bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Interfacial Delamination on Channel Cracking of Brittle Thin Films
Authors: Pang Yaoyu , Huang Rui
Published: April 2011

Channeling cracks in low-k dielectrics have been observed to be a key reliability issue for advanced interconnects. The constraint effect of surrounding materials including stacked buffer layers has been studied. This paper analyzes the effect of interfacial delamination on the fracture condition of brittle thin films on elastic substrates. It is found that stable delamination along with the growth of a channel crack is possible only for a specific range of elastic mismatch and interface toughness. An effective energy release rate is defined to account for the influence of interfacial delamination on both the driving force and the fracture resistance, which can be significantly higher than the case assuming no delamination.
Wafer Level Chip Size Packaging Technology for Bulk Acoustic Wave Filters
Authors: Yamada Hajime , Aizawa Naoko , Fujino Hiroyuki , Koshido Yoshihiro , Yoshino Yukio
Published: April 2011

Wafer level chip size packages (WL-CSP) have been successfully fabricated for bulk acoustic wave (BAW) filters. WL-CSP has been completed at the wafer level prior to dicing. Two silicon wafers are used as a die and a lid for chip size packaging. Both device and lid wafers have the same expansion coefficient and the package is strong enough to withstand the thermal stress. The package has a hermetic seal with copper-tin intermetallic bonding. The bonded wafers are then thinned by grinding. Via holes are formed by reactive ion etching (RIE) and filled by copper electroplating. The package has solder bumps on each terminal, ready for flip-chip assembly. We have succeeded to produce CSP-BAW filters with a hermetically sealed cavity, which is 840 micrometers squared and 280 micrometers in height including solder bumps.
Texture Evolution and Stress in Silver Thin Films on Different Substrates Using X-ray Diffraction
Authors: Zoo Yeongseok , Alford Terry L.
Published: April 2011

Substrate surface roughness effects on Ag film texture were investigated using pole figure analysis. X-ray diffraction results confirmed that Ag thin films on smooth SiO2 substrates had strong {111} texture when compared with Ag films on PEN. It was noted that the difference of strain energy density (δEε) in Ag film on PEN (0.039 MPa) was almost 5 times greater than that on SiO2 (0.0084 MPa). The comparison between surface and strain energies revealed that the {111} texture of Ag thin film on SiO2 was explained by minimization of the surface energy and the weaker {111} texture of Ag on PEN was a result of reduced diffusion length of Ag adatoms on the rough PEN surface.
The Effects of the LDD process on Short-channel effects in Nanoscale Charge Trapping Devices
Authors: Kim Moon Kyung , Chae SooDoo , Kim Chung Woo , Kim Joo Yeon , Lee Jo-won , Tiwari Sandip
Published: April 2011

In the use of single/few electrons in distributed storage for non-volatile, low power, and fast memories, providing statistical reproducibility at the nanoscale is a key challenge since relative variance has dependence and the devices operate with limited number of storage sites. We have used defects at interfaces of dielectrics to evaluate this reproducibility and the performance of memories. These experiments show that nearly 100 electrons can be stored at 30 nm dimensions, sufficient for reproducibility, and that a minimum of tunneling oxide thickness is required to assure reliable retention characteristics. Different tunneling oxide thicknesses and the effect of LDD process are investigated to draw these conclusions.
Investigation of Resistive Switching at SrRuO3/Cr-doped SrZrO3/Metal Junctions
Authors: Lee Hwan-Soo
Published: April 2011

We have investigated charge transport properties with current perpendicular to the plane across the interface between a Cr-doped SrZrO3 perovskite oxide film and different top electrode metals. The measured resistance showed a wide variation depending on the top electrode metal, and suggested the interfacial properties with respect to contacting electrode metal kinds are responsible for the change in I-V characteristics (IVCs). The observed I-V curves were modeled with the equation I(V) = aV+bV2, where the variation of a was related to the work function of the metal whereas the variation of b was related to the oxygen affinity of the metal, consistent with space charge limited conduction through a defected interface. Additionally, the resistive switching was attributed to a change in both the a and the b coefficients. We speculate that voltage (or current) induced vacancy motion can account for a change in trap density in the oxide near the metallic electrical contact, and thus trapping or detrapping of charge carriers, showing the conductivity modulation across the junction.
Electrical Study of Ferromagnet Metal Gate MOS Diode: Towards a Magnetic Memory Cell Integrated on Silicon
Authors: Kanoun Mehdi , Benabderrahmane Rabia , Duluard Christophe , Baraduc Claire , Bruyant Nicolas , Achard Hérvé , Bsiesy Ahmad
Published: April 2011

This work focuses on electrical characterisation of NiFe/SiO2/Si diodes that can be used as spin injection into silicon for future spintronic devices. Capacitance-voltage characteristics show a large increase of the Si/SiO2 interfacial state density compared to Al/SiO2/Si diodes. This result suggests that nickel and/or iron may have diffused across the SiO2 layer. Consistently the current-voltage experimental characteristics can be accounted for by using trap assisted electron transport mechanism. These traps may be attributed to ferromagnet atoms in the oxide bulk.
Characterization of Sn, Zn, In, and Sb-Containing GeSe Alloys for Phase-Change Electronic Memory Applications
Authors: Campbell Kris , Davis Morgan G. , Peloquin Jeffrey M.
Published: April 2011

