Papers by Keyword: Self-Assembled Monolayer (SAM)

Abstract: A new technique, direct photodegradation of self-assembled monolayers (SAM), to obtain surface energy gradients on Si substrates was demonstrated. The gradient surface, with hydrophobic to hydrophilic gradients, was prepared by two steps: Firstly, a homogeneous fluoroalkylsilane SAM film was deposited by a chemical vapor deposition on a Si substrate. Secondly, a controlled photodegradation technique was directly applied to the homogeneous FAS-SAM surface. The surface energy gradient was then obtained due to the different intensity of photoirradiation in the different positions along the photodegraded path on the SAM surfaces. The resulting surface displayed a gradient of wettability (with the contact angle of water changing from 55° to 18°) over a distance of 4.2 mm. The water droplet was driven by surface energy gradient and spontaneously moved from the hydrophobic to hydrophilic surface. During the moving process, the water droplet accelerated firstly and then decelerated. The peak velocity was about 23.3 mm/s. The velocity is dependent on the gradient of the surface energy.

Abstract: A surface with surface energy gradient was fabricated by using a controlled photodegradation technique of a fluoroalkylsilane self-assembled monolayer (SAM) using irradiation of vacuum ultraviolet light (wavelength=172 nm). Visualization experiments were carried out to investigate the motion behaviors of water droplets on horizontal gradient surfaces. System free energy conversion was analyzed to understand the mechanics of the droplet self-motion. The results show that the liquid droplets were self-propelled to move from hydrophobic region to hydrophilic region on horizontal gradient surfaces. The motion process of the water droplet experienced an accelerating stage and a decelerating stage. The velocity of 2 mL water droplet reached to a maximum of 23.28 mm/s. In the droplet motion on the horizontal gradient surface, the deformation and spread of the droplet continuously release out the interfacial and gravitational potential energy, which offers the kinetic energy for the droplet motion. However, the released interfacial energy is three orders of magnitude larger than the released gravitational potential energy. Thus, the released interfacial energy is the main source of driven energy for the droplet motion. The theoretical analysis is consistent with the experimental results.

Abstract: Four calixarene supramolecular compounds, RCT, PCT, MRCT, and TBCA as active materials, were immobilized on gold substrates of quartz crystal microbalance (QCM) sensors by using L-cysteine self-assembled monolayer (SAM) as a linker. The RCT immobilized QCM sensor possessed the best response characteristics for methanol molecule when the assembling concentration of RCT reached 1.0 mg/mL. The frequency shift response value of the RCT immobilized QCM sensor was in direct proportion to the concentration of methanol vapor with a range of 0 ~ 6000 ppm. Comparing with a gas chromatography, the proposed QCM sensor could be well used for the determination of methanol vapor with a recovery rate of 98.01 ~ 103.9 %, and the two methods showed a well consistent examination result. Also, the sensor possessed good reproducibility and stability, showing that the RCT immobilized QCM sensor can be applied for the detection of the methanol vapor of atmospheric polutants in our living environment.

Abstract: The electrochemical behaviors and sensing application of 100nm-gold plate electrode based on 6-amino-1-hexanethiol (6-AHT) self-assembled monolayer (SAM) have been investigated in this paper. The 6-AHT assembled nano gold plate electrode exhibited a nice linear potential performance of responding to Hg2+ in the range of 1.0×10-8—1.0×10-6 mol/L with a slope of 42.57 mV/-pC (25°C) in Tris-HCl buffer solution (pH=5.0). No obvious interferences were observed from Na+, K+, Ba2+, Mg2+, Ca2+, and Cr3+. The detection limit can be evaluated to 8.0×10-9 mol/L. In addition, the electrode possessed good stability and reproducibility with a recovery rate of 96.50-103.67%, indicating that it can be used for the determination of Hg2+ content in environmental waste water samples. The sensing mechanism of 6-AHT monolayer has also been discussed by the formation of coordination structure between amino groups of the thiol molecules and the mercury ions.

Abstract: Metal deposition on self-assembled monolayers (SAMs) with different terminal organic functional groups is a growing area of research and the metal-organic interface has been extensively studied in the past two decades. Apart from impacting existing technologies, it may have a profound impact on the emerging future technologies such as molecular electronics. The morphology of the deposited metals is strongly influenced by the nature of the chemical interactions occurring at the interface of the organic functional group (OFG) of the SAM and the deposited metal. Our interest for such studies stems from different perspective, as we are interested in determining the impact of the interface on the morphology and hence the magnetic properties of the deposited magnetic materials. We have sputtered a magnetic material, permalloy (Ni79Fe21), on self-assembled monolayers of polar and nonpolar molecules, and have observed contrasting magnetic behaviors of permalloy on these surfaces. We have observed the formation of uniform film on polar regions and cluster are formed on nonpolar regions. Further investigations reveal that the cluster formation gives rise to superparamagnetism, while the uniform film shows a usual ferromagnetic behavior. The observed contrast in morphology and magnetism of Py is attributed to different growth mechanisms arising from difference in polarity of the SAM surfaces.

