bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Plasma Damage on the Material Composition and Electrical Performance of Different Generations of SiOC(H) Low k Films
Authors: Humbert Aurelie , Badaroglu Didem Ernur , Hoofman Romano J.O.M
Published: April 2011

The degradation of SiOC(H) low-k films upon plasma treatments has been investigated. Three generations of SiOC(H) low-k dielectrics (k=3.0, k=2.6 and k=2.3) were used. The low-k materials have been exposed to N2O, NH3, O2, H2, He, Ar and N2 based plasmas, representing the most commonly-used plasmas during interconnect integration. For all plasma-treated samples, an increase in k-value and decrease in breakdown voltage was observed. These observations could be attributed to chemical degradation, in particular to carbon depletion and OH-bond formation. The latter leads to moisture adsorption, which was confirmed by contact angle measurements and FTIR spectra. The N2O plasma treatment was found to be the most aggressive for all low-k dielectrics studied. It drastically increases the k-value and the leakage current and results in complete carbon removal on the top-surface. This effect is most pronounced on the most porous material. On the other hand, an in-situ helium plasma shortly after low-k deposition enhances the resistance to chemical degradation upon exposure to other plasmas, even for the most aggressive ones. For the argon and reactive pre-clean plasmas, only small compositional changes were observed. In conclusion, it can be said that not only the plasma treatments have to be tuned in accordance with the low k integration requirements, but also attention has to be paid to limit moisture absorption during integration.
Influence of Grain Orientation on the Microstructural Characterization in Cu During (self)-Anneal using a Surface Acoustic wave Technique
Authors: Sekiguchi Atsuko , Vanstreels Kris , DeMuynck Steven , D'Haen Jan , Brongersma Sywert H
Published: April 2011

This paper describes the influence of microstructure, or more specifically grain orientation and grain size, on the in-line monitoring of copper interconnect properties during (self)-anneal using surface acoustic wave spectroscopy (SAWS). In electroplated Cu after (self)-anneal the SAWS frequency is lower for samples annealed at higher temperature because of the lower porosity induced elasticity. In sputtered Cu, the SAWS frequency shows a clear correlation with grain size, which is induced by a strong re-orientation of the copper film from the as-deposited (111) texture (E=190 GPa) to a strongly (100) textured super grain structure (E=78GPa).
A Novel MO Precursor for Metal Tantalum and Tantalum Nitride Film
Authors: Sekimoto Kenichi , Furukawa Taishi , Oshima Noriaki , Tada Ken-ichi , Yamakawa Tetsu
Published: April 2011

A novel tantalum precursor, bis(ethylcyclopentadienyl)hydridocarbonyltantalum (Ta(EtCp)2(CO)H EtCp:ethylcyclopentadienyl), for chemical vapor deposition (CVD) and atomic layer deposition (ALD) was synthesized. The molecular structure of this precursor was determined by 1H and 13C NMR, IR, ICP-AES and elemental analysis. This precursor is liquid at room temperature, and its vapor pressure and decomposition temperature indicates that this precursor is suitable for CVD and ALD process.

The composition analysis of metal tantalum films deposited by thermal CVD revealed that the concentration of carbon was larger than tantalum. On the other hand, an argon plasma CVD technique reduced the carbon concentration drastically.
Cu Resistivity in Narrow lines: Dedicated Experiments for Model Optimization
Authors: Maitrejean Sylvain , Gers Roland , Mourier Thierry , Toffoli Alain , Passemard Gérard
Published: April 2011

As the dimensions of interconnects shrink, the confinement effects associated with a very small grain size lead to a significant increase in the resistivity of the metal. Cu resistivity models have been proposed using the classical Fuch and Sondheimer approach for surface effect, and the Mayadas and Shatzkes approach for the grain boundary effect. In these models, three adjustable parameters must be used. Good agreement between experimental data and models can easily be obtained. However, numerous fitting parameter sets can be used with equivalent fitting quality and opposite physical meaning. In this work, experiments dedicated to model parameter extraction are proposed and released. They are based on the used of Cu lines with various line widths and heights. Classical resistivity increase with line width and line height decrease is observed. The resistivity behaviour is modelled. In this case, limited fitting parameter options are obtained. For Cu narrow lines confined with Ta, these parameters suggest maximum surface effect, medium grain boundary effect and low impurity content inside the lines.
The Copper Corrosion and Sulfur Contamination Generated by a Three-Step Copper Chemical-Mechanical Polishing Process
Authors: Liu Chun-Ping , Ho Yen-Shih , Hu Tien-Chen , Tseng Bae-Heng
Published: April 2011

This article shows the root cause of Cu corrosion and sulfur contamination due sulfite vapor reflow through drainpipe of load cup to the original three-step Cu CMP equipment. Now, we provide a solution which to modify the arrangement of the drainpipe in original three-step Cu CMP equipment. This is an effective implement for reduction the defects of Cu corrosion and sulfur contamination from long-term observations.
Relationship Between Interfacial Adhesion and Dielectric Reliability of Cu Alloy Films
Authors: Yi Seol-Min , Jang Kwang-Ho , Huh Yong-Hak , Park Young-Bae , Joo Young-Chang
Published: April 2011

