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The carbon–carbon double bond can be polymerized either by free radical or ionic methods. The difference arises because the π-bond of a vinyl monomer can respond appropriately to the initiator species by either homolytic or heterolytic bond breakage as shown in Eq. 8.1.

Polymers can be synthesized by polymerizing monomers with ring structure as shown in Table 11.1. The polymerization of these compounds has some aspects of both chain and step polymerizations as far as kinetics and mechanisms are concerned. Table 11.1 Examples of polymers prepared by ring-opening polymerization [1] Polymer type Polymer repeating group Monomer structure Monomer type Polyalkene Open image in new window Open image in new window Cyclic alkene Polyether Open image in new window Open image in new window Cyclic ethera Polyesterb Open image in new window Open image in new window Lactone Polyamide Open image in new window Open image in new window Lactam Polysiloxane Open image in new window Open image in new window Cyclic siloxane Polyphosphazene Open image in new window Open image in new window Hexachloro-cyclotriphosphazenec Polyamine Open image in new window Open image in new window Aziridened aEpoxide (x = 2); oxetane (x = 3) bRing opening of cyclic oligomers has also been developed cPhosphonitrilic chloride trimer dAlso called alkyleneimine

The polymerization of unsaturated monomers typically involves a chain reaction. In a chain polymerization, one act of initiation may lead to the polymerization of thousands of monomer molecules

The chemical composition, configuration and molecular arrangement determine the structure of polymer. The physical structure of polymer is the morphology of polymer

The chemical and physical properties of polymers are dependent on their chemical and physical structures and molecular weight. Their relationship related to the chemical, mechanical, thermal, electrical, and optical properties [1–3] are discussed below.

Recently, the perovskite solar cells draw lots of attentions because of low cost, solution-processable and promising high efficiency. The power conversion efficiency (PCE) is rapidly reached to a certified value of 20.1%. However, the conventional electron transport layer (ETL) of the device needs to be sintered over 500 °C which is high energy-consumption process and cannot use on flexible substrate. Therefore, many research groups endeavor to develop low-temperature solution processable electron transport material in perovskite solar cells. In this review, we present systematic and critical discussions on the evolution of perovskite solar cells from meso-superstructure solar cells (MSSCs) to low-temperature solution processed planar heterojunction (PHJ) perovskite solar cells. This review will provide a guideline for the fabrication of high PCE perovskite solar cell using solution process at temperature of 150 °C or under, which has potential to achieve large scale fabrication by roll-to-roll technique for commercial products in near future.

This work shows that the surface properties of nanoparticles are very important for a particle size near 5 nm in diameter or less. A simple theoretical formula is derived to quantitatively predict the size of nanoparticles for which the surface properties become significant. Experimental evidence using electroluminescence from CdS nanoparticles of 5 nm in diameter is also provided to verify the significance of the surface properties. With different processing procedures or capping layers, the surface or surface states dominate the optical characteristics of the CdS nanoparticles and sometimes play even more important roles than internal atoms.

A new approach to induce self-vertical phase separation of nanoparticle/polymer hybrid solar cells is reported by introducing fluorinated small molecules into the active layer. The formation of a vertically gradient structure improves not only polymer organization but also charge transport efficiency, thus increasing the photovoltaic cell performance by a factor of 5.

Titanium dioxide nanofibers were synthesized and applied in flexible composite films that are easy to handle and recycle after use. The nanofibers were obtained in a multi-step procedure. First, sodium titanate nanofibers were prepared from TiO2 nanoparticles through the alkali hydrothermal method. In the next step, sodium hydrogen titanate nanofibers were made by washing the sodium titanate nanofibers in HCl solution. Finally, the sodium hydrogen titanate nanofibers were transformed to TiO2 anatase nanofibers by calcination in air. The photocatalytic activity of TiO2 anatase nanofibers were evaluated and compared to a TiO2 nanoparticle catalyst by decomposing methyl orange dye in aqueous solutions. The achieved reaction rate constant of TiO2 anatase nanofibers was comparable to that of Degussa P25. Paper-like flexible composite films were prepared by co-filtrating aqueous dispersions of TiO2 catalyst materials and cellulose. The composite films made from the nanofibers exhibit better mechanical integrity than those of the nanoparticle-cellulose composites.

