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Low Temperature PECVD Silicon Oxide For Devices And Circuits On Flexible Substrates
Authors: Meitine Mark , Sazonov Andrei
Published: June 2019

The aim of this research is to develop low temperature gate dielectric/passivation layer for μc-Si and poly-Si based devices and circuits compatible with plastic substrates.

The PECVD silicon oxide films were fabricated from mixture of silane and nitrous oxide at 250 °C, 120 °C and 75 °C. Helium, argon and nitrogen were used as diluent gases to optimize density, stress, uniformity, and electronic properties.

Chemical composition and bonding in the films were studied by FTIR spectroscopy. The absorption peak at 1075-1080 cm-1 observed in the spectrum of each film corresponds to SiO2 stretching mode. No presence of SiH stretching or NH-stretching vibrations was found in the FTIR spectra of the samples.

Film uniformity was varied from 1.44 % to 5.60 % for 3“×3” area. Four wafers were processed at the same time. The deposited films have compressive stress varied from 0.063 GPa to 0.117 GPa. Respective film density is in the range from 1.63 g/cm3 to 1.77 g/cm3.

The electronic properties were studied on MOS capacitors with 200 nm thick SiOx. The dielectric permittivity was in the range between 2.03 and 3.57. The dielectric breakdown at 9 MV/cm was observed for the films deposited at 120 °C. The films deposited at higher temperatures are characterized by lower leakage current density, which was 3.7.10-10 A/cm2 for the sample deposited at 250 °C, 9.10-9 A/cm2 for 120 °C, and 2.2.10-8 A/cm2 for 75 °C at 5 MV/cm.

The a-Si:H based TFTs were fabricated using low temperature oxide as gate dielectric. TFTs demonstrate threshold voltage (3.02 – 4.12 V) and mobility (0.12 – 0.59 cm2/Vs) comparing with those using silicon nitride.
Nanotectonics: Direct Fabrication of All-Inorganic Logic Elements and Micro-Electro-Mechanical Systems from Nanoparticle Precursors
Authors: Wilhelm Eric J. , Jacobson Joseph
Published: June 2019

The reduced melting point and high solubility of inorganic nanoparticles have been shown to be useful in the low-temperature solution-based fabrication of semiconductor devices. These inks have been patterned using various techniques to form inorganic logic elements, multi-layer structures, and MEMS. Here we report a new technique known as offset liquid embossing that is used to print the nanoparticle inks. Structures created include multiple layers of gold and spin-on-glass printed without the need for etching or planarization, and 100 nm resolution.
High-quality inkjet-printed multilevel interconnects and inductive components on plastic for ultra-low-cost RFID applications
Authors: Molesa Steven , Redinger David R. , Huang Daniel C. , Subramanian Vivek
Published: June 2019

In recent years, there has been tremendous interest in all-printed electronics as a means of achieving ultra-low-cost electronic circuits with uses in displays and disposable electronics applications such as RFID tags. While there have been a few demonstrations of printed organic transistors to date, there has been little work on the associated passive component and interconnection technologies required to enable the development of all-printed RFID circuits. In particular, low-resistance conductors are crucial to achieve the high-Q inductors necessary for RFID. Here, we demonstrate inkjetted nanoparticle-Au conductors on plastic with sheet resistances as low as 0.03 ohms/square. We describe the optimization of the jetting parameters, and their impact on final film morphology and electrical properties. We also demonstrate a bridging technology based on an inkjetted polyimide interlevel dielectric. Using this process, we demonstrate multilevel interconnect and passive component structures including conductor patterns, crossover bridges, and tapped planar spiral inductors. Together, these represent an important step towards the realization of all-printed RFID.
A Basic Concept of Novel Hybrid Opto-Elctronic Integrated Systems with Textile Structures
Authors: Tanaka Kuniaki
Published: June 2019

According to the situation recognition of a basic limit of electronics expansion in silicon planar technology, one proposal based on a new technology completely different from planar structure is done here. The new concept of the technology is “textile structure” for integrated optoelectronic circuit. The background of the new concept is shown from some historical view point. The concept is also discussed as an opto-electronic united circuit and a “Clothes” level system from application-view point. Characteristics and elemental technology of the textile hybrid system are considered for future development of this concept. Several concrete compositions and characteristics of the proposed system are compared with those of present technology to construct a new electronics system. This proposal is also discussed in flexible electronics concept.
An Inverter Woven from Flat Component Fibers for e-Textile Applications
Authors: Bonderover Eitan , Wagner Sigurd , Suo Zhigang
Published: June 2019

In the most fundamental approach, e-Textile circuits will be made by weaving component fibers into circuits. The weaving pattern will determine the circuit function. A key requirement of such e-Textile circuits is reliable electrical contact between fibers. Contacts which rely only on the pressure between fibers are preferred since they preserve the drapability of real fabrics. Since thin-film device fabrication technology is planar, the component fibers, made by the slit-film technique, are flat. Thus a slight edge-to-edge curvature (with a radius of curvature as large as 500mm) can either prevent or promote electrical contact. Using fibers with thin-film transistors of amorphous silicon, we study the processes that produce the desired fiber curvature. A layer of stressed silicon nitride is used to create the curvature. The stress in this layer can be controlled by the deposition parameters. We present successful fabrication of curved fibers with vastly improved electrical contact. We also present electrical characterization of woven transistor circuits
Gallium zinc oxide coated polymeric substrates for optoelectronic applications
Authors: Fortunato E. , Gonçalves A. , Marques A. , Assunção V. , Ferreira I. , Águas H. , Pereira L. , Martins R.
Published: June 2019