Two-terminal electronic devices consisting of stacks of chalcogenide layers containing GeTe, Ge40Se60, SnTe, or SnSe have shown promise for application as electronic phase-change memories (Campbell, K.A. and Anderson, C.M., Microelectronics Journal 38, 52–59 (2007)). Here, we report the synthesis of (Ge40Se60)100−zMz alloys where M = Sn, In, Sb, and Zn, and the corresponding bulk material Raman spectra and differential scanning calorimetry data in order to explore material compositions that might be useful for producing a multi-state phase-change memory device.
First-principles Calculations on the Zn1-xMgxO Window Layer Material for CIS Thin Film Solar Cells
Authors: Maeda Tsuyoshi , Shigemi Akio , Wada Takahiro
Published: April 2011

We have theoretically evaluated the phase stability and electronic structure of a Zn1-xMgxO solid solution. The enthalpies of formation for both the wurtzite and rocksalt phases of Zn1-xMgxO were calculated using a plane-wave pseudopotential method within the density functional formalism. For 0 < x < 0.5, the calculated enthalpies of formation (&[Delta]H) for the wurtzite phases were lower than those for the rocksalt phases. On the other hand, for x > 0.75, the &[Delta]H values for the wurtzite phase were larger than those for the rocksalt phases. This indicates that the wurtzite phase is more stable for a Zn1-xMgxO solid solution with 0 < x < 0.5, while the rocksalt phase is more stable for a solid solution with x > 0.75. The band gaps of a wurtzite Zn1-xMgxO solid solution increase with increasing Mg content. MgO substitution on Zn1-xMgxO largely affects the conduction band leaving the valence band nearly unchanged. The conduction band minimum (CBM) shifted to higher energy with increasing Mg content. These theoretical results qualitatively agree with the experimental results for Zn1-xMgxO thin films fabricated by RF magnetron co-sputtering.
Validation of the p-type Behavior of an Ag-doped ZnSe Film Grown Heteroepitaxially on GaAs(100) Substrate
Authors: Narushima Takashi , Yanagita Hiroaki , Orita Masahiro
Published: April 2011

To validate p-type semiconducting behavior in Ag-doped ZnSe, single-crystal films were grown on GaAs(100) substrates using an evaporation method with ZnSe and Ag2Se powder sources. The heteroepitaxial relationship between ZnSe(100) and GaAs(100) was observed using X-ray diffraction and transmission electron microscopy; secondary phases containing silver or silver selenide were not detected. A film doped with Ag at 1 1020 atm·cm-3 had a conductivity of 1.5 x 10-5 S·cm-1. The hot-probe test indicated p-type polarity, with a clear and reproducible rectifying characteristic demonstrated by forming a ZnSe:Ag/p-GaAs:Zn junction. The work function of a ZnSe:Ag film measured by ultraviolet photoelectron spectroscopy was 6.3 eV. The ZnSe:Ag film is suitable as an injection layer in widegap semiconductor devices and organic light-emitting diodes.
On the Origins of Impurities in CdTe-Based Thin Film Solar Cells
Authors: Emziane Mahieddine , Halliday Douglas P. , Durose Ken , Romeo Nicola , Bosio Alessio
Published: April 2011

We present a multi-element study of impurities in CdTe/CdS photovoltaic cells, aimed at understanding their origins and impact on devices. Our investigation was based on calibrated secondary ion mass spectrometry (SIMS) depth profiling, with Na, Zn, Sn, O, Sb, Si, Cl, In, Cu and Pb being studied. The solar cell structures were grown by sputtering and close-space sublimation, and some of them were further processed (CdCl2 and Br2-methanol) for the purpose of comparison. Using source materials of different purity allowed us to establish the origins of impurities. We found that some elements increased in concentration upon processing, namely Cl (x100), Na (x10), and In (x1.5). The concentrations of Si, Cu, Zn, Sn and Sb found in a processed device were largely unchanged - and are similar to those found in a high purity single crystal CdTe reference sample.
Optical Absorption at Digitally and Continuously Graded Indium Gallium Nitride Schottky Barriers
Authors: Praharaj Choudhury Jayant
Published: April 2011

We present numerical calculations of the optical absorption characteristics of graded Indium Gallium Nitride Schottky Barriers, and study their implications for photovoltaic and photodetector applications. We consider the two cases of digital and continuous grading because of their different effects on the collection of photo-generated carriers due to band discontinuities. Composition grading can achieve desired spectral response between the ranges of 0.7 eV and 3.43 eV afforded by the Indium Gallium Nitride alloy system. The presence of spontaneous and piezoelectric polarizations in this material system adds bulk and/or interface bound charges in graded layers. This has a non-trivial effect on the band profile seen by the photo-generated carriers. The layer thicknesses needed for optimal absorption characteristics are well above the theoretical critical thickness limits reported in the literature for abrupt heterojunctions. However, experimental data about critical thicknesses is scarce, especially for graded compositions. Therefore, we calculate the characteristics of the Schottky barrier for the case of spontaneous polarization only and also for the case of both spontaneous and piezoelectric polarization assuming no relaxation. The low or even negative Schottky barrier heights at low Gallium composition necessitates the use of high Gallium composition layers next to the metal, in order to suppress the excessive dark currents
Quantitative Measurement of Dopant Concentration Profiling by Scanning Nonlinear Dielectric Microscopy
Authors: Ishikawa Kenya , Honda Koichiro , Cho Yasuo
Published: April 2011