Low-shrinkage resin-based photocurable liquid crystalline epoxy nanocomposite has been investigated with regard to its application as a dental restoration material. The nanocomposite consists of an organic matrix and an inorganic reinforcing filler. The organic matrix is made of liquid crystalline biphenyl epoxy resin (BP), an epoxy resin consisting of cyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ECH), the photoinitiator 4-octylphenyl phenyliodonium hexafluoroantimonate and the photosensitizer champhorquinone. The inorganic filler is silica nanoparticles (∼70-100 nm). The nanoparticles were modified by an epoxy silane of γ-glycidoxypropyltrimethoxysilane to be compatible with the organic matrix and to chemically bond with the organic matrix after photo curing. By incorporating the BP liquid crystalline (LC) epoxy resin into conventional ECH epoxy resin, the nanocomposite has improved hardness, flexural modulus, water absorption and coefficient of thermal expansion. Although the incorporation of silica filler may dilute the reinforcing effect of crystalline BP, a high silica filler content (∼42 vol.%) was found to increase the physical and chemical properties of the nanocomposite due to the formation of unique microstructures. The microstructure of nanoparticle embedded layers was observed in the nanocomposite using scanning and transmission electron microscopy. This unique microstructure indicates that the crystalline BP and nanoparticles support each other and result in outstanding mechanical properties. The crystalline BP in the LC epoxy resin-based nanocomposite was partially melted during exothermic photopolymerization, and the resin expanded via an order-to-disorder transition. Thus, the post-gelation shrinkage of the LC epoxy resin-based nanocomposite is greatly reduced, ∼50.6% less than in commercialized methacrylate resin-based composites. This LC epoxy nanocomposite demonstrates good physical and chemical properties and good biocompatibility, comparable to commercialized composites. The results indicate that this novel LC nanocomposite is worthy of development and has potential for further applications in clinical dentistry.

We demonstrate here that the nanostructure of poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM) bulk heterojunction (BHJ) can be tuned by inorganic nanoparticles (INPs) for enhanced solar cell performance. The self-organized nanostructural evolution of P3HT/PCBM/INPs thin films was investigated by using simultaneous grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence wide-angle X-ray scattering (GIWAXS) technique. Including INPs into P3HT/PCBM leads to (1) diffusion of PCBM molecules into aggregated PCBM clusters and (2) formation of interpenetrating networks that contain INPs which interact with amorphous P3HT polymer chains that are intercalated with PCBM molecules. Both of the nanostructures provide efficient pathways for free electron transport. The distinctive INP-tuned nanostructures are thermally stable and exhibit significantly enhanced electron mobility, external quantum efficiency, and photovoltaic device performance. These gains over conventional P3HT/PCBM directly result from newly demonstrated nanostructure. This work provides an attractive strategy for manipulating the phase-separated BHJ layers and also increases insight into nanostructural evolution when INPs are incorporated into BHJs.

In this study, single-electron transistors and memory cells with Au colloidal islands linked by C60 derivatives have been fabricated by hybridization of top–down advanced electron-beam lithography and bottom–up nanophased-material synthesis techniques. Low-temperature transport measurements exhibit clear Coulomb-blockade-type current–voltage characteristics and hysteretic-type gate-modulated current. The hysteresis is attributed to the presence of electrically isolated charge–storage islands. With the guidance provided by Monte Carlo simulation, we propose a circuit model and give an estimate of the sample parameters.

