bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diamond Based Ion-Sensitive Field Effect Transistors for Cellular Biosensing
Authors: Bennett Andrew , Gaudin Olivier , Williams Oliver A. , Foord John S. , Jackman Richard B. 
Published: April 2011

ABSTRACTThe use of a chemically inert and essentially biocompatible material for cellular biosensing is an attractive idea. In this context we have studied the operation of diamond-based ion-sensitive field effect transistors (ISFETs) within solutions of varying pH, and alkali-halide concentrations. In particular, we report the use of an inexpensive diamond substrate material, often referred to as ‘black’ diamond. pH sensitivity was observed when devices based on hydrogen-terminated p-type surfaces where employed, provide some surface oxidation was performed prior to their use. Variation in the threshold voltage for ISFET operation of the order of 20mV/pH unit was determined. In terms of operation in potassium iodide solution, we have shown that the device is shows selective sensitivity to the iodide species, despite the equi-molar presence of both K+ and I- species. The origin of this selectivity is discussed.
Persistent Photoinduced Changes in Charge States of Donors and Acceptors in Hydrothermally Grown ZnO
Authors: Giles Nancy C. , Jiang Yongquan , Yang Xiaocheng , Evans S. M. , Halliburton L. E. 
Published: April 2011

ABSTRACTBulk ZnO grown by the hydrothermal technique was investigated using electron paramagnetic resonance (EPR), photoluminescence (PL), and infrared absorption (FTIR) techniques. Isolated subsitutional lithium is the dominant acceptor and could be detected using EPR or PL. A large concentration of neutral Li+-OH− centers were observed using FTIR data. EPR spectra assigned to Mn, Co, Ni, Fe, and Group III (Al, Ga) donors were also observed. Photoinduced changes in the charge states of the different deep and shallow centers were produced using 325 nm light, and the stability of these changes were monitored with EPR during pulsed thermal anneals. The charge-state changes for some defects were persistent and remained up to 300 K. These impurities, when present in device structures, may act as stable charge trapping sites.
Transition Metal-Doped ZnO: A Comparison of Optical, Magnetic, and Structural Behavior of Bulk and Thin Films
Authors: Fenwick William E. , Kane Matthew H. , Fang Zaili , Zaidi Tahir , Li Nola , Rengarajan Varatharajan , Nause Jeff , Ferguson Ian T. 
Published: April 2011

ABSTRACTTransition metal-doped ZnO bulk crystals and thin films have been investigated to determine the effects of transition metal incorporation on optical, magnetic, and structural properties of ZnO. A modified melt growth technique was used to grow bulk Zn1-xMnxO, Zn1-xCoxO, and Zn1-xFexO. Optical transmission measurements show an apparent shift in absorption edge with increasing transition metal incorporation. Raman spectroscopy also shows increasing lattice disorder with increasing transition metal concentration. ZnO thin films doped with Ni, Co, and Gd were grown by metalorganic chemical vapor deposition (MOCVD). While the Co-doped thin films showed antiferromagnetic behavior, magnetic hysteresis was observed in the Ni-doped and Gd-doped thin films. Structural quality was verified with X-ray diffraction (XRD), and optical properties were investigated using room temperature photoluminescence (PL) and optical transmission measurements. Properties of ZnO:TM bulk crystals and thin films are compared and used to discuss possible origins of ferromagnetism in these materials.
Growth and Characterization of Homoepitaxial ZnO Thin Films Grown by CVD
Authors: Neumann Christian , Sann Joachim , Lautenschläger Stefan , Bertram Frank , Christen Jürgen , Bläsing Jürgen , Krost Alois , Meyer Bruno K. 
Published: April 2011

ABSTRACTZnO as a direct wide-band-semiconductor with its band gap of 3.3 eV at room temperature is a promising optoelectronic material. The main obstacle in the ZnO system is its lack of achieving reproducible p-type conductivity. The main reasons for this are the high residual intrinsic and extrinsic defect concentrations which are still not completely understood.Homoepitaxial growth of ZnO and thus minimization of intrinsic defects due to lattice mismatch and incorporation of residual substrate species could be a solution to overcome these problems. Despite the availability of ZnO bulk single crystals reports regarding ZnO homoepitaxy are still quite rare. In this paper we report on a successful homoepitaxial growth of ZnO thin films by chemical vapor deposition (CVD).Atomic force microscopy shows that two-dimensional epitaxial growth was achieved without any additional buffer layer. With a rocking curve full width at half maximum (FWHM) of 17 arcsec the deposited films show a superior crystalline quality compared to its substrate. The optical quality of the epitaxial films has been characterized laterally by cathodoluminescence and spectrally by photoluminescence. Excitonic emissions at 4K are as narrow as 110 μeV. A dependence of the appearance of excitonic emissions from the growth polarity can be shown which is attributed to different incorporation rates of extrinsic defects.
Orders of Magnitude Reduction in Threading Dislocations in ZnO Grown on Facet-Controlled GaN
Authors: Chua Soo Jin , Zhou Hai Long , PAN Hui , Osipowicz Thomas 
Published: April 2011