Using a scanning nonlinear dielectric microscopy (SNDM), we observed two standard Si samples with epitaxial staircase structures, which have known dopant density values calibrated by using secondary ion mass spectroscopy (SIMS). As the result, good quantitative correlation between dopant density values and SNDM signals was obtained without the phenomenon of contrast reversal effect, which is associated with conventional scanning capacitance microscopy (SCM) measurements. Thus, it is expected that SNDM will be an effective method for observing the quantitative measurement of two-dimensional dopant profiling on semiconductor devices.
SPM-based Electrical Characterization of Aged Waspaloy Microstructures
Authors: Kelekanjeri G. Siva Kumar V. , Gerhardt Rosario A
Published: April 2011

The results of SPM-based localized electrical examination of precipitation hardened Waspaloy microstructures using Electrostatic Force Microscopy (EFM) and Current-Atomic Force Microscopy (I-AFM) are reported herein. The measurements were conducted on two differently etched specimens with the same initial microstructure. Selective etching by preferentially removing the γ′ or the γ phase resulted in a non-uniform surface topography leaving the less reactive phase standing in relief relative to the depressed phase. The presence of a non-uniform surface topography affected the measured EFM response by causing an inhomogeneous surface voltage distribution. A non-linear tip-surface interaction could have further complicated the measured EFM response by making it non-localized. The EFM phase obeyed a supplementary behavior upon reversing the polarity of the DC bias. Using I-AFM, the tip current was found to be the highest at γ-γ′ interphase boundaries, which was attributed to the relaxation of the lattice atoms in the relief zone formed upon etching.
Green Light Emitting Diodes under Photon Modulation
Authors: Li Yufeng , Senawiratne Jayantha , Xia Yong , Zhu Mingwei , Zhao Wei , Detchprohm Theeradetch , Wetzel Christian M
Published: April 2011

With an external laser excitation, the electroluminescence (EL) of GaInN/GaN green light emitting diodes (LEDs) grown on sapphire by metal organic vapor phase epitaxy has been investigated. The EL was found significantly enhanced under this bias and the difference can not merely be attributed to additional photoluminescence (PL). Under 325 nm photon bias, the EL enhancement starts at its highest value and decreases along with an increase of the LED current. Under 408 nm and 488 nm bias, it increases first to a value smaller than that of the 325 nm bias and then decreases with a much lower rate along the current increase. The EL enhancement is attributed to the more efficient carrier injection into quantum wells (QWs) resulting from the screening of the QW polarization by photon bias. Therefore, an enhanced balance of majority and minority carriers was obtained resulting in a better radiative recombination rate. Meanwhile, the current-voltage characteristics show a negative current first and then a voltage reduction as forward voltage increases. The reverse photocurrent indicates carrier loss due to the solar cell effect in our LED device while at high current region the carrier loss is attributed to another effect controlled by the external electrical field. At the balance point of those two effects, the EL enhancement is the highest. These findings clarify the transition from highly efficient radiative recombination at low current density to the region of efficiency droop at high current densities.
Electron Band Structure of MnGaN
Authors: Alexandrov Dimiter , Dietz Nikolaus , Ferguson Ian , Yu Hang
Published: April 2011

Investigation of the properties of MnxGa1-xN semiconductor alloy is performed on the basis of LCAO electron band structure of this semiconductor. The authors model this alloy on the basis of Mn substitutions on Ga sites and it is identified that the ternary semiconductor MnxGa1-xN has two tetrahedral binary constituents – GaN and MnN. It is found that the sp3 hybrid orbital of the N atom attracts an electron from the 3d orbital of the Mn atom and thus the Mn-N bonding becomes of sp3 type. In this way the total electron spin of the 3d orbital of the Mn atom becomes 3/2, which determines that the energy levels 4F, 4D, 4P and 4G belonging to this orbital to be occupied. LCAO electron band structure of wurtzite MnxGa1-xN for points Γυc1 and Γυv15 (υ = 1, 2, 3, 4, 5) is calculated by previously developed method and the positions of the levels 4F, 4D, 4P and 4G in this structure are determined. It is found dependence of the total electron spin of the Mn atom on the position of the Fermi level in the electron band diagram of MnxGa1-xN. Also it is found that the total spin depends on electron inter-band transitions as well. The optical properties of the wurtzite MnxGa1-xN are determined as well.
New Metal Nitride Compounds: Can they be Synthesized at High-Pressures?
Authors: Kroll Peter
Published: April 2011

We apply our procedure of including nitrogen fugacity into thermochemical calculations to compute phase diagrams in the rhenium-nitrogen and ruthenium-nitrogen systems. The combination of first-principle and thermochemical calculations let us predict the sequential nitridation of Re at high-pressure/high-temperature conditions. At 3000 K, Re will react with nitrogen at about 32 GPa yielding ReN. Formation of ReN2 with CoSb2-type structure is predicted for pressures exceeding 50 GPa at this temperature. The recently proposed marcasite-type RuN2 will be attainable at 3000 K at pressures above 30 GPa from a mixture of Ru and RuN2.
Materials and Techniques of Thai Painting
Authors: Eremin Katherine , Stenger Jens , Khandekar Narayan , Huang Jo Fan , Betley Theodore , Aspuru-Guzik Alan , Vogt Leslie , Kassal Ivan , Speakman Scott
Published: April 2011