Abstract: BaTiO3 thin film was prepared by the self-assembled monolayers technique and liquid phase deposition. The effects of pH values and the deposition temperature on the formation of BaTiO3 film were studied. The results showed that the Si substrate was in the precursor solution with 0.025mol/L (AHFT/BN/BA=1:1:3) and pH= 1.5. At 45°C deposited for 8h and annealed at 600°C for 2h, the BaTiO3 film with higher crystalline was prepared on the functionalized Si substrate. XRD and SEM tests showed that the film deposited in the precursor solution with different pH values appeared BaTiO3 characteristic peaks on the surface of every crystal. As pH values increased to 1.5 from 0.5, the strength of the film diffraction peak increased. But the width of the peak became smaller and the crystalline increased. When pH value was 2, due to the self-polymerized deposition of [Ti(OH)6]2-, it was easy to form the larger particles on the substrate. When the deposition temperature was 45°C, the acicular BaTiO3 film formed with the regular order and homogeneous planeness on the substrate. When the deposition temperature was between 55°C and 60°C, the dewatering and polymerizing speed between [Ti(OH)6]2- ions was higher than that between [Ti(OH)6]2- and -OH. The adsorption of the film to the Si substrate was weakened. It was easy for the film to fall off.

Abstract: HfO2 thin film was successfully prepared on the silicon substrate by the Liquid Phase Deposition (LPD) and functionalized organic self-assembled monolayers (SAMs) method. Measurement of contact angle showed that SAMs surface characteristics changed from hydrophobic to hydrophilic after UV irradiation. Photographs of Metallographic Microscope showed that octadecyl trichlorosilane-self- assembled monolayers (OTS-SAMs) had an active effect on the deposition of HfO2 thin film. XRD, SEM and AFM images indicated that the HfO2 thin film with cubic crystal structure was smooth, uniform and dense. Its grain size was between 40-100 nm and the height of thin film varies between 20 and 100 nm.

Abstract: The formation of self-assembled monolayers (SAMs) by specific organic molecules with appropriate anchor groups on semiconductor surfaces may be used to probe the chemical state and quality of the surface or to achieve surface passivation. Molecules with thiol anchor groups are able to bond to hydrogen-terminated germanium surfaces (Ge-S bond). We have prepared SAMs of alkylthiols with different head groups on germanium. Since the surface preparation of germanium is neither well understood nor developed, the controlled preparation of an oxide-free completely H-terminated surface which is a prerequisite for SAM formation of alkylthiols turned out to be a major challenge. Several approaches have been studied. The characterization of the germanium surface prior to and after SAMs formation has been performed by AFM, XPS, Synchrotron-TXRF and -NEXAFS.

Abstract: This paper introduces a new method of surface modification by self-assembled monolayer (SAM) and polymer monolayer grafting. Since most of the glass surfaces lack the reactive functional group, an activation process with 3-(trimethoxysilyl)propyl methacrylate(TPM) is used in our experiment to generate the vinyl reactive sites on the substrate surface for further graft polymerization. The TPM saline layer acts as the “anchor” part to link the functional part onto the surface of substrate. The paper summarizes the surface modifications by the polymerizations of PEGMA, AA(Acrylic acid) and NVP(Nitrogen-vinyl-2-pyrrolidone) respectively and their applications for protein adsorption and cell adhesion through a series of measurements. In previous research, AA and NVP had also been adopted for surface treatment and had achieved good results. The substrate can be glass, alumina, silicon, metals or stainless steel. We choose glass as our substrate during the experiment.

Abstract: In this work, the self-assembled monolayers of γ-aminopropyltrimethoxysilane and octadecyltrichlorosilane were prepared on titanium films, radiated and solidified by ultraviolet radiation/ozone photochemical process. The characterization and friction properties of titanium film, APS SAMs, OTS SAMs and the radiated APS SAMs, OTS SAMs were explored by atomic force microscopy and friction force microscopy. The effects of functional groups, sliding velocity, load and ultraviolet radiation/ozone photochemical process on friction properties of SAMs were analyzed. The experimental results show that the titanium film coated with SAMs, especially under ultraviolet radiation/ozone, is exhibited with a good friction property. The friction property of APS SAMs is better than OTS SAMs under or no ultraviolet radiation/ozone. The friction force increases with the increasing of sliding velocity and decreases with the increasing of load.