Cu alloy has been suggested to enhance reliabilites in future technology. To evaluate the effects of alloying elements on electrical and mechanical reliabilities, Mg and Ru were chosen as alloying elements. Because alloying elements to Cu should not increase resistivity over comparable value to pure Cu, the resistivity of pure Cu, Cu-0.7at%Mg alloy and Cu-2.2at%Ru alloy was compared. Time dependent dielectric breakdown (TDDB) under bias-temperature stress (BTS) tests were accomplished to evaluate the effect of alloying elements on dielectric reliability. The standard four point bending experiments were conducted to measure critical interfacial adhesion energy of conducting metal to SiO2. The relationship of the effect of alloying elements on reliabilities to distribution of alloying elements was analyzed using Auger Electron Spectroscopy (AES). Our results show alloying Mg to Cu can enhance reliability by forming self-passivating layer on its surface and interface while Ru does not.
Novel Reducing Chemistry for Supercritical Fluid Deposition of Copper
Authors: Momose Takeshi , Ohkubo Tomohiro , Sugiyama Masakazu , Shimogaki Yukihiro
Published: April 2011

We study new deposition chemistry in Cu-SCFD (supercritical fluid deposition), especially effect of acetone is investigated as reducing agent and additives into H2 reducing Cu-SCFD. Acetone reduction yields Cu film deposition onto Ru coated Si substrate, because Ru has catalytic effect to generate reducing agent from acetone. When acetone is added into H2 reducing chemistry, the solubility of precursor is enhanced approximately 50 %, which is so-called “entrainer effect”. Ethanol can enhance the deposition of Cu in H2 reduction chemistry, which is a solvent effect. Two effects of entrainer effect by acetone and solvent effect by ethanol works independently, without interfering each other.
Feasibility Study for Usage of Diluted Fluorine for Chamber Clean Etch Applications as an Environmental Friendly Replacement of NF3
Authors: Hellriegel Ronald , Hintze Bernd , Winzig Hubert , Albert Matthias , Bartha Johann W. , Schwarze Thomas , Pittroff Michael
Published: April 2011

Deposition steps in CVD and ALD applications usually not only cover the surface of the substrate surface but also the walls of the chamber inside. Regular removal of those residuals has to be done to obtain stable and repeatable deposition results with uniform surfaces at acceptable particle levels. The high requirements to sustain stable processes has lead to more frequent chamber cleans. NF3 has emerged as the main clean gas for remote clean applications. While it meets the above mentioned requirements and is considered to fit easily into the fab gas supply it is relatively expensive. The work presented here investigates argon/nitrogen diluted fluorine (F2) as an alternative clean gas with a significantly reduced environmentally destructive global warming emission (GWP). The cleaning behaviour with respect to different materials (SiON, TaN, TiN, W, SiO2) was studied. It is found that in general argon/nitrogen diluted fluorine achieves etch rates comparable to those obtained by NF3 when the comparison is based on the amount of fluorine transported into the reactor.
Silicon Microchannel Array as a Basis of Biosensor Device
Authors: Lomzov Alexander , Vandysheva Natalia , Bublikov Alexander , Pyshnyi Dmitry , Romanov Sergei
Published: April 2011

This work shows the possibilities of using the silicon-based microchannel array (Si-MCA) as a 3D-solid support of DNA probes and studying of application of optical methods for DNA hybridization direct analysis. It was obtained that amount of immobilized oligodeoxyribonucleotides on the Si-MCA surface is enhanced with lighting of Si-MCA microchannel. The sample of 160 μm thickness succeeded in immobilizing oligonucleotides 40 times as much as the standard glass slides having the same external surface. The application of Si-MCA as a carrier of DNA allows doing direct analysis of nucleic acids in infrared region by the FTIR method that essentially simplifies creation of a biosensor based on the Si-MCA. It is indicated that using of the Si-MCA as a diffraction grating in visible and UV spectra allows simplifying the spectral analysis of biochemical reaction. It was success confidently to distinguish the mediums differing on the refractive index by dn=0.006.
Electrospun Tungsten Oxide Nanofibers: Fabrication and Characterization
Authors: Wang Guan , Huang Xianrong , Yang Xiaoqing , Gouma Pelagia-Irene , Dudley Michael
Published: April 2011

Tungsten oxide nanofibers have been successfully fabricated in a way based on electrospinning technique. A DMF solution of Poly(Vinyl Acetate)(PVAc, Mw=500,000) was mixed with tungsten isopropoxide to form a viscous precursor solution. Composite nanofibers were obtained by electrspinning this viscous solution. By calcination of the composite fibers, pure tungsten oxide nanofibers were obtained with controllable diameters of around 100 nm. Morphology of the fibers has been characterized by SEM and TEM. The relationship between solution concentration and ceramic nanofiber morphology has been studied. The detailed structure evolution process has been investigated by synchrotron based in-situ XRD. Specific phases of the oxide nanofibers at various calcination temperatures have been obtained from the in-situ XRD spectrum.
Formation of Highly Porous Gas-sensing Films by In-situ Thermophoretic Deposition of Nanoparticles from Aerosol Phase
Authors: Sahm Thorsten , Rong Weizhi , Barsan Nicolae , Mädler Lutz , Friedlander Sheldon K. , Weimar Udo
Published: April 2011

