigated experimentally. Next, we review experimental studies of laser emission from single ZnO nanowires under different experimental conditions. We emphasize the special features resulting from the sub-wavelength dimensions by presenting our results on single ZnO nanowires lying on a substrate. At present, the mechanism of lasing in ZnO (nanowires) is the subject of a strong debate that is considered at the end of this review.

  13. The effects of doping and shell thickness on the optical and magnetic properties of Mn/Cu/Fe-doped and Co-doped ZnS nanowires/ZnO quantum dots/SiO2 heterostructures

    NASA Astrophysics Data System (ADS)

    Cao, Jian; Yang, Jinghai; Yang, Lili; Wei, Maobin; Feng, Bo; Han, Donglai; Fan, Lin; Wang, Bingji; Fu, Hao

    2012-07-01

    In this paper, we demonstrated the encapsulation of Mn/Cu/Fe-doped and co-doped ZnS nanowires (NWs) and ZnO quantum dots (QDs) with a layer of mesoporous SiO2 shell for the purpose of integrating dual emission and ferromagnetism property into one common nanostructure at room temperature. Within the ZnS:Mn2+Cu2+Fe2+/ZnO@SiO2 nanocomposites, ZnS:Mn2+Cu2+Fe2+ NWs and ZnO QDs provided color-tunable visible emission and UV emission, respectively. The color-tunable visible emission in the ZnS:Mn2+Cu2+Fe2+ NWs can be obtained by adjusting the concentrations of Mn2+, Cu2+, and Fe2+ ions. The ferromagnetism of the ZnS:Mn2+Cu2+Fe2+ NWs was observed around room temperature, the mechanism of which was explained by the super-exchange mechanism. The results of the effect of the ZnO QDs shell thickness on the optical properties of the ZnS:Mn2+/ZnO@SiO2 nanocomposites showed that the luminescence intensity of the yellow-orange emission and UV emission reached the highest value when the ratio of ZnS:Mn2+/ZnO equaled 1:5.

  14. Non-polar p-type Zn0.94Mn0.05Na0.01O texture: Growth mechanism and codoping effect

    NASA Astrophysics Data System (ADS)

    Zhang, L. Q.; Lu, B.; Lu, Y. H.; Ye, Z. Z.; Lu, J. G.; Pan, X. H.; Huang, J. Y.

    2013-02-01

    The microstructure and crystal orientations of polycrystalline films crucially affect the properties and performance of the films. Controlling preferred orientations (PO) and related film morphology are necessary to obtain the desirable properties. In this paper, we demonstrate a rational and effective route toward the realization of non-polar p-type ZnO thin film with surface texture on quartz substrate through Mn-Na codoping. It is uncovered experimentally and theoretically that mono-doping of Mn creates opportunity to realize PO from polar (c-axis) to non-polar ((101¯0), (101¯1), and (112¯0)) changing. With Mn-Na codoping, an acute modulation of the growth behavior and electrical conductivity of the film have been revealed, leading to weak p-type non-polar Zn0.94Mn0.05Na0.01O (ZMNO) texture. The dominant mechanism for the non-polar self-texture in the current paper is deliberately elucidated as resulting from the interplane surface diffusion with the cooperative effect of impurity dopants. The ZMNO films exhibit p-type conduction with hole concentration of 9.51 × 1015-1.86 × 1017 cm-3 and enhanced room temperature (RT) ferromagnetism possessing a saturation magnetization (Ms) of 1.52 μB/Mn. The results have potential applications in development of non-polar optoelectronic devices such as lighting emitting diodes (LEDs).

  15. Specifications of ZnO growth for heterostructure solar cell and PC1D based simulations

    PubMed Central

    Hussain, Babar; Ebong, Abasifreke

    2015-01-01

    This data article is related to our recently published article (Hussain et al., in press [1]) where we have proposed a new solar cell model based on n-ZnO as front layer and p-Si as rear region. The ZnO layer will act as an active n-layer as well as antireflection (AR) coating saving considerable processing cost. There are several reports presenting use of ZnO as window/antireflection coating in solar cells (Mansoor et al., 2015; Haq et al., 2014; Hussain et al., 2014; Matsui et al., 2014; Ding et al., 2014 [2], [3], [4], [5], [6]) but, here, we provide data specifically related to simultaneous use of ZnO as n-layer and AR coating. Apart from the information we already published, we provide additional data related to growth of ZnO (with and without Ga incorporation) layers using MOCVD. The data related to PC1D based simulation of internal and external quantum efficiencies with and without antireflection effects of ZnO as well as the effects of doping level in p-Si on current–voltage characteristics have been provided. PMID:26587557

  16. Thermally induced growth of ZnO nanocrystals on mixed metal oxide surfaces.

    PubMed

    Inayat, Alexandra; Makky, Ayman; Giraldo, Jose; Kuhnt, Andreas; Busse, Corinna; Schwieger, Wilhelm

    2014-06-23

    An in situ method for the growth of ZnO nanocrystals on Zn/Al mixed metal oxide (MMO) surfaces is presented. The key to this method is the thermal treatment of Zn/Al layered double hydroxides (Zn/Al LDHs) in the presence of nitrate anions, which results in partial demixing of the LDH/MMO structure and the subsequent crystallization of ZnO crystals on the surface of the forming MMO layers. In a first experimental series, thermal treatment of Zn/Al LDHs with different fractions of nitrate and carbonate in the interlayer space was examined by thermogravimetry coupled with mass spectrometry (TG-MS) and in situ XRD. In a second experimental series, Zn/Al LDHs with only carbonate in the interlayer space were thermally treated in the presence of different amounts of an external nitrate source (NH4NO3). All obtained Zn/Al MMO samples were analysed by electron microscopy, nitrogen physisorption and powder X-ray diffraction. The gas phase formed during nitrate decomposition turned out to be responsible for the formation of crystalline ZnO nanoparticles. Accordingly, both interlayer nitrate and the presence of ammonium nitrate led to the formation of supported ZnO nanocrystals with mean diameters between 100 and 400 nm, and both methods offer the possibility to tailor the amount and size of the ZnO crystals by means of the amount of nitrate.

  17. Specifications of ZnO growth for heterostructure solar cell and PC1D based simulations.

    PubMed

    Hussain, Babar; Ebong, Abasifreke

    2015-12-01

    This data article is related to our recently published article (Hussain et al., in press [1]) where we have proposed a new solar cell model based on n-ZnO as front layer and p-Si as rear region. The ZnO layer will act as an active n-layer as well as antireflection (AR) coating saving considerable processing cost. There are several reports presenting use of ZnO as window/antireflection coating in solar cells (Mansoor et al., 2015; Haq et al., 2014; Hussain et al., 2014; Matsui et al., 2014; Ding et al., 2014 [2], [3], [4], [5], [6]) but, here, we provide data specifically related to simultaneous use of ZnO as n-layer and AR coating. Apart from the information we already published, we provide additional data related to growth of ZnO (with and without Ga incorporation) layers using MOCVD. The data related to PC1D based simulation of internal and external quantum efficiencies with and without antireflection effects of ZnO as well as the effects of doping level in p-Si on current-voltage characteristics have been provided.

  18. Aluminoborosilicate glasses codoped with rare-earth elements as radiation-protective covers for solar cells

    SciTech Connect

    Malchukova, E. V. Abramov, A. S.; Nepomnyashchikh, A. I.; Terukov, E. I.

    2015-06-15

    The radiation hardness of aluminoborosilicate glasses codoped with rare-earth ions of Sm, Gd or Sm, Eu in various ratios is studied. The effect of codoping and β irradiation at a dose of 10{sup 9} Gr on the optical transmission and electron paramagnetic resonance spectra is examined. It is found that the introduction of Sm and Gd codopants in a 1 : 1 ratio reduces the number of radiation defects and raises the transmission of irradiated glasses in the visible spectral range.

  19. New insights into the band-gap narrowing of (N, P)-codoped TiO2 from hybrid density functional theory calculations.

    PubMed

    Long, Run; English, Niall J

    2011-10-04

    The electronic properties of anatase-TiO(2) codoped by N and P at different concentrations have been investigated via generalized Kohn-Sham theory with the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional for exchange-correlation in the context of density functional theory. At high doping concentrations, we find that the high photocatalytic activity of (N, P)-codoped anatase TiO(2) vis-à-vis the N-monodoped case can be rationalized by a double-hole-mediated coupling mechanism [Yin et al., Phys. Rev. Lett. 2011, 106, 066801] via the formation of an effective N-P bond. On the other hand, Ti(3+) and Ti(4+) ions' spin double-exchange results in more substantial gap narrowing for larger separations between N and P atoms. At low doping concentrations, double-hole-coupling is dominant, regardless of the N-P distance.

  20. The electronic and optical properties of Eu/Si-codoped anatase TiO2 photocatalyst

    NASA Astrophysics Data System (ADS)

    Lin, Yanming; Jiang, Zhenyi; Hu, Xiaoyun; Zhang, Xiaodong; Fan, Jun

    2012-03-01

    The electronic and optical properties of Eu/Si-codoped anatase TiO2 are investigated using the density functional theory. The calculated results show that the synergistic effects of Eu/Si codoping can effectively extend the optical absorption edge, which can lead to higher visible-light photocatalytic activities than pure anatase TiO2. To verify the reliability of our calculated results, nanocrystalline Eu/Si-codoped TiO2 is prepared by a sol-gel-solvothermal method, and the experimental results also indicate that the codoping sample exhibits better absorption performance and higher photocatalytic activities than pure TiO2.

  1. Effect of aluminium doping on structural and optical properties of ZnO thin films by sol-gel method

    SciTech Connect

    Vijayaprasath, G.; Murugan, R.; Ravi, G. E-mail: gravicrc@gmail.com; Hayakawa, Y.

    2015-06-24

    We systematically investigated the structural, morphological and optical properties of 0.05 mol % Al doped ZnO (Al:ZnO) thin films deposited on glass substrates by sol-gel spin coating method. The influences of Al doping in ZnO thin films are characterized by Powder X-ray diffraction study. ZnO and Al:ZnO thin films have showed hexagonal wurtzite structure without any secondary phase in c-axis (002) orientation. The SEM images also proved the hexagonal rod like morphologies for both films. All the films exhibited transmittance of 70-80% in the visible range up to 800 nm and cut-off wavelength observed at ∼390 nm corresponding to the fundamental absorption of ZnO. The band gap of the ZnO thin films slightly widened with the Al doping. The photoluminescence properties have been studied for Al: ZnO thin films and the results are presented in detail.

  2. A comprehensive review of ZnO materials and devices

    NASA Astrophysics Data System (ADS)

    Özgür, Ü.; Alivov, Ya. I.; Liu, C.; Teke, A.; Reshchikov, M. A.; Doǧan, S.; Avrutin, V.; Cho, S.-J.; Morkoç, H.

    2005-08-01

    The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. Lett. 16, 439 (1970)]. In terms of devices, Au Schottky barriers in 1965 by Mead [Phys. Lett. 18, 218 (1965)], demonstration of light-emitting diodes (1967) by Drapak [Semiconductors 2, 624 (1968)], in which Cu2O was used as the p-type material, metal-insulator-semiconductor structures (1974) by Minami et al. [Jpn. J. Appl. Phys. 13, 1475 (1974)], ZnO /ZnSe n-p junctions (1975) by Tsurkan et al. [Semiconductors 6, 1183 (1975)], and Al /Au Ohmic contacts by Brillson [J. Vac. Sci. Technol. 15, 1378 (1978)] were attained. The main obstacle to the development of ZnO has been the lack of reproducible and low-resistivity p-type ZnO, as recently discussed by Look and Claflin [Phys. Status Solidi B 241, 624 (2004)]. While ZnO already has many industrial applications owing to its piezoelectric properties and band gap in the near ultraviolet, its applications to optoelectronic devices has not yet materialized due chiefly to the lack of p-type epitaxial layers. Very high

  3. Realizing ferromagnetic ordering in SnO2 and ZnO nanostructures with Fe, Co, Ce ions.

    PubMed

    Verma, Kuldeep Chand; Kotnala, R K

    2016-07-14

    We report the defects/vacancies that attribute to room temperature ferromagnetism in SnO2 in contrast to ZnO [Phys. Chem. Chem. Phys., 2016, 18, 5647], which has observed ferromagnetic ordering below room temperature, since both the systems involve similar dopant Fe, Co, and Ce ions. The Fe, Co, Ce doped SnO2 nanostructures were synthesized by a sol-gel process. The Rietveld refinement of the X-ray diffraction data detects a rutile SnO2 structure, with structural defects due to the deformation of the unit cell with doping. The pure, Fe and Co doped SnO2 have nanoparticle formation that is induced to nanorods with Ce co-doping. However, ZnO retained a nanorod-type shape with Fe and Co ions and changed to nanoparticles with Ce co-doping. The rutile SnO2 structure and defect formation with Fe, Co, and Ce ions is also confirmed with Raman vibrational modes. The observed lattice defects due to oxygen vacancies are shown by the photoluminescence study. The weak room temperature ferromagnetism is observed with Fe and Co ions in SnO2, which is enhanced with Ce ions. The zero field (ZFC) and field cooling magnetic measurements indicate an improvement in magnetization with a cusp in the ZFC curve at low temperature, observed due to an antiferromagnetic transition. It also induced variations in the magnetic coercive field due to the phenomenon of superparamagnetism, spin glasses, and magnetic clustered growth. This can be further confirmed with ac magnetic susceptibility measurements that show magnetic transitions as well as frequency dispersive and dependent behaviors of χ'(T)/χ''(T). However, the Fe, Co, Ce doped ZnO exhibit paramagnetic behavior at room temperature due to favorable antiferromagnetic interactions and have a ferromagnetic transition at low temperature with little ferromagnetic cluster growth.

  4. Dilute Magnetic Semiconductors from Electrodeposited ZnO Nanowires

    SciTech Connect

    Athavan, Nadarajah; Konenkamp, R.

    2011-02-02

    We present experimental results on the magnetic properties of doped ZnO nanowires grown at 80 8C in electrodeposition. We show that impurities such as Al, Mn, Co, and Cu can be incorporated in the nanowires by adding the corresponding metal salts to the electrolyte solution. At concentration levels of a few atomic percent we find the impurity concentration in the solid to be approximately proportional to the precursor concentration in solution. ZnO nanowrires doped with Cu, Co, and Mn show superparamagnetic response at room temperature, while undoped and Al-doped wires show no discernible magnetic response. The results indicate that with Cu, Mn, and Co doping dilute magnetic semiconductors can be prepared.

  5. Nitrogen/Sulfur-Codoped Carbon Materials from Chitosan for Supercapacitors

    NASA Astrophysics Data System (ADS)

    Li, Mei; Han, Xianlong; Chang, Xiaoqing; Yin, Wenchao; Ma, Jingyun

    2016-08-01

    d-Methionine and chitosan have been used for fabrication of nitrogen/sulfur-codoped carbon materials by a hydrothermal process followed by carbonization at 750°C for 3 h. The as-prepared carbon materials showed enhanced electrochemical performance, combining electrical double-layer capacitance with pseudocapacitance owing to the doping with sulfur and nitrogen. The specific capacitance of the obtained carbon material reached 135 F g-1 at current density of 1 A g-1, which is much higher than undoped chitosan (67 F g-1). The capacitance retention of the carbon material was almost 97.2% after 5000 cycles at current density of 1 A g-1. With such improved electrochemical performance, the nitrogen/sulfur-codoped carbon material may have promising potential for use in energy-storage electrodes of supercapacitors.

  6. Polarity Effects of Substrate Surface in Epitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; George, M. A.; McCarty, P.

    1999-01-01

    Epitaxial ZnO films were grown on the two polar surfaces (0-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films are also deposited on the (000 I) Al203 substrates. It is found that the two polar surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which are strongly inference the epitaxial film growth. The morphology and structure of epitaxial films on the ZnO substrates are different from the film on the Al203 substrates. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite Surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth using reactive sputtering deposition.

