Structural Characterization of Aldehyde-Terminated Self-Assembled Monolayers

Abstract

The structure of aldehyde-terminated alkanethiol self-assembled monolayers (SAMs) on Au(111) is investigated using scanning tunneling microscopy (STM), atomic force microscopy (AFM), and density functional theory (DFT) calculations. For the first time, the structures of aldehyde-terminated SAMs are revealed with molecular resolution. SAMs of 11-mercapto-1-undecanal exhibit the basic (radical3xradical3)R30 degrees periodicity and form various c(4x2) superstructures upon annealing. In conjunction with DFT studies, the models of the (radical3xradical3)R30 degrees and the c(4x2) superstructures are constructed. In comparison with alkanethiol SAMs, the introduction of aldehyde-termini results in smaller domain size, lower degree of long-range order, large coverage of disordered areas, and higher density of missing molecules and other point defects within domains of closely packed molecules. The origin of these structural differences is mainly attributed to the strong dipole-dipole interactions among the aldehyde termini.

Deformation and Hyperfine Structures of Dendrimers Investigated by Scanning Tunneling Microscopy

“…Fourth generation PAMAM-OH dendrimer solutions (10% weight in methanol, Sigma-Aldrich), fifth generation PAMAM-OH dendrimer solutions (5% weight in methanol, Sigma-Aldrich), n-octanethiol (98%, Sigma-Aldrich), and ndecanethiol (96%, Sigma-Aldrich), referred to hereafter as C 8 and C 10 27 The substrate mica was maintained via two quartz lamps at 350°C under a base pressure of 2 × 10 -7 Torr. The evaporation rate was 0.3 nm/s and final thickness of Au films were 170-190 nm.…”

Surface plasmon resonance for detecting clenbuterol: Influence of monolayer structure

“…The monolayer structure is considered to influence the sensitivity and stability; therefore, researchers direct their efforts to form an ideal monolayer structure that is close-packed and defect-free. However, analyses by the scanning probe microscope reveal that monolayers consist of ordered and disordered domains [20][21][22][23][24].…”

High-Resolution Imaging of Polyethylene Glycol Coated Dendrimers via Combined Atomic Force and Scanning Tunneling Microscopy

“…A silicon cantilever (AC-240, Olympus) was used for imaging and nanoshaving. The probe has a typical force constant of k = 1.0 N/m as measured by the thermal noise method [ 16 , 18 , 20 , 21 ]. During tapping mode imaging, the cantilever was modulated by a driving frequency of 74 kHz and amplitude of 87 nm (1.0 V).…”

“…STM images were taken using a walker-type scanner (UHV 300, RHK Technologies, Inc.), under ambient pressure and temperature [ 18 , 19 ]. STM tips were prepared by etching tungsten wires electrochemically at 2.0 V in 3.0 M NaOH solutions using a homemade potentiostat to monitor the etching process [ 18 , 19 ]. All STM images were acquired in constant current mode with typical bias voltages ranging from 0.4 to 0.9 V and tunneling currents from 10 to 40 pA.…”