Highly transparent and conductive ZnO:Ga thin films were produced by rf magnetron sputtering at room temperature on polyethylene naphthalate substrates. The films present a good electrical and optical stability, surface uniformity and a very good adhesion to the polymeric substrates. The lowest resistivity obtained was 5×10-4 Ωcm with a sheet resistance of 15 Ω/sqr and an average optical transmittance in the visible part of the spectra of 80 %. It was also shown that by passivating the polymeric surface with a thin SiO2 layer, the electrical and structural properties of the films are improved nearly by a factor of 2.
Silicon Nanocrystal Nucleation as a Function of the Annealing Temperature in SiOx Films
Authors: Daldosso N. , Das G. , Dalba G. , Larcheri S. , Grisenti R. , Mariotto G. , Pavesi L. , Rocca F. , Priolo F. , Franzò G. , Irrera A. , Miritello M. , Pacifici D. , Iacona F.
Published: June 2019

Si nanocrystals (Si-nc) embedded in amorphous silica matrix have been obtained by thermal annealing of substoichiometric SiOx films, deposited by PECVD (plasma enhanced chemical vapour deposition) technique with different amount of Si concentrations (42 and 46 at.%). Both nucleation and evolution of Si-nc together with the changes of the amorphous matrix have been studied as a function of the annealing temperature. The comparison of x-ray absorption measurements in Total Electron Yield (TEY) mode at the Si k-edge with photoluminescence (PL), FTIR and Raman spectra, allowed clarifying the processes of Si-nc formation and structural evolution as a function of the annealing temperature and Si content.
Exceptionally High Radiative Efficiencies in Silicon
Authors: Green M.A. , Wang A. , Zhao J. , Trupke T. , Cho E-C. , Xia J.
Published: June 2019

Although silicon is known as a poor emitter of light, recent work has demonstrated silicon light emission efficiencies in the range normally associated with III-V semiconductors. The present paper explores the light emission efficiency potential of silicon as well as the scope for implementing silicon optical functions into high density integrated circuits.
Erbium-silicon-oxide Nano-complexes Prepared by Wet Chemical Synthesis
Authors: Isshiki H. , Dood M.J.A. de , Kimura T. , Polman A.
Published: June 2019

An entirely new method to fabricate optically active and carrier-mediated excitable erbium complexes on silicon is presented. The Er-Si-O nano-complexes are formed by spin-coating a Si (100) substrate with an ErC13 solution, followed by a rapid thermal oxidation and annealing sequence (RTOA). Intense room-temperature luminescence is observed from the Er-Si-O nano-complexes, with a line width as narrow as 4 meV at room temperature. The Er emission at 1.53 μm can be excited both directly and through photo carriers. Formation and optical activation of the Er-Si-O nano-complexes are discussed. In addition, an application of the wet chemical synthesis technique to incorporation of the Er-Si-O nano-complexes into nano-porous silicon waveguides is demonstrated.
Formation and Electric Properties of Disordered Yb Layers on Si(111)7×7 Surface
Authors: Galkin Nickolay G. , Goroshko Dmitrii L. , Gouralnik Alexander S. , Dotsenko Sergei A. , Boulatov Andrei N.
Published: June 2019

Interface formation in Yb/Si(111) system has been investigated by AES and EELS spectroscopy and in situ Hall measurements at room temperature. It was found that interface formation process may be divided into five stages: 1) two-dimensional growth of Yb, 2) intermixing and formation of two-dimensional Yb silicide, 3) formation of 3D silicide islands, 4) growth of Yb on 3D silicide islands, 5) coalescence of 3D Yb – Yb silicide islands and formation of continuos Yb film. We attribute the observed character of conductivity in Yb/Si(111) system to the evolution of morphological and electrical properties of the growing Yb layer (2D Yb, silicide, metal) rather than to the changes within the space charge layer under the surface. Some amplitude oscillations have been observed in sheet conductivity, hole mobility and surface hole concentration within the coverage range below 6 ML where formation of a continuos Yb silicide film completes. Conductivity oscillations are explained by transition from semiconductor-type conductivity at the first growth stages (two-dimensional Yb growth) to metal-like conductivity of 2D and 3D Yb silicide films.
Integrated Silicon Infrared Microspectrometers
Authors: Kong S.-H. , Graaf G. de , Wolffenbuttel R.F.
Published: June 2019

Design, fabrication and performance of a microspectrometer for operation in the infrared spectral range between 1 and 8 μm and fabricated in silicon are presented. The opto-electrical system is composed of two bonded silicon wafers, which have been subjected to microelectronic process compatible micromachining to enable co-integration of the optical components (an aluminum based grating, an optical path in crystalline silicon and an array of integrated polysilicon thermocouples) with readout circuits in silicon. The FWHM is smaller than 0.5 μm at λ= 5 μm. The performance is compared to alternatives and directions for improving the selectivity are given.
Spectroscopic Properties and Phase-separation Effect of Europium-doped Sodium Borosilicate Glasses
Authors: Ding J. Y. , Yin C.K. , Shih P.Y. , Yung S.W.
Published: June 2019

