bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled Passivation and Luminescence Blue Shifts of Isolated Silicon Nanocrystals
Authors: Biteen Julie S. , Tchebotareva Anna L. , Polman Albert , Lewis Nathan S. , Atwater Harry A.
Published: June 2019

We have performed a comparative study of oxide- and nonoxide-passivated silicon nanocrystals to probe the role of the silicon/oxygen interface in low coverage, non-interacting silicon nanocrystal systems. Ensembles of Si nanocrystals characterized by a narrow distribution and diameters of 2–5 nm were synthesized by ion implantation into SiO2 films followed by a high-temperature anneal in Ar. The nanocrystals were removed from the SiO2 film matrix and deposited on Si substrates using a chemical etch in HF, leaving a hydrogen-terminated surface. A natural oxide layer grows on these surfaces in air. We characterized the morphology of the samples with atomic force microscopy (AFM) and the spectroscopic properties with photoluminescence (PL) and X-Ray photoelectron spectroscopy. We found that the PL energy of Si nanocrystals can be shifted by particle size reduction and hydrogen or oxygen termination. Further, PL peak energy shifts upon etching and oxidation were consistent with the model of Wolkin et al. that proposes that for very small radii, a silicon-oxygen double bond will produce deep interface states which red shift the luminescence.
Electrochemical characterization of blue-emitting polyfluorene LEP
Authors: Grizzi Ilaria , Foden Clare , Goddard Simon , Towns Carl
Published: June 2019

In an operating LED, electrons are injected into the polymer's LUMO level from the cathode and holes from the anode into the polymer's HOMO level. The value of the electron affinity (EA) is usually inferred (often incorrectly) from the experimental HOMO level energy and the value of the optical band gap. Using carefully controlled experimental conditions we can now directly access the EA position. Reduction events have been observed on poly(9,9-dioctylfluorene) (F8) and blue emitting polymers based on 9,9-dioctylfluorene. This event is consistent and reversible. As predicted by theory, the LUMO level is entirely delocalised over F8 blocks. An EA of approx. –2.3eV, equal to that of F8, is therefore a common feature of blue polymers containing sequences of 9,9-dioctylfluorene. Blue emitting 9,9-dioctylfluorene -triarylamine AB copolymers containing either 4-sec-butylphenyl diphenyl amine (TFB) or N,N'-bis(4-butylphenyl)-N,N'-diphenyl phenylenediamine (PFB) are characterized by an electron affinity of –2.1eV. This result shows that the LUMO wave function in these systems is localized on the Ph-F8-Ph units. In the case of PFB homopolymer the LUMO level is again localized, this time on the biphenyl unit at the junction of each 2 repeating units. The EA for this material is therefore lower than in the previous cases: -1.84eV, as a result of the increased localization of the LUMO wave function Electrochemical characterisation provides a direct probe for the dynamic of the charge injection in a polymer system, as the HOMO and LUMO are the states into which the holes and electrons are injected. Electrochemical measurement together with theoretical modelling gives a more complete understanding of molecular properties and behaviour. However, electrochemical measurements are not necessarily relevant to the optical energy gap, as the optical excitation does not necessarily involve molecular orbitals probed by electrochemical methods.
Study of the MDMO-PPV/metal interface and PCBM/metal interface by electroabsorption spectroscopy
Authors: Reynaert J. , Jin Y.D. , Aernouts T. , Geens W. , Borghs G. , Mertens R. , Heremans P.
Published: June 2019

In this work, we study the workfunction alignment of organic compounds and electrodes evaporated on top of these organic materials by means of electroabsorption (EA). The organic materials of this study are poly[2-methoxy-5-(3',7'-dimethyloctyloxyl)]-1,4-phenylene vinylene (MDMO-PPV) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM). The electrodes are Al, Au, LiF/Au and LiF/Au, the latter two with a 1 nm thick layer of LiF, as well as with co-evaporation of LiF and the metal. In case of the MDMO-PPV, LiF enhances the built-in potential and thus reduces the electron injection barrier. Equal built-in potentials for a co-evaporated LiF:metal contact suggest doping is happening at the MDMO-PPV/metal interface. Unlike predicted by the Au and Al workfunction value, the built-in potentials for the PCBM/Al and PCBM/Au interface are equal. This suggests that Fermi level pinning occurs at these interfaces. The presence of a thin LiF layer screens the charge transfer from the metal to the PCBM.
Focused Microwave-assisted Synthesis of 2,5-Dihydrofuran Derivatives as Electron Acceptors for Highly Efficient Nonlinear Optical Chromophores
Authors: Liu Sen , Haller Marnie A. , Luo Jingdong , Jang Sei-Hum , Ma Hong , Dalton Larry R. , Jen Alex K.-Y.
Published: June 2019

A diversified family of 2,5-dihydrofuran derivatives has been synthesized as a new class of highly efficient and tunable electron acceptors using the single-mode focused microwave irradiation. High poling efficiency and very large electro-optic coefficients (r33 values of 128 and 116 pm/V at 1.3 μm) have been demonstrated using 2-dicyanomethylen-3-cyano-4,5,-dimethyl-5-trifluoromethyl-2,5-dihydrofuran (CF3-TCF)-based chromophores as dopant in poly(methyl methacrylate) (PMMA) and a high glass-transition temperature polyquinoline (PQ-100) respectively. Excellent dipole alignment stability has also been demonstrated in the guest/host composite at 85°C. Multi-functionalized NLO chromophores based on hydroxy containing 2,5-dihydrofuran acceptors were also synthesized through microwave methodology for further characterizations.
Energy Level Alignment at Fullerene/Phthalocyanine Interface Studied by Electron Spectroscopies
Authors: Ishii Hisao , Seko Atsushi , Kawakami Akira , Umishita Kazunori , Ouchi Yukio , Seki Kazuhiko
Published: June 2019

