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Substrate Interface (substrate + interface)
Selected AbstractsUse of Reversal Nanoimprinting of Nanoparticles to Prepare Flexible Waveguide Sensors Exhibiting Enhanced Scattering of the Surface Plasmon ResonanceADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Dehui Wan Abstract A flexible surface plasmon resonance (SPR)-based scattering waveguide sensor is prepared by directly imprinting hollow gold nanoparticles (NPs) and solid gold NPs onto flexible polycarbonate (PC) plates,without any surface modification,using a modified reversal nanoimprint lithography technology. Controlling the imprinting conditions, including temperature and pressure, allows for the fine adjustment of the depths of the embedded metal NPs and their SPR properties. This patterning approach exhibits a resolution down to the submicrometer level. A 3D finite-difference time domain simulation is used to examine the optical behavior of light propagating parallel to the air/substrate interface within the near-field regime. Consistent with the simulations, almost an order of magnitude enhancement in the scattering signal after transferring the metal NPs from the glass mold to the PC substrate is obtained experimentally. The enhanced signal is attributed to the particles' strong scattering of the guiding-mode waves (within the waveguide) and the evanescent wave (above the waveguide) simultaneously. Finally, the imprinting conditions are optimized to obtain a strongly scattering bio/chemical waveguide sensor. [source] Large-area epitaxial silicon solar cells based on industrial screen-printing processesPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 8 2005Filip Duerinckx Abstract Thin-film epitaxial silicon solar cells are an attractive future alternative for bulk silicon solar cells incorporating many of the process advantages of the latter, but on a potentially cheap substrate. Several challenges have to be tackled before this potential can be successfully exploited on a large scale. This paper describes the points of interest and how IMEC aims to solve them. It presents a new step forward towards our final objective: the development of an industrial cell process based on screen-printing for >,15% efficient epitaxial silicon solar cells on a low-cost substrate. Included in the discussion are the substrates onto which the epitaxial deposition is done and how work is progressing in several research institutes and universities on the topic of a high-throughput epitaxial reactor. The industrial screen-printing process sequence developed at IMEC for these epitaxial silicon solar cells is presented, with emphasis on plasma texturing and improvement of the quality of the epitaxial layer. Efficiencies between 12 and 13% are presented for large-area (98,cm2) epitaxial layers on highly doped UMG-Si, off-spec and reclaim material. Finally, the need for an internal reflection scheme is explained. A realistically achievable internal reflection at the epi/substrate interface of 70% will result in a calculated increase of 3,mA/cm2 in short-circuit current. An interfacial stack of porous silicon layers (Bragg reflectors) is chosen as a promising candidate and the challenges facing its incorporation between the epitaxial layer and the substrate are presented. Experimental work on this topic is reported and concentrates on the extraction of the internal reflection at the epi/substrate interface from reflectance measurements. Initial results show an internal reflectance between 30 and 60% with a four-layer porous silicon stack. Resistance measurements for majority carrier flow through these porous silicon stacks are also included and show that no resistance increase is measurable for stacks up to four layers. Copyright © 2005 John Wiley & Sons, Ltd. [source] Formation of "air-gap" structure at a GaN epilayer/substrate interface by using an InN interlayerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003A. Yamamoto Abstract We propose a new technique for "air-gap" formation at a GaN/sapphire interface by using an InN interlayer. This is aimed to grow epitaxial GaN films with reduced stress and cracks. First, an InN interlayer of about 0.2 ,m thick is grown at 600 °C in atmospheric pressure. Then a 30 nm-thick GaN buffer layer is grown on the InN layer at 550 °C. The substrate temperature is ramped up to 1000 °C in the NH3 flow, and finally a 1.5 ,m-thick GaN epilayer is grown on the annealed GaN buffer layer using nitrogen carrier gas. Consequently, an "air-gap" structure is naturally formed close to the substrate surface. During the ramping period of substrate temperature, the InN layer decomposes due to its thermal instability and metallic In is formed. It is found that metallic In drops as a result of InN decomposition contribute to the air-gap formation. No cracks are found on the GaN surface and a reduced stress in the layer is confirmed by PL and Raman shift measurements. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigations of p-type signal for ZnO thin films grown on (100) GaAs substrates by pulsed laser depositionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006D. J. Rogers Abstract In this work we investigated ZnO films grown on semi-insulating (100) GaAs substrates by pulsed laser deposition. Samples were studied using techniques including X-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy, Raman spectroscopy, temperature dependent photoluminescence, C-V profiling and temperature dependent Hall measurements. The Hall measurements showed a clear p-type response with a relatively high mobility (,260 cm2/V s) and a carrier concentration of ,1.8 × 1019 cm,3. C-V profiling confirmed a p-type response. XRD and Raman spectroscopy indicated the presence of (0002) oriented wurtzite ZnO plus secondary phase(s) including (101) oriented Zn2As2O7. The results suggest that significant atomic mixing was occurring at the film/substrate interface for films grown at substrate temperatures of 450 ºC (without post-annealing). (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of the relative humidity on film formation by vapor induced phase separationPOLYMER ENGINEERING & SCIENCE, Issue 4 2003H. Caquineau The formation of polymer films produced by the phase separation process occurring when a cast poly(etherimide)/N-Methyl-2-Pyrrolidone solution was exposed to humid air was studied. It was found that above a relative humidity value of 27%, the films presented a cell-like structure. The size of the cells was shown to decrease when the relative humidity increased. This effect was more pronounced at the film/substrate interface than near the surface. A cell-size gradient from one face of the film to the other was also clearly observed. A phenomenological model has been proposed to explain the morphology obtained by a phase separation induced by the water vapor in the studied system, takin into account thermodynamics and kinetics considerations. In this model, the cell-like structure setting up is shown to result from a nucleation and growth process accompanied by a coalescence coarsening. It was illustrated by a composition path on the ternary phase diagram. It was shown how the relative humidity influenced the film composition leading to the preferential nucleation compared to the growth and coalescence of the cells. Finally, it was found that the cell-size anisotropy resulted in the solvent and non-solvent mass transfers in the film, bringing to the fore the determining role of kinetics. [source] Investigation on the oxidation behaviour of gamma titanium aluminides coated with thermal barrier coatingsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 7 2008R. Braun Abstract In the present study, the applicability of thermal barrier coatings (TBCs) on ,-TiAl alloys was investigated. Two alloys with the chemical compositions of Ti-45Al-8Nb-0.2B-0.15C and Ti-45Al-1Cr-6Nb-0.4W-0.2B-0.5C-0.2Si were used. Before TBC deposition, the specimens were pre-oxidised in laboratory air or low partial pressure oxygen atmosphere. Yttria partially stabilised zirconia top coats were then deposited using electron-beam physical vapour deposition (EB-PVD). The oxidation behaviour of the ,-TiAl specimens with TBC was studied by cyclic oxidation testing in air at 850 and 900,°C. Post-oxidation analysis of the coating systems was performed using scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS). No spallation of the TBC was observed for pre-oxidised specimens of both alloys when exposed to air at 850,°C for 1100 cycles of 1,h dwell time at high temperature. SEM micrographs of the thermally grown oxide scale revealed outer mixed TiO2/Al2O3 protrusions with a columnar structure. The protrusions contained small particles of zirconia and a low amount of about 0.5 at% zirconium was measured by EDS analysis throughout this outer oxide mixture. The TBCs exhibited excellent adherence on the oxide scale. Intercolumnar gaps and pores in the root area of the TBC were filled with titania and alumina. Below the outer columnar oxide scale, a broad porous zone of predominant titania was observed. The transition region between the oxide scale and substrate consisted of a discontinuous nitride layer intermixed with alumina particles and intermetallic phases rich in niobium formed at the nitride layer/substrate interface. When thermally cycled at 900,°C, the oxide scales on the alloy Ti-45Al-8Nb-0.2B-0.15C pre-oxidised in low partial pressure oxygen spalled off after 540 cycles. For the sample with TBC, spallation was observed after 810 cycles. Failure occurred in the thermally grown oxide near the oxide/nitride layer interface. Microstructural examinations revealed again oxide scales with columnar structure beneath the zirconia top coat and good adherence of the TBC on the thermally grown oxides formed at 900,°C. [source] Dissipation of inclusions in HgCdTe/CdTe films under the influence of laser shock wavesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004Vitaly Yakovyna Abstract Using HgCdTe/CdTe structures as an example, the study of the effect of laser shock waves on the narrow-gap semiconductors with high density of inhomogeneties as well as on the epitaxial layer/substrate interface are presented. It is found that laser shock wave treatment is an effective way to reduce the relative volume of precipitates in semiconductors. The technique is very promising for developing a low-temperature tool for modification of device structures parameters. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Surface-Transfer Doping of Organic Semiconductors Using Functionalized Self-Assembled Monolayers,ADVANCED FUNCTIONAL MATERIALS, Issue 8 2007W. Chen Abstract Controlling charge doping in organic semiconductors represents one of the key challenges in organic electronics that needs to be solved in order to optimize charge transport in organic devices. Charge transfer or charge separation at the molecule/substrate interface can be used to dope the semiconductor (substrate) surface or the active molecular layers close to the interface, and this process is referred to as surface-transfer doping. By modifying the Au(111) substrate with self-assembled monolayers (SAMs) of aromatic thiols with strong electron-withdrawing trifluoromethyl (CF3) functional groups, significant electron transfer from the active organic layers (copper(II) phthalocyanine; CuPc) to the underlying CF3 -SAM near the interface is clearly observed by synchrotron photoemission spectroscopy. The electron transfer at the CuPc/CF3 -SAM interface leads to an electron accumulation layer in CF3 -SAM and a depletion layer in CuPc, thereby achieving p-type doping of the CuPc layers close to the interface. In contrast, methyl (CH3)-terminated SAMs do not display significant electron transfer behavior at the CuPc/CH3 -SAM interface, suggesting that these effects can be generalized to other organic-SAM interfaces. Angular-dependent near-edge X-ray absorption fine structure (NEXAFS) measurements reveal that CuPc molecules adopt a standing-up configuration on both SAMs, suggesting that interface charge transfer has a negligible effect on the molecular orientation of CuPc on various SAMs. [source] Vertical Phase Separation in Poly(3-hexylthiophene): Fullerene Derivative Blends and its Advantage for Inverted Structure Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Zheng Xu Abstract A method which enables the investigation of the buried interfaces without altering the properties of the polymer films is used to study vertical phase separation of spin-coated poly(3-hexylthiophene) (P3HT):fullerene derivative blends. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analysis reveals the P3HT enrichment at the free (air) surfaces and abundance of fullerene derivatives at the organic/substrate interfaces. The vertical phase separation is attributed to the surface energy difference of the components and their interactions with the substrates. This inhomogeneous distribution of the donor and acceptor components significantly affects photovoltaic device performance and makes the inverted device structure a promising choice. [source] Antireflective Nanoparticle Arrays Enhance the Efficiency of Silicon Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Dehui Wan Abstract In this study, the phenomenon of light trapping in Si solar cells coated with metal (Au) and dielectric (TiO2, SiO2) nanoparticles (NPs) is systematically investigated. In contrast to previous reports, herein it is proposed that the photocurrent enhancement of solar cells should be attributed to the limited antireflection ability of the Au NP arrays. In other words, the Au NP arrays might not enhance the absorption of the active layer in cells when no light is reflected from the air,substrate interface. Therefore, the Au NPs are replaced with dielectric NPs, which possess lower extinction coefficients, and then the antireflection property of the TiO2 NP arrays is optimized. A simple, rapid, and cheap solution-based method is used to prepare close-packed TiO2 NP films on Si solar cells; these devices exhibit a uniform and remarkable increase (ca. 30%) in their photocurrents. To the best of the authors' knowledge, this uniform photocurrent enhancement is greater than those obtained from previously reported metal and dielectric NP,enhanced Si wafer-based solar cells. [source] Lateral Inhomogeneity in the Electronic Structure of a Conjugated Poly(3-hexylthiophene) Thin FilmADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Kaname Kanai Abstract How annealing influences the morphology of a highly regioregular poly(3-hexylthiophene) (RR-P3HT) film at the substrate interface as well as the lateral inhomogeneity in the electronic structure of the film are elucidated. Whereas previous studies have reported that high-molecular-weight (MW) RR-P3HT films tend to show low crystallinity even after annealing, it is found that high-MW RR-P3HT does show high crystallinity after annealing at high temperature for a long time. Photoemission electron microscopy (PEEM), X-ray photoemission spectroscopy, and ultraviolet photoemission spectroscopy results clearly resolve a considerable lateral inhomogeneity in the morphology of RR-P3HT film, which results in a variation of the electronic structure depending on the local crystallinity. The PEEM results show how annealing facilitates crystal growth in a high-MW RR-P3HT