bluuebunny/crossref_metadata_2025 huggingface dataset:
Sub Surface Material Characterization using High Frequency Eddy Current Spectroscopy
Authors: Heuer Henning , Hillmann Susanne , Klein Marcus , Meyendorf Norbert
Published: February 2010

By launching new processes introduced by nano science into much more conventional industrial applications fast, robust and economical reasonable inspection methods are required for process control and quality assurance. Coming from high tech industries e.g. semiconductor industries the methods available for thin film characterization and quality control are complex and often require scientific skilled personal. High frequency eddy current spectroscopy in reflection or transmission configuration allows a contactless measurement of e.g. copper thin films on silicon with a thickness resolution better that 5 nm. Due to the insensitivity of the transmission mode to dislocations or slight tilting of the sample the high frequency eddy current method is a practicable method for thin film characterization under industrial environment.
Surfactant Effects of Indium on the Growth of AlN/GaN Distributed Bragg Reflectors via Metal Organic Vapor Phase Epitaxy
Authors: Rodak L E , Miller Christopher M , Korakakis D
Published: February 2010

Distributed Bragg Reflectors (DBRs) remain critical to the fabrication of various nitride based optoelectronic devices. In particular, DBRs are often employed for cavity formation in Resonant Cavity Light Emitting Diodes (RCLEDs) to enhance and obtain a more directional emission and also in Vertical Cavity Surface Emitting Lasers (VCSELs). As a result, epitaxially grown reflectors are attractive for direct integration in the device, reduced processing requirements, and the formation of narrow cavities. In the III-Nitride material system, Aluminum Nitride (AlN) and Gallium Nitride (GaN) offer a large contrast in refractive index and are therefore well suited for fabricating DBRs with high reflectivity and wide bandwidths using relatively few periods. However, material cracking arising from to the 2.4% lattice mismatch and difference in thermal expansion coefficient decreases reflectivity and is detrimental to the efficiency of subsequent device fabrication. Several techniques, such as superlattice insertion layers or the growth of AlxIn1-xN layers, have been employed to reduce strain and cracking in such structures. In this work, results of the use of indium as a surfactant in the Metal Organic Vapor Phase Epitaxy (MOVPE) of AlN/GaN DBRs will be discussed. Specifically, this study targets AlN/GaN DBRs with peak reflectivity at ranging from 465 nm to 540 nm. Indium has been used as a surfactant during growth by introducing trimethylindium into the system. It has been shown that crack formation is dependent on the flow of the indium precursor despite minimal indium incorporation into the lattice. Image processing techniques were used to quantify the crack length per square millimeter and it was observed that indium has a significant effect on the crack formation and can be used to reduce the total crack length in these structures by a factor of two.
Distribution of Hydrogen- and Vacancy-Related Donor and Acceptor States in Helium-Implanted and Plasma-Hydrogenated Float-Zone Silicon
Authors: Job Reinhart , Niedernostheide Franz-Josef , Schulze Hans-Joachim , Schulze Holger
Published: February 2010

The formation and evolution of hydrogen- and vacancy-related donor and acceptor states were studied in helium-implanted and subsequently hydrogen plasma-treated n-type Float-Zone (FZ) silicon wafers by means of two-point-probe Spreading Resistance (SR) measurements. He+-implantation was executed at 3.75 MeV and 11 MeV at fluences of 1×1014 cm−2. Post-implantation 13.56-MHz RF-plasma hydrogenations were carried out at 150 W either for 15 min or 1 hour, applying substrate temperatures between 350 °C and 500 °C. Enhanced donor concentrations as well as acceptor-like states were observed in the subsurface layers of the treated FZ Si samples after 15-min post-implantation H-plasma exposures. Under appropriate process conditions, the latter ones compensated for the n-type doping, so that even buried p-type layers were created. The experimental results indicated that oxygen played a central role in the formation of the acceptor-like states.
Low Temperature Copper Deposition by PE-ALD
Authors: Mao Jiajun , Eisenbraun Eric , Omarjee Vincent , Lanslot Clement , Dussarrat Christian
Published: February 2010

With the continuing scaling in device sizes, sputtered copper is not expected to achieve the conformality and surface coverage requirements to be an effective seed layer for electrochemical deposition in sub-32nm features. Additionally, the metallization demands of high aspect ratio TSVs in 3D-architectures pose similar challenges. In this work, a manufacturable low temperature Cu PE-ALD process has been developed employing a novel O and F-free precursor. The ALD process conditions are correlated with key film properties, including deposition rate, composition, step coverage, and resistivity. Additionally, the influence of precursor substituents on the deposition rate and preliminary integration performance are discussed.
Low Frequency Noise Correlation between Electrical and Optical Signals for Predicting Degradation in Organic Light Emitting Diodes
Authors: Chua Soo Jin , Huang Sha , Ke Lin
Published: February 2010