Interfacial band offset and band bending of organic semiconductors are critical to understand and improve organic photovoltaic cells. In this study, the energy level alignment of fullerene(C60) / metal-free phthalocyanine (H2Pc) interface which is one of the model interfaces of organic photovoltaic cells has been investigated using UV and X-ray photoemissions. For both ‘H2Pc on C60’ and “C60 on H2Pc' interfaces, 0.3 eV downward energy level shift was observed in XPS at the interface formation. This energy shift is quite steep in contrast to the band bending observed for C60/metal interfaces in our previous study, where thickness of 500nm was required to achieve 0.21eV band bending to get Fermi level alignment between metal electrode and C60. To clarify the origin of the band bending, the effect of the insertion of C60-H2Pc co-deposited layer between C60 and H2Pc layers was also investigated. The result suggested that possible doping of H2Pc to C60 is not main origin of the observed energy shift. We also found that the vacuum level shift at H2Pc/C60 interface is strongly dependent on the deposition sequence of the interface formation.
Metal vs. Polymer Electrodes in Organic Devices: Energy Level Alignment, Hole Injection, and Structure
Authors: Koch N. , Nickel B. , Ghijsen J. , Elschner A. , Schwartz J. , Pireaux J.-J. , Kahn A.
Published: June 2019

L We have investigated the electronic, structural, and charge injection properties of interfaces formed between three electroactive conjugated organic materials, i.e., N, N'-bis-(1-naphthyl)-N, N'-diphenyl1-1,1-biphenyl1-4,4'-diamine (á-NPD), pentacene, p-sexiphenyl, and two high work function electrode materials, i.e., gold and the conducting polymer poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS). Ultraviolet photoelectron spectroscopy shows that the hole injection barrier between the three organic materials and PEDOT:PSS is lower by 0.6-1.0 eV as compared to Au, despite a similar work function of the pristine electrode material surfaces (ca. 5 eV). This very large difference is due to an effective change of the metal work function due to the deposition of organic molecules, i.e., a decrease of the Au surface dipole due to adsorption. Accordingly, model device structures built from á-NPD and pentacene on the two different electrode materials show much higher current densities for hole injection from PEDOT:PSS than from Au. Hole injection from Au for á-NPD devices is independent of deposition sequence and substrate. Pentacene devices exhibit significant asymmetries in that respect, due to a strong dependence of the morphology and preferred molecular orientation of the crystalline material on the substrate, as shown by atomic force microscopy and X-ray diffraction. Consequently, great care must be taken when modeling current-voltage characteristics of devices comprised of crystalline organic solids, especially when the influence of film thickness or different substrate materials is to be studied.
Trivalent Europium Complexes Using Dendritic â-Diketone Ligands
Authors: Case Patrick J. , Harper Aaron W.
Published: June 2019

A series of photon harvesting lanthanide complexes have been synthesized by chelating dendritic â-diketone ligands to Eu+3. The ligands are modified benzoyltrifluoroacetone units (BTFA) with poly(aryl ether) dendron attachments. These ligands impose a very large asymmetric nature to the first coordination sphere of europium compared to previous dendritic compounds. These complexes exhibit europium emission with no residual emission from the ligands as the dendritic subunits increase from G-0 to G-3. This is due to both antenna and site isolation effects. These complexes mimic light harvesting organisms seen in Nature. When these intensities are compared throughout the series, an increase in intensity is seen where [(G2)BTFA]3Eu is the brightest, with [(G3)BTFA]3Eu being less intense than the G-2 complex. However, the lifetime data indicates that the G-3 complex is the longest lived species.
EL Properties of Polyfluorene Copolymers Containing Hole-Transporting Carbazole Group
Authors: Hwang Do-Hoon , Lee Jong-Don , Park Moo-Jin , Lee Ji-Hoon , Lee Chang-Hee
Published: June 2019

An alkoxyphenyl substitutued new polyfluorene derivative, poly(9,9-bis(4'-n-octyloxyphenyl) fluorene) (PBOPF) was synthesized through Ni(0) mediated polymerization. Blue light-emitting PBOPF shows peak PL at 426 nm. No significant excimer emission was observed even after annealing the polymer film at 100 oC for 2h. Aseries of random copolymers of 2,7-dibromo-9,9-bis(4'-n-octyloxyphenyl)) fluorene (BOPF) and 2,7-dibromo-N-(2'-ethylhexyl)carbazole (EHC) were also synthesized through Ni(0) mediated polymerization. Carbazole comonomer was introduced to improve hole-transporting properties of PBOPF. The synthesized poly(BOPF-co-EHC)s showed similar UV-visible absorption and PL emission to PBOPF. EL devices were fabricated in an ITO/PEDOT/polymer/Ca/Al configuration. The EL devices using copolymers showed improved device performance than the device using PBOPF homopolymer due to a more balanced charge transport.
Scanning-tunneling spectroscopy on conjugated polymer films
Authors: Kemerink M. , Alvarado S.F. , Koenraad P.M. , Janssen R.A.J. , Salemink H.W.M. , Wolter J.H.
Published: June 2019