We have developed an improved small-angle X-ray scattering (SAXS) model and analysis methodology to quantitatively evaluate the nanostructures of a blend system. This method has been applied to resolve the various structures of self-organized poly(3-hexylthiophene)/C61-butyric acid methyl ester (P3HT/PCBM) thin active layer in a solar cell from the studies of both grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence X-ray diffraction (GIXRD). Tuning the various length scales of PCBM-related structures by a different annealing process can provide a flexible approach and better understanding to enhance the power conversion of the P3HT/PCBM solar cell. The quantitative structural characterization by this method includes (1) the mean size, volume fraction, and size distribution of aggregated PCBM clusters, (2) the specific interface area between PCBM and P3HT, (3) the local cluster agglomeration, and (4) the correlation length of the PCBM molecular network within the P3HT phase. The above terms are correlated well with the device performance. The various structural evolutions and transformations (growth and dissolution) between PCBM and P3HT with the variation of annealing history are demonstrated here. This work established a useful SAXS approach to present insight into the modeling of the morphology of P3HT/PCBM film. In situ GISAXS measurements were also conducted to provide informative details of thermal behavior and temporal evolution of PCBM-related structures during phase separation. The results of this investigation significantly extend the current knowledge of the relationship of bulk heterojunction morphology to device performance.

As a potential solution for patients to retrieve their lost salivary gland functions, tissue engineering of an auto-secretory device is profoundly needed. Under serum-free environment, primary human parotid gland acinar (PGAC) cells can be obtained. After reaching confluence, PGAC cells spontaneously form three-dimension (3D) cell aggregations, termed post-confluence structure (PCS), and change their behaviors. Poly (lactic-co-glycolic acid) (PLGA) has been widely used in the field of biomedical applications because of its biodegradable properties for desired functions. Nonetheless, the role of PLGA in facilitating PGAC cells to form PCS has seldom been explored to recover epithelial characteristics. In this study, PGAC cells were found to have a greater tendency to form PCS on PLGA than on tissue culture polystyrene (TCPS). By tracing cell migration paths and modulating E-cadherin activity with specific inhibitor or antibody, we demonstrated that the static force of homophilic interaction on surfaces of individual cells, but not the dynamics of cell migration, played a more important role in PCS formation. Thus, PLGA was successfully confirmed to support PGAC cells to form more PCS through the effects on enhancing E-cadherin expression, which is associated with FAK/ILK/Snail expression in PGAC cells. This result indicates that selective appropriate biomaterials may be potentially useful in generating 3D PCS on two-dimension (2D) substrate without fabricating a complex 3D scaffold.

We study the effects of bifunctional linker on the optical properties of ZnO nanocolumn-linker-CdSe quantum dots heterostructure. The CdSe quantum dots are anchored on the surface of ZnO nanocolumns through either aliphatic linker of 3-aminopropyl trimethoxysilane (APS) or aromatic linker of p-aminophenyl trimethoxysilane (APhS). X-ray photoelectron spectroscopy is used to confirm the bifunctional linker bound onto CdSe quantum dots and onto the ZnO nanocolumns. The TEM study reveals a CdSe quantum dot shell of about 15 nm coated on the ZnO nanocolumns. The photoluminance (PL) spectroscopy and time-resolved PL spectroscopy of ZnO nanocolumn-linker-CdSe quantum dots reflects that the photo-induced electron transfer across the interface of ZnO and CdSe through the aromatic APhS is more efficient than the aliphatic APS. This study demonstrates that through the usage of appropriate surface linker, the charge transfer rate across the interfaces of donor/acceptor (D/A) heterostructure can be improved for potential photovoltaic cell applications.

In the past few years, we have fabricated nanoscale La 0.7 Sr 0.3 MnO 3 periodic arrays with unique optical and magnetic properties successfully. These periodic patterns were made by La 0.7 Sr 0.3 MnO 3 resist that can be developed under a nontoxic and environmental friendly manner using pure water. The resist is also capable to exhibit both positive and negative resist behaviors depending on the electron beam dosage. Thus, these special characteristics are used to fabricate and tune periodic structure thin film having controlled optical reflectance properties in the wavelength of 300 nm to 800 nm with one fixed design electron beam pattern by simply changing the electron beam dosage only. Additionally, the magnetization of La 0.7 Sr 0.3 MnO 3 patterns can be enhanced by post sintering the sample at 900 °C after electron beam irradiation. Therefore, our study provides a one-step, simple, and convenient alternative technique for the fabrication of tunable optical structure and nanoscale magnetic patterns, which form the building blocks for the study of optoelectronic and magnetic devices in nanoscale periodic arrays.