The Low Frequency Noise (LFN) characteristics of Organic Light Emitting Diodes (OLEDs) were investigated in relation to device degradation. The standard layer structure of indium tin oxide (anode), hole transport layer, Alq3, Lithium Fluoride and Aluminium (cathode) was used. With duration of operation, the device degradation is characterized by an eventual drop in the luminance level and the electroluminescence efficiency. Additionally, the driving voltage at a fixed current and the LFN increase gradually during device degradation, accompanied with the formation of non-emissive areas (dark spots). It is found that the coefficient of correlation between voltage fluctuations across the device and low frequency fluctuations of the optical signals remains constant for an initial period and then decreases exponentially with duration of operation and is a sensitive parameter to predict OLED device lifetime. For a number of OLEDs driven at constant current, the device with higher initial correlation coefficient possesses a longer lifetime. The direct relation between LFN correlation and device lifetime can be explained by carrier recombination mechanisms at the microscopic level. An increase in trap density can reduce the internal radiative recombination rate which at the macroscopic level is reflected by a decrease in the correlation coefficient.
Synthesis and Characterization of Tb-doped AlBNO Films for Electroluminescence Devices
Authors: Masumoto Keiko , Iwano Yuta , Kimura Chiharu , Aoki Hidemitsu , Sugino Takashi
Published: February 2010

Tb-doped AlBNO (AlBNO:Tb) films with various composition ratios are investigated for luminescence layers of inorganic electroluminescence(EL) devices. Luminescence layers with a wide bandgap and a low dielectric constant are required to realize high performance of EL devices. The ultraviolet-visible radiation absorption measurement and capacitance-voltage (C-V) measurement show that the AlBNO:Tb films have wider bandgap and lower dielectric constant than ZnS which is put to practical use as the host material of the luminescence layer. Photoluminescence (PL) measurement indicates that PL intensity increases with increasing B composition ratio in the range of 5 % - 10 %. Moreover, the suppression factor of the PL intensity can be understood through the annealing experiment. The PL intensity of the film with 800 °C annealing is about 10 times larger than that of the film without annealing. X-ray photoelectron spectroscopy (XPS) measurement suggests that Tb4+ ions decrease compared with Tb3+ ions after annealing treatment. O atoms in the AlBNO:Tb film are dissociated from Tb and bonded to B atoms by annealing treatment. This suggests that decrease of Tb4+ ions is related to increase of the PL intensity.
Pre-applied Inter Chip Fill Material and Process for Advanced 3D Chip Stack
Authors: Horibe Akihiro , Yamada Fumiaki
Published: February 2010

To pursue further performance improvement of semiconductor devices, threedimensional (3D) chip integration with TSV would be one of the key technologies in the next decade. Inter Chip Fill (ICF) is a resin to fill gaps between chips, and it would be an important component for highly reliable and durable 3D integrated devices. High performance 3D devices require fine pitch interconnections with small bumps for high pin count with high bandwidth. Smaller bumps lead to narrow gap design between stacked chips inevitably, and the narrow gap is expected to reduce heat resistance and thermo-mechanical stress. However it makes resin filling and flux cleaning processes harder. A preapplied ICF process is one of the potential methods to fill the narrow gaps with a resin. The material is halfcured resin applied on a wafer by spin-coating or film-lamination before chip integration. Flux cleaning process can be eliminated by adding fluxing function in the resin components. Major concerns of multiple chip 3D stacking process are repeated high temperature cycles of metal-joining, and long process time as a result. We are proposing “Stack Joining process” that enables 3D multi chip joining at one time instead of sequential chip by chip joining. In this process, multiple chips are aligned and temporarily stacked sequentially using adhesivity which the ICF has between Tg and initiation temperature of polymerization, and finally all metal bumps of stacked chips are melted and joined altogether. This process can substantially reduces repeated high temperature cycles and process time. As a result this technique could mitigate degradation of device materials.

We successfully stacked chips by using the pre-applied ICF which was designed for advanced 3D chip stack having full area array and narrow gap (less than 10um) connections. In this paper, we explain the Stack Joining process flow and conditions. We also discuss the cause of mechanical stress within the stacked chip and required material features of the pre-applied ICF and device structure to reduce the stress.
Determination of Defects Concentration from C-V and G-V Curves in a MOSFET Structure
Authors: Abboud Nadine , Habchi Roland
Published: February 2010

The gate oxides of Si based MOSFET devices are subjected to a high field in order to induce defects in the oxide bulk and at the Si/SiO2 interface. The defects are characterized by a series of gate to source capacitance and conductance measurements. Shifts in the flat band voltage and the threshold voltage are observed and are related to the position of charged defects. The difference of the equivalent charge between the two types of defects is also determined. Conductance measurements are performed to determine the difference of interface states concentration as a function of the high field exposure time.
Uniaxial magnetic anisotropy induced by vicinal surfaces in half metallic La0.7Sr0.3MnO3 thin films
Authors: Perna Paolo , Jiménez Erika , Terán Francisco J. , Méchin Laurence , Camarero Julio , Miranda Rodolfo
Published: February 2010

We present a detailed study of the angular dependence of the magnetization reversal at room temperature of well characterized epitaxial La0.7Sr0.3MnO3 (001) thin films grown onto SrTiO3 (001) vicinal substrates. The step edges at the substrate surface promote a topological modulation of the films along the step direction, breaking the four-fold magneto crystalline symmetry and favoring a two-fold magnetic anisotropy term. The competition between the biaxial and uniaxial anisotropy is depicted within the framework of the current theory, resulting in a vanishing biaxial contribution. The films hence show the magnetization easy (hard) direction parallel (perpendicular) to the steps direction. The thickness-dependent of both anisotropy and magnetization reversal are discussed in terms of topographic changes.
Switching characteristics and magnetoresistance of Co-based multilayered perpendicular magnetic tunnel junctions
Authors: Tadisina Zeenath Reddy , Natarajarathinam Anusha , Gupta Subhadra
Published: February 2010

