Dodecanethiol Research Articles

Surface-Enhanced Raman Spectroscopy of Dodecanethiol-Bound Silver Nanoparticles at the Liquid/Liquid Interface

Adsorption and domain formation of dodecanethiol (DT)-bound silver nanoparticles (SNPs) at the cyclohexane/water interface were studied by means of total internal reflection (TIR) light scattering microscopy and TIR surface-enhanced Raman scattering (SERS). By the TIR light scattering microscopy, the extent of the interfacial adsorption and domain formation of SNP was observed, which was produced by the reaction between citrate-reduced SNPs in the aqueous phase and DT in the cyclohexane phase. The Raman spectra of DT on SNP showed that the relative intensity ratios of gauche to trans conformers in the nu(C-S) band region decreased with the increase of the initial concentration of DT, suggesting the change from the liquidlike structure to the solidlike structure of the DT. The residue of the negative charges on the SNPs at the interface was detected by the resonance SERS (SERRS) peaks of the adsorbed cationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine (TMPyP). The efficiency of the interfacial SNPs domains as a SERS substrate for TMPyP strongly depended on the adsorption state of the DT.

One-Pot Synthesis of New-Phase AgInSe2 Nanorods

AgInSe2 nanorods with a previously unknown orthorhombic phase isostructural to AgInS2 have been prepared by the thermolysis of [(PPh3)2AgIn(SeC{O}Ph)4] in a mixture of oleylamine (OA) and dodecanethiol (DT) at 185 degrees C. A systematic study indicates that the ratio of surfactants is crucial for obtaining both monodispersed nanorods and the new orthorhombic phase AgInSe2. The AgInSe2 nanorods have been characterized by TEM, XRPD, EDX, and XPS.

Surface Morphology and Wetting Characteristics of Sized Cellulose Imitations

Wetting characteristics of cellulosic substrates designed by partially imitating sized paper surfaces were investigated with regard to the surface morphology by contact angle measurement, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy. The contact angles of water droplets on cellulose films decreased with increasing surface roughness at the nm level according to Wenzel's theory. Binary alkanethiolate self-assembled monolayer (SAM) prepared as a hydrophobic surface model of size components demonstrated the characteristic water repellency of Cassie's theory. These two surface-design methods were combined to control the surface morphology of sized cellulose imitations. Vaporized Au colloids were deposited on the cellulose film, and subsequently dodecanethiol (DT) self-assembled only at the Au positions. The AFM phase images confirmed that the total Au coverage was less than 20% of the substrate surface, but the water repellency of the model cellulosic surface attained ca. 103 deg, which is almost as high as that of the DT-SAM surface (ca. 112deg). These results strongly suggest that the surface morphology involved both in substrate roughness and size distribution must be an important factor in the sizing enhancement, and a good sizing response appears without complete coverage of the hydrophilic substrates by the hydrophobic size components.

Influence of synthetic parameters on the size, structure, and stability of dodecanethiol-stabilized silver nanoparticles

Metal nanoparticles (NP) are very attractive because of their size- and shape-dependent properties. A widely used preparation of ligand-stabilized metal NP is the two-phase liquid–liquid method using dodecanethiol (DT) as ligand. This work presents various procedures to synthesize dodecanethiol-capped silver NPs, all of them based on a two-phase liquid–liquid method. Small alterations in the synthetic parameters lead to dramatic modifications in the nanoparticles' average size, size distribution width, stability, and structure, as well as in their ability to self-assemble.

Synthesis of spherical silver nanoparticles by digestive ripening, stabilization with various agents, and their 3-D and 2-D superlattice formation

Capped nanoparticles of silver were synthesized via the solvated metal atom dispersion (SMAD) technique followed by a digestive ripening procedure producing gram quantities of monodisperse spherical nanoparticles. This shows for the first time that a digestive ripening protocol is possible for an element other than gold. The particle size and optical spectra were found to be dependent on the capping agent used. Particles capped with dodecane thiol had a mean diameter of 6.6 ± 1 nm, while trioctyl phosphine capped particles were 6.0 ± 2 nm determined via TEM microscopy. These particles were found to organize into two- and three-dimensional superlattices with a well defined geometry through self-assembly in a liquid solution, that was dictated by the ligand used resulting in a triangular or circular lattice.