Scanning-tunneling spectroscopy experiments have been performed on conjugated polymer films and have been compared to a three-dimensional numerical model for charge injection and transport. It is found that field enhancement near the tip apex leads to significant changes in the injected current, which can amount to more than an order of magnitude, and can even change the polarity of the dominant charge carrier. As a direct consequence, the single-particle band gap and band alignment of the organic material can be directly obtained from tip height-voltage (z-V) curves, provided that the tip has a sufficiently sharp apex.
Balanced Charge Injection and Singlet Exciton Quenching in Bilayer Organic Electroluminescent Devices
Authors: Ganzorig Chimed , Fujihira Masamichi
Published: June 2019

We demonstrate here balancing between hole and electron injection in bilayer organic tris(8-hydroxyquinoline)aluminum (Alq3) based electroluminescent (EL) devices by measuring current-voltage (I-V) characteristics of single-carrier devices with different thickness and by comparing the device performance with various chemically modified ITO. We measure I-V characteristics due to holes in hole-only bilayer devices with various modified ITO anodes and those due to electrons in electron-only single-layer devices with C6H5COOLi(2 nm)/Al cathode. Here, hole-only devices are those, in which only holes are carriers and the current due to electrons is negligible. We found that the I-V characteristics observed for the hole-only bilayer devices with UV-ozone and ClC6H4COCl treated ITO were comparable to the I-V characteristics for the electron-only single-layer device of ITO(as-cleaned)/Alq3(150 nm)/C6H5COOLi(2 nm)/Al. In other words, hole and electron injections are well balanced when we use UV-ozone and ClC6H4COCl treated ITO anodes. EL characteristics have shown that luminance decreased clearly for bilayer organic EL devices with an Al cathode where electron injection was not enhanced significantly. The decrease in EL efficiency can be attributed to unbalanced hole and electron injection. The unbalanced injection results in excess of one carrier type that does not contribute to light emission, and results in deactivation of 1Alq3 at high currents due to quenching 1Alq3 by large excess of Alq3+. in the emission zone.
Loss Process in Efficiency of Blue Organic Electroluminescent Devices
Authors: Enatsu Yasuo , Ganzorig Chimed , Fujihira Masamichi
Published: June 2019

We report EL characteristics of blue organic electroluminescent (EL) devices with a hole transport layer (HTL) as an emitter i.e. ITO/NPD/BCP/Alq3/Cs(0.5 nm)/Al. Here, ITO, NPD, BCP, and Alq3 are abbreviations for indium-tin-oxide, 4,4'-bis[N-(1-naphthyl)-N-phenylamino]- biphenyl, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, and tris(8-hydroxyquinoline) aluminum, respectively. Three different chemically modified ITO electrodes were used. As a hole-injecting buffer layer, copper phthalocyanine (CuPc) or 4,4',4''-tris-(3-methylphenylphenylamino) triphenylamine (MTDATA) was used in this study. We found that the luminance increased less than linearly with an increase in current for all EL devices studied even when hole and electron injection were enhanced. The luminance loss in the device is attributed to quenching singlet excited states (1NPD*) by large excess radical cations (NPD+.) accumulated in the emission zone due to large overlap between a fluorescence spectrum of 1NPD* and an absorption spectrum of NPD+.. In addition, 1NPD* can be also quenched by radical anions (NPD-.) when excess electrons are injected.
In-situDevelopment and Study of Conducting Polymer Electrodes on PVDF Substrates for Electro-Acoustic Application in Cochlear Implants
Authors: Dwivedi Arpit , Roseman Rodney
Published: June 2019

Sensorineural hearing loss (profound deafness) is a result of the inability of the transductory structures in the cochlea (organ of Corti) to convert the mechanical displacement of the basilar membrane to neural signals. A class of devices known as Cochlear Implants can significantly enhance the hearing ability in these patients. Fundamentally different from the existing cochlear implant technology, are the totally implantable piezoelectric based devices that are being developed. The unit is completely self-contained, designed to work without any signal amplifiers or transmission elements, greatly simplifying the stimulation process, and enhancing the cosmetic appearance of the patient. These devices utilize the bending piezoelectric effect. Device design consists of arrays of elements of piezoelectric polymer films with conducting polymer electrodes embedded in a flexible substrate with the whole device coated with an insulating layer. The incoming mechanical energy (pressure waves) into the cochlea generates electrical charge by virtue of the piezoelectric effect of the film. The generated charge is fed to electrical connections evaporated on the substrate and is used to stimulate surviving nerve fibers in the cochlea. In certain environments where acoustic impedance matching is limited by size constraints and conducting liquid medium, the advantage of polymer based devices over ceramics and metal based devices, are their flexibility, low acoustic impedance, and high sensitivity. However, in order to utilize these useful properties, the electrode material is an important issue, since the conventionally used metal electrodes, have high acoustic impedance and also impose mechanical clamping on the soft polymer which can significantly reduce the electromechanical efficiency of the transducer. Due to its flexibility, strong coherent interfaces, and significantly improved acoustic transparency, such an all-polymer electroactive system is compared to a metal-polymer system of similar design and also compared to the current technology.
Nanocrystalline semiconductor LEDs with simple structure and high efficiency
Authors: Bertram Dietrich , Weiler Volker , Talapin Dimitri , Weller Horst
Published: June 2019