Gas sensors based on tin dioxide nanoparticles show high sensitivity to reducing and oxidizing gases. Dry aerosol synthesis applying the flame spray pyrolysis was used for manufacture and directly (in-situ) deposit nanoparticles on sensor substrates. For the first time this technique has been used to synthesize a combination of two stacked porous layers for gas sensor fabrication. Compared to state-of-the-art techniques, aerosol technology provides a direct and versatile method to produce homogeneous nanoparticle films. Two different sensing layers were deposited directly on interdigital ceramic substrates. These porous bottom layers consisted either of pure tin dioxide or palladium doped tin dioxide. The top layer was a palladium doped alumina nanoparticle film which served as a chemical filter. The fabricated gas sensors were tested with methane, CO and ethanol. In case of CH4 detection, the pure tin dioxide sensor with the Pd/Al2O3 filter layer showed higher sensor signals and significantly improved analyte selectivity with respect to water vapor compared to single tin dioxide films. At temperatures up to 250°C the Pd-doping of the tin dioxide strongly increased the sensitivity to all gases. At higher temperatures the sensor signal significantly decreased for the Pd/SnO2 sensor with a Pd/Al2O3 filter on top indicating high catalytic activity.
Zinc Oxide Thin Films used as an Ozone Sensor at Room Temperature
Authors: Pimentel Ana Claudia , Gonçalves Alexandra , Marques António , Martins Rodrigo , Fortunato Elvira
Published: April 2011

In this paper we present results of intrinsic/non doped zinc oxide deposited at room temperature by rf magnetron sputtering able to be used as a semiconductor material on electronic devices, like for example ozone gas sensors and ultra-violet detectors. The produced films are polycrystalline with a c-axis preferential orientation parallel to the substrate. The films present a resistivity that varies from 4.0×10−2 Ωcm to 1.0×109 Ωcm depending on the deposition conditions used in this study (rf power density and oxygen partial pressure) without changing the optical properties (an average transmittance of 85 % and an optical band gap energy ≈3.44 eV). When exposed to UV light the sensor response exceeds more than 5 orders of magnitude recovering to the initial state in the presence of ozone. The sensitivity of the films is improved when the oxygen partial pressure increases and the rf power density decreases which are directly related to the structural properties of the films.
Nanoparticle Metal-Oxide Films on Microhotplate Platforms: Fabrication and Gas-Sensitive Properties
Authors: Tomchenko Alexey , Marquis Brent
Published: April 2011

In this presentation, we discuss the development of nanostructured sensor materials based on nanoparticulate metal-oxide suspensions deposited onto MEMS μHPs by microprinting. The preparation of the suspensions is described; the precise control over the thickness of the films through the composition of the metal-oxide suspensions is demonstrated. The procedure of microprinting is described. The deposited films are evaluated as chemical sensors. The sensor performance of the microsensors – sensitivity, stability, speed of operation, and selectivity – is compared with that of analogous traditional thick-film sensors.
Investigation of a Novel Light-blue-emitting Fluorescent Guest/Host System with Excellent Lifetime
Authors: van Gemmern Philipp , Grabowski Stefan P. , Boerner Herbert , van Elsbergen Volker , Löbl Hans-Peter , Young Edward , Heil Holger , Fortte Rocco , Becker Heinrich , Heuken Michael , Kalisch Holger , Jansen Rolf H.
Published: April 2011

In this work, organic light emitting devices (OLEDs) based on a blue-emitting fluorescent guest/host-system from Merck OLED Materials GmbH is investigated. OLEDs comprising a hole transport layer (HTL), the emissive film Merck Blue Host:Merck Blue Guest (MBH:MBG), a hole-blocking film and the electron transport layer (ETL) were prepared by vacuum thermal evaporation. The hole-blocking capabilities of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) and the host material MBH were investigated. By employing an additional HBL, the current efficiency could be increased from 5.7 to 7.4 cd/A. Furthermore, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) doping of the HTL was investigated. Devices with 4,7-diphenyl-1,10-phenanthroline (BPhen) or 1,3,5-Tris-(N-phenylbenzimidazol-2-yl)benzene (TPBI) as alternative ETLs were fabricated and conclusions were drawn regarding the charge balance in the devices. It was found that employing tris-(8-hydroxyquinoline) aluminum (Alq3) as ETL leads to the best lifetimes of about 2000 hours at a constant current of 20 mA/cm2 while p-doping in combination with BPhen as ETL leads to the highest efficiency of 5.7 lm/W max. and 4.4 lm/W at 1000 cd/m2.
Ultrafast Carrier Dynamics and Recombination in Green Emitting InGaN MQW LED
Authors: Cartwright Alexander N. , Cheung M. C-K. , Shahedipour-Sandvik F. , Grandusky J. R. , Jamil M. , Jindal V. , Schujman S. B. , Schowalter L. J. , Wetzel C. , Li P. , Detchprohm T. , Nelson J. S.
Published: April 2011

Time-resolved photoluminescence studies can provide useful information for the development of InGaN/GaN heterostructures for long wavelength visible emitters. In this paper, we present results of time-resolved photoluminescence from samples grown using two different approaches to achieve green emission from InGaN/GaN MQWs. In one approach, samples, with high indium incorporation, were grown on a high quality AlN substrate to achieve green emission. The resulting photoluminescence decay of the green luminescence is long-lived and non-exponential. Quantitative analysis showed that the decay has a stretched-exponential characteristic, typical of InGaN/GaN MQW with potential fluctuation along the growth plane. This carrier localization, in a structure with low defect density, proves to be an effective means to achieve green emission. In another approach, a piezoelectric Stark-like ladder effect is used. In this case, a methodical layer-by-layer growth homogeneity optimization process was adopted to achieve an optical transition below the electron to heavy-hole (e1hh1) transition when the quantum well is subjected to the strong piezoelectric polarization dipole. This approach has proven to be successful in achieving green luminescence on conventional sapphire substrates. The resulting photoluminescence decay at 14 K, of a sample grown by this approach, is single exponential and shorter in duration than the decay observed in the first approach. This exponential decay is consistent with previous AFM studies that revealed a homogeneous active region.
Effects of Nitrogen Reactive Species on Germanium Plasma Nitridation Processes
Authors: Sugawara Takuya , Sreenivasan Raghavasimhan , McIntyre Paul C.
Published: April 2011

