bluuebunny/crossref_metadata_2025 huggingface dataset:
Advanced Organic-inorganic Hybrid Coatings Having Both High Gas Barrier Properties and Abrasion Resistance
Authors: Nishiura Katsunori , Takaki Toshihiko , Nakaura Makoto
Published: April 2011

It is important to develop flexible transparent polymer films having high gas barrier properties and abrasion resistance because new applications involving transparent polymer films for flat panel displays require these properties. We report on organic-inorganic hybrid coatings of polyvinylalcohol (PVA)/polyacrylicacid (PAA)-silica, which have high gas barrier properties almost equivalent to those achieved by the dry coating process. The hybrid coatings were prepared by the sol-gel reaction of alkoxysilane in a PVA/PAA aqueous solution. In order to obtain transparent coating films, 3-aminopropyltrimethoxysilane (APTMOS) was used as a compatibilizer in the sol-gel reaction of tetramethoxysilane (TMOS). No structure could be seen in the TEM of the cross-sectional coating layer, indicating that polymers and silica were mixed homogeneously. PVA/PAA-silica hybrid coatings were shown to have excellent abrasion resistance based on the ΔHaze index. O2 permeability of PVA/PAA-silica hybrid coatings evaluated by MOCON under the conditions of 23°C, 90% RH was lower than that of PVA/PAA polymer coating, which suggests that silica affects the barrier property of the hybrid coating in humid conditions. Furthermore, O2 permeability decreased as silica content increased in the coatings. Unexpectedly, high gas barrier properties appeared when the silica content exceeded 50 wt%. From the result of element distribution analysis measured by EF-TEM, it was confirmed that phase separation occurred between PVA/PAA and silica on a nanometer scale and silica forms continuous structures, which are considered to suppress O2 permeability.
Thermal and Pressure Sensing by Chemoreceptive Neuron MOS Transistors (CνMOS) with PVDF Coating
Authors: Jacquot Blake , Muñoz Nini , Kan Edwin C.
Published: April 2011

This paper reports the integration of poled 10μm +/- 1μm P(VDF-TrFe) copolymer thin films with an adapted non-volatile, foundry-compatible CMOS structure (CνMOS) for the potential purposes of in-vivo piezoelectric and pyroelectric sensing. This structure allows for direct, reliable interaction between the sensing transducer and the highly sensitive MOSET gate stack without the need for an external reference electrode or chopper, as other designs may require.
Interactions Between Carbon Nanotubes and Bacteria
Authors: Raja Pavan M. V. , Ajayan Pulickel M. , Nalamasu Omkaram , Sharma Anurag
Published: April 2011

While carbon nanotubes (CNTs) possess diverse application potential ranging from polymer nanocomposites to nanostructured therapeutic devices, their environmental implications are still not well understood. In this study, we conducted experiments to monitor changes in bacterial physiology as a consequence of interactions with the CNTs. Our experiments included a common anaerobe,Escherichia coli, in an SWNT system as a model for understanding the environmental implications of CNTs. Observations over several weeks indicated that the bacteria in the presence of SWNTs showed significant morphological changes, that included elongation. It is interesting to note that similar morphological changes have been reported in response to extreme temperature and pressure, chemical agents, and quantum dots. In this presentation, the authors will present further physiological evidence, such as bacterial growth and substrate consumption rates, towards defining a possible bacteria-CNT interaction model consistent with these experimental observations, and will discuss the overall environmental implications.
Bulk AlN Crystal Growth on SiC Seeds and Defects Study
Authors: Lu Peng , Edgar J H , Cao C , Hohn K , Dalmau R , Schlesser R , Sitar Z
Published: April 2011

Sublimation growth of AlN was performed on Si-face, 8 ° off-axis 4H-SiC (0001) and 3.5 ° off-axis 6H-SiC (0001) seeds. AlN layers 500 - 900 μm thick and 20 mm in diameter were grown at 1830 °C by consecutive growths and continuous growth. The c-axis growth rate was approximately 8 - 18 μm/hr. On both the 8 ° and 3.5° off-axis SiC substrates, “step” features formed on the AlN surface with uniform terrace width and step density. The step heights and terrace widths increased as the AlN grew thicker. In addition, a single facet of 9 mm × 5 mm formed on the top of the layer grown on the 3.5 ° off-axis SiC. High resolution x-ray diffraction showed the AlN (00.2) 2θ value shifted from pure AlN toward SiC. Approximately 3 – 4 at% of SiC was detected at the surface of the AlN by XPS. Molten KOH/NaOH etching revealed that both samples had Al-polar surface with dislocation densities on the order of 106-107 cm−2. The cross-section etching showed the re-nucleation layer and void defects at the interfaces of the consecutive growths.
Growth and Polarity Control of GaN and AlN on Carbon-face SiC by Metalorganic Vapor Phase Epitaxy
Authors: Fu Yi , Ni Xianfeng , Xie Jingqiao , Biyikli N , Fan Qian , Chevtchenko S , Özgür Ü , Morkoç Hadis , Ke You , Devaty Robert , Choyke W. J. , Inoki C. K. , Kuan T. S.
Published: April 2011