Europium oxide has been doped into sodium borosilicate (NBS) glasses (8Na2O-32B2O3- 60SiO2- xEu2O3) at various concentration levels. The glass raw materials were calcined at 800°C and melted at 1380°C and transparent glasses with slightly red color were obtained by quenching the melt in air. Thermal analyses and other experimental results showed excellent glass forming capability with Tg around 480 to 520°C at various doping concentrations. A typical deformation temperature of the europium-doped NBS glasses is around 570-660°C with densities around 2.45 to 2.6 g/cm3. The doped NBS glasses were further heat-treated at 560°C for phase-separation. Scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), thermomechanical analysis (TMA), optical absorption spectrometer and fluorescence emission spectrometer were used to explore properties of the glasses.
CW and Time-Resolved Photoluminescence Analysis of Silicon Implanted Glass Low-Temperature Annealed at Different Times
Authors: Lin Gong-Ru , Lin Chun-Jung
Published: June 2019

The effects of annealing time on continuous-wave (CW) and nanosecond time-resolved (TR) photoluminescence (PL) spectra of silicon-ion-implanted Borosilicate glass (BSO:Si+) annealing at 500°C are characterized. A broadband CWPL of the as-implanted BSO:Si+ at 450-530 nm is observed, and the luminescent peak is found to slightly red-shift after annealing for 90 min. The increasing CWPL intensity reveals that the natural oxygen vacancy (NOV, ΞSi Si-SiΞ) related irradiative defect is highly activated during 30-min annealing, however, which abruptly decreases with the annealing lengthens to 60-min or longer. The TRPL analysis indicates a non-radiative recombination process with a sub-picosecond lifetime for the blank BSO and the as-implanted BSO:Si+ samples, which gradually disappears as the BSO:Si+ is long-term annealed. The irradiative luminescent lifetime of the 60-min annealed BSO:Si+ is lengthened from 1.7 ns to 2.8 ns, which reveals that the density of the NOV defect is decreasing by at least one order of magnitude. A longer irradiative decay with nearly identical lifetime is also found in all annealed BSO:Si+. The ratios of TRPL peak intensities for different samples correlate well with those observed in CWPL measurement, however, the weighting factors of TRPL intensities for the latter two decaying components are vicissitudinous each other in different samples BSO:Si+. This interprets a significant evolution among different decaying mechanisms during the annealing process.
Hydrogen Passivation Kinetics of Si Nanocrystals in SiO2
Authors: Wilkinson Andrew R. , Elliman Robert G.
Published: June 2019

Hydrogen passivation of non-radiative defects increases the luminescence intensity from silicon nanocrystals. In this study, photoluminescence (PL) and time-resolved PL were used to investigate the chemical kinetics of the hydrogen passivation process. Isochronal and isothermal annealing sequences were used to determine the reaction kinetics for the absorption and desorption of hydrogen, using the generalised consistent simple thermal (GST) model proposed by Stesmans for Pb defects at planar Si/SiO2 interfaces. This included determination of the activation energies and rate constants for the forward and reverse reactions as well as the associated spread in activation energies. The reaction kinetics determined from such measurements were found to be in excellent agreement with those for the passivation of Pb defects at planar Si/SiO2 interfaces, suggesting the nanocrystal emission process is also limited by such defects. These results provide useful model data as well as insight into the processing conditions needed to achieve optimum passivation in H2. As an extension to the work, a preliminary study into passivation by atomic hydrogen was pursued via a post-metallization Al anneal (alneal). A considerable gain in luminescence efficiency was achieved over the previously optimised passivation in H2.
The Origin Of The 0.78 eV Luminescence Band In Strained Layer SiGe/Si
Authors: Kenyon Anthony J. , Steinman Edward A. , Pitt Christopher W. , Hole David E. , Vdovin Vladimir I.
Published: June 2019

The photoluminescence band around 0.78 eV that is sometimes seen in strained layer SiGe samples or deformed silicon containing a high density of dislocations has been attributed to the presence of oxygen complexes. In this study we have prepared a set of Si0.9Ge0.1 samples by MBE which have then been implanted with iron, erbium, or oxygen in order to study the effect of implanted impurities on photoluminescence in the technologically important region around 1.5 microns.

Following implantation with oxygen, two luminescence bands appear around 0.85 eV and 0.78 eV, respectively. However, these bands are not present in either the unimplanted sample or those subject to Er or Fe implantation. The correlation between oxygen doping and the appearance of these bands supports the conjecture that they are associated with oxygen complexes.
Experimental and Theoretical Joint Study on the Electronic and Structural Properties of Silicon Nanocrystals Embedded in SiO2: active Role of the Interface Region
Authors: Daldosso N. , Luppi M. , Dalba G. , Pavesi L. , Rocca F. , Priolo F. , Franzò G. , Iacona F. , Degoli E. , Magri R. , Ossicini S.
Published: June 2019

The local environment of light emitting silicon nanocrystals (Si-nc) embedded in amorphous SiO2 has been studied by x-ray absorption spectroscopy (XAS) and by ab-initio total energy calculations. Si-nc have been formed by PECVD deposition of SiOx with different Si content (from 35 to 42 at.%) and thermal annealing at high temperature (1250 °C). The comparison between total electron yield (TEY) and photoluminescence yield (PLY) spectra has allowed the identification of a modified region of SiO2 (about 1 nm thick) surrounding the Si-nc, which participates to the light emission of Si-nc. Total energy calculations, within the density functional theory, clearly show that Si-nc are surrounded by a cap-shell of stressed SiO2 with a thickness of about 1 nm. The optoelectronic properties show the appearance of localized states not only in the Si-nc core region but also in the modified SiO2 region.
Si Nanocrystals as Sensitizers for Er PL in SiO2
Authors: Forcales M. , Wojdak M. , Klik M.A.J. , Gregorkiewicz T. , Gusev O. B. , Franzò G. , Pacifici D. , Priolo F. , Iacona F.
Published: June 2019