Perpendicularly magnetized magnetic tunnel junctions (pMTJ) using Co based multilayers as free and reference layers have been optimized for perpendicular magnetic anisotropy (PMA) and high tunneling magnetoresistance (TMR). The effect of seed layers, Co thickness and Co/Ni thickness ratio on the anisotropy of these multilayer films has been studied. Intermixing of these multilayers was analyzed by local electrode atom probe (LEAP). The effect of Co thickness, Pd thickness and number of Co/Pd bilayers on the anisotropy and coercivity of the [Co/Pd]n multilayer films have been studied for both free and reference layers. The magnetic behavior of these PMA systems was studied by alternating gradient magnetometer. CoFeB/MgO/CoFeB trilayers sandwiched between the PMA multilayer material systems were studied. The transport properties of the patterned MTJ stacks were measured by PPMS from 10K to 400 K. A maximum TMR of 10% at 10K (5-10% at 300 K) was obtained for these perpendicular MTJ’s (pMTJ), regardless of whether they were magnetically annealed for MgO-CoFeB crystallization or not, indicating that the fcc-bcc-fcc transitions from the fcc multilayers to the bcc CoFeB/MgO/CoFeB do not promote the “giant MgO TMR effect” caused by symmetry filtering.
Single Molecular Magnet - Gold Nanoparticle Composites
Authors: Balaji Gopalan , Bovenkamp Gudrun , Palshin Vadim , Kumar Challa
Published: February 2010

The past decade has witnessed a great interest in single molecule magnets (SMM) especially those based on manganese such as Mn12-acetate due to their potential applications in ultrahigh density data storage and quantum computing devices. The focus so far has been in finding different derivatives of Mn or other complexes based on transition elements in order to raise the blocking temperature of single-molecule magnets (SMMs). Herein we propose a fundamentally new approach of generating new category of SMMs through formation of composite structures by binding SMMs on to nanoparticles. In this report, we present the synthesis and characterization of single molecular magnet - gold nanoparticle composite- Mn12-cysteinate functionalized gold nanoparticles.
How does an Ultrathin Cobalt Film Response to the Presence of a Neighboring Pentacene Layer
Authors: Chan Yuet-Loy , Hung Ya-Jyuan , Wang Chia-Hao , Lin Ying-Chang , Chiu Ching-Yuan , Lai Yu-Ling , Chang Hsu-Ting , Lee Chih-Hao , Hsu Yao-Jane , Wei Der-Hsin
Published: February 2010

The interfacial regimes of cobalt/pentacene/cobalt (Co/Pc/Co) trilayers were emulated through the ultrathin pentacene/cobalt (Pc/Co) and cobalt/pentacene (Co/Pc) bilayers. Employing the magneto-optical Kerr effect (MOKE) measurement, we found the coercivity of Co bottom film in a thickness of 3.4 nm experienced a slight reduction upon the adsorption of Pc molecules. For the bilayers prepared with reversed order of deposition, the Co film deposited on a 6.4 nm Pc layer showed no observable ferromagnetic order at room temperature until its thickness reached 3 nm. After the onset of magnetic order, the x-ray images acquired on Pc/Co revealed a complicated magnetization patterns comparing to those observed on Co/Pc bilayers. Because the spin-polarized carriers will interact with the environment along their transport path, the presence of a non-magnetic layer and the occurrence of complicated domain structures suggested the spin-polarized carriers would experience a greater disturbance on their spin coherence when crossing the Pc/Co interface.
Electronic and Magnetic Properties of Small Co-O Quantum Wires
Authors: Pozhar Liudmila A , Mavromichalis Constantine
Published: February 2010

Electronic and magnetic properties of small Co-O atomic clusters (“quantum wires”) have been studied in the framework of the Hartree-Fock (HF) method. The obtained results indicate that non-stoichiometric Co - O molecules with more than two O atoms possess at least one remarkably stretchable O-O bond that may facilitate significant re-construction of such molecules to larger structures. This re-construction may result in energetically favorable spin re-alignment in “antiferromagnetic” HF singlet Co-O molecules converting the singlets to larger “ferromagnetic” HF triplets and pentets. Such a spin re-alignment is energetically favorable, and may happen at the antiferromagnet-ferromagnet interface in “critical” core (Co) – shell (CoO) exchange-biased nanoclusters, providing for minimization of the surface energy, and leading to a loss of exchange bias. The obtained results are in agreement with available experimental and computational data.
Magnetic and Electronic Properties of Fe0.1Sc0.9N/ScN(001)/MgO(001) Films Grown by Radio-Frequency Molecular Beam Epitaxy
Authors: Constantin Costel , Wang Kangkang , Chinchore Abhijit , Chia Han-Jong , Markert John , Smith Arthur R
Published: February 2010

