Template-stripped Gold Surfaces Research Articles

Atomic force microscopy and in situ-annealing X-ray diffraction study on template-stripped gold substrates for optimum self-assembled monolayer deposition

Literature is well supplied with studies of gold deposit on mica for fabricating ultra-flat template-stripped gold surface. Gold on silicon has not received much attention. Our study optimizes the deposition rates, annealing temperatures and time to obtain a template-stripped gold surface with a very low roughness and large (111) oriented crystallites. Atomic force microscopy is performed in tapping and peak force mode to evaluate the surface roughness. The crystallite size is obtained from in situ X-ray diffraction measurements during annealing. We find out that a deposition rate of 0.2 nm/s with a 40 min annealing at 400°C gives the best result (0.21±0.04) nm.

Conductive Self-Assembled Monolayers of Paramagnetic {CoII } and { } Coordination Clusters on Gold Surfaces.

Two polynuclear cobalt(II,III) complexes, [Co5(N3)4(N-n-bda)4(bza·SMe)2] (1) and [Co6(N3)4(N-n-bda)2(bza·SMe)5(MeOH)4]Cl (2), where Hbza·SMe = 4-(methylthio)benzoic acid and N-n-H2bda = N-n-butyldiethanolamine, were synthesized and fully characterized by various techniques. Compound 1 exhibits an unusual, approximately C2-symmetric {CoII} core of two isosceles Co3 triangles with perpendicularly oriented planes, sharing a central, high-spin CoII ion residing in a distorted tetrahedral coordination environment. This central CoII ion is connected to four outer, octahedrally coordinated low-spin CoIII ions via oxo bridges. Compound 2 comprises a semi-circular {} motif of four non-interacting high-spin CoII and two low-spin CoIII centers in octahedral coordination environments. Self-assembled monolayers (SAMs) of 1 and 2 were physisorbed on template-stripped gold surfaces contacted by an eutectic gallium-indium (EGaIn) tip. The acquired current density-voltage (I-V) data revealed that the cobalt-based SAMs are more electrically robust than those of the previously reported dinuclear {CuIILnIII} complexes with Ln = Gd, Tb, Dy, or Y (Schmitz et al., 2018a). In addition, between 170 and 220°C, the neutral, mixed-valence compound 1 undergoes a redox modification, yielding a {Co5}-based coordination cluster (1-A) with five non-interacting, high-spin octahedral CoII centers as indicated by SQUID magnetometry analysis in combination with X-ray photoelectron spectroscopy and infrared spectroscopy. Solvothermal treatment of 1 results in a high-nuclearity coordination cluster, [Co10(N3)2(N-n-bda)6(bza·SMe)6] (3), containing 10 virtually non-interacting high-spin CoII centers.

Mixed carboranethiol self-assembled monolayers on gold surfaces

Carboranethiol self-assembled monolayers on metal surfaces have been shown to be very convenient systems for surface engineering. Here we have studied pure and mixed self-assembled monolayers (SAMs) of three different carboranethiol (CT) isomers on gold surfaces. The isomers were chosen with dipole moments pointing parallel to (m-1-carboranethiol, M1), out of (m-9-carboranethiol, M9) and into (o-1-carboranethiol, O1) the surface plane, in order to investigate the effect of dipole moment orientation on the film properties. In addition, influence of the substrate surface morphology on the film properties was also studied by using flame annealed (FA) and template stripped (TS) gold surfaces. Contact angle measurements indicate that in M1/M9 and M1/O1 mixed SAMs, M1 is the dominant species on the surface even for low M1 ratio in the growth solution. Whereas for O1/M9 mixed SAMs no clear evidence could be observed indicating dominance of one of the species over the other one. Though contact angle values were lower and hysteresis values were higher for SAMs grown on TS gold surfaces, the trends in the behavior of the contact angles with changing mixing ratio were identical for SAMs grown on both substrates. Atomic force microscopy images of the SAMs on TS gold surfaces indicate that the films have similar morphological properties regardless of mixing ratio.