film. [source] Low-Temperature Superionic Conductivity in Strained Yttria-Stabilized ZirconiaADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Michael Sillassen Abstract Very high lateral ionic conductivities in epitaxial cubic yttria-stabilized zirconia (YSZ) synthesized on single-crystal SrTiO3 and MgO substrates by reactive direct current magnetron sputtering are reported. Superionic conductivities (i.e., ionic conductivities of the order ,1 ,,1cm,1) are observed at 500,°C for 58-nm-thick films on MgO. The results indicate a superposition of two parallel contributions , one due to bulk conductivity and one attributable to conduction along the film,substrate interface. Interfacial effects dominate the conductivity at low temperatures (<350,°C), showing more than three orders of magnitude enhancement compared to bulk YSZ. At higher temperatures, a more bulk-like conductivity is observed. The films have a negligible grain-boundary network, thus ruling out grain boundaries as a pathway for ionic conduction. The observed enhancement in lateral ionic conductivity is caused by a combination of misfit dislocation density and elastic strain in the interface. These very high ionic conductivities in the temperature range 150,500,°C are of great fundamental importance but may also be technologically relevant for low-temperature applications. [source] A new method for measuring ice adhesion strength at an ice,substrate interfaceHYDROLOGICAL PROCESSES, Issue 4 2006M. Javan-Mashmool Abstract This research focuses on the development of a direct technique for measuring atmospheric ice adhesion strength using embedded piezoelectric film sensors at the ice-substrate interface. The substrate is a small aluminium beam on which PVDF piezoelectric sensors are bonded. The composite beam formed by aluminium and an ice layer is submitted to sinusoidal stress at the interface by a shaker on which one end of the beam is clamped. The piezoelectric charge coefficient is used to predict the electric charge density induced on the piezoelectric film, which enables us to develop a macroscopic and direct measurement technique for determining mechanical stresses at the atmospheric-ice-substrate interface. The preliminary results obtained show that adhesive failure was obtained for each test for a frequency close to the natural resonance frequency of the aluminium beam. Within the limitations of the experimental conditions, it was possible using this approach to obtain ice adhesion strengths in accordance with those obtained in the literature. This demonstrates the feasibility of this simple ice adhesion testing method. Copyright © 2006 John Wiley & Sons, Ltd. [source] Implant Surface Modification Using Laser Guided Coatings: In Vitro Comparison of Mechanical PropertiesJOURNAL OF PROSTHODONTICS, Issue 5 2008Asvin Vasanthan DDS Abstract Purpose: Plasma-sprayed hydroxyapatite (HA)-coated implants show failures along the coating,substrate interface due to poor bond strength. We analyzed HA coatings obtained by pulsed laser deposition (PLD) and compared them to commercially used plasma-sprayed coatings with respect to their bond strength to titanium alloy (Ti-6Al-4V), as well as surface roughness alterations produced by each of the two deposition methods. Materials and Methods: Twelve titanium alloy disks were plasma-sprayed under commercial implant coating conditions, and 24 titanium alloy disks were coated using PLD. All coatings were characterized by the presence of the different calcium phosphate (CaP) phases. The plasma-sprayed coatings (n = 12) were predominantly HA, and the pulsed laser-deposited coatings were hydroxydyapatite (n = 12) and HA coating with a tetra calcium phosphate (TTCP) phase (n = 12). The surface roughness was analyzed before and after the coating processes to assess roughness changes to the surface by the coatings. The adhesive bond strengths of these coatings to the substrate titanium alloy was tested and compared. Scheffé's test was used to analyze the statistical significance of the data. Results: The surface roughness alteration following PLD was a decrease of 0.2 ,m, whereas following plasma spraying the decrease was 1.0 ,m. Bond strengths were as follows [mean (SD) in MPa]: pulsed laser-deposited HA coatings: 68.3 (17.8); pulsed laser-deposited HA with tetra-CaP: 55.2 (21.1); plasma-sprayed HA 17.0 (2.8). The multivariate Scheffé's test revealed that HA coatings obtained by PLD had significantly increased bond strengths compared with the plasma sprayed ones (p, 0.05). Conclusions: HA coatings obtained by PLD showed greater adherence to titanium alloy. PLD offers an alternative method to produce thinner coatings with better adherence properties, along with precise control over the deposition process. [source] Properties of Compositionally Graded BiScO3,PbTiO3 Thin Films Fabricated by a Sol,Gel ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2007Hai Wen The compositionally graded BiScO3,PbTiO3 (BSPT) thin films were fabricated on Pt/Ti/SiO2/Si by a sol,gel method. For the up-graded thin film, the PbTiO3 content increased from the film,substrate interface to the surface of the