ABSTRACTZnO is grown by chemical vapour deposition on {1 1 -2 2} GaN planes formed by epitaxial layer overgrowth. Window stripes in a SiO2 mask are oriented in the <1 -1 0 0> direction of the GaN film. Triangular GaN ridge are formed during ELO growth by metal organic chemical vapour deposition. A flat (0 0 0 1) ZnO plane is grown on each triangular cross-section ridge and it is found that the ZnO film has dislocation density reduced by two orders of magnitude compared to that of the GaN substrate.
Cathodoluminescence Study of Indented ZnO Crystals
Authors: Jiménez Juan , Avella Manuel , Jiménez Juan , Rodríguez Tomás , Callahan Michael , Grant E. , Rakes K. , Bliss David , Wang Buguo 
Published: April 2011

ABSTRACTVickers indentations of ZnO crystals grown by te hydrothermal method wer studied by cathodoluminescence. The plastic deformation induced defects, which have influence on the luminescence spectrum. The main changes in the luminescence response concern the generation of non radiative recombination centers, but also a band close to the first order phonon replica of the free exciton is observed to appear in the regions deformed by the indentation. Besides, deep levels are also generated. The result of this is a relative increase of the defect related bands respect to the dominant bound exciton emission.
Electrical Characterization of Isotype n-ZnO/n-GaN Heterostructures
Authors: Alivov Yahya , Bo Xiao , Akarca-Biyikli Sena , Qian Fan , Johnstone Daniel , Lopatiuk-Tirpak Olena , Chernyak Leonid , Litton Cole , Morkoç Hadis 
Published: April 2011

ABSTRACTElectrical properties of n-ZnO/n-GaN isotype heterostructures obtained by rf-sputtering of ZnO films on GaN layers grown by metal-organic vapour phase epitaxy are discussed. Current-voltage (I-V) characteristics of the n-ZnO/n-GaN diodes revealed highly rectifying behavior with forward and reverse currents ∼1.43×10-2 A/cm2 and ∼2.4×10-4 A/cm2, respectively, at ±5 V. From the Arrhenius plot built using temperature dependent current-voltage characteristics (I-V-T) an activation energy 0.125 eV was derived for the reverse bias leakage current path, and 0.62 eV for the band offset from forward bias measurements. From electron-beam induced current measurements the minority carrier diffusion length in ZnO was estimated in the range 0.125-0.175 mm, depending on excitation conditions. The temperature dependent EBIC measurements yielded an activation energy of 0.462 ± 0.073 V.
Cathodoluminescence Study of Hydrothermal Zn1-xMgxO Alloy Crystals
Authors: Mass Julio , Avella Manuel , Jiménez Juan , Callahan Michael , Grant E. , Rakes K. , Bliss David , Wang Buguo 
Published: April 2011

ABSTRACTHydrothermal ZnMgO crystals were studied by cathodoluminescence. The high energy shift of the excitonic luminescence demonstrates the Mg incorporation in the ZnO lattice in at a few percent. The spectral parameters of the luminescence emission show a marked dependence of the incorporation of defects and Mg on the growth facet. This growth sector selectivity shows similar trends to those observed in hydrothermal ZnO crystals. The in depth distribution of Mg was studied varying the acceleration voltage of the excitation e-beam, showing a slight accumulation of Mg close to the surface.
Effect of Cryogenic Temperature Deposition of Various Metal Contacts to Bulk, Single-Crystal n-type ZnO
Authors: Wright Jon , Stafford L. , Gila B. P. , Norton D. P. , Pearton S. J. , Wang Hung-Ta , Ren F. 
Published: April 2011

