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Device Structures (device + structure)

Distribution by Scientific Domains

Polymers and Materials Science	63%
Engineering	18%

Distribution within Polymers and Materials Science

General & Introductory Materials Science	71%
Polymer Science & Technology General	14%

Selected Abstracts

White-Light Emission from a Single Polymer with Singlet and Triplet Chromophores on the Backbone

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 24 2006
Hongyu Zhen
Abstract Summary: A strategy to generate an efficient white-light emission has been developed by mixing fluorescence and phosphorescence emission from a single polymer. Fluorene is used as the blue-emissive component, benzothiadiazole (BT) and the iridium complex [(btp)2Ir(tmd)] are incorporated into a polyfluorene backbone, respectively, as green- and red-emissive chromophores by Suzuki polycondensation. By changing the contents of BT and [(btp)2Ir(tmd)] in the polymer, the electroluminescence spectrum from a single polymer can be adjusted to achieve white-light emission. A white polymeric light-emitting diode (WPLED) with a structure of ITO/PEDOT:PSS/PVK/PFIrR1G03/CsF/Al shows a maximum external quantum efficiency of 3.7% and the maximum luminous efficiency of 3.9 cd,·,A,1 at the current density of 1.6 mA,·,cm,2 with the CIE coordinates of (0.33, 0.34). The maximum luminance of 4,180 cd,·,m,2 is achieved at the current density of 268 mA,·,cm,2 with the CIE coordinates of (0.31, 0.32). The white-light emissions from such polymers are stable in the white-light region at all applied voltages, and the electroluminescence efficiencies decline slightly with the increasing current density, thus indicating that the approach of incorporating singlet and triplet species into the polymer backbone is promising for WPLEDs. Structure of PFIrR1G04 and the EL spectra of its devices under various voltages. Device structure: ITO/PEDOT:PSS/PVK/polymer/CsF/Al. [source]

Review of electronic and optical properties of semiconducting ,-conjugated polymers: applications in optoelectronics

POLYMER INTERNATIONAL, Issue 10 2004
André Moliton
Abstract A general overview of the optoelectronic properties of ,-conjugated polymers is presented. Two types of polymer are discerned: interchangeable structures of the same energy (degenerate), such as polyacetylene; and non-degenerate polymers, such as poly(para -phenylene). The band structures of degenerate and non-degenerate polymers are related to their conductivities in doped and non-doped states. In both cases, disorder and impurities play an important role in conductivity. Polarons, bipolarons and excitons are detailed with respect to doping and charge transfers. Given the fibrillic nature of these materials, the variable range hopping (VRH) law for semiconducting polymers is modified to account for metallic behaviours. Optoelectronic properties,electroluminescence and photovoltaic activity,are explained in terms of HOMO and LUMO bands, polaron-exciton and charge movement over one or more molecules. The properties of H- or J-type aggregates and their effects on transitions are related to target applications. Device structures of polymer light-emitting diodes are explicitly linked to optimising polaron recombinations and overall quantum efficiencies. The particularly promising use of ,-conjugated polymers in photovoltaic devices is discussed. Copyright © 2004 Society of Chemical Industry [source]

Photophysics and Photocurrent Generation in Polythiophene/Polyfluorene Copolymer Blends