  7. High-performance ZnO thin-film transistor fabricated by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Oh, Byeong-Yun; Kim, Young-Hwan; Lee, Hee-Jun; Kim, Byoung-Yong; Park, Hong-Gyu; Han, Jin-Woo; Heo, Gi-Seok; Kim, Tae-Won; Kim, Kwang-Young; Seo, Dae-Shik

    2011-08-01

    We report the fabrication and characteristics of a ZnO thin-film transistor (TFT) using a 50 nm thick ZnO film as an active layer on an Al2O3 gate dielectric film deposited by atomic layer deposition. Lowering the deposition temperature allowed the control of the carrier concentration of the active channel layer (ZnO film) in the TFT device. The ZnO TFT fabricated at 110 °C exhibited high-performance TFT characteristics including a saturation field-effect mobility of 11.86 cm2 V-1 s-1, an on-to-off current ratio of 3.09 × 107 and a sub-threshold gate-voltage swing of 0.72 V decade-1.

  8. Atomic Oxygen Sensors Based on Nanograin ZnO Films Prepared by Pulse Laser Deposition

    SciTech Connect

    Wang Yunfei; Chen Xuekang; Li Zhonghua; Zheng Kuohai; Wang Lanxi; Feng Zhanzu; Yang Shengsheng

    2009-01-05

    High-quality nanograin ZnO thin films were deposited on c-plane sapphire (Al{sub 2}O{sub 3}) substrates by pulse laser deposition (PLD). Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to characterize the samples. The structural and morphological properties of ZnO films under different deposition temperature have been investigated before and after atomic oxygen (AO) treatment. XRD has shown that the intensity of the (0 0 2) peak increases and its FWHM value decreases after AO treatment. The AO sensing characteristics of nano ZnO film also has been investigated in a ground-based atomic oxygen simulation facility. The results show that the electrical conductivity of nanograin ZnO films decreases with increasing AO fluence and that the conductivity of the films can be recovered by heating.

  9. Residual and intentional n-type doping of ZnO thin films grown by metal-organic vapor phase epitaxy on sapphire and ZnO substrates

    NASA Astrophysics Data System (ADS)

    Brochen, Stéphane; Lafossas, Matthieu; Robin, Ivan-Christophe; Ferret, Pierre; Gemain, Frédérique; Pernot, Julien; Feuillet, Guy

    2014-03-01

    ZnO epilayers usually exhibit high n-type residual doping which is one of the reasons behind the difficulties to dope this material p-type. In this work, we aimed at determining the nature of the involved impurities and their potential role as dopant in ZnO thin films grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire and ZnO substrates. In both cases, secondary ion mass spectroscopy (SIMS) measurements give evidence for a strong diffusion of impurities from the substrate to the epilayer, especially for silicon and aluminum. In the case of samples grown on sapphire substrates, aluminum follows Fick's diffusion law on a wide growth temperature range (800-1000°C). Thus, the saturation solubility and the diffusion coefficient of aluminum in ZnO single crystals have been determined. Furthermore, the comparison between SIMS impurity and effective dopant concentrations determined by capacitance-voltage measurements highlights, on one hand a substitutional mechanism for aluminum diffusion, and on the other hand that silicon acts as a donor in ZnO and not as an amphoteric impurity. In addition, photoluminescence spectra exhibit excitonic recombinations at the same energy for aluminum and silicon, indicating that silicon behaves as an hydrogenic donor in ZnO. Based on these experimental observations, ZnO thin films with a controlled n-type doping in the 1016-1019cm-3 range have been carried out. These results show that MOVPE growth is fully compatible with the achievement of highly Al-doped n-type thin films, but also with the growth of materials with low residual doping, which is a crucial parameter to address ZnO p-type doping issues.

  10. White-light emitting Eu3+ co-doped ZnO/Zn2SiO4:Mn2+ composite microphosphor

    NASA Astrophysics Data System (ADS)

    Ramakrishna, P. V.; Murthy, D. B. R. K.; Sastry, D. L.

    Eu3+ co-doped ZnO/Zn2SiO4:Mn2+ composites were synthesized via conventional solid state reaction route and were characterized by X-ray diffraction (XRD) scanning electron microscopy (SEM) and Fourier transform infra-red (FTIR) techniques. XRD studies reveal the presence of both ZnO and Zn2SiO4 phases. Photoluminescence properties of the samples were studied using 266 Nd-YAG laser excitations. Emission bands observed at ˜400 nm are ascribed to ZnO phosphor. The green emission bands at 530 nm is associated with the presence of Mn2+ ion, while orange (˜583) and red (615 nm) bands are supposed to be due to the presence of Eu3+ doped Zn2SiO4 phosphor. Energy transfer from power dependence of the sample for electric dipole transition (615 nm) was studied under 532 nm excitation by varying the power from 0.1 to 4.5 W. The estimated colour correlated temperature (CCT) values are found to be ˜4875 and 4458 K under 266 nm and 532 nm laser (0.5 W) excitations. These values are close to those of tubular fluorescent or cool white/daylight compact fluorescent (CFL) (˜5000 K) lamps. The present composite phosphor may have potential application in display devices.

  11. NIR luminescence studies on Er3+:Yb3+ co-doped sodium telluroborate glasses for lasers and optical amplifer applications

    NASA Astrophysics Data System (ADS)

    Annapoorani, K.; Murthy, N. Suriya; Marimuthu, K.

    2016-05-01

    Er3+:Yb3+ co-doped Sodium telluroborate glasses were prepared with the chemical composition (49.5-x)B2O3+25TeO2+5Li2CO3+10ZnO+10NaF+0.5Er2O3+xYb2O3 (where x= 0.1, 0.5, 1.0 and 2.0 in mol %) following the melt quenching technique. With the addition of Yb3+ ions into Er3+ ions in the prepared glasses, the absorption cross-section values were found to increase due to the effective energy transfer from 2F5/2 level of Yb3+ ions to the 4I11/2 level of Er3+ ions. The fluorescence around 1550 nm correspond to the 4I13/2→4I15/2 transition was observed under 980 nm pumping. Among the present glasses, integrated intensity was found to be higher for 1.0 mol% Yb3+ ion glass. The parameters such as stimulated emission cross- section, Gain bandwidth and quantum efficiency of the 4I13/2→4I15/2 transition was found to be higher for the NTBE1.0Y glass and the same is suggested for potential NIR lasers and optical amplifier applications.

  12. (Ti/Zr,N) codoped hematite for enhancing the photoelectrochemical activity of water splitting.

    PubMed

    Pan, Haijun; Meng, Xiangying; Liu, Dongyan; Li, Song; Qin, Gaowu

    2015-09-14

    In this theoretical study, first-principles calculations were carried out to explore the photocatalytic activity of cation (Ti or Zr) and anion (N) compensated codoped hematite based on density functional theory (DFT). For (Ti/Zr,N) codoped hematite, the band edges of the conduction band and the valence band move close to each other, leading to an obvious bandgap reduction. Compared with the pure hematite, the optical absorption coefficient of codoped hematite is significantly enhanced in the visible light region. The charge distribution at the conduction band minimum (CBM) and valence band maximum (VBM) is spatially separated after codoping, which is beneficial for extending the carrier lifetime. More interestingly, the CBM becomes electronically delocalized in (Ti,N) doped hematite, which indicates better carrier transport properties in the bulk system. Due to these special features of (Ti/Zr,N) codoped hematite, an improved photocatalytic performance can be expected.

  13. Defect engineering of ZnO

    NASA Astrophysics Data System (ADS)

    Weber, M. H.; Selim, F. A.; Solodovnikov, D.; Lynn, K. G.

    2008-10-01

    The defect responsible for the transparent to red color change of nominally undoped ZnO bulk single crystals is investigated. Upon annealing in the presence of metallic Zn as reported by Halliburton et al. and also Ti and Zr a native defect forms with an energy level about 0.7 eV below the conduction band. This change is reversible upon annealing in oxygen. Optical transmission data along with positron depth profiles and annealing studies are combined to identify the defect as oxygen vacancies. Vacancy clustering occurs at about 500 °C if isolated zinc and oxygen vacancies. In the absence of zinc vacancies, clusters form at about 800 °C.

  14. Room temperature ferromagnetism in Mn doped ZnO: Co nanoparticles by co-precipitation method

    NASA Astrophysics Data System (ADS)

    Pazhanivelu, V.; Selvadurai, A. Paul Blessington; Zhao, Yongsheng; Thiyagarajan, R.; Murugaraj, R.

    2016-01-01

    In this present work, the Mn2+ and Co2+ ions doping and co-doping effect on the structural, vibrational, morphological, optical and magnetic behaviors of ZnO based dilute magnetic semiconductors are reported. The Zn0.95Co0.05O (ZC), Zn0.95Mn0.05O (ZM) and Zn0.90Co0.05Mn0.05O (ZCM) samples were prepared by co-precipitation method. From the XRD analysis, it was observed that on the doping of Mn2+ ion in ZnO matrix, decreases their crystalline nature as well as the crystallite size significantly. The Raman spectra, Photoluminescence and electron paramagnetic resonance spectroscopy measurements reveal that the presence of defects in prepared samples. The UV-DRS spectroscopic exhibits the incorporation of dopant ions and their effect on the band gap subsequently. The magnetization measurements suggest the room temperature ferromagnetism (RTFM) in the prepared samples. The observed RTFM phenomenon was discussed based on the defects and grain confinement.

  15. Tailoring the refractive index of aluminum doped zinc oxide thin films by co-doping with titanium

    NASA Astrophysics Data System (ADS)

    Wei, Tiefeng; Lan, Pinjun; Yang, Ye; Zhang, Xianpeng; Tan, Ruiqin; Li, Yong; Song, Weijie

    2012-12-01

    The refractive index of transparent conductive oxides has a direct effect on the transmission of lights into thin film solar cells. Here we report the study of improving the refractive index of aluminum doped zinc oxide through titanium co-doping. The Al-Ti co-doped zinc oxide (ATZO) thin films with different Ti doping concentration were deposited on glass substrates by radio frequency magnetron sputtering with ATZO targets in an argon atmosphere. The structural, optical and electrical properties of the thin films were investigated using X-ray diffraction, ultraviolet-visible-near-infrared spectroscopy and hall measurements, respectively. The results showed that the as-deposited thin films were all textured along c-axis and perpendicular to the surface of substrate. The average transmittance in the visible region were more than 80% for all the ATZO thin films. The minimum resistivity of the obtained ATZO (1 wt% TiO2 doping) thin films were 2.6 × 10-3 Ω cm and 1.4 × 10-3 Ω cm before and after annealing in vacuum, respectively. The refractive index of the thin films (at λ0 = 550 nm) increased from 1.91 to 2.05 as the TiO2 content increased from 0 wt% to 3 wt%.

  16. The evolution and mechanisms of unintentional doping in ZnO epitaxial growth

    NASA Astrophysics Data System (ADS)

    Wu, Kongping; Zhu, Shunming; Gu, Shulin

    2012-10-01

    In this study, the authors investigate the evolution of the electrical and optical properties of ZnO epilayers grown by the metal-organic chemical vapor deposition method on c-sapphire substrates. The electrical and optical properties of ZnO buffer were investigated by temperature-dependent Hall (TDH), CV and PL. According to fit TDH data, two shallow donors were found in ZnO buffer film, with their activation energy at about 50meV and 10meV, respectively. The shallow donor at the energy of about 50meV has also been assigned from fitted results of PL spectra. According to the reported results and our experiments, the shallow donor at 50meV has then been ascribed to the diffused Al from sapphire during high temperature annealing and epitaxial growth process. All these reveal that the high background-carrier concentration in the HT-grown ZnO epilayer originates from the thermally enhanced diffusion of Al atoms from the sapphire substrate. Therefore, the AlZn shallow donors should be the main origin of the high background-carrier concentration in the HT-grown ZnO epilayers.

  17. Differential Toxicity of Bare and Hybrid ZnO Nanoparticles in Green Pea (Pisum sativum L.): A Life Cycle Study

    PubMed Central

    Mukherjee, Arnab; Sun, Youping; Morelius, Erving; Tamez, Carlos; Bandyopadhyay, Susmita; Niu, Genhua; White, Jason C.; Peralta-Videa, Jose R.; Gardea-Torresdey, Jorge L.

    2016-01-01

    The effect of surface or lattice modification of nanoparticles (NPs) on terrestrial plants is poorly understood. We investigated the impact of different zinc oxide (ZnO) NPs on green pea (Pisum sativum L.), one of the highest consumed legumes globally. Pea plants were grown for 65 d in soil amended with commercially available bare ZnO NPs (10 nm), 2 wt% alumina doped (Al2O3@ZnO NPs, 15 nm), or 1 wt% aminopropyltriethoxysilane coated NPs (KH550@ZnO NP, 20 nm) at 250 and 1000 mg NP/kg soil inside a greenhouse. Bulk (ZnO) and ionic Zn (zinc chloride) were included as controls. Plant fresh and dry biomass, changes in leaf pigment concentrations, elements (Zn, Al, Si), and protein and carbohydrate profile of green pees were quantified upon harvest at 65 days. With the exception of the coated 1000 mg/kg NP treatment, fresh and dry weight were unaffected by Zn exposure. Although, all treated plants showed higher tissue Zn than controls, those exposed to Al2O3@ZnO NPs at 1000 mg/kg had greater Zn concentration in roots and seeds, compared to bulk Zn and the other NP treatments, keeping Al and Si uptake largely unaffected. Higher Zn accumulation in green pea seeds were resulted in coated ZnO at 250 mg/kg treatments. In leaves, Al2O3@ZnO NP at 250 mg/kg significantly increased Chl-a and carotenoid concentrations relative to the bulk, ionic, and the other NP treatments. The protein and carbohydrate profiles remained largely unaltered across all treatments with the exception of Al2O3@ZnO NPs at 1000 mg/kg where sucrose concentration of green peas increased significantly, which is likely a biomarker of stress. Importantly, these findings demonstrate that lattice and surface modification can significantly alter the fate and phytotoxic effects of ZnO NPs in food crops and seed nutritional quality. To the authors' knowledge, this is the first report of a life cycle study on comparative toxicity of bare, coated, and doped ZnO NPs on a soil-grown food crop. PMID:26793219

  18. A Comparison of ZnO and ZnO(-)

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Arnold, James (Technical Monitor)

    1998-01-01

    Ab initio electronic structure calculations are performed to support and to help interpret the experimental work reported in the proceeding manuscript. The CCSD(T) approach, in conjunction with a large basis set, is used to compute spectroscopic constants for the X(exp 1)Epsilon(+) and (3)II states of ZnO and the X(exp 2)Epsilon(+) state of ZnO(-). The spectroscopic constants, including the electron affinity, are in good agreement with experiment. The ZnO EA is significantly larger than that of O, thus relative to the atomic ground state asymptotes, ZnO(-) has a larger D(sub o) than the (1)Epsilon(+) state, despite the fact that the extra electron goes into an antibonding orbital. The changes in spectroscopic constants can be understood in terms of the X(exp 1)Epsilon(+) formally dissociating to Zn (1)S + O (1)D while the (3)II and (2)Epsilon(+) states dissociate to Zn (1)S + O (3)P and Zn (1) and O(-) (2)P, respectively.

  19. Study of the wettability of ZnO nanofilms

    NASA Astrophysics Data System (ADS)

    Subedi, Deepak Prasad; Madhup, Dinesh Kumar; Sharma, Ashish; Joshi, Ujjwal Man; Huczko, Andrzej

    2012-04-01

    Al-doped and un-doped ZnO thin films deposited on quartz substrates by the nebulized spray pyrolysis method were studied to investigate the wettability of the surface. The main objective of the present study was to investigate the wettability of ZnO thin film by changing the concentration of Al doping. Microstructure and water contact angles of the films were measured by scanning electron microscopy (SEM) and using a contact angle goniometer. SEM studies revealed that the grain size within the film increases with the doping concentration. The contact angles were studied to see the effect of aluminum doping on the hydrophilicity of the film. ZnO films were found to be hydrophobic in nature. A good correlation was observed between the SEM micrographs and contact angle results. The nature of the film was found to change from being hydrophobic to hydrophilic after the treatment in low-pressure DC glow discharge plasma, which, however, was reversible with the storage time.

