Showing papers on "Silicon published in 2005"

Micrometre-scale silicon electro-optic modulator

Abstract: Metal interconnections are expected to become the limiting factor for the performance of electronic systems as transistors continue to shrink in size. Replacing them by optical interconnections, at different levels ranging from rack-to-rack down to chip-to-chip and intra-chip interconnections, could provide the low power dissipation, low latencies and high bandwidths that are needed. The implementation of optical interconnections relies on the development of micro-optical devices that are integrated with the microelectronics on chips. Recent demonstrations of silicon low-loss waveguides, light emitters, amplifiers and lasers approach this goal, but a small silicon electro-optic modulator with a size small enough for chip-scale integration has not yet been demonstrated. Here we experimentally demonstrate a high-speed electro-optical modulator in compact silicon structures. The modulator is based on a resonant light-confining structure that enhances the sensitivity of light to small changes in refractive index of the silicon and also enables high-speed operation. The modulator is 12 micrometres in diameter, three orders of magnitude smaller than previously demonstrated. Electro-optic modulators are one of the most critical components in optoelectronic integration, and decreasing their size may enable novel chip architectures.

A continuous-wave Raman silicon laser

Abstract: Achieving optical gain and/or lasing in silicon has been one of the most challenging goals in silicon-based photonics because bulk silicon is an indirect bandgap semiconductor and therefore has a very low light emission efficiency. Recently, stimulated Raman scattering has been used to demonstrate light amplification and lasing in silicon. However, because of the nonlinear optical loss associated with two-photon absorption (TPA)-induced free carrier absorption (FCA), until now lasing has been limited to pulsed operation. Here we demonstrate a continuous-wave silicon Raman laser. Specifically, we show that TPA-induced FCA in silicon can be significantly reduced by introducing a reverse-biased p-i-n diode embedded in a silicon waveguide. The laser cavity is formed by coating the facets of the silicon waveguide with multilayer dielectric films. We have demonstrated stable single mode laser output with side-mode suppression of over 55 dB and linewidth of less than 80 MHz. The lasing threshold depends on the p-i-n reverse bias voltage and the laser wavelength can be tuned by adjusting the wavelength of the pump laser. The demonstration of a continuous-wave silicon laser represents a significant milestone for silicon-based optoelectronic devices.

An all-silicon Raman laser

Abstract: With the growing use of optoelectronics in information technology, manipulating light is almost as important as manipulating electrons. Unfortunately silicon, workhorse of modern microelectronics, is next to useless in optical applications. There has been a massive effort to overcome silicon's inadequacies, and ways of coaxing silicon to handle light are under development but a key component — the laser — has been problematic. Last year a silicon laser was produced, but it involved metres of optical fibre. Now workers in Intel's research labs have come up with an all-silicon laser on a single chip. The device is compact and readily integrated with other silicon components. The possibility of light generation and/or amplification in silicon has attracted a great deal of attention1 for silicon-based optoelectronic applications owing to the potential for forming inexpensive, monolithic integrated optical components. Because of its indirect bandgap, bulk silicon shows very inefficient band-to-band radiative electron–hole recombination. Light emission in silicon has thus focused on the use of silicon engineered materials such as nanocrystals2,3,4,5, Si/SiO2 superlattices6, erbium-doped silicon-rich oxides7,8,9,10, surface-textured bulk silicon11 and Si/SiGe quantum cascade structures12. Stimulated Raman scattering (SRS) has recently been demonstrated as a mechanism to generate optical gain in planar silicon waveguide structures13,14,15,16,17,18,19,20,21. In fact, net optical gain in the range 2–11 dB due to SRS has been reported in centimetre-sized silicon waveguides using pulsed pumping18,19,20,21. Recently, a lasing experiment involving silicon as the gain medium by way of SRS was reported, where the ring laser cavity was formed by an 8-m-long optical fibre22. Here we report the experimental demonstration of Raman lasing in a compact, all-silicon, waveguide cavity on a single silicon chip. This demonstration represents an important step towards producing practical continuous-wave optical amplifiers and lasers that could be integrated with other optoelectronic components onto CMOS-compatible silicon chips.

