silicon and octadecyltrichlorosilane

The growth of semiconductor crystals and thin films plays an essential role in industry and academic research. Considering the environmental damage caused by energy consumption during their fabrication, a simpler and cheaper method is desired. In fact, preparing semiconductor materials at lower temperatures using solution chemistry has potential in this research field. We found that solution chemistry, the physical and chemical properties of the substrate surface, and the phase diagram of the multicomponent compound semiconductor have a decisive influence on the crystal structure of the material. In this study, we used self-assembled monolayers (SAMs) to modify the silicon/glass substrate surface and effectively control the density of the functional groups and surface energy of the substrates. We first employed various solutions to grow octadecyltrichlorosilane (OTS), 3-mercaptopropyl-trimethoxysilane (MPS), and mixed OTS-MPS SAMs. The surface energy can be adjusted between 24.9 and 50.8 erg/cm(2). Using metal sulfide precursors in appropriate concentrations, AgIn5S8 crystals can be grown on the modified substrates without any post-thermal treatment. We can easily adjust the nucleation in order to vary the density of AgIn5S8 crystals. Our current process can achieve AgIn5S8 crystals of a maximum of 1 μm in diameter and a minimum crystal density of approximately 0.038/μm(2). One proof-of-concept experiment demonstrated that the material prepared from this low temperature process showed positive photocatalytic activity. This method for growing crystals can be applied to the green fabrication of optoelectronic materials.

Topics: Glass; Indium; Microscopy, Electron, Scanning; Organosilicon Compounds; Particle Size; Photoelectron Spectroscopy; Semiconductors; Silanes; Silicon; Silver; Sulfur; Surface Properties; Temperature

Surface energies are commonly used to determine the adhesion forces between materials. However, the component of surface energy derived from long-range forces, such as van der Waals forces, depends on the material's structure below the outermost atomic layers. Previous theoretical results and indirect experimental evidence suggest that the van der Waals energies of subsurface layers will influence interfacial adhesion forces. We discovered that nanometre-scale differences in the oxide layer thickness of silicon wafers result in significant macroscale differences in the adhesion of isolated gecko setal arrays. Si/SiO(2) bilayer materials exhibited stronger adhesion when the SiO(2) layer is thin (approx. 2 nm). To further explore how layered materials influence adhesion, we functionalized similar substrates with an octadecyltrichlorosilane monolayer and again identified a significant influence of the SiO(2) layer thickness on adhesion. Our theoretical calculations describe how variation in the SiO(2) layer thickness produces differences in the van der Waals interaction potential, and these differences are reflected in the adhesion mechanics. Setal arrays used as tribological probes provide the first empirical evidence that the 'subsurface energy' of inhomogeneous materials influences the macroscopic surface forces.

Topics: Models, Chemical; Nanostructures; Silanes; Silicon; Silicon Dioxide

A new strategy to improve silicon-based endodontic treatment tightness by dentine hydrophobization is presented in this work: root dentine was silanized to obtain a hydrophobic dentine-sealer interface that limits fluid penetration. This strategy was based on the grafting of aliphatic carbon chains on the dentine through a silanization with the silane end groups [octadecyltrichlorosilane (OTS) and octadecyltriethoxysilane]. Dentine surface was previously pretreated, applying ethylenediaminetetraacetic acid and sodium hypochlorite, to expose hydroxyl groups of collagen for the silane grafting. Collagen fibers exposure after pretreatment was visible with scanning electron microscopy, and Fourier transform infrared (FTIR) spectroscopy showed their correct exposition for the silanization (amide I and II, with 1630, 1580, and 1538 cm⁻¹ peaks corresponding to the vibration of C=O and C--N bonds). The grafting of aliphatic carbon chains was confirmed by FTIR (peaks at 2952 and 2923 cm⁻¹ corresponding to the stretching of C--H bonds) and by the increasing of the water contact angle. The most efficient hydrophobization was obtained with OTS in ethyl acetate, with a water contact angle turning from 51° to 109°. Gas and liquid permeability tests showed an increased seal tightness after silanization: the mean gas and water flows dropped from 2.02 × 10⁻⁸ to 1.62 × 10⁻⁸ mol s⁻¹ and from 10.8 × 10⁻³ to 5.4 × 10⁻³ µL min⁻¹, respectively. These results show clear evidences to turn hydrophilic dentine surface into a hydrophobic surface that may improve endodontic sealing.