The materials and techniques employed in 18th to 20th century art works from Thailand have received little attention compared to those of other Asian countries, most notably China and Japan. A multi-disciplinary study of Thai manuscripts and banner paintings aims to characterize the materials used, inorganic and organic pigments and binders, and the painting techniques employed. Samples from these works have been analyzed by a range of techniques, including x-ray flourescence (XRF), Raman spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive microanalysis (SEM-EDS). The results suggest a change in palette from the 18th to 20th century due to the introduction of imported pigments, most notably emerald green, Prussian blue and chrome yellow, during the 19th and early 20th century. The analyses show that the green pigment used on most 18th century manuscripts is an organic copper salt, a hydrated copper citrate, which has not previously been identified on art works. The occurrence of this on a number of different art works suggests deliberate manufacture of this unusual pigment. The color of the copper citrates differs depending on their hydration state and they are easily dehydrated and re-hydrated. This suggests some alteration of the original manuscript pigments might be expected, raising questions as to the original color of the pigment and whether the visual appearance has altered with time. In order to assess this, the pigments found on the art works must be fully characterized and any variations identified. The study includes laboratory based sythesis with pure reagents and synthesis following a recipe for refinement of verdigris given in a 17th century Venetian manuscript.
Molecular Dynamics Study of Electron Irradiation Damages in Carbon Nanomaterials
Authors: Yasuda Masaaki , Majima Takashi , Kimoto Yoshihisa , Tada Kazuhiro , Kawata Hiroaki , Hirai Yoshihiko
Published: April 2011

Molecular dynamics (MD) studies are carried out to investigate the electron irradiation damages in carbon nanomaterials. The interaction between an incident electron and a carbon atom is modeled based on the Monte Carlo method using the elastic scattering cross section. The electron irradiation damages in graphen, graphite, single-walled carbon nanotube (SWNT) and carbon nanopeapod are demonstrated. The cross-links among the nanostructures caused by the knock-on effect are observed as typical damages. The dependence of the damages on the electron primary energy is also shown for the SWNT.
Stabilization Mechanisms in Multiwalled Peapods
Authors: Scipioni Roberto , Oshiyama Atsushi , Ohno Takahisa
Published: April 2011

We discuss the energetics of Double walled Carbon nanotubes (DWCNT) peapods as compared to their single walled (SWNCNT) counterparts. We show that filling DWCNT with C60 fullerenes is energetically more favourable than SWNTs. Essentially two mechanisms are responsible for this phenomenon: 1] the interalyer state between the tubes which acts as repository of charge, 2] The Van der Waals interactions with the outer tubes. We discuss in some details the first effect using pseudopotential DFT, LDA first principles simulations for the two peapods C60@(15,0) and C60@(15,0)-(24,0)
Carbon Cones - a Structure with Unique Properties
Authors: Helgesen Geir , Knudsen Kenneth D. , Pinheiro Jean Patrick , Skjeltorp Arne T. , Svåsand Eldrid , Heiberg-Andersen Henning , Elgsaeter Arnljot , Garberg Torgunn , Naess Stine Nalum , Raaen Steinar , Tverdal Merete F. , Yu Xiaofeng , Melø Thor Bernt
Published: April 2011

Large-scale production of perfect conical carbon nanostructures that are fundamentally different from the other nanocarbon materials, such as buckyballs and nanotubes, can be made using the so-called Kvaerner Carbon Black & Hydrogen Process. This involves pyrolysis of hydrocarbons using a torch plasma process. The carbon cones that occur appear in five distinctly different forms. In addition, disk-shaped particles may be produced. Here we report about the current status for the experimental research and theoretical modeling of these particles, which have properties different from the other known forms of carbon.
Fabrication of Closed packed Single-walled Carbon Nanotube film with nanometer thickness
Authors: Matsui Jun , Yamamoto Kohei , Miyashita Tokuji
Published: April 2011

Closed packed film of single-walled carbon nanotubes (SWCNTs) with nanometer thickness was fabricated using a liquid-liquid interface. SWCNT was solubilized into water using sodium dodecyl sulfate as a surfactant. The SWCNTs in SDS-water suspension were used as a water phase and n-hexane was added to the suspension to form a liquid-liquid interface. After addition of ethanol to the mix solution, SWCNTs were assembled at the interface. The film form at the interface was transferred onto a silicon substrate. The AFM image of the transferred film shows a closed packed SWCNT film with a few nanometers thicknesses.
Investigation of Blistering Phenomena in Hydrogen-Implanted GaN and AlN for Thin Film Layer Transfer Applications
Authors: Singh Rajendra , Scholz R. , Christiansen S. H. , Goesele U.
Published: April 2011

High dose hydrogen implantation-induced blistering phenomena in GaN and AlN have been investigated for potential thin film layer transfer applications. GaN and AlN were implanted with 100 keV H2+ ions with various ion doses in the range of 5´1016 to 2.5´1017 cm−2. After implantation the samples were annealed at higher temperatures up to 800°C in order to observe the formation of surface blisters. In the case of GaN only those samples that were implanted with a dose of 1.3´1017 cm−2 or higher showed surface blistering after post-implantation annealing. For AlN the samples those were implanted with a dose of 1.0´1017 or 1.5´1017 cm−2 displayed surface blistering after post-implantation annealing. Cross-sectional transmission electron microscopy was utilized to observe the microscopic defects that eventually cause surface blistering. Large area microcracks, as revealed in the XTEM images, were clearly observed in the case of both GaN and AlN after post-implantation annealing. A comparison of the hydrogen implantation-induced blistering in GaN and AlN has also been presented.
Growth and Characterization of InSb films on Si (001)
Authors: Tran Lien , Dobbert Julia , Hatami Fariba , Masselink W. Ted
Published: April 2011

The replacement of native oxides with deposited oxides in CMOS technology opens the door to replacing the Si with semiconductors without high-quality native oxides. For example, the use of InSb in logic applications could allow much lower operating voltages and power dissipation due to the InSb channels reaching saturation at significantly lower electric fields. Epitaxy of InSb onto Si could be done directly or using an intermediate layer such as GaP, GaAs, or InP. In the current work we describe the growth of InSb on Si (001) and discuss the structural and electrical properties of the resulting InSb films. The samples were characterized in terms of background electron concentration, mobility, deep level traps, Hall sensitivity, and x-ray rocking curve width.

