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Nanoparticles of Au, Pd, and Pt form spontaneously as thin, morphologically complex metallic films upon various semiconducting or metal substrates such as Ge(100), Cu, Zn, and Sn, via galvanic displacement from aqueous metal salt solutions. Patterning of these high surface area metal films into ordered structures utilizing photolithography, microcontact printing (μ-CP), and dip-pen nanolithography (DPN) is demonstrated on flat Ge(100), and (for μ-CP) on rough Zn foil.

Thin noble metal films have been prepared as a result of the immersion of germanium substrates into dilute, aqueous solutions of AuCl4-, PdCl42-, or PtCl42-, respectively. Deposition proceeds via galvanic displacement in the absence of fluoride, pH adjusters, complexing agents, or external reducing agents. This manner of metal deposition serves as a cost-effective, high-throughput methodology with control over surface morphology and deposition rate by modulation of plating parameters such as concentration, temperature, and immersion time.

Porous silicon is a material of intense technological and fundamental interest, due to its high surface area, quantum confinement effects, light emission, and complex nanoscale architecture. There is a strong desire to be able to control the surface properties of this versatile material at will through functionalization with monolayers bound through the stable silicon-carbon bond. Incredibly, the surface chemistry of porous silicon is often very different from that of a silicon-based molecule, or a flat surface, due to interesting electronic effects resulting from both the semiconducting and nanoscale characteristics of the material. Recent results outlining the rapid progress of silicon-carbon bond formation on porous silicon surfaces will be described.

Hydride abstraction by triphenylcarbenium cations in the presence of terminal alkynes and alkenes results in hydrosilylation at room temperature on hydride-terminated porous silicon surfaces, leading to alkenyl- and alkyl-terminated surfaces, respectively. A wide range of surface terminations are possible as the reaction conditions tolerate a variety of functional groups. Silicon−carbon bond formation is substantiated by Fourier transform infrared and 13C solid-state NMR spectroscopies, in addition to chemical and stability studies. Generation of an energetic surface silicon-based positive charge is thus a viable route to the formation of silicon−carbon bonds via hydrosilylation, a step previously postulated for the mechanism of exciton-mediated hydrosilylation on photoluminescent nanocrystalline silicon.

Phase-pure and crystalline Zn3P2 nanoparticles (≈3—15 nm) are prepared by two different solution-phase strategies using precipitation from a 1-octadecene solution of P(octyl)3 (TOP) and ZnMe2 (348 °C, 2 h) followed by flocculation of nanoparticles with PrOH.

The self-assembly of block copolymer (BCP) thin films is a versatile method for producing periodic nanoscale patterns with a variety of shapes. The key to attaining a desired pattern or structure is the annealing step undertaken to facilitate the reorganization of nanoscale phase-segregated domains of the BCP on a surface. Annealing BCPs on silicon substrates using a microwave oven has been shown to be very fast (seconds to minutes), both with and without contributions from solvent vapor. The mechanism of the microwave annealing process remains, however, unclear. This work endeavors to uncover the key steps that take place during microwave annealing, which enable the self-assembly process to proceed. Through the use of in situ temperature monitoring with a fiber optic temperature probe in direct contact with the sample, we have demonstrated that the silicon substrate on which the BCP film is cast is the dominant source of heating if the doping of the silicon wafer is sufficiently low. Surface temperatures as high as 240°C are reached in under 1 min for lightly doped, high resistivity silicon wafers (n- or p-type). The influence of doping, sample size, and BCP composition was analyzed to rule out other possible mechanisms. In situ temperature monitoring of various polymer samples (PS, P2VP, PMMA, and the BCPs used here) showed that the polymers do not heat to any significant extent on their own with microwave irradiation of this frequency (2.45 GHz) and power (∼600 W). It was demonstrated that BCP annealing can be effectively carried out in 60 s on non-microwave-responsive substrates, such as highly doped silicon, indium tin oxide (ITO)-coated glass, glass, and Kapton, by placing a piece of high resistivity silicon wafer in contact with the sample-in this configuration, the silicon wafer is termed the heating element. Annealing and self-assembly of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) and polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) BCPs into horizontal cylinder structures were shown to take place in under 1 min, using a silicon wafer heating element, in a household microwave oven. Defect densities were calculated and were shown to decrease with higher maximum obtained temperatures. Conflicting results in the literature regarding BCP annealing with microwave are explained in light of the results obtained in this study. © Published 2014 by the American Chemical Society.