Fe0.1Sc0.9N with a thickness of ˜ 380 nm was grown on top of a ScN(001) buffer layer of ˜ 50 nm, grown on MgO(001) substrate by radio-frequency N-plasma molecular beam epitaxy (rf-MBE). The buffer layer was grown at TS ˜ 800 oC, whereas the Fe0.1Sc0.9N film was grown at TS ˜ 420 oC. In-situ reflection high-energy electron diffraction measurements show that the Fe0.1Sc0.9N film growth starts with a combination of spotty and streaky pattern [indicative of a combination of smooth and rough surface]. After ˜ 10 minutes of growth, the pattern converts to a spotty one [indicative of a rough surface]. Towards the end of the Fe0.1Sc0.9N film growth, the spotty patterns transform into even spottier, but also ring-like indicating a polycrystalline behavior. Superconducting quantum interference device magnetic measurements show a ferromagnetic to paramagnetic transition of TC ˜ 370 – 380 K. We calculated a magnetic moment per atom of μ(Fe0.1Sc0.9N) = 0.037 Bohr magneton/ Mn-atom. Based on the carrier concentration measurements (nS(Fe0.1Sc0.9N) = 2.086 × 1019 /cm3), we find that iron behaves as an acceptor. Comparisons are made with similar MnScN (001)/ScN(001)/MgO(001) system.
The Interplay of Nanocontact and Electrical Properties of ZnO and InP Nanowires and Polyaniline Nanofibers
Authors: Lin Yen-Fu , Jian Wen-Bin
Published: February 2010

The interface problems in nanomaterial based electronics play important roles. We have learned that the nanocontact, due to its reduced contact area, could give a high electrical contact resistance and a nonlinear current-voltage behavior though the specific contact resistance is in the same order of magnitude as that of macroscopic contacts. Through the current-voltage and temperature behaviors, the nanocontact properties could be categorized into Ohmic and Schottky types. The electrical properties of the nanowire based two-probe devices could be rationalized as two Ohmic contacts, one Ohmic and one Schottky contacts, and two back-to-back Schottky contacts. Moreover, the nanocontact could be treated as a one-dimensional disordered electron system for further studies. After the intrinsic nanowire and contact resistances are separated from each other, the electron transport and the carrier concentration of native doping in ZnO and InP nanowires can be determined. The nanowires are determined to have low carrier concentrations, implying a high sensitivity to light and gas. The contact and nanowire dominated two-probe devices are exposed to light and gas to identify the contact effects. In addition to the inorganic nanowires, the organic nanomaterials, the HCl-doped polyaniline nanofibers, can be analyzed by using the same approach. The dielectrophoresis technique is implemented to position nanofibers into an electron-beam lithographically patterned nanogap. To shine the electron-beam on contact areas, the organic/inorganic nanocontact resistance is reduced so as to probe the intrinsic electrical property of a single polyaniline nanofiber.
Growing Zn0.90Co0.10O Diluted Magnetic Semiconductors by r. f. Sputtering System
Authors: Can Musa Mutlu , Firat Tezer , Özcan Şadan
Published: February 2010

Zn0.90Co0.10O particles, synthesized by mechanical milling and thermal treatment, were pressed at 25 tons to form a 2” target for a radio frequency (r. f.) magnetron sputtering system. Using this target, thin films were deposited on (0001) oriented sapphire (α-Al2O3) substrates under 30W, 60W and 120W r. f. powers. Structural analyses of these films were done with X-Ray Diffractometer (XRD), Energy Dispersive X-Ray Spectrometry (EDS), X-Ray Photo Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The ZnO films were deposited with (0002) preferred direction, which was coherent to (0001) ordered α-Al2O3. Impurity phases, such as Co clusters, CoO and Co3O4, were not detected with the surface analyses of Zn0.90Co0.10O thin films. Substituted Co atoms in the host ZnO matrix were identified by the binding energy peak of Co2p3/2, 781.3±0.4eV, and the energy difference of ∼15.61±0.03eV between Co2p1/2 and Co2p3/2. These results also proved that there were no Co clusters or Co3O4 phases in the lattice. Homogeneity of Co atoms in the lattice was shown by EDS spectra. It was understood that the higher r. f. power caused the more homogeneous distribution of Co and Zn atoms in thin films. Distributions of Co and Zn on the film surface, deposited under 120W, were found as 8.1±0.1% (normalized atomic ratio) and 91.7±0.7% (normalized atomic ratio), respectively, and the surface roughness of thin film was demonstrated by AFM figures as 14.2±0.1nm.
Effects of Growth Parameters on Surface-morphological, Structural, Electrical and Optical Properties of AZO Films by RF Magnetron Sputtering
Authors: Kuo Shou-Yi , Lin Wei-Ting , Chang Liann-Be , Jeng Ming-Jer , Lu Yong-Tian , Hu Sung-Cheng
Published: February 2010

500 nm-thick aluminum-doped zinc oxide (ZnO:Al) thin film is usually used as a front transparent conductive oxide (TCO) contact on photovoltaic devices, and for this application is often deposited by a reactive radio-frequency (r.f.) magnetron sputtering system from a ceramic target. This work reports on the preparation and characterization of AZO thin films on Corning 1737 glass substrates grown by reactive r.f.-magnetron sputtering from a ZnO ceramic target with 2 wt% Al content. It was found that the growth parameters, such as chamber pressure, working power, and deposition temperature, have significant influences on the properties of AZO films. According to the experimental results: (1) Films were polycrystalline showing a strong preferred c-axis orientation. (2) With increasing working power, the resistivity decreased, and mobility and the carrier concentration increased. (3) Lower deposition temperature leads to a decrease in resistivity, with 2.5×10-4 Ω-cm representing the lowest resistivity reached.
Nanoscale Modification of Graphene Transport Properties by Ion Irradiation
Authors: Giannazzo Filippo , Sonde Sushant , Raineri Vito , Rimini Emanuele
Published: February 2010

