On Octadecyltrichlorosilane Research Articles

Tip-Enhanced Raman Spectroscopy of Combed Double-Stranded DNA Bundles

Double-stranded (ds) DNA of a λ-phage virus are combed on octadecyltrichlorosilane (OTS)-modified borosilicate glass substrates and investigated by means of tip-enhanced Raman spectroscopy (TERS) u...

Sulphur bridged [22]annulene[2.1.2.1] based organic field-effect transistors: interplay of the steric bulk and charge transport

New, neutral, slightly puckered aromatic meso-substituted tetrathia[22]porphyrin(2.1.2.1) macrocyclic architectures display efficacious p-type semiconductor behaviour with improved on/off ratios.

Site-selective Deposition of Graphene Oxide Layer on Patterned Self-assembled Monolayer

Abstract Patterned graphene oxide (GO) layer is prepared by site-selective deposition of GO on patterned self-assembled monolayer (SAM). Deep ultraviolet (DUV) exposure on octadecyltrichlorosilane (OTS) SAM through photomask produces hydrophobic/hydrophilic pattern, and the hydrophilic region is reacted with aminopropyltriethoxysilane (APTES), which is preferentially wetted with GO through ionic interaction between carboxylic acid groups of GO and amino groups of APTES SAM. As-prepared GO pattern can be further transformed to chemically reduced graphene oxide (RGO) pattern after chemical reduction with hydrazine. Both Raman and electrical conductivity measurements confirm the successive preparation of RGO pattern.

Neutral tetrathia[22]annulene[2.1.2.1] based field-effect transistors: improved on/off ratio defies ring puckering

New, neutral, slightly puckered aromatic meso-substituted tetrathia[22]annulene[2.1.2.1] macrocyclic architectures display p-type semiconductor behaviour and constitute molecular field-effect transistors with high on/off ratios (8.67 × 10(6)) and high mobility (0.23 cm(2) V(-1) s(-1)) in thin films deposited on octadecyltrichlorosilane (OTS) modified SiO(2).

Enhancement of water transport through the liquid–vapor interface by surfactants

Interactions between surfactants and water were monitored from the perspective of liquid–vapor interfaces. The surfactants studied were chosen to be the paradigms of the three major types of amphiphilic molecules: the anionic surfactant (e.g. sodium dodecyl sulfate), the cationic surfactant (e.g. dodecyltrimethylammonium chloride), and the nonionic surfactant (e.g., n-dodecyl-β-D-maltoside). Droplets were deposited on octadecyltrichlorosilane (OTS) covered silicon surfaces and their contact angle and contact base diameter were observed as a function of time to obtain information on the drying dynamics. Using a new method to evaluate the solubility parameters of liquids via evaporating sessile droplets, information on the assembling of surfactants as well as their interfacial behavior at the water–vapor interface is extracted. It is concluded that surfactants accelerate drying in pre-micellar solutions. Formation of micelles retards this acceleration. Surfactants, depending on the type and concentration, interfere with the intermolecular force among liquid, with the most significant influence observed around the critical micelle concentration. Monomers with hydrogen bond-forming head groups and longer tails influence the liquid more than the other types of surfactants. Small electrolyte molecules affect the drying dynamics of ionic surfactant solutions more than nonionic surfactant solutions.

Measurement of dwell times of spin polarized rubidium atoms on octadecyltrichlorosilane- and paraffin-coated surfaces

We report the measurement of dwell times of spin polarized Rb atoms on octadecyltrichlorosilane (OTS)- and paraffin-coated surfaces. We find that at a cell temperature of 72 °C the dwell times for OTS- and paraffin-coated surfaces are 0.9±0.1 μs and 1.8±0.2 μs, respectively. Since the relaxation probability on paraffin is almost one order of magnitude smaller than that on OTS, the longer dwell time for paraffin indicates that the average strength of the interactions experienced by Rb atoms while they are inside paraffin is much weaker than while they are inside OTS.