Nanocrystalline semiconductor particles exhibit a size dependent bandgap emission, due to size quantisation effects. These particles are derived from solution chemistry and can be made monodisperse under the right synthesis conditions. Compared to organic materials, the inorganic nanoparticles show much higher stability against oxidation and degradation, which makes them an interesting candidate for LEDs and displays. So far, LEDs based on semiconductor nanoparticles typically included low stability organic materials to provide charge injection. The talk will present a new class of nanoparticle LEDs, made without sensitive organic materials. These LEDs show high efficiencies, well defined color throughout the red to green part of the visible spectrum and improved stability under ambient conditions without excessive encapsulation. Using high quality monodisperse suspensions, high color purity is achieved for the emission which paves the road to cheap, high quality displays based on inorganic semiconductor nanoparticles.
Investigation of the electronic properties of cyclopentadithiophene polymers and copolymers
Authors: Coppo Paolo , Turner Michael L. , Cupertino Domenico C. , Yeates Stephen G.
Published: June 2019

Cyclopentadithiophene based homopolymers and copolymers have been investigated as semiconductor layers in field effect transistors. They generally show low hole mobilities due to a disordered amorphous structure in the solid state. FET mobility can be enhanced in the homopolymer, although this results in poor on/off ratio of the device. The low mobilities may be attributed to the presence of solubilizing alkyl chains normal to the long axis of the polymer which prevent the self assembly of the polymer into an ordered π-stacked configuration.
The Effects of Structural Disorder on the Luminescence Quenching in Poly(phenylene vinylene)
Authors: Moses Daniel , Schmechel Roland , Heeger Alan J.
Published: June 2019

Luminescence quenching experiments on oriented and drop-cast poly(phenylene vinylene), (PPV), films identify the excitons in these polymer films as Wannier-Mott excitons. The data are interpreted in terms of a distribution of exciton binding energies (Eb). We find that the width of this distribution is well correlated with the degree of structural disorder. The relatively small mean EbEb, approximately 60 meV, results in field-induced exciton disociation that limits the quantum efficiency obtained from polymer-based light emitting diodes (PLEDs) which typically are operated at applied fields of 106 V/cm or greater where the field-induced exciton disociation is significant. We present data and analysis that support these conclusions, as well as a discussion on the implications of our findings on polymer-based display technology.
Source / drain contacts in organic polymer thin film transistors
Authors: Martin Sandrine , Hamilton Michael C. , Kanicki Jerzy
Published: June 2019

Organic polymer based thin-film transistors (OP-TFTs) look very promising for flexible organic electronics. In this paper, we describe devices based on a gate-planarized structure and using spin-coated organic polymer. We have analyzed the role of the device source and drain contacts and we present data indicating Schottky behavior of the contacts in OP-TFTs. In addition, we describe a quantitative evaluation of the source drain series resistances and extract the OP-TFT intrinsic electrical parameters.
The Crystal Sructure of Anthracene up to 22 GPa: a X-ray Diffraction Study
Authors: Oehzelt Martin , Heimel Georg , Resel Roland , Puschnig Peter , Hummer Kerstin , Ambrosch-Draxl Claudia , Takemura Kenichi , Nakayama Atsuko
Published: June 2019

The aim of this study is to investigate the crystalline structure of anthracene C14H10 under high pressure performing angle dispersive x-ray diffraction experiments using synchrotron radiation in combination with Rietveld refinements and rigid body approximation. High hydrostatic pressure was applied up to 27.8 GPa using a diamond anvil cell. Full structural information (molecular orientations and lattice constants) is given up to a pressure of 20.3 GPa. At the highest pressure of 22.7 GPa the unit cell volume is decreased by 36.8%. Fourier transformation of the diffracted intensities reveals the electron density distribution within the unit cell. A pressure induced increase of the electron densities between adjacent molecules is observed. These findings are shown to be in agreement with theoretical calculations and hint towards the evolution of the anisotropic conductivity with pressure.
Sol-gel Nanohybrid Materials Incorporating Functional Thiacalixarenes for Non-Linear Optical Applications
Authors: Desroches C. , Parola S. , Cornu D. , Miele P. , Baldeck P. L. , Lopes C.
Published: June 2019

Macrocyclic thiacalixarenes have interesting non-linear optical properties. Thiacalixarenes bearing phenylazo, imino, ethynylic groups or platinum derived acetylides on the upper rims were designed, prepared and fully characterised. They showed interesting properties for optical limiting. Moreover these macrocycles are highly soluble in organic solvents and can easily be embedded in inorganic matrix using the sol-gel routes.

Thiacalixarene based class I and II solid-state materials were prepared and their optical limiting behaviour was investigated.
Pulsed Laser Deposition of Aluminum Tris-8-hydroxyquinline and TPD Thin Films
Authors: Ebihara Kenji , Shin Pail-Kyun , Ohshima Tamiko , Kurihara Hiroshi , Ikegami Tomoaki , Yamaguchi Toshihisa , Sakai Takamasa
Published: June 2019

Thin films of low molecular weight electroluminescence (EL) materials, Alq3 (aluminum tirs-8-hydoroxyquinline), TPD (N,N'-diphenyl-N,N'-bis (3methylphenyl)-(1,1'-biphenyle)-4, 4'-diamine) were deposited by pulsed laser ablation (PLA) method using KrF excimer laser and Nd:YAG laser. Optical absorption property, surface morphology and photoluminescence of the films were investigated. Alq3 films by Nd:YAG laser show slight absorption at around 400 nm, and TPD films by either KrF laser or Nd:YAG laser showed absorption at 320 nm and 360 nm. It was found that TPD thin films for EL devices can be deposited by PLAmethod usig Nd:YAG laser.
Photochemical Patterning Approaches for Multicolor Polymer Light Emitting Devices
Authors: Pogantsch A. , Trattnig G. , Rentenberger S. , Langer G. , Keplinger J. , Tillmann H. , Hörhold H.-H. , Scherf U. , Kern W. , Zojer E.
Published: June 2019