Strong quantum-confined Stark effect in germanium quantum-well structures on silicon

Abstract: Silicon chips dominate electronics while optical fibres dominate long-distance information transfer. Recent work, in search of the best of both worlds, has led to silicon devices capable of modulating light; these show promise but still rely on weak physical mechanisms found in silicon itself. Now a team working at Stanford University and at Hewlett-Packard's Palo Alto labs has developed thin germanium ‘quantum well’ nanostructures grown on silicon that generate a strong quantum-mechanical effect capable of turning light beams on and off. Their performance rivals the best seen in any material. This development may allow silicon/germanium chips to handle both electronics and optics, uniting computing and communications at the integrated chip level. Silicon is the dominant semiconductor for electronics, but there is now a growing need to integrate such components with optoelectronics for telecommunications and computer interconnections1. Silicon-based optical modulators have recently been successfully demonstrated2,3; but because the light modulation mechanisms in silicon4 are relatively weak, long (for example, several millimetres) devices2 or sophisticated high-quality-factor resonators3 have been necessary. Thin quantum-well structures made from III-V semiconductors such as GaAs, InP and their alloys exhibit the much stronger quantum-confined Stark effect (QCSE) mechanism5, which allows modulator structures with only micrometres of optical path length6,7. Such III-V materials are unfortunately difficult to integrate with silicon electronic devices. Germanium is routinely integrated with silicon in electronics8, but previous silicon–germanium structures have also not shown strong modulation effects9,10,11,12,13. Here we report the discovery of the QCSE, at room temperature, in thin germanium quantum-well structures grown on silicon. The QCSE here has strengths comparable to that in III-V materials. Its clarity and strength are particularly surprising because germanium is an indirect gap semiconductor; such semiconductors often display much weaker optical effects than direct gap materials (such as the III-V materials typically used for optoelectronics). This discovery is very promising for small, high-speed14, low-power15,16,17 optical output devices fully compatible with silicon electronics manufacture.

Guiding, modulating, and emitting light on Silicon-challenges and opportunities

Abstract: Silicon photonics could enable a chip-scale platform for monolithic integration of optics and microelectronics for applications of optical interconnects in which high data streams are required in a small footprint. This paper discusses mechanisms in silicon photonics for waveguiding, modulating, light amplification, and emission. These mechanisms, together with recent advances of fabrication techniques, have enabled the demonstration of ultracompact passive and active silicon photonic components with very low loss.

Engineering silicon oxide surfaces using self-assembled monolayers.

Abstract: Although a molecular monolayer is only a few nanometers thick it can completely change the properties of a surface. Molecular monolayers can be readily prepared using the Langmuir-Blodgett methodology or by chemisorption on metal and oxide surfaces. This Review focuses on the use of chemisorbed self-assembled monolayers (SAMs) as a platform for the functionalization of silicon oxide surfaces. The controlled organization of molecules and molecular assemblies on silicon oxide will have a prominent place in bottom-up nanofabrication, which could revolutionize fields such as nanoelectronics and biotechnology in the near future. In recent years, self-assembled monolayers on silicon oxide have reached a high level of sophistication and have been combined with various lithographic patterning methods to develop new nanofabrication protocols and biological arrays. Nanoscale control over surface properties is of paramount importance to advance from 2D patterning to 3D fabrication.

High-yield plasma synthesis of luminescent silicon nanocrystals.