Single layers of graphene (SLG) mechanically exfoliated from highly oriented pyrolytic graphite and deposited on SiO2/Si were irradiated with C+ ions at different fluences (from 1013 to 1014 cm-2), in order to modify the transport properties in controlled way. Using a method based on scanning probe microscopy, local measurements of the electron mean free path (l) have been carried out both on pristine and ion irradiated SLG. A lateral inhomogeneity of l was found in both cases, with an increasing spread in the distribution of l for larger fluences. Before irradiation, the spread was explained by the inhomogeneous distribution of charged impurities on SLG surface and/or at the interface with SiO2. After irradiation, lattice vacancies cause a local reduction of l in the damaged regions.
Boron Doping in Hot Filament MCD and NCD Diamond Films
Authors: Zimmer Jerry , Hantschel Thomas , Chandler Gerry , Vandervorst Wilfried , Peralta Maria
Published: February 2010

Conductive diamond films are essential for electronic applications of diamond but there is still a poor understanding of the effects that growth conditions, grain size and film thickness have on the ultimate conductivity of the film. One of the unique advantages of hot filament diamond is the ability to grow both MCD and NCD films to moderate thicknesses over large areas with little or no change in morphological characteristics such as grain size. In addition the grain size of the film can be altered without the necessity of adding additional gases to the process or unduly increasing the carbon to hydrogen ratio. This gives us an opportunity to investigate electrical conductivity as a function of grain size and thickness within a simple methane, hydrogen, and boron chemical environment over areas which are large enough to support significant production levels of MEMS and other diamond based electronics. In this study the boron source was selected to be trimethyl boron gas to avoid any source of oxygen which could alter the growth conditions and to guarantee that any byproducts of the dopant would be primarily methyl based. The films were grown to various thicknesses up to 5 micrometers and grain sizes from NCD to full MCD at all thicknesses. This paper explores the effects of both grain size and film thickness on the electrical conductivity of the film as well as the absolute doping levels within the film.
The Outlook for Diamond in Raman Laser Applications
Authors: Mildren Richard Paul
Published: February 2010

Efficient and practical Raman lasers based on single crystal diamond are now realizable owing to the availability of optical quality crystals grown by chemical vapour deposition. In this paper, the performance characteristics of diamond Raman lasers is summarized and the results compared to other materials. The outlook for diamond Raman lasers is discussed and key challenges for material development highlighted.
Effect of Substitutional or Chemisorbed Nitrogen on the Diamond (100) Growth Process
Authors: Larsson Karin
Published: February 2010

The present paper outlines the energetic and kinetic effect by substitutional N, or by coadsorbed NHx (x =1, 2), on one of the key growth steps in the CVD growth mechanism of diamond (100); H abstraction by gaseous H radical species from the (100) surface plane. Theoretical calculations were performed based on Density Functional Theory under periodic boundary conditions. Substitutionally positioned N was shown to have a large effect on the H abstraction process. The H abstraction energy from the diamond surface was greatly improved with N positioned in C layer 2. In order to outline the effect by N on the growth rate, the barriers of energies were calculated. The barrier of abstraction was shown to substantially decrease with N substitutionally positioned in the second C layer, leading to an improvement of the abstraction reaction rate by approximately a factor of 3.
Surface potential of functionalised nanodiamond layers
Authors: Kratochvílová Irena , Taylor Andrew , Fendrych Frantisek , Kovalenko Alexander , Nesládek Milos
Published: February 2010

Carbon nanomaterials especially ultrananocrystalline diamond and nanocrystalline diamond films have attracted more and more interest due to their unique electrical, optical and mechanical properties, which make them widely used for different applications (e.g. MEMS devices, lateral field emission diodes, biosensors and thermoelectrics). Nanocrystalline diamond can also offer novel advantages for drug delivery development. Recent studies have begun to use nanocrystalline diamond for in-vivo molecular imaging and bio-labeling. To enable grafting of complex bio-molecules (e.g. DNA) the surface of ND requires specific fictionalization (e.g. H, OH, COOH & NH2). Due to the surface dipoles of functionalised nanodiamond band bending at the surface can be easily induced and from the measured band bending we can deduce the type of the fictionalization on the surface. The surface potential of H-terminated and OH terminated nanodiamond layers was investigated by Kelvin probe microscope. From the change of the surface potential value (as the departure of the material surface from the state of electrical neutrality is reflected in the energy band bending) the work function of the H-terminated nanodiamond layer was established to be lower than OH-terminated nanodiamond layer. The surface potential difference can be explained by the surface dipole induced by the electro-negativity difference between the termination atoms.
Deep UV Photodetectors fabricated from CVD Single Crystal Diamond
Authors: Bevilacqua Mose , Jackman Richard B.
Published: February 2010

Deep UV detection using a single crystal diamond (SCD) substrate without a homoepitaxial layer has been demonstrated using a defect passivation treatment. Despite evidence of surface damage on the SCD, the treatments lead to highly effective photoconductive devices, displaying six-orders of discrimination between deep UV and visible light and a responsivity as high as 100A/W, equivalent to an external quantum efficiency of 700, similar to the best values for devices based on high quality homoepitaxial layers. Impedance spectroscopic investigations suggest that the treatment used reduces the impact of less resistive surface material, most likely defects left from substrate polishing.
Diamond Photodiodes for X-ray Applications
Authors: Smedley John , Keister Jeffrey W. , Muller Erik M. , Jordan-Sweet Jean , Bohon Jen , Distel James , Dong Bin
Published: February 2010

