A contact angle and ToF-SIMS study of SAM-thiol interactions on polycrystalline gold

A process of chemical differentiation of neighboring Au features on a substrate (for biosensing applications) involves a step, where after electrochemical removal of a self-assembled monolayer (SAM) from one feature, another SAM is deposited onto it by incubation with a different thiol. During this incubation step, other undesorbed features are also exposed to this thiol which may lead to a partial SAM-thiol exhange, the extent of which is a function of time. Here, such surface reactions were followed on polystalline Au in both directions using contact angle measurements and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The thiols involved were dodecanethiol (DDT) which forms SAM promoting adsorption of proteins and 11-mercaptoundecyl)tri(ethylene glycol) (TPEG) whose SAM prevents such adsorption. The surface reactions in both directions cannot be described by a simple pseudo-first-order kinetics. It was found that while the DDT SAM interaction with a TPEG solution leads eventually to a total replacement, the reverse process, TPEG SAM interaction with DDT, leads to no noticeable exchange over the first 3 h and then asymptotically approaches ∼50% replacement.     

Variable temperature STM study of Co deposition on a dodecanethiol self assembled monolayer

The present scanning tunneling microscopy study reports on the growth processes of Co vapor-deposited on a dodecanethiol (DDT) self-assembled monolayer (SAM)/Au(111). We observe strongly modified surface and depth diffusions of Co adatoms depending on the growth temperature. Co deposited at 300 K shows an extremely incomplete regime of condensation on the organic layer. Besides, Co penetrates the DDT monolayer and resides at the DDT/Au(111) interface as 2D clusters. This phenomenon takes place through defects in the SAM which are transient channels. In contrast, Co deposited at 50 K shows a complete condensation and nucleates on defects of the SAM layer as 3D islands sitting most likely on top of the DDTs. These results are of interest in the growing field of organic spintronics where the quality of the organic/ferromagnetic interface is a key issue.     

One-step synthesis of silica-coated magnetite nanoparticles by electrooxidation of iron in sodium silicate solution

In the present study, solid-solution gold?Cplatinum (Au?CPt) nanoparticles with controllable compositions were fabricated by high-intensity femtosecond laser irradiation of an aqueous solution of gold and platinum ions without any chemicals and complicated processes. Transmittance electron microscopy revealed that the single nanometer-sized particles were fabricated by femtosecond laser irradiation of mixed aqueous solutions of gold and platinum ions. The crystalline structure of nanoparticles was characterized by electron and X-ray diffractions. Contrary to the bulk Au?CPt binary systems, which commonly contain a pair of diffraction peaks between pure gold and platinum peaks because of its large miscibility gap in phase diagram, or mixture of Au and Pt, the diffraction peaks of Au?CPt nanoparticles fabricated in the experiment showed a characteristic of the fcc-type lattice. Moreover, the diffraction patterns shifted monotonically from the peak position of pure gold to that of pure platinum as the fractions of platinum ions in the solution were increased. These observations strongly imply that the Au?CPt nanoparticles were solid solution with intended compositions. This technique is not only simple and environmentally friendly, but also applicable to other binary and ternary systems.     

Single layer gold islands at the interface between a self-assembled monolayer and the Au(111) substrate: A high-resolution STM study

Physical vapor deposition of gold onto a self-assembled monolayer (SAM) of octanethiol on Au(111) has been studied at the molecular level in ultra-high vacuum (UHV) using atomic-resolution scanning tunneling microscopy (STM). A specially prepared SAM with not only the usual etch pits but also co-existing phases and domain boundaries is used for the purpose of studying details of the nucleation process. Etch pits are found to be filled by deposited Au atoms. At the same time, preferential nucleation and growth of gold islands at intersections of different domains, as well as inside the domains of the less dense striped phase, is observed. We find no gold islands within the densely-packed (√3 × √3)R30° phase. High-resolution STM imaging shows that the SAM over the newly formed gold islands adopts the same structure as that in the immediate surroundings.     