Topics: Dental Materials; Dentin; Humans; Hydrophobic and Hydrophilic Interactions; Materials Testing; Microscopy, Electron, Scanning; Root Canal Filling Materials; Root Canal Therapy; Silanes; Silicon; Spectroscopy, Fourier Transform Infrared

In this article, we present the transport and magnetotransport of high-quality graphene transistors on conventional SiO(2)/Si substrates by modification with organic molecule octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs). Graphene devices on OTS SAM-functionalized substrates with high carrier mobility, low intrinsic doping, suppressed carrier scattering, and reduced thermal activation of resistivity at room temperature were observed. Most interestingly, the remarkable magnetotransport of graphene devices with pronounced quantum Hall effect, strong Shubnikov-de Haas oscillations, a nonzero Berry's phase, and a short carrier scattering time also confirms the high quality of graphene on this ultrasmooth organic SAM-modified platform. The high-performance graphene transistors on the solution-processable OTS SAM-functionalized SiO(2)/Si substrates are promising for the future development of large-area and low-cost fabrications of graphene-based nanoelectronics.

Topics: Graphite; Magnetics; Membranes, Artificial; Particle Size; Silanes; Silicon; Surface Properties; Titanium; Transistors, Electronic

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an emerging technique for the determination of the molecular weight of biomolecules and their non-covalent complexes without fragmentation. One problem with this technique is the use of excess amounts of matrices, which may produce intense fragment ions and/or clusters at low mass ranges between 1 and 800 Da. These fragments lead to interference, especially concerning the signals of small target molecules. Here, a simple, reusable, and quite inexpensive approach was demonstrated to improve the effectiveness of laser desorption/ionization mass spectrometry (LDI-MS) analysis, especially for small molecules, without using matrix molecules. In this study, substrates with controllable morphologies and thicknesses were developed based on the self-assembly of silane molecules on silicon surfaces using N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) and octadecyltrichlorosilane (OTS) molecules. Prepared substrates with nano-overlayers were successfully used in the analysis of different types of small target molecules, namely acrivastine, L-histidine, L-valine, L-phenylalanine, L-arginine, L-methionine and angiotensin I. Our substrates exhibited clear peaks almost without fragmentation for all target molecules, suggesting that these surfaces provide a number of important advantages for LDI-MS analysis, such as ease of preparation, costs, reusability, robustness, easy handling and preventing fragmentation.

Topics: Angiotensin I; Arginine; Histidine; Methionine; Nanostructures; Organosilicon Compounds; Phenylalanine; Polyamines; Silanes; Silicon; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Valine

Materials with chemical micropatterned surface have broad applications in many fields. In this article, we report a simple one-step UV lithography method to activate inert hydrocarbon monolayers for spontaneous formation of water and covalently immobilized protein micropatterns on the surface. Two types of hydrocarbon monolayers including octadecyltrichlorosilane (OTS) on silicon oxide and 1-hexadecene on hydrogen-terminated silicon were studied. It was found that after UV modifications, water can form micropatterns spontaneously on both surfaces. Furthermore, when protein solutions were used, covalently immobilized protein micropatterns can be formed. Our XPS results and controlled reducing experiments showed that UV exposure transformed inert monolayers into active surfaces with aldehyde groups, which are responsible for the covalent immobilization of proteins. The method reported herein can be applied under ambient conditions without having a high vacuum system. It can also be extended to pattern other biomolecules bearing amine groups.

Topics: Animals; Humans; Hydrocarbons; Immobilized Proteins; Oxides; Silanes; Silicon; Silicon Compounds; Ultraviolet Rays

Self-assembled monolayer films of octadecyltrichlorosilane were prepared on silicon substrates using hexadecane, toluene, chloroform, and dichloromethane to determine the effects of solvent on molecular packing and tribological properties. Topographical atomic force microscopy images were used to evaluate the film quality and determine surface roughness, and tribological measurements, including friction, adhesion, and elasticity, provided additional information on the local nanoscale packing of the films. Our results showed that solvent viscosity and polarity affected the tribological properties of the films, with films prepared using hexadecane exhibiting superior properties. Langmuir-Blodgett experiments indicated that intermolecular interactions were stronger between octadecyltrichlorosilane and hexadecane molecules than for any other solvent in this study. These results demonstrate that solvent properties are an important consideration in monolayer film preparation and optimization for friction controlled surfaces.