  20. Nucleation and growth of ZnO on PMMA by low-temperature atomic layer deposition

    SciTech Connect

    Napari, Mari Malm, Jari; Lehto, Roope; Julin, Jaakko; Arstila, Kai; Sajavaara, Timo; Lahtinen, Manu

    2015-01-15

    ZnO films were grown by atomic layer deposition at 35 °C on poly(methyl methacrylate) substrates using diethylzinc and water precursors. The film growth, morphology, and crystallinity were studied using Rutherford backscattering spectrometry, time-of-flight elastic recoil detection analysis, atomic force microscopy, scanning electron microscopy, and x-ray diffraction. The uniform film growth was reached after several hundreds of deposition cycles, preceded by the precursor penetration into the porous bulk and island-type growth. After the full surface coverage, the ZnO films were stoichiometric, and consisted of large grains (diameter 30 nm) with a film surface roughness up to 6 nm (RMS). The introduction of Al{sub 2}O{sub 3} seed layer enhanced the initial ZnO growth substantially and changed the surface morphology as well as the crystallinity of the deposited ZnO films. Furthermore, the water contact angles of the ZnO films were measured, and upon ultraviolet illumination, the ZnO films on all the substrates became hydrophilic, independent of the film crystallinity.

  1. Acceptors in ZnO

    SciTech Connect

    Mccluskey, Matthew D.; Corolewski, Caleb; Lv, Jinpeng; Tarun, Marianne C.; Teklemichael, Samuel T.; Walter, Eric D.; Norton, M. G.; Harrison, Kale W.; Ha, Su Y.

    2015-03-21

    Zinc oxide (ZnO) has potential for a range of applications in the area of optoelectronics. The quest for p-type ZnO has focused much attention on acceptors. In this paper, Cu, N, and Li acceptor impurities are discussed. Experimental evidence shows that these point defects have acceptor levels 3.2, 1.5, and 0.8 eV above the valence-band maximum, respectively. The levels are deep because the ZnO valence band is quite low compared to conventional, non-oxide semiconductors. Using MoO2 contacts, the electrical resistivity of ZnO:Li was measured and showed behavior consistent with bulk hole conduction for temperatures above 400 K. A photoluminescence peak in ZnO nanocrystals has been attributed to an acceptor, which may involve a zinc vacancy. High field (W-band) electron paramagnetic resonance measurements on the nanocrystals revealed an axial center with g = 2.0033 and g = 2.0075, along with an isotropic center at g = 2.0053.

  2. Acceptors in ZnO

    SciTech Connect

    McCluskey, Matthew D. Corolewski, Caleb D.; Lv, Jinpeng; Tarun, Marianne C.; Teklemichael, Samuel T.; Walter, Eric D.; Norton, M. Grant; Harrison, Kale W.; Ha, Su

    2015-03-21

    Zinc oxide (ZnO) has potential for a range of applications in the area of optoelectronics. The quest for p-type ZnO has focused much attention on acceptors. In this paper, Cu, N, and Li acceptor impurities are discussed. Experimental evidence indicates these point defects have acceptor levels 3.2, 1.4, and 0.8 eV above the valence-band maximum, respectively. The levels are deep because the ZnO valence band is quite low compared to conventional, non-oxide semiconductors. Using MoO{sub 2} contacts, the electrical resistivity of ZnO:Li was measured and showed behavior consistent with bulk hole conduction for temperatures above 400 K. A photoluminescence peak in ZnO nanocrystals is attributed to an acceptor, which may involve a Zn vacancy. High field (W-band) electron paramagnetic resonance measurements on the nanocrystals revealed an axial center with g{sub ⊥} = 2.0015 and g{sub //} = 2.0056, along with an isotropic center at g = 2.0035.

  3. C, N co-doped TiO2/TiC0.7N0.3 composite coatings prepared from TiC0.7N0.3 powder using ball milling followed by oxidation

    NASA Astrophysics Data System (ADS)

    Hao, Liang; Wang, Zhenwei; Zheng, Yaoqing; Li, Qianqian; Guan, Sujun; Zhao, Qian; Cheng, Lijun; Lu, Yun; Liu, Jizi

    2017-01-01

    Ball milling followed by heat oxidation was used to prepared C, N co-doped TiO2 coatings on the surfaces of Al2O3 balls from TiC0.7N0.3 powder. The as-prepared coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectrophotometer (UV-vis). The results show that continuous TiC0.7N0.3 coatings were formed after ball milling. C, N co-doped TiO2/TiC0.7N0.3 composite coatings were prepared after the direct oxidization of TiC0.7N0.3 coatings in the atmosphere. However, TiO2 was hardly formed in the surface layer of TiC0.7N0.3 coatings within a depth less than 10 nm during the heat oxidation of TiC0.7N0.3 coatings in carbon powder. Meanwhile, the photocatalytic activity evaluation of these coatings was conducted under the irradiation of UV and visible light. All the coatings showed photocatalytic activity in the degradation of MB no matter under the irradiation of UV or visible light. The C, N co-doped TiO2/TiC0.7N0.3 composite coatings showed the most excellent performance. The enhancement under visible light irradiation should attribute to the co-doping of carbon and nitrogen, which enhances the absorption of visible light. The improvement of photocatalytic activity under UV irradiation should attribute to the synergistic effect of C, N co-doping, the formation of rutile-anatase mixed phases and the TiO2/TiC0.7N0.3 composite microstructure.

  4. Double-Hole-Mediated Codoping on KNbO3 for Visible Light Photocatalysis.

    PubMed

    Wang, Guangzhao; Huang, Yuhong; Kuang, Anlong; Yuan, Hongkuan; Li, Yang; Chen, Hong

    2016-10-03

    In this theoretical study, the double-hole-mediated codoping strategy has been adopted to improve the photocatalytic activity of cubic KNbO3 as compared with the corresponding individual doping. The strong double-hole-mediated dopant-dopant coupling significantly reduces the effective bandgaps for the anionic-anionic (N-N, P-P, N-P, C-S) codoped systems with removing the appearing acceptor states above the Fermi level. No dopant-O coupling occurs in the cationic-anionic (V-C, Ti-P, Ti-N, Zr-P, Zr-N, Sc-S, Y-S) codoped systems. The V-C and Ti-P codoping could lead to narrowed bandgaps without unfilled localized states appearing above the Fermi level. N, Ti, Zr, Sc, Y monodoping and Ti-N, Zr-P, Zr-N, Sc-S, Y-S codoping introduce unoccupied impurity states between the valence band maximum and conduction band minimum, which makes them unfavorable for photocatalysis as these impurity states may serve as electron-hole recombination centers. For P-P, N-P, and C-S codoped systems, the intermediate states are higher or close to the hydrogen evolution potential, which is thermodynamically unfavorable for production of both oxygen and hydrogen. Producing hydrogen only, the N-N and C-S codoped KNbO3 materials will be good choices for Z-scheme photocatalysis. V, S, and V-C codoped KNbO3 may be promising visible light photocatalysts for water splitting, as they have suitable effective bandgaps without the introduction of unoccupied impurity states above the Fermi level, and they also own proper band edge positions with respect to the water redox level. The calculated optical absorption curves also indicate that C, V, and S monodoping and N-N, V-C, and Ti-P codoping can effectively enhance the visible light absorption.

  5. Preparation of new morphological ZnO and Ce-doped ZnO

    SciTech Connect

    Chelouche, A.; Djouadi, D.; Aksas, A.

    2013-12-16

    ZnO micro-tori and cerium doped hexangulars ZnO have been prepared by the sol-gel method under methanol hypercritical conditions of temperature and pressure. X-ray diffraction (XRD) measurement has revealed the high crystalline quality and the nanometric size of the samples. Scanning electron microscopy (SEM) has shown that the ZnO powder has a torus-like shape while that of ZnO:Ce has a hexangular-like shape, either standing free or inserted into the cores of ZnO tori. Transmission electron microscopy (TEM) has revealed that the ZnO particles have sizes between 25 and 30 nm while Ce-doped ZnO grains have diameters ranging from 75 nm to 100 nm. Photoluminescence spectra at room temperature of the samples have revealed that the introduction of cerium in ZnO reduces the emission intensity lines, particularly the ZnO red and green ones.

  6. Fabrication and characterization of ZnO nanowires grown on Ti substrate

    NASA Astrophysics Data System (ADS)

    Meng, Gang; Fang, Xiaodong; Tao, Ruhua; Dong, Weiwei; Deng, Zanhong; Zhou, Shu

    2009-07-01

    Zinc oxide (ZnO) with a wide band gap of 3.37 eV, and a large exciton binding energy of 60 mV at room temperature, is one of the most important n-type semiconductor, that has potential applications in the area of short-wavelength optoelectronic devices, gas sensors, solar cells, and field emitters. Some advanced nanodevices based on one-dimensional (1-D) ZnO nanomaterials have been successfully demonstrated in the past few years. The types of substrate have a great influence on the properties of ZnO nanostrctural devices. Semiconductor substrates such as Si and Al2O3 were widely used for the collection or epitaxial growth of ZnO nanostructures, for metal substrate, Fe and Cu foil has also been used as substrate, there are few reports on ZnO nanowires grown on Ti foil, Ti is an important electrode metal that ohmic contact can be appropriately achieved, which is critical for semiconductor device application. Besides, both Ti and ZnO show good biocompatibility, it is expected that ZnO nanowires/ Ti show good performance on bio-sensors. In this paper, 1-D ZnO nanostructures have been successfully fabricated on the conductive Ti substrate via a vapor phase transport (VPT) method by carbothermal reduction of ZnO and graphite powder mixture in a tube furnace at 850°C. The final products were characterized by means of field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), high-solution transmission electron microscope (HRTEM) (equipped with selected area electron diffraction, SAED), and photoluminescence (PL) spectroscopy. FE SEM results show that dense, ultra-long (>10μm), and locally aligned ZnO nanowire arrays were grown on the Ti foil. The diameter of nanowires exhibits a wide range from 150 nm to about 500nm. Structural characterizations (XRD, SAED, HRTEM) indicate the as synthesized nanostructures have a ZnO wurtzite structure and are perfect single crystalline without any defects or impurities. The growth direction is [0001]. Optical

  7. The Effect of the Oxygen Plasma Treatment for ITO and ZnO Nanorods on the Electroluminescence of ZnO Nanorod/MEH-PPV Heterostructure Devices

    NASA Astrophysics Data System (ADS)

    Zhao, Su-Ling; Wang, Yong-Sheng; Gao, Song; Yang, Yi-Fan; Xu, Zheng

    2013-03-01

    Series devices of ITO/ZnO/ZnO nanorods/MEH-PPV/Al have been fabricated. ITO and ZnO nanorods of some devices are treated by O2 plasma. The electroluminescence of different devices is detected under different biases. UV electroluminescence of ZnO nanorods at 380nm is observed in all the devices. The intensity of 380nm increases when both ITO and ZnO nanorods are treated. The turn-on voltage of the treated device is lower than that of the non-treated device, and the EL power is enhanced. When the thickness of MEH-PPV is sufficiently thin, only 380 nm electroluminescence, besides a weak defect emission at 760 nm, is detected. The enhancement mechanism of the electroluminescence of the treated devices is discussed.

  8. Dynamics of iron-acceptor-pair formation in co-doped silicon

    SciTech Connect

    Bartel, T.; Gibaja, F.; Graf, O.; Gross, D.; Kaes, M.; Heuer, M.; Kirscht, F.; Möller, C.; Lauer, K.

    2013-11-11

    The pairing dynamics of interstitial iron and dopants in silicon co-doped with phosphorous and several acceptor types are presented. The classical picture of iron-acceptor pairing dynamics is expanded to include the thermalization of iron between different dopants. The thermalization is quantitatively described using Boltzmann statistics and different iron-acceptor binding energies. The proper understanding of the pairing dynamics of iron in co-doped silicon will provide additional information on the electronic properties of iron-acceptor pairs and may become an analytical method to quantify and differentiate acceptors in co-doped silicon.

  9. Toward a durable superhydrophobic aluminum surface by etching and ZnO nanoparticle deposition.

    PubMed

    Rezayi, Toktam; Entezari, Mohammad H

    2016-02-01

    Fabrication of suitable roughness is a fundamental step for acquiring superhydrophobic surfaces. For this purpose, a deposition of ZnO nanoparticles on Al surface was carried out by simple immersion and ultrasound approaches. Then, surface energy reduction was performed using stearic acid (STA) ethanol solution for both methods. The results demonstrated that ultrasound would lead to more stable superhydrophobic Al surfaces (STA-ZnO-Al-U) in comparison with simple immersion method (STA-ZnO-Al-I). Besides, etching in HCl solution in another sample was carried out before ZnO deposition for acquiring more mechanically stable superhydrophobic surface. The potentiodynamic measurements demonstrate that etching in HCl solution under ultrasound leads to superhydrophobic surface (STA-ZnO-Al(E)-U). This sample shows remarkable decrease in corrosion current density (icorr) and long-term stability improvement versus immersion in NaCl solution (3.5%) in comparison with the sample prepared without etching (STA-ZnO-Al-U). Scanning electron micrograph (SEM) and energy-dispersive X-ray spectroscopy (EDX) confirmed a more condense and further particle deposition on Al substrate when ultrasound was applied in the system. The crystallite evaluation of deposited ZnO nanoparticles was carried out using X-ray diffractometer (XRD). Finally, for STA grafting verification on Al surface, Fourier transform infrared in conjunction with attenuated total reflection (FTIR-ATR) was used as a proper technique.

  10. Luminescent Properties and Mechanism of Gd1-x-yAlO3Eux,REy

    NASA Astrophysics Data System (ADS)

    Luo, Lan; Liu, Qing-Feng; Liu, Qian

    2005-01-01

    GAP:Eu,Re(Gd1-x-yAlO3:Eux, REy, RE=Pr or Ce) powders were prepared by a nitrate-citrate process. It is found that luminescent intensity decreases when GAP:Eu is co-doped with Pr or Ce. The phenomena of spectra prove that there is a resonant energy transfer between Eu and Pr, by the absorption and emission of lower-energy phonon, and also Ce sensitizer decreases the activator energy level from host→Eu. The two factors are considered to be the main reasons for decrease of the luminescent intensity for the co-doped GAP:Eu,Re.

  11. One-dimensional ZnO nanostructures.

    PubMed

    Jayadevan, K P; Tseng, T Y

    2012-06-01

    The wide-gap semiconductor ZnO with nanostructures such as nanoparticle, nanorod, nanowire, nanobelt, nanotube has high potential for a variety of applications. This article reviews the fundamentals of one-dimensional ZnO nanostructures, including processing, structure, property, application and their processing-microstructure-property correlation. Various fabrication methods of the ZnO nanostructures including vapor-liquid-solid process, vapor-solid growth, solution growth, solvothermal growth, template-assisted growth and self-assembly are introduced. The characterization and properties of the ZnO nanostructures are described. The possible applications of these nanostructures are also discussed.

  12. Photocatalytic oxidation of propylene on La and N codoped TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Jinfeng; Li, Haiyan; Zong, Lanlan; Li, Qiuye; Wang, Xiaodong; Zhang, Min; Yang, Jianjun

    2015-02-01

    Lanthanum- and nitrogen-codoped TiO2 photocatalysts was synthesized using orthorhombic nanotubes titanic acid as the precursor by a simple impregnation and subsequent calcination method. The morphology, phase structure, and properties of La- and N-codoped TiO2 were well characterized by transmission electron microscopy, X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectra. The La-/N-codoped TiO2 showed excellent photoactivity of propylene oxidation compared with the single-doped TiO2 and La-/N-codoped P25 TiO2 nanoparticles under visible light irradiation. The origin of the enhancement of the visible light-responsive photocatalytic activity was discussed in detail.

  13. Optical parameters and upconversion fluorescence in Tm3+/Yb3+ codoped tellurite glass

    NASA Astrophysics Data System (ADS)

    Huang, Q. J.; Wang, Q. P.; Chang, J.; Zhang, X. Y.; Liu, Z. J.; Yu, G. Y.