The patterning of conjugated polymers for multicolored electroluminescence applications is a current topic of research in polymer device technology. Several techniques including direct writing approaches such as ink-jet printing have been proposed to solve this challenge. We present an approach to tuning the (electro)luminescence color of a film consisting of a blend of conjugated polymers after its deposition by means of UV-irradiation in the presence of an active agent. This promises to be an alternative, highly parallel approach towards multicolored electroluminescence.
Insulating Biomaterials Research for Implantable Microelectronic Devices
Authors: Edell David J.
Published: June 2019

Developments in the field of BioMEMS share many of the same issues encountered in the development of neural interface technology that has been underway for many decades. In addition to issues of function, other issues such as biocompatibility and bioresistance have also presented great challenges. The focus of this paper is on the development and testing of electrically insulating biomaterials for micro-devices that can be implanted in biological systems. A variety of accelerated degradation and accelerated detection of degradation techniques have been developed and are used to screen candidate materials. Direct tests of mechanical properties, adhesion, and chemical resistance are used for further assessment. Promising materials indicate what chemistry might be suitable for development of a Chemical Vapor Deposited (CVD) thin film coating. CVD coatings are under development that may be useful for insulation of very small, micromachined elements of an implantable device while only increasing the size of the device by a few micrometers. Materials passing in-vitro testing are then considered for in-vivo testing. Novel instrumentation for testing devices in-vivo has been developed.
Single Cell Based Microelectrode Array Biosensors
Authors: Yang Mo , Prasad Shalini , Zhang Xuan , Ozkan Mihrimah , Ozkan Cengiz S.
Published: June 2019

Extracellular potential is an important parameter which indicates the electrical activity of live cells. Membrane excitability in osteoblasts plays a key role in modulating the electrical activity in the presence of chemical agents. The complexity of cell signal makes interpretation of the cellular response to a chemical agent very difficult. By analyzing shifts in the signal power spectrum, it is possible to determine a frequency spectrum also known as Signature Pattern Vectors (SPV) specific to a chemical. It is also essential to characterize single cell sensitivity and response time for specific chemical agents for developing detect-to-warn biosensors. We used a 4x4 multiple Pt microelectrode array to spatially position single osteoblast cells, by using a gradient AC field. Fast Fourier Transformation (FFT) and Wavelet Transformation (WT) analyses were used to extract information pertaining to the frequency of firing from the extracellular potential.
Fabrication and Simulation of Amorphous Carbon Cantilever Structures
Authors: Chua Daniel H.C. , Milne W.I. , Yu L.J. , Sheeja D. , Tay B.K.
Published: June 2019

In view of the superior bio-compatibility of amorphous carbon (a-C) films, a study has been carried out on the fabrication and simulation of free-standing amorphous carbon microcantilevers. The fabrication of micro-structure was carried out by a single photolithography step. A 1.7micro-meter thick, low stress, smooth (Rrms ∼0.75nm) a-C films were deposited by filtered cathodic vacuum arc deposition (FCVA) system, in conjunction with high substrate pulse biasing on patterned n-doped Si >100< substrates. Subsequently, the photoresist was lifted-off in acetone and which is followed by undercutting of the cantilever structures in 40% KOH solution. The deflection of the free-standing cantilever structures was measured using an optical profiler, and the stress in the a-C cantilever structures was independently calculated from the deflection of the cantilever beam and the total tilt angle. This stress value is compared with the stress in the film measured from the film-substrate sandwich by radius of curvature technique. Simulation of the cantilever assembly was carried out to obtain the deflection and stress distribution. The simulated parameters are compared with the experimental results.
Multi-Site, Neurotransmitter-Based Retinal Interface
Authors: Peterman Mark C. , Fishman Harvey A.
Published: June 2019

Nearly all retinal prosthetics have focused on electrical stimulation of the nervous system. We are developing a novel prosthetic interface for the retina based on neurotransmitter delivery. In the past, we have demonstrated the ability to stimulate individual rat pheochromacytoma cells (PC12 cell line) using microfluidic delivery through micron-sized apertures. This delivery was highly reproducible, very controllable, and quantifiable. But this early stage device was limited to a single stimulation site and crude microfluidics. Here, we present the next stage in microfluidic retinal prosthetics with a multi-stimulation site device that incorporates more advanced control over the microfluidic delivery. We created an array of apertures in a thin silicon nitride membrane, to which we can deliver neurotransmitters in an addressable manner. Excitable cells (PC12) are seeded on the device and imaged using Ca2+-sensitive dyes with a confocal microscope. We can then excite the cells at an array of multiple precise locations near the apertures, demonstrating the next step in neurotransmitter-based retinal prosthetics.
Functionalization of carbon nanotubes for self assembly applications
Authors: Ravindran Sathyajith , Chaudhary Sumit , Ozkan Mihrimah , Ozkan Cengiz S.
Published: June 2019