Single crystal high purity CVD diamonds have been metallized and calibrated as photodiodes at the National Synchrotron Light Source (NSLS). Current mode responsivity measurements have been made over a wide range (0.2-28 keV) of photon energies across several beamlines. Linear response has been achieved over ten orders of magnitude of incident flux, along with uniform spatial response. A simple model of responsivity has been used to describe the results, yielding a value of 13.3±0.5 eV for the mean pair creation energy. The responsivity vs. photon energy data show a dip for photon energies near the carbon edge (284 eV), indicating incomplete charge collection for carriers created less than one micron from the metallized layer.
Electrospray Deposition of Diamond Nanoparticle Nucleation Layers for Subsequent CVD Diamond Growth
Authors: Fox Oliver J.L. , Holloway James O.P. , Fuge Gareth M. , May Paul W. , Ashfold Mike N.R.
Published: February 2010

Nucleation is the rate-determining step in the initial stages of most chemical vapour deposition processes. In order to achieve uniform deposition of diamond thin films it is necessary to seed non-diamond substrates. Here we discuss a simple electrospray deposition technique for application of 5 nm diamond seed particles onto substrates of various sizes. The influence of selected parameters, such as experimental spatial arrangement and colloidal properties, are analysed in optimizing the method by optical and electron microscopy, both before and after nanocrystalline diamond deposition on the seed layer. The advantages and limitations of the electrospray method are highlighted in relation to other commonly exploited nucleation techniques.
Hydrogen Incorporation in MPCVD Nanocrystalline Diamond Films During the Deposition Process
Authors: Ballutaud Dominique , Pinault Marie-Amandine , Jomard François , Lusson Alain , Saada Samuel
Published: February 2010

Hydrogen incorporation is studied in two Microwave Plasma CVD nanocrystalline diamond films deposited with prolongated BIAS or not during the growth step. The hydrogen content and bonding forms are analysed by Secondary Ion Mass Spectrometry, Raman and Fourier Transformer Infrared Spectroscopy. Our results show a high hydrogen concentration up to 3.1021 cm-1, as expected in nanocrystalline diamond, and in good agreement with the sp2 phase rate measured by Raman spectroscopy . The FTIR spectra exhibit two sharp peaks at 2850 and 2920 cm-1 and show that a fraction of hydrogen is bonded to sp3 CH2 groups. Hydrogen desorption experiments are performed to analyse the local structure modification of the diamond films.
Development of Diamond-Based X-ray Detection for High Flux Beamline Diagnostics
Authors: Bohon Jen , Smedley John , Muller Erik M. , Keister Jeffrey W.
Published: February 2010

High quality single crystal and polycrystalline CVD diamond detectors with platinum contacts have been tested at the white beam X28C beamline at the National Synchrotron Light Source under high-flux conditions. The voltage dependence of these devices has been measured under DC and pulsed-bias conditions, establishing the presence or absence of photoconductive gain in each device. Linear response has been achieved over eleven orders of magnitude when combined with previous low flux studies. Temporal measurements with single crystal diamond detectors have resolved the ns scale pulse structure of the NSLS.
Transitions of Boron Carbide to B-C-N Thin Film
Authors: Bao Ruqiang , Yan Zijie , Chrisey Douglas B.
Published: February 2010

Boron carbon nitride (B-C-N) thin films are attractive due to their potential as hard coatings and as semiconductors with varying band gap. Both B-C-N (BC0.24N0.24) thin films and boron carbide (B4C) thin films were deposited by radio-frequency magnetron sputtering at room temperature. Also, the transition of boron carbide to B-C-N was studied by bombarding the boron carbide thin film by ∼1 uA/cm2 4 keV N+ ions. The results show that the UV-Vis transmittance of B-C-N thin films is better than that of amorphous boron carbide and both B-C and B-N bonds exist in our B-C-N thin films. The nitrogen in our B-C-N thin films bonded with boron causes the XPS B 1s core level to shift 2 eV from that in the B4C boron carbide thin film. Ion bombardment shows that the N+ ion primarily reacts with boron to form B-N and this reaction causes the environmental change of carbon in the thin film and then the XPS C 1s core level to shift to 283.5 eV from 282.8 eV.
Electrical Resistance of Single-Wall Carbon Nanotubes with Determined Chiral Indices
Authors: Lin Letian , Qin Lu-Chang , Washburn Sean , Paulson Scott
Published: February 2010

The properties of a carbon nanotube (CNT), in particular a single-wall carbon nanotube (SWNT), are highly sensitive to the atomic structure of the nanotube described by its chirality (chiral indices). We have grown isolated SWNTs on a silicon substrate using chemical vapor deposition (CVD) and patterned sub-micron probes using electron beam lithography. The SWNT was exposed by etching the underlying substrate for transmission electron microscope (TEM) imaging and diffraction studies. For each individual SWNT, its electrical resistance was measured by the four-probe method at room temperature and the chiral indices of the same SWNT were determined by nano-beam electron diffraction. The contact resistances were reduced by annealing to typically 3-5 kΩ. We have measured the I-V curve and determined the chiral indices of each nanotube individually from four SWNTs selected randomly – two are metallic and two are semiconducting. We will present the electrical resistances in correlation with the carbon nanotube diameter as well as the band gap calculated from the determined chiral indices for the semiconducting carbon nanotubes. These experimental results are also discussed in connection with theoretical estimations.
In-situ TEM-STM Observations of SWCNT Ropes/tubular Transformations
Authors: Solá Franscisco , Lebrón-Colón Marisabel , Ferreira F. , Fonseca Luis F. , Meador Michael A. , Marín Carlos J.
Published: February 2010