Trapping of V(benzene)2 sandwich clusters in a n-alkanethiol self-assembled monolayer matrix

V(benzene)₂ sandwich cluster cations produced in the gas phase were size-selectively deposited onto a self-assembled monolayer of n-hexadecanethiols (HDT-SAM) chemisorbed on a Au(111) surface as well as onto a bare Au(111) surface. The thermal chemistry of the neutralized clusters on each substrate was studied with temperature programmed desorption (TPD). From the analyses of the threshold in the TPD, the desorption activation energies of the clusters deposited were determined to be 64.4 ±12.8 kJ/mol for the Au(111) and 130 ±10 kJ/mol for the HDT-SAM. The remarkably large desorption activation energy from the SAM suggests that the deposited clusters are incorporated into the SAM matrix and firmly trapped inside the alkyl chains of the SAM.     

Self-assembly of human plasma fibrinogens on binary organosilane monolayers with micro domains

The adsorption behavior and self-assembly of human plasma fibrinogen (HPF) on binary methyl- and amino-terminated self-assembled monolayers (SAMs) were investigated by atomic force microscopy (AFM). The binary SAMs were fabricated through self-assembly mechanism of organosilane molecules. The height of domains is the domain height is 0.8 ± 0.2 nm from the AFM topographic image. It corresponds to the domain height is 0.8 ± 0.2 nm from the AFM topographic image. It corresponds to the difference between the length of the alkyl chain of octadecyltrichlorosilane (OTS) and that of n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS). The fibrinogen solution used ultrapure water as the solvent and its pH was adjusted at 3 and 10. From the AFM results at pH 3, HPF only formed network structures on the OTS domains of the binary SAM at early immersion times, and then the network structures expanded and connected between OTS domains through the AHAPS surface at long immersion times. In this case, a few HPFs are discretely adsorbed on the AHAPS surface. However, HPF is uniformly adsorbed on the binary SAM under the other conditions of pH.     

硫氰酸铵-氯化十六烷基吡啶-水体系浮选分离Au（Ⅲ）的研究

研究了氯化十六烷基吡啶和硫氰酸铵分离Au（Ⅲ）的行为及Au（Ⅲ）与一些金属离子分离的条件。结果表明,在水溶液中,Au（Ⅲ）与氯化十六烷基吡啶和硫氰酸铵形成不溶于水的三元缔合物Au（SCN）4-.CPC＋,此三元缔合物沉淀浮于水相上层形成界面清晰的液-固两相。当溶液中氯化十六烷基吡啶和硫氰酸铵的浓度分别为7.0×10-4mol/L和5.0×10-3mol/L时,Au（Ⅲ）可与Mn（Ⅱ）,Ni（Ⅱ）,Co（Ⅱ）,Fe（Ⅱ）,Mg（Ⅱ）,Al（Ⅱ）和Cd（Ⅱ）进行分离,对合成水样中的Au（Ⅲ）进行了分离和测定,Au（Ⅲ）的浮选率达到98.6%以上,其他金属离子的浮选率都在4.5%以下。该方法具有简便、快速和不污染环境等特点,在微量金的分离和富集分析中有一定的实用价值。     

Reaction‐Induced Phase‐Separation in Polyoxyethylene/Polystyrene Blends. II. Structure Development

Abstract

The morphology development in model polymer blends was investigated in relation to the processing pathway. Reaction‐induced phase separation was used to make polyoxyethylene (POE) and polystyrene (PS) blends from a solution of POE/styrene. As the styrene underwent polymerization by photo‐initiation with ultraviolet light, phase separation, and phase inversion were induced, whereby the POE became the matrix phase. Optical microscopy showed that liquid–liquid (L–L) phase separation occurred soon after the styrene polymerization was initiated. Nucleation and growth was identified as the mechanism of L–L phase separation. Polystyrene/styrene‐rich domains formed in a POE/styrene‐rich matrix. The domain size developed until arrested by the POE liquid–solid phase separating and crystallizing, since the experiments were conducted below the melt temperature of POE. The POE crystal growth process also followed a nucleation and growth mechanism. The time to the onset of crystallization was observed to decrease as the POE content increased, until the POE formed a saturated solution in styrene. As the crystallization onset time decreased, the PS‐rich domain size also decreased. The phase diagram previously established can now be used to describe (and predict) the number density and size of the PS‐rich domains in the POE matrix of the blends.     