Growth and polarity control of GaN and AlN on carbon-face SiC (C-SiC) by metalorganic vapor phase epitaxy (MOVPE) are reported. The polarities of GaN and AlN layers were found to be strongly dependent on the pre-growth treatment of C-SiC substrates. A pre-flow of trimethyaluminum (TMAl) or a very low NH3/TMAl ratio results in Al(Ga)-polarity layers on C-SiC. Otherwise, N-polarity layers resulted. The polarities of AlN and GaN layers were conveniently determined by their etching rate in KOH or H3PO4, a method reported earlier. We suggest that the Al adatoms, which have a high sticking coefficient on SiC, form several Al adlayers on C-SiC and change the incorporation sequence of Ga(Al) and N leading to metal polarity surface. In addition, the hexagonal pyramids, typical on N-polarity GaN surface, are absent on N-polarity GaN on off-axis C-SiC owing to high density of terraces on off-axis C-SiC. The properties of GaN layers grown on C-SiC are studied by X-ray diffraction.
Mg-doped N-polar InN Grown by RF-MBE
Authors: Muto Daisuke , Naoi Hiroyuki , Takado Shinya , Na Hyunseok , Araki Tsutomu , Nanishi Yasushi
Published: April 2011

We have investigated the growth properties of Mg-doped N-polar InN films grown by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). We found that the Mg-doped InN films had smaller grain size than non-doped films, and furthermore the grain size decreased with an increase in Mg doping amount. Non-doped InN exhibited a single X-ray diffraction (XRD) peak of (0002) h-InN. On the other hand, the Mg-doped InN produced a weak XRD peak of (111) c-InN in addition to a strong peak of (0002) h-InN. These results indicate that the Mg doping decreased the surface migration length of In atoms. From Hall-effect measurements, all the samples were shown to have n-type conductivity. Mg-doped InN grown with Mg cell temperatures of 130 and 135°C had carrier concentrations that were about half (i.e., ∼4.5×1018 cm−3) that of the non-doped InN. However, the carrier concentration tended to increase with further supply of Mg. These results indicate that Mg-doping causes a trade-off between a carrier decreasing effect from the Mg acceptors and a carrier increasing effect from defects caused by the poor surface migration of In atoms.
Experimental Analysis of the Spontaneous Polarization Field in GaN by UHV-cathodoluminescence
Authors: Finke Martina , Fuhrmann Daniel , Rossow Uwe , Hangleiter Andreas
Published: April 2011

Cathodoluminescence spectra of GaInN quantum well structures show a strong change of intensity and a emission energy shift during electron beam irradiation. Measurements on samples with quantum well positions varying in depth show, that the spontaneous field, witch is usually screened by surface charges, penetrates the sample in a timescale of minutes and reduces the quantum confined Stark effect.
Erbium-doped GaN epilayers synthesized by metal-organic chemical vapor deposition
Authors: Ugolini C. , Nepal N. , Lin J. Y. , Jiang H. X. , Zavada J. M.
Published: April 2011

GaN is an excellent host for Er due to the low thermal quenching of radiative intra-4f Er3+ transitions at 1.54 μm. Er doped GaN structures are promising for emitters and amplifiers operating at the main telecommunication wavelength. In recent studies, Er doped III-Nitride epilayers were obtained by ion implantation, hydride vapor phase epitaxy (HVPE), metal organic molecular beam epitaxy (MOMBE), or molecular beam epitaxy (MBE). But, in-situ Er doping of III-nitride epilayers has not been achieved by metal organic chemical vapor deposition (MOCVD), mostly due to the low vapor pressure and lack of suitable, metal organic Er sources. Since n and p type III-nitride epilayers with excellent electrical properties and high crystalline quality are easily achieved by the MOCVD method, in-situ incorporation of Er into III-nitride materials by MOCVD is a very attractive method for creating highly efficient optoelectronic devices operating at 1.54 μm. We report on the experimental study and synthesis of Er doped GaN by MOCVD. Photoluminescence (PL) with above and below bandgap excitation energies were employed to study the optical properties of Er doped GaN. PL spectra of these Er doped layers exhibit a strong 1.54 μm emission, corresponding to the intra-4f transition of the 4I13/2 (first excited state) to the 4I15.2 (ground state) of Er3+. The mechanisms of optical transitions involving different excitation energies, and potential applications of Er doped GaN structures in the communication wavelength are also discussed.
Preparation of High Conductive Cubic Boron Nitride Thin Films by in-situ zinc Doping
Authors: Nose Kenji , Yoshida Toyonobu
Published: April 2011

Silicon and zinc were doped to cubic boron nitride (cBN) thin films by sputtering bulk dopant sources during the film deposition. Concentrations of these two elements showed different in-plane distributions, presumably caused by the difference of the sticking probability on the growing surface. Silicon impurity did not behave as an active dopant in cBN. However, zinc doping enhanced the electric conductivity from 10−8 to 10−2 (Ω−1cm−1) as the zinc concentration increased from undoped to approximately 2 %.
The Influence of Device Structure on High-electric-field Effects and Reliability of AlGaN/GaN HFETs
Authors: Kuang Weiwei , Trew Robert J , Bilbro Griff L , Liu Yueying
Published: April 2011

AlGaN/GaN HFETs have demonstrated excellent RF performance, but the devices still suffer from a reliability problem. The decrease of the dc current and RF output power over time is attributed to gate tunneling which is determined by the magnitude of electric field at the gate edge. In this work, in order to improve the reliability of AlGaN/GaN HFETs, a 2D drift-diffusion tool is used to explore the relationship between the magnitude of electric field and different device structures through modifications of the 2DEG sheet charge density, AlGaN barrier layer thickness, AlGaN doping concentration and gate to drain spacing. The effect of field plates is also investigated. It was found that decreasing 2DEG sheet charge density results in much improved reliability, although the current and output power are somewhat reduced.
Effects of Surface Treatments on Optical Properties of GaN
Authors: Fujimoto Gakuyo , Fujii Katsushi , Minegishi Tsutomu , Goto Hiroki , Goto Takenari , Yao Takafumi
Published: April 2011