Topics: Microscopy, Atomic Force; Silanes; Silicon; Solvents; Spectroscopy, Fourier Transform Infrared

We conducted time-dependent, in situ x-ray reflectivity measurements on the formation of substrate-supported lipid monolayers and bilayers at solid-liquid interfaces, buried under an aqueous buffer with various concentrations (5, 10, 20, 40, and 50 microg/ml ) of lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The DOPC bilayer is formed on the hydrophilic surface of a bare Si substrate, while the DOPC monolayer is formed on a hydrophobic octadecylthricholorsilane (OTS) monolayer-coated Si substrate. The evolution of the reflectivity curves from the lipid bilayers is well described by lateral growth of bilayer islands, consistent with the rupture and fusion model for the adsorption of lipid vesicles to solid-liquid interfaces. By contrast, the formation of the lipid monolayer on OTS-coated Si occurs through a relatively fast coverage of the entire interfacial area, followed by an increase in the monolayer thickness. For both monolayers and bilayers, the rate of lipid layer growth increases with increasing lipid concentration in the buffer solution.

Topics: Adsorption; Biophysics; Dose-Response Relationship, Drug; Electrons; Lipid Bilayers; Lipids; Membrane Lipids; Molecular Conformation; Phosphatidylcholines; Phospholipids; Silanes; Silicon; Surface Properties; Time Factors; X-Rays

Even though the inkjet technology has been recognized as one of the most promising technologies for electronic and bio industries, the full understanding of the dynamics of an inkjet droplet at its operating conditions is still lacking. In this study, the normal impact of water droplets on solid substrates was investigated experimentally. The size of water droplets studied here was 46 microm and was much smaller than the most of the previous studies on drop impact. The Weber number (We) and Reynolds number (Re) were 0.05-2 and 10-100, respectively, and the Ohnesorge number was fixed at 0.017. The wettability of the solid substrate was varied by adsorbing a self-assembled monolayer of octadecyltrichlorosilane followed by the exposure to UV-ozone plasma. The impact scenarios for low We impacts were found to be qualitatively different from the high to moderate We impacts. Neither the development of a thin film and lamella under the traveling sphere nor the entrapment of small bubbles was observed. The dynamics of droplet impact at the conditions studied here is found to proceed under the combined influences of inertia, surface tension, and viscosity without being dominated by one specific mechanism. The maximum spreading factor (beta), the ratio of the diameter of the wetted surface and the drop diameter before impact, was correlated well with the relationship ln beta=0.090 ln We/(fs-cos theta)+0.151 for three decades of We/(fs-cos theta), where theta is the equilibrium contact angle, and fs is the ratio between the surface areas contacting the air and the solid substrate. The result implies that the final shape of the droplet is determined by the surface phenomenon rather than fluid mechanical effects.

Topics: Adsorption; Membranes, Artificial; Silanes; Silicon; Silicon Dioxide; Surface Properties; Water; Wettability

Heparin was covalently immobilized onto a silicon surface by two different methods, carbodiimide-based immobilization and photo-immobilization. In the former method, a (3-aminopropyl) trimethoxysilane (APTMS) self-assembled monolayer (SAM) or multilayer was first coated onto the silicon surface as the bridging layer, and heparin was then attached to the surface in the presence of water-soluble carbodiimide. In the latter method, an octadecyltrichlorosilane (OTS) SAM was coated on the silicon surface as the bridging layer, and heparin was modified by attaching photosensitive aryl azide groups. Upon UV illumination, the modified heparin was then covalently immobilized onto the surface. The hydrophilicity of the silicon surface changed after each coating step, and heparin aggregates on APTMS SAM and OTS SAM were observed by atomic force microscopy (AFM). In vitro haemocompatibility assays demonstrated that the deposition of APTMS SAM, APTMS multilayer and OTS SAM enhanced the silicon's haemocompatibility, which was further enhanced by the heparin immobilization. There is no evident distinction regarding the haemocompatibility between the heparin-immobilized surfaces by both methods. However, heparin on silicon with APTMS SAM and multilayer as the bridging layers is very unstable when tested in vitro with a saline solution at 37 degrees C, due to the instability of APTMS SAM and multilayer on silicon. Meanwhile, photo-immobilized heparin on silicon with OTS SAM as the bridging layer showed superb stability.