Total Integration of the Sample Injection,Microdroplet Reaction,Phase Separation,Real-Time Optical Detection,and Recovery of Diverse Silver–Gold Bimetallic Nanoalloys in a Continuous Process

Microfluidic droplet generators have garnered great attention due to the uniformity, high-throughput capability, and facile experimental setup. To maximize the potentials of droplet technology as a chemical/biological nanoliter-scale reactor, the downstream processes such as separation of the aqueous and oil phase, real-time monitoring of the products formed in droplets, and the final product recovery from the droplets is necessary. In this study, the droplet is utilized as a chemical reactor to synthesize a variety of Ag and Au bimetallic nanoalloys in a fully integrated microsystem including sample injection, a T-junction droplet generator, droplet reaction, water–oil phase separation, real-time UV–vis absorbance detection, and product recovery. The flow rate of the Ag nanoparticle (NP) solution and the HAuCl₄ solution was tuned to generate different molar ratios of Ag and Au components. The in-line UV–vis absorbance spectrometer displays a peak shift of the Ag/Au bimetallic alloys depending on the molar ratio of Ag/Au in the continuous process, enabling to judge the kind of the Ag/Au alloys in situ and collect a variety of Ag/Au nanoalloys. Thus, the desired nanomaterials can be obtained with minimal trial and error, saving time and cost.     

The formation of sub-10 nm nanohole array on block copolymer thin films on gold surface using surface neutralization based on O2 plasma treatment and self-assembled monolayer

Blockcopolymer (BCP) lithography is an emerging nanolithography technique for fabrications of various nanoscale devices and materials. In this study, self-assembled BCP thin films having cylindrical nanoholes were prepared on gold by surface neutralization using self-assembled monolayer (SAM). Oxygen plasma treatment was investigated as a way to enhance the functionality of Au surface toward SAM formation. After surface neutralization, well-ordered nanoholes with 9 to 20 nm diameters were formed inside BCP thin films on Au surfaces through microphase separation. The effects of oxygen plasma treatment on the formation of BCP nanopattern were investigated using surface analysis techniques including X-ray photoelectron spectroscopy (XPS) and water contact angle measurement. Au nanodot arrays were fabricated on gold film by utilizing the BCP nanotemplate and investigated by atomic force microscopy (AFM).     

Metal deposition onto thiol-covered gold: Platinum on a 4-mercaptopyridine SAM

In this study we describe details of a new technique that allows to deposit metal on top of a self-assembled monolayer (SAM). Monoatomic high platinum islands were formed on a 4-mercaptopyridine SAM on Au(1 1 1) by first immersing the SAM-covered gold electrode in an aqueous solution of K₂PtCl₄ without potential control to allow Pt(II) ions to form a complex with the pyridine nitrogen. The complexed Pt(II) ions were then reduced electrochemically to Pt(0) after transferring the electrode to a Pt(II) ion-free solution. Upon reduction, monoatomic high Pt islands were observed in STM, the total coverage depending on the time for complexation. Ex situ angle-resolved XPS studies reveal that the Pt islands indeed reside on top of the SAM.     

Adsorption behaviors of V2O5 nanowires on binary mixed self-assembled monolayers

The adsorption behaviors of V₂O₅ nanowires on binary mixed self-assembled monolayers (SAMs) were investigated with variation of the mixing ratio of two differently terminated thiolates on Au. Hydroxyl-covered V₂O₅ nanowires showed a preferential adsorption on amine (NH₂)-terminated thiolates over methyl (CH₃)-terminated ones. However, on the binary mixed SAM of NH₂- and CH₃-terminated thiols, the adsorption behavior did not follow a simple expectation based upon the electrostatic interaction. The total number of adsorbed V₂O₅ nanowires increased with the mole fraction of NH₂-terminated thiolates up to χNH₂∼0.5, then it decreased with further increase of χNH₂. The height distribution of adsorbed nanowires showed that the relative portion of the agglomerated wires thicker than 3.5 nm to individual wires thinner than 3.5 nm increased up to χNH₂∼0.75 and then it decreased with further increase of χNH₂. The dispersion of molecules with polar-functional groups as well as the molecular ordering of mixed SAMs is attributed to such adsorption behaviors of V₂O₅ nanowires.     