Sensitization of Er3+ photoluminescence in SiO2 layers by silicon nanocrystals has been investigated under resonant and nonresonant pulsed optical pumping. We observed that the very efficient channel of erbium excitation introduced by the nanocrystals can be saturated when very high pulsed photon flux is used. While this channel is saturated, tuning to the resonant excitation wavelength results in an increase of erbium-related photoluminescence, indicating that direct and indirect excitations can take place simultaneously.
Microscopic Structure of Er-Related Optically Active Centers in Si
Authors: Przybylinska H. , Vinh N. Q. , Andreev B.A. , Krasil'nik Z. F. , Gregorkiewicz T.
Published: June 2019

A successful observation and analysis of the Zeeman effect on the near 1.54 μm photoluminescence spectrum in Er-doped crystalline MBE-grown silicon are reported. A clearly resolved splitting of 5 major spectral components was observed in magnetic fields up to 5.5 T. Based on the analysis of the data the symmetry of the dominant optically active center was conclusively established as orthorhombic I (C2v), with g‼≈18.4 and g⊥≈0 in the ground state. The fact that g⊥≈0 explains why EPR detection of Er-related optically active centers in silicon may be difficult. Preferential generation of a single type of an optically active Er-related center in MBE growth confirmed in this study is essential for photonic applications of Si:Er.
Defect Mediated and Resonant Optical Excitation of Er3+Ions in Silicon-rich Silicon Oxide
Authors: Kuritsyn D. , Kozanecki A. , Przybylińska H. , Jantsch W.
Published: June 2019

We study sensitization of the4I13/2–4I15/2Er3+luminescence at 1.54 μm in silicon-rich silicon oxide (SRSO) in the whole range of blue-green pump wavelengths. We show that, in general, defects due to excess Si in silica act as luminescence sensitizers. They cause a wide excitation band with a long wave length limit of 600 nm. For monochromatic excitation the maximum luminescence yield is still smaller than for resonant excitation within the 4f shell of Er without additional Si. The large enhancement of the excitation cross section for electrical excitation reported in the literature is plausible, however, as the wide excitation band makes good use of the wide energy distribution of hot carriers. We suggest that the dominant factors, which limit the excitation efficiency of Er3+, are distance dependence of the transfer rate and little spectral overlap of the interacting states.
Self-Assembly Optical Components
Authors: Lazarev Pavel I. , Paukshto Michael V. , Sidorenko Elena N.
Published: June 2019

We report a new method of Thin Crystal Film deposition. In the present paper we describe the method of crystallization, structure, and optical properties of Bisbenzimidazo[2,1-a:1',2',b']anthra[2,1,9-def:6,5,10-d'e'f']-diisoquinoline-6,9-dion (mixture with cis-isomer) (abbreviated DBI PTCA) sulfonation product. The Thin Crystal Film has a thickness of 200-1000 nm, with anisotropic optical properties such as refraction and absorption indices. X-ray diffraction data evidences a lyotropic liquid crystalline state in liquid phase and crystalline state in solid film. Anisotropic optical properties of the film make it useful in optical devices, e.g. liquid crystal displays.
Absorption and Luminescence Properties of Sequentially Random- and Defined Copolymers Based on Poly(fluorene-benzothiadiazole)
Authors: Herguth Petra , Kim Joo Hyun , Jiang Xuezhong , Liu Michelle S. , Jen Alex K-Y.
Published: June 2019

The emission wavelength in conjugated copolymers is determined by the various monomers used, their sequence in the polymer backbone, the effective conjugation length of the material, and intra- and intermolecular interactions of the different units. This paper will discuss the influence of conjugation length as well as the influence of intramolecular charge-transfer on the absorption and emission properties. Fluorene, benzothiadiazole and a third comonomer (fluorene, xylene or triphenylamine) were used as building blocks. The influence of monomer sequence is probed as well by comparing sequentially random copolymers to their sequentially defined ones with identical monomer ratios. Model oligomers were also made for comparison.
Novel Divalent Osmium Complexes: Synthesis, Characterization, Tuning of Emission, and use in Organic Light Emitting Diodes
Authors: Carlson Brenden , Phelan Gregory D. , Kim Joo H. , Jen Alex K.-Y. , Dalton Larry
Published: June 2019

In this work we present the synthesis and characterization of several novel osmium complexes of the form [Os(N-N)2 L-L]2+ 2Ts- or [Os(L-L)2 N-N]2+ 2Ts- designed for organic light emitting device (OLED) applications. In the complex notation N-N represents a derivative of 2,2'-bipyridine or 1,10-phenanthroline and L-L represents a strong π-acid arsine or phosphine ligand. Several counterions have been used and include tosylate, hexafluorophosphate, triflate, heptafluorobutyrate, chloride, bromide, and iodide. The complexes feature 3MLCT emission that ranges from 611-650 nm, which makes them suitable as an emission source for red OLEDs. Phosphorescent quantum yields as high as 45% and emission lifetimes as short as 400 nanoseconds have been reached. The complexes were incorporated into OLED and give off red, orange, yellow, and green electrophosphorescence. Red devices have been created using polyvinylcarb/2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole, polyvinylnapthalene/2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole, and polyfluorene host materials. OLEDs have been created which give brightness up to 3000 cd m-2 and efficiency up to 2.2% at 632 nm emission.
Energetics of mer/fac isomers in metal tris(8-hydroxyquinoline) chelates: Implications on charge conduction in organic light-emitting devices
Authors: Ferris Kim F. , Sapochak Linda S. , Rodovsky Deanna , Burrows Paul E.
Published: June 2019