We report the controlled synthesis of multi-walled Carbon Nanotube-Quantum Dot (CNT-QD) heterojunctions using the Ethylene Carbodiimide Coupling procedure (EDC). Thiol stabilized ZnS capped CdSe quantum dots containing amine terminal groups (QDNH2) were conjugated with acid treated Multi-Walled Carbon Nanotubes (MWCNT) ranging from 400 nm to 4νm in length. SEM, TEM and FTIR were used to characterize the conjugation process.
A microfluidic device with integrated impedance detection for λ-DNA
Authors: Park Myung-Il , Hong Jonging , Yoon Dae Sung , Park Chong-Ook , Im Geunbae
Published: June 2019

The large optical detection systems that are typically utilized at present may not be able to reach their full potential as portable analysis tools. Accurate, early, and fast diagnosis for many diseases requires the direct detection of biomolecules such as DNA, proteins, and cells. In this research, a glass microchip with integrated microelectrodes has been fabricated, and the performance of electrochemical impedance detection was investigated for the biomolecules. We have used label-free λ-DNA as a sample biomolecule. By changing the distance between microelectrodes, the significant difference between DW and the TE buffer solution is obtained from the impedance-frequency measurements. In addition, the comparison for the impedance magnitude of DW, the TE buffer, and λ-DNA at the same distance was analyzed.
Biosensing in microfluidic channels using Fluorescence Polarization
Authors: Yadavalli Vamsi K. , Pishko Michael V.
Published: June 2019

Microfabricated microfluidic devices provide useful platforms for sensing and conducting immunoassays for high throughput screening and drug discovery. Here, Fluorescence Polarization has been used as a technique for probing binding events within 500 micron and smaller microfluidic channels fabricated in poly (dimethyl siloxane) (PDMS). The binding of concanavalin A to a lectin-dextran and a glycoproteinacetylcholinesterase has been used to demonstrate the homogeneous, ratioing format of fluorescence polarization for the quick and accurate determination of extremely low (nanomole) concentrations. Polarization has also been used to sense for a poly-aromatic hydrocarbon (PAH) within a microfluidic channel using binding to an antibody. We have also demonstrated a simple pH sensor based on the change in anisotropy of a pH sensitive fluorophore. The ease of fabrication and measurement using such polarization-based devices make them extremely suitable for micro-sized sensors, assays and total analysis systems.
From BioMEMS to Bionanotechnology: Integrated BioChips for the Detection of Cells and Microorganisms
Authors: Bashir R. , Akin D. , Gómez R. , Li H. , Chang W.J. , Gupta A.
Published: June 2019

This paper reviews the interdisciplinary work performed in our group in recent years to develop micro-integrated devices to characterize biological entities. We present the use of electrical and mechanically based phenomena to perform characterization and various functions needed for integrated biochips. One sub-system takes advantage of the dielectrophoretic effect to sort and concentrate cells within a micro-fluidic biochip. Another sub-system measures impedance changes produced by the metabolic activity of cells to determine their viability. A third sub-system is used to detect the mass of bacteria as they bind to micro-mechanical silicon cantilevers. These devices with an electronic signal output can be very useful in producing practical systems for rapid detection and characterization of cells for a wide variety of applications in the food safety and health diagnostics industries.
Surface Modification for Protein Resistance Using a Biomimetic Approach
Authors: Dalsin Jeffrey L. , Messersmith Phillip B.
Published: June 2019

In recent years the immobilization of poly(ethylene glycol) (PEG) on surfaces has proved to be one of the most attractive methods to prevent biological fouling of surfaces. We have developed a paradoxical biomimetic PEGylation strategy that exploits the adhesive characteristics of proteins secreted by marine mussels—one of nature's most notorious foulers. Linear PEGs were coupled to peptides containing 3,4-dihydroxyphenylalanine (DOPA), an unusual amino acid which is found in high concentration in these so-called mussel adhesive proteins. Using surface plasmon resonance, we have demonstrated enhanced resistance to protein adhesion on gold substrates modified with the DOPA-containing PEGs.
Mimicking the Formation of Biomineral Composites through Deposition of Calcium Carbonate Thin-Films on Modified Fiber Net Templates
Authors: Ajikumar Parayil Kumaran , Lakshminarayanan Rajamani , Suresh Valiyaveettil
Published: June 2019

Thin films of calcium carbonate were deposited on the surfaces of synthetic substrates using a simple biomimetic pathway. The Nylon 66 fiber knit pre-adsorbed with acidic polymers was used as a template for the controlled deposition of CaCO3 thin film. The presence of the soluble macromolecules on the fiber knit surface was characterized using ATR-FTIR spectroscopy. The characterization of the mineral films was carried out using scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive Xray scattering (EDX) studies.
Reconfigurable Hydrophobic/Hydrophilic Surfaces Based on Self-Assembled Monolayers
Authors: Deval Joanne , Umali Teodoro A. , Spencer Brandee L. , Lan Esther H. , Dunn Bruce , Ho Chih-Ming
Published: June 2019

The fabrication of micron-scale channels and reaction chambers using micromachining techniques has created devices with large surface to volume ratios. As a result, surface properties play a major role in determining the behavior of micromachined devices. In this work, we present strategies that can be used to reconfigure surfaces from hydrophobic to hydrophilic or from hydrophilic to hydrophobic. The reversible nature of the surface is made possible by using deposition and removal of biomolecules or amphiphiles on self-assembled monolayers (SAMs). When the initial surface was hydrophobic (using a CH3-terminated SAM on the surface, water contact angle ∼100), it was rendered hydrophilic (water contact angle ≤60°) using monolayer adsorption of avidin protein. To retrieve the hydrophobicity, the avidin was subsequently removed using non-ionic surfactant octyl-β-D-glucopyranoside. Moreover, by incorporating a biotinylated poly(ethyleneglycol), the avidin-coated surface was resistant to further non-specific adsorption. If the initial surface was hydrophilic (using a CO2H-terminated SAM on the surface, water contact angle ≤20°), it was rendered hydrophobic (water contact angle >90°) using monolayer amphiphilic octadecylamine adsorption. The hydrophilicity was restored after subsequently removing the amphiphile using anionic surfactant sodium lauryl sulfate. Both types of surfaces showed excellent reversibility and demonstrated the ability to control surface wettability.
Intrafibrillar Mineralization of Collagen using a Liquid-Phase Mineral Precursor
Authors: Olszta Matthew J. , Douglas Elliot P. , Gower Laurie B.
Published: June 2019