Roles of reactive species of germanium and silicon plasma nitridation were investigated by comparing nitrogen plasma chemistry and oxynitride layer physical properties. In high pressure remote plasma nitridation process, hydrogen containing neutral radicals (NH* and H*) were important to nitride germanium and silicon substrates. This process required high substrate temperature to nitride germanium substrate, whereas silicon substrates could be nitrided at low substrate temperature. In low pressure RLSA plasma nitridation process, N2+ ion species acted as dominant reactive species. Using this process, germanium could be nitrided at low substrate temperature without hydrogen and high nitrogen concentration (~22at.%) GeON was obtained.
Wet Chemical Cleaning of Germanium Surfaces for Growth of High-k Dielectrics
Authors: Amy Sandrine Rivillon , Chabal Yves J , Amy Fabrice , Kahn Antoine , Krugg Cristiano , Kirsch Paul
Published: April 2011

One of the major difficulties preventing the wide use of germanium (epi or bulk) as a gate material is the poor stability of its oxide, leading to reproducibility and reliability issues. In contrast to silicon, the nature and thickness of Ge “native” oxides are history dependent, and most phases of germanium oxide are water-soluble. As a result, the procedures for passivating Ge surfaces with hydrogen (HF last) are more complex and less forgiving.

We have used infrared absorption spectroscopy and x-ray photoelectron spectroscopy to investigate the nature of oxidized and H-terminated Ge surfaces. The GeO2, GeO and GeC phases have been identified and quantified as a function of processing conditions. The stability of the H-terminated surfaces has been examined in air and in controlled environments. The H-passivated Ge surfaces are found to be much less stable in air than H-terminated Si surfaces.
Impact of TiN/HfO2 Integration on Carrier Mobility
Authors: Casse Mikael , Thevenod Laurent , Guillaumot Bernard , Tosti Lucie , Cosnier Vincent , Mitard Jerome , Reimbold Gilles , Billon Thierry , Mouis Mireille , Boulanger Fabien
Published: April 2011

We have investigated the impact of a metal gate (TiN) and high-k dielectric (HfO2) on the carrier mobility. We have shown that strong remote Coulomb scattering (RCS) due to charges in the HfO2 layer (either grown by ALD or MOCVD) mostly degrades the mobility at low/medium field. High amount of charges (>1013cm-2) is needed to explain the 30% degradation observed in devices with a thin interface layer. These additional coulombic interactions are effective for bottom oxide up to 2nm. We have developed a RCS model to fully explain the experimental data. The influence of the metal gate is also evidenced. The latter has a significative impact on the Si/SiO2 interface roughness, and may induce some additional coulombic interactions.
Ru/Ta Alloying Behavior and its Implications for Laminate Based CMOS Integration
Authors: Lisoni Judit G. , Schram Tom , Witters Thomas , Van Hoornick Nausikaa , Yamada Naoki , De Gendt Stefan
Published: April 2011

The microstructural and electrical characterizations of RuxTa1-x alloys obtained from Ru-Ta laminates are presented. The films were deposited on SiO2 and HfO2 and capped with TiN to avoid oxidation of the top surface. The alloys were attained by post-anneal thermal treatments in the range of 500-1000 °C in Ar atmosphere. Co-sputtered RuxTa1-x alloys were used as references. In particular, Ru0.4Ta0.6 phase could be obtained when the Ru-Ta laminate was annealed at 1000 °C. The alloying reaction is limited either by the tantalum nitride or oxide formation being the source for Nitrogen the TiN capping used on top of the stack and the Oxygen either the dielectric films or the one stuffing the films after exposure to the atmosphere.

Independent of the Ta content a mid gap work function was obtained. Measured WF's in laminate-obtained alloys and alloys themselves differ from other literature data, where a more n-type like WF are measured, and indicating process dependence. In the present study mid-gap or rather p-type work functions were found, 4.5 eV < WF < 4.9 eV.
Non-contact Corona-Kelvin based Metrology for High-k Dielectric Characterization with an Extension to Micro-Scale Measurement
Authors: Wilson Marshall , Marinskiy Dmitriy , Almeida Carlos , Kochey Joseph N. , Byelyayev Anton , Savtchouk Alexandre , D'Amico John , Findlay Andrew , Jastrzebski Lubek , Lagowski Jacek
Published: April 2011