Samples were grown using molecular-beam epitaxy in a Riber-Compact 21T system. Antimony was supplied with a Veeco valved cracker cell. Vicinal Si(001) substrates offcut by 4º toward [110] were prepared by repeated oxidation and oxide-removal and then loaded into the MBE system. After the substrate temperature had been increased to about 820ºC, the surface shows a clear 24 reconstruction and appears to be free of oxide. This reconstruction remains until the substrate temperature reaches 1015ºC, at which temperature a 21 appears, indicating a dominance of double-height steps. After allowing the substrate to cool to the intended growth temperature for InSb, it is exposed to cracked Sb, resulting in the surface going from 21 to 11. This 11 reconstruction remains throughout the subsequent InSb deposition. InSb was deposited with a Sb/In flux ratio of about 5 and a growth rate of 0.2 nm/s. We have investigated growth temperatures between 300 and 420ºC for growth. To prevent the formation of the defects we introduced in some samples GaSb/AlSb supperlattice buffer layer. The best structural quality has been achieved at a growth temperature of 420ºC using GaSb/AlSb supperlattice buffer layer, resulting in our best electron mobility of 2.6104 cm2/Vs for a 2m film at room temperature. The samples grown at 420°C have the narrowest x-ray rocking curve width (FWHM of about 950 arcsec). Deep level noise spectra indicate the existence of the deep levels. The sample with the best crystal quality and highest mobility has the lowest traps. The deep levels have a temperature dependent behavior.
GaN Electrochemical Probes and MEMS on Si
Authors: Heinle Ulrich , Benkart Peter , Daumiller Ingo , Kunze Mike , Sönmez Ertugrul
Published: April 2011

AlGaN /GaN HEMT structures were used for liquid and gas sensors. The sensitivity of pH sensors was determined after clean-in-place tests. A multigas measurement at 330°C is presented. A piezo-driven mechanical actor is demonstrated and used as a variable capacitor. GaN on silicon logic circuitry is demonstrated at 250°C.
High Optical Quality GaN Nanopillars Grown on (111) Si Using Molecular Beam Epitaxy
Authors: Vajpeyi Agam Prakash , Tsiakatouras G. , Adikimenakis A , Tsagaraki K. , Androulidaki M , Georgakilas Alexandros
Published: April 2011

The spontaneous growth of GaN nanopillars on (111) Si by plasma assisted molecular beam epitaxy has been investigated. The growth of GaN nanopillars on Si is driven by the lattice mismatch strain energy on Si and the high surface energy of the nitrogen stabilized (0001) GaN surface. A higher growth rate of nanopillars compared to a compact GaN film suggests the diffusion of Ga atoms from the uncovered substrate areas to the nucleated GaN nanopillars. The GaN nanopillars were characterized by field-emission scanning electron microscopy (FE-SEM), photoluminescence, and micro Raman spectroscopy. SEM image revealed that average diameter of GaN nanopillars was in the range of 70-100nm and an average height of 600nm. The photoluminescence (PL) spectra indicate the good emission property of the nanopillars. The low temperate PL spectrum exhibited an emission peak at 3.428eV besides a sharp excitonic peak. PL and Raman spectra indicate that GaN nanopillars are fully relaxed from lattice and thermal strain.
Nondestructive defect measurement and surface analysis of 3C-SiC on Si (001) by electron channeling contrast imaging
Authors: Picard Yoosuf N. , Locke Christopher , Frewin Christopher L. , Myers-Ward Rachael L. , Caldwell Joshua D. , Hobart Karl D. , Twigg Mark E. , Saddow Stephen E.
Published: April 2011

The electron channeling contrast imaging (ECCI) technique was utilized to investigate atomic step morphologies and dislocation densities in 3C-SiC films grown by chemical vapor deposition (CVD) on Si (001) substrates. ECCI in this study was performed inside a commercial scanning electron microscope using an electron backscatter diffraction (EBSD) system equipped with forescatter diode detectors. This approach allowed simultaneous imaging of atomic steps, verified by atomic force microscopy, and dislocations at the film surface. EBSD analysis verified the orientation and monocrystalline quality of the 3C-SiC films. Dislocation densities in 3C-SiC films were measured locally using ECCI, with qualitative verification by x-ray diffraction. Differences in the dislocation density across a 50 mm diameter 3C-SiC film could be attributed to subtle variations during the carbonization process across the substrate surface.
Fabrication and Characterization of Ferroelectric Polymer/TiO2/Al-doped ZnO Structures
Authors: Aizawa Koji
Published: April 2011