SELF-ASSEMBLED METAL QUANTUM DOTS

Long-range order of uniform in size and regular in shape 2D arrays of Au@TOAB-DT nanoparticles (4.9 nm) were formed by a displacement reaction of the outer-shells from tetraoctylammonium bromide (TOAB) to dodecanethiol (DT) molecules at room temperature. The displacement reaction has utilized both superior size and shape control of Au@TOAB nanoparticles and uniform dispersion capability of Au@DT nanoparticles to achieve an extraordinarily large in extent (3 μ m × 3 μ m ) regular nanoparticle lattice structure. Self-assembled NiSi quantum dot arrays have been grown on relaxed epitaxial Si 0.7 Ge 0.3 on (001) Si . The formation of the one-dimensional ordered structure is attributed to the nucleation of NiSi nanodots on the surface undulations induced by step bunching on the surface of SiGe film owing to the miscut of the wafers from normal to the (001) Si direction. The two-dimensional, pseudo-hexagonal structure was achieved under the influence of repulsive stress between nanodots.

Versatility of Aqueous Micellar Solutions for Self-Assembled Monolayers Engineering

Self-assembly of aliphatic as well as aromatic thiol-terminated molecules was achieved onto a variety of gold surfaces using aqueous micellar solutions. Scanning tunneling microscopy experiments allowed us to demonstrate that the increase in the density of self-assembled monolayers (SAMs) prepared from micellar aqueous solvent compared to that prepared from ethanol directly originates from the decrease in defect density in the SAM (etch pits, domain boundaries) and not from a denser local packing of the molecules. Extending the use of such an aqueous solvent to various conjugated molecules, we report for the first time the insertion of these molecules from an aqueous solution in a dodecanethiol (DT) SAM and the ligand-exchange on the surface of DT stabilized gold nanoparticles deposited as a Langmuir-Blodgett film. Finally, we show that aqueous micellar DT solutions allow the preparation of DT SAMs on gold through a micropatterned resist mask. These results make possible the use of water to deliver molecules on a solid substrate to build molecular devices in a way compatible with lithography requirements in microelectronic processes.

Self-assembled Au nanoparticle superlattice via a displacement reaction

Long-range order, uniform in size, and regular in shape two-dimensional (2-D) arrays of core-shell structure Au nanoparticles have been synthesized. A reaction involving the displacement of the outer shells from tetraoctylammonium bromide (TOAB) to dodecanethiol (DT) molecules was used to form Au@TOAB-DT nanoparticles at room temperature (RT). The displacement reaction has used both superior size and shape control of Au@TOAB nanoparticles and uniform dispersion capability of Au@DT nanoparticles to achieve an extraordinarily large in extent (3 µm×3 µm), regular nanoparticle lattice structure. From ultraviolet (UV)-visible spectra, it was inferred that the interaction between the inner core and outer shell of Au@TOAB nanoparticles is weaker than that of Au@TOAB-DT and Au@DT samples. As a result, the ability of the TOAB outer shell to protect the Au@TOAB nanoparticles is weaker so that the system is more prone to agglomerate. On the other hand, the strong interactions between the inner core and outer shell for Au@TOAB-DT and Au@DT nanoparticles led to a predominantly 2-D structure.