In-line monitoring of the electrical properties of high-k dielectrics in logic or memory fab-lines has become increasingly important in the semiconductor industry. Non-contact corona-Kelvin based metrology can be used to affectively monitor in-line key dielectric properties. Furthermore, we present an important extension of this metrology to the micro-scale that allows measurement of dielectric properties on test sites as small as 40μm × 70μm. This is achieved through miniaturization of the corona charging apparatus and of the Kelvin probe without a sacrifice in precision or repeatability. Corona-Kelvin micro-metrology allows for the monitoring of the critical dielectric properties directly on product wafers that can then be returned to the fab-line for continued processing. Application examples are given for dielectric capacitance of advanced dielectrics and for the properties of an oxide-nitride-oxide (ONO) memory structure. In the latter case we demonstrate programming and erasing of the ONO structure realized by corona charging. We also use the measured flatband voltage and total charge to identify the location of the programmed charge at the first SiO2/Si3N4 interface in the ONO structure.
Highly Scalable ALD-deposited Hafnium Silicate Gate Stacks for Low Standby Power Applications
Authors: Swerts Johan , Deweerd Wim , Wang Chang-gong , Fedorenko Yanina , Delabie Annelies , Shero Eric , Zhao Chao , Maes Jan Willem , De Gendt Stefan , Wilk Glen
Published: April 2011

The electrical performance of hafnium silicate (HfSiOx) gate stacks grown by atomic layer deposition (ALD) has been evaluated in capacitors and transistors. First, scaling potential of HfSiOx layers was studied as function of composition and thickness. It is shown that the equivalent oxide thickness scales down with decreasing layer thickness and increasing Hf-content. The gate leakage (at Vfb-1V), however, is mainly determined by the physical layer thickness. For the same equivalent oxide thickness (EOT) target, the lowest leakage is observed for the layers with the highest Hf-content. Leakage values as low as 1x10-3 A/cm2 for an equivalent oxide thickness of 1.3 nm have been obtained. Second, the thermal stability against crystallization of the ALD HfSiOx has been studied and related to their electrical properties. The thermal stability of HfSiOx decreases with increasing Hf-content that necessitates the use of nitridation. The influence of various annealing conditions on the nitrogen incorporation is also studied. Finally, the effect of HfSiOx composition and postdeposition nitridation is discussed on transistor level. TaN metal gate transistor data indicate that nitridation reduces the gate leakage and that Hf-rich HfSiOx layers show the best scaling potential, i.e., highest performance for the lowest gate leakage.
Study of Magnetron Sputter Deposition of Metal Gate Electrodes
Authors: Ye Mengqi , Liu Dave , Ding Peijun , Hung Steven , Ahmed Khaled
Published: April 2011

A systematic study of magnetron sputter deposition of metal gate is presented. On-wafer probes were used to measure ion current and floating voltage. Charge monitoring wafers was used to evaluate charging damage. C-V measurements showed that the interface trap density of metal gated MOS capacitors was reduced with thicker dielectric layer thickness and with the insertion of ALD deposited buffer layer. Lower pressure, higher sputtering power, and pulsed DC sputtering were found to cause larger plasma damage to the ultra-thin dielectric layer, most likely due to increased energetic particle bombardment as a result of higher plasma density and higher ion and neutral energies.
Structural and Optical Properties of Amorphous Ge2Sb2Te5
Authors: Li Heng , Ju T. , Herring T. , Taylor P. C. , Williamson D. L. , Nelson M. J. , Inglefield C. E.
Published: April 2011

The optical and structural properties of amorphous sputtered films of Ge2Sb2Te5 depend strongly on the preparation conditions. Films grown at higher growth rates exhibit greater local strains as indicated by the slope of the optical absorption in the exponential “band-tail” region, but these films also incorporate smaller densities of oxygen impurities. At slower growth rates the band-tail slopes are sharper (smaller local strains) but there is greater oxygen incorporation. We will discuss several experiments that suggest that the local strain relief in the films grown at slower growth rates is due to a greater ability of the atoms to rearrange on the growing surface and not to increased oxygen incorporation. Small angle x-ray scattering experiments show that the films exhibit small elliptical “voids” with long axes perpendicular to the growing surface. The approximate dimensions of these voids are 3 × 20 nm. These films can be switched optically with little change in surface topography as measured by atomic force microscopy. Electron spin resonance measurements indicate that paramagnetic defects exist in some films but are either absent or below the detection limit (~ 1018 cm-3) in most films. The implications of these results for the switching mechanisms will be discussed.
Fast Photodarkening in Amorphous and Liquid Chalcogenide
Authors: Sakaguchi Yoshifumi , Tamura Kozaburo
Published: April 2011

Transient photo-induced optical absorption in amorphous and liquid As2Se3 was investigated using a nanosecond pulsed laser and a specially designed optical cell. The measurements have been performed in the second and minute domain and the nanosecond and microsecond domain. From the measurements in the second and minute domain using repeated illumination, we observed the accumulation of photo-induced absorption and the decay after stopping the illumination. The durable photodarkening was also observed after the decay. The accumulated photoinduced change becomes smaller with increasing temperature and approaches to be zero around the glass transition temperature. From the measurements in the nanosecond and microsecond domain, the transient photodarkening in the time domain responded for each pulsed laser was observed. This fast photodarkening was observed even in the liquid state. This is contrast to the cases of the durable photodarkening and the transient photodarkening in the second and minute domain. The origin of the observed photoinduced changes is discussed.
Phase Transformations in Bulk (Ge2Se7)88Bi5Sb7
Authors: Adriaenssens Guy J.
Published: April 2011

Annealing at 150 °C induces phase separation in amorphous (Ge2Se7)88Bi5Sb7 bulk samples. Spectrally resolved steady-state photoconductivity measurements indicate the presence of crystalline Bi2Se3 clusters in the annealed material, but also the subsequent gradual disappearance of this microstructure at room temperature. Similar annealing-induced metastable changes are observed in other elements of a (Ge2Se7)88BixSb12-x sample series.
Chemical Route Fabricated Magnetic Structure Exhibiting a Negative Permeability at Infrared Frequencies
Authors: Liu Hui , Zhao Xiaopeng
Published: April 2011