Silicon is the cornerstone material of the semiconductor industry. As feature sizes on chips continue to decrease in size, the ratio of surface to bulk increases, and as a result, the role of surface defects, surface states and other subtle features play larger roles in the functioning of the device. Although silicon oxides have served the industry well as the passivation chemistry of choice, there is interest in expanding the repertoire of accessible and efficient chemical functional strategies available for use, and to fully understand the nature of these interfaces. For new applications such as molecular electronics on silicon and biochips, for example, there is a need to avoid the layer of intervening insulating oxide: A well-defined linkage of organic molecules through a silicon-carbon bond has great promise and appeal. Hydrosilylation, the insertion of an alkene or alkyne into a surface Si-H bond, is an ideal approach to producing these covalent Si-C bonds, and can be carried out in a number of ways. Light-promoted hydrosilylation is promising because it is clean and direct and can be patterned via masking; it requires no additional reagents such as catalysts or input of thermal energy and thus may have reduced surface contamination and numbers of defects. In this perspective, we start by making connections between the molecular silane literature, and the first reports of UV-mediated hydrosilylation of an alkene on a silicon surface, a reaction that was assumed to operate via a radical mechanism. We then describe the unexpected development of four new mechanisms that have no obvious parallels with the molecular silane literature, and take place as a result of the solid state electronics of the underlying silicon itself. From exciton involvement, to the influence of plasmonics, to the role of photoemission, the area of silicon surface hydrosilylation has become incredibly rich, and undoubtedly still contains new reactivity to be discovered. © 2013 American Chemical Society.

Porous silicon has received considerable attention lately due to its unique optical properties and use in sensor applications. The utility of this material can be further advanced with the aid of new surface chemical modification methods. Here we describe two transition metal mediated reactions that allow for the mild and chemoselective functionalization of porous silicon. The first method utilizes rhodium carbene chemistry to modify porous silicon surfaces with esters and amides. The second technique exploits a pt-based Karstedt's catalyst to affect the hydrosilylation of porous silicon with alkenes. The mildness and selectivity of the hydrosilylation is highlighted by modification of n-type porous silicon matrix with an 8-residue cyclic peptide.

Three reactions are discussed which accomplish a high degree of substitution of the silicon hydride bonds on the porous silicon (pSi) surface with silicon–carbon bonds. Lewis acid mediated (LAM) and white light-promoted (LP) hydrosilylation of alkynes and alkenes gives surfaces with alkenyl and alkyl residues, respectively. Evidence for the silicon–carbon bonds is given by solid-state NMR spectroscopy of free-standing pSi material. The extent of the substitution of the surface bonds is termed reaction efficiency (E) which is measured by the change in the integrated area of the silicon hydride stretch region in FTIR spectra (2000–2200 cm—1). The LAM hydrosilylation gives a higher E value than the LP reaction. The E value of the LAM reaction is believed to be limited by the efficiency of the catalyst diffusion throughout the porous structure. In the case of the LP reaction, it is limited by the relative quantity of visible light-exposed material in comparison to the entire amount of IR-apparent silicon hydride bonds. The cathodic electrografting (CEG) reaction gives directly attached alkynyl residues via reduction of a silicon hydride bond to generate alkynyl carbanions, which then react with silicon–silicon bonds.

The stability of derivatized mesoporous silicon mirrors in simulated human blood plasma has been assessed. The rate at which they are dissolved in-vivo is predicted to be tunable by surface chemistry over timescales of weeks to years, and high reflectivity can be maintained until the bottom of the multilayer stack starts to corrode. Such biodegradable optical components could be utilized to direct and define optical path lengths for therapeutic treatments and minimally-invasive diagnostics.

Covalently bonded organic monolayers on semiconductor surfaces are potentially important for the fabrication of novel electronic devices and sensors. In contrast to the recent interest in and development of methods for monolayer formation on silicon surfaces, only one wet chemical route has been previously published for germanium surfaces. We present novel strategies to prepare organic monolayers on hydride-terminated Ge(100) surfaces utilizing the available Ge−H bonds as chemical handles. The new hydride-terminated Ge(100) surface was prepared by utilizing an efficient preparation method involving soaking in an aqueous 10% HF solution. Lewis acid mediated hydrogermylation of alkynes and alkenes on the hydride-terminated Ge(100) surfaces results in alkenyl and alkyl surfaces, respectively, bound through Ge−C bonds. Thermal treatment of hydride-terminated Ge surface with neat alkenes and alkynes, or solutions in mesitylene, also results in similar organic monolayers. Finally, these two approaches were cont...