ABSTRACTThe development of reliable and thermally stable Ohmic and Schottky contacts to ZnO is one of the critical issues related to the fabrication of ZnO-based UV light emitters/detectors and field effect transistors. To date, a number of different metallization schemes and surface cleaning procedures prior to metal deposition have been examined for rectifying contacts on n-ZnO. While these reports have shown that low reactive metals such as Au, Ag and Pd form rectifying contacts with Schottky barrier heights in the 0.6-0.8 eV range, the thermal stability of these contacts is usually extremely poor, with degradation occurring even at 60°C for Au/n-ZnO. One approach to achieving increased barrier heights that has proven successful for GaAs, InP, InGaAs and other compound semiconductors is the use of cryogenic deposition temperatures. In this context, we report in this work on the effect of cryogenic temperature metal deposition on the contact properties of Pd, Pt, Ti, and Ni on single-crystal n-type ZnO. Deposition at both room and low temperature produced contacts with Ohmic characteristics for Ti and Ni metallizations. In comparison, both Pd and Pt contacts showed rectifying characteristics after deposition. All rectifying contacts exhibited barrier heights around 1-2 eV and idealities between 1 and 2. Low temperature deposition gave higher resistances in comparison to room temperature deposition for all cases. Larger contacts also corresponded to an increase in resistance. Changes in contact behavior were measured on Pd to anneal temperatures of ∼300°C, showing an increase in barrier height along with a decrease in ideality with increasing temperature. This difference with annealing temperature is in sharp contrast to previous results for Au contacts to ZnO. There were no differences in near-surface stoichiometry for the different deposition temperatures; however low temperature contacts demonstrated some cracking in Pt and Pd, probably due to surface stress.
Microstructure and Electrical Property Correlations in Ga:ZnO Transparent Conducting Thin Films
Authors: Bhosle Vikram , Narayan Jagdish 
Published: April 2011

ABSTRACTWe report the correlations between processing, microstructure and electrical properties of Ga doped ZnO films. Films with varying grain size were grown on amorphous glass by changing the substrate and pulsed laser deposition variables. The results corresponding to these films were compared with those from epitaxial single crystal films grown on (0001) sapphire. Microstructural characteristics were analyzed in detail by using X-ray diffraction and transmission electron microscopy. Electrical properties were evaluated by resistivity measurements in the temperature range of 15-300K and Hall measurements at room temperature. It was observed that the grain boundaries and orientation of grains (texture characteristics) affected the carrier concentration and the mobility considerably in nanocrystalline films deposited on glass substrates. This effect is envisaged to occur as a result of trapping of electrons and build up of a potential barrier across the grain boundaries. However, the resistivity in nanocrystalline films could be decreased significantly by carefully controlling the deposition conditions. For a film deposited on glass at 2000C and 1 mtorr of oxygen partial pressure, we attained a minimum resistivity value of 1.8 × 10-4Ω-cm. As a comparison, the epitaxial films on sapphire substrates showed a resistivity of 1.4 × 10-4 Ω-cm, deposited at 4000C and pressure of 2.4 × 10-2 torr. Role of grain boundaries and defects in controlling the carrier generation and transport is considered in detail and possible mechanisms limiting the electrical conductivity in films with different microstructures are identified.
Opto-Electronic Properties and Stability of Artificial Zinc Oxide Molecules
Authors: Pozhar Liudmila A , Brown Gail J. 
Published: April 2011

ABSTRACTThe Hartree-Fock (HF), restricted open shell HF (ROHF), and multiconfiguration self-consistent field (CI/CASSCF/MCSCF) approximations are used to study computationally the electronic properties of zinc oxide artificial molecules whose structure and composition have been derived from those of the symmetry elements of the wurtzite bulk lattice of zinc oxide. Such molecules may provide realistic models for small ZnO quantum dots (QDs) synthesized in “vacuum” or quantum confinement (such as that of well-defined nanopore arrays of silica and alumina membranes) using variety of methods in particular, supercritical fluid deposition. The computational direct optical transition energy (OTE) of the confined molecule appears to be several times smaller than that of the corresponding vacuum cluster. The charge and spin density distributions of these molecules (CDDs and SDDs, respectively) differ significantly, revealing dramatic effects of quantum confinement on electronic properties of Zn-O clusters. The obtained results suggest that manipulations with the electronic properties of the confined clusters by sophisticated design of their quantum confinement may provide means for synthesis of Zn-O – based electronic materials that combine a wide, tunable band gap with large, tunable exciton binding energy.
Epitaxial Growth of ZnO Thin Films on SiC Prepared by Chemical Solution Deposition
Authors: Park Young-Sik , Jeon Young-Sun , Jeon Kyung-Ok , Kang Bo-An , Hwang Kyu-Seog , Jeong Ju-Hyun , Lee Young-Hwan 
Published: April 2011