Electronic structure calculations for the mer and fac-isomers of aluminum tris (8-hydroxyquinoline) (Alq3) and the methyl-substituted series, nMeq3Al (n = 3 - 7) are presented. From these data, we estimate their relative abundances in Alq3 thin films and the resultant trap state energies. Ab initio computations performed at the SCF level suggest a significantly higher stability (6 - 7.5 kcal/mol) of the mer-isomer over the facial form, whereas MP2 treatment of electron correlation effects lowers the difference to (4 - 4.5 kcal/mol). Substitution of the Al+3 metal ion with the larger ions Ga+3 and In+3 increases the energetic preference of the meridianal form by 2.7 kcal/mol and decreases it by 0.8 kcal/mol, respectively. Trap state energies calculated by previously proposed methodologies show little difference between mer and fac trap states. These results suggest that the existence of the facial isomer in thin films of metal trisquinolates is unlikely to significantly affect charge conduction.
Imaging individual chains and aggregates on conjugated polymer films
Authors: Kemerink M. , van Duren J.K.J. , Jonkheijm P. , Koenraad P.M. , Janssen R.A.J. , Salemink H.W.M. , Wolter J.H.
Published: June 2019

We demonstrate a novel method to visualize individual molecular chains in the surface layer of organic semiconducting polymer films of arbitrary thickness. The method is based on scanning force microscopy and employs a combination of a sensitive phase detection system and metal coated tips with a low (∼1 N/m) spring constant and a relatively high Q factor (∼200). The molecularly resolved morphology is observed in phase images that are taken simultaneously with the topography. Surprisingly, we found that, when the tip apex radius exceeds the intermolecular spacing in the surface layer, surface aggregates –when present- are visualized. In both cases, the phase contrast is shown to result from van der Waals interaction between the conjugated backbone of the polymer chains and the metallic tip, and can quantitatively be described by a simple harmonic oscillator model. We have employed this method to study the morphology of poly(p-phenylene vinylene) (PPV) derivatives with different substitutions.
Halogenation of ORMOSIL: A Promising Rout for Tailoring Optical Absorptions
Authors: Fardad Amir , Liang Wei , Zhang Yadong , Case Bryson , Jiang Shibin , Peyghambarian Nasser
Published: June 2019

Fluorinated and photo-imageable precursors are synthesized through a Barbier-Grignard reaction for 1550-nm window. The precursors are used for the sol-gel process of integrated optic components for silica-on-silicon technology. Material compositions and process parameters are optimized to achieve internal absorptions >0.1 dB/cm and propagation losses of about 0.5 dB/cm at 1550 nm. Compact 1×16 Beam splitters are designed and fabricated which exhibit >0.3 dB power uniformity, >0.1 dB PDL and 1.5 dB coupling loss. By hybrid integration of the passive splitters and in-house fiber amplifiers, amplifying splitters are demonstrated at various signal intensities.
Electrosynthesis and Properties of Conducting Polythiophene Derivative Using Co-surfactants in Aqueous Medium.
Authors: Moustafid T.El. , Gregory R.V. , Brenneman K.R. , Lessner P.M.
Published: June 2019

The electrosynthesis of poly (3, 4-ethylenedioxythiophene) from its monomer 3, 4-ethylenedioxythiophene with doping by a mixture of lithium tosylate and co-surfactants sodium dodecylsulfate and sodium poly (4-styrenesulfonate) was performed. An anionic surfactant in aqueous solution was used to increase monomer solubility in water and reduce the potential oxidation relative to acetonitrile medium. Polymer films were synthesized by cyclic voltammetry and galvanostatic methods and characterized by IR, AFM and SEM spectroscopy.
Synthesis and Characterization of Novel Platinum Acetylide Oligomers
Authors: Cooper Thomas M. , Hall Benjamin C. , McLean Daniel G. , Rogers Joy E. , Burke Aaron R. , Turnbull Kenneth , Weisner Andrew
Published: June 2019

As part of an effort to develop a spectroscopic structure-property relationship in platinum acetylide oligomers, we have prepared a series of bidentate Pt(PBu3)2L2 compounds. The ligand was the series o-syd-C6H4-CΞC-(C6H4-CΞC)n-H, n = 0,1,2. The terminal oligomer unit consisted of a sydnone group ortho to the acetylene carbon. The compounds were characterized by various methods, including 13C-NMR, ground state absorption, fluorescence, phosphorescence and laser flash photolysis. The acetylenic 13C-NMR resonances showed sydnone influences that decreased with increasing number of monomer units. The ground state absorption spectra were slightly red shifted from those of the baseline oligomers not having a sydnone group. The low temperature emission and excitation spectra showed complex dependence on excitation and emission wavelengths, suggesting the chromphores resided in a distribution of solvent environments and conformations. Finally, broad triplet state absorption spectra were observed, with absorption throughout the visible and near infrared regions.
Green OLED's: Electroluminescence and the electrical carrier transport
Authors: Pereira L. , Pontes R. , Lopes P.
Published: June 2019

Organic Light Emitting Diodes (OLED) based on metal chelate complexes (Alq3) as the emmiting layer has been prepareded and studied in order to characterise their optical and electrical properties. Electrical measurements have been performed in order to establish the nature of carrier transport. The results point to a trap charge-limited conduction (TCL) with characteristic trap energy near 0.13 eV. In electroluminescence a large green band with a maximum at 2.4 eV was found as a result of three overlapping bands that are correlated with the organic layers. The origin of this luminescence spectrum was analysed.
Oligo(phenylenevinylene)s end-capped with phenothiazine or triphenylamine
Authors: Detert H. , Sadovski O.
Published: June 2019