Constructive Nanolithography by Chemically Modified Tips: Nanoelectrochemical Patterning on SAMs/Au

Nanoelectrochemical patterning of 1-hexadecanethiol (HDT) monolayer on Au(111) was realized by thiol-modified conductive atomic force microscopy (AFM) tips in a fashion of mild oxidation of top methyl groups of the monolayers. Pt-coated tips modified by a hydrophobic and appropriate thick monolayer of thiol (e.g., HDT) can significantly increase the bias threshold and extend the bias range suitable for the constructive nanolithography (CNL) in comparison with those tips unmodified or modified by hydrophilic monolayers. Furthermore, the switchover from the CNL to the deep oxidation can be governed by the reductive desorption of thiol monolayers from the tip surface when appropriate thiol-modified tips are used. A hydrophobic HDT/tip can exhibit a CNL bias range with an extent of 5.3 V, much wider than the reported extents of the CNL bias ranges on octadecyl trichlorosilane (OTS)/silicon surfaces by unmodified tips. The resulting CNL patterns were shown to have potential as multifunctional templates by guiding the self-assembly of OTS and the site-defined immobilization of aminopropyltriethoxysilane-modified alpha-Fe2O3 nanoparticles.

Novel Semiconductors Based on Functionalized Benzo[d,d′]thieno[3,2-b;4,5-b′]dithiophenes and the Effects of Thin Film Growth Conditions on Organic Field Effect Transistor Performance

A series of benzo[d,d]thieno[3,2-b;4,5-b]dithiophene (BTDT) derivatives, end-functionalized with phenyl (P) and benzothiophenyl (BT), were synthesized and characterized. A facile, one-pot synthesis of BTDT was developed which enables the efficient realization of a new BTDT-based semiconductor series for organic thin-film transistors (OTFTs). The crystal structure of P-BTDT was determined via single-crystal X-ray diffraction. Various combinations of dielectric surface treatment methods, substrate temperature, and deposition flux rate sequences have significant effects on device performance. Films deposited on octadecyltrichlorosilane (OTS)-treated SiO2 substrates under properly adjusted substrate temperature and deposition flux rate achieve an efficaceous compromise between high film crystallinity and good film grain interconnectivity, resulting in good OTFT performance, with mobility greater than 0.70 cm2 V−1 s−1 and Ion/Ioff greater than 108.

Area-Selective Atomic Layer Deposition of Lead Sulfide: Nanoscale Patterning and DFT Simulations

Area-selective atomic layer deposition (ALD) of lead sulfide (PbS) was achieved on octadecyltrichlorosilane (ODTS)-patterned silicon substrates. We investigated the capability of ODTS self-assembled monolayers (SAMs) to deactivate the ALD PbS surface reactions as a function of dipping time in ODTS solution. The reaction mechanism was investigated using density functional theory (DFT), which showed that the initial ALD half-reaction is energetically unfavorable on a methyl-terminated SAM surface. Conventional photolithography was used to create oxide patterns on which ODTS SAMs were selectively grown. Consequently, PbS thin films were grown selectively only where ODTS was not present, whereas deposition was blocked in regions where ODTS was grown. The resulting fabricated patterns were characterized by scanning electron microscopy and Auger electron spectroscopy, which demonstrated that ALD PbS was well confined to defined patterns with high selectivity by ODTS SAMs. In addition, AFM lithography was employed to create nanoscale PbS patterns. Our results show that this method can be applied to various device-fabrication processes, presenting new opportunities for various nanofabrication schemes and manifesting the benefits of self-assembly.

Titanyl Phthalocyanine (TiOPc) Organic Thin Film Transistors With Highly π-π Interaction