A pair of solution-processed metal oxides is introduced near the electrodes to improve the inverted polymer solar cells. With the paired metal oxides, the conversion efficiency is notably enhanced to above 5%.

The molecular orientation in amphiphilic hemicyanine Langmuir-Blodgett (LB) films has been studied quantitatively by Fourier transform infrared (FTIR) spectroscopy and second harmonic generation (SHG). From the analysis of transmission and reflection absorption (RA) spectra of FTIR, the tilt angles to the surface normal of the hydrocarbon chain axis and the chromophore of amphiphilic hemicyanine LB film were estimated to be 24' and 43O, respectively. The SHG measurements yielded a chromophore tilt angle of 44O. Both techniques have shown consistent results for the chromophore orientation in the hemicyanine LB film.

We report bright white-light electroluminescence (EL) from a diode structure consisting of a ZnO nanorod (NR) and a p-type conducting polymer of poly(fluorine) (PF) fabricated using a hydrothermal method. ZnO NRs are successfully grown on an organic layer of PF using a modified seeding layer. The EL spectrum shows a broad emission band covering the entire visible range from 400 to 800 nm. White-light emission is possible because the ZnO-defect-related emission from the ZnO NR/PF heterostructure is enhanced to become over thousand times stronger than that from the usual ZnO NR structure. This strong green-yellow emission associated with the ZnO defects, combined with the blue PF-related emission, results in the white-light emission. Enhancement of the ZnO-defect emission is caused by the presence of Zn(OH)(2) at the interface between the ZnO NRs and PF. Fourier transform infrared spectroscopy reveals that the absorption peaks at 3441, 3502, and 3574 cm(-1) corresponding to the OH group are formed at the ZnO NR/PF heterostructure, which confirms the enhancement of defect emission from the ZnO NR/PF heterostructure. The processing procedure revealed in this work is a convenient and low-cost way to fabricate ZnO-based white-light-emitting devices.

There is a growing interest in developing low-band gap conjugated polymers via synthesis of copolymers containing alternating units of different pi-electron-donating/accepting capabilities. In this study, electronic and optical properties of conjugated copolymers containing fluorene and thiophene/cyclopentadithiophene derivatives are determined using density function theory and semiempirical ZINDO calculations. A remarkable linear correlation is found between the amount of charge transfer between the donor-acceptor pair, the band gap, the bandwidth, and the oscillator strength of S(0)-->S(1) electronic transition (ground state to first excited state) of the copolymers. Strong pi-electron withdrawing substituents, such as dicyanoethenyl and carbonyl groups, on the thiophene moiety effectively reduce the band gap of the copolymers. However, the reduction of band gap is frequently accompanied by a linear reduction in bandwidths and in the oscillator strength of S(0)-->S(1) transition. For very strong pi-electron withdrawing thiophene derivatives, the occurrence of maximum oscillator strength may even shift from S(0)-->S(1) to S(0)-->S(n>1) (ground state to a higher excited state), giving a blue shift in maxima absorption peak and a red shoulder in the UV-vis spectra as reported in recent experimental measurements. Therefore, the achievement of low band gap for conjugated polymers with alternating arrangement of pi-electron-donating/accepting moieties may be achieved at a cost of lowering electron mobility and optical efficiency and sometimes a blue-shift in the major optical (UV-vis) absorption.

The solution processable poly(3-hexylthiophene)(P3HT)/TiO2-nanorod hybrid material for solar cells has been successfully demonstrated. A critical issue for using hybrid heterojunction concept is the interface properties which affect the exciton separation efficiency and bi-carrier transport. To improve the interface properties, we replace the insulating surfactant on TiO2 nanorod surface with a more conductive oligomer, carboxylate terminated 3-hexylthiophene (P3HT-COOH). The enhancement of exciton separation efficiency due to better organic-inorganic interfacial compatibility can be obtained. The electron mobility for transporting in the TiO2 network is improved. A power conversion efficiency has been increased 3 times by using this new hybrid material without optimization as compared with the hybrid without P3HT-COOH modification.