    2010-04-01

    Tm3+/Yb3+ codoped tellurite glass has been prepared. Density, refractive index, optical absorption, Judd-Ofelt parameters and spontaneous transition probabilities of Tm3+ have been measured and calculated, respectively. Intense blue three-photon upconversion fluorescence and S-band (1470 nm) fluorescence were investigated under the excitation of a 980 nm diode laser at room temperature. Judd-Ofelt parameters, strong blue three-photon upcoversion emission of Tm3+ in glass indicate that Tm3+/Yb3+ codoped tellurite glass is a promising blue color upconversion optical and laser material. In addition, experiment results showed the 980 nm laser was more efficient than 808 nm laser when pumping Tm3+/Yb3+ codoped tellurite glass, Tm3+/Yb3+ codoped tellurite glass also could be a promising material for S-band amplification.

  14. Effects of co-dopants on the magnetic properties of Ni-Zn ferrites

    NASA Astrophysics Data System (ADS)

    Wang, Sea-Fue; Hsu, Yung-Fu; Chou, Kai-Mou; Tsai, Jeng-Ting

    2015-01-01

    In this study, substitution of co-dopants into the Ni0.4Zn0.6Fe2O4 ceramic was performed. Al3+, Sn4+ and Ti4+ ions were added to the Ni0.4Zn0.4Li0.10Fe2.10O4 ceramic to improve magnetic properties. After sintering, all samples were indexed on a spinel structure and no detectable second phase was observed. When the concentration of dopants increased, the grain size of the Ni-Zn ferrites increased from 1.40 to 6.05 μm and the saturation magnetization declined from 428.8 emu/cm3 to 374.0 emu/cm3. Amongst the systems investigated, the Ni0.4Zn0.4Li0.10Al0.050Fe2.050O4, Ni0.4Zn0.425Li0.10Ti0.025Fe2.050O4, and Ni0.4Zn0.450Li0.10Ti0.050Fe2.000O4 ceramics revealed promising magnetic properties for applications. The measured initial permeability and quality factor were respectively 291.9 and 45.1 for the Ni0.4Zn0.4Li0.10Al0.050Fe2.050O4 ceramic, 316.9 and 42.5 for the Ni0.4Zn0.425Li0.10Ti0.025Fe2.050O4 ceramic, 429.4 and 34.8 for the Ni0.4Zn0.450Li0.10Ti0.050Fe2.000O4 ceramic. The high initial permeability and quality factor values associated with good electrical resistivity (>106 Ω-cm) qualify the ceramics for high frequency applications.

  15. Nondestructive In Situ Identification of Crystal Orientation of Anisotropic ZnO Nanostructures

    DTIC Science & Technology

    2009-08-05

    O ne-dimensional nano- and micro- structures such as wires, rods, belts , and tubes of various met- als and semiconductors have attracted in- creased...RESULTS AND DISCUSSION In this paper, we will primarily focus on ZnO nano- belts and nanorods of two different types, although the general features can be...diffraction pattern, the ZnO belt in Figure 2a has the (0001) or (0001̄) as the top and bottom large facets, in other words, the growth direction in a

  16. A Hybrid Density Functional Theory Study of Band Gap Tuning in ZnO through Pressure

    NASA Astrophysics Data System (ADS)

    Zhao, Bo-Tao; Duan, Yi-Feng; Shi, Hong-Liang; Qin, Li-Xia; Shi, Li-Wei; Tang, Gang

    2012-11-01

    The structural transformation and electronic structure of ZnO under hydrostatic pressure are investigated using the HSE06 range-separated hybrid functional. We show that wurtzite ZnO under pressure undergoes a structural transition to a graphite-like phase. We also find that the band gap of wurtzite phase is always direct, whereas the new phase can display either direct or indirect band structure. Furthermore, the gap is greatly enhanced by pressure and no semi-metallic phase is observed. This is drastically different from our previous results of AlN and GaN [Appl. Phys. Lett. 100 (2012) 022104].

  17. Polarity effects in the x-ray photoemission of ZnO and other wurtzite semiconductors

    NASA Astrophysics Data System (ADS)

    Allen, M. W.; Zemlyanov, D. Y.; Waterhouse, G. I. N.; Metson, J. B.; Veal, T. D.; McConville, C. F.; Durbin, S. M.

    2011-03-01

    Significant polarity-related effects were observed in the near-surface atomic composition and valence band electronic structure of ZnO single crystals, investigated by x-ray photoemission spectroscopy using both Al Kα (1486.6 eV) and synchrotron radiation (150 to 1486 eV). In particular, photoemission from the lowest binding energy valence band states was found to be significantly more intense on the Zn-polar face compared to the O-polar face. This is a consistent effect that can be used as a simple, nondestructive indicator of crystallographic polarity in ZnO and other wurtzite semiconductors.

  18. Evolution of crystal structure during the initial stages of ZnO atomic layer deposition

    DOE PAGES

    Boichot, R.; Tian, L.; Richard, M. -I.; ...

    2016-01-05

    In this study, a complementary suite of in situ synchrotron X-ray techniques is used to investigate both structural and chemical evolution during ZnO growth by atomic layer deposition. Focusing on the first 10 cycles of growth, we observe that the structure formed during the coalescence stage largely determines the overall microstructure of the film. Furthermore, by comparing ZnO growth on silicon with a native oxide with that on Al2O3(001), we find that even with lattice-mismatched substrates and low deposition temperatures, the crystalline texture of the films depend strongly on the nature of the interfacial bonds.

  19. Many-body electronic structure calculations of Eu-doped ZnO

    NASA Astrophysics Data System (ADS)

    Lorke, M.; Frauenheim, T.; da Rosa, A. L.

    2016-03-01

    The formation energies and electronic structure of europium-doped zinc oxide has been determined using DFT and many-body G W methods. In the absence of intrisic defects, we find that the europium-f states are located in the ZnO band gap with europium possessing a formal charge of 2+. On the other hand, the presence of intrinsic defects in ZnO allows intraband f -f transitions otherwise forbidden in atomic europium. This result corroborates with recently observed photoluminescence in the visible red region S. Geburt et al. [Nano Lett. 14, 4523 (2014), 10.1021/nl5015553].

  20. CdS nanoparticles sensitization of Al-doped ZnO nanorod array thin film with hydrogen treatment as an ITO/FTO-free photoanode for solar water splitting

    PubMed Central

    2012-01-01

    Aluminum-doped zinc oxide (AZO) nanorod array thin film with hydrogen treatment possesses the functions of transparent conducting oxide thin film and 1-D nanostructured semiconductor simultaneously. To enhance the absorption in the visible light region, it is sensitized by cadmium sulfide (CdS) nanoparticles which efficiently increase the absorption around 460 nm. The CdS nanoparticles-sensitized AZO nanorod array thin film with hydrogen treatment exhibits significantly improved photoelectrochemical property. After further heat treatment, a maximum short current density of 5.03 mA cm−2 is obtained under illumination. They not only are much higher than those without CdS nanoparticles sensitization and those without Al-doping and/or hydrogen treatment, but also comparable and even slightly superior to some earlier works for the CdS-sensitized zinc oxide nanorod array thin films with indium tin oxide (ITO) or fluorine-doped tin oxide (FTO) as substrates. This demonstrated successfully that the AZO nanorod array thin film with hydrogen treatment is quite suitable as an ITO/FTO-free photoanode and has great potentials in solar water splitting after sensitization by quantum dots capable of visible light absorption. PMID:23098050

  1. Eu/Tb codoped spindle-shaped fluorinated hydroxyapatite nanoparticles for dual-color cell imaging.

    PubMed

    Ma, Baojin; Zhang, Shan; Qiu, Jichuan; Li, Jianhua; Sang, Yuanhua; Xia, Haibing; Jiang, Huaidong; Claverie, Jerome; Liu, Hong

    2016-06-02

    Lanthanide doped fluorinated hydroxyapatite (FAp) nanoparticles are promising cell imaging nanomaterials but they are excited at wavelengths which do not match the light sources usually found in a commercial confocal laser scanning microscope (CLSM). In this work, we have successfully prepared spindle-shaped Eu/Tb codoped FAp nanoparticles by a hydrothermal method. Compared with single Eu doped FAp, Eu/Tb codoped FAp can be excited by a 488 nm laser, and exhibit both green and red light emission. By changing the amounts of Eu and Tb peaks, the emission in the green region (500-580 nm) can be decreased to the benefit of the emission in the red region (580-720 nm), thus reaching a balanced dual color emission. Using MC3T3-E1 cells co-cultured with Eu/Tb codoped FAp nanoparticles, it is observed that the nanoparticles are cytocompatible even at a concentration as high as 800 μg ml(-1). The Eu/Tb codoped FAp nanoparticles are located in the cytoplasm and can be monitored by dual color-green and red imaging with a single excitation light at 488 nm. At a concentration of 200 μg ml(-1), the cytoplasm is saturated in 8 hours, and Eu/Tb codoped FAp nanoparticles retain their fluorescence for at least 3 days. The cytocompatible Eu/Tb codoped FAp nanoparticles with unique dual color emission will be of great use for cell and tissue imaging.

  2. Plasmon-enhanced Electrically Light-emitting from ZnO Nanorod Arrays/p-GaN Heterostructure Devices

    PubMed Central

    Lu, Junfeng; Shi, Zengliang; Wang, Yueyue; Lin, Yi; Zhu, Qiuxiang; Tian, Zhengshan; Dai, Jun; Wang, Shufeng; Xu, Chunxiang

    2016-01-01

    Effective and bright light-emitting-diodes (LEDs) have attracted broad interests in fundamental research and industrial application, especially on short wavelength LEDs. In this paper, a well aligned ZnO nanorod arrays grown on the p-GaN substrate to form a heterostructured light-emitting diode and Al nanoparticles (NPs) were decorated to improve the electroluminescence performance. More than 30-folds enhancement of the electroluminescence intensity was obtained compared with the device without Al NPs decoration. The investigation on the stable and transient photoluminescence spectraof the ZnO nanorod arrays before and after Al NPs decoration demonstrated that the metal surface plasmon resonance coupling with excitons of ZnO leads to the enhancement of the internal quantum efficiency (IQE). Our results provide aneffective approach to design novel optoelectronic devices such as light-emitting diodes and plasmonic nanolasers. PMID:27181337

  3. The electronic and optical properties of Eu/Si-codoped anatase TiO{sub 2} photocatalyst

    SciTech Connect

    Lin Yanming; Jiang Zhenyi; Zhang Xiaodong; Hu Xiaoyun; Fan Jun

    2012-03-05

    The electronic and optical properties of Eu/Si-codoped anatase TiO{sub 2} are investigated using the density functional theory. The calculated results show that the synergistic effects of Eu/Si codoping can effectively extend the optical absorption edge, which can lead to higher visible-light photocatalytic activities than pure anatase TiO{sub 2}. To verify the reliability of our calculated results, nanocrystalline Eu/Si-codoped TiO{sub 2} is prepared by a sol-gel-solvothermal method, and the experimental results also indicate that the codoping sample exhibits better absorption performance and higher photocatalytic activities than pure TiO{sub 2}.

  4. Enhanced optical absorption and photocatalytic activity of anatase TiO2 through (Si,Ni) codoping

    NASA Astrophysics Data System (ADS)

    Lin, Yanming; Jiang, Zhenyi; Zhu, Chaoyuan; Hu, Xiaoyun; Zhang, Xiaodong; Zhu, Haiyan; Fan, Jun

    2012-08-01

    The electronic and optical properties of (Si,Ni)-codoped anatase TiO2 are investigated using the density functional theory. The calculated results indicate that the synergistic effects of (Si,Ni) codoping can effectively extend the optical absorption edge, which can lead to higher visible-light photocatalytic activity than pure anatase TiO2. To verify the reliability of our calculated results, nanocrystalline (Si,Ni)-codoped TiO2 is synthesized by a sol-gel-solvothermal method, and experimental results also show that the (Si,Ni)-codoped sample exhibits better absorption performance and higher photocatalytic activities than pure TiO2.

  5. Fabrication of high performance field-effect transistors and practical Schottky contacts using hydrothermal ZnO nanowires.

    PubMed

    Opoku, Charles; Dahiya, Abhishek Singh; Oshman, Christopher; Daumont, Christophe; Cayrel, Frederic; Poulin-Vittrant, Guylaine; Alquier, Daniel; Camara, Nicolas

    2015-09-04

    The production of large quantities of single crystalline semiconducting ZnO nanowires (NWs) at low cost can offer practical solutions to realizing several novel electronic/optoelectronic and sensor applications on an industrial scale. The present work demonstrates high-density single crystalline NWs synthesized by a multiple cycle hydrothermal process at ∼100 °C. The high carrier concentration in such ZnO NWs is greatly suppressed by a simple low cost thermal annealing step in ambient air at ∼450 °C. Single ZnO NW FETs incorporating these modified NWs are characterized, revealing strong metal work function-dependent charge transport, unobtainable with as-grown hydrothermal ZnO NWs. Single ZnO NW FETs with Al as source and drain (s/d) contacts show excellent performance metrics, including low off-state currents (fA range), high on/off ratio (10(5)-10(7)), steep subthreshold slope (<600 mV/dec) and excellent field-effect carrier mobility (5-11 cm(2)/V-s). Modified ZnO NWs with platinum s/d contacts demonstrate excellent Schottky transport characteristics, markedly different from a reference ZnO NW device with Al contacts. This included abrupt reverse bias current-voltage saturation characteristics and positive temperature coefficient (∼0.18 eV to 0.13 eV). This work is envisaged to benefit many areas of hydrothermal ZnO NW research, such as NW FETs, piezoelectric energy recovery, piezotronics and Schottky diodes.

  6. Electronic structure of cation-codoped TiO2 for visible-light photocatalyst applications from hybrid density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Long, Run; English, Niall J.

    2011-04-01

    The electronic structures of Mg/Ca- and/or Mo/W- (mono- and co-) doped anatase TiO2 have been investigated via generalized Kohn-Sham theory with the Heyd-Scuseria-Ernzerhof hybrid functional for exchange-correlation {J. Heyd et al., [J. Chem. Phys. 118, 8207 (2003)], J. Heyd et al., [J. Chem. Phys. 124, 219906 (2006)], and J. Paier et al., [J. Chem. Phys. 125, 249901 (2006)]}, in the context of density functional theory. Gap narrowing is small for monodoping, which also creates impuritiy bands in the "forbidden gap," either as acceptor or donor states, limiting possible utility as visible-light photocatalysts. However, codoping of Mg/Ca and Mo/W not only induces appreciable gap narrowing, but also serves to passivate the impurity bands, which can harvest visible-light to a greater extent. Considering ionic radii, Mg and Mo should constitute the best cation-pair.

  7. Persistent photoconductivity in ZnO nanowires: Influence of oxygen and argon ambient

    NASA Astrophysics Data System (ADS)

    Madel, M.; Huber, F.; Mueller, R.; Amann, B.; Dickel, M.; Xie, Y.; Thonke, K.

    2017-03-01

    ZnO nanowires typically show persistent photoconductivity (PPC), which depends in their temporal behaviour on the ambient. We investigate ZnO nanowires in oxygen and argon ambient and analyze the PPC both on the short and on the long time scale to sort out the underlying mechanisms. Wavelength dependent excitation shows the energy barrier for the PPC to be around 150 meV below the band gap of ZnO, independent of the ambient atmosphere. In photocurrent measurements at constant wavelength, a log-logistic dependence of the conductivity on the partial oxygen pressure is observed. The experimental results are compared to a model of Bonasewicz et al. [J. Electrochem. Soc. 133, 2270 (1986)] and can be explained by oxygen adsorption processes occurring on the surface of the ZnO nanowires. From temperature dependent measurements of the decay times in oxygen and argon ambient, the related activation energies for the fast and slow decay processes are determined. Comparing our results to theoretical calculations of energy levels of intrinsic defects [Janotti and Van de Walle, Phys. Status Solidi B 248, 799 (2011)], we find oxygen vacancies to be related to the fast decay processes, whereas adsorption and desorption processes of oxygen on the ZnO nanowire surface account for the slow part.