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Christopher R. McNeill
Abstract Here, studies on the evolution of photophysics and device performance with annealing of blends of poly(3-hexylthiophene) with the two polyfluorene copolymers poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2,,2,,-diyl) (F8TBT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) are reported. In blends with F8TBT, P3HT is found to reorganize at low annealing temperatures (100,°C or below), evidenced by a redshift of both absorption and photoluminescence (PL), and by a decrease in PL lifetime. Annealing to 140,°C, however, is found to optimize device performance, accompanied by an increase in PL efficiency and lifetime. Grazing-incidence small-angle X-ray scattering is also performed to study the evolution in film nanomorphology with annealing, with the 140,°C-annealed film showing enhanced phase separation. It is concluded that reorganization of P3HT alone is not sufficient to optimize device performance but must also be accompanied by a coarsening of the morphology to promote charge separation. The shape of the photocurrent action spectra of P3HT:F8TBT devices is also studied, aided by optical modeling of the absorption spectrum of the blend in a device structure. Changes in the shape of the photocurrent action spectra with annealing are observed, and these are attributed to changes in the relative contribution of each polymer to photocurrent as morphology and polymer conformation evolve. In particular, in as-spun films from xylene, photocurrent is preferentially generated from ordered P3HT segments attributed to the increased charge separation efficiency in ordered P3HT compared to disordered P3HT. For optimized devices, photocurrent is efficiently generated from both P3HT and F8TBT. In contrast to blends with F8TBT, P3HT is only found to reorganize in blends with F8BT at annealing temperatures of over 200,°C. The low efficiency of the P3HT:F8BT system can then be attributed to poor charge generation and separation efficiencies that result from the failure of P3HT to reorganize. [source]

Study of Energy Transfer and Triplet Exciton Diffusion in Hole-Transporting Host Materials

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Chao Wu
Abstract A device structure is used in which the hole-transporting layer (HTL) of an OLED is doped with either fluorescent or phosphorescent emitters, that is, anode/HTL-host/hole blocker/electron-transporting layer/cathode. The HTL hosts have higher HOMO energy allowing holes to be transported without being trapped by dopant molecules, avoiding direct recombination on the dopant. The unconventional mismatch of HOMO energies between host and dopant allow for the study of energy transfer in these host/guest systems and triplet exciton diffusion in the HTL-host layers of OLED devices, without the complication of charge trapping at dopants. The host materials examined here are tetraaryl- p- phenylenediamines. Data shows that Förster energy transfer between these hosts and emissive dopant in devices is inefficient. Triplet exciton diffusion in these host materials is closely related to molecular structure and the degree of intermolecular interaction. Host materials that contain naphthyl groups demonstrate longer triplet exciton diffusion lengths than those with phenyl substituents, consistent with DFT calculations and photophysical measurements. [source]

Optically-Pumped Lasing in Hybrid Organic,Inorganic Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2009
Myoung Hoon Song
Abstract Here, the use of metal oxide layers both for charge transport and injection into an emissive semiconducting polymer and also for the control of the in-plane waveguided optical modes in light-emitting diodes (LEDs) is reported. The high refractive index of zinc oxide is used to confine these modes away from the absorbing electrodes, and include a nano-imprinted grating in the polymer layer to introduce distributed feedback and enhance optical out-coupling. These structures show a large increase in the luminescence efficiency over conventional devices, with photoluminescence efficiency increased by up to 45%. Furthermore, optically-pumped lasing in hybrid oxide polymer LEDs is demonstrated. A tuneable lasing emission is also obtained in a single device structure by employing a graduated thickness of a zinc oxide inter-layer. This demonstrates the scope for using such architectures to improve the external efficiency of organic semiconductor LEDs, and opens new possibilities for the realization of polymer injection lasers. [source]

Novel Heteroleptic CuI Complexes with Tunable Emission Color for Efficient Phosphorescent Light-Emitting Diodes,