Single-walled carbon nanotubes (SWCNTs) prepared by the HiPco process were purified using a modified gas phase purification technique. A TEM-STM holder was used to study the morphological changes of SWCNT ropes as a function of applied voltage. Kink formation, buckling behavior, tubular transformation and eventual breakdown of the system were observed. The tubular formation was attributed to a transformation from SWCNT ropes to multi-walled carbon nanotube (MWCNT) structures. It is likely mediated by the patching and tearing mechanism which is promoted primarily by the mobile vacancies generated due to current-induced heating and, to some extent, by electron irradiation.
On the Relation of Mechanical Deformation and Electrical Properties of BN Nanotubes
Authors: Ghassemi Hessam , Lee Chee Huei , Yap Yoke Khin , Shahbazian Yassar Reza
Published: February 2010

Using a novel in-situ scanning tunneling microcopy integrated into a 200Kv transmission electron microscopy, we have shown that boron nitride nanotubes (BNNTs) posses remarkable flexibility and convert from insulator to semi-conductor upon bending. To measure the electrical properties, the BNNT was bent between two gold contacts constructing a metal-semiconductor-metal circuit. The resistivity of the BNNT under bending condition was measured to be ∼460 MΩ from the experimentally recorded current-voltage data. Our finding suggests that mechanical straining can improve the electrical transport in BN nanotubes via reducing the band gap.
Systematic Study of Work Functions of Single-walled Carbon Nanotubes
Authors: Kato Koichiro , Saito Susumu
Published: February 2010

The work function is one of the crucial quantities in understanding their field emission properties and applying carbon nanotubes to electronic devices. We perform the systematic study of work functions of 44 kinds of isolated single-walled carbon nanotubes in the framework of the density functional theory. It has been revealed that the first-principles study plays a very important role for predicting various properties of carbon nanotubes. In general, we have to perform the structural relaxation in order to know the accurate electronic properties of carbon nanotubes. Therefore we carry out the complete geometrical relaxations for 44 kinds of carbon nanotubes and evaluate their work functions. The diameters (D) of nanotubes studied satisfy 0.3 < D < 2.0 nm. Especially, we focus on the small diameter carbon nanotubes. We determine the values of work functions from the difference between the Fermi level and the vacuum level. In the semiconducting carbon nanotubes, the Fermi level is chosen at the midgap. As a result, it is found that the carbon nanotubes should be classified into three classes according to the diameter and chiral-angle dependences of work functions.
Field Emission Response from Multiwall Carbon Nanotubes Grown on Different Metallic Substrates
Authors: Lahiri Indranil , Seelaboyina Raghunandan , Choi Wonbong
Published: February 2010

Carbon nanotubes (CNT) have seen a wide variety of applications, spread well beyond the semiconductor industries - especially in field emission related devices. For its widest possible application, it has become very much important to grow CNTs on a variety of metallic substrates and understand their field emission response. In the present study, multiwall CNTs (MWCNT), grown on pure metallic substrates like Cu, Al and W, were subjected to field emission tests under DC and AC bias. Choice of diffusion barrier layer and catalyst was also varied, to verify their effects on the emission response. Field emission behaviors from all such structures were compared with MWCNTs grown on Si. It was found that the MWCNTs grown on pure Cu substrate showed excellent field electron emission response, in terms of low turn-on field, high emission current, long time stability and very high field enhancement factor.
Carbon Nanotube Assisted Electrical Treeing for Vascular Network Synthesis
Authors: Behler Kristopher D. , Wetzel Eric D.
Published: February 2010

Electrical treeing (ET) is a stepwise dielectric breakdown process that generates a branched, hollow network of tubules in the dielectric between the electrode and ground. In this study, the controlled growth of electrical trees (ETs) in epoxies is demonstrated as a technique for fabricating synthetic vascular systems in engineering materials. A number of experimental conditions are explored, including AC versus DC voltage and geometric arrangement of the electrode and ground. AC growth tends to induce highly branched, “bush-like” trees while DC growth tends to produce lower-order branched structures. In addition, treating electrode surfaces with multi-walled carbon nanotubes (MWCNTs) is shown to promote ET initiation, most likely due to enhancements in the local electric field intensity. The utility of these structures for vascular applications is demonstrated by filling the channels with dyed liquids.
The Effect of Reaction Driving Force on Copper Nanoparticle Preparation by Liquid Phase Reduction Method
Authors: Liu Qingming , Zhou Debi , Nishio Kazuaki , Salman Salah , Ichino Ryoichi , Okido Masazumi
Published: February 2010

Copper nanoparticle was prepared by liquid phase reduction technique. Cu2+ was reduced to copper particle by adopting different types of reductants. Ascorbic acid (C6H8O6), phosphinic acid (H3PO2), titanium sulfate (Ti2(SO4)3) and sodium borohydride (NaBH4) were chosen as reductant, respectively. The effect of reaction driving force upon the average size of copper particle was investigated in the paper. It can be concluded that there is a firm relationship between the reaction driving force and the average size of copper particle. The average size of copper particle decreases with the increasing of reaction driving force.
Core/Shell Composite of Self-Assembled Hierarchical Bismuth Oxide/Europium Doped Gadolinium Oxide for Scintillating Detection
Authors: Tseng Teng-Kuan , Choi Jihun , Davidson Mark , Holloway Paul H
Published: February 2010