Topics: Animals; Anticoagulants; Biocompatible Materials; Calcium; Carbodiimides; Carbohydrate Sequence; Hemoglobins; Heparin; Indicators and Reagents; Materials Testing; Microscopy, Atomic Force; Molecular Sequence Data; Photochemistry; Propylamines; Rats; Silanes; Silicon; Surface Properties; Ultraviolet Rays

Surface-templated nanostructures on the highly oriented pyrolytic graphite (HOPG) basal plane were created by controlled Cs+- or Ga+)ion bombardment, followed by subsequent oxidation at high temperature, forming molecule corrals. The corrals were then used for template growth of SiOx/Si nanostructures. We demonstrate here that, for SiOx/Si nanostructures formed in controlled molecule corrals, the amount of silicon deposited on the surface is directly correlated with the corral density, making it possible to generate patterned SiOx/Si nanostructures on HOPG. Since the size, depth, position, and surface density of the nanostructures can be controlled on the HOPG, it is possible to produce surfaces with patterned or gradient functionalities for applications in fields such as biosensors, microelectronics, and biomaterials (e.g., neuron pathfinding). If desired, the SiOx structures can be reduced in size by etching in dilute HF, and further oxidation of the nanostructures is slow enough to provide plenty of time to functionalize them using ambient and solution reactions and to perform surface analysis. Organosilane monolayers on surface-templated SiOx/Si nanostructures were examined by X-ray photoelectron spectroscopy, time-of-flight secondary ion mas spectrometry, and atomic force microscopy. Silanes with long alkyl chains such as n-octadecyltrichlorosilane (C18) were found to both react on SiOx/Si nanostructures and to condense on the HOPG basal plane. Shorter-chain silanes, such as 11-bromoundicyltrimethoxysilane (C11) and 3-mercaptopropyltrimethoxysilane (C3) were found to react preferentially with SiOx/Si nanostructures, not HOPG. The SiOx/Si nanostructures were also found to be stable toward multiple chemical reactions. Selective modification of SiOx/Si nanostructures on the HOPG basal plane is thus achievable.

Topics: Cesium; Gallium; Graphite; Molecular Structure; Nanostructures; Oxidation-Reduction; Oxides; Particle Size; Silanes; Silicon; Silicon Compounds; Surface Properties; Temperature

Topics: Electrochemistry; Electrodes; Iron; Magnetics; Metal Nanoparticles; Microscopy, Atomic Force; Nanoparticles; Nanotechnology; Oxygen; Platinum; Silanes; Silicon; Surface Properties

This paper presents a new method for the patterning of self-assembled monolayers (SAMs) using UV light. Azidoformate-terminated SAMs starting from 18-acetoxy-octadecyltrichlorosilane SAMs on silicon, prepared for the first time, are electrophilic and photosensitive, and can be patterned by UV irradiation through a mask. The resulting structured surfaces are still electrophilic and can be reacted with nucleophilic functions, for example, primary amines.

Topics: Azides; Formates; Membranes, Artificial; Particle Size; Photochemistry; Silanes; Silicon; Surface Properties; Ultraviolet Rays

Low-pressure low-frequency NH3 plasmas have been used for the surface modification of bulk polyethylene films and of octadecyltrichlorosilane (OTS) self-assembled monolayers deposited on oxidized silicon wafers. The incorporation of nitrogen-containing groups by the plasma treatment has been followed by contact angle measurements and by X-ray photoelectron spectroscopy. The surface degradation of the OTS monolayers due to plasma etching has been measured separately by optical ellipsometry with subnanometric accuracy. Our data show clear evidence for the existence of an optimum treatment time, yielding a high density of NH2 functional groups without significant variation of the structural features of the organic material. Self-assembled monolayers appear as excellent model systems to characterize the effects of plasma discharges on polyolefins. In particular, they allow testing the influence of molecular orientation, packing density, and crystallinity on the final results.