Abstract: Light emission from silicon based on quantum confinement in nanoscale structures has sparked intense research into this field ever since its discovery about 15 years ago A barrier to the widespread utilization of luminescent silicon nanocrystals in such diverse application areas as optoelectronics, solid-state lighting for general illumination, or fluorescent agents for biological applications has been the lack of a simple, high-yield synthesis approach Here we report a scaleable single-step synthesis process for luminescent silicon nanocrystals based on a low-pressure nonthermal plasma

Application of NaYF 4 : Er 3 + up-converting phosphors for enhanced near-infrared silicon solar cell response

Abstract: Erbium-doped sodium yttrium fluoride (NaYF4:Er3+) up-conversion phosphors were attached to the rear of a bifacial silicon solar cell to enhance its reponsivity in the near-infrared. The incident wavelength and light intensity were varied and the resulting short circuit current of the solar cell was measured. A close match between the spectral features of the external quantum efficiency and the phosphor absorption is consistent with the energy transfer up-conversion process. The peak external quantum efficiency of the silicon solar cell was measured to be (2.5±0.2)% under 5.1 mW laser excitation at 1523 nm, corresponding to an internal quantum efficiency of 3.8%.

Field-effect electroluminescence in silicon nanocrystals.

Abstract: There is currently worldwide interest in developing silicon-based active optical components in order to leverage the infrastructure of silicon microelectronics technology for the fabrication of optoelectronic devices. Light emission in bulk silicon-based devices is constrained in wavelength to infrared emission, and in efficiency by the indirect bandgap of silicon. One promising strategy for overcoming these challenges is to make use of quantum-confined excitonic emission in silicon nanocrystals. A critical challenge for silicon nanocrystal devices based on nanocrystals embedded in silicon dioxide has been the development of a method for efficient electrical carrier injection. We report here a scheme for electrically pumping dense silicon nanocrystal arrays by a field-effect electroluminescence mechanism. In this excitation process, electrons and holes are both injected from the same semiconductor channel across a tunnelling barrier in a sequential programming process, in contrast to simultaneous carrier injection in conventional pn-junction light-emitting-diode structures. Light emission is strongly correlated with the injection of a second carrier into a nanocrystal that has been previously programmed with a charge of the opposite sign.

Beyond the Rayleigh scattering limit in high-Q silicon microdisks: theory and experiment.

Abstract: Using a combination of resist reflow to form a highly circular etch mask pattern and a low-damage plasma dry etch, high-quality-factor silicon optical microdisk resonators are fabricated out of silicon-on-insulator (SOI) wafers. Quality factors as high as Q = 5×10^6 are measured in these microresonators, corresponding to a propagation loss coefficient as small as α ~ 0.1 dB/cm. The different optical loss mechanisms are identified through a study of the total optical loss, mode coupling, and thermally-induced optical bistability as a function of microdisk radius (5-30 µm). These measurements indicate that optical loss in these high-Q microresonators is limited not by surface roughness, but rather by surface state absorption and bulk free-carrier absorption.

Water‐Soluble Photoluminescent Silicon Quantum Dots

Abstract: For silicon quantum dots to be used in biomedical applications it is essential that they have a substantial photoluminescence quantum yield in the visible region, have a fast radiative recombination rate, and are water soluble and hydrophilic to prevent aggregation and precipitation in a biological environment. The chemical process used to terminate the surfaces of the silicon quantum dots changes the internal electronic structure and thus plays an important role in the resultant emission wavelength and radiative lifetime, and ultimately determines the solubility. [18] Silicon quantum dots with an oxide surface passivation typically display a dipole-forbidden yellow-red emission with radiative lifetimes of 10 3 –10 6 s. [18, 26] This slow rate of recombination limits the use of oxide-passivated silicon quantum dots in biological imaging. However, silicon quantum dots with a hydrogen or carbon surface passivation have electric-dipole-allowed direct band gap transitions that lead to blue photoluminescence with fast recombination rates of 10 8 –10 9 s. [18, 20]