We propose a quasi-periodic dendritic resonant magnetic model that can be used for the realization of the negative permeability at infrared frequencies. The numerical simulation exhibits a magnetic response when the incident light is perpendicular to the plane of the model. The copper dendritic structures are prepared by the electro-deposition method. And the transmission spectrum of this dendritic structure shows a magnetic response at infrared frequencies with a maximum transmission ¨C7.95dB. Further studies demonstrate that the magnetic response relate to the fractal dimension of the dendritic structure to a certain extent.
Negative Permeability of Single-ring Split Ring Resonator in the Visible Light Frequency Region
Authors: Tanaka Takuo , Ishikawa Atsushi , Kawata Satoshi
Published: April 2011

Negative permeability of single-ring split ring resonator (s-SRR) is theoretically investigated in the visible light frequency region [1, 2]. To estimate magnetic responses of conductive elements precisely, we determined internal impedance by considering the delay of the current inside the metal structure. The increase of the surface resistivity, which is the real part of the internal impedance, results in the decrease of the resonator's Q-value. This means the degradation of the tunable range of the permeability. The increase of the internal reactance results in the reduction of the resonant frequency. In our calculation, the surface resistivity saturates at the inherent frequency of each metal as the frequency increases. On the silver case, the saturation value is 0.4 Ω and this value is remarkably smaller than that of gold and copper. On the other hand, the internal reactance is increasing as the frequency increases independently of metal. We concluded that the internal reactance is dominant factor to realize the negative magnetic permeability in the optical frequency region. We also show the frequency dependence of the magnetic permeability of s-SRRs. In the case of s-SRRs made of copper, the minimum value of the magnetic permeability becomes positive value at 550 THz even in the high filling factor condition (11%). In the case of s-SRRs made of gold, only on the filling factor was 11%, the minimum value of the magnetic permeability takes negative value in the entire visible range. On the other hand, the silver SRR exhibits negative magnetic permeability in the visible range even under the low filling factor condition of 3%. Moreover, we concluded that reducing the geometrical capacitance and using silver for SRR are necessary to realize the negative magnetic permeability in the visible light range.
Functionalisation of Textiles with Nanotechnology
Authors: Textor Torsten , Schröter Frank , Schollmeyer Eckhard
Published: April 2011

The present development of textile market is connected with an ever increasing demand for new functionalities for highly specific applications. At the same time, the industrial supply has been restricted to only a few types of synthetic fibers. Given that background, surface modification became one of the most important topics to create new textiles. Beside other techniques, the functionalisation of fibers by making use of concepts of the nanotechnology is part of our work for several years. Coatings based on nanosols and inorganic-organic hybrid polymers, derived from sol-gel process, have an immense potential for creative modifications of surface properties and can be applied with a comparatively low technical effort and at moderate temperatures. The coatings often combine properties of organic polymers with those of ceramic materials [1-11]. Therefore those hybrid polymers are of an enormous interest for technical textiles. The basic materials offer the opportunity to produce very hard but flexible coatings, especially by filling or modifying the networks with nano-particles. Approaches to modify these systems by various inorganic or organic substances can lead to a huge number of additional functionalities which are increasingly demanded from the textile industries [12-18]. Coatings of a thickness of less then one micron can act as effective barriers against chemical attacks, super-repellent surfaces can be created, or the wear-resistance of textile materials can be improved. Coatings incorporating nanoparticles as employed in sun creams protect sensitive polymers against decomposition due to ultraviolet radiation. Ballistic body wear based on fabrics protects against gun attacks but generally not against knives. For these products, thin coatings based on inorganic-organic hybrid polymers filled with alumina nanoparticles were found to give good stab-resistance. Further approaches deal e.g. with reversible photochromic coatings – coatings that change its color if irradiated with sun light -, (superpara-)magnetic hybrid polymers or medical systems based on porous sol-gel-coatings with immobilized drugs that are released in contact with skin. This paper will focus on approaches to improve ballistic body wear with respect to stab-resistance, UV-protection and water and oil repellence.
Suspension of Silver Oxide Nanoparticles in Chitosan Solution and its Antibacterial Activity in Cotton Fabrics
Authors: Hu Zhigang , Zhang Jin , Chan Wing Lai , Szeto Yau Shan
Published: April 2011

New stable silver oxide suspension in chitosan solution was prepared from a mixture of silver nitrate and chitosan in dilute acetic acid as precursor, in which the complex interactions between silver ion and chitosan was also investigated through various instrumentation method seriously. The suspension was charactized through laser scan, infrared ray spectroscopy (IR), ultraviolet-visible spectroscopy (UV-vis) and X-ray diffraction (XRD), which indicated that the interactions between silver and chitosan in its precursor were destroyed partially. The measurements of the nanoparticles through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) disclosed the spherical profiles of these silver oxide nanoparticles of 10-20nm in average. Cotton fabrics treated by this emulsion were entitled remarkable antibacterial activity against S aureus and E. coli at pH 5 and 7 with sightless color effect and good washing fastness.
Controlled Conductive Polymer Coating on Wood Microfibers via Layer-by-layer Nanoassembly
Authors: Agarwal Mangilal , McDonald John , Lvov Yuri , Varahramyan Kody
Published: April 2011