The structural formation of methylthiolate SAMs on Au(1 1 1) for short deposition times from solution

Scanning tunnelling microscopy was used to investigate the structural formation of methylthiolate self-assembled monolayers on Au(1 1 1). SAMs were prepared by exposing the gold crystal to an ethanol-dimethyldisulfide solution for immersion times of 12 min, 12 h, and 24 h. After preparation the formation of a () rect. striped phase was found. For this phase, the immersion time is the key parameter determining the size and number of ordered domains. Annealing induced a phase transition leading to large domains in a (3×4) structure. The annealing temperature determines whether a mixed phase of both structures or only the (3×4) structure are formed. We find no influence of the immersion time on the formation of the second structure. A structure model is presented for both phases on the basis on the same building block containing two methylthiolate molecules and a gold ad-atom.     

结晶紫-H2O体系浮选分离Au（SCN）4-

研究了结晶紫-H2O体系浮选分离A u（SCN）4-的行为及与一些金属离子分离的条件。结果表明,在水溶液中,Au（Ⅲ）与结晶紫（CV）和硫氰酸铵形成不溶于水的三元缔合物A u（SCN）4-.CV＋,此三元缔合物沉淀浮于水相上层形成界面清晰的液-固两相。当溶液中结晶紫和硫氰酸铵的浓度分别为7.0×1-0 4m ol/L和5.0×1-0 3mol/L时,Au（Ⅲ）可与R h（Ⅲ）、G a（Ⅲ）、Mn（Ⅱ）、A l（Ⅲ）、Ni（Ⅱ）、Cd（Ⅱ）、F e（Ⅱ）、Mg（Ⅱ）和Sn（Ⅳ）离子分离。该方法具有简便、快速和不污染环境等特点,在微量金的分离和富集分析中有一定的实用价值。     

PNIPAM线性链与凝胶在二元溶剂中相变的变温NMR研究

通过对聚N-异丙基丙烯酰胺（PNIPAM）水溶液和凝胶在水和甲醇混合溶剂中的¹H NMR谱图以及弛豫时间(T₁与T₂)等多种NMR参数随温度变化的研究,发现PNIPAM大分子的基团质子NMR信号、溶剂的弛豫时间都可以用来灵敏表征PNIPAM在二元溶剂中的相变行为. 在PNIPAM凝胶中,温度升到LSCT以上,溶剂峰由单峰变为双峰,分别对应于受限在大分子网络内的受限溶剂和排除到大分子网络外的自由溶剂,两者的弛豫时间存在明显差异. 在PNIPAM溶液中,溶剂峰在相变前后并没有显著变化. 通过PNIPAM溶胀在water/alcohol混合溶剂中的相变研究进一步证实了PNIPAM与不同溶剂之间的相互作用强弱.      

Photopatterning of gold and copper surfaces by using self-assembled monolayers

A photolithographic technique was successfully employed to generate micropatterns of gold and copper by using self-assembled monolayer (SAMs) as resist materials. Copper patterns were successfully prepared from SAMs of 11-mercaptoundecanoic acid (MUA) and dodecanethiol (DDT) on Cu after UV irradiation followed by etching but gold patterns were prepared only from the SAM of MUA and not from the SAM of DDT, which revealed the difference of photooxidation of the metal–sulfur bond on SAMs. However, the maximum resolution of the pattern was about 1.0 μm on gold and 5.0 μm on copper. This may be due to lower quality packing of SAM on copper than gold. Ellipsometric and cyclovoltammetric observation of SAMs during the UV irradiation indicated the gradual removal of SAMs on copper and gold. Photopatterning of gold and copper by using SAM is more compatible with the current microelectronics process and is complementary to the microcontact printing technique.     