Effects of capping thiols on the laser-induced fusion of gold nanoparticles and deposition onto glass substrates in cyclohexane

On irradiation with pulsed 532-nm laser light, dodecanethiol (DT)-capped gold nanoparticles (DT-Au) aggregate and fuse in organic solvents. As a result of particle destabilization, the particles are deposited onto a glass substrate immersed in a colloidal cyclohexane solution. Generally, the properties of gold nanoparticles depend strongly on the surface conditions of the particles. In this report, small amounts of immobilized DT molecules were replaced with 1,6-hexanedithiol (HD) molecules, giving gold nanoparticles capped with DT and HD, denoted as (DT + HD)-Au. The amount of HD in (DT + HD)-Au was determined to be ∼6% by elemental analysis. Interestingly, the absorption spectra of DT-Au and (DT + HD)-Au indicated that both particles have similar stabilities in colloidal solution. Despite this, the activities of these gold nanoparticles after laser irradiation differed dramatically. When (DT + HD)-Au was used instead of DT-Au, the degree of growth and deposition of gold nanoparticles was accelerated and the deposited particles were huge, reaching sizes of several hundreds of nanometers.

Self-assembled organic thin films on electroplated copper for prevention of corrosion

Self-assembled organic thin films of dodecanethiol (DT), mercaptobenzothiazole (MBT), benzotriazole (BTA), imidazole (IMD) and benzothiazole (BT) are formed by adsorption on the surface of copper thin film used in ultralarge-scale integrated circuits. The films are characterized by x-ray photoelectron spectroscopy. The inhibition of corrosion of these organic thin films is investigated in aerated 0.5 M H2SO4 solutions by electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The presence of these films reduced corrosion by blocking the copper surface from the oxygen dissolved in the acid medium. The relative inhibition efficiencies of these inhibiting agents in preventing copper oxidation are found to be in the order of DT>MBT>BT>BTA>IMD. The effectiveness of the inhibitors increased with the temperature, concentration of the inhibitors, and duration of immersion in the solution. An adsorption model is proposed on the basis of variation of the impedance according to the inhibitor concentration. The stability and packing of the inhibitors on the surface appear to be the most important factors in determining the inhibitive efficiency of the inhibitors.

Degradation of dodecanethiol in dodecane by γ-irradiation and improvement by sensitization

Sulfur-containing organic compounds, such as mercaptans, are widely distributed in petroleum. A novel refining method for the degradation of mercaptans in petroleum was put forward and investigated by means of γ-irradiation in this paper. Dodecanethiol (DCT) dissolved in dodecane was employed as the simulation of petroleum. The results showed that the chemical rate constants for the degradation reaction could be described with the first-order rate model. Irradiation with low-dose rate gave rise to a high removal efficiency and a high energy efficiency when the radiation dose was the same. The degradation process was improved greatly by oxygen, and the demanded irradiation dose was reduced markedly. Some chemicals were selected as radio-sensitizers to improve the degradation of dodecanethiol. The degradation processes were enhanced by acetone and carbon tetrachloride, and the degradation efficiencies increased by over 25%, respectively. The main degradation product of dodecanethiol was didodecyl disulfide. Meanwhile, the amount of degradation for dodecane was slight. It would be a potential alternative to degradation of mercaptan compounds in petroleum by γ-irradiation.

Direct comparison of the electronic coupling efficiency of sulfur and selenium alligator clips for molecules adsorbed onto gold electrodes

Scanning tunneling microscopy experiments have been performed to compare the electronic coupling provided by S and by Se used as alligator clips for bisthiol- and biselenol-terthiophene molecules adsorbed onto gold. The molecules were inserted in a dodecanethiol (DT) self-assembled monolayer. Their apparent height above the dodecanethiol matrix was used as a measure of the electronic coupling strength corresponding to S and Se, respectively. We show that the insertion behaviors of the two molecules are qualitatively the same, and that Se provides systematically a better coupling link than S, whatever the tunneling conditions.

Ruthenium Nanoparticles: Size, Shape, and Self-Assemblies

Ruthenium nanoparticles were prepared by reduction of RuCl3 in a liquid polyol. The mean particle size was restricted to the 1−6 nm range by appropriate choice of the reduction temperature and the acetate ion concentration in the solution. Very narrow particle diameter distributions were obtained. In some samples, among nearly isotropic particles, platelets with aspect ratios as low as 1/4 were detected. Colloidal solutions in toluene were obtained by coating the metal particles with dodecane thiol. Self-assemblies of 4-nm-sized coated particles were studied on a transmission electron microscope grid. The dodecane thiol concentration in the colloidal solution was found to determine, within the particle monolayer, the formation of either columnar units made up of edgewise stacked platelets, or a hexagonal network with a mean distance between the particles of 2 nm. The stacking of hexagonal arrays of particles was also studied, and both closed-packed and noncompact stackings were found. In the noncompact st...