Removing artificial oxide layer is important for fabrication process of semiconductor devices. We employed photoluminescence for optical, reflection high energy electron diffraction, atomic force microscope, and Nomarski microscope for surface analysis. We found that it is more difficult to remove the oxide layer made by O-plasma such as in O-plasma asher than that of native one. Our result reached that HF etching is effective for removal of the artificial oxide layer without changing surface morphology. In addition, (NH4)2Sx treatment after HF etching reduces donor bound exciton drastically which is dominant luminescence near the band edge at low temperature.
Development of Aluminum Nitride/Platinum Stack Structures for an Enhanced Piezoelectric Response
Authors: Kabulski Adam , Harman John , Famouri Parviz , Korakakis Dimitris
Published: April 2011

Aluminum nitride (AlN) films are being investigated for piezoelectric and high temperature applications, but the piezoelectric response is still much lower than that of more common piezoelectric materials such as lead zirconate titanate or zinc oxide. A method of maximizing the piezoelectric response of aluminum nitride has been explored by depositing stack structures composed of aluminum nitride and platinum. These stack structures were created by depositing a thin, ∼50nm, metal layer in between thicker, ∼150-350nm, layers of the piezoelectric film. Platinum was chosen as the metal interlayer due to the tendency of AlN to become highly c-oriented when deposited on Pt. An electric field was applied across the structure and displacements were measured using a Laser Doppler Vibrometer. A maximum piezoelectric coefficient d33 was found to be over two times larger than the theoretical value for AlN (3.9pm/V). However, some of the stack structures were found to be conductive when measuring the displacement. I-V measurements as well as Fowler-Nordheim theory and plots were applied to investigate tunneling due to high electric fields in the structures.
Electroreflectance Spectra of InGaN/AlGaN/GaN p-n-Heterostructures
Authors: Yunovich Alexander E. , Avakyants Lev , Badgutdinov Mansur , Bokov Pavel , Chervyakov Anatoly , Shirokov Stanislav , Vasileva Elena , Feopentov Anatoly , Snegov Fedor , Bauman Dmitry , Yavich Boris
Published: April 2011

Electroreflectance (ER) spectra of InGaN/AlGaN/GaN p-n- heterostructures with multiple quantum wells (MQW) are studied. Structures with MQW InGaN/GaN were grown for blue LEDs by MOCVD technology and “flip-chip” mounted. The ER spectral maxima correspond to the high energy side of electroluminescence spectral line. The ER spectra caused by Franz-Keldysh effect are approximated by Aspnes theory. The ER spectra in a range 400 ÷ 800 nm have interference bands caused by the change of refraction index in the structure.
Vertically Increasing Well Thickness and In Content in GaInN MQW's due to V-shaped Pits
Authors: Bremers Heiko , Hoffmann L. , Fuhrmann D. , Rossow U. , Hangleiter A.
Published: April 2011

In this work we investigate the influence of V-shaped pits on the growth of GaInN-GaN MQW's by TEM and x-ray diffraction measurements. We have grown different MQW's using low-pressure MOVPE and studied the influence of the number of QW's as well as of the depth of V-shaped pits. During the growth of the samples a material transport takes place from the pits to the c-plane. We show that the thickness of the GaInN QW's and of the GaN barriers is increased due to material transport. With increasing number of quantum wells the diameter of the pits increases, which leads to a super linear increase of these thicknesses. We present a model which describes the change in thickness due to material transport. Another consequence of material transport is a lateral fluctuation in thickness with a characteristic length on the order of the distances between the dislocations.
Investigation of Optical Properties of Nitrogen Incorporated Sb based Quantum Well and Quantum Dots for Infrared Sensors Application
Authors: Kim Seongsin M , Yuen Homan B , Hatami Fariba , Moto Akihiro , Chin Alan , Harris James S
Published: April 2011

We report the growth and characterization of a new dilute nitride, InNAsSb/InAs, by solid source molecular beam epitaxy. Optimizing growth conditions for nitrogen incorporation has resulted in high-quality InNAsSb epilayers without any structural degradation, as confirmed by high-resolution x-ray diffraction. Optical properties were investigated by temperature dependent and excitation power dependent photoluminescence. We obtained mid-infrared luminescence around 4 mm at low temperature, which reveals strong carrier localization behavior at low temperature induced by nitrogen interacted with antimony. The band alignment of InNAsSb/InAs can be type-I and instead of conventional type-II, InAsSb/InAs, and a conduction band offset, Ec,of ∼102meV was obtained.
Investigation of The Electrical and Chemical Properties of Plasma-Treated AlGaN
Authors: Cao Xian-An , Piao H. , LeBoeuf S. F. , Lin J. Y. , Jiang H. X.
Published: April 2011

The surface properties of n-type AlxGa1−xN (x=0-0.5) exposed to inductively couple plasma were studied systematically using metal contact measurements and X-ray photoelectron spectroscopy (XPS). Cl2/BCl3 and Ar plasma treatment considerably increased the surface conductivity of AlxGa1−xN (x<0.3) and thus improved the characteristics of Ti/Al-based ohmic contacts, but degraded the surface and contact properties of AlxGa1−xN (x≥0.3). XPS measurements revealed a significant increase in oxygen incorporation and energy shifts of the core-level spectra in plasma-treated samples. In contrast to an upward shift of the surface Fermi level in plasma-treated GaN, the surface Fermi level moved away from the conduction band in Al0.5Ga0.5N upon plasma treatment. These findings suggest that the nature of plasma damage in AlGaN appears to be a function of the Al mole fraction. Plasma-induced defects in high-Al AlGaN may act as deep-level compensation centers, degrading the surface electrical properties and contact characteristics.
Synthesis of sub-micron diamond films on Si(100) for thermal applications by BEN-MPCVD
Authors: Saada Samuel , Arnault Jean-Charles , Rocha Licinio , Bergonzo Philippe
Published: April 2011