ABSTRACTZinc oxide (ZnO) thin films have emerged as one of the most promising oxide materials owing to their optical and electrical properties, together with their high chemical and mechanical stability. Chemical solution deposition (CSD) is attractive technique for obtaining ZnO thin films and has the advantages of easy control of the film composition and easy fabrication of a larger-area thin film at low cost. In this work, epitaxial ZnO thin films on SiC substrate were prepared by using a CSD method with a zinc naphthenate precursor. Precursor films were pyrolyzed at 500°C for 10 min in air and finally annealed at 600°C, 700°C, 800°C and 900°C for 30 min in air. Crystallinity and in-plane alignment of the films were investigated by X-ray diffraction theta-2 theta scan and pole-figure analysis. Scanning electron microscope, scanning probe microscope, and He-Cd laser (325 nm) are used to detect the surface morphology and photoluminescence of the films. The effects of annealing temperature on crystallinity and epitaxy of the films will be fully discussed on the basis of the results of X-ray diffraction analysis.
Influence of the Particle Size on Acoustic Phonon Modes of ZnO Nanocrystals
Authors: Yadav Harish Kumar , Sreenivas K. , Gupta Vinay , Singh S. P. , Sundarakannan B. , Katiyar R. S. 
Published: April 2011

ABSTRACTSize dependence of the low frequency vibrational spectra of ZnO nanocrystals prepared using chemical method has been investigated. Optical transmission spectra of the ZnO colloid solution exhibit a shift in the onset of the absorption band edge from 332 to 350 nm due to particle growth. X-ray diffraction analysis of the prepared ZnO nanocrystals exhibit peaks corresponding to the hexagonal wurtzite structure. Two peaks with unusually very high intensity were observed in the low frequency (∼ 10- 25 cm-1) Raman spectra of these nanocrystals. The peak position of these phonon modes shifted towards lower frequencies as the size of the nanocrystals increases and assigned to the confinement of acoustic phonons in ZnO nanocrystals.
Enhancement of Field Emission Current from ZnO Nanorods Fabricated by Two Step Chemical Vapor Deposition with Laser Ablation of ZnO
Authors: Hirate Takashi , Kimpara Takashi , Takizawa Kazumoto , Satoh Tomomasa 
Published: April 2011

ABSTRACTWe fabricated well-aligned ZnO nanorods with thin diameter by two-step chemical vapor deposition method combined with laser ablation of a sinterd ZnO target. Firstly, well-aligned ZnO nanorods with thick diameter of about 110 nm are grown on an n-Si (111) wafer. Next, a thin ZnO nanorod with about 30 nm diameter is grown on the center of the flat tip of each well-aligned and thick ZnO nanorod by controlling a flow rate of oxygen. Although thick ZnO nanorods do not emit a recognizable field emission current, thin ZnO nanorods with 1500 nm length show a field emission current of 500 μA under an electric field of 31 V/μm.
Synthesis of Water Soluble PbSe Quantum Dots
Authors: Etgar Lioz , Lifshitz Efrat , Tannenbaum Rina 
Published: April 2011

ABSTRACTWater-soluble PbSe semiconductor quantum dots (QDs) with near-infrared absorption of 1100-2520 nm (corresponding to a diameter of 3-13 nm) were synthesized using 2-aminoethanthiol. The oleic acid stabilizing ligands used in the traditional synthesis of PbSe were exchanged with the 2-aminoethanethiol (AET) ligands, which promoted the solubilization of the QDs in an aqueous medium. This occurred due to the attraction of the surrounding water molecules to the exposed amino-group, thus allowing the particles to reside in the water environment. The water-soluble PbSe QDs have very narrow size distribution (σ ≈ 4.5-5.5%). Transmission electron microscopy (TEM), spectrophotometric measurements, and Fourier transform infrared (FTIR) spectroscopy indicate that the morphology, size, size distribution and chemical composition of the PbSe QDs remained unchanged during the transfer to an aqueous medium. In conclusion, the ability to synthesize water soluble PbSe QDs with stable properties and uniform size distribution will allow them to have substantial advantages for biological applications such as biosensors and drug delivery.
Monoatomic Chains Deposited onto Silicon Steps Studied by Density Functional and Scattering Theories
Authors: Mazzone Anna 
Published: April 2011