In this article, the polymer photovoltaic devices based on the poly(3-hexylthiophene) /TiO 2 nanorods hybrid material is present. An enhancement in the device performance can be achieved by removing or replacing the insulating surfactant on the TiO 2 nanorods surface with a more conductive ligand, which can play the role to assist charge separation efficiency or also to prevent from back recombination, giving a large improvement in the short circuit current and fill factor. The relatively high power conversion efficiency of 2.2 % under simulated A.M. 1.5 illumination (100 mW/cm 2 ) can be achieved, providing a route for fabricating low-cost, environmentally friendly polymer photovoltaic devices by all-solution processes.

The characteristics of a nanocomposite consisting of the blue-emitting polymer polyfluorene and ZnO nanowires are reported. The electroluminescence spectrum of the white light emission is from about 400 nm to 750 nm.

We demonstrated that lipid-enclosed CdSe quantum dots (LEQDs) can function as versatile contrast agents in epi-detection third harmonic generation (THG) microscopy for biological applications in vivo. With epi-THG intensities 20 times stronger than corresponding fluorescence intensities from the same LEQDs under the same conditions of energy absorption, such high brightness LEQDs were proved for the abilities of cell tracking and detection of specific molecular expression in live cancer cells. Using nude mice as an animal model, the distribution of LEQD-loaded tumor cells deep in subcutaneous tissues were imaged with high THG contrast. This is the first demonstration that THG contrast can be manipulated in vivo with nanoparticles. By linking LEQDs with anti-Her2 antibodies, the expression of Her2/neu receptors in live breast cancer cells could also be easily detected through THG. Compared with fluorescence modalities, the THG modality also provides the advantage of no photobleaching and photoblinkin g effects. Combined with a high penetration 1230 nm laser, these novel features make LEQDs excellent THG contrast agents for in vivo deep-tissue imaging in the future.

In this work, we present the evolution of optical constants varying with distinct annealing temperature for poly (3- hexylthiophene) (P3HT) and 6,6-phenyl C61-butyric acid methyl ester (PCBM). With calculation of the transmission and reflection spectra in P3HT:PCBM photovoltaic device , the optical properties correlation to annealing temperature is studied. The solar cell power conversion efficiency and optical absorption is compared simultaneously. Finally, the electric field amplitude in the device is discussed for detailed explanation of thermal annealing effects on the organic photovoltaic device performance.

With the insertion of SiO(2) nanoparticles in the oxide layer, near-lasing actions such as threshold behavior and resonance modes are observed at the Si bandgap energy of metal-oxide-silicon (MOS) structure. The threshold current is ~12 mA . The SiO(2) nanoparticles cause simultaneous localization of electrons and holes to enhance phonon-assisted radiative recombination. Electroluminescence at Si bandgap energy is increased to orders of magnitude larger than in similar MOS structures without SiO(2) nanoparticles. The efficient light emission at the Si bandgap energy indicates that a direct bandgap nature is not necessarily the basic requirement for radiative recombination.

This paper aims to propose a 3D nanostructured organic-inorganic hybrid photovoltaic device based on the ZnO nanostructures/poly(3-hexylthiophene)(P3HT):TiO 2 nanorods hybrids by solution processes at low temperature. An array of ZnO nanorods with a larger size of ~50 nm in diameter and ~180 nm in length are grown to provide direct pathways for efficient charge collection. TiO 2 nanorods with a size of ~5 nm in diameter and ~20-30 nm in length are incorporated into polymer to facilitate charge separation and transport by providing increased interfacial area and more effective transport pathway. The device performance with the inclusion of TiO 2 nanorods exhibits a seven times increase in the short circuit current with respect to that without TiO 2 nanorods.

P3HT-P2VP block copolymers were synthesized using anionic macroinitiation of a vinyl end-functionalized P3HT. With different block ratio of P2VP to P3HT, the block copolymers exhibit sphere, cylinder, lamellae, and nanofiber nanostructures.