Diamond is the ultimate candidate for heat-spreading applications because of its extreme thermal management properties. The synthesis of sub-micron diamond films is of great interest for SOD (Silicon On Diamond) wafer technology as well as for specific thermal device applications. The challenge here is the necessity to fabricate ultra-thin layers (down to 100 nm) that are continuous and homogeneous. We studied the Bias Enhanced Nucleation (BEN) pretreatment on microwave plasma reactors in order to have very high nucleation densities (> to 1011 cm−2) and optimised the following growth step of the process to obtain sub-micron covering diamond films. In this study, we focus on the bias step parameters to increase the nucleation rate and to limit the growth rate during the bias step. Then, we performed a growth step to control the morphology of the films. We obtained diamond films with thickness lower than 80 nm and with a 6 nm Root-Mean-Square roughness.
Effects of High D.C. Hias Voltage on the Properties of Diamond-Like Carbon Films
Authors: Yang Boqian , Zhang Hongxin , Wang Xinpeng , Feng Xianping
Published: April 2011

Diamond-like carbon (DLC) films were synthesized using pulsed plasma sputtering deposition techniques. Microscope and Raman scattering techniques were used to study the effects of bias voltages on the properties of diamond-like carbon films. With d.c. bias voltage up to 1000V, the smooth and thick DLC films together with a few nanoparticles were obtained. An increase of the d.c. bias voltage up to 2000V yielded thicker DLC films but its surface became slightly rough and size of particles became large. The crystalline properties of these particles were studied. A tiny diamond peak from Raman spectrum was also observed.
Electron Emission Mechanism of Doped CVD Diamond Characterized Using Combined XPS/UPS/FES System
Authors: Yamaguchi Hisato , Saito Ichitaro , Kudo Yuki , Masuzawa Tomoaki , Yamada Takatoshi , Kudo Masato , Takakuwa Yuji , Okano Ken
Published: April 2011

Electric field of less than 5 V/μm is enough to extract electrons from diamond, whereas field of one to two orders of magnitude higher is needed to extract electrons from metal emitter tips. Despite such low-threshold field, the difficulty in clarification of electron emission mechanism is the factor preventing diamond from being used in a practical use. Quite a few numbers of possible mechanisms were proposed to better understand the origin and properties of the observed emission. Most of these mechanisms were, however, based on the conventional I (Emission current)-V (Anode voltage) characteristics. Energy distribution of the field-emitted electrons is essential in direct clarification of the mechanism. In this study, combined XPS/UPS/FES system was used to characterize the electron emission mechanism of doped chemical vapor deposited (CVD) diamond. The results indicated successful observation of the origin of field-emitted electrons from doped CVD diamond comparison with natural diamond, used as a reference.
Nanofabrication of Diamond-like Carbon Templates for Nanoimprint Lithography
Authors: Tao L. , Ramachandran S. , Nelson C. T. , Overzet L. J. , Goeckner M. J. , Lee G. S. , Hu W.
Published: April 2011

Diamond like carbon (DLC) films were deposited on Si and then patterned to form 40 nm features as nanoimprint templates. A plasma enhanced chemical vapor deposition (PECVD) system with CH4 precursor was used to deposit DLC films on Si and quartz substrates. Then these films were characterized using Raman spectroscopy, atomic force microscopy (AFM), nanoindentation, and contact angle measurement. By varying the RF power and pressure of the PECVD, DLC films with good uniformity, smooth surfaces (<0.2 nm RMS), low surface energy (∼40 mJ/m2), and high hardness (∼22 GPa) were achieved. Nanoimprint lithography and liftoff process were used to pattern Cr mask on DLC films. An inductively coupled plasma (ICP) etching process was performed with CF4 to transfer the patterns into the DLC films to form nanostructured template for nanoimprint. Water contact angles on the patterned DLC templates were measured and it was stable at about 70° under thermal annealing at 180 °C for more than 12 hours. With these DLC templates, UV and reversal UV nanoimprint lithography were carried out on SU-8 at typical imprint conditions and then the fidelity of pattern-transfer was investigated. These experimental results indicate that DLC is an excellent material for nanoimprint templates because of its high wear resistance, robust low surface energy, UV transparency, and ease of patterning.
Surface and Electrochemical Studies of Thin Film Diamond
Authors: Foord John , Opperman David
Published: April 2011

The behavior of diamond electrodes for electrochemical applications in aqueous media containing the protein bovine serum albumin has been explored, to examine the degree of electrode poisoning which occurs. Although the diamond electrode retains good activity in such solutions, electrode fouling is found at long contact times due to protein adsorption. Two adsorption processes are observed. The first is a simple physical adsorption mechanism, and can be simply reversed by washing the electrode in water. The second mechanism is only observed when negative potentials are applied to the diamond electrode and is attributed to the attraction and reaction of the positively charged protein at the electrode interface. Electrode poisoning is also observed in the presence of power ultrasound, although the electrochemical signals are usefully enhanced under these conditions due to enhanced mass transport to the electrode surface.
Spatially Resolved Study of Magnesium Incorporation in Zn1-xMgxO Nanostructures
Authors: Schirra Martin , Reiser Anton , Prinz Günther Michael , Schneider Raoul , Sauer Rolf , Thonke Klaus
Published: April 2011