One-dimensional hole gas in germanium/silicon nanowire heterostructures

Abstract: Two-dimensional electron and hole gas systems, enabled through band structure design and epitaxial growth on planar substrates, have served as key platforms for fundamental condensed matter research and high-performance devices. The analogous development of one-dimensional (1D) electron or hole gas systems through controlled growth on 1D nanostructure substrates, which could open up opportunities beyond existing carbon nanotube and nanowire systems, has not been realized. Here, we report the synthesis and transport studies of a 1D hole gas system based on a free-standing germanium/silicon (Ge/Si) core/shell nanowire heterostructure. Room temperature electrical transport measurements clearly show hole accumulation in undoped Ge/Si nanowire heterostructures, in contrast to control experiments on single-component nanowires. Low-temperature studies show well-controlled Coulomb blockade oscillations when the Si shell serves as a tunnel barrier to the hole gas in the Ge channel. Transparent contacts to the hole gas also have been reproducibly achieved by thermal annealing. In such devices, we observe conductance quantization at low temperatures, corresponding to ballistic transport through 1D subbands, where the measured subband energy spacings agree with calculations for a cylindrical confinement potential. In addition, we observe a “0.7 structure,” which has been attributed to spontaneous spin polarization, suggesting the universality of this phenomenon in interacting 1D systems. Lastly, the conductance exhibits little temperature dependence, consistent with our calculation of reduced backscattering in this 1D system, and suggests that transport is ballistic even at room temperature.

Diameter-dependent growth direction of epitaxial silicon nanowires.

Abstract: We found that silicon nanowires grown epitaxially on Si (100) via the vapor−liquid−solid growth mechanism change their growth direction from 〈111〉 to 〈110〉 at a crossover diameter of approximately 20 nm. A model is proposed for the explanation of this phenomenon. We suggest that the interplay of the liquid−solid interfacial energy with the silicon surface energy expressed in terms of an edge tension is responsible for the change of the growth direction. The value of the edge tension is estimated by the product of the interfacial thickness with the surface energy of silicon. For large diameters, the direction with the lowest interfacial energy is dominant, whereas for small diameters the surface energy of the silicon nanowire determines the preferential growth direction.

Photographic surveying of minority carrier diffusion length in polycrystalline silicon solar cells by electroluminescence

Abstract: Photographic surveying of the minority carrier diffusion length distribution in polycrystalline silicon solar cells was proposed Light emission from the cell under the forward bias was captured by a charge coupled device camera We have found that the intensity distribution of light emission clearly agreed with the mapping of minority carrier diffusion length in polycrystalline silicon active layers The emission intensity had a one-to-one relationship with the minority carrier diffusion length, which yielded a semiquantitative analysis method of the diffusion length mapping and the detection of the deteriorated areas

Analytical potential for atomistic simulations of silicon, carbon, and silicon carbide

Abstract: We present an analytical bond-order potential for silicon, carbon, and silicon carbide that has been optimized by a systematic fitting scheme. The functional form is adopted from a preceding work [Phys. Rev. B 65, 195124 (2002)] and is built on three independently fitted potentials for $\mathrm{Si}\mathrm{Si}$, $\mathrm{C}\mathrm{C}$, and $\mathrm{Si}\mathrm{C}$ interaction. For elemental silicon and carbon, the potential perfectly reproduces elastic properties and agrees very well with first-principles results for high-pressure phases. The formation enthalpies of point defects are reasonably reproduced. In the case of silicon stuctural features of the melt agree nicely with data taken from literature. For silicon carbide the dimer as well as the solid phases B1, B2, and B3 were considered. Again, elastic properties are very well reproduced including internal relaxations under shear. Comparison with first-principles data on point defect formation enthalpies shows fair agreement. The successful validation of the potentials for configurations ranging from the molecular to the bulk regime indicates the transferability of the potential model and makes it a good choice for atomistic simulations that sample a large configuration space.

Controlled growth of well-aligned ZnO nanorod array using a novel solution method.

Abstract: A simple method of synthesizing nanomaterials and the ability to control the size and position of them are crucial for fabricating nanodevices. In this work, we developed a novel ammonia aqueous solution method for growing well-aligned ZnO nanorod arrays on a silicon substrate. For ZnO nanorod growth, a thin zinc metal seed layer was deposited on a silicon substrate by thermal evaporation. Uniform ZnO nanorods were grown on the zinc-coated silicon substrate in aqueous solution containing zinc nitrate and ammonia water. The growth temperature was as low as 60−90 °C and a 4-in. wafer size scale up was possible. The morphology of a zinc metal seed layer, pH, growth temperature, and concentration of zinc salt in aqueous solution were important parameters to determine growth characteristics such as average diameters and lengths of ZnO nanorods. We could demonstrate the discrete controlled growth of ZnO nanorods using sequential, tailored growth steps. By combining our novel solution method and general photolit...