  8. The electronic, magnetic and optical properties of ZnO doped with doubles impurities (Cr, Fe): An LDA-SIC and Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Salmani, El Mehdi; Laghrissi, Ayoub; Lamouri, Rachida; Ez-Zahraouy, Hamid; Benyoussef, Abdelilah

    2017-01-01

    Electronic structure, magnetic and optical properties of ZnO doped with single and double impurities Zn1-xCrxO, Zn1-xFexO, and Zn1-2xCrxFexO (x=0.03 and 0.06) are investigated using first-principles calculations. Based on the Korringa-Kohn-Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of doubles impurities (Cr, Fe) doped ZnO. To support our results, we apply the self-interaction-corrected local density approximation (SIC-LDA) to study the electronic structure, optical and magnetic properties of Co-doped ZnO with doubles impurities (Cr, Fe) showing that the half-metallic ferromagnetic state still persists. The stability of the ferromagnetic state compared with the spin-glass state is investigated by comparing their total energies. The exchange interactions obtained from first principle calculations and used in a classical Ising model by a Monte Carlo approach resulted in ferromagnetic states with high Neel temperature.

  9. Ferromagnetic semiconductor nanoclusters: Co-doped Cu2O

    NASA Astrophysics Data System (ADS)

    Antony, Jiji; Qiang, You; Faheem, Muhammad; Meyer, Daniel; McCready, David E.; Engelhard, Mark H.

    2007-01-01

    5% Co-doped cuprous oxide dilute magnetic semiconducting cluster film composed of two different sizes of crystalline nanoclusters, prepared using sputtering-aggregation technique is found to be ferromagnetic at 400K. With the increase in average crystallite size from 4.2to8nm, the coercivity increased. Magnetic field up to 2T is applied and saturation magnetization is achieved at 3kOe field in both cases. Cu2O phase is observed from cluster film deposited on Si wafer when analyzed using x-ray diffraction. Co in Cu2O host reveals a +2 oxidation state via x-ray photoelectron spectroscopy. Positive magnetoresistance from samples exhibits a temperature dependent decrease.

  10. Electronic structure and ferromagnetism of Mn implanted n-type and p-type ZnO

    NASA Astrophysics Data System (ADS)

    Petit, Leon; Schulthess, Thomas; Svane, Axel; Temmerman, Walter; Szotek, Zdzislawa

    2004-03-01

    The prediction of room temperature magnetism in Mn doped ZnO has generated considerable interest in this compound, both from the experimental and theoretical point of views. In order to take into account the strong on-site correlations of the rather localized d-electrons, we use the self-interaction corrected (SIC)-LSD approximation. Within this scheme, the 3d electron manifold is considered to consist of both localized and itinerant states, both of which are treated on an equal footing, by adding a contribution for each d-electron to localize. By varying the relative proportions of localized and delocalized states, the most favourable (groundstate) configuration can be established. Our calculations show that the 3d electrons in Mn doped ZnO prefer to localize. We furthermore have studied the effects on the electronic structure, when Zn_1-xMn_xO is codoped with N atoms (n-type ZnOMn), and Ga and Sn atoms (n-type ZnOMn) respectively.

  11. Direct formation of InN-codoped p-ZnO/n-GaN heterojunction diode by solgel spin-coating scheme.

    PubMed

    Huang, Chun-Ying; Lee, Ya-Ju; Lin, Tai-Yuan; Chang, Shao-Lun; Lian, Jan-Tian; Lin, Hsiu-Mei; Chen, Nie-Chuan; Yang, Ying-Jay

    2014-02-15

    In this work p-ZnO/n-GaN heterojunction diodes were directly formed on the Si substrate by a combination of cost-effective solgel spin-coating and thermal annealing treatment. Spin-coated n-ZnO films on InN/GaN/Si wafers were converted to p-type polarity after thermal treatment of proper annealing durations. X-ray diffraction (XRD) analysis reveals that InN-codoped ZnO films have grown as the standard hexagonal wurtzite structure with a preferential orientation in the (002) direction. The intensity of the (002) peak decreases for a further extended annealing duration, indicating the greater incorporation of dopants, also confirmed by x-ray photoelectron spectroscopy and low-temperature photoluminescence. Hall and resistivity measurements validate that our p-type ZnO film has a high carrier concentration of 3.73×10¹⁷ cm⁻³, a high mobility of 210 cm²/Vs, and a low resistivity of 0.079 Ωcm. As a result, the proposed p-ZnO/n-GaN heterojunction diode displays a well-behaving current rectification of a typical p-n junction, and the measured current versus voltage (I-V) characteristic is hence well described by the modified Shockley equation. The research on the fabrication of p-ZnO/n-GaN heterojunctions shown here generates useful advances in the production of cost-effective ZnO-based optoelectronic devices.

  12. Enhancement of the memory effects for nonvolatile memory devices fabricated utilizing ZnO nanoparticles embedded in a Si3N4 layer.

    PubMed

    Oh, Do-Hyun; Cho, Woon-Jo; Son, Dong Ick; Kim, Tae Whan

    2010-05-01

    ZnO nanoparticles embedded in a Si3N4 layer by using spin-coating and thermal treatment were fabricated to investigate the feasible applications in charge trapping regions of the metal/oxide/nitride/oxide/p-Si memory devices. The magnitude of the flatband voltage shift of the capacitance-voltage (C-V) curve for the Al/SiO2/ZnO nanoparticles embedded in Si3N4 layer/SiO2/p-Si memory device was larger than that of Al/ZnO nanoparticles embedded in SiO2 layer/p-Si and Al/SiO2/Si3N4/SiO2/p-Si devices. The increase in the flatband voltage shift of the C-V curve for the Al/SiO2/ZnO nanoparticles embedded in Si3N4 layer/SiO2/p-Si memory device in comparison with other devices was attributed to the existence of the ZnO nanoparticles or the interface trap states between the ZnO nanoparticles and the Si3N4 layer resulting from existence of ZnO nanoparticles embedded in the Si3N4 layer.

  13. Synthesis and characterization of Cu, Fe co-doped ZnO nano-particles synthesized by solution combustion method

    NASA Astrophysics Data System (ADS)

    Gupta, Dikshita; Ghanshyam, Kotnala, R. K.; Negi, N. S.

    2013-06-01

    Zn0.94Cu0.01Fe0.05O (ZCFO) nanoparticles were synthesized by chemical solution method and their crystallographic, micro structural and magnetic properties were investigated at different annealing temperatures 100°C, 250°C, and 450°C respectively. Ferromagnetic behavior was observed from VSM at room temperature, ZCFO powder annealed at 100°C shows paramagnetism and those annealed at 250°C, 350°C and 450°C shows distinct ferromagnetic behavior.

  14. Enhancement of photoluminescence properties in ZnO/AlN bilayer heterostructures grown by atomic layer deposition

    SciTech Connect

    Zhu, Shang-Bin; Lu, Hong-Liang Zhang, Yuan; Sun, Qing-Qing; Zhou, Peng; Ding, Shi-Jin; Zhang, David Wei; Zhang, Qiu-Xiang

    2015-01-15

    The AlN/ZnO bilayer heterostructures were deposited on Si (100) substrate by thermal atomic layer deposition. X-ray diffraction results show that the crystallinity of polycrystalline ZnO layer is enhanced by amorphous AlN capping layer. Compared with ZnO thin film, ZnO/AlN bilayer with 10.7 nm AlN capping layer exhibits three times enhanced near band edge (NBE) emission from the photoluminescence measurements. In addition, the near band edge emission from the ZnO can be further increased by ∼10 times through rapid thermal annealing at 600 °C. The underlying mechanisms for the enhancement of the NBE emission after coating AlN capping layer and thermal treatment are discussed. These results suggest that coating of a thin AlN layer and sequential thermal treatments can effectively tailor the luminescence properties of ZnO film.

  15. Spectroscopic properties of Er3+/Yb3+ Co-doped zinc boro-tellurite glasses for 1.5 xB5m broadband optical amplifiers

    NASA Astrophysics Data System (ADS)

    Suthanthirakumar, P.; Karthikeyan, P.; Vijayakumar, R.; Marimuthu, K.

    2015-06-01

    A new series of Er3+/Yb3+ co-doped Zinc boro-tellurite glasses with the chemical composition (40-x-y)B2O3+ 25TeO2+20ZnO+15BaO+xYb2O3+yEr2O3 (where x = 0.1, 0.5, 1 and 3; y =1 in wt %) were prepared by melt quenching technique and their spectroscopic behavior were studied through UV-Vis-NIR absorption and NIR luminescence measurements. The bonding parameters (β ¯ and δ) and Judd-Ofelt (JO) intensity parameters Ωλ (λ=2, 4 and 6) have been calculated from the band positions of the absorption spectra. A broad near-infrared emission band at 1540 nm with a full width at half maximum around 80 nm was observed from the NIR luminescence spectra by monitoring an excitation at 980 nm. The absorption cross-section and emission cross-section for the4I13/2→4I15/2 transition of the Er3+ ions were also determined using McCumber theory and the results were discussed and reported.

  16. Geometric, electronic and optical properties of zinc/tin codoped In2O3 modulated by the bixbyite/corundum phase transition

    NASA Astrophysics Data System (ADS)

    Lu, Ying-Bo; Li, Y. H.; Ling, Z. C.; Cong, Wei-Yan; Zhang, Peng; Xin, Y. Q.; Yang, T. L.

    2016-02-01

    As transparent conducting oxides (TCOs), In2O3 in the high pressure phase attracts extensive research interests. Because physical properties are determined by the geometric structures, we investigate the electronic and optical properties of Zn/Sn codoped In2O3 materials (IZTO) being modulated by the bixbyite/corundum phase transition via Density Functional Theory calculations. For IZTO in high pressure phase, i.e. corundum phase, Sn/Zn dopant pair tends to form face-sharing ZnO6 and SnO6 octahedrons. The radius differences between Zn2+/Sn4+ dopants and In3+ host cations make Jahn-Teller effect occur and IZTO transform from bixbyite to corundum phase under a slight higher pressure than that of pure In2O3. Although Zn/Sn cosubstitution of In ions may increase the free carrier effective mass m * near the band edge, when IZTO crystal transforms to corundum phase, the more dense packing structure results in stronger cation s-orbital overlaps than in bixbyite phase, which makes m * recover to a smaller value. In addition, corundum IZTO has a larger indirect band gap and a high dopant solubility. So these investigations may open a new way to search for TCOs materials with low indium content.

  17. Synthesis of Cr and La-codoped SrTiO3 nanoparticles for enhanced photocatalytic performance under sunlight irradiation.

    PubMed

    Tonda, Surendar; Kumar, Santosh; Anjaneyulu, Oruganti; Shanker, Vishnu

    2014-11-21

    In this study, we report a facile polymeric citrate strategy for the synthesis of Cr,La-codoped SrTiO3 nanoparticles. The synthesized samples were well characterized by various analytical techniques. The UV-vis DRS studies reveal that the absorption edge shifts towards the visible light region after doping with Cr, which is highly beneficial for absorbing the visible light in the solar spectrum. More attractively, codoping with La exhibits greatly enhanced photocatalytic activity for the degradation of Rhodamine B under sunlight irradiation. The optimum photocatalytic activity at 1 atom% of Cr,La-codoped SrTiO3 nanoparticles is almost 6 times higher than that of pure SrTiO3 nanoparticles and 3 times higher than that of Cr-doped SrTiO3 nanoparticles. The high photocatalytic performance in the present photocatalytic system is due to codoping with La, which acts as a most effective donor for stabilizing Cr(3+) in Cr,La-codoped SrTiO3 nanoparticles. More importantly, the synthesized photocatalysts possess high reusability. A proposed mechanism for the enhanced photocatalytic activity of Cr,La-codoped SrTiO3 nanoparticles was also investigated by trapping experiments. Therefore, our results not only demonstrate the highly efficient visible light photocatalytic activity of the Cr,La-codoped SrTiO3 photocatalyst, but also enlighten the codoping strategy in the design and development of advanced photocatalytic materials for energy and environmental applications.

  18. Half-metallicity and magnetism of Ti2Ni1-x CoxAl1-y Siy inverse Heusler alloys

    NASA Astrophysics Data System (ADS)

    Zhou, Ting; Feng, Yu; Chen, Xiaorui; Yuan, Hongkuan; Chen, Hong

    2017-02-01

    Half-metallicity and magnetism of Ti2Ni1-x CoxAl1-y Siy, which are obtained by Co/Si substitutions for Ni/Al of inverse Heusler alloy Ti2NiAl, are investigated by first-principle calculations based on density functional theory (DFT). The optimized lattice constants of the doped systems all conform to the Vegard law as the increase of the impurity concentration, and the magnetic moments obey the Slater-Pauling rule when the half-metallicity is retained. The defect formation energies of the codoped systems are lower than those of the monodoped systems due to the charge compensation effects, thus the Co+Si codoping is more favorable in energy than the Co/Si monodoping. Furthermore, for the Co and Si monodoped systems, the Co monodoping retains the minority-spin bandgap unchanged although the Fermi level moves towards high energy region, and the Si monodoping leads to the minority-spin bandgap narrowing and even the loss of half-metallicity at the high concentration, while for the Co+Si codoped systems, the majority of the codoped compounds obviously show more stable half-metallicity and the minority-spin gap get widened. In particular, the minority-spin band gap of the codoped compounds Ti2Ni0.5Co0.5Al0.5Si0.5 , Ti2Ni0.25Co0.75Al0.5Si0.5 , and Ti2NiCo Al0.25Si0.75 are widened distinctly and their Fermi level are adjusted to the middle of the minority-spin gap, indicating that they possess robust half-metallicity and thus they are promising candidates for spintronics applications.

  19. Experiments and simulation on diffusion and activation of codoped with arsenic and phosphorous germanium

    NASA Astrophysics Data System (ADS)

    Tsouroutas, P.; Tsoukalas, D.; Bracht, H.

    2010-07-01

    We report arsenic and phosphorus diffusion experiments and activation related phenomena in codoped germanium substrates utilizing conventional thermal annealing. Chemical profiles were obtained by secondary ion mass spectroscopy, sheet resistance was estimated by the Van der Pauw method. Our study covers the temperature range from 600 to 750 °C. We accurately described the dopant profiles with a quadratic dependence of the dopants diffusion coefficient on the free electron concentration. In our simulations we considered the dopant pile-up near the surface and dopant loss owing to outdiffusion during the annealing. Although the double donor codoping technique exhibited no advantage over monodoping with P concerning the level of activation and junction depth, it was interesting to observe the different diffusion behavior of the two dopants. Whereas the diffusion of As indicates a retardation under codoping the diffusion of P remains either unaffected or is slightly enhanced by codoping. The activation level of the codoped samples remains lower compared to the respective monodoped samples, except for the highest annealing temperature.

  20. Preparation and photocatalytic activity of nonmetal Co-doped titanium dioxide photocatalyst

    NASA Astrophysics Data System (ADS)

    Sun, Xiaogang; Xing, Jun; Qiu, Jingping

    2016-06-01

    A series of boron and sulfur co-doped titanium dioxide (TiO2) photocatalysts were prepared by a sol-gel method using boric acid, thiourea and tetrabutyl titanate [Ti(OC4H9)4] as precursors. The photoabsorbance of as-prepared photocatalysts was measured by UV-Vis diffuse reflectance spectroscopy (DRS), and its microstructure was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and N2 adsorption-desorption measurements. The prepared photocatalysts consisted of the anatase phase mainly in the form of spherical particles. The photocatalytic performance was studied by photodegradation of methyl blue (MB) in water under UV and visible light irradiation. The calcination temperature and the codoping content influenced the photoactivity. The synergistic effect of boron and sulfur co-doping played an important role in improving the photocatalytic activity. In addition, the possibility of cyclic usage of codoped TiO2 was also confirmed, the photocatalytic activity of TiO2 remained above 91% of that of the fresh sample after being used four times. It was shown that the co-doped TiO2 could be activated by visible light and could thus be potentially applied for the treatment of water contaminated by organic pollutants.

  1. Preparation, characterization and visible light photocatalytic activity of silver, nitrogen co-doped TiO2 photocatalyst

    NASA Astrophysics Data System (ADS)

    Khan, Matiullah; Ramin Gul, Sahar; Li, Jing; Cao, Wenbin; Mamalis, Athanasios G.