Monodisperse oligo(phenylenevinylene)s end-capped with arylamines have been prepared via Horner Olefinations from bisphosphonates and arylaminobenzaldehydes. The influences of the conjugation length, different arylamine end groups, and of side chains with various electronic character on the electrical and optical properties of the chromophores are investigated. The elongation of the π-conjugated segment from 3 to 5 rings gives rise to bathochromic shifts of the electronic spectra and a slight increase of the oxidation potential. The same but more pronounced is true when the central electron donating ethers are replaced by the strong acceptor alkylsulfone. The electronic spectra of chromophores with triphenylamine and with N-alkylphenothiazines as end groups are quite similar, but the heterocyclic unit reduces the oxidation potential. The incorporation of a chromophor into a segmented copolymer has only negligible effect on the optical and electrical properties.
Chemical Environment Effects on the Photophysical Behavior of Two-Photon Materials
Authors: Collette Jeremy C. , Harper Aaron W.
Published: June 2019

A set of six new two-photon engineered diethylamino-substituted styryl pyrazine (DEASP) dyes have been developed as chemically responsive chromophores. This work employs UV/Vis spectroscopy to draw structure-optical property relationships and to quantify the solvatochromic effect observed for these dyes. Absorbance profiles for each of these dyes have been measured in 22 solvents ranging from very nonpolar (TMS) to very polar (water). Absorbance maxima of the longest wavelength π→π transitions have been correlated to nine empirical scales of solvent polarity, and a comparative analysis is presented. Dimroth & Reichardt's and Kamlet & Taft's single parameter scales have been recalculated with spectral data obtained for the six DEASP dyes. The correlation of these established and recalculated scales are shown and discussed. DEASP chromophores are found to exhibit high sensitivity to their chemical environment and exceptional range as solvatochromic probes. Current models of solvatochromism, based on dipolar probes, cannot account for the solvatochromism observed in our quadrupolar dyes, and fail to describe the effect of the chemical environment on this family of twophoton dyes. The need to develop a more universal model of solvation incorporating higher order moment contributions is apparent.
Gated Nonlinear Transport in Organic Thin Film Transistors
Authors: Hamadani Behrang H. , Natelson Douglas
Published: June 2019

Charge transport in poly(3-hexylthiophene) field effect transistors has been studied in a series of devices with channel lengths ranging from 3 μm down to 200 nm over a broad range of temperatures and gate voltages. We report gate-modulated highly nonlinear transport at temperatures below ∼200 K that is consistent in form with a Poole-Frenkel-like hopping mechanism in the space charge limited current regime. There is also consistency between this behavior and the hypothesis that density of localized states is strongly energy dependent. We also observe what appears to be a crossover from thermally activated to nonthermal hopping below 30 K.
Intra-Grain and Oligo-Grain Top-Contact Organic Thin film Transistors
Authors: Verlaak Stijn , Jonge Stijn De , Noppe Stijn , Janssen Dimitri , Steudel Soeren , Vusser Stijn De , Heremans Paul
Published: June 2019

We describe and demonstrate a micromachined shadowmask that allows the realization of intra-grain and oligo-grain top-contact organic thin film transistors (OTFTs). First experimental results of OTFT's show that for small channel lengths, grain boundary barriers indeed appear to dominate the output characteristics of OTFTs.
Field Effect of Fullerene Thin Film Studied by Displacement Current Measurements and Infrared Absorption Spectroscopy in The Multiple Reflection Geometry
Authors: Ogawa S. , Kimura Y. , Ishii H. , Niwano M.
Published: June 2019

Au/fullerene(C60)/SiO2/Si field effect transistor (FET) has been investigated to examine the behavior of carrier injection by using displacement current measurement (DCM) and infrared absorption spectroscopy in the multiple internal reflection (MIR-IRAS). At the first scan of DCM, an increasing displacement current due to electron injection was clearly observed above a threshold voltage in forward scan, while no flow-back of the injected electrons was observed, indicating that almost all electrons injected in the scan were trapped. The capacitance obtained from the increasing current suggests that the electrons injected from a Au electrode spread laterally along C60/SiO2 to some extent. At the further scans of DCM, the threshold voltage was shifted to higher voltage, and the lateral spread of the electron was quite suppressed due to the space charge of the filled traps. These results clearly demonstrate that DCM is a useful method to examine the behavior of carriers in field effect transistor (FET) devices. The spectral change in MIR-IRAS observed under bias voltage for electron injection is also reported.
CuInS2/PEDOT Photovoltaic Structure
Authors: Bereznev Sergei , Konovalov Igor , Kois Julia , Mellikov Enn , Öpik Andres
Published: June 2019