The effects of various organic monolayers on the surface of porous silicon on the electrochemiluminescence (ECL, also referred to as electroluminescence in the literature) characteristics were investigated. Surfaces were terminated with alkyne, alkene, and alkyl functionalities through cathodic electrografting (CEG), Lewis acid-mediated hydrosilylation (LA), and anodic electrografting (AEG), respectively. ECL was induced through the known formic acid/sodium formate electron injection system. Alkyl-terminated surfaces produced through AEG yielded the brightest emission of any of the functionalized surfaces although ECL emission was about half as intense as that from the underivatized Si−H-terminated surface. The lifetime, however, was extended by a factor of 2, and these surfaces demonstrate an unprecedented recharging phenomenon. When ECL ceases, a brief 10 s application of a cathodic bias restores most of the ECL emission intensity. This process can be cycled about 10 times, and results in a substantiall...

Lewis acid mediated hydrosilylation of alkynes and alkenes on non-oxidized hydride-terminated porous silicon derivatizes the surface with alkenyl and alkyl functionalities, respectively. A very broad range of chemical groups may be incorporated, allowing for tailoring of the interfacial characteristics of the material. The reaction is shown to protect and stabilize porous silicon surfaces from atmospheric or direct chemical attack without compromising its valuable material properties such as high porosity, surface area and visible room-temperature photoluminescence. The reaction is shown to act on alkenes and alkynes of all possible regiochemistries (terminal and internal alkynes; mono-, cis- and trans-, di-, tri-, and tetrasubstituted alkenes). FTIR as well as liquid- and solid-state NMR spectroscopies show anti-Markovnikov addition and cis stereochemistry in the case of hydrosilylated terminal alkynes. Material hydrosilylated with long-chain hydrophobic alkynes and alkenes shows a substantially slower surface oxidation and hydrolysis rate in air as monitored by long-term FTIR monitoring and chemography. BJH and BET measurements reveal that the surface area and average pore size of the material are reduced only slightly after hydrosilylation, indicating that the porous silicon skeleton remains intact. Elemental analysis and SIMS depth profiling show a consistent level of carbon incorporation throughout the porous silicon which demonstrates that the reaction occurs uniformly throughout the depth of the film. The effects of functionalization on photoluminescence were investigated and are shown to depend on the organic substituents.

Reactions that efficiently form Si–C bonds between silanes and unsaturated carbon–carbon bonds are widely known in molecular, solution phase chemistry. The possibility of covalent functionalization of porous silicon surfaces, which have similar chemical moieties to certain classes of molecular silanes, is intriguing. In this paper we describe approaches toward hydrosilylation of alkynes and alkenes and bis-silylation of alkynes utilizing known solution phase Lewis acid and late transition metal catalysts on silicon hydride terminated porous silicon surfaces. Both EtAlCl2 and Wilkinson's catalyst, RhCl(PPh3)3, effectively induce hydrosilylation of alkynes and alkenes. Bissilylation using palladium-based complexes, however, did not occur and thermally induced hydrosilylation took place in its stead. The Lewis acid mediated hydrosilylation is extremely efficient and yields highly stabilized surfaces. When Wilkinson's catalyst and palladium complexes are utilized, on the other hand, extensive oxidation upon exposure to air is observed.