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007
Q. Zhang
Abstract A series of orange-red to red phosphorescent heteroleptic CuI complexes (the first ligand: 2,2,-biquinoline (bq), 4,4,-diphenyl-2,2,-biquinoline (dpbq) or 3,3,-methylen-4,4,-diphenyl-2,2,-biquinoline (mdpbq); the second ligand: triphenylphosphine or bis[2-(diphenylphosphino)phenyl]ether (DPEphos)) have been synthesized and fully characterized. With highly rigid bulky biquinoline-type ligands, complexes [Cu(mdpbq)(PPh3)2](BF4) and [Cu(mdpbq)(DPEphos)](BF4) emit efficiently in 20,wt,% PMMA films with photoluminescence quantum yield of 0.56 and 0.43 and emission maximum of 606,nm and 617,nm, respectively. By doping these complexes in poly(vinyl carbazole) (PVK) or N -(4-(carbazol-9-yl)phenyl)-3,6-bis(carbazol-9-yl) carbazole (TCCz), phosphorescent organic light-emitting diodes (OLEDs) were fabricated with various device structures. The complex [Cu(mdpbq)(DPEphos)](BF4) exhibits the best device performance. With the device structure of ITO/PEDOT/TCCz:[Cu(mdpbq)(DPEphos)](BF4) (15,wt,%)/TPBI/LiF/Al (III), a current efficiency up to 6.4,cd,A,1 with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.61, 0.39) has been realized. To our best knowledge, this is the first report of efficient mononuclear CuI complexes with red emission. [source]

MIMO handheld antenna design approach using characteristic mode concepts

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2008
Jonathan Ethier
Abstract In handheld communications devices there is not much room for the placement of antennas. This problem is exacerbated when more than one antenna is needed for use in a MIMO communications system. It is then useful to be able to utilize some of the existing device structure to form the required antennas. In this article, we show how the characteristic mode theory can be used to achieve this in a way that results in antennas with the low envelope correlation preferred for MIMO antennas. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1724,1727, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23509 [source]

Optimization of underlying layer and the device structure for group-III-nitride-based UV emitters on sapphire

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
K. Iida
Abstract Epitaxial lateral overgrowth (ELO) was applied for the growth of AlGaN on a sapphire substrate by metalorganic vapor phase epitaxy. Among several processes, the ELO of AlGaN on grooved AlGaN showed the best surface morphology and the lowest dark-spot density of 1×108 cm,2 as measured using cathodoluminescence. The light output power of a UV LED fabricated on ELO-Al0.25Ga0.75N on grooved Al0.25Ga0.75N was the strongest among several UV LEDs fabricated by different processes. The effect of the Al composition in the electron-blocking (EB) layer on the performance of UV LEDs was investigated. The UV LED with a low-Al-content EB layer showed high output power under a low-injection condition, while the output power of a UV LED with a high-Al-content EB layer did not saturate even under a high-injection condition. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Organic electroluminescent devices using europium complex-doped poly(N -vinylcarbazole)

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2004
Tingxi Li
Abstract Electroluminescence (EL) properties of europium (Eu) complex-doped poly(N -vinylcarbazole) (PVK) were investigated. A device structure of glass substrate/indium-tin oxide/hole-injection layer/Eu complex-doped PVK/hole-blocking layer/electron transport layer/electron-injection layer/Al was employed. Red emission originating from Eu complex was observed. Relatively high luminance of 50,cd/m2 and an efficiency of 0.2% were obtained. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Multifunctional Triphenylamine/Oxadiazole Hybrid as Host and Exciton-Blocking Material: High Efficiency Green Phosphorescent OLEDs Using Easily Available and Common Materials