This paper reports on layer-by-layer (LbL) self-assembly of poly (3, 4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) conducting polymer on lignocellulose wood microfibers to make conducting paper. Polycation such as poly(allylamine hydrochloride) (PAH) was used with polyanionic PEDOT-PSS to construct the multilayers. The physical characterization of the microfiber was done using roughness step tester (RST) and surface profilometer (TENCOR). Thickness of the coated film was estimated using a quartz crystal micro-balance. Current – Voltage characterization was performed using a Keithley measurement system after each self-assembly of PEDOT-PSS to study the electrical properties of the coated film. It was observed that the conductivity of the microfiber was proportional to the number of polyelectrolyte bilayers deposited. The measured conductivities ranged from (1 to 5) × 10-3 Scm-1 to 1 to 10 Scm-1 for different bilayers of PEDOT-PSS on wood microfibers. It was also observed that the conductivity of the nano-coated fibers is dependent upon the salt concentration used in PAH polycations to from the multilayer. In this work we are developing scale integration from nano, to micro and macro (nanocoating-microfibers-macropaper). The results obtained show great promise for the development of smart paper technology and its contribution to the economic development of the nation.
Modified Cotton Fiber Surface for Apatite Growth and Cell Affinity
Authors: Fei Bin , To Shing Shun Tony , Qi Kaihong , Xin John H.
Published: April 2011

In order to bring widely distributed polysaccharides materials into more medical applications, cotton fiber surfaces were modified into substrates for apatite deposition. Using a solid phase reaction, cotton fibers were conveniently carboxylated in large scale. The carboxylated cotton fibers were coated by apatite in a biomimetic way. Through soaking in a concentrated simulated body fluid (SBF × 5), nano-size apatite particles rapidly and finely grew on the fiber surfaces. The nucleation and growth of apatite was investigated with the aid of scanning electron microscopy (SEM). In comparison to pure cotton, the cotton coated with apatite showed improved cell affinity to osteoblast-like cells.
Polypyrrole-coated Large Deformation Strain Fabric Sensor and its Properties Study
Authors: Cheng Xiaoyin , Tsang H. Y. J. , Li Y. , Leung M. Y. , Tao X. M. , Cheng X. X. , Xue P. , Yuen C. W. M.
Published: April 2011

Conductive-polymer coated fabrics have been investigated as intelligent materials in the past years. In this paper, a flexible fabric strain sensor coated with polypyrrole is reported, which is featured with high sensitivity, good stability and large deformation. It is fabricated by chemical vapor deposition at low temperature. The effects of temperature, humidity, acid and alkaline medium have been assessed. The conductivity-strain tests reveal the sensor exhibits a high strain sensitivity of ~160 for a deformation as large as 50%, while its good stability is indicated by a small loss of conductivity after the thermal and humidity aging tests, and supported by the slight change in conductivity and sensitivity over a storage of eighteen months. The acid and alkaline solution mainly decreased their initial conductivity but have the slight effect to their sensitivity. The flexible fabric strain sensor is expected to be a promising “soft” smart material in the smart garment, wearable hardware and biomedical applications.
Size-Related Plasticity Effects in AFM Silicon Cantilever Tips
Authors: Kopycinska-Mueller Malgorzata , Geiss Roy H. , Hurley Donna C.
Published: April 2011

We are developing dynamic atomic force microscopy (AFM) techniques to determine nanoscale elastic properties. Atomic force acoustic microscopy (AFAM) makes use of the resonant frequencies of an AFM cantilever while its tip contacts the sample surface at a given static load. Our methods involve nanosized silicon probes with tip radius R ranging from approximately 10 nm to 150 nm. The resulting radius of contact between the tip and the sample is less than 20 nm. However, the contact stress can be greater than a few tens of GPa, exceeding the theoretical yield strength of silicon by a factor of two to four. Our AFAM experiments indicate that, contrary to expectation, tips can sometimes withstand such stresses without fracture. We subjected ten tips to the same sequence of AFAM experiments. Each tip was brought into contact with a fused quartz sample at different static loads. The load was systematically increased from about 0.4 μN to 6 μN. Changes in tip geometry were observed in images acquired in a scanning electron microscope (SEM) between the individual AFAM experiments. All of the tips with R < 10 nm broke during the first AFAM experiments at static loads less than 1.6 μN. Tips with R > 40 nm plastically deformed under such loads. However, a group of tips with R from 25 nm to 30 nm neither broke nor deformed during the tests. In order to reach higher contact stresses, two additional tips with similar values of R were used in identical experiments on nickel and sapphire samples. Although the estimated stresses exceeded 40 GPa, we did not observe any tip fracture events. Our qualitative observations agree with more systematic studies performed by other groups on various nanostructures. The results emphasize the necessity of understanding the mechanics of nanometer-scaled bodies and the impact of size effects on measurements of mechanical properties on such scales.
Size-Dependent Elastic Moduli of FCC Crystal Nanofilms
Authors: Chang Shih-Hsiang , Chang I-Ling
Published: April 2011

A semi-continuum model is constructed to study the size effects on the mechanical properties of face-cubic-center crystal structure nanofilms. Unlike the classical continuum theory, the current model directly takes the discrete nature in the thickness direction into consideration. In-plane and out-plane Poisson's ratios as well as in-plane Young's modulus are investigated with this model. It is found that the values of the Young's modulus and Poisson's ratio depend on the film thickness and approach the respective bulk values asymptotically.
Stress Driven Rearrangement Instability of Crystalline Films with Electromechanical Interaction
Authors: Chung Peter , Clayton John , Cole Melanie M , Grinfeld Michael , Grinfeld Pavel , Nothwang William
Published: April 2011