Over the past decade, there has been increasing interest in functionalizing silicon surfaces, avoiding the ubiquitous oxide overlayer utilized in most integrated circuits based upon silicon. While silicon is clearly the backbone material of the microelectronics industry, an understanding of its surface chemistry still remains in preliminary stages. The native oxide overlayer on silicon chips has served admirably well for most microelectronic applications but as the features on integrated circuits become increasingly small, the ability to tailor the interfacial properties of the surface is extremely desirable. As the well known Moore’s law describes, the number of devices on an integrated circuit has been increasing exponentially since the early 1960’s, approximately doubling every year to 18 months. The smallest feature on a Pentium processor chip is now about 300 nm, and both industry and academia look to make even tinier surface features and devices as the state-of-the-art moves from ultra-to giga-scale integration, with over 10 to 100 million transistors per chip. Because the surface properties of these nanoscale devices will have crucial effects on their performance, new surface terminations and the chemical tools to access them are required. Integrated circuit technology on silicon wafers, developed primarily by the microelectronics industry, has benefited not only computer manufacturers and users, but a host of other industries and research areas. Silicon devices are now utilized for microelectromechanical systems (MEMS), microfluidics and micrototal analytical systems (μ-TAS), biosensors and other bioanalytical applications, micro-optics and micro-reactors, for example. Each of these applications requires different interfacial characteristics, and thus the need for very general chemical approaches is substantially broadened. In the case of silicon-based devices that will contact biological fluids or samples, a simple oxide overlayer is highly unstable at the usual pH’s encountered (> pH 7), corroding rapidly under ambient conditions. A method to stabilize the surface, keeping the underlying electronic properties intact and enabling the attachment of specific binding elements for recognition events, for instance, is necessary. In order to respond to these requirements, we and others are pursuing the development of the chemical tools for functionalization of silicon surfaces utilizing organometallic chemistry. Through production of an organic monolayer on the surface of bulk silicon bound through stable silicon-carbon bonds, as shown in figure 1, we can tap into the vast repertoire of chemical transformations available through organic chemistry, permitting precise modulation of surface properties. The anticipated result of this approach is a simple set of reactions to create any stabilized surface upon demand. Through further chemistry, these surfaces can be built upon, leading to increasingly sophisticated interfaces for a wide range of applications. There are, in fact, three technologically important variations of

Silicon chips form the backbone of modern computing and yet until recently, the surface chemistry of this technologically essential material has remained relatively unexplored. As the size of devices on silicon wafers shrink (towards gigascale integration), the surface characteristics play increasingly crucial roles in the proper functioning of the device since the ratio of surface atoms/bulk escalates. While surface oxide has served thus far as the main passivation route, there is strong interest in precisely tailoring the interface properties, not only for microelectronics, but other applications including sensors, MEMS and biologically active surfaces. As a result, organometallic and organic chemistry has become essential for the synthesis of functional, modifiable monolayers, bound to non-oxidized silicon surfaces through silicon–carbon bonds. The latest approaches towards preparation of monolayers through Si–C bonds on both flat and photoluminescent porous silicon are described. Wet chemical techniques, accessible to most organometallic/organic chemists are highlighted, but recent developments using UHV conditions also receive attention.

By illumination with white light porous silicon surfaces can be functionalized with alkynes and alkenes (see scheme). The hydrosilylation reactions are very simple to perform and lead to stable, patterned surfaces. This methodology opens new opportunities in the technological applications of porous silicon in both integrated circuits and sensors.

Lewis acid mediated hydrosilylation on porous silicon surfaces permits facile incorporation of a wide variety of functionalities through stable silicon–carbon bonds. The surfaces demonstrate high chemical stability with respect to hydrofluoric acid and aqueous base. The effects of the covalently bound surface groups on photoluminescence have been investigated and it was noted that alkyl and alkenyl termination induced only small decreases in photoluminescence efficiency. Aromatic substituents conjugated through a vinyl group, however, bring about almost complete quenching of the observed photoluminescence, regardless of substitution with either electron withdrawing (chloride) or donating (methyl) functionalities. The photoluminescence fatigue of dodecyl terminated surfaces in air for 12–16 h periods has been monitored and compared to unfunctionalized porous silicon. In air, the photoluminescence of dodecyl terminated surfaces degrades faster than the unfunctionalized porous silicon but under inert atmosphere (nitrogen), the rate of photoluminescence fatigue is slow in both cases and approximately equivalent.

Recent reports have shown that cyclic peptides composed of an even number of alternating d- and l-amino acids can adopt flat, disklike conformations and stack through backbone−backbone hydrogen-bonding to form extended nanotubular structures. The present work details a general strategy for limiting this self-assembly process through backbone alkylation, giving rise to cylindrical β-sheet peptide dimers. Scope and limitations of dimerization are examined through NMR, FT-IR, mass spectral, and X-ray crystallographic studies of 20 cyclic peptides varying in ring size, location and identity of backbone alkyl substituents, and amino acid composition. The cyclic peptides are shown to self-assemble both in solution and in the solid state through the expected antiparallel β-sheet hydrogen-bonding network. While solution dimerization by cyclic octapeptides appears general, peptides with alternative smaller or larger ring sizes fail to self-associate. Formation of cylindrical β-sheet ensembles is found to tolerate ...