Characterization of 700-nm-thick poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)]/TiO2/Al-doped ZnO (AZO) structures on a glass substrate were investigated. In this study, the sputtered TiO2 films as insulator were used for the reduction of leakage current. The leakage current density of the fabricated Pt/P(VDF/TrFE)/AZO and Pt/P(VDF/TrFE)/170-nm-thick TiO2/AZO structures were approximately 8.7 and 3.9 nA/cm2 at the applied voltage of 10 V, respectively. In the polarization vs. voltage characteristics, the fabricated Pt/P(VDF/TrFE)/TiO2/AZO structures showed hysteresis loops caused by ferroelectric polarization. The remnant polarization (2Pr) and coercive voltage (2Vc) measured from a saturated hysteresis loop at the frequency of 50 Hz were approximately 12 μC/cm2 and 105 V, respectively. These results suggest that the insertion of TiO2 film is available for reducing the gate leakage current without changing the ferroelectric properties.
Organic Field Effect Transistor using BaTiO3-Mn Doped and P(VDF-TrFE) for Non Volatile Memory Application
Authors: Pattnaik Sambit , Garg Ashish , Katiyar Monica
Published: April 2011

Here, we report fabrication of an organic field effect transistor that can be used as a memory device. We have evaluated inorganic ferroelectric insulator manganese doped barium titanate(BTO), organic poly(vinylidene fluoride trifluoroethylene) P(VDF-TrFE), and their composite. The inorganic and organic ferroelectrics were fabricated using low cost process of spin coating followed by annealing to enhance crystallinity. The ferroelectric phase evolution is assessed by X-ray diffraction, MIM structure is used to study polarization behaviour and leakage current. Finally, OFETs are fabricated using thermal evaporation of 75 nm of pentacene. Gold electrodes of 70 nm were evaporated for the top contact devices keeping W/L=40. The OFET devices, for BTO/P(VDF-TrFE) composite insulator, showed memory effect with shift in threshold voltage of 8.5 ± 1.5V.
Resistive Electrical Switching of Cu+ and Ag+ based Metal-Organic Charge Transfer Complexes
Authors: Mueller Robert , Billen Joris , Katzenmeyer Aaron , Goux Ludovic , Wouters Dirk J. , Genoe Jan , Heremans Paul
Published: April 2011

Memory cells based on Cu+ and Ag+ metal-organic charge-transfer complexes, as for example CuTCNQ (where TCNQ denotes 7,7',8,8'-tetracyanoquinodimethane), are well known for their bistable resistive electrical switching since 1979. The switching mechanism however remained unclear for very long time. In this contribution we describe the different views (bulk vs. interfacial switching), give evidence for interfacial switching in the case of CuTCNQ, and present a model allowing explaining the bipolar resistive electrical switching by an interfacial effect, even for experiments considered until now as proof for bulk switching. The proposed switching mechanism is based on bridging of an ion-permeable layer (or gap) by conductive Cu channels, which are formed and dissolved by an electrochemical reaction implying monovalent Cu+ cations, originating from a solid ionic conductor (as for example CuTCNQ). The model was furthermore generalized to other memory systems consisting of a permeable layer and a solid ionic conductor, including also inorganic solid ionic conductors as for example Ag2S.
Reversible Electrical Resistance Switching in GeSbTe Thin Films: An Electrolytic Approach without Amorphous-Crystalline Phase-Change
Authors: Pandian Ramanathaswamy , Kooi Bart J. , Palasantzas George , De Hosson Jeff Th. M.
Published: April 2011

Besides the well-known resistance switching originating from the amorphous-crystalline phase-change in GeSbTe thin films, we demonstrate another switching mechanism named ‘polarity-dependent resistance (PDR) switching’. The electrical resistance of the film switches between a low- and high-state when the polarity of the applied electric field is reversed. This switching is not connected to the phase-change, as it only occurs in the crystalline phase of the film, but connected to the solid-state electrolytic behavior i.e. high ionic conductivity of (Sb-rich) GeSbTe under an electric field. I-V characteristics of nonoptimized capacitor-like prototype cells of various dimensions clearly exhibited the switching behavior when sweeping the voltage between +1 V and -1 V (starting point: 0 V). The switching was demonstrated also with voltage pulses of amplitudes down to 1 V and pulse widths down to 1 microsecond for several hundred of cycles with resistance contrasts up to 150 % between the resistance states. Conductive atomic force microscopy (CAFM) was used to examine PDR switching at nanoscales in tip-written crystalline marks, where the switching occurred for less than 1.5 V with more than three orders of resistance contrasts. Our experiments demonstrated a novel and technologically important switching mechanism, which consumes less power than the usual phase-change switching and provide opportunity to bring together the two resistance switching types (phase-change and PDR) in a single system to extend the applicability of GeSbTe materials.
Current Conduction Mechanism for Non-volatile Memory Fabricated with Conductive Polymer Embedded Au Nanocrystals
Authors: Lee Jong Dae , Seung Hyun Min , Han Byeong Il , Lee Gon-Sub , Park Jea-gun
Published: April 2011