Controlling the formation of Au nanoparticles using functionalized molecular buffer layers

Nanoparticles of gold are produced by evaporation of gold atoms onto functionalized self-assembled monolayers (SAMs). SAMs of dodecanethiol (DT) and mercaptoundecanoic acid (MUA) on Au(1 1 1) are used as substrates and the gold particles are imaged with a scanning tunneling microscope. Gold atoms evaporated on DT monolayers diffuse rapidly to the interface between the molecular layer and the gold substrate where they form two-dimensional islands of 1 ML in height. In the case of monolayers of MUA, the strong interaction between evaporated gold and the acid group of the molecule gives rise to effective pinning of the gold atoms on top of the molecular layer and leads to the growth of three-dimensional gold nanocrystals.

Measurements of the potential dependence of electric field magnitudes at an electrode using fluorescent probes in a self-assembled monolayer

Abstract This report details the measurement of the dependence of the electric field magnitude in the electrical double layer on applied potential for a metal/organic thin film/electrolyte system. The self-assembled monolayers (SAMs) used in these experiments were formed from n-alkyl thiols on roughened Ag and roughened or smooth Au electrodes. The electric field magnitudes were calculated from the Stark shifts of a cationic fluorescent probe, an (aminostyryl)pyridinium derivative, that was immobilized in the SAM. Attention is focused on two gold-supported SAMs, one in which the probe was embedded within the SAM, and another in which the probe was external to the SAM. The composition of the monolayers and the orientation of the probe and n-alkyl thiol molecules within them were characterized using ex situ reflection-absorption Fourier transform infrared spectroscopy (RA-FTIR). For the case in which the probe was embedded within a dodecane thiol SAM, the change in electric field magnitude was determined to be 3×105 V cm−1 per volt change in the applied potential, while for the case of the probe outside of a propyl thiol SAM a value of 4×104 V cm−1 per volt change in the applied potential was obtained. These values are considerably smaller than expectations based on existing models for the potential distributions within such structures, and possible reasons for this behavior are discussed. The fluorescence intensity from the probe was observed to depend on potential, an effect that is also discussed. Measurements of the Stark shift versus applied potential at different ionic strengths provide a value of the potential of zero charge for these SAMs of −0.4 V versus SCE, in good agreement with previously measured values. The conditions under which fluorescent probes can be used effectively at metal electrodes are also discussed.

Photoemission Study of Thiol-Capped Gold Nanoparticles

AbstractA photoemission study of dodecanethiol (DT)-capped Au nanoparticles on the highly oriented pyrolytic graphite (HOPG) substrates has been carried out in order to investigate in detail the electronic structures of metallic nanoparticles supported on the substrates. The present DT-capped Au nanoparticles show that the leading edge in the photoemission spectra near the Fermi level is not the Fermi edge, with the midpoint of the steep slope being away from the Fermi level. From these results, we discuss the electronic structures of DT-capped Au nanoparticles, especially nanoparticle-HOPG substrate interaction.

Optically Induced Switching of Azobenzene Containing Self Assembling Monolayers Investigated by Kelvin Probe and Scanning Force Microscopy

The light induced switching of self-assembled monolayers containing azobenzenes is observed in situ by the Kelvin probe method. The switching process is optimized by preparing monolayers from mixed solutions of azobenzene thiols and n-alkylene thiols. In a film the efficiency of the E/Z-isomerization depends on both the spacer length between azobenzene group and gold surface as well as the free volume in the film, tuned by the n-alkylene thiol fraction in the mixture. An optimum was found in a mixed self-assembling film containing 33% 4-fluoromethyl-4′-(10-carboxy-decyloxy) azobenzene in a dodecane thiol matrix. The structure of the films were characterized by FTIR and AFM.