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
Youtian Tao
Abstract A new triphenylamine/oxadiazole hybrid, namely m -TPA- o -OXD, formed by connecting the meta -position of a phenyl ring in triphenylamine with the ortho -position of 2,5-biphenyl-1,3,4-oxadiazole, is designed and synthesized. The new bipolar compound is applicable in the phosphorescent organic light-emitting diodes (PHOLEDs) as both host and exciton-blocking material. By using the new material and the optimization of the device structures, very high efficiency green and yellow electrophosphorescence are achieved. For example, by introducing 1,3,5-tris(N -phenylbenzimidazol-2-yl)benzene (TPBI) to replace 2, 9-dimethyl-4,7-diphenyl-1, 10-phenanthroline (BCP)/tris(8-hydroxyquinoline)aluminium (Alq3) as hole blocking/electron transporting layer, followed by tuning the thicknesses of hole-transport 1, 4-bis[(1-naphthylphenyl)amino]biphenyl (NPB) layer to manipulate the charge balance, a maximum external quantum efficiency (,EQE,max) of 23.0% and a maximum power efficiency (,p,max) of 94.3 lm W,1 are attained for (ppy)2Ir(acac) based green electrophosphorescence. Subsequently, by inserting a thin layer of m -TPA- o -OXD as self triplet exciton block layer between hole-transport and emissive layer to confine triplet excitons, a ,EQE,max of 23.7% and ,p,max of 105 lm W,1 are achieved. This is the highest efficiency ever reported for (ppy)2Ir(acac) based green PHOLEDs. Furthermore, the new host m -TPA- o -OXD is also applicable for other phosphorescent emitters, such as green-emissive Ir(ppy)3 and yellow-emissive (fbi)2Ir(acac). A yellow electrophosphorescent device with ,EQE,max of 20.6%, ,c,max of 62.1 cd A,1, and ,p,max of 61.7 lm W,1, is fabricated. To the author's knowledge, this is also the highest efficiency ever reported for yellow PHOLEDs. [source]

Novel Heteroleptic CuI Complexes with Tunable Emission Color for Efficient Phosphorescent Light-Emitting Diodes,

Cover Picture: A Novel Method to Orient Semiconducting Polymer Films (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2005
Mater.
Abstract A new technique for orienting thin polymer semiconductor films is reported by Österbacka and co-workers on p.,1095. The technique uses the mechanical force of a shrinking polymer transferred through a polymer multilayer structure. The orientation is obtained using three polymer layers, where the uppermost layer shrinks resulting in orientation of the semiconductor film beneath the intermediate layer. The topmost and intermediate polymer films are removed to reveal the oriented surface. The cover shows a crossed-polarizer microscopy image of an oriented regio-regular poly(3-hexylthiophene) film. We present a new technique for orienting polymer semiconductor thin films. In our technique, polymer chains are rigorously oriented without using any mechanical tools and with minimal risk of film contamination. The technique is based on the mechanical force resulting from the in-plane shrinkage exerted by a shrinker (top layer) that is used to orient the semiconductor beneath an intermediate layer; the latter acting as a force mediator. The chain orientation is demonstrated by several techniques such as crossed-polarizer microscopy, atomic force microscopy, grazing-incidence X-ray diffraction, and polarized absorption. The orientation geometry is controlled by the shrinking process and the shrinker area. The semiconductivity of the film only stems from the transistor device structures under study, and the method can therefore be generalized. [source]

Device Performance of APFO-3/PCBM Solar Cells with Controlled Morphology

ADVANCED MATERIALS, Issue 43 2009
Cecilia M. Björström Svanström
Polymer/fullerene solar cells with three different device structures: A) diffuse bilayer, B) spontaneously formed multilayer, and C) vertically homogenous thin films, are fabricated. The photocurrent/voltage performance is compared and it is found that the self-stratified structure (B) yields the highest energy conversion efficiency. [source]

Interface Engineering of Inorganic Thin-Film Solar Cells , Materials-Science Challenges for Advanced Physical Concepts

ADVANCED MATERIALS, Issue 42 2009
Wolfram Jaegermann
Abstract The challenges and research needs for the interface engineering of thin-film solar cells using inorganic-compound semiconductors are discussed from a materials-science point of view. It is, in principle, easily possible to define optimized device structures from physical considerations. However, to realize these structures, many materials' limitations must be overcome by complex processing strategies. In this paper, interface properties and growth morphology are discussed using CdTe solar cells as an example. The need for a better fundamental understanding of cause,effect relationships for improving thin-film solar cells is emphasized. [source]