We report the visible light emission of organic-inorganic light emitting devices by low-cost spin-coating. Different nanoparticles, CdSe, ZnO and Eu2O3, are employed to form organic-inorganic hybrid composites and generate the R-G-B and white light emission, while N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) and polymethyl methacrylate (PMMA) are adopted as the organic matrices. We further investigate the hybrid composite film by scanning near-field optical microscope and find that phase-segregation enhances the electroluminescence of ZnO composite film. Meanwhile, the homogeneity of the Eu2O3 composite film improves the white light emission.

We report electroluminescence from ZnO nanoparticle-based devices prepared by the spin-coating process. The TPD enhances electrons and holes to recombine in the ZnO nanoparticles. The optimal device exhibits a narrow spectrum at 392 nm.

Photovoltaic devices based on the conjugated polymer (poly(2-methoxy-5-(2'-ethyl)(hexyloxy)1,4-phenylenevinylene) (MEH-PPV) / TiO 2 nanorods hybrid materials are investigated. It is found that efficient charge separation occurs at the interfaces of MEH-PPV/ TiO 2 nanorods, accompanying with a significant quench in the photoluminescence (PL) intensity and a decrease of PL lifetime with increasing TiO 2 nanorod concentrations. The device based on the MEHPPV/ TiO 2 nanorod hybrid material shows power efficiency about 2.2% at the incident light with a wavelength of 565 nm. The transport properties of the solar cells are further investigated and discussed.

Through molecular design and synthesis, we have synthesized many nanoparticles and fabricated into optoelectronic devices. Au-C/sub 60/ arrays were deposited on the top of pairs of gold electron to single electron transistors. Silica nanoparticles were used to create nano-structure on silicon and fabricated into infared light emitting diode (LED). CdS and CdSe nanoparticles have been fabricated into visible light LEDs. CdSe nanoparticles can be infiltrated into self-assembled photonic crystal to modulate light emission and light reflection. CdS nanoparticles were hybrid with MEH-PPV to fabricate photovoltaic devices.

By coating CdSe nano-crystals on an InGaN/GaN quantum well structure, polychromatic LEDs emitting blue and red lights have been implemented. The blue photons emitted by the quantum well structure are absorbed by the CdSe nano-crystals for emitting red light. By fabricating holes on the quantum well structure for filling up the nano-crystal solution, the red emission efficiency can be improved.

Summary form only given. We report the possibility of breaking the indirect-bandgap limitation to efficiently generate light from Si. We theoretically and experimentally discovered that carrier localization could enhance radiative recombination corresponding to bandgap energy of Si for orders of magnitudes. Nearly lasing actions corresponding to Si bandgap energy were even observed with the enhanced radiative recombination. Because of the indirect-bandgap nature of Si, the probability of electron-hole recombination is very low without the involvement of phonons. However, phonon involvement causes the process to be like simultaneous collision of three particles (electron, hole, and phonon), so the probability is also very low. If an electron and a hole already form an exciton, the process will be like a two-particle collision, exciton vs. phonon. The probability then greatly increases. Based on such a concept, we derive a formula for the emission from Si with phonon and exciton involvement. To have the localization of electrons and holes in the same region, we use nanoparticles in the oxide layer of the conventional metal-oxide-semiconductor (MOS) structures. The nanoparticles cause the thickness of the oxide layer to be nonuniform and lead to the following two effects. First, as the MOS structure is forward biased, the band bending of Si toward the thin oxide is more severe than the thick oxide, resulting in three-dimensional potential wells for carrier confinement. Second, in the region with the thin oxide, more carriers tunnel to Si through the thin oxide layer than through the thick oxide layer. As a result, electrons and holes have the similar spatial confinement near the Si/SiO/sub 2/ interface. The above mechanisms significantly enhance the electroluminescence.

Electroluminescence (EL) at Si bandgap energy is significantly enhanced with the insertion of SiO/sub 2/ nanoparticles in the oxide layer of the metal-oxide-silicon (MOS) structures on n-type Si. The nanoparticles have a size of 12 nm. The measured EL efficiency is enhanced to be near 10/sup -4/. Furthermore, near-lasing actions like the threshold behavior and resonance modes are observed. The reason is because nanoparticles cause the simultaneous localization of electrons and holes, making the process of the phonon-assisted radiative recombination of electron-hole pairs more like two-particle (exciton-phonon) collision than three-particle (electron-hole-phonon) collision. Thus the probability of radiative recombination increases to enhance EL at Si bandgap energy.