Surprisingly Big Rectification Ratios for a Very Small Unimolecular Rectifier

To shrink electrical circuits beyond the looming practical limits of Moore's "Law", it has been a common goal to create carbon-based components. Here is the first example of a new class of donor-σ-acceptor rectifiers: hemibiquinones (HBQs). HBQs possess donor and acceptor moieties that are electronically isolated by inter-ring torsion. A HBQ-dinitrile self-assembles on a template-stripped gold surface through directed chemisorption, forming a 1.1 nm-thick monolayer. Rectification is measured through the monolayer or single molecules by using three different top electrode arrangements. Even though the HBQs are composed of relatively weak electrophores, rectification ratios ranging from 5 to 160 were observed at 2.5 V.

Interactions between Molecularly Smooth Gold and Mica Surfaces across Aqueous Solutions

Using a surface force balance, we measured the forces between an ultrasmooth (0.2 nm rms roughness) template-stripped gold surface and a molecularly smooth mica surface. Comparison of these forces in both low salt (conductivity water, equivalent to 10(-6)-10(-5) M 1:1 salt) and high salt (10 mM KClO4) regimes enabled us to examine the properties of water layers confined between a metal and a dielectric to films of a few nanometers or less in thickness. We find that the long-range forces between gold and mica are similar to those between two mica surfaces, indicating a net effective negative charge density on the gold similar to that on the mica. Differences were more pronounced at small separations, manifested by the larger jump-in distance in pure water and the weaker hydration repulsion in high salt between a gold and a mica surface compared with two mica surfaces. However, despite these short-ranged differences, replacing one mica surface with gold does not measurably alter the viscosity of nanoconfined water layers, either as free molecules or as bound hydration layers, relative to their confinement by two mica sheets.

Formation of a Flat Conductive Polymer Film Using Template-Stripped Gold (TSG) Surface and Surface-Graft Polymerization for Scanning Multiprobe Data Storage

A thin conductive polymer recording medium with angstrom-scale surface roughness has been formed on template-stripped gold (TSG) surface by surface-graft polymerization for scanning multiprobe data storage. A gold film is deposited on a mica plate, which is bonded onto the silicon substrate with a gold film using gold-gold direct bonding technique. By removing the mica plate, gold surface with the angstrom-scale surface roughness is formed. A conductive polymer film as a recording medium is deposited on the TSG surface by the surface-graft polymerization. As a result, the polymer film with small roughness is obtained. Thus, the use of the TSG surface is efficient way to form the flat conductive polymer film. Finally, reversible electrical modification on the polymer film is demonstrated using atomic force microscopy. These results show the possibility that this formation method of the conductive polymer film provides rewritable recording media with small roughness for scanning multiprobe high-density data storage. [DOI: 10.1380/ejssnt.2008.202]

Solid-State Bonding Technique for Template-Stripped Ultraflat Gold Substrates

A simple procedure using gold diffusion bonding for the preparation of template-stripped gold (TSG) surfaces is described. TSG surfaces are useful for surface studies because a very consistent flat gold surface with few defects can be easily prepared. We have developed a method of producing TSG surfaces that relies only on gold diffusion bonding rather than epoxies. The resulting substrates are free from concerns of solvent compatibility, heat stability, and impurities. Bonding of centimeter-sized substrates is performed at 300 degrees C for 2 h using a vise and aluminum foil.

Influence of the foundation layer on the layer-by-layer assembly of poly-L-lysine and poly(styrenesulfonate) and its usage in the fabrication of 3D microscale features.

The layer-by-layer (LBL) assembly of a polypeptide, poly-L-lysine (PLL), with poly(styrenesulfonate) sodium salt (PSS) on flat template-stripped gold (TSG) surfaces precoated with a self-assembled monolayer of alkanethiols terminated with positive (pyridinium), negative (carboxylic acid), and neutral [hexa(ethylene glycol)] groups is investigated. Both the topography and the rate of film thickness growth are found to be strongly dependent on the initial surface foundation layer. LBL assembly of PLL and PSS on patterned TSG surfaces produced by micro contact printing leads to structurally distinct microscale features, including pillars, ridges, and wells, whose height can be controlled with nanometer precision.