Four-wave mixing in silicon wire waveguides.

Abstract: We report the observation of four-wave mixing phenomenon in a simple silicon wire waveguide at the optical powers normally employed in communications systems. The maximum conversion efficiency is about -35 dB in the case of a 1.58-cm-long silicon wire waveguide. The nonlinear refractive index coefficient is found to be 9×10-18 m2/W. This value is not negligible for dense wavelength division multiplexing components, because it predicts the possibility of large crosstalk. On the other hand, with longer waveguide lengths with smaller propagation loss, it would be possible to utilize just a simple silicon wire for practical wavelength conversion. We demonstrate the wavelength conversion for data rate of 10-Gbps using a 5.8-cm-long silicon wire. These characteristics are attributed to the extremely small core of silicon wire waveguides.

All-optical switches on a silicon chip realized using photonic crystal nanocavities

Abstract: We demonstrate all-optical switching in the telecommunication band, in silicon photonic crystals at high speed (∼50ps), with extremely low switching energy (a few 100fJ), and high switching contrast (∼10dB). The devices consist of ultrasmall high-quality factor nanocavities connected to input and output waveguides. Switching is induced by a nonlinear refractive-index change caused by the plasma effect of carriers generated by two-photon absorption in silicon. The high-quality factor and small mode volume led to an extraordinarily large reduction in switching energy. The estimated internal switching energy in the nanocavity is as small as a few tens of fJ, indicating that further reduction on the operating energy is possible.

Handbook of Ceramic Composites

Abstract: Preface Ceramic Fibers Oxide Fibers A R Bunsell Non-oxide (Silicon Carbide) Fibers J A DiCarlo and H-M Yun Non-oxide/Non-oxide Composites Chemical Vapor Infiltrated SiC/SiC Composites (CVI SiC/SiC) J Lamon SiC/SiC Composites for 1200 C and Above J A DiCarlo, H-M Yun, G N Morscher, and R T Bhatt Silicon Melt Infiltrated Ceramic Composites (HiPerCompTM) G S Corman and K L Luthra Carbon Fibre Reinforced Silicon Carbide Composites (C/SiC, C/C-SiC) W Krenkel Silicon Carbide Fiber-Reinforced Silicon Nitride Composites R T Bhatt MoSi2-Base Composites M G Hebsur Ultra High Temperature Ceramic Composites M J Gasch, D T Ellerby and S M Johnson Non-oxide/Oxide Composites SiC Fiber-Reinforced Celsian Composites N P Bansal In Situ Reinforced Silicon Nitride - Barium Aluminosilicate Composite K W White, F Yu and Y Fang Silicon Carbide and Oxide Fiber Reinforced Alumina Matrix Composites Fabricated Via Directed Metal Oxidation A S Fareed SiC Whisker Reinforced Alumina T Tiegs Mullite-SiC Whisker and Mullite-ZrO2-SiC Whisker Composites R Ruh NextelTM 312/Silicon Oxycarbide Ceramic Composites S T Gonczy and J G Sikonia Oxide/Oxide Composites Oxide-Oxide Composites K A Keller, G Jefferson and R J Kerans WHIPOX All Oxide Ceramic Matrix Composites M Schmucker and H Schneider Alumina-Reinforced Zirconia Composites S R Choi and N P Bansal Glass andGlass-Ceramic Composites Continuous Fibre Reinforced Glass and Glass-Ceramic Matrix Composites AR Boccaccini Dispersion-Reinforced Glass and Glass-Ceramic Matrix Composites J A Roether and A R Boccaccini Glass Containing Composite Materials: Alternative Reinforcement Concepts AR Boccaccini

Optical gain and stimulated emission in periodic nanopatterned crystalline silicon.