Many researchers have investigated organic nonvolatile memory devices as one of candidates device for next generation nonvolatile memory because of their low-cost, flexible and simple fabrication. The memory phenomenon in these devices is based on the electrical bistability of the material, which has two resistance states. We report memory effect in organic molecules based on electrical bistability of the materials and the bistable phenomenon was observed in poly(N-vinylcarbazole) (PVK) layer, containing a high density of Au nanocrystals and sandwiched between Al electrodes. The device was fabricated on cleaned SiO2. First, Al for the bottom electrode was deposited on SiO2 substrate by thermal evaporation in a vacuum chamber (pressure ∼10−6 torr). The PVK was dissolved with chloroform, spin-coated on the Al electrode, and baked at 120¡ÆC for 2 min to evaporate the solvent away. Subsequently, a 5-nm-thick Au film was deposited on the PVK. Additional PVK was then spin-coated on the Au film and baked. Next, the device was cured at 300¡É for 2 h in air to produce the Au nano-crystals. This device showed good nonvolatile memory characteristics. It was confirmed that it shows several region of current levels, (ION, IOFF, IINTER). When the voltage increased from zero in the OFF state (low conductivity state), the current increased rapidly at the threshold voltage (Vth), and presented a regime of negative differential resistance (NDR) after writing. Moreover ON and OFF states could be set at voltages at Vprogram (or Vp) and Verase (or Ve), respectively, and could be read at 1 V. After the device was programmed by sweeping the voltage from 0 to Vp, the current followed the high conductivity state and stayed in the ON state. And the device was programmed by sweeping the voltage from 0 to Ve, the current followed the low conductivity state and stayed in the OFF state. Furthermore, they exhibited seven different reversible current paths (intermediate states) capable for approving electron charge or discharge on surface of Au nanocrystals by sweeping the voltage from 0 to VNDR. Our results demonstrate that the fundamental parameters of the device were stable; the values of Vth, Vp, and Ve were ∼2.8, ∼4, and ∼8 V, respectively. In particular, this device exhibited excellent nonvolatile memory behavior, with bistability (ION/IOFF) of >1×102 and an intermediate state for multi-bit operation. We suggest that the current conduction mechanism clearly follow space-charge-limited(SCLC) for low conductivity state, thermionic field emission for electron charge(writing) or discharge(erasing), and F-N tunneling after erasing.
Theoretical Research of Loop Formation Process in Conducting Polymers
Authors: Turaeva Nigora , Oksengendler Boris
Published: April 2011

Conducting polymers promise a wider range of successful devices than traditional semiconductors. Differing from the traditional semiconductors in conducting polymers the topology of the system may be significant. Some of the important features such optic and electric properties can be changed largely by loop formation. In this work the loop formation process in conducting polymers has been considered by means of the Green-function method for the electronic spectra fixing. It was shown that at the changing of connectivity of quasi-one dimensional simple polymer strand due to the loop formation two local electronic states are appeared in the electronic spectra of the system. We supposed such model can be important for optic properties of such polymer systems with loops, increase the reaction ability of local loop area, loop stabilization due to the electron-conformational interaction in conducting polymers.
Surface Polymerization of the Thiophen Molecules in Chemically Adsorbed Monolayer
Authors: Yamamoto Shin-ichi , Ogawa Kazufumi
Published: April 2011

Using the time-averaged dielectrophoretic force from an applied electric field, we have observed the assembly of a chemically adsorbed monomolecularlayer (CAM) into microwires, connections, and an electric path according to the location within field regions of a lithographically patterned array of two platinum (Pt) electrodes. A Pt electrode/monolayer/Pt electrode junction was fabricated by the self-assembly of a rigid monomolecular, namely 3-{6-{11-(Trichlorosilyl) undecanoyl} hexyl} thiophene (TEN) with thiophen groups, in the lateral direction between the Pt gap electrodes. The technique of a conductive probe AFM (CP-AFM) has been used to investigate the forward bias conduction properties of a TEN film grown by a wet process deposition on a glass substrate. The self-assembly depends on: (1) the ideal rigidity of the chemically adsorptive monomolecular layer (CAM) and (2) the strong affinity of the thiophen end groups of the CAM for the Pt electrode. The current–voltage (I–V) characteristics of the conjugated thiophen junction exhibited stepwise features at room temperature. The (I–V) characteristics can be explained as an electron transport through the junction. From the results in the atmosphere, the conductivity of a lateral conjugated polythiophen group was calculated to be 5.0×104 S/cm. Understanding and using these effects will allow the controlled fabrication and the positioning of microwires or connections at densities far above what is now achievable.
Effect of thermal annealing on the performance of polysilane based organic light emitting diode
Authors: Singh Ranbir , Katiyar Monica
Published: April 2011

Polysilanes, being ó bonded, are promising materials for emission in ultraviolet/near ultraviolet (UV/NUV) region and exhibit adequate charge mobility for fabricating practical devices. This study contributes to the understanding of the effects of thermal annealing on the performance of organic light-emitting diodes (OLEDs) made of poly (n-butylphenyl-silane) (PS-4). OLEDs having indium tin oxide (ITO)/poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) PEDOT: PSS/poly (n-butylphenylsilane) (PS-4)/lithium fluoride (LiF)/Al device structure were fabricated. PS-4 is spin coated and annealed for one hour at different temperatures (90-120°C). EL Spectra from these devices consists of white emission along with the UV peak. Current density-voltage (J-V), photoluminescence (PL) and electroluminescence (EL) spectra are also measured. White emission is significantly suppressed when PS-4 is annealed at higher temperature and threshold voltage is lowest at 110°C annealing temperature. This is correlated with PL emission and structural properties of PS-4 films. Surface morphology of PS-4 was measured using atomic force microscopy (AFM). The results are explained in terms of effect of annealing of polymer films on interchain interactions.
Low Mass Organic Semiconductor-polymer Dielectric Nanocomposites: Influence of the Guest-host Interactions on the OTFT Characteristics
Authors: Madec Marie-Beatrice , Crouch David J , Rincon-LLorente Gonzalo , Yeates Stephen G
Published: April 2011