A novel three dimensional (3D) self-assembled hierarchical bismuth oxide was prepared via a sol-gel synthesis with the aid of capping agent of polyethylene glycol-8000 (PEG-8000) at 85 ℃ in 45 min. The morphology evolution was studied versus reaction time and interpreted in terms of growth mechanisms. The as-grown 3D hierarchical flower-like bismuth oxide was crystalline cubic gamma-phase. The morphology and crystal phase of these 3D cubic gamma-phase bismuth oxide flowers were not changed with heating up to 600 ℃. The flower-like morphology was attributed to modification of the growth kinetics by the capping agent from the PEG-OH bond bridging with bismuth ions. Europium doped gadolinium oxide shell were further deposited on the bismuth oxide cores through sol-gel synthesis showing good photoluminescence characteristics at 610 and 622 nm under the excitation at 280 nm.
Fabrication of the Cerium Oxide Nanocrystal Film with Heterogeneous Ligand Structures
Authors: Hojo Daisuke , Togashi Takanari , Adschiri Tadafumi
Published: February 2010

Sufficiently dense films of cerium oxide nanocrystals modified with decanoic acid, with sizes of ˜9 nm, were fabricated on the surface by modifying a silicon substrate with 3,4-dihydroxyhydrocinnamic acid, where catechol group lied at the top. By doing this, no further pretreatment for the modified cerium oxide nanocrystals is required to fix them chemically on the substrate. Selective adhesion between nanocyrstals and the substrate for the two-dimensional assembly can be attributed to the chemical bonding formed by on-site ligand exchange between carboxyl and catechol groups.
Inter-molecular Electronic Transfer
Authors: Král Karel , Menšík Miroslav
Published: February 2010

The transport of electric charge is an important phenomenon in the systems like interacting quantum dots and molecules, and in polymers, including DNA molecules. We expect that in these nanostructure systems the key role is played by the interaction of the charge carriers with the optical phonons. We show the role of the multiple scattering of the charge carriers on the optical phonons in the inter-molecular transfer. The charge carrier transport based on this mechanism will be discussed theoretically and compared with the earlier experimental results on the charge transport in molecular Donor-Acceptor charge transfer crystals and also in other systems. In order to treat theoretically the electron transfer between two zero-dimensional nanostructures, we will use the model of two interacting quantum dots coupled by the electron inter-dot tunneling mechanism. A connection with the popular Marcus semiclassical charge transfer theory between molecules is also shown. We will use the nonequilibrium quantum electronic transport theory based on the nonequilibrium Green's functions.
Fabrication of Two Dimensional Array of Silica Nanospheres on GaN Using Spin Coating Method and Nomarski Image Processing
Authors: Lee Kyoungnae , yalamanchili hyma , Dawson J. M. , Korakakis D
Published: February 2010

Large-scale two dimensional ordering of silica nanospheres on GaN substrates was fabricated using spin-coating and observed using Matlab-based Nomarski image processing, which was developed to calculate the surface coverage of 2D and 3D ordering of silica nanospheres on GaN substrates. Optimal spin coating condition and SDS concentration were investigated with Nomarski image processing and an SEM. The details on spin coating process parameters or SDS concentration vs. surface coverage of silica nanospheres on GaN substrate are discussed, along with a theoretical exploration of the effects of nanosphere patterning on photonic crystals fabricated using this method.
Effect of Doping on the Structural and Optical Properties of Microwave-Assisted Synthesis of ZnSe@ZnS Core-Shell Quantum Dots
Authors: Bailon-Ruiz Sonia J , Perales-Perez Oscar , Singh Surinder P , Voyles Paul M
Published: February 2010

Pure and Cu-doped quantum dots of ZnSe@ZnS were synthesized in aqueous phase using microwave irradiation at 140 °C. X-ray diffraction analyses suggested the development of a ZnSe-ZnS structure. UV-vis measurements evidenced that the presence of Cu species in quantum dots caused the blue shift of exciton peaks with respect to pure, i.e. non doped ones. Photoluminescence spectra of quantum dots synthesized at Zn/Cu mole ratios of 1/0.001 and 1/0.005 exhibited a very strong emission peak centered on ˜ 515 nm. On the contrary, a weak emission peak was observed at 412 nm in pure ZnSe@ZnS quantum dots. The observed emission at 515 nm was attributed to the internal doping of Cu species, which should have induced d-d transitions in the host lattice. Quenching of the luminescence at 515 nm was observed for nominal Cu concentrations above 0.005 mM.
Synthesis and Properties of Monometallic and Bimetallic Silver and Gold Nanoparticles
Authors: Guerrero Dib Xavier Enrique , Ortiz-Méndez Ubaldo , Sepúlveda-Guzmán Selene , Kharisova Oxana Vasilievna , Ferrer Domingo , José-Yacamán Miguel
Published: February 2010

Synthesis of Au, Ag monometallic, and Au-Ag bimetallic nanoparticles have been synthesized by successive reduction of metal salts with ascorbic acid on prefabricated seeds in the presence of cetyltrimethylammonium bromide (C16H33)N(CH3)3Br (CTAB), as a cationic surfactant, is presented in this paper. This coverage method for the prefabricated seeds is uniform, although in some cases deviations from a spherical shape are observed with the formation of nanorods or nanoprisms. Results using high-resolution STEM-XEDS elemental mapping suggest that the actual distribution of the two metals within the multilayer spheres may involve partial alloying of the metals.