Electrical Scanning Probe Microscopy on Active Organic Electronic Devices

ADVANCED MATERIALS, Issue 1 2009
Liam S. C. Pingree
Abstract Polymer- and small-molecule-based organic electronic devices are being developed for applications including electroluminescent displays, transistors, and solar cells due to the promise of low-cost manufacturing. It has become clear that these materials exhibit nanoscale heterogeneities in their optical and electrical properties that affect device performance, and that this nanoscale structure varies as a function of film processing and device-fabrication conditions. Thus, there is a need for high-resolution measurements that directly correlate both electronic and optical properties with local film structure in organic semiconductor films. In this article, we highlight the use of electrical scanning probe microscopy techniques, such as conductive atomic force microscopy (c-AFM), electrostatic force microscopy (EFM), scanning Kelvin probe microscopy (SKPM), and similar variants to elucidate charge injection/extraction, transport, trapping, and generation/recombination in organic devices. We discuss the use of these tools to probe device structures ranging from light-emitting diodes (LEDs) and thin-film transistors (TFT), to light-emitting electrochemical cells (LECs) and organic photovoltaics. [source]

Hot-electron numerical modelling of short gate length pHEMTs applied to novel field plate structures

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2003
Shahzad Hussain
Abstract Hot-electron numerical simulations were carried out in order to simulate the DC parameters of pseudomorphic high electron mobility transistors (pHEMTs). The hot-electron effects were studied by simulating several HEMT device structures. Hot-carrier injection in the substrate and the formation of the peak of electric field in the channel were studied in detail. The inclusion of a field-plate contact in a multiple recessed pHEMT structure lowered the peak value of the electric field by 24% compared with the conventional pHEMT. These devices were modelled by solving the two-dimensional Poisson, current continuity and energy transport equations consistently with the time-independent Schrödinger wave equation. Appropriate Ohmic boundaries are discussed here and implemented in the simulations of pHEMT structures. A new integral approximation is used to calculate electron densities and electron energy densities for degenerate approximations. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Model order reduction of linear and nonlinear 3D thermal finite-element description of microwave devices for circuit analysis

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2005
Raphaël Sommet
Abstract Electrothermal models of power devices are necessary for the accurate analysis of their performances. For this reason, this article deals with a methodology to obtain an electrothermal model based on a reduced model of a 3D thermal finite-element (FE) description for its thermal part and on pulsed electrical measurements for its electrical part. The reduced thermal model is based on the Ritz vector approach, which ensures a steady-state solution in every case. An equivalent SPICE subcircuit implementation for circuit simulation is proposed and discussed. An extension of the method to a nonlinear reduced model based on the Kirchoff transformation is also proposed. The complete models have been successfully implemented in circuit simulators for several HBT or PHEMT device structures. Many results concerning devices and circuits are presented, including simulation of both the static and dynamic collector-current collapse in HBTs due to the thermal phenomenon. Moreover, the results in terms of the circuit for an X-band high-power amplifier are also presented. As for the nonlinear approach, results concerning an homogeneous structure is given. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. [source]

Growth and characterization of ZnMgTe/ZnTe layered structures grown by molecular beam epitaxy

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2010
S. Imada
Abstract ZnMgTe/ZnTe layered structures were grown on ZnTe substrates by molecular beam epitaxy, and the crystal structures were characterized using X-ray diffraction methods. This structure would be the waveguide for various optoelectronic devices. Therefore, the crystal quality of this layered structure would be very crucial for the realization of high performance devices. ZnMgTe is lattice mismatched to ZnTe, and the increase of the ZnMgTe layer thickness or Mg mole fraction ratio would result in the crystal quality deterioration of the layered structure. The critical layer thickness (CLT) was theoretically derived, and various structures with various ZnMgTe layer thickness and Mg mole fraction were grown. The lattice mismatch strain relief and crystal quality of those samples were investigated by means of X-ray reciprocal space mapping (RSM) and cross sectional transmission electron microscopy (TEM). The dislocation formation and the lattice mismatch relaxation were confirmed for various samples and it was revealed that the calculated CLT values could be used as an appropriate guideline to design the dislocation free and high performance device structures (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Carrier transport studies of dichromatic InGaN-based LEDs with spacer bandgap dependence