Structures based on combination of electrically conductive polymers with inorganic semiconductors are currently intensively investigated with the aim to prepare low-cost, largearea and flexible photovoltaic devices. In this study, multilayer structures consisting of CuInS2 (CIS) and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonate (PSS) thin films were prepared and investigated for photovoltaic applications. Polycrystalline CIS absorber layers were synthesized on top of a layered structure on Cu tape substrate using socalled non-vacuum CISCuT technique. Thin PEDOT buffer layers doped with PSS were deposited onto KCN etched and vacuum annealed CIS films. The deposition was performed using the spin-casting technique from an aqueous dispersion of PEDOT/PSS mixed with Nmethylpyrrolidone, isopropanol, glycerin and epoxysilane additives. Optimal deposition parameters for stable PEDOT films with a good adherence to the surface of CIS were selected experimentally. The morphology and thickness of prepared films and structures was determined using SEM technique. Average film thickness was about of 1.5 μm for CIS and 50 nm for PEDOT films. Current-voltage and impedance characteristics were measured. Significant photovoltage and photocurrent of the photovoltaic structures were observed under standard illumination intensity. The best structure showed an open-circuit voltage of 510 mV and a shortcircuit current density of 20.2 mA/cm2.
Structural and Spectroscopic Study of Langmuir-Schäfer Films of Bis Zn-Ethane-Bridged Porphyrins Dimer
Authors: Panzera G. , Conoci S. , Coffa S. , Pignataro B. , Sortino S. , Valli L. , Borovkov V.V. , Inoue Y.
Published: June 2019

Thin films (1-24 layers) of bis-zinc ethane-bridged porphyrin dimer (1) have been transferred on solid surfaces, by the Langmuir- Schäfer (LS) horizontal method. The related surface pressurearea isotherm curve shows that in dependence of the film pressure different condensed phases may occur in the monolayer. The inspection of the monolayer by Brewster Angle Microscopy (BAM) reveals the presence of peculiar networks whose structural features seemingly change upon film compression. On the other hand, the Scanning Force Microscopy (SFM) analysis performed on LS films shows fractal networks constituted by nanoscopic supramolecular aggregates, whose shape and size depend again on the LS deposition surface pressure. Finally, also UV-vis spectroscopy measurements indicates that the absorption is almost linearly related to the film thickness that is directly connected to the surface pressure.
Synthesis of a Zero-Birefringence Optical Polymer by the Birefringent Crystal DopantMethod
Authors: Ohkita Hisanori , Mukoh Masaki , Tagaya Akihiro , Koike Yasuhiro
Published: June 2019

Birefringence induced by the orientation of polymer main chains during an injectionmolding or extrusion processing restricts the application of optical polymers to optical devices that require maintaining the polarization state of incident light. We propose the “birefringent crystal dopant method” to compensate the birefringence of polymers by homogeneous doping with an opposite birefringent needle-like crystal. Strontium carbonate (SrCO3) was selected for this method and synthesized, with particle lengths of 50-200nm and aspect ratios of 2-5. SrCO3 was doped into poly(MMA/BzMA= 78/22(wt./wt.)) film. The film was uniaxially drawn at 130°C and 4mm/min. For the first time, the positive birefringence of the drawn copolymer film at a wavelength of 633nm was compensated by doping with 0.3wt.% of SrCO3 without losing transparency and thermostability.
Spontaneous Orientation of Alq3 Molecule in Evaporated Film and Its Vanishment by Light Irradiation
Authors: Sugi Keiji , Ishii Hisao , Kimura Yasuo , Niwano Michio , Hayashi Naoki , Ouchi Yukio , Ito Eisuke , Seki Kazuhiko
Published: June 2019

Recently we found high and persistent spontaneous buildup of the surface potential upon vacuum vapor deposition of tris(8-hydroxyquinolinato) aluminum(III)(Alq3) on Au substrate under dark conditions (28 V for 560 nm thick Alq3 film). Such giant potential is removed by visible-light irradiation. These natures of the film suggest the possible applications to various organic devices such as memory devices. In this study, we investigated the retention time of the giant potential and the mechanism of the light-induced depolarization in order to discuss the feasibility of the device applications. The observed decay rate of the surface potential in vacuum condition was roughly 10 % loss in 10 years, which is enough for memory devices. As to the decay rate by light-irradiation, the observed rate was successfully reproduced by a theoretical simulation based on the photo-induced randomization of oriented Alq3 molecules.
New Liquid Crystalline Semiconductors And Their Fabrication in Organic Field Effect Transistor Devices
Authors: Heeney Martin , Graham David , Shkunov Maxim , Sparrowe David , Giles Mark , Bailey Clare
Published: June 2019

The performance of the semiconducting component in organic field effect transistors (OFET's), is a key parameter in the advancement of organic electronic devices. This work describes the development of solution processible liquid crystalline semiconductors, both main chain rigid rod polymers and small molecule polymerisable liquid crystals, referred to as reactive mesogens. New conjugated main chain polymeric semiconductors have been designed, synthesised, and their performance in transistor devices is reported. Small molecule liquid crystalline semiconductors, which contain reactive end groups, were also prepared, and their design, characterisation, and performance in transistor devices is discussed.
Semiconductor Quantum Dots for Multicolor Fluorescence Imaging and Spectroscopy of Single Cancer Cells
Authors: Gao Xiaohu , Nie Shuming , Coulter Wallace H.
Published: June 2019

Luminescent quantum dots (QDs) are emerging as a new class of biological labels with unique properties and applications that are not available from traditional organic dyes and fluorescent proteins. Here we report new developments in using semiconductor quantum dots for quantitative imaging and spectroscopy of single cancer cells. We show that both live and fixed cells can be labeled with multicolor QDs, and that single cells can be analyzed by fluorescence imaging and wavelength-resolved spectroscopy. These results raise new possibilities in cancer imaging, molecular profiling, and disease staging.
Large Area, High Aspect Ratio Microelectrode Arrays
Authors: Merritt Charles D. , Falkenstein Paul L. , Justus Brian L.
Published: June 2019