Potential control of horseradish peroxidase immobilization on gold electrode

A new approach based on potential control was firstly used for the immobilization of horseradish peroxidase (HRP) as the model protein. The self-assembly monolayer (SAM) was prepared with 2-aminoethanethiol (AET) on the gold electrode. The charge on HRP was adjusted by means of the acidity of the phosphate buffer solution (PBS) for dissolving the HRP. The influence of electric potential on HRP immobilization was investigated by means of colorimetric immunoassay of enzyme-substrate interaction (CIESI) using an automatic plate reader. The HRP modified electrodes were characterized with X-ray photoelectron spectroscopy (XPS) as well as atomic force microscope (AFM) on template-stripped gold surface. The potential for maximum immobilization of HRP was near the zero charge potential. The result indicates that controlled potential can affect the course of HRP immobilization without the loss of enzymic activity. It is of great significance for the control of biomolecular self-assembly and the intrinsic electric device.

Electric potential control of DNA immobilization on gold electrode

The assembly of synthetic, controllable molecules is one of the goals in nanotechnology. The primary objective of this contribution is to selectively immobilize DNA on gold via electric potential control. The self-assembly monolayer (SAM) was prepared with 2-aminoethanethiol (AET) on the gold electrode. A new approach based on electric potential was firstly used to control DNA immobilization covalently onto the SAM with the activation of 1-ethyl-3(3-dimethyl-aminopropyl)-carbodiimide (EDC) and N-hydroxysulfosuccinimide (NHS) in low ionic strength solution. The influence of electric potential on DNA immobilization was investigated by means of cyclic voltammogram, A.C. impedance, auger electron spectrometer as well as atomic force microscope (AFM) on template-stripped gold surface. The result proves that controlled potential can affect the course of DNA immobilization. More negative potential can restrain the DNA immobilization, while the more positive potential can accelerate the DNA immobilization. It is of great significance for the control of DNA self-assembly and will find wide application in the fields of DNA-based devices.

Template-stripped gold surfaces with 0.4-nm rms roughness suitable for force measurements: Application to the Casimir force in the 20–100-nm range

Using a template-stripping method, macroscopic gold surfaces with root-mean-square roughness $<~0.4 \mathrm{nm}$ have been prepared, making them useful for studies of surface interactions in the nanometer range. The utility of such substrates is demonstrated by measurements of the Casimir force at surface separations between 20 and 100 nm, resulting in good agreement with theory. The significance and quantification of this agreement are addressed, as well as some methodological aspects regarding the measurement of the Casimir force with high accuracy.

Origin of the multiple voltammetric desorption waves of long-chain alkanethiolate monolayers chemisorbed on annealed gold electrodes

Abstract This paper examines possible factors responsible for the voltammetric fine structure exhibited from the reductive desorption and oxidative redeposition of long-chain alkanethiolate monolayers on smooth gold electrodes. Results reveal that the fine structure is connected to the local order of the adlayer. This conclusion is based on a series of characterizations of monolayers formed from hexadecanethiol (HDT) and octadecanethiol (ODT) on annealed mica-supported gold (Au/mica) and on template-stripped gold (TSG). For annealed Au/mica, a pair of overlapping waves separated by 20–100 mV are found for both the desorption and the redeposition process. In contrast, the voltammetry of the TSG system exhibits a single wave for the two processes. Findings from morphological assessments (oxidative stripping of iodine, scanning tunneling microscopy, and underpotential metal deposition of lead) of the underlying substrates reveal that the differences in the voltammetry are connected to a subtle difference in the microscopic roughness of the two substrates. The morphological data indicate that the surfaces of annealed Au/mica and of TSG are strongly (111)-terraced, but that the sizes of the (111) terraces at TSG are significantly smaller. As a consequence, the TSG surface has a higher density of steps. Since the adlayer domain size is ultimately limited by the microscopic topography of the substrate, the voltammetric differences observed for the two types of substrates are attributed to differences in the ordering of the adlayer. A description of the differences in the processes for the desorption and redeposition is proposed and is examined within the context of recent interpretations.