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
Shih-Wei Feng
Abstract Carrier transport of dichromatic InGaN-based LEDs with AlGaN spacer bandgap dependence has been studied. TREL measurements show that carrier dynamics could be well explained by the combined effects of carrier effective mass, carrier mobility, quantum confinement, and device structures. The experimental results provide important information for device designs. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electroluminescent properties of a partially-conjugated hyperbranched poly(p -phenylene vinylene)

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3 2006
Benhu Fan
Abstract In this paper, the electroluminescent properties of a new partially-conjugated hyperbranched poly (p -phenylene vinylene) (HPPV) were studied. The single layer light-emitting device with HPPV as the emitting layer emits blue-green light at 496,nm, with a luminance of 160,cd/m2 at 9,V, a turn-on voltage of 4.3,V and an electroluminescent efficiency of 0.028,cd/A. By doping an electron-transport material [2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole, PBD] into the emitting layer and inserting a thin layer of tris(8-hydroxy-quinoline)aluminum (Alq3) as electron transporting/hole blocking layer for the devices, the electroluminescent efficiency of 1.42,cd/A and luminance of 1700,cd/m2 were achieved. The results demonstrate that the devices with the hyperbranched polymers as emitting material can achieve high efficiency through optimization of device structures. Copyright © 2006 John Wiley & Sons, Ltd. [source]

GaAs converters for high power densities of laser illumination

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 4 2008
E. Oliva
Abstract Photovoltaic power converters can be used to generate electricity directly from laser light. In this paper we report the development of GaAs PV power converters with improved conversion efficiency at high power densities. The incorporation of a lateral conduction layer (LCL) on top of the window layer resulted in a considerable gain in efficiency at high illumination levels. Additional performance improvements were obtained by using a metal electrode grid design and antireflection coating optimised for monochromatic and inhomogeneous laser light. Maximum monochromatic (810,nm) optical-to-electrical conversion efficiency of 54·9% at 36·5,W/cm2 has been achieved. The characteristics of laser power converters with p/n and n/p polarity are discussed in this paper. Moreover, different materials and doping levels were applied in the LCL. The performance of these different device structures at high laser intensity is presented and discussed. It is shown that the lateral series resistance of the cell has a major impact on the overall device performance. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Covalent Attachment of Bacteriorhodopsin Monolayer to Bromo-terminated Solid Supports: Preparation, Characterization, and Protein Stability

CHEMISTRY - AN ASIAN JOURNAL, Issue 7 2008
Yongdong Jin Dr.
Abstract The interfacing of functional proteins with solid supports and the study of related protein-adsorption behavior are promising and important for potential device applications. In this study, we describe the preparation of bacteriorhodopsin (bR) monolayers on Br-terminated solid supports through covalent attachment. The bonding, by chemical reaction of the exposed free amine groups of bR with the pendant Br group of the chemically modified solid surface, was confirmed both by negative AFM results obtained when acetylated bR (instead of native bR) was used as a control and by weak bands observed at around 1610,cm,1 in the FTIR spectrum. The coverage of the resultant bR monolayer was significantly increased by changing the pH of the purple-membrane suspension from 9.2 to 6.8. Although bR, which is an exceptionally stable protein, showed a pronounced loss of its photoactivity in these bR monolayers, it retained full photoactivity after covalent binding to Br-terminated alkyls in solution. Several characterization methods, including atomic force microscopy (AFM), contact potential difference (CPD) measurements, and UV/Vis and Fourier transform infrared (FTIR) spectroscopy, verified that these bR monolayers behaved significantly different from native bR. Current,voltage (I,V) measurements (and optical absorption spectroscopy) suggest that the retinal chromophore is probably still present in the protein, whereas the UV/Vis spectrum suggests that it lacks the characteristic covalent protonated Schiff base linkage. This finding sheds light on the unique interactions of biomolecules with solid surfaces and may be significant for the design of protein-containing device structures. [source]