We report on the growth of Zn1-xMgxO nanopillars on a-plane sapphire by the vapor liquid solid (VLS) process. The as-grown nano structures are characterized by scanning electron microscopy (SEM), spatially resolved cathodoluminescence (SEM-CL), and integral photoluminescence (PL). The investigation with SEM applying different secondary electron detectors confirms that the pillars are grown by the VLS process. Integral PL experiments reveal an average value of 7% Mg incorporated in the Zn1-xMgxO nano structures. Both ZnO- and Zn1-xMgxO– related luminescence features are observed. The direct incorpoaration of Mg into single pillars is demonstrated with SEM-CL, and different Mg concentrations are found. First annealing experiments on the sample at 850°C lead to an almost complete breakdown of the ZnO- and Zn1-xMgxO– related near band-edge luminescence, whereas the structural properties of the sample morpholgy remain nearly unchanged.
Ferromagnetic Mn-Mn Interactions in Low Doped Zn1-xMnxO Thin Films
Authors: BenMahmoud Aroussi , von Bardeleben H.Jurgen , Mauger Alain , Cantin Jean Louis , Chikoidze Ekaterina , Dumont Yves
Published: April 2011

We have studied by electron paramagentic resonance spectroscopy the Mn2+ EPR spectra in low doped (x=0.03) Zn1-xMnxO films of n-type conductivity prepared by metalorganic chemical vapour deposition. Contrary to higher doped films with x=0.07, the x=0.03 film shows a weak ferromagnetic Mn-Mn interaction which we attribute to the presence of moderate deep donors leading to magnetic polaron formation.
Study of the Temperature Dependence of E2 and A1(LO) Modes in ZnO
Authors: Alarcon-Llado Esther , Cusco Ramon , Ibanez Jordi , Artus Luis , Jimenez Juan , Wang Buguo , Callahan Michael
Published: April 2011

Raman scattering measurements were carried out on a bulk, single crystal of wurtzite ZnO over a temperature range from 80 to 760 K and the temperature-dependent shift and broadening of the E2high and A1(LO) modes was analyzed. The E2high mode exhibits a visibly asymmetric line shape that can be related to the interaction with the continuum of acoustic two-phonon density of states. A Fermi resonance model was used to describe the E2high temperature dependence. On the other hand, the anharmonic shift and broadening of the A1(LO) mode are adequately accounted for by a decay model with a dominating Ridley channel involving TO and LA modes. Phonon lifetimes of ∼0.9 and 0.5 ps are found for the E2high and A1(LO) modes, respectively, which corroborates that anharmonic decay involves in both cases a three-phonon process. The A1(LO)lifetime is one order of magnitude lower than that of GaN, which suggests that hot phonon effects should be expected to play a less relevant role in carrier relaxation in ZnO as compared with GaN.
A Solution Method for Large-scale Selective Growth of Aligned ZnO Nanorods
Authors: Hahn Yoon-Bong , Umar Ahmad , Kim Sang Hoon , Im Yeon Ho , Hahn Yoon Bong
Published: April 2011

A facile and convenient aqueous route has been employed to synthesize well -aligned ZnO nanorods. Field emission scanning electron microscopy studies of ZnO nanorod arrays grown at 70°C on ZnO/Si substrates show fine homogeneous surface. The average diameter of ZnO nanorod is in between 50-60 nm .The length of each nanorod is about 400-500 nm. Structural analysis showed that the ZnO nanorods are single crystalline with wurtzite hexagonal phase. Room temperature photoluminescence spectra of the ZnO nanorod arrays exhibit ultra violet emission and green emission. In addition, selective growth of ZnO nanorods on patterned ITO glass substrate is obtained. Each nanorod has diameter of 50 - 70 nm and their length upto 500 nm. XRD pattern shows that ZnO nanorods on patterned ITO substrate are single crystalline in nature with wurtzite hexagonal phase. The room temperature photoluminescence from the aligned ZnO nanorods showed a strong ultra violet emission at 378 nm and broad deep level visible emission at 580 nm.
Surface Preparation of Single Crystals for ZnO Homoepitaxy
Authors: Neumann Christian , Lautenschläger Stefan , Graubner Swen , Volbers Niklas , Meyer Bruno K , Bläsing Jürgen , Krost Alois
Published: April 2011

For the homoepitaxial growth of ZnO it is inevitable to obtain a regular crystalline single crystal surface prior to growth. Commercially available, hydrothermally grown ZnO single crystals show amorphous surfaces due to mechanical cutting and polishing.
Here we present the results of a thermal treatment on these ZnO single crystals. After annealing, a regular crystalline oxygen terminated surface can be obtained. Changes in surface roughness, residual defect concentration and electrical properties can be shown. The bulk crystallinity though was not affected.
Growth and Characterization of Mg0.15Zn0.85O Thin Films by Pulsed Laser Deposition
Authors: Wei Wei , Jin Chunming , Doraiswamy Anand , Narayan Roger J , Narayan Jagdish
Published: April 2011

Mg0.15Zn0.85O thin films were grown on fused silica substrates at different substrate temperatures using pulsed laser deposition. X-ray diffraction and transmission electron microscopy were used to investigate the structure of the films. High resolution transmission electron microscopy showed that the film contained small grains with low angle boundaries. The optical properties of the films were investigated using absorption spectra. The bandgap energy values of the films was determined by fitting the absorption data.
Electrical Characterization of Defect States in Local Conductivity Domains in ZnO:N,As Layers
Authors: Krtschil Andre , Dadgar Armin , Diez Annette , Krost Alois
Published: April 2011