AbstractThe objective of this research is to obtain uniform vacuum-deposition triclinic phase II crystal of titanyl phthalocyanine (α-TiOPc) films from various TiOPc crystal forms. The crystal structure and morphology of vacuum-deposited TiOPc films can be manipulated by deposition rate and substrate temperature. Crystal structure was determined by X-ray diffraction (XRD). Thin film morphology was analyzed by scanning electron microscope (SEM). Highly ordered α-TiOPc film with an edge-on molecular orientation was deposited on octadecyltrichlorosilane (OTS) treated Si/SiO2 surface. All TiOPc crystal forms, such as amorphous, α and γ phases, provided the triclinic phase II crystal of TiOPc. The full width at half maximum (FWHM) of the peak at 7.5 degree in XRD spectra was 0.23, 0.27 and 0.29 for γ, α and amorphous powder when substrate temperature maintained at 180°C, respectively. The FWHM of the 7.5 degree peak can be achieved 0.22 deposited from all crystal forms at elevated temperature higher than 220°C. The α-TiOPc deposition film exhibited an excellent p-type semiconducting behavior in air with dense packing structure due to the close π–π molecular packing. The devices, field-effect mobility range from 0.02 to 0.26 cm2/V s depending on various process parameters. The on/off current ratio (Ion/Ioff) is over 105. The TiOPc OTFTs will be applied as multi-parameter gas sensor in the near future.

Quinoid heteropentacenes as promising organic semiconductors for field-effect transistor applications

We report on a quinoid heteropentacene as p-type semiconductor in organic field-effect transistors. Both single crystal and thin-film transistors were fabricated with 7,14-diphenyl-chromeno[2,3-b]xanthene (DPCX). In this small molecule organic semiconductor the field-effect mobility is as high as 0.16 cm2/Vs in single-crystal devices and 0.01 cm2/Vs in thin-film devices. In addition, the devices show favorable properties such as near zero onset/threshold voltages and a small current hysteresis. X-ray diffraction experiments show the molecules to be arranged in slipped stacks and to have a flat backbone in the crystals. For thin films of DPCX the situation is complicated by the coexistence of a thin-film phase with the bulk phase. However, a comparison of DPCX thin films on octadecyltrichlorosilane (OTS)-treated and bare SiO2 gate dielectrics provides clear evidence that the OTS surface treatment leads to organic thin films with a better structural order. The low-cost synthesis and purification of DPCX along with the improved processability and the good electrical characteristics suggest that quinoid heteropentacenes are promising materials for organic field-effect transistors.

Optimizing molecular orientation for high performance organic thin film transistors based on titanyl phthalocyanine

In this paper, organic thin film transistors based on titanyl phthalocyanine were fabricated on octadecyltrichlorosilane (OTS) stripe modified Si/SiO2 substrates. The p-type transistor exhibited high performance with a hole mobility of ∼4.25 cm2V−1s−1 and an on/off ratio greater than 3.1 × 107 on 1 µm wide OTS stripe modified substrates. The charge transport anisotropy was observed in devices fabricated with channels parallel and perpendicular to the OTS stripes, indicating that the molecular orientation was optimized and arranged in a more ordered style. The high performance of the devices showed their potential for application in organic circuits.

Reversible electrowetting on silanized silicon nitride

Electrowetting is a phenomenon that has received increasing attention in recent years. It offers much promise for applications in lab-on-a-chip devices, liquid lenses, and optical displays. The contact angle can be controlled electrically facilitating the transport of liquid droplets by electrocapillary forces. This paper focuses on the requirements of the dielectric layers in electrowetting on dielectric; firstly, to provide the required dielectric qualities, that is, sufficient dielectric strength and high capacitance and, secondly, to satisfy the surface wetting characteristics, that is, sufficiently high hydrophobicity and low contact angle hysteresis. We present experimental work that, firstly, compares the dielectric characteristics of several insulating layers and secondly, proposes silanization as a way to form hydrophobic layers for electrowetting. The relation between electrowetting and dielectric breakdown was tested by means of measuring the contact angle of a water droplet placed between two electrodes on an insulated surface. The leakage current and resistance between these electrodes were measured as a function of applied voltage for the following dielectric coatings: silicon dioxide, silicon nitride and Parylene C. We compare the contact angle response of electrowetting on octadecyltrichlorosilane (OTS) monolayers and plasma-enhanced chemical vapour deposition Teflon-like fluoropolymer layers. The contact angle hysteresis of the OTS monolayers is clearly lower and this results in reversible electrowetting, that is, the hydrophobicity is sufficient to avoid contact line pinning and dewetting occurs on removal of an applied potential.