Morphological,Thermal and Mechanical Properties of Compatibilized Nylon 6/ABS Blends

Super‐tough nylon 6/ABS blends were prepared by using styrene/acrylonitrile/maleic anhydride co‐polymer (SAM) as a compatibilizer. The variations in morphology, mechanical behavior, and crystallinity associated with the reaction of the SAM with the nylon were characterized. The results showed that the addition of SAM to nylon 6/ABS blends enhanced the interfacial adhesion between nylon 6 and ABS, and this led to the decrease of ABS domain size and the improvement of mechanical properties of their blends. Moreover, it could be found that the crystallinity and phase morphology changed with the variation of SAM.     

Growth kinetics of self-assembled monolayers of thiophene and terthiophene on Au(111): An infrared spectroscopic study

The growth kinetics of self-assembled monolayers (SAMs) of thiophene compounds on Au(111) surfaces was revealed by Fourier-transform infrared reflection absorption spectroscopy (FT-IR-RAS). Thiophene and terthiophene form well-ordered SAMs on Au(111) surfaces by immersing gold substrates into their ethanol solutions for ca. 15 h. Gibbs free energies for the adsorption processes of thiophene and terthiophene were found to be identical. However, the growth and molecular orientation of SAMs are different between two thiophene compounds. Terthiophene in SAMs orients parallel to the surface. The SAM growth of terthiophene obeys a time-dependent Langmuir scheme. On the other hand, the thiophene SAM undergoes a two-step growth process with unique molecular orientations. In the primary phase, thiophene assumes a parallel orientation on the Au(111) surface. In the second phase, thiophene is oriented close to the normal of the surface. The different growth process between thiophene and terthiophene is attributable to the topology of sulfur positions in the molecules. Received 23 May 2001 and Received in final form 11 February 2002     

Interfacial kinetic enhancement of metal ion adsorption on binary mixed self-assembled monolayers

The adsorption of metal ions, a type of surface reaction on binary mixed self-assembled monolayers (SAMs) on a gold surface composed of 1,6-hexanedithiol (HDT) with 11-mercaptoundecanoic acid (MUA), was monitored by in situ surface plasmon resonance (SPR) measurements. The differential SPR reflectance (ΔR) enables the kinetics of adsorption of Pt²⁺ on the mixed SAMs to be investigated. Unlike single HDT SAM, kinetic analyses of the mixed SAMs showed that the rate of adsorption of Pt²⁺ was enhanced and that it was highly dependent on the fraction of MUA present. These SPR measurements suggest that the adsorption rate of metal ions can be readily manipulated simply by using mixed SAMs.     

Quantitative analysis of mixed self-assembled monolayers using ToF-SIMS

The spacing of chemical functional groups on self-assembled monolayers (SAMs) plays an important role in controlling the density of biomolecules in biochips and biosensors. In this sense, a mixed SAM made of two different terminal groups is a useful organic surface since spacing can be easily controlled by changing a relative mole fraction in a mixture solution. In this study, an acetylene-OCH₂O(EG)₃(CH₂)₁₁S-S(CH₂)₁₁(EG)₃OCH₂O-propene (Eneyne) SAM and mixed SAMs made by a mixture of (S(CH₂)₁₁(EG)₃OCH₂O-acetylene)₂ (Diyne) and (S(CH₂)₁₁(EG)₃OCH₂O-propene)₂ (Diene) were produced on gold substrates and measured by using ToF-SIMS. The secondary ion yield ratio of [Au·S(CH₂)₁₁(EG)₃OCH₂O-acetylene]⁻ to [Au·S(CH₂)₁₁(EG)₃OCH₂O-propene]⁻ was measured for each mixed SAM and plotted as a function of the mole fraction of Diyne to Diene in a SAM solution. The ion yield ratio of a mixed SAM produced from a solution with a mole fraction of 0.5 (i.e., 1:1 mixture) was 0.3, which corresponded well to the ion yield ratio measured from an Eneyne SAM. A time-dependent experiment of Eneyne SAM formation and immersion experiment of Eneyne SAM into Diyne solution or into Diene solution were performed. The relative ion yield ratio of 0.3 was due to a different secondary ion formation and not due to the difference in the amount of adsorbates on the surface, nor to the different binding strengths onto the gold surface. Our study shows that a mixed SAM with well-controlled spacing can be produced and quantified by using the ToF-SIMS technique.