film, while the down-grade thin film showed the opposite trend. The graded thin films exhibited single-phase structures and dense microstructures. The dielectric and ferroelectric properties of the thin films were investigated. The results showed that the compositionally graded BSPT thin films had similar remanent polarization value but a higher dielectric constant, dielectric tunability, and piezoelectric coefficient d33 compared with the homogeneous thin film with a composition of 0.36BiScO3,0.64PbTiO3 at the morphotropic phase boundary. [source] The Morphology and Dynamics of Substrate Effects on Spinodal Decomposition in Binary Mixtures with Short-Range PotentialMACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006Li-Tang Yan Abstract Summary: The SDSD of binary mixture with short-range potential is numerically simulated in 3D by cell dynamic system (CDSs), focusing on the phase morphology and dynamics in the parallel cross-sections. The formation mechanism and growth law of the wetting layer are analyzed taking thermal noise effects into account. The simulated results show that the phase inversion in the parallel cross-sections can be observed near the substrate interface. Without thermal noise, the growth law of the wetting layer is simply logarithmic. However, when the strength of thermal noise is large enough, the LS growth law can be found for a short-range surface field. The results demonstrate that thermal noise can increase the extent of phase separation and lead to a transformation between partial and complete wetting for the substrate interface. The evolution of the phase in the parallel cross-sections obeys the LS growth law and is self-similar regardless of the effects of thermal noise. Simulated pattern evolution at different values of z at ,,=,1,000 with G,=,0. [source] Interfacial characteristics of film insert molded polycarbonate film/polycarbonate-acrylonitrile-butadiene-styrene substrate, part 1: Influence of substrate molecular weight and film thicknessPOLYMER ENGINEERING & SCIENCE, Issue 12 2006Y.W. Leong Adhesion properties between a polycarbonate (PC)/acrylonitrile-butadiene-styrene blend substrate and PC films of various thicknesses, bonded through film insert molding, were investigated. The use of various molecular weights of PC and incorporation of PC-oligomer in the blend substrate has been found to severely affect the adhesion strength and alter the delamination characteristics at the film,substrate interface. Thicker films were able to increase film,substrate adhesion, apart from providing added impact resistance to a brittle substrate. Polym. Eng. Sci. 46:1674,1683, 2006. © 2006 Society of Plastics Engineers [source] Quasi-static analysis of microstrip lines with variation of substrate thickness in transverse directionINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 3 2003S. Khoulji Abstract This article is devoted to the analysis of microstrip lines printed on dielectric substrates with transversely varying thickness using the quasi-static approximation and the method of lines. Discretization lines of varying length, according to the layer thickness, are used and only the Laplace wave equation has to be solved. The numerical results presented herein permit the illustration of the effect of arbitrarily curved substrate interfaces along the transverse direction on the characteristics of the microstrip structures under consideration. The behavior of the per unit length parameters of these structures as a function of the shape of these substrates' cross section is studied in depth. Furthermore, the effects of the finite metallization thickness and losses are also investigated in detail. The results that are obtained are consistent with those published in the literature. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 194,205, 2003. [source] Modulation of mobility in homoepitaxially-grown AlGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009J. A. Grenko Abstract We report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi-insulating c-axis GaN substrates. Room temperature Hall mobilities up to 1805 cm2/Vs at sheet carrier densities of 0.77x1013 cm,2 have been measured. By varying the GaN buffer layer thickness in these homoepitaxially-grown Al0.25Ga0.75N/GaN heterostructures, we observed a buffer-induced modulation of the room temperature 2DEG sheet carrier densities and Hall mobilities. The increase in sheet carrier density and corresponding decrease in mobility as the GaN buffer layer thickness is reduced below 0.75 ,m is related to the presence of Si impurities at the bulk GaN substrate/epitaxial interface. Capacitance-voltage measurements and SIMS analysis confirm the presence of Si impurities at the surface prior to and after epitaxial growth. The factor of 2 reduction in the room temperature mobility is consistent with a predicted theoretical mobility reduction based on intersubband scattering. We have also been able to separate the contributions to the 2DEG carrier density from the ionized donors and the polarization field; the magnitude of each is ,5x1012 cm,2. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||