Intrafibrillar mineralization of type-I collagen with hydroxyapatite (HA) is the basis of the complex biological composite known as bone, which from a material science perspective is a fascinating example of an interpenetrating bioceramic composite. Using a polymer-induced liquid-precursor (PILP) process, collagen substrates were highly infiltrated with a liquid-phase mineral precursor to calcium carbonate (CaCO3). At sections of partially mineralized collagen, banded mineral patterns were observed perpendicular to the collagen fibrils, while other fibrils were completely mineralized. An acid etch, used to preferentially remove superficial mineral, further revealed such banded patterns in fully mineralized samples. Removal of the collagen matrix with a dilute hypochlorite solution showed an interpenetrating mineral phase, with mineral disks that spanned the diameter of the pre-existing collagen fibrils, supporting our hypothesis that intrafibrillar mineralization can be achieved via capillary action applied to a liquid-phase mineral precursor.
Surface Plasmon Resonance Spectroscopic Study on Pore-Forming Behavior of Streptolysin O on Supported Phospholipid Bilayers
Authors: Wilkop Thomas , Xu Danke , Cheng Quan
Published: June 2019

A novel supported bilayer membrane was formed on top of a hydrophobic spacer layer of hexyl thioctate (HT) and its application in the detection of pore forming toxins was demonstrated. The formation kinetics, effect of different flow rates on the fusion process of vesicles and perforation by incubation with streptolysin O (SLO) and pristine membranes were investigated. Individual layers of the multilayer structure were successfully characterized with surface plasmon resonance (SPR), and the resulting spectra were analyzed in order to determine the layer thickness and other membrane properties. The interaction of SLO with the pristine biomimetic membrane resulted in a pronounced change in the reflectivity spectrum. Elements of these spectral changes were analyzed to explain the process of toxin binding and pore formation taking place on the lipid membrane.
Composition and Surface Topography Effects on Apatite-Forming Ability of Ceramic-Polymer Composites
Authors: Rea Susan M. , Best Serena M. , Bonfield William
Published: June 2019

HAPEXTM (40 vol% hydroxyapatite in a high-density polyethylene matrix) and AWPEX (40 vol% apatite-wollastonite glass ceramic in a high density polyethylene matrix) are composites designed to provide bioactivity and to match the mechanical properties of human cortical bone. HAPEXTM has had clinical success in middle ear and orbital implants, and there is great potential for further orthopaedic applications of these materials. However, more detailed in vitro investigations must be performed to better understand the biological interactions of the composites and so the bioactivity of each material was assessed in this study. Specifically, the effects of controlled surface topography and ceramic filler composition on apatite layer formation in acellular simulated body fluid (SBF) with ion concentration similar to those of human blood plasma were examined. Samples were prepared as 1 cm × 1 cm × 1 mm tiles with polished, roughened, or parallel-grooved surface finishes, and were incubated in 20 ml of SBF at 36.5 °C for 1, 3, 7, or 14 days. The formation of a biologically active apatite layer on the composite surface after immersion was demonstrated by thin-film x-ray diffraction (TF-XRD), environmental scanning electron microscopy (ESEM) imaging and energy dispersive x-ray (EDX) analysis. Variations in sample weight and solution pH over the period of incubation were also recorded. Significant differences were found between the two materials tested, with greater bioactivity in AWPEX than HAPEXTM overall. Results also indicate that within each material the surface topography is highly important, with rougher samples correlated to earlier apatite formation.
Quantum Dots Stabilized By Genetically Engineered Proteins
Authors: Ding S.-Y. , Rumbles G. , Jones M. , Tucker M.P. , Nedeljkovic J. , Wall J. , Himmel M.E.
Published: June 2019

Colloidal quantum dots (QDs) exhibit unique optical and electronic properties due to their physical size and the semi-conductor material from which they are made [1,2]. While the isolated properties of these nanoparticles offer a number of potential applications, such as bioimaging, their future use in novel electronic devices will require large arrays of known order. The assembling of these arrays is non-trivial and requires a monodisperse sample of quantum dots in order to facilitate the self-assembling process [3,4]. We propose first to validate the concept of using natural and/or recombined (genetic engineered) proteins to build stable, water soluble QD-protein conjugates [5]. Eventually, strategies to design these structures with highly controlled patterns will emerge.
Osteoblast-like Cell Response to Apatite-Wollastonite/Polyethylene Bone Replacement Composites
Authors: Rea Susan M. , Brooks Roger A. , Best Serena M. , Bonfield William
Published: June 2019