    2015-06-01

    TiO2 photocatalyst codoped with Silver (Ag) and Nitrogen (N) with different Ag doping concentrations is successfully synthesized by hydrothermal method. The as-synthesized samples are characterized through x-ray diffraction (XRD), Transmission electron microscopy (TEM), UV-vis. absorption spectra and x-ray photoelectron spectroscopy (XPS). The photocatalytic response is evaluated by the photodegradation of methylene blue under visible light irradiations. All synthesized samples are composed of pure anatase phase with good crystallinity. The absorption edge of codoped TiO2 is shifted towards visible light region. X-ray photoelectron spectroscopy confirmed the existence of silver and nitrogen in the codoped samples. All the codoped samples demonstrated improved photocatalytic activity compared to pure TiO2. Among the different codoped samples, the one with silver doping concentration of 4 at. % exhibited the highest photoactivity.

  2. Ultraviolet-driven white light generation from oxyfluoride glass co-doped with Tm3+-Tb3+-Eu3+

    NASA Astrophysics Data System (ADS)

    Kuznetsov, A. S.; Nikitin, A.; Tikhomirov, V. K.; Shestakov, M. V.; Moshchalkov, V. V.

    2013-04-01

    Tm3+-Tb3+-Eu3+ co-doped oxyfluoride glasses, doped with about 3.0 mol. % TmF3, 0.25 mol. % TbF3, and 0.25 mol. % EuF3, have been prepared by melt quenching technique. Under excitation at commercial 365 nm, the rare-earth co-dopants are all directly excited and emit in the blue, green, and red, respectively, without appreciable energy transfer amongst the co-dopants. Tint of the white luminescence can be adjusted by changing the ratio of the co-dopants. Properties of the glass host promote excellent dissolution of the co-dopants and low non-radiative decay rate. The white emission at 365 nm excitation is suitable for light emitting diodes applications.

  3. Sn/Be Sequentially co-doped Hematite Photoanodes for Enhanced Photoelectrochemical Water Oxidation: Effect of Be2+ as co-dopant

    PubMed Central

    Annamalai, Alagappan; Lee, Hyun Hwi; Choi, Sun Hee; Lee, Su Yong; Gracia-Espino, Eduardo; Subramanian, Arunprabaharan; Park, Jaedeuk; Kong, Ki-jeong; Jang, Jum Suk

    2016-01-01

    For ex-situ co-doping methods, sintering at high temperatures enables rapid diffusion of Sn4+ and Be2+ dopants into hematite (α–Fe2O3) lattices, without altering the nanorod morphology or damaging their crystallinity. Sn/Be co-doping results in a remarkable enhancement in photocurrent (1.7 mA/cm2) compared to pristine α–Fe2O3 (0.7 mA/cm2), and Sn4+ mono-doped α-Fe2O3 photoanodes (1.0 mA/cm2). From first-principles calculations, we found that Sn4+ doping induced a shallow donor level below the conduction band minimum, which does not contribute to increase electrical conductivity and photocurrent because of its localized nature. Additionally, Sn4+-doping induce local micro-strain and a decreased Fe-O bond ordering. When Be2+ was co-doped with Sn4+-doped α–Fe2O3 photoanodes, the conduction band recovered its original state, without localized impurities peaks, also a reduction in micro-strain and increased Fe-O bond ordering is observed. Also the sequence in which the ex-situ co-doping is carried out is very crucial, as Be/Sn co-doping sequence induces many under-coordinated O atoms resulting in a higher micro-strain and lower charge separation efficiency resulting undesired electron recombination. Here, we perform a detailed systematic characterization using XRD, FESEM, XPS and comprehensive electrochemical and photoelectrochemical studies, along with sophisticated synchrotron diffraction studies and extended X-ray absorption fine structure. PMID:27005757

  4. Sn/Be Sequentially co-doped Hematite Photoanodes for Enhanced Photoelectrochemical Water Oxidation: Effect of Be(2+) as co-dopant.

    PubMed

    Annamalai, Alagappan; Lee, Hyun Hwi; Choi, Sun Hee; Lee, Su Yong; Gracia-Espino, Eduardo; Subramanian, Arunprabaharan; Park, Jaedeuk; Kong, Ki-Jeong; Jang, Jum Suk

    2016-03-23

    For ex-situ co-doping methods, sintering at high temperatures enables rapid diffusion of Sn(4+) and Be(2+) dopants into hematite (α-Fe2O3) lattices, without altering the nanorod morphology or damaging their crystallinity. Sn/Be co-doping results in a remarkable enhancement in photocurrent (1.7 mA/cm(2)) compared to pristine α-Fe2O3 (0.7 mA/cm(2)), and Sn(4+) mono-doped α-Fe2O3 photoanodes (1.0 mA/cm(2)). From first-principles calculations, we found that Sn(4+) doping induced a shallow donor level below the conduction band minimum, which does not contribute to increase electrical conductivity and photocurrent because of its localized nature. Additionally, Sn(4+)-doping induce local micro-strain and a decreased Fe-O bond ordering. When Be(2+) was co-doped with Sn(4+)-doped α-Fe2O3 photoanodes, the conduction band recovered its original state, without localized impurities peaks, also a reduction in micro-strain and increased Fe-O bond ordering is observed. Also the sequence in which the ex-situ co-doping is carried out is very crucial, as Be/Sn co-doping sequence induces many under-coordinated O atoms resulting in a higher micro-strain and lower charge separation efficiency resulting undesired electron recombination. Here, we perform a detailed systematic characterization using XRD, FESEM, XPS and comprehensive electrochemical and photoelectrochemical studies, along with sophisticated synchrotron diffraction studies and extended X-ray absorption fine structure.

  5. Mechanism of Zn Particle Oxidation by H2O and CO2 in the Presence of ZnO.

    PubMed

    Weibel, David; Jovanovic, Zoran R; Gálvez, Elena; Steinfeld, Aldo

    2014-11-25

    In this work we investigate the mechanism of Zn oxidation with CO2 and/or H2O to produce solar derived fuels (CO and/or H2) as part of the Zn/ZnO thermochemical redox cycle. It has been observed that the ZnO contamination of Zn produced by solar thermal reduction of ZnO (solar Zn) facilitates oxidation of the metallic Zn by CO2 and H2O, allowing for nearly complete conversion at temperatures as low as 350 °C. Reaching the same reaction extent starting with pure Zn requires considerably higher temperatures which imposes use of unconventional hard-to-operate reaction configurations utilizing Zn as vapor. The mechanism of this enhancement is investigated by studying the oxidation of solid Zn diluted with ZnO or Al2O3 at 350-400 °C utilizing thermogravimetry. It is found that ZnO acts as the site for the oxidation of Zn originating from the vapor phase, thereby serving as a sink for Zn vapor and maintaining the driving force for sustainable Zn sublimation. As this Zn sublimation competes with the growth of an impervious ZnO scale over the surface of the remaining solid Zn, the presence of the ZnO increases the reaction extent according to the magnitude of its surface area. This mechanism is supported by energy-dispersive X-ray (EDX) spectroscopy, revealing a substantial deposition of produced ZnO over the surface of the ZnO-seeded Al2O3 diluent.

  6. Photovoltaic study of dye sensitized solar cells based on TiO2, ZnO:Al3+ nanoparticles

    NASA Astrophysics Data System (ADS)

    Sánchez Godoy, H. E.; Rodríguez-Rojas, R. A.; Castañeda-Contreras, J.; Marañón-Ruiz, V. F.; Pérez-Ladrón de Guevara, H.; López-Luke, T.; De la Rosa-Cruz

    2015-10-01

    A technique to fabricate dye (rhodamine B) sensitized solar cells based on Titanium Oxide (TiO2) and Zinc Oxide (ZnO) nanoparticles are reported. The TiO2 was synthesized using the sol-gel method and the ZnO was synthesized by hydrolysis method to obtain nanoparticles of ~ 5 nm and 150 nm respectively. ZnO was doped with Al3+ in order to enhance the photovoltaic efficiency to promote the electrons mobility. The photovoltaic conversion characterization of films of TiO2, ZnO and ZnO:Al3+ nanoparticles is also reported. The generated photocurrent was measured by two methods; one of those uses a three electrode electrochemical cell and the other use an electronic array where the cells were exposed to UV lamp and the sun light. The role of the TiO2, ZnO and Al3+ doped ZnO nanoparticles is discussed to obtain a better efficiency in the generation of photocurrent (PC). The results exhibited by the electrochemical cell method, efficiencies of 0.55 (PC=187 μA/cm2) and 0.22 (PC=149 μA/cm2) for TiO2 and undoped ZnO respectively. However, when ZnO is doped with Al3+ at the higher concentration the efficiency was 0.44. While using the electronic array the results exhibited efficiencies of 0.31 (PC=45 μA/cm2) and 0.09 (PC=16 μA/cm2) for TiO2 and undoped ZnO respectively. However, when ZnO is doped with Al3+ at the higher concentration the efficiency was 0.44 and 0.48 for electrochemical cell and electronic array respectively. This shows that Al3+ enhances the photogenerated charge carriers increasing the mobility of electrons.

  7. Cobalt-doped ZnO nanowires on quartz: Synthesis by simple chemical method and characterization

    NASA Astrophysics Data System (ADS)

    Vempati, Sesha; Shetty, Amitha; Dawson, P.; Nanda, Karunakar; Krupanidhi, S. B.

    2012-03-01

    The synthesis of cobalt-doped ZnO nanowires is achieved using a simple, metal salt decomposition growth technique. A sequence of drop casting on a quartz substrate held at 100 °C and annealing results in the growth of nanowires of average (modal) length ˜200 nm and diameter of 15±4 nm and consequently an aspect ratio of ˜13. A variation in the synthesis process, where the solution of mixed salts is deposited on the substrate at 25 °C, yields a grainy film structure which constitutes a useful comparator case. X-ray diffraction shows a preferred [0001] growth direction for the nanowires while a small unit cell volume contraction for Co-doped samples and data from Raman spectroscopy indicate incorporation of the Co dopant into the lattice; neither technique shows explicit evidence of cobalt oxides. Also the nanowire samples display excellent optical transmission across the entire visible range, as well as strong photoluminescence (exciton emission) in the near UV, centered at 3.25 eV.

  8. Optical properties of ZnO nanostructures.

    PubMed

    Djurisić, Aleksandra B; Leung, Yu Hang

    2006-08-01

    We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.

  9. Eu/Tb codoped spindle-shaped fluorinated hydroxyapatite nanoparticles for dual-color cell imaging

    NASA Astrophysics Data System (ADS)

    Ma, Baojin; Zhang, Shan; Qiu, Jichuan; Li, Jianhua; Sang, Yuanhua; Xia, Haibing; Jiang, Huaidong; Claverie, Jerome; Liu, Hong

    2016-06-01

    Lanthanide doped fluorinated hydroxyapatite (FAp) nanoparticles are promising cell imaging nanomaterials but they are excited at wavelengths which do not match the light sources usually found in a commercial confocal laser scanning microscope (CLSM). In this work, we have successfully prepared spindle-shaped Eu/Tb codoped FAp nanoparticles by a hydrothermal method. Compared with single Eu doped FAp, Eu/Tb codoped FAp can be excited by a 488 nm laser, and exhibit both green and red light emission. By changing the amounts of Eu and Tb peaks, the emission in the green region (500-580 nm) can be decreased to the benefit of the emission in the red region (580-720 nm), thus reaching a balanced dual color emission. Using MC3T3-E1 cells co-cultured with Eu/Tb codoped FAp nanoparticles, it is observed that the nanoparticles are cytocompatible even at a concentration as high as 800 μg ml-1. The Eu/Tb codoped FAp nanoparticles are located in the cytoplasm and can be monitored by dual color--green and red imaging with a single excitation light at 488 nm. At a concentration of 200 μg ml-1, the cytoplasm is saturated in 8 hours, and Eu/Tb codoped FAp nanoparticles retain their fluorescence for at least 3 days. The cytocompatible Eu/Tb codoped FAp nanoparticles with unique dual color emission will be of great use for cell and tissue imaging.Lanthanide doped fluorinated hydroxyapatite (FAp) nanoparticles are promising cell imaging nanomaterials but they are excited at wavelengths which do not match the light sources usually found in a commercial confocal laser scanning microscope (CLSM). In this work, we have successfully prepared spindle-shaped Eu/Tb codoped FAp nanoparticles by a hydrothermal method. Compared with single Eu doped FAp, Eu/Tb codoped FAp can be excited by a 488 nm laser, and exhibit both green and red light emission. By changing the amounts of Eu and Tb peaks, the emission in the green region (500-580 nm) can be decreased to the benefit of the emission in the

  10. Diode-pumped femtosecond mode-locked Nd, Y-codoped CaF2 laser

    NASA Astrophysics Data System (ADS)

    Zhu, Jiangfeng; Zhang, Lijuan; Gao, Ziye; Wang, Junli; Wang, Zhaohua; Su, Liangbi; Zheng, Lihe; Wang, Jingya; Xu, Jun; Wei, Zhiyi

    2015-03-01

    A passively mode-locked femtosecond laser based on an Nd, Y-codoped CaF2 disordered crystal was demonstrated. The Y3+-codoping in Nd : CaF2 markedly suppressed the quenching effect and improved the fluorescence quantum efficiency and emission spectra. With a fiber-coupled laser diode as the pump source, the continuous wave tuning range covering from 1042 to 1076 nm was realized, while the mode-locked operation generated 264 fs pulses with an average output power of 180 mW at a repetition rate of 85 MHz. The experimental results show that the Nd, Y-codoped CaF2 disordered crystal has potential in a new generation diode-pumped high repetition rate chirped pulse amplifier.

  11. DFT study of Ag and La codoped BaTiO3

    NASA Astrophysics Data System (ADS)

    Maldonado, Frank; Stashans, Arvids

    2017-03-01

    Density functional theory and generalized gradient approximation including a Hubbard-like term was used in the present work to analyse structure as well as electronic and electrical properties of Ag and La codoped BaTiO3 material. Intrinsic oxygen vacancy defect has been taken into consideration throughout the calculations. Results on atomic shifts indicate the significance of Coulomb electrostatic interaction in finding equilibrium state of the system. It is shown that the n-type electrical conductivity should be expected as a result of codoping. Computed concentrations of free-carriers manifest the advantage of codoping procedure compared to the single impurity doping in the BaTiO3 crystal. It is also shown that oxygen vacancy alone can produce the n-type conductivity.

  12. Using Atom-Probe Tomography to Understand Zn O ∶Al /SiO 2/Si Schottky Diodes

    NASA Astrophysics Data System (ADS)

    Jaramillo, R.; Youssef, Amanda; Akey, Austin; Schoofs, Frank; Ramanathan, Shriram; Buonassisi, Tonio

    2016-09-01

    We use electronic transport and atom-probe tomography to study Zn O ∶Al /SiO 2/Si Schottky diodes on lightly doped n - and p -type Si. We vary the carrier concentration in the ZnOAl films by 2 orders of magnitude, but the Schottky barrier height remains nearly constant. Atom-probe tomography shows that Al segregates to the interface, so that the ZnOAl at the junction is likely to be metallic even when the bulk of the ZnOAl film is semiconducting. We hypothesize that the observed Fermi-level pinning is connected to the insulator-metal transition in doped ZnO. This implies that tuning the band alignment at oxide/Si interfaces may be achieved by controlling the transition between localized and extended states in the oxide, thereby changing the orbital hybridization across the interface.

