Formation and Thermal Stability of Ordered Self-Assembled Monolayers by the Adsorption of Amide-Containing Alkanethiols on Au(111)

Abstract

We examined the surface structure, binding conditions, electrochemical behavior, and thermal stability of self-assembled monolayers (SAMs) on Au(111) formed by N-(2-mercaptoethyl)heptanamide (MEHA) containing an amide group in an inner alkyl chain using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) to understand the effects of an internal amide group as a function of deposition time. The STM study clearly showed that the structural transitions of MEHA SAMs on Au(111) occurred from the liquid phase to the formation of a closely packed and well-ordered β-phase via a loosely packed α-phase as an intermediate phase, depending on the deposition time. XPS measurements showed that the relative peak intensities of chemisorbed sulfur against Au 4f for MEHA SAMs formed after deposition for 1 min, 10 min, and 1 h were calculated to be 0.0022, 0.0068, and 0.0070, respectively. Based on the STM and XPS results, it is expected that the formation of a well-ordered β-phase is due to an increased adsorption of chemisorbed sulfur and the structural rearrangement of molecular backbones to maximize lateral interactions resulting from a longer deposition period of 1 h. CV measurements showed a significant difference in the electrochemical behavior of MEHA and decanethiol (DT) SAMs as a result of the presence of an internal amide group in the MEHA SAMs. Herein, we report the first high-resolution STM image of well-ordered MEHA SAMs on Au(111) with a (3 × 2√3) superlattice (β-phase). We also found that amide-containing MEHA SAMs were thermally much more stable than DT SAMs due to the formation of internal hydrogen networks in MEHA SAMs. Our molecular-scale STM results provide new insight into the growth process, surface structure, and thermal stability of amide-containing alkanethiols on Au(111).

Molecular Self-Assembly and Adsorption Structure of 2,2′-Dipyrimidyl Disulfides on Au(111) Surfaces

“…The binding energies of the 2p 3/2 peaks of S1, S2, and S3 species for three SAM samples were observed at around 160.95–161.29, 162.04–162.12, and 163.38–163.68 eV, respectively, suggesting the presence of three sulfur species in the SAMs. S1 and S2 peaks are assigned to bound sulfurs on the gold surface, whereas the S3 peak is assigned to unbound sulfur, as demonstrated by many previous works [ 6 , 9 , 16 , 49 , 50 , 51 , 52 , 53 ]. Similarly bound S2 peaks with a strong intensity are usually observed for closely packed various thiolate SAMs on the gold surface, whereas similarly bound S1 peaks with weak intensity are often observed for loosely packed thiolate SAMs, and/or as a result of the existence of atomic sulfurs formed via the cleavage of S-C bonds during SAM formation of S-containing organic molecules, or formed via the thermal decomposition of thiolate SAMs on gold [ 6 , 49 , 50 ].…”

“…Figure 5 shows XPS peaks in the region of S 2p for 2PymS SAMs on Au(111) formed in a 0.01 mM at different solution pH values: (a) pH = 2, (b) pH = 7, and (c) pH = 12. It is well known that the S 2p peak appeared as a doublet consisting of 2p 3/2 and 2p 1/2 components in a 2:1 intensity ratio due to spin–orbital splitting [ 6 , 9 , 16 , 49 , 50 , 51 ]. XPS measurements revealed the existence of three sulfur peaks labeled S1 (red color), S2 (blue color), and S3 (green color) for 2PymS SAMs on Au(111).…”

“…Self-assembled monolayers (SAMs) provide a very convenient and powerful method to control the surface and interface characteristics of various metal surfaces via modifying the chemical structure of adsorbates with different active anchoring groups and molecular backbones [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. Due to their advantages, SAMs have been applied to various nanotechnological applications in nanopatterning [ 1 ], biosensors [ 11 ], bioelectronics [ 12 ], solar cells [ 13 , 14 ], and molecular electronics [ 15 , 16 , 17 , 18 ].…”

Rationale Design for Anchoring Pendant Groups of Zwitterionic Polymeric Medical Coatings

“…The major contributing factors for having a dense 2-AE on stainless steel are the coordinative binding of carboxylic acids onto metal oxides and internal hydrogen bond networks between amide groups . The van der Waals forces between alkyl spacers of 11-AU did not seem to help the formation of a tightly packed and well-ordered thin film on the steel.…”

Specific Detection of Uropathogenic Escherichia coli via Fourier Transform Infrared Spectroscopy Using an Optical Biosensor

“…This response involves several steps that are crucial for the fabrication of biosensors, such as the use of novel materials as substrates. , Substrates based on silicon (Si) have shown promising results in biomaterial applications (micro- and optoelectronic devices, memory chips, and sensitive biosensors) due to their semiconducting properties and biocompatibility; in addition, surface modifications and biomolecule anchoring can be easily achieved . Silicon is a material that, through chemical modification of the surface through the creation of self-assembled monolayers (SAMs), can obtain interfacial properties on its surface . SAMs are organized into three groups: the first is a group that binds to the surface and is known as the anchoring group; the second is a linker group that joins the anchoring group with the terminal or final group; and the latter determines the properties of the surface after SAMs treatment.…”