The morphology and organic field effect transistor (OFETs) properties of two component blends of semicrystalline 6,13-bis(triisopropylsilylethinyl)pentacene (TIPS-pentacene) with selected amorphous and semi-crystalline low permittivity side chain aromatic insulating binders deposited at room temperature under vacuum from a good solvent are reported. When blended with an amorphous binder there is evidence from XPS for strong interaction between TIPS-pentacene and binder in the solidified film giving rise to twisted TIPS-pentacene crystals containing dislocations. Due to this strong interaction we see no evidence of segregation of TIPS-pentacene towards the active interface and hence we observe a rapid fall off in saturated hole mobility at a active concentration less than 50 wt-%. When blended with a crystalline binder there is no evidence from XPS of any interaction between TIPS-pentacene and binder in the solidified film. We propose that when a crystalline binder is used, which crystallizes more slowly from solution than TIPS-pentacene, we observe stratification of the active material to both interfaces and as a result an increase of saturated hole mobility to 0.4 cm2/Vs at 20 wt-% in isotactic poly(vinylbisphenyl). The potential application of the approach are in the formulation of low cost organic semiconductors whose solution and solid state properties can be fine tuned by careful binder selection.
Ionic Impurities in Poly(vinyl alcohol) Gate Dielectrics and Hysteresis Effects in Organic Field Effect Transistors
Authors: Egginger Martin , Irimia-Vladu Mihai , Schwödiauer Reinhard , Tanda Andreas , Bauer Siegfried , Sariciftci Serdar Niyazi
Published: April 2011

Poly(vinyl alcohol) (PVA) is a water based dielectric often used as a coating layer in paper industry. Due to its water solubility PVA is also interesting as gate insulator in organic field effect transistors. Depending on the preparation of the PVA gate, transistors with and without hysteresis can be produced, with applications in organic electronic circuits or memory elements. In the production of PVA, a major side product is sodium acetate, an ionic salt not completely removed during industrial purification. Such ionic impurities likely influence the hysteresis in PVA based organic field effect transistors. While a hysteresis is desirable in memory elements it is unwanted in transistors for electronic circuits. Ways to prepare transistors with a desired transfer characteristic are described, for example by using electronic grade products directly from the purchaser of PVA, or by employing PVA purified by means of dialysis. Measurements are performed with metal-insulator-metal (MIM) structures and organic field effect transistors (OFETs), where Buckminsterfullerene C60 is employed as organic semiconductor.
High-mobility Organic Single-crystal Transistors with Amorphous Fluoropolymer Gate Insulators
Authors: Uno Mayumi , Tominari Yukihiro , Takeya Jun
Published: April 2011

High-mobility rubrene single-crystal field-effect transistors are built on highly water- and oil-repellent fluoropolymer gate insulators. Roughness is intentionally introduced at the surface once to provide good adhesion to metal films and photoresist polymers for stable bottom electrodes. Before constructing interfaces with rubrene crystals, smoothness of the fluoropolymer surface is recovered by annealing at a moderate temperature to maximize mobility of the carriers induced near the interfaces. The estimated mobilities in the saturation region reproducibly exceeded 15 cm2/Vs for all the ten devices fabricated in this method and reach 30 cm2/Vs for the best two samples among them. The results demonstrate that the water-repellency and smoothness of the dielectric polymers are favorable in the excellent transistor performance.
Effect of Hot Band Annealing on Microstructure of Semi-Processed Non-Oriented Low Carbon Electrical Steels
Authors: Gutiérrez Emmanuel J. , Castañeda  , Rodriguez Armando Salinas
Published: April 2011

Effects of hot band annealing on the final microstructure and magnetic properties of cold rolled and annealed non-oriented grain Si-Al electrical steel strips are investigated. Microstructures are characterized using optical and scanning electron microscopy and magnetic properties are determined using a vibrating sample magnetometer. It is shown that annealing of hot rolled bands at temperatures between 800 and 850 °C causes rapid decarburization and development of a microstructure consisting of large columnar ferrite grains free of secondary particles. This microstructure leads, after cold rolling and a fast annealing treatment, to large grain microstructures similar to those observed in production scale, fully processed strips. It is observed that the final grain size increases with the final annealing temperature, leading to a significant improvement of the magnetic properties. Therefore, hot band annealing technology can be an attractive alternative processing route for the manufacture of non-oriented grain low carbon Si-Al processed electrical steel strips.
Quantitative Electronic Structure Analysis of α-AL203 Using Spatially Resolved Valence Electron Energy-Loss Spectra
Authors: MÜllejans Haral , Bruley J. , French R. H. , Morris P. A.
Published: April 2011

Valence electron energy-loss (EEL) spectroscopy in a dedicated scanning transmission electron microscope (STEM) has been used to study the Σ11 grain boundary in α-A12O3 in comparison with bulk α-A12O3. The interband transition strength was derived by Kramers-Kronig analysis and the electronic structure followed from quantitative critical point (CP) modelling. Thereby differences in the acquired spectra were related quantitatively to differences in the electronic structure at the grain boundary. The band gap at the boundary was slightly reduced and the ionicity increased. This work demonstrates for the first time that quantitative analysis of spatially resolved (SR) valence EEL spectra is possible. This represents a new avenue to electronic structure information from localized structures.
Nanoindentation on Contamination-Free gold Films Using the Atomic Force Microscope
Authors: Schaefer D. M. , Reifenberger R.
Published: April 2011

Nanoindentation experiments on high quality Au films were performed in vacuum using an atomic force microscope. In these experiments, elastic behavior was observed until loading forces greater than ∼ 20 nN were applied. For loads larger than this, systematic changes in the jump-to-contact, loading/unloading and lift-off regions of the data occur. These observations are consistent with a transition from elastic to inelastic behavior during indentation.