  13. Nitrogen-fluorine co-doped titania inverse opals for enhanced solar light driven photocatalysis.

    PubMed

    Rahul, T K; Sandhyarani, N

    2015-11-21

    Three dimensionally ordered nitrogen-fluorine (N-F) co-doped TiO2 inverse opals (IOs) were fabricated by templating with polystyrene (PS) colloidal photonic crystals (CPCs) by infiltration. During preparation, the TiO2 precursor was treated with a mixture of nitric acid and trifluoroacetic acid to facilitate N-F co-doping into the TiO2 lattice. Enhanced solar light absorption was observed in the samples as a consequence of the red shift in the electronic band gap of TiO2 due to N-F co-doping. The photonic band gap (PBG) of these TiO2 IO films was tuned by varying the sphere size of the PS CPC templates. The as-prepared N-F co-doped TiO2 IO films were used as photocatalysts for the degradation of Rhodamine B (RhB) dye under solar light irradiation. A significant enhancement in the photocatalytic activity was observed in N-F co-doped TiO2 IO films prepared using PS spheres of 215 nm as a template, with the red edge of the PBG closer to the electronic band gap (EBG) of TiO2. 100% of the dye molecules were degraded within 2 minutes under direct solar irradiation, which is one of the fastest reaction times ever reported for RhB degradation in the presence of TiO2 photocatalysts. The N-F co-doped TiO2 IO film prepared using PS of 460 nm with its PBG centered at 695 nm also showed good photocatalytic activity. It was found that the IO films displayed improved photocatalytic activity in comparison to ordinary nanocrystalline (nc)-TiO2 films. The enhancement could be attributed to the bandgap scattering effect and the slow photon effect, leading to a significant improvement in solar light harvesting.

  14. Nitrogen-fluorine co-doped titania inverse opals for enhanced solar light driven photocatalysis

    NASA Astrophysics Data System (ADS)

    Rahul, T. K.; Sandhyarani, N.

    2015-10-01

    Three dimensionally ordered nitrogen-fluorine (N-F) co-doped TiO2 inverse opals (IOs) were fabricated by templating with polystyrene (PS) colloidal photonic crystals (CPCs) by infiltration. During preparation, the TiO2 precursor was treated with a mixture of nitric acid and trifluoroacetic acid to facilitate N-F co-doping into the TiO2 lattice. Enhanced solar light absorption was observed in the samples as a consequence of the red shift in the electronic band gap of TiO2 due to N-F co-doping. The photonic band gap (PBG) of these TiO2 IO films was tuned by varying the sphere size of the PS CPC templates. The as-prepared N-F co-doped TiO2 IO films were used as photocatalysts for the degradation of Rhodamine B (RhB) dye under solar light irradiation. A significant enhancement in the photocatalytic activity was observed in N-F co-doped TiO2 IO films prepared using PS spheres of 215 nm as a template, with the red edge of the PBG closer to the electronic band gap (EBG) of TiO2. 100% of the dye molecules were degraded within 2 minutes under direct solar irradiation, which is one of the fastest reaction times ever reported for RhB degradation in the presence of TiO2 photocatalysts. The N-F co-doped TiO2 IO film prepared using PS of 460 nm with its PBG centered at 695 nm also showed good photocatalytic activity. It was found that the IO films displayed improved photocatalytic activity in comparison to ordinary nanocrystalline (nc)-TiO2 films. The enhancement could be attributed to the bandgap scattering effect and the slow photon effect, leading to a significant improvement in solar light harvesting.

  15. Effect of the H2 plasma treatment of a seed layer on the synthesis of ZnO nanorods using a microwave hydrothermal method

    NASA Astrophysics Data System (ADS)

    Koo, Horng-Show; Lin, Ching-Cheng; Chen, Yao-Ju; Peng, Cheng-Hsiung; Chen, Mi

    2014-01-01

    The effect of H2 plasma treatment of a seed layer on the synthesis and characterization of zinc oxide (ZnO) nanorods is determined. Using an Al-doped ZnO (AZO) thin film as a seed layer, well-aligned ZnO nanorods are rapidly grown on an indium tin oxide (ITO)-coated glass substrate using a microwave hydrothermal method. The deposited AZO substrate was previously treated with H2 plasma. The effect of H2 plasma treatment of the seed layer on the alignment, growth rate, and crystallinity of the ZnO nanorods is determined. It is shown that the alignment and growth rate of the ZnO nanorods depend on the characteristics and roughness of the seed layer, which are improved by H2 plasma treatment. Various characterization methods such as X-ray diffraction (XRD), cathodoluminescence (CL), transmission electron microscopy (TEM), and X-ray photoemission spectroscopy (XPS) are used to determine the characteristic quality of the ZnO nanorods. A fundamental model of the effect of H2 plasma treatment on the seed layer and ZnO growth using a microwave hydrothermal process is also presented.

  16. Growth of vertically aligned ZnO nanorods using textured ZnO films

    PubMed Central

    2011-01-01

    A hydrothermal method to grow vertical-aligned ZnO nanorod arrays on ZnO films obtained by atomic layer deposition (ALD) is presented. The growth of ZnO nanorods is studied as function of the crystallographic orientation of the ZnO films deposited on silicon (100) substrates. Different thicknesses of ZnO films around 40 to 180 nm were obtained and characterized before carrying out the growth process by hydrothermal methods. A textured ZnO layer with preferential direction in the normal c-axes is formed on substrates by the decomposition of diethylzinc to provide nucleation sites for vertical nanorod growth. Crystallographic orientation of the ZnO nanorods and ZnO-ALD films was determined by X-ray diffraction analysis. Composition, morphologies, length, size, and diameter of the nanorods were studied using a scanning electron microscope and energy dispersed x-ray spectroscopy analyses. In this work, it is demonstrated that crystallinity of the ZnO-ALD films plays an important role in the vertical-aligned ZnO nanorod growth. The nanorod arrays synthesized in solution had a diameter, length, density, and orientation desirable for a potential application as photosensitive materials in the manufacture of semiconductor-polymer solar cells. PACS 61.46.Hk, Nanocrystals; 61.46.Km, Structure of nanowires and nanorods; 81.07.Gf, Nanowires; 81.15.Gh, Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.) PMID:21899743

  17. The microstructure of erbium-ytterbium co-doped oxyfluoride glass-ceramic optical fibers

    NASA Astrophysics Data System (ADS)

    Augustyn, Elżbieta; Żelechower, Michał; Stróż, Danuta; Chrapoński, Jacek

    2012-04-01

    Oxyfluoride transparent glass-ceramics combine some features of glasses (easier shaping or lower than single crystals cost of fabrication) and some advantages of rare-earth doped single crystals (narrow absorption/emission lines and longer lifetimes of luminescent levels). Since the material seems to be promising candidate for efficient fiber amplifiers, the manufacturing as well as structural and optical examination of the oxyfluoride glass-ceramic fibers doped with rare-earth ions seems to be a serious challenge. In the first stage oxyfluoride glasses of the following compositions 48SiO2-11Al2O3-7Na2CO3-10CaO-10PbO-11PbF2-3ErF3 and 48SiO2-11Al2O3-7Na2CO3-10CaO-10PbO-10PbF2-3YbF3-1ErF3 (in molar%) were fabricated from high purity commercial chemicals (Sigma-Aldrich). The fabricated glass preforms were drawn into glass fibers using the mini-tower. Finally, the transparent Er3+ doped and Er3+/Yb3+ co-doped oxyfluoride glass-ceramic fibers were obtained by controlled heat treatment of glass fibers. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. X-ray diffraction examination (XRD) at each stage of the glass-ceramic fibers fabrication confirmed the undesirable crystallization of preforms and glass fibers has been avoided. The fibers shown their mixed amorphous-crystalline microstructure with nano-crystals of size even below 10 nm distributed in the glassy host. The crystal structure of the grown nano-crystals has been determined by XRD and confirmed by electron diffraction (SAED). Results obtained by both techniques seem to be compatible: Er3FO10Si3 (monoclinic; ICSD 92512), Pb5Al3F19 (triclinic; ICSD 91325) and Er4F2O11Si3 (triclinic; ICSD 51510) against to initially expected PbF2 crystals.

  18. Modeling of Yb3+/Er3+-codoped microring resonators

    NASA Astrophysics Data System (ADS)

    Vallés, Juan A.; Gălătuş, Ramona

    2015-03-01

    The performance of a highly Yb3+/Er3+-codoped phosphate glass add-drop microring resonator is numerically analyzed. The model assumes resonant behaviour of both pump and signal powers and the dependences of pump intensity build-up inside the microring resonator and of the signal transfer functions to the device through and drop ports are evaluated. Detailed equations for the evolution of the rare-earth ions levels population densities and the propagation of the optical powers inside the microring resonator are included in the model. Moreover, due to the high dopant concentrations considered, the microscopic statistical formalism based on the statistical average of the excitation probability of the Er3+ ion in a microscopic level has been used to describe energy-transfer inter-atomic mechanisms. Realistic parameters and working conditions are used for the calculations. Requirements to achieve amplification and laser oscillation within these devices are obtainable as a function of rare earth ions concentration and coupling losses.

  19. Yb3+/Ho3+-codoped antimony-silicate optical fiber

    NASA Astrophysics Data System (ADS)

    Żmojda, Jacek; Dorosz, Dominik; Kochanowicz, Marcin; Miluski, Piotr; Dorosz, Jan

    2012-05-01

    The emission properties of Yb3+/Ho3+-codoped antimony-silicate optical fiber has been investigated. Luminescence at 2.1 μm corresponding to 5I7--> 5I8 transition in holmium was obtained by energy transfer between Yb3+ and Ho3+ ions. According to the Dexter-Miyakawa model, the parameters of energy migration CDD of the 2F5/2 (Yb3+) <--> 2F5/2 (Yb3+) transition and direct energy transfer CDA of the 2F5/2 (Yb3+) --> 5I6 (Ho3+) transition was calculated. The optimization of the activator content and the concentration ratio were conducted with the purpose of maximizing the efficiency of energy transfer. It made possible to select best-suited glass which was used to manufacture double-clad optical fiber. Strong and narrow bands of spontaneous emission which formed as a result of energy transfer between ytterbium and holmium ions were observed in the fiber under exciting with radiation at 978 nm wavelength.

  20. Yb3+/Ho3+-codoped antimony-silicate optical fiber

    NASA Astrophysics Data System (ADS)

    Żmojda, Jacek; Dorosz, Dominik; Kochanowicz, Marcin; Miluski, Piotr; Dorosz, Jan

    The emission properties of Yb3+/Ho3+-codoped antimony-silicate optical fiber has been investigated. Luminescence at 2.1 μm corresponding to 5I7--> 5I8 transition in holmium was obtained by energy transfer between Yb3+ and Ho3+ ions. According to the Dexter-Miyakawa model, the parameters of energy migration CDD of the 2F5/2 (Yb3+) <--> 2F5/2 (Yb3+) transition and direct energy transfer CDA of the 2F5/2 (Yb3+) --> 5I6 (Ho3+) transition was calculated. The optimization of the activator content and the concentration ratio were conducted with the purpose of maximizing the efficiency of energy transfer. It made possible to select best-suited glass which was used to manufacture double-clad optical fiber. Strong and narrow bands of spontaneous emission which formed as a result of energy transfer between ytterbium and holmium ions were observed in the fiber under exciting with radiation at 978 nm wavelength.

  1. Nd3+, Y3+-codoped SrF2 laser ceramics

    NASA Astrophysics Data System (ADS)

    Li, Weiwei; Mei, Bingchu; Song, Jinghong

    2015-09-01

    0.15 at.% Nd3+, 5 at.% Y3+-codoped SrF2 laser ceramic based on single crystal was prepared by extensive plastic deformation. Microstructure, optical and laser properties of the Nd3+, Y3+:SrF2 ceramic were investigated. The lasing of Nd3+, Y3+-codoped SrF2 ceramics with diode pumping have been observed and true CW laser operation around 1057 nm and 1050 nm was obtained with a slope efficiency of 31.9%. In particular, the fracture toughness of the ceramic is 0.98 MPa m1/2, which is approximately two times higher than that of single crystal.

  2. Suppression of boron-oxygen defects in Czochralski silicon by carbon co-doping

    SciTech Connect

    Wu, Yichao; Yu, Xuegong He, Hang; Chen, Peng; Yang, Deren

    2015-03-09

    We have investigated the influence of carbon co-doping on the formation of boron-oxygen defects in Czochralski silicon. It is found that carbon can effectively suppress the formation of boron-oxygen defects. Based on our experiments and first-principle theoretical calculations, it is believed that this effect is attributed to the formation of more energetically favorable carbon-oxygen complexes. Moreover, the diffusion of oxygen dimers in carbon co-doped silicon also becomes more difficult. All these phenomena should be associated with the tensile stress field induced by carbon doping in silicon.

  3. Room and low temperature luminescence properties of CaSO4: Dy , Tm codoped with Li

    NASA Astrophysics Data System (ADS)

    Can, N.; Karalı, T.; Wang, Y.; Townsend, P. D.; Prokic, M.; Canimoglu, A.

    2009-08-01

    Rare earths, especially Dy or Tm doped CaSO4 phosphors are actively studied. They have high sensitivity, a large dynamic range, thermal stability and ease of preparation. Nevertheless, they can be enhanced by inclusion of lithium and this study reports some effects of lithium co-dopant on the TL and radioluminescence (RL) emissions of two TL phosphors. Addition of Li as a co-dopant ion was made either during chemical preparation of the phosphors, or as a binder component mixed with the basic phosphors matrix during the process of pressing and sintering the TLD pellets.

  4. First-principles study of Be doped CuAlS2 for p-type transparent conductive materials

    NASA Astrophysics Data System (ADS)

    Huang, Dan; Zhao, Yu-Jun; Tian, Ren-Yu; Chen, Di-Hu; Nie, Jian-Jun; Cai, Xin-Hua; Yao, Chun-Mei

    2011-06-01

    CuAlS2 has attracted much attention recently as a p-type transparent conductive material. In this paper, we investigate the site preference of substitutional Be in CuAlS2 and the transition level of BeAl using the first-principles calculation. We find that Be would be doped effectively at Al sites in CuAlS2 as a good p-type dopant. In addition, we speculate that Be-Mg or Be-Zn codoped CuAlS2 could have a mobility enhancement and thus a good p-type conductivity due to low lattice distortion.

  5. Influence of Se/N Codoping on the Structural, Optical, Electronic and Photocatalytic Properties of TiO₂.

    PubMed

    Gurkan, Yelda Y; Kasapbasi, Esra; Turkten, Nazli; Cinar, Zekiye

    2017-03-07

    Se(4+) and N(3-) ions were used as codopants to enhance the photocatalytic activity of TiO₂ under sunlight irradiation. The Se/N codoped photocatalysts were prepared through a simple wet-impregnation method followed by heat treatment using SeCl₄ and urea as the dopant sources. The prepared photocatalysts were well characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-diffuse reflectance spectroscopy (UV-DRS), scanning electron microscopy (SEM) and Raman spectroscopy. The codoped samples showed photoabsorption in the visible light range from 430 nm extending up to 580 nm. The photocatalytic activity of the Se/N codoped photocatalysts was evaluated by degradation of 4-nitrophenol (4-NP). The degradation of 4-NP was highly increased for the Se/N codoped samples compared to the undoped and single doped samples under both UV-A and sunlight irradiation. Aiming to determine the electronic structure and dopant locations, quantum chemical modeling of the undoped and Se/N codoped anatase clusters was performed using Density Functional Theory (DFT) calculations with the hybrid functional (B3LYP) and double-zeta (LanL2DZ) basis set. The results revealed that Se/N codoping of TiO₂ reduces the band gap due to mixing of N2p with O2p orbitals in the valence band and also introduces additional electronic states originating from Se3p orbitals in the band gap.

  6. Characterization of SDC-Al2O3 solid electrolyte

    NASA Astrophysics Data System (ADS)

    Ramesh, S.; Raju, K. C. James; Reddy, C. Vishnuvardhan

    2012-06-01

    SDC20-Al2O3 materials were synthesized through the sol-gel method. Dense SDC20-Al2O3 ceramics were obtained through sintering the pellets at 1300°C. SDC20-Al2O3 materials were characterized by XRD, SEM and impedance spectroscopy. XRD measurements indicate that synthesized materials crystallized in cubic structure. Average crystallite size of the samples was in the range 11-12 nm. The relative density of SDC20-Al2O3 samples was over 95% of the theoretical density. Addition of Al2O3 promotes densification. Surface morphology was analyzed using SEM. The two-probe a.c. impedance spectroscopy was used to study the total ionic conductivity of doped and co-doped ceria in the temperature range 350-700°C. The SDC20-Al2O3 composition showed improved total ionic conductivity and minimum activation energy.

  7. Half-metallic ferromagnetism in Cu doped ZnO?

    NASA Astrophysics Data System (ADS)

    Ye, Lin-Hui; Freeman, A. J.