Topics: Ammonia; Membranes, Artificial; Polyethylene; Sensitivity and Specificity; Silanes; Silicon; Spectrometry, X-Ray Emission; Surface Plasmon Resonance; Surface Properties; Time Factors; Wettability

The growth kinetics and morphologies of self-assembled monolayers deposited by contact printing 7-octenyltrichlorosilane (OCT) and octadecyltrichlorosilane (OTS) on Si(100) were studied by ellipsometry and atomic force microscopy. We found that, for both OCT and OTS, full monolayers could be obtained at room temperature after printing times of 120-180 s; the printing-based monolayer assembly processes follow apparent Langmuir adsorption kinetics, with the measured film growth rates increasing both with the ambient humidity and with concentration of the ink used to load the stamp. At a dew point of 10 degrees C and an ink concentration (in toluene) of 50 mM, the observed film growth rate constant is 0.05 s(-)(1). When the printing was carried out at a lower ambient humidity (dew points of 1-3 degrees C), the measured rates of assembly were approximately a factor of 2 slower. Increasing the deposition temperature from 25 to 45 degrees C under these conditions increased the film growth rate only slightly. The morphology of the films depends on the identity of the ink. Uniform, high-coverage films could be obtained readily from the eight-carbon chain length adsorbate OCT, provided that the stamp was not overloaded with the ink; for high concentrations outside of the optimal range, the surface presented significant numbers of adsorbed particles ascribed, in part, to siloxane polymers formed by hydrolysis of the ink on the stamp before printing. In marked contrast, for the 18-carbon adsorbate OTS, the printed films always consisted of a mixture of a uniform monolayer plus adsorbed polysiloxane particles. The different film morphologies seen for OCT and OTS are proposed to result from the different transfer efficiencies of the organotrichlorosilane relative to polysiloxane hydrolysis products formed during the printing process. These transfer efficiencies exhibit sensitivities related to the permeation of the poly(dimethylsiloxane) (PDMS) stamp by the silane reagents. Short-chain inks such as OCT evidently permeate the PDMS stamp more deeply than longer-chain inks such as OTS. This difference, and the different diffusion rates of ink vs oligomeric silane hydrolysis products, determines the film morphology obtained by contact printing. The mass transfer dynamics of the process thus yield surface layers derived from varying quantities of siloxane oligomers, which subsequently transfer to the substrate along with unhydrolyzed silane adsorbate during the printing st

Topics: Adsorption; Dimethylpolysiloxanes; Hydrolysis; Kinetics; Membranes, Artificial; Microscopy, Atomic Force; Particle Size; Sensitivity and Specificity; Silanes; Silicon; Silicones; Surface Properties; Time Factors

Specular neutron reflection has been used to determine the structure and composition of bovine beta-casein adsorbed on a solid surface from an aqueous phosphate-buffered solution at pH 7. The protein was adsorbed on a hydrophobic monolayer self-assembled from deuterated octadecyltrichlorosilane solution on a silicon (111) surface. A two-layer structure formed consisting of one dense layer of thickness 23 +/- 1 angstroms and a surface coverage of 1.9 milligrams per square meter adjacent to the surface and an external layer protruding into the solution of thickness 35 +/- 1 angstroms and 12 percent protein volume fraction. The structure of the (beta-casein) layer is explained in terms of the charge distribution in the protein.

Topics: Adsorption; Animals; Caseins; Cattle; Deuterium; Hydrogen-Ion Concentration; Mathematics; Neutrons; Scattering, Radiation; Silanes; Silicon

We have recently developed x-ray diffraction methods to derive the profile structure of ultrathin lipid multilayer films having one to five bilayers (e.g., Skita, V., W. Richardson, M. Filipkowski, A.F. Garito, and J.K. Blasie. 1987. J. Physique. 47:1849-1855). Furthermore, we have employed these techniques to determine the location of a monolayer of cytochrome c bound to the carboxyl group surface of various ultrathin lipid multilayer substrates via nonresonance x-ray diffraction (Pachence, J.M., and J.K. Blasie. 1987. Biophys. J. 52:735-747). Here an intense tunable source of x-rays (beam line X9-A at the National Synchrotron Light Source at the Brookhaven National Laboratory) was utilized to measure the resonance x-ray diffraction effect from the heme-Fe atoms within the cytochrome c molecular monolayer located on the carboxyl surface of a five monolayer arachidic acid film. Lamellar x-ray diffraction was recorded for energies above, below, and at the Fe K-absorption edge (E = 7,112 eV). An analysis of the resonance x-ray diffraction effect is presented, whereby the location of the heme-Fe atoms within the electron density profile of the cytochrome c/arachidic acid ultrathin multilayer film is indicated to +/- 3 A accuracy.

Topics: Cytochrome c Group; Eicosanoic Acids; Heme; Iron; Lipid Bilayers; Molecular Conformation; Protein Binding; Protein Conformation; Silanes; Silicon; X-Ray Diffraction