ABSTRACTThe purpose of this study is the assessment of the properties of deposited atomic chains. Therefore linear chains of covalent and metallic atoms, i.e. As and Ag,deposited onto monolayer SA steps onto Si(100) have been considered. Their study is based on a semi-empirical Hamiltonian, used for the evaluation of both the electronic structure and the conductance, and the calaculations analyze the binding energy of chains of variable length deposited onto steps in the light of the analogous energy of free-standing chains and of chains deposited onto the Si(100) surface. This comparison shows that the stability of the chains has a primary dependence on the type of the substrate, rather than on the chain length and composition, and increases in the order: free standing,deposited onto SA,deposited onto Si(100). The central result of the calculations of the conductance is that the dependence on the type of the substrate and on the chain composition parallels the one of the binding energy.
Control of Spontaneous Emission from Colloidal Quantum Dots in a Polymer Microcavity
Authors: Menon Vinod , Valappil Nikesh , Zeylikovich Iosef , Gayen Taposh , Das Bidyut , Alfano Robert R 
Published: April 2011

ABSTRACTWe report the fabrication of a one dimensional microcavity structure embedded with colloidal CdSe/ZnS core/shell quantum dots using solution processing. The microcavity structures were fabricated by spin coating alternating layers of polymers of different refractive indices (poly-vinylcarbazole, and poly-acrylic acid) to form the distributed Bragg reflectors (DBRs). Greater than 90% reflectivity was obtained using ten periods of the structure. The one dimensional microcavity was formed by sandwiching a λ/n thick defect layer between two such DBRs. The microcavity demonstrated directionality in emission and well behaved dispersion characteristics. Room temperature time-resolved photoluminescence measurements carried out on this structure showed six fold enhancement of spontaneous emission rate. The photoluminescence decay time of the quantum dots was found to be ∼ 1 ns while for the quantum dots embedded in the microcavity it was ∼150 ps.
Selective-Area Growth of Self-Assembled InAs-QDs by Metal Mask Method for Optical Integrated Circuit Applications
Authors: Ozaki Nobuhiko , Takata Yoshiaki , Ohkouchi Shunsuke , Sugimoto Yoshimasa , Ikeda Naoki , Watanabe Yoshinori , Kitagawa Yoshinori , Mizutani Akio , Asakawa Kiyoshi 
Published: April 2011

ABSTRACTWe have developed a selective-area-growth (SAG) method of self-assembled InAs quantum dots (QDs) using a metal-mask (MM) combined with molecular beam epitaxy for realizing photonic crystal (PC) based ultra-small and ultra-fast all-optical devices (PC-SMZ and PC-FF). Successful SAG of QDs was confirmed by atomic-force-microscopy observations and photoluminescence (PL) measurements. High density and high uniformity comparable to those of conventional QDs grown without the MM were achieved; the QD density was 4 × 1010cm-2 and a linewidth of the PL peak was around 30meV at room temperature. In addition, insertion of a strain-reducing layer on the grown QD was effective for varying the PL peak wavelength of the QD from 1240nm to 1320nm without any extra optical degradation. The MM method reported here is promising for achieving the all optical devices, PC-SMZ and PC-FF, which require SAG of QDs and a QD ensemble with a different absorption-peak wavelength in a different area.
Real-time Observation of Nucleation and Evolution of InAs Quantum Dots on GaAs(001) During MBE
Authors: Kamiya Itaru , Matsuura Kohtaro , Higashinakagawa Tsuyoshi 
Published: April 2011

ABSTRACTSelf-assembled (SA) quantum dots (QDs) have been widely studied due to the facileness in their preparation. Unlike other types of QDs that require complicated fabrication processes, SA QDs are prepared merely by depositing materials that have different bandgaps and lattice constants to the with respect to the substrate by epitaxial crystal growth techniques. InAs QDs on GaAs(001) grown by MBE or MOCVD have been a typical example, and their optoelectronic properties have been extensively investigated. For device applications, it is essential that their size and spatial distribution are controlled. However, since SA QDs are formed through random processes, it is not easy to achieve size and distribution uniformity without prior processing the substrate prior to crystal growth. A number of studies have been performed to understand the fundamental mechanisms of SA QD formation that would provide us with information to achieve such goal.
Here, we performed real-time observation of SA InAs QD growth on GaAs(001) by MBE. In contrast to most previous reports that employed growth interruption, by following the time transient of RHEED specular beam in detail, we obtained information about nucleation and evolution of the QDs, and have been able to distinguish processes that are dependent and independent of growth rate. In addition, the results reveal that surface migration of In/As atoms and their incorporation into QDs, with the aid of the wetting layer, can be observed. We will also provide a quantitative discussion on these processes.