A method is described for the fabrication of arrays of conducting, high aspect-ratio microwires for use as electrodes. The electrode arrays are fabricated by electrochemical deposition of metals, including Ni, Pt, Ag, Au and Rh, in channel glass templates having parallel, uniform, hollow channels with diameters that range from sub-micrometer to over 100 micrometers. The metals completely fill the hollow channels, yielding highly uniform electrodes with aspect ratios on the order of 1000 or more. The glass template electrically insulates the electrodes from one another. The electrode array wafers are cut and polished to a thickness ranging from about 100 to 2000 micrometers. The overall surface area is as large as 1 square centimeter. Alternatively, the wafers can be partially etched with acid to remove some of the glass matrix surrounding the electrodes, exposing an array of bare, solid wire stubs. The high aspect ratio microelectrode arrays were initially fabricated in order to provide the electrical interface for an intraocular retinal prosthesis, but have additional applications including biological and chemical sensing. Arrays with different channel sizes, different electrode spacing (with pitch from approximately 3R to 20R, where R is the electrode radius), and different geometrical arrangement are presented.
Ultrananocrystalline Diamond-Biomolecular Composites: Towards BioMEMS
Authors: Grynaviski N. M. Haralampus , Auciello O. , Carlisle J. A. , Gerbi J. E. , Gruen D. M. , Moore J. F. , Zinovev A. , Firestone M. A.
Published: June 2019

The surface functionalization of ultrananocrystalline (UNCD) thin films has been investigated to develop biocomposite materials for use as BioMicroElectroMechanical Systems (BioMEMS). Specifically, hydrophobic, hydrogen-terminated UNCD films have been synthesized using a microwave plasma chemical vapor deposition technique then surface functionalized using a two-step modification procedure. This procedure produces a mixed submonolayer comprised of chloro- and hydroxyl- terminated alkyl chains chemisorbed to the UNCD surface. This surface modification procedure serves to provide functional groups that will allow for the subsequent attachment of a wide variety of biological macromolecules (e.g., proteins, biomembranes) and the ability to tune the hydrophilic nature of the diamond. The resultant materials have been characterized using surface-sensitive spectroscopies (NEXAFS and XPS).
Effects of Single-Walled Carbon Nanotube on Polymerase Chain Reaction
Authors: Cui Daxiang , Tian Furong , Kong Yong , Ozkan Cengiz S. , Titushikin Igor , Gao Huajian
Published: June 2019

Polymerase Chain Reaction (PCR) is a complicated gene amplification process using Mg2+ as an assistant factor of Taq enzyme. Influence of single-walled carbon nanotube on that reaction was investigated with scanning electron microscope (SEM), transmission electron microscope TEM) and quantitative PCR product analysis. Results showed that adding single-walled carbon nanotubes in the reaction liquid with a concentration of less than 3 νg/νl increase the amounts of PCR products. But more carbon nanotubes cause a great reduction of the PCR products. Similar effects were observed in the reaction without Mg2+. Possible reason could be the aggregation of reaction components caused by small amount of additive carbon nanotubes, which increases reaction probability. Our observations suggest that small amount of carbon nanotube could be used as an assistant factor to improve the PCR reaction.
Electric Field-Assisted Positioning of Neurons on Pt Microelectrode Arrays
Authors: Prasad Shalini , Yang Mo , Zhang Xuan , Ni Yingchun , Parpura Vladimir , Ozkan Cengiz. S. , Ozkan Mihrimah
Published: June 2019

Characterization of electrical activity of individual neurons is the fundamental step in understanding the functioning of the nervous system. Single cell electrical activity at various stages of cell development is essential to accurately determine in in-vivo conditions the position of a cell based on the procured electrical activity. Understanding memory formation and development translates to changes in the electrical activity of individual neurons. Hence, there is an enormous need to develop novel ways for isolating and positioning individual neurons over single recording sites. To this end, we used a 3x3 multiple microelectrode array system to spatially arrange neurons by applying a gradient AC field. We characterized the electric field distribution inside our test platform by using two dimensiona l finite element modeling (FEM) and determined the location of neurons over the electrode array. Dielectrophoretic AC fields were utilized to separate the neurons from the glial cells and to position the neurons over the electrodes. The neurons were obtained from 0-2-day-old rat (Sprague-Dawley) pups. The technique of using electric fields to achieve single neuron patterning has implications in neural engineering, elucidating a new and simpler method to develop and study neuronal activity as compared to conventional microelectrode array techniques.
Use of Flexible Materials with a Novel Pressure Driven Equibiaxial Cell Stretching Device for Mechanical Stimulation of Single Mammalian Cells
Authors: Kubicek James D. , Brelsford Stephanie , LeDuc Philip R.
Published: June 2019

Mechanical stimulation of single cells has been shown to affect cellular behavior from the molecular scale to ultimate cell fate including apoptosis and proliferation. In this, the ability to control the spatiotemporal application of force on cells through their extracellular matrix connections is critical to understand the cellular response of mechanotransduction. Here, we develop and utilize a novel pressure-driven equibiaxial cell stretching device (PECS) combined with an elastomeric material to control specifically the mechanical stimulation on single cells. Cells were cultured on silicone membranes coated with molecular matrices and then a uniform pressure was introduced to the opposite surface of the membrane to stretch single cells equibiaxially. This allowed us to apply mechanical deformation to investigate the complex nature of cell shape and structure. These results will enhance our knowledge of cellular and molecular function as well as provide insights into fields including biomechanics, tissue engineering, and drug discovery.