Apatite-wollastonite (A-W)/high-density polyethylene composite (AWPEX) materials have been designed to match the mechanical strength of human cortical bone and to provide favorable bioactivity, with potential use in many orthopaedic applications. To better understand AWPEX properties, the effects of surface finish and ceramic filler size and content on osteoblast-like cell attachment, proliferation, and differentiation were examined. Glass ceramic content was tested at 30 and 50 vol% and median particle size at 4.5 and 7.7 μm. Samples were prepared as 10 × 10 × 1 mm3 tiles with polished or roughened surfaces, sterilized by gamma irradiation (2.5 Mrad), and characterized by SEM, surface energy, and surface profilometry. Saos-2 human osteoblastlike cells were cultured on each surface at an initial concentration of 4500 cells/cm2 in McCoy's medium and incubated at 37C in a humidified atmosphere with 5% CO2 for 1, 3, or 7 days. At each time point, adenosine triphosphate (ATP) and alkaline phosphatase (ALP) levels were measured to assess cell number and osteoblast differentiation. Significant differences were found at 7 days, confirmed by ANOVA post-hoc testing using Bonferroni's correction. Overall, increased exposure of the A-W phase in AWPEX through surface polishing, higher volume fraction, and/or larger particle size, was found to lead to an improved cell response.
Amelogenin Induces Biomimetic Mineralization at Specific pH
Authors: Habelitz Stefan , Ford Dustin , Marshall Sally J. , DenBesten Pamela K. , Balooch Mehdi , Marshall Grayson W. , Li Wu
Published: June 2019

Amelogenin proteins are assumed to control the calcification of dental enamel with a nanoscale precision that facilitates the formation of fibrous apatite crystals organized in a remarkable microstucture. In this study, recombinant full-length human amelogenin induced protein-guided mineralization and the formation of an enamel-like composite material at specific physical-chemical conditions as observed by atomic force microscopy (AFM). Amelogenin bound specifically to fluoroapatite crystals (FAP) of a glass-ceramic substrate at Ca2+ and PO43- concentrations similar to in-vivo conditions and at pH 8. Layers up to 400 nm high, containing elongated crystals, formed on the (001)-planes of FAP within 24h in supersaturated solutions. In contrast, (hk0)-faces grew by only 10-30 nm, but showed nanospheres aligned parallel to the c-axis of FAP. At pHs different from 8, proteins bound non-specifically to substrate and layers on FAP reached only 5-15 nm thickness. Micro-Raman spectroscopy and AFM revealed the formation of a composite material that resembled a structure and composition comparable to human enamel. These observations suggest that certain conditions are required to activate amelogenin to control and promote crystal growth of apatite along the c-axis and to synthesize an enamel-like material.
Synthesis and Electronic Transport Studies of Single-Crystalline In2O3 Nanowires
Authors: Li Chao , Zhang Daihua , Han Song , Liu Xiaolei , Tang Tao , Lei Bo , Zhou Chongwu
Published: June 2019

Single crystalline In203 nanowires were successful synthesized using a laser ablation method. Extensive material characterization such as X-ray diffraction (XRD) and selected area electron diffraction (SAED) revealed a cubic crystal structure for these nanowires with [110] as the growth direction. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are used to determine the diameter and length of our nanowires. By using monodispersed gold clusters as the catalyst, these nanowires can be grown with well-defined diameters around 10 nm. Individual In2O3 nanowires have been utilized to construct field effect transistors, which confirmed In2O3 nanowires as n-type semiconductors and exhibited on / off ratios as high as 104 at room temperature. The temperature-dependence of the conductance revealed thermal emission as the dominating transport mechanism. Our work can lead to important applications such as chemical sensing for In2O3 nanowires.
Supercritical Fluids as New Reaction Media to Synthesize Nanostructured Materials
Authors: Aymonier Cyril , Desmoulins-Krawiec Sophie , Loppinet-Serani Anne , Weill François , Cansell François
Published: June 2019

Supercritical fluids exhibit a range of unusual properties that can be exploited for the development of new reactions for material synthesis. These reactions are different from those performed in classical solid-state chemistry. Supercritical fluids are interesting as reaction media for the synthesis of nanostructured materials because fluid properties such as density, viscosity, diffusivity and solubility of reagents can be continuously tuned from gas to liquid with small variations in pressure and temperature. Moreover, supercritical fluid processing offers the possibility of using solvents with low toxicity that result in nanostructured materials free of solvent contamination. The process developed at ICMCB obtains nanostructured materials by chemically transforming a metal precursor inside a supercritical fluid. The synthesis of nanostructured materials such as metals, oxides or nitrides is possible at lower temperatures than the classic solid-state chemistry route. Based on experimental results and simulations, the nanostructured material nature, size and morphology can be continuously adjusted as a function of the operating condutions. Our process provides a great contribution in the development of self-assembled nanostructured materials by controlling the chemical composition, size, morphology and the surface properties of nanobricks.
Fluorinated Surfactant Templating of Ordered Nanoporous Silica
Authors: Rankin Stephen E. , Tan Bing , Lehmler Hans-Joachim , Knutson Barbara L.
Published: June 2019

We will describe the first synthesis of ordered mesoporous silica using a fluorinated surfactant template. Nitrogen adsorption, x-ray diffraction and TEM results will be presented that show that at room temperature, we form particles with well-ordered 2D hexagonal pores using a cationic surfactant with a partially fluorinated octyl (C8) tail. The pore diameter determined by the inflection in the nitrogen adsorption isotherm is on the order of 2.6 nm and the pore size distribution is very narrow. Consistent diameters are found with a modified Kelvin equation approach and with nonlocal density functional theory. The same pore size and long-range order are found for a range of surfactant to silica ratios.