Spinodal Dewetting of Thin Films with Large Interfacial Slip: Implications from the Dispersion Relation

We compare the dispersion relations for spinodally dewetting thin liquid films for increasing magnitude of interfacial slip length in the lubrication limit. While the shape of the dispersion relation, in particular the position of the maximum, are equal for no-slip up to moderate-slip lengths, the position of the maximum shifts to much larger wavelengths for large slip lengths. Here, we discuss the implications of this fact for recently developed methods to assess the disjoining pressure in spinodally unstable thin films by measuring the shape of the roughness power spectrum. For polystyrene (PS) films on octadecyltrichlorosilane (OTS) covered Si wafers (with slip length b approximately 1 microm), we predict a 20% shift of the position of the maximum of the power spectrum which should be detectable in experiments.

Spatial control over atomic layer deposition using microcontact-printed resists

Area-selective thin film growth by atomic layer deposition (ALD) has been achieved on octadecyltrichlorosilane (ODTS) patterned substrates. Patterned hydrophobic self-assembled monolayers (SAMs) were first transferred to silicon and yttria-stabilized zirconia (YSZ) substrates by microcontact printing. Subsequently, films of either HfO 2 or Pt were grown selectively on the SAM-free regions of the surface, while ALD was blocked in regions where ODTS was present. The deposited pattern was readily observed through scanning electron microscopy and scanning Auger imaging, demonstrating that soft lithography is a simple and promising method to achieve area-selective ALD. The selectivity of the soft lithography-based method and the subsequent pattern resolution was compared for Pt versus HfO 2. It was found that using ODTS films, it is easier to achieve complete deactivation of Pt than HfO 2.

Dendritic Saccharide Surfactant Polymers as Antifouling Interface Materials to Reduce Platelet Adhesion

Here, we report on the synthesis of dendritic saccharide surfactant polymers as antifouling interface materials to reduce platelet adhesion. An acetal-protected poly(amidoamine) (PAMAM) dendron (5, G = 2) was first synthesized by using aminoacetaldehyde dimethyl acetal (1) as the starting material to provide a monovalent focal structure with dimethyl acetal-protected aldehyde functionality. Maltose dendron (M4, 6) was obtained by reacting the peripheral amine groups of acetal-dendron (5) with maltonolactone. The dendritic surfactant polymers (9) were then synthesized via a two-step method by sequential addition of maltose dendron and hexanal to react with the amine groups on the poly(vinylamine) (PVAm) backbone. Surface activity of the amphiphilic glycopolymers at the air/water interface was demonstrated by reduction in water surface tension. Adsorption of the amphiphilic glycopolymers at the solid/water interface was examined on octadecyltrichlorosilane (OTS)-coated coverslips by water contact angle measurements. A nanoscale understanding of surface-induced self-assembly of the dendritic surfactant polymer on highly oriented pyrolytic graphite (HOPG) was gained using AFM operated in fluid tapping mode. A lateral ordering of adsorbing surfactant polymer was visualized with a pattern in strands 60 degrees out of alignment. The static platelet adhesion tests show that the hexyl side chains can facilitate adsorption of the surfactant polymers onto hydrophobic substrates, while the maltose dendron side chains can provide a dense canopy of protective glycocalyx-like layer as an antifouling interface to reduce platelet adhesion.

Area Selective Atomic Layer Deposition by Soft Lithography

AbstractArea selective HfO2 thin film growth through atomic layer deposition (ALD) has been achieved on octadecyltrichlorosilane (ODTS) patterned Si substrates. Patterned hydrophobic self-assembled monolayers (SAMs) were first transferred to Si substrates by micro-contact printing. Using hafnium-tetrachloride or tetrakis(dimethylamido) hafnium(IV) and water as ALD precursors, amorphous HfO2 layers were then grown selectively on the SAM-free regions of the surface where native hydroxyl groups nucleate growth from the vapor phase. The HfO2 pattern was readily observed through scanning electron microscopy and scanning Auger imaging, demonstrating that soft lithography is a simple and promising method to achieve area selective ALD. To evaluate the selectivity, the resolution of the soft lithography based method was compared with that of area selective ALD of HfO2 by selective surface modification of patterned silicon oxide obtained using long-time SAM exposure. It was found that the selective surface modification showed much higher spatial resolution and selectivity, an observation consistent with previous studies indicating that highly ordered and densely packed ODTS films were important to achieve complete deactivation.