P- and n-type conductivity domains in dual-doped ZnO:As+N layers grown by metal organic vapor phase epitaxy on GaN/sapphire templates were electrically microcharacterized by scanning capacitance (SCM) and scanning surface potential microscopy (SSPM) techniques with respect to their defect states. The p-type domains were found to be dominated by two acceptors with thermal activation energies of about 80 and 270 meV as observed by transient SCM scans at different temperatures. Optically excited SSPM scans revealed defect-to-band-transitions at 400, 459, and 505 nm omnipresent in both domain types as well as a shallower transition at 377 nm exclusively in the p-type regions. According to the similar energy levels the optical transitions at 377 and 400 nm are assigned to acceptor states, whereby the 80meV-acceptor is probably responsible for the conversion from n- to p-type in the domains.
Formation of Nanovoids and Nanocolumns in High Dose Hydrogen Implanted ZnO Bulk Crystals
Authors: Singh Rajendra , Scholz R. , Gösele U. , Christiansen S. H.
Published: April 2011

ZnO(0001) bulk crystals were implanted with 100 keV H2+ ions with various doses in the range of 5×1016 to 3×1017 cm-2. The ZnO crystals implanted up to a dose of 2.2×1017 cm-2 did not show any surface exfoliation, even after post-implantation annealing at temperatures up to 800°C for 1 h while those crystals implanted with a dose of 2.8×1017 cm-2 or higher exhibited exfoliated surfaces already in the as-implanted state. In a narrow dose window in between, controlled exfoliation could be obtained upon post-implantation annealing only. Cross-sectional transmission electron microscopy (XTEM) of the implanted ZnO samples showed that a large number of nanovoids were formed within the implantation-induced damage band. These nanovoids served as precursors for the formation of microcracks leading to the exfoliation of ZnO wafer surfaces. In addition to the nanovoids, elongated nanocolumns perpendicular to the ZnO wafer surfaces were also observed. These nanocolumns showed diameters of up to 10 nm and lengths of up to 500 nm. The nanocolumns were found in the ZnO wafer even well beyond the projected range of hydrogen ions.
Structure-Property Relationships in the xZnO-(1-x)alpha-Fe2O3 Nanoparticle System
Authors: Sorescu Monica , Diamandescu Lucian , Wood Jason
Published: April 2011

The xZnO-(1-x)α-Fe2O3 nanoparticles system has been obtained by mechanochemical activation for x=0.1, 0.3 and 0.5 and for ball milling times ranging from 2 to 24 hours. Structural and morphological characteristics of the zinc-doped hematite system were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy. As ZnO is not soluble in hematite in the bulk form, the present study clearly demonstrates that the solubility limits of an immiscible system can be extended beyond the limits in the solid state by mechanochemical activation. Moreover, this synthesis route allowed us to reach nanometric particle dimensions, which would make the materials very important for gas sensing applications.
Preparation of Shape and Size-Controlled Zinc Oxide Nanostructures by Chemical Spray Pyrolysis Technique
Authors: Dedova Tatjana , Krunks Malle , Mere Arvo , Klauson Jelena , Volobujeva Olga
Published: April 2011

Highly structured layers comprising of vertically aligned zinc oxide rods, tripods or platelets were fabricated by spray pyrolysis method at temperatures of 510-550 °C. The zinc chloride solution was pulverized onto the preheated substrates of glass and ITO, SnO2, ZnO covered glass substrates with the help of compressed air as a carrier gas. ZnO layers were characterized by scanning electron microscopy and Raman spectroscopy. C-axis orientated ZnO nanorod arrays of well-developed hexagonal rods with length from some hundreds of nanometers up to some microns and with diameter from 70 nm up to 900 nm . The rise of both the growth temperature and solution concentration increases rod dimensions. Deposition of the solutions with the concentration of 0.05 up to 0.2 mol/l results in structured layers composed of rods on glass substrates. Using ITO, SnO2 and ZnO thin film covered glasses diluted solutions should be used to obtain ZnO nanorods. Alcoholic solutions allow deposit thinner rods and reduce the deposition temperature. Very strong and relatively narrow E2 Raman bands indicate that ZnO rods prepared by spray pyrolysis technique are of high crystal quality.
Soft-chemistry Route to P-I-N Heterostructured Quantum Dot Electroluminescence Device: All Solution-processed Polymer-Inorganic Hybrid QD-EL Device
Authors: Kwon Soon-Jae , Cho Kyung-Sang , Choi Byoung-Lyong , Kim Byung-Ki
Published: April 2011

p-i-n heterostructured quantum-dot electroluminescence (QD-EL) device was fabricated by soft-chemical process, which shows a low turn-on voltage comparable to OLEDs. To construct the multilayered device structure, p-type polymer semiconductor was deposited on the ITO glass by sequential process of coating and thermal curing, thereupon a few monolayers of QD was spin-coated. n-type metal-oxide film was deposited on top of the QD luminescence layer by sol-gel method, providing a facile and low-cost route for the ETL fabrication. Prior to solution-processed ETL construction, a post-treatment is performed using cross-linking agent, in order to chemically-immobilize the QDs. As a cathodic electrode, relatively air-stable aluminum was deposited. The constituent material as well as the electronic band structure of the integrated device guarantees operating stability in air and low turn-on voltage.
Virtual Synthesis and Optoelectronic Properties of Prismatic Artificial Molecules of In-N and Zn-O: Comparative Studies
Authors: Pozhar Liudmila A , Brown Gail J , Mitchel William C
Published: April 2011