Abstract: Persistent efforts have been made to achieve efficient light emission from silicon1,2,3,4,5,6,7 in the hope of extending the reach of silicon technology into fully integrated optoelectronic circuits, meeting the needs for high-bandwidth intrachip and interchip connects8. Enhanced light emission from silicon is known to be theoretically possible9,10, enabled mostly through quantum-confinement effects2,3,4. Furthermore, Raman-laser conversion was demonstrated in silicon waveguides11,12. Here we report on optical gain and stimulated emission in uniaxially nanopatterned silicon-on-insulator using a nanopore array as an etching mask13. In edge-emission measurements, we observed threshold behaviour, optical gain, longitudinal cavity modes and linewidth narrowing, along with a collimated far-field pattern, all indicative of amplification and stimulated emission14,15,16,17. The sub-bandgap 1,278 nm emission peak is attributed to A-centre mediated phononless direct recombination between trapped electrons and free holes18,19,20. The controlled nanoscale silicon engineering, combined with the low material loss in this sub-bandgap spectral range and the long electron lifetime in such A-type trapping centres, gives rise to the measured optical gain and stimulated emission and provides a new pathway to enhance light emission from silicon.

Visible and near-infrared responsivity of femtosecond-laser microstructured silicon photodiodes.

Abstract: We investigated the current-voltage characteristics and responsivity of photodiodes fabricated with silicon that was microstructured by use of femtosecond-laser pulses in a sulfur-containing atmosphere. The photodiodes that we fabricated have a broad spectral response ranging from the visible to the near infrared (400-1600 nm). The responsivity depends on substrate doping, microstructuring fluence, and annealing temperature. We obtained room-temperature responsivities as high as 100 A/W at 1064 nm, 2 orders of magnitude higher than for standard silicon photodiodes. For wavelengths below the bandgap we obtained responsivities as high as 50 mA/W at 1330 nm and 35 mA/W at 1550 nm.

Fundamental boron-oxygen-related carrier lifetime limit in mono- and multicrystalline silicon

Abstract: Boron-doped crystalline silicon is the most relevant material in today's solar cell production. Following the trend towards higher efficiencies, silicon substrate materials with high carrier lifetimes are becoming more and more important. In silicon with sufficiently low metal impurity concentrations, the carrier lifetime is ultimately limited by a metastable boron–oxygen-related defect, which forms under minority-carrier injection. We have analysed 49 different Czochralski-grown silicon materials of numerous suppliers with various boron and oxygen concentrations. On the basis of our measured lifetime data, we have derived a universal empirical parameterisation predicting the stable carrier lifetime from the boron and oxygen content in the crystalline silicon material. For multicrystalline silicon it is shown that the predicted carrier lifetime can be regarded as a fundamental upper limit. Copyright © 2005 John Wiley & Sons, Ltd.

Hybrid silicon evanescent laser fabricated with a silicon waveguide and III-V offset quantum wells.

Abstract: A novel laser that utilizes a silicon waveguide bonded to AlGaInAs quantum wells is demonstrated. This wafer scale fabrication approach allows the optical waveguide to be defined by CMOS-compatible silicon processing while optical gain is provided by III-V materials. The AlGaInAs quantum well structure is bonded to the silicon wafer using low temperature oxygen plasma-assisted wafer bonding. The optically pumped 1538 nm laser has a pulsed threshold of 30 mW and an output power of 1.4 mW.

Silicon Nanocrystals: Size Matters

Abstract: This paper reviews new approaches to size-controlled silicon-nanocrystal synthesis. These approaches allow narrowing of the size distribution of the nanocrystals compared with those obtained by conventional synthesis processes such as ion implantation into SiO 2 or phase separation of sub-stoichiometric SiO x layers. This size control is realized by different approaches to introducing a superlattice-like structure into the synthesis process, by velocity selection of silicon aerosols, or by the use of electron lithography and subsequent oxidation processes. Nanocrystals between 2 and 20 nm in size with a full width at half maximum of the size distribution of 1 nm can be synthesized and area densities above 10 1 2 cm - 2 can be achieved. The role of surface passivation is elucidated by comparing Si/SiO 2 layers with superlattices of fully passivated silicon nanocrystals within a SiO 2 matrix. The demands on silicon nanocrystals for various applications such as non-volatile memories or light-emitting devices are discussed for different size-controlled nanocrystal synthesis approaches.