Zinc phosphide (Zn3P2) is a promising earth-abundant material for thin film photovoltaic applications, due to strong optical absorption and near ideal band gap. In this work, crystalline zinc phosphide nanoparticles are synthesized using dimethylzinc and tri-n-octylphosphine as precursors. Transmission electron microscopy and X-ray diffraction data show that these nanoparticles have an average diameter of ∼8 nm and adopt the crystalline structure of tetragonal α-Zn3P2. The optical band gap is found to increase by 0.5 eV relative to bulk Zn 3P2, while there is an asymmetric shift in the conduction and valence band levels. Utilizing layer-by-layer deposition of Zn 3P2 nanoparticle films, heterojunction devices consisting of ITO/ZnO/Zn3P2/MoO3/Ag are fabricated and tested for photovoltaic performance. The devices are found to exhibit excellent rectification behavior (rectification ratio of 600) and strong photosensitivity (on/off ratio of ∼10²). X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy analyses reveal the presence of a thin 1.5 nm phosphorus shell passivating the surface of the Zn3P 2 nanoparticles. This shell is believed to form during the nanoparticle synthesis.

Block copolymer (BCP) self-assembly is an effective and versatile approach for the production of complex nanopatterned interfaces. Monolayers of BCP films can be harnessed to produce a variety of different patterns, including lines, with specific spacings and order. In this work, bilayers of cylinder-forming polystyrene-block-polydimethylsiloxane block copolymer (PS-b-PDMS) were transformed into arrays of silica lines with half the pitch normally attained for conventional monolayers, with the PDMS acting as the source for the SiO x. The primary hurdle was ensuring the bilayer silica lines were distinctly separate; to attain the control necessary to prevent overlap, a number of variables related to the materials and self-assembly process were investigated in detail. Developing a detailed understanding of BCP film swelling during solvent annealing, blending of the PS-b-PDMS with PS homopolymer, utilization of a surface brush layer, and adjustment of the plasma exposure conditions, distinct and separate silica lines were prepared. On the microscale, the sample coverage of PS-b-PDMS bilayers was investigated and maximized to attain >95% bilayers under defined conditions. The bilayer BCP structures were also amenable to graphoepitaxy, and thus, dense and highly ordered arrays of silica line patterns with tightly controlled width and pitch were fabricated and distributed uniformly across a Si surface. © 2013 American Chemical Society.

High conductivity poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) was spray cast to form highly flexible transparent electrodes for forward- and inverted-mode organic solar cells (OSCs). A multiple solvent ink containing ethylene glycol was developed, and a post-deposition annealing step contributed to a high conductivity of 1070±50 S cm-¹. Sheet resistance and transmission at a wavelength of 550 nm were controlled within 24-259 Ω □-¹ and 71-95%, respectively, which are amongst the best-reported combined characteristics. Forward-mode OSCs with spray coated PEDOT:PSS anodes yielded a power conversion efficiency of 3.2%. Mechanical bending and stretching tests demonstrated that the flexibility of these PEDOT:PSS layers were far superior to that of ITO: elastic moduli were reduced by more than an order of magnitude, and the resistance increased far more slowly under both uniaxial stretching and bending to progressively smaller radii of curvature. With these experiments, the minimum radii of curvature and maximum uniaxial strains at which acceptable performance is maintained were investigated. Collectively, our results illustrate a promising future for the scalable printing of low-cost PEDOT:PSS-based flexible transparent electrodes. © 2012 Crown All rights reserved.

Asymmetric hydrogenation of the imines ArC(Me)NCH2Ph (Ar = C6H5 (2), 4-MeOC6H4 (3)) with Rh[(−)-bdpp](NBD)ClO4 (1) as the catalyst precursor in the presence of reverse AOT micelles results in enhan...

Iron oxide-doped photonic crystals are a simple means to wrap fluid droplets and control their movement. But they are also clever because they can be 'bar-coded' and have in-built sensing capabilities, which makes them exceptional candidates for microfluidic devices.