The Hartree-Fock (HF), restricted open shell HF (ROHF), configuration interaction (CI), complete active space (ICASCF), and multiconfiguration self-consistent field (MCSCF) methods provide sophisticated fundamental theory-based, computational tools to study structure, composition,chemistry and electronic properties of small artificial molecules composed of semiconductor compound atoms. These tools are used to synthesize virtually several prismatic In-N and Zn-O artificial molecules whose structure is derived from that of the symmetry elements of the respective wurtzite bulk lattices. Applications of spatial constraints to the atomic coordinates allow modeling molecular synthesis in quantum confinement, to obtain pre-designed molecules with tunable electronic properties. Relaxation of these constraints, or optimization, leads to the corresponding molecules synthesized in “vacuum”. The development of computational templates of the studied artificial molecules synthesized in confinement reflects effects of quantum confinement on the electronic level structure, bonding, the direct optical transition energy, and charge and spin density distributions of the molecules. Comparison of the structure and properties of these molecules to those of their vacuum counterparts leads to a conclusion that a small changes in atomic positions in otherwise structurally similar molecules cause a significant change in their electronic properties. Thus, the electronic properties of artificial molecules can be tuned by changing their synthesis conditions that are defined by atomistic details of quantum confinement where the molecules are synthesized.
Guided Self Assembly of InAs Quantum Dots on a Cleaved Facet
Authors: Uccelli Emanuele , Schuh Dieter , Bauer Jochen , Bichler Max , Finley Jonathan J. , Grayson Matthew , Abstreiter Gerhard , Fontcuberta i Morral Anna
Published: April 2011

The long range ordering of epitaxial semiconductor quantum dots (QDs) has been obtained by combing self assembly with the cleaved edge overgrowth technique. The introduction of nanometer thick AlAs stripes on a (110) oriented GaAs surface avoids the misfit dislocation growth mechanism of InAs on GaAs (110) and drives the formation of array of QDs. Atomic Force Microscopy (AFM) investigations highlight that InAs QDs only nucleate in chain like structure on Al-rich regions. Here, we present experimental results that demonstrate the ability to create ordered QDs lattices and discuss the conditions under which preferential growth of QDs on the AlAs stripes occurs.
First-principles Calculations of Energetic Properties of Vacancies, Mn-atomic Defects in CdTe
Authors: Merad Ghouti , Rerbal Benali , Aourag Hafid , Cibert Joël
Published: April 2011

An atomistic modelling based on density functional theory within the framework of the local density approximation is used to show the trends in the energetic properties of single and double defects in CdTe semiconductor, without phase transformation. A systematic study of vacancies, Mn substituting Cd atoms in a supercell structure consisting of 16-atoms is presented. The changes of structural properties and lattice parameters due to the addition of Mn-atomic type defects in CdTe matrix are compared, and the number of vacancies is also determined from the total energy calculations.
Modelling Size-Selected Growth of Nanodots by Using Reaction Kinetic Approach
Authors: Nevalainen Kirsi , Rusanen Marko , Koponen Ismo T.
Published: April 2011

The size selection of nanodots during the growth is modelled by using the reaction kinetic model with reaction rates for dot size dependent attachment and detachment processes, related to the free energy of dots. Long-lived metastable state is found near the minimum of free energy, but the kinetics of the growth causes the peak to overshoot the location of minimum of the energy. The size distribution of dots is shown to be nearly Gaussian with minor skewness originated from kinetics. However, it is argued that this skewness is inherently related to the effect of overshooting, and thus to the formation of the long lived metastable state with size selected nanodots. Based on RKM, a simple continuum model is derived to describe the size selection and narrowing of the size distribution.
Structural and Magnetic Characterization of MOCVD Grown GaMnN and GaFeN Nanostructures
Authors: Gupta Shalini , Kang Hun , Kane Matthew H. , Park Eun Hyun , Ferguson Ian T.
Published: April 2011

The growth of Ga1-xMnxN and Ga1-xFexN nanostructures was carried out by MOCVD. Introduction of transition metals (TM) Mn and Fe in GaN nanostructures enhanced the nucleation of the nanostructures resulting in reduced lateral dimensions and increased nanostructure density. The Ga1-xMnxN nanostructures showed hysteresis behavior at 5K. Room temperature ferromagnetism was obtained in the Ga1-xFexN nanostructures unlike its bulk counterpart. This paper presents the growth and magnetization study of Ga1-xTMxN nanostructures. These structures could be used to enhance the efficiency of spintronic devices.
Spray Produced Coral-Shaped Assemblies of MnS Nanocrystal Clusters
Authors: Amirav Lilac , Lifshitz Efrat
Published: April 2011

A novel spray-based technique enables the production of high quality, free, uncoated semiconductor nanocrystals. Their collection, following spray droplet desolvation during flight, could result in unusual structures. We report on spray-produced ordered clusters (∼50nm diameter) of MnS nanocrystals with grain size range of 1-2nm, and their assembly into micron-sized coral-shaped fractal aggregates. Ballistic cluster-particle aggregation, with the introduction of physical interaction between particles, is suggested as a model for the assemblies' growth.
Photo-Induced Structural Changes in Titanium Alkoxides for Directing Molecular Assembly
Authors: Musgraves J. David , Potter B.G. , Sewell Robin M. , Boyle Timothy J.
Published: April 2011