We discover that SiO/sub 2/ nanoparticles could significantly improve electroluminescence (EL) at Si bandgap energy from metal-oxide-silicon (MOS) structures for orders of magnitudes. Furthermore, the nanoparticle-modified MOS exhibits nearly lasing actions like the threshold behavior and resonance modes.

The significance of surface states in nano-structures is studied using CdS nanoparticles. Spectral features like peak red-shift due to organic capping and influence of surface states have been observed. The pronounced enhancement of emission from surface states can be dominant with certain modiciation of CdS nanoparticles. Spectral behaviors of electroluminescence in different temperature are also studied.

The fabrication of CdS-nanoparticle light emitting diodes (LEDs) on Si and their properties at room temperature and variant temperatures are reported. Due to passivation of p- hydroxyl thiophenol group around nanoparticles, 86-meV spectral shift of free exciton transition at room temperature is observed. Controlled conditions for the preparation of CdS-nanoparticle LED such as heat treatment and/or with oxygen-rich environment are found to have significant influences on emission spectra. Radiative recombination of carriers trapped in oxygen-impurity level of 273 meV presents in samples prepared in oxygen-rich environment. Coalescence of nanoparticles into bulk form also occurs to contribute to increased magnitude of luminescence. Spectral behaviors of electroluminescence with varied temperature are studied.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report that electroluminescence (EL) at Si bandgap energy is significantly enhanced from the nano-structured metal- oxide-semiconductor (MOS) devices on silicon. The nano- structure is constructed by inserting SiO 2 nanoparticles with the size of 12 nm in the oxide layer. The measured EL efficiency of the nano-structured MOS devices is enhanced to be near 10 -4 , which exceeds the limitation imposed by the indirect bandgap nature of silicon. We also observed the nearly lasing behaviors such as the threshold and resonance modes in the EL characteristics. The enhanced EL efficiency is attributed to simultaneous localization of electrons and holes to form exciton by nano-structure. This causes the process of the phonon-assisted radiative recombination of electron-hole pair more like two-particle (exciton-phonon) collision than three-particle (electron- hole-phonon) collision.

A stretchable organic digital information storage device has been developed, which potentially advances the development of future smart and digital stretchable electronic systems. The stretchable organic memory with a buckled structure was configured by a mechanically flexible and elastic graphene bottom electrode and polymer compound. The current–voltage curve of the wrinkled memory device demonstrated electrical bistability with typical write-once-read-many times memory features and a high ON/OFF current ratio (∼105). Even under repetitive stretching, the stretchable organic memory exhibited excellent electrical switching functions and memory effects. We believe the first proof-of-concept presentation of the stretchable organic nonvolatile memory may accelerate the development of information storage device in various stretchable electronic applications, such as stretchable display, wearable computer and artificial skin. Stretchable and foldable electronic devices are very attractive, not only for their practicality but also for their potential in as-yet-undeveloped applications, such as artificial electronic skin. Now, Yang-Fang Chen from the National Taiwan University and co-workers have constructed a stretchable organic memory device. Although a variety of flexible organic electronic devices have already been built, which include transistors or solar cells, building stretchable memory devices has remained a challenge. This is because they typically contain a brittle metal electrode, and their fabrication also involves processes — such as spin coating — that are incompatible with flexible substrates. The researchers circumvented these issues by buckling both a graphene, rather than metallic, electrode and the active memory layers over a pre-stretched poly(dimethylsiloxane) elastomer. When the pre-strain was released, the materials adopted a wrinkled structure that endowed them with flexibility. The resulting device showed good electrical switching behavior and memory effects after several stretch/release cycles. A stretchable wrinkled organic memory has been successfully demonstrated. The stretchable organic memory with a graphene bottom electrode possesses rippled structures. The stretchable organic memory exhibits excellent electrical switching behaviors and memory effects even under repetitive stretching. It is believed that this stretchable organic memory may be beneficial for digital information storage in future stretchable electronic systems.