Long-chain acyl thioesters prepared by solvent-free thioesterification and transthioesterification catalysed by microbial lipases

Long-chain acyl thioesters (thio wax esters) have been prepared in high (80% to more than 90%) yields by solvent-free esterification of fatty acids (lauric, myristic, palmitic and stearic acids) with long-chain thiols, such as decane thiol, dodecane thiol, tetradecane thiol and hexadecane thiol, catalysed by lipases from Candida antarctica (Novozym) and Rhizomucor miehei (Lipozyme) in the presence of a 0.4-nm molecular sieve. In the thioesterification reaction Novozym was a more effective biocatalyst than Lipozyme. The extent of thioesterification increased with increasing molar ratio of fatty acid to alkane thiol (1:1 to 3:1) and with temperature (40 °C compared to 60 °C), as well as with the amount of the enzyme preparation and the amount of 0.4-nm molecular sieve. Decreasing the chain length of the alkane thiol from C16 to C10 also increased the extent of thioesterification. Lipase-catalysed solvent-free transthioesterification of fatty acid methyl esters with alkane thiols was less effective for the preparation of acyl thioesters than was thioesterification of fatty acids with alkane thiols. In transthioesterification, Lipozyme was slightly more effective as a biocatalyst than Novozym.

Experimental investigations of the electrical transport properties of dodecanethiol and bisthiolterthiophene molecules embedded in metal-molecule-metal junctions

The electrical transport properties of dodecanethiol (DT) and 2.5''-bis(acetylthio)-5.2'5'.2''-terthienyl (T3) embedded in metal-molecule-metal junctions are investigated. Scannning tunelling microscopy imaging and I- V curves recorded on mechanically breakable junctions allow us to observe a marked difference in the electrical behaviour of these molecules: in particular, steps have been observed in the I- V characteristics of gold-T3-gold junctions, which are not found in the gold-DT-gold ones.

Molecular orientation determined by second-harmonic generation: Self-assembled monolayers

Monolayers of 12-(4-nitroanilino)-dodecane thiol $[{\mathrm{O}}_{2}{\mathrm{N}--\mathrm{C}}_{6}{\mathrm{H}}_{4}{\mathrm{\ensuremath{-}}\mathrm{N}\mathrm{H}(\mathrm{C}\mathrm{H}}_{2}{)}_{12}\mathrm{SH}](\mathrm{NAT})$ adsorbed on polycrystalline gold substrates were investigated in a gaseous environment and in ethanol. Contributions of comparable magnitude from the metal substrate, the adsorbate-substrate interaction, and the p-nitro aniline moiety $(p\mathrm{NA})$ require phase-sensitive and polarization-dependent second-harmonic-generation (SHG) measurements. The susceptibility of the $p\mathrm{NA}$ end group is separated by comparative experiments with n-alkane thiols. Evaluation of the orientation of the $p\mathrm{NA}$ moiety requires phase information about the SHG signal. Intensity data alone produce ambiguous results. The tilt angle determined by SHG is shown to be strongly dependent on the model applied. For the NAT film in an inert gas atmosphere, the tilt angle \ensuremath{\vartheta} of the $p\mathrm{NA}$ group calculated from the SHG experiments is compared with the value of 53\ifmmode^\circ\else\textdegree\fi{} obtained by linear techniques. Agreement is only achieved if local-field factors are neglected and if a two-layer model is assumed to describe the linear optical properties of the system. Immersion of the NAT film in ethanol causes a change of the tilt angle of the $p\mathrm{NA}$ end group to a more upright position of about \ensuremath{\vartheta}=36\ifmmode^\circ\else\textdegree\fi{}. A detailed discussion reveals that the accuracy and reliability of SHG data to determine the orientation of molecules depend critically on the precision by which molecular properties are known and on the model describing the linear optical properties.