    2004-03-01

    It has been shown that diluted magnetic semiconductors could form by hole doping into ZnO(T.Dietl, et al.,) Science 287, 1019(2000). In this work doping by non-magnetic Cu into ZnO has been simulated by the accurate ab initio FLAPW method(E.Wimmer, H.Krakauer, M.Weinert, and A.J.Freeman, Phys. Rev. B 24), 864(1981), and references therein, using GGA to represent the exchange-correlation potential. For a 1/8 doping concentration which is simulated by a 16 atom supercell, we find magnetic moments of 0.58 μB on Cu, and 0.08 μB or 0.05 μB on neighboring O. Decreasing the doping concentration to 1/16 causes the magnetic moments change by 0.005 μ_B. In the ferromagnetic (FM) phase, the system is half-metallic. The hole states on the Fermi surface are mainly determined by Cu 3d and O 2p hybridization. The calculated exchange splitting is 0.45 eV which opens a half-metallic gap of 0.30 eV. For comparison with the FM phase, several anti-ferromagnetic (AFM) phases are being investigated using the doubled supercell. To design possible diluted magnetic semiconductors, simulations of doping by other non-magnetic ions into ZnO are also in progress.

  8. Band edge modulation and interband optical transition in AlN:Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} nanotubes

    NASA Astrophysics Data System (ADS)

    Huang, Pu; Shi, Jun-jie; Zhang, Min; Jiang, Xin-he; Zhong, Hong-xia; Ding, Yi-min; Lu, Jing; Wang, Xihua

    2014-04-01

    AlN nanotubes (NTs) have many novel characteristics and great potential applications in electronic and optoelectronic nanodevices. However, little is known about the influence of Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} co-doping effects on their optical properties. Here, we focus on investigating the electronic structures, clarify the interband optical transition mechanism and give a clear atomic picture for the important electron/hole localization centre in AlN:Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} NTs using the GGA-1/2 method. We find that the Mg_{{\\rm{Al}}} doping efficiency can be improved effectively due to O_{{\\rm{N}}} doping in AlN NTs. The Mg_{{\\rm{Al}}} and O_{{\\rm{N}}} form Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} defect complex easily along the AlN NT axis (C-axis). The Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} defect complex can result in a remarkable charge transfer around it and modify the valence band maximum and conduction band minimum significantly. Meanwhile, the Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} defect complex also forms the important exciton localization centre and effectively enhances the interband radiative recombination rate. Moreover, the light emission/absorption sensitively depends on its polarization. The parallel polarized light ({\\mathbf{E}}\\shortparallel {\\rm{C}}) is much stronger than the perpendicular one ({\\mathbf{E}}\\bot {\\rm{C}}). The Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} co-doping thus paves a new way for improving the performance of electronic and optoelectronic nanodevices based on AlN NTs.

  9. Development of Solution-Processed ZnO Nanorod Arrays Based Photodetectors and the Improvement of UV Photoresponse via AZO Seed Layers.

    PubMed

    Zhang, Yuzhu; Xu, Jianping; Shi, Shaobo; Gao, Yanyan; Wang, Chang; Zhang, Xiaosong; Yin, Shougen; Li, Lan

    2016-08-31

    Designing a rational structure and developing an efficient fabrication technique for bottom-up devices offer a promising opportunity for achieving high-performance devices. In this work, we studied how Al-doped ZnO (AZO) seed layer films influence the morphology and optical and electrical properties for ZnO aligned nanorod arrays (NRs) and then the performance of ZnO NRs based ultraviolet photodetectors (UV PDs) with Au/ZnO NRs Schottky junctions and p-CuSCN/n-ZnO NRs heterojunctions. The PD with AZO thin film with 0.5 at. % Al doping (named as AZO (0.5%)) exhibited more excellent photoresponse properties than that with pristine ZnO and AZO (1%) thin films. This phenomenon can be ascribed to the good light transmission of the AZO layer, increased density of the NRs, and improved crystallinity of ZnO NRs. The PDs based on CuSCN/ZnO NRs heterojunctions showed good rectification characteristics in the dark and self-powered UV photoresponse properties with excellent stability and reproducibility under low-intensity illumination conditions. A large responsivity located at 365 nm of 22.5 mA/W was achieved for the PD with AZO (0.5%) thin film without applied bias. The internal electric field originated from p-CuSCN/n-ZnO NRs heterojunctions can separate photogenerated carriers in ZnO NRs and drift toward the corresponding electrode.

  10. Nanostructured Al-ZnO/CdSe/Cu2O ETA solar cells on Al-ZnO film/quartz glass templates

    PubMed Central

    2011-01-01

    The quartz/Al-ZnO film/nanostructured Al-ZnO/CdSe/Cu2O extremely thin absorber solar cell has been successfully realized. The Al-doped ZnO one-dimensional nanostructures on quartz templates covered by a sputtering Al-doped ZnO film was used as the n-type electrode. A 19- to 35-nm-thin layer of CdSe absorber was deposited by radio frequency magnetron sputtering, coating the ZnO nanostructures. The voids between the Al-ZnO/CdSe nanostructures were filled with p-type Cu2O, and therefore, the entire assembly formed a p-i-n junction. The cell shows the energy conversion efficiency as high as 3.16%, which is an interesting option for developing new solar cell devices. PACS: 88.40.jp; 73.40.Lq; 73.50.Pz. PMID:22136081

  11. Nanostructured Al-ZnO/CdSe/Cu2O ETA solar cells on Al-ZnO film/quartz glass templates

    NASA Astrophysics Data System (ADS)

    Wang, Xianghu; Li, Rongbin; Fan, Donghua

    2011-12-01

    The quartz/Al-ZnO film/nanostructured Al-ZnO/CdSe/Cu2O extremely thin absorber solar cell has been successfully realized. The Al-doped ZnO one-dimensional nanostructures on quartz templates covered by a sputtering Al-doped ZnO film was used as the n-type electrode. A 19- to 35-nm-thin layer of CdSe absorber was deposited by radio frequency magnetron sputtering, coating the ZnO nanostructures. The voids between the Al-ZnO/CdSe nanostructures were filled with p-type Cu2O, and therefore, the entire assembly formed a p-i-n junction. The cell shows the energy conversion efficiency as high as 3.16%, which is an interesting option for developing new solar cell devices. PACS: 88.40.jp; 73.40.Lq; 73.50.Pz.

  12. Morphology engineering of ZnO nanostructures for high performance supercapacitors: Enhanced electrochemistry of ZnO nanocones compared to ZnO nanowires.

    PubMed

    He, Xiaoli; Yoo, Joung; Lee, Min; Bae, Joonho

    2017-04-06

    In this work, the morphology of ZnO nanostructures is engineered to demonstrate enhanced supercapacitor characteristics of ZnO nanocones (NCs) compared to ZnO nanowires (NWs). ZnO NCs are obtained by chemically etching ZnO NWs. Electrochemical characteristics of ZnO NCs and NWs are extensively investigated to demonstrate morphology dependent capacitive performance of one dimensional ZnO nanostructures. Cyclic voltammetry measurements on these two kind of electrodes in three electrode cell confirms that ZnO NCs exhibit high specific capacitance of 378.5 F g-1 at a scan rate of 20 mV s-1, which is almost twice that of ZnO NWs (191.5 F g-1). The charge-discharge and EIS measurements also clearly results in enhanced capacitive performance of NCs as evidenced by higher specific capacitances and lower internal resistance. Asymmetric spuercapacitors are fabricated using activated carbon (AC) as negative electrode and ZnO NWs and NCs as positive electrodes. The ZnO NC//AC can deliver a maximum specific capacitance of 126 F g-1 at a current density of 1.33 A g-1 with an energy density of 25.2 W h kg-1 at the power density of 896.44 W kg-1. In contrast, ZnO NW//AC displays 63% of capacitance obtained from ZnO NC//AC supercapacitor. The enhanced performances of NCs are attributed to higher surface area of ZnO nanostructures after the morphology is altered from NWs to NCs.

  13. Carrier transport in flexible organic bistable devices of ZnO nanoparticles embedded in an insulating poly(methyl methacrylate) polymer layer

    NASA Astrophysics Data System (ADS)

    Son, Dong-Ick; Park, Dong-Hee; Choi, Won Kook; Cho, Sung-Hwan; Kim, Won-Tae; Kim, Tae Whan

    2009-05-01

    The bistable effects of ZnO nanoparticles embedded in an insulating poly(methyl methacrylate) (PMMA) polymer single layer by using flexible polyethylene terephthalate (PET) substrates were investigated. Transmission electron microscopy (TEM) images revealed that ZnO nanoparticles were formed inside the PMMA polymer layer. Current-voltage (I-V) measurement on the Al/ZnO nanoparticles embedded in an insulating PMMA polymer layer/ITO/PET structures at 300 K showed a nonvolatile electrical bistability behavior with a flat-band voltage shift due to the existence of the ZnO nanoparticles, indicative of trapping, storing, and emission of charges in the electronic states of the ZnO nanoparticles. The carrier transport mechanism of the bistable behavior for the fabricated organic bistable device (OBD) structures is described on the basis of the I-V results by analyzing the effect of space charge.

  14. Enhance the light-harvesting capability of the ITO-free inverted small molecule solar cell by ZnO nanorods.

    PubMed

    Lin, Ming-Yi; Wu, Shang-Hsuan; Hsiao, Li-Jen; Budiawan, Widhya; Boopathi, Karunakara Moorthy; Tu, Wei-Chen; Chang, Yia-Chung; Chu, Chih-Wei

    2016-08-08

    The ITO-free inverted SMPV1:PC71BM solar cells with an Al doped ZnO (AZO) transparent electrodes are fabricated. The AZO thin film prepared by pulsed laser deposition (PLD) technique exhibits high transmission (>85%) and low sheet resistance (~30 Ω/sq) and the power conversion efficiency (PCE) of devices based on AZO electrode can reach around 4%. To further enhance the light harvesting of the absorption layer of solar cells, ZnO nanorods interlayer is grown on the AZO layer before the deposition the active layer. The absorption spectrums of devices under various conditions are also simulated by RCWA method to identify the optical saturation length of the ZnO nanorods. The PCE of ITO-free inverted small molecule solar cell improved with ZnO nanorods can reach 6.6%.

  15. Optimizing performance of Cu2O/ZnO nanorods heterojunction based self-powered photodetector with ZnO seed layer

    NASA Astrophysics Data System (ADS)

    Wang, Chang; Xu, Jianping; Shi, Shaobo; Zhang, Yuzhu; Gao, Yanyan; Liu, Zeming; Zhang, Xuguang; Li, Lan

    2017-04-01

    The Cu2O films were electrodeposited on ZnO nanorod arrays (NRs) and the Cu2O/ZnO NRs heterojunctions were formed. The optical-electronic response of the heterojunctions was investigated. The diameter size and crystal quality of ZnO NRs were modified by the seed layer. ZnO NRs with good crystal quality were obtained on the 0.5% Al doped ZnO seed layer film (named as AZO (0.5%)). The devices based on the Cu2O/ZnO NRs heterojunction exhibit excellent stability and reproducibility of the self-powered photoresponse properties. The device with AZO (0.5%) seed layer demonstrates the high photoresponsivity of 60-70 mA/W in the violet and blue light with a fast response speed at zero applied bias.

  16. Boron, bismuth co-doping of gallium arsenide and other compounds for photonic and heterojunction bipolar transistor devices

    DOEpatents

    Mascarenhas, Angelo

    2015-07-07

    Isoelectronic co-doping of semiconductor compounds and alloys with acceptors and deep donors is sued to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. For example, Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, B and Bi, to customize solar cells, and other semiconductor devices. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  17. Low-Temperature Heteroepitaxial Growth of Single-Domain V-Doped ZnO Films on c-Face Sapphire

    NASA Astrophysics Data System (ADS)

    Chiba, Hiroshi; Mori, Tatsuya; Kawashima, Tomoyuki; Washio, Katsuyoshi

    2015-05-01

    High-quality single-domain (ZnO[11-20]//Al2O3[10-10]) ZnO heteroepitaxial growth on c-face sapphire [Al2O3(0001)] substrate at low temperature was investigated by vanadium (V) doping at growth temperatures between 150°C and 450°C using radiofrequency (RF) magnetron sputtering. In low-temperature growth at 150°C and 200°C, 30° twisted domains (ZnO[10-10]//Al2O3[10-10]) were eliminated and good in-plane crystal orientation was obtained for V doping of about 2 at.% to 3 at.%. Single domains were grown from the early stage. From the changes of surface morphology and growth rate, it was considered that migration during the growth was enhanced due to the increase of the diffusion energy of adatoms, while random nucleation was suppressed.

  18. Thermal conductivity of self-assembled nano-structured ZnO bulk ceramics

    SciTech Connect

    Zhao, Yu; Yan, Yongke; Kumar, Ashok; Wang, Hsin; Porter, Wallace D

    2012-01-01

    In this study, we describe the changes in thermal conductivity behavior of ZnO-Al micro- and nano-two-phase self-assembled composites with varying grain sizes. The reduction in thermal conductivity values of micro-composites was limited to {approx}15% for ZnO-4% Al. However, nano-composites exhibited large reduction, by a factor of about three, due to uniform distribution of nano-precipitates (ZnAl2O4) and large grain boundary area. Interestingly, the micro-composites revealed continuous decrease in thermal conductivity with increase in Al substitution while the nano-composites exhibited the lowest magnitudes for 2% Al concentration. Raman spectra indicated that phonon confinement in ZnO-Al nano-composites causes drastic decrease in the value of thermal conductivity.

  19. Sustainable synthesis of metals-doped ZnO nanoparticles from zinc-bearing dust for photodegradation of phenol.

    PubMed

    Wu, Zhao-Jin; Huang, Wei; Cui, Ke-Ke; Gao, Zhi-Fang; Wang, Ping

    2014-08-15

    A novel strategy of waste-cleaning-waste is proposed in the present work. A metals-doped ZnO (M-ZnO, M = Fe, Mg, Ca and Al) nanomaterial has been prepared from a metallurgical zinc-containing solid waste "fabric filter dust" by combining sulfolysis and co-precipitation processes, and is found to be a favorable photocatalyst for photodegradation of organic substances in wastewater under visible light irradiation. All the zinc and dopants (Fe, Mg, Ca and Al) for preparing M-ZnO are recovered from the fabric filter dust, without any addition of chemical as elemental source. The dust-derived M-ZnO samples deliver single phase indexed as the hexagonal ZnO crystal, with controllable dopants species. The photocatalytic activity of the dust-derived M-ZnO samples is characterized by photodegradation of phenol aqueous solution under visible light irradiation, giving more prominent photocatalytic behaviors than undoped ZnO. Such enhancements may be attributed to incorporation of the dust-derived metal elements (Fe, Mg, Ca and Al) into ZnO structure, which lead to the modification of band gap and refinement of grain size. The results show a feasibility to utilize the industrial waste as a resource of photodegradating organic substances in wastewater treatments.

  20. Improving NaI:TI with non-luminescent cation co-doping (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yang, Kan; Menge, Peter R.

    2016-09-01

    Thallium activated sodium iodide (NaI:Tl) is one of the most widely used gamma-ray scintillators. Commercially available NaI:Tl scintillators are typically characterized by a gamma-ray energy resolution of 6.5% at 662 keV and a scintillation decay time constant of 230 ns. Energy resolution, non-proportionality and scintillation decay time are improved when the crystal is co-doped with alkaline earth metals. The energy resolution of NaI:Tl+ is improved to 5.3% and the decay time is simultaneously reduced to 170 ns with Sr or Ca co-doping. The improvement in energy resolution, non-proportionality and decay time is likely due to the suppression of slow scintillation processes in NaI:Tl. We also demonstrated that Li+ can be substantially incorporated into the matrix of NaI under an optimized crystal growth process. The incorporation of Li+ introduces efficient neutron detection capability into an already successful gamma scintillator. Single crystals of Li co-doped NaI show similar gamma performance as standard NaI:Tl. Exceptional gamma-neutron pulse shape discrimination (PSD) has been demonstrated in all Li co-doped NaI crystals with up to 8% Li concentration. PSD Figure-of-Merits are up to 4.4 depending on Li content.