Synthesis and characterization of poly(vinyl amine)‐based amphiphilic comb‐like dextran glycopolymers by a two‐step method

AbstractPoly(vinyl amine) (PVAm)‐based amphiphilic glycopolymers were synthesized by a two‐step method, that is dextran molecules (Dex, Mw = 1500) were attached to the PVAm backbone by reacting amine groups with dextran lactone, and then, hexanoyl groups (Hex) were attached by reacting the PVAm free amine groups with N‐(hexanoyloxy)succinimide. By adjustment of the feed ratios of Dex/Hex, amphiphilic comb‐like glycopolymers with various hydrophilic and hydrophobic balances were prepared, and their structures were characterized by 1H NMR. Surface activity of the amphiphilic glycopolymers at the air/water interface was demonstrated by reduction in water surface tension. Adsorption of the amphiphilic glycopolymers at the solid/water interface was examined on octadecyltrichlorosilane (OTS)‐coated coverslips by water contact angle measurements. The results show that the amphiphilic glycopolymers need about 20 mol % of dextran attachment to make an effective hydrophilic coating. In comparison with the one‐step reaction by addition of dextran lactone and alkyl succinimide simultaneously, the two‐step approach can attach Dex on PVAm as high as possible in the first step, and offers quantitative advantages in controlling the ratio of hydrophilic and hydrophobic chains along the PVAm backbone, resulting in increased water solubility for the final amphiphilic glycopolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 192–199, 2006

Two-Dimensional Diffusion of Prodan on Self-Assembled Monolayers Studied by Fluorescence Recovery after Photobleaching

Fluorescence recovery after photobleaching (FRAP) is used to determine diffusion constants for the dye molecule 6-propionyl-2-dimethylaminonaphthalene (prodan) on silica and on a variety of organic monolayers grafted onto silica. Similar diffusion constants of ∼2 × 10-7 cm2/s are found for prodan on chlorotrimethylsilane (CTS) based self-assembled monolayers and on silanated poly(ethylene glycol) based monolayers. The similar diffusion constants are intriguing given the different surface free energies of these surfaces. No dye recovery is observed on octadecyltrichlorosilane (OTS) based monolayers or on clean silica surfaces. No significant change in the diffusion constant is observed with varying relative humidity on any of the surfaces. A mechanism for the diffusion of dye on these four surfaces is discussed. A simple surface energy argument may explain why diffusion is extremely limited on both very hydrophobic and very hydrophilic surfaces, but is allowed on surfaces with intermediate polarities. Additionally, we suggest, in the case of CTS vs OTS based monolayers, that the presence of disorder in the CTS based monolayer is important for rapid diffusion. Similar concepts are presented for the other systems examined.

A DFT Study of the Al2O3 Atomic Layer Deposition on SAMs: Effect of SAM Termination

The atomistic mechanism of the initial atomic layer deposition (ALD) reaction of trimethylaluminum [Al(CH3)3, TMA] on octadecyltrichlorosilane (OTS)-based self-assembled monolayers (SAMs) with different functional termination groups was investigated using density functional theory (DFT). The adsorption of TMA on −NH2-terminated OTS involves formation of a dative bond between the amine lone pair and the Al atom of TMA and is exothermic by 0.86 eV. Conversion of the dative bond to a covalent bond through a four-centered H transfer from the NH2 to the methyl group of TMA to form methane involves a barrier that is 1.22 eV above the adsorbed complex and is exothermic by 0.94 eV. Reaction between TMA and the −OH-terminated SAM results in an adsorption energy of 0.60 eV. Although the dative bond is weaker, the barrier to converting the dative bond to a covalent bond to form methane is only 0.65 eV relative to the complex structure and the overall reaction is exothermic by 1.44 eV. The reaction of TMA with the me...