The effects of ultraviolet irradiation on a heteroleptic titanium alkoxide ((OPy)2Ti(4MP)2) have been investigated. The molecule has been studied in solution and in thin film form using FTIR and Raman spectroscopies. Quantum computational modeling was used to associate vibrational modes with structural moieties present in the molecule. In all cases examined, a preferential photoinduced modification in vibrational resonances linked to the 4-mercaptophenol (4MP) ligand was observed. In contrast, little or no change was exhibited in the vibrational structure of the OPy ligands.
Self Assembled Patterns of Gold Nanoclusters in Silicon (100) Produced by Metal Vapour Vacuum Arc Ion Implantation
Authors: Venkatachalam Dinesh Kumar , Sood Dinesh Kumar , Bhargava Suresh Kumar
Published: April 2011

Self assembled gold nanoclusters are attractive building blocks for future nanoscale sensors and optical devices due to their exciting catalytic properties. Recently several methods have been employed to produce nanoclusters on solid substrates, which result in a random spatial distribution of the clusters. In this work, we have achieved ordered circular patterns of gold nanoclusters in Silicon (100) substrates by Au ion implantation followed by thermal annealing. This unique phenomenon is observed only above a critical threshold implantation dose and anneal temperature. Based on a systematic study (SEM, XTEM and XRD) of the growth and morphology of the nanoclusters, we propose a tentative model for the formation mechanism of this unusual self-assembled pattern.
Quantum-Cross Tunneling Junction for High Density Memory
Authors: Kaiju Hideo , Kondo Kenji , Ishibashi Akira
Published: April 2011

We calculated transport properties of edge-to-edge quantum cross structure that consists of two metal nano-ribbons having edge-to-edge configuration with a tunnel barrier and showed current-voltage characteristics depending on the metal-ribbon thickness (5-30 nm), the barrier height (0.5-1.5 eV) and the barrier thickness (0.5-1.0 nm). Interesting behavior of transport properties is that the metal-ribbon thickness affects the current density due to the quantization of nano-ribbon and also the current density, being dependent on the barrier height and the barrier thickness, decreases with high and thick barrier. These calculated results indicate that we can precisely obtain the information on the material sandwiched between two electrodes, such as the barrier height and the barrier thickness, by a fit of experimental data to our derived equation, and these approaches result in a distinction between the sandwiched material and the electrode.
Memory Effects in Manganese Perovskites. Experiment and Theory
Authors: Noginova Natalia , McClure J. , Gavrilenko V. , Novikov D
Published: April 2011

Electrically induced quasi-permanent changes in low-field conductivity have been observed in single crystals of LaGa1-xMnxO3 in the broad range of Mn ion concentrations. The memory effects can last for a long time at room temperature and can be easily erased by heating up to Tc ∼300 C. The temperature dependence of the resistivity has a sharp drop around the phase transformation temperature, pointing to the role of phase transformation processes. The switching between high resistance and low resistance states is demonstrated. We explain our experimental data in terms of thermo induced local phase transition with the oxidation of Mn ions. The results of the ab initio calculations of the electron energy structure in Jahn-Teller-distorted and non-distorted cells confirm the mechanism suggested.
Nanoline Templating of metals and the underlying surface processes
Authors: Owen James Hugh Gervase , Miki Kazushi
Published: April 2011

Bi nanolines, which self-assemble on Si(001), have been used as templates for the deposition of a variety of metals: noble metals, transition metals, and Gr. III metals. The different metals show a variety of behaviours on this surface, from a strong interaction in the case of In and Al, to a very weak interaction in the case of Ag. The different phenomena are discussed in terms of a balance of different competing surface mechanisms, such as diffusion and nucleation, which drives the observed behaviours.
Quasi-Ordered Nano-Sized Structure On Surface Of Oxide Crystals
Authors: Doichinovic Iavn , Dojcilovic Jablan , Popovic Dusan , Puric Jagos , Kulagin Nicolay Alex
Published: April 2011

An article is given of research of SEM, AFM and optic data of pure and doped strontium titanate as bulk single crystals and nano-scale sized samples before and after plasma treatment. Quasi-ordered system of nano-scale sized triangle piramids was discovered on surface of separate doped samples after plasma treatment
Supramolecular Self-Assemblies as High-Density Data-Storage Media
Authors: Wintjes Nikolai , Wahl Markus , Kiebele Andreas , Stohr Meike , Schintke Silvia , Spillmann Hannes , Güntherodt Hans-Joachim , Gade Lutz , Bonifazi D , Cheng F , Diederich F , Jung Thomas
Published: April 2011

The affordable and reproducible creation of nanoscale functional material layers is a key desire towards the progressing miniaturization of devices and the continuous increase of data storage densities. While top-down structuring costs are exploding, the self-assembly [1] of dedicated building blocks in functional molecular layers provides an alternative to produce structures in the few nanometer range. Several different approaches, exploit characteristic materials properties for this purpose: A) the dedicated assembly of two dimensional molecular layers on prepatterned surfaces provides the basis for structural transitions involving only some hundred molecules. These transitions can be reversibly triggered by an electric field. [2] B) The complex balance of inter-molecular interactions with adsorbate-adsorbent interactions provides the basis for tuning the assembly. Long range ordering is a crucial requirement to match self-assembled functional devices with top-down manufactured methods for addressing and operation. [3] C) Using larger molecular entities and conformational flexure [4], even larger periodicity functional arrays can be manufactured by extending site blocking mechanisms to nearest neighbour interactions. [5] D) By a hierarchical two step approach, i.e. the initial assembly of a specific host-layer and the second step assembly of molecular guests upon this host layer, a wealth of new molecular properties is achievable in extended supra-molecular layers. [6] All these new supra-molecular self-assembled systems offer a valid alternative toward the fabrication of reproducibly identical and addressable “molecular switches” which are impossible to achieve by using established lithographic methods.