Erbium in silicon

Abstract: The overlap of the principal luminescence band of the erbium ion with the low-loss optical transmission window of silica optical fibres, along with the drive for integration of photonics and silicon technology, has generated intense interest in doping silicon with erbium to produce a silicon-based optical source Silicon is a poor photonic material due to its very short non-radiative lifetime and indirect band gap, but it has been hoped that the incorporation of optically active erbium ions into silicon will permit the development of silicon-based light sources that will interface with both CMOS technology and optical fibre communications Some years into this activity, there have now been a wide range of experimental studies of material growth techniques, optical, physical and electrical properties, along with a considerable body of theoretical work dealing with the site of the erbium ion in silicon, along with activation and deactivation processes This paper reviews the current state of what remains an active field, summarizing results from a range of studies conducted over the last few years, and points to further developments by considering the prospects for successful photonic integration of erbium and silicon

Efficient surface grafting of luminescent silicon quantum dots by photoinitiated hydrosilylation.

Abstract: We suggest a method for efficient (high-coverage) grafting of organic molecules onto photoluminescent silicon nanoparticles. High coverage grafting was enabled by use of a modified etching process that produces a hydrogen-terminated surface on the nanoparticles with very little residual oxygen and by carefully excluding oxygen during the grafting process. It had not previously been possible to produce such a clean H-terminated surface on free silicon nanoparticles or, subsequently, to produce grafted particles without significant surface oxygen. This allowed us to (1) prepare air-stable green-emitting silicon nanoparticles, (2) prepare stable dispersions of grafted silicon nanoparticles in a variety of organic solvents from which particles can readily be precipitated by addition of nonsolvent, dried, and redispersed, (3) separate these nanoparticles by size (and therefore emission color) using conventional chromatographic methods, (4) protect the particles from chemical attack and photoluminescence quench...

σ-π molecular dielectric multilayers for low-voltage organic thin-film transistors

Abstract: Very thin (2.3-5.5 nm) self-assembled organic dielectric multilayers have been integrated into organic thin-film transistor structures to achieve sub-1-V operating characteristics. These new dielectrics are fabricated by means of layer-by-layer solution phase deposition of molecular silicon precursors, resulting in smooth, nanostructurally well defined, strongly adherent, thermally stable, virtually pinhole-free, organosiloxane thin films having exceptionally large electrical capacitances (up to ≈2,500 nF·cm-2), excellent insulating properties (leakage current densities as low as 10-9 A·cm-2), and single-layer dielectric constant (k)of ≈16. These 3D self-assembled multilayers enable organic thin-film transistor function at very low source-drain, gate, and threshold voltages (<1 V) and are compatible with a broad variety of vapor- or solution-deposited p- and n-channel organic semiconductors. gate insulator molecular multilayer organic dielectric self-assembly

Desorption/Ionization on Silicon Nanowires

Abstract: Dense arrays of single-crystal silicon nanowires (SiNWs) have been used as a platform for laser desorption/ionization mass spectrometry of small molecules, peptides, protein digests, and endogenous and xenobiotic metabolites in biofluids. Sensitivity down to the attomole level has been achieved on the nanowire surfaces by optimizing laser energy, surface chemistry, nanowire diameter, length, and growth orientation. An interesting feature of the nanowire surface is that it requires lower laser energy as compared to porous silicon and MALDI to desorb/ionize small molecules, therefore reducing background ion interference. Taking advantage of their high surface area and fluid wicking capabilities, SiNWs were used to perform chromatographic separation followed by mass analysis of the separated molecules providing a unique platform that can integrate separation and mass spectrometric detection on a single surface.