It was demonstrated, on general thermodynamic grounds, that, in non-hydrostatically stressed elastic systems, phase and grain interfaces undergo morphological destabilization due to different mechanisms of “mass rearrangement”. Destabilization of free surfaces due to the combined action of mass rearrangement in the presence of electrostatic field has been well known since the end of the 19th century. Currently, morphological instabilities of thin solid films with electro-mechanical interactions have found various applications in physics and engineering. In this paper, we investigate the combined effects of the stress driven rearrangement instabilities and the destabilization due to the electro-mechanical interactions. The paper presents relevant results of theoretical studies for ferroelectric thin films. Theoretical analysis involves highly nonlinear equations allowing analytical methods only for the initial stage of unstable growth. At present, we are unable to explore analytically the most important, deeply nonlinear regimes of growth. To avoid this difficulty, we developed numerical tools facilitating the process of solving and interpreting the results by means of visualization of developing morphologies.
Properties of the surface-modified layer of plasma-oxidized poly(dimethylsiloxane)
Authors: Mills Kristen L. , Zhu Xiaoyue , Lee Donghee , Takayama Shuichi , Thouless M. D.
Published: April 2011

Exposure of poly(dimethylsiloxane) (PDMS) to oxygen plasma creates a thin, stiff surface-modified layer that reaches a submicron depth. Due to a significant modulus mismatch between the stiff surface-modified layer and the compliant bulk PDMS the surface-modified layer forms intricate patterns of surface buckles when under compressive stress and nano-cracks when under tensile stress. It is desirable to be able to design patterns of nano-cracks, or at least to have an understanding of them. Among the properties necessary to do this are the thickness and elastic modulus of the surface-modified layer. Due to the very small length scale of the surface-modified layer, it is a significant challenge to measure these properties. In this proceedings paper, a two-step method is described for determining the thickness and elastic modulus of the surface-modified layer using the atomic force microscope (AFM). First, nanoindentation is performed from which the bending stiffness of the surface-modified layer is calculated. Second, the surface-modified layer thickness is determined by using phase imaging on the cross-section of oxidized PDMS to map the region of the relatively stiffer surface-modified layer.
Synthesis of Silicon Carbonitride for the Machining of Resonant Nanomechanical Biosensors
Authors: Fishcer Lee M. , Wilding Neal , Gel Murat , Evoy Stephane
Published: April 2011

We report a study on the plasma-enhanced chemical vapor deposition of silicon carbonitride, as well as the resonant behavior of nanomachined SiCN structures. Films with thicknesses of 1 um, and 200 nm were deposited at varying gas ratios using ammonia (NH3), nitrogen (N2), and diethylsilane (DES) as precursors. X-ray photoelectron spectroscopy revealed high nitrogen and low carbon content in films deposited at high NH3:DES gas flow ratios. Selected samples annealed at varying temperatures experienced shifts in stress towards tensile of Δσ = 235 MPa, 432 MPa, 724 MPa, and 1140 MPa, at annealing temperatures of T = 400 °C, 500 °C, 600 °C, and 700 °C respectively. Infrared spectroscopy reported a loss of incorporated hydrogen as a mechanism of stress modulation. Resonant assaying of cantilevers fabricated from 200 nm-thick SiCN yielded root-modulus-over-density values of √(E/ρ) = 6.95 × 103 m/s and √(E/ρ) = 8.35 × 103 m/s, comparable to those of silicon.
Nanocomposites for Neural Interfaces
Authors: Kmecko Tanja , Hughes Gareth , Cauller Larry , Lee Jeong-Bong , Romero-Ortega Mario
Published: April 2011

We have fabricated micro-probes consisting of gold microelectrode sites (500 μm long and 12 μm wide) modified with conductive polymers and carbon nanotubes to achieve intimate contact with the nervous system. The fabrication process includes photolithography, electroplating and micromachining techniques. In order to obtain a high quality neural contact, we have investigated the preparation and characterization of neural interface materials. Electrochemical polymerization using potentiostatic and galvanostatic methods was used to optimize the surface of the metal electrode sites. Scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to study the surface morphology, electrochemical properties, and stability of electrodeposited polymers. Cytotoxicity tests using fibroblasts and Schwann cells were performed to evaluate the biocompatibility of the micro-probes and neural interface materials. Dorsal root ganglion (DRG) in vitro preparation was used to evaluate neuronal cell cell adhesion to the electrode. Polypyrrole (PPy) and poly(3,4-ethylendioxythiophene) (EDOT) with various thicknesses and dopants were deposited onto microelectrode sites from aqueous solution. Our results demonstrate that we can control the morphology, size and electrical properties of PPy and PEDOT by changing the polymerization conditions and adding dopant structures, such as chloride and carbon nanotubes (CNT). It was observed that the addition of carbon nanotubes favors the formation of nodules and increases the surface roughness. Also, electrochemical impedance spectroscopy revealed that conductive polymer composites lower the impedance of gold microelectrodes by three orders of magnitude. We found that PPy and PEDOT carbon nanotubes composite coated electrodes maintain intimate contact with axons. Using these conductive polymer composites, high quality nerve spike signals can be detected and electrical stimulation of axons can be achieved.