Functionalization of a Self-Assembled Monolayer Driven by Low-Energy Electron Exposure (original) (raw)
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Electron Transmission through Self-Assembled Monolayers
The Journal of Physical Chemistry B, 1999
Electron transmission through a series of self-assembled monolayer films is studied using an iterative Green's function method with absorbing boundary conditions. The nuclear-electron interactions are calculated using suitable pseudopotentials, and the Hamiltonian is evaluated using a discrete variable representation. The presence of electronegative head groups on the metal surface gives rise to much lower transmission through the layers. The presence of these headgroups also produces asymmetric transmission effects where the transmission coefficient depends on the incident direction of the electron, as observed in recent STM measurements. Longer alkane chains (up to 18 carbon atoms) are more ordered due to the self-assembly process and have higher transmission coefficients at lower electron energies. This collective effect is observable experimentally and is not a property of single molecules in which transmission probabilities decay roughly exponentially with chain length.
Field effects on electron conduction through self-assembled monolayers
Applied Physics Letters, 2006
The electronic conduction through the self-assembled monolayer ͑SAM͒ can be modulated by the electric potential applied to the silicon gate electrode surrounding the SAM. The dependence of the current through SAM on the gate voltage can be explained that the renormalized molecular energy levels are swept through the window between the Fermi levels of the source and drain electrodes. The effects of the lowest unoccupied molecular orbital and a hybrid energy level near the Fermi level in the transmission spectrum can be identified.
Electron-beam-induced damage in self-assembled monolayers
Journal of Physical Chemistry, 1996
Highly organized monolayers formed from the self-assembly of octadecyl derivatives on oxide-covered Si and Ti substrates have been exposed to electron beam impact under typical conditions used in lithographic patterning. A combination of X-ray photoelectron spectroscopy, ellipsometry, infrared spectroscopy, and liquid drop contact angle measurements show that the major effect of irradiation is the loss of H, Via cleavage of C-H bonds, to form a carbonaceous residue with a surface containing oxygenated functional groups.
Rough and Fine Tuning of Metal Work Function via Chemisorbed Self-Assembled Monolayers
Advanced Materials, 2009
Many chemical and biochemical processes in nature involve charge transport across organic/inorganic interfaces, [1][2][3] which determines the performance of organic electronic devices. To achieve efficient charge transport between the electrode and organic molecules, the metal work function has to match the energy level of either the highest occupied or lowest unoccupied molecular orbitals of the molecule, which usually requires adjustments in the metal work function. One of the most common methods used for modification of metal work functions is the adsorption of organic layers. By adsorbing an organic layer onto the electrode surface, one creates a dipole barrier for the charge-carrier transport between the electrode and the organic electronic device. The surface dipole of the organic film depends on the dipole moment of the molecules forming the film, their electrostatic interactions and, for chemisorbed layers, the dipole at the interface due to partial charge transfer between the molecules and the surface. In particular, self-assembled monolayers (SAMs) of thiols are widely used for modification of the work function of gold electrodes. It has been shown that for these systems the charge transfer between the molecules and the gold is under 0.05e and, therefore, the chemical component of the interfacial dipole is negligibly small. The work-function change in these systems is thus mainly determined by the dipole moments of individual molecules, the structure of the monolayer, and dipole depolarization in the SAM. The electrostatic interaction inside SAMs leads to a decrease in the surface dipole of the SAM, compared to that expected from the gas-phase dipoles. Depolarization effects thus significantly decrease the accessible range of changes in SAM-induced metal work functions.
ACS Applied Materials & Interfaces, 2014
Self-assembled monolayers (SAMs) of organic molecules can be used to tune interface energetics and thereby improve charge carrier injection at metal−semiconductor contacts. We investigate the compatibility of SAM formation with high-throughput processing techniques. Therefore, we examine the quality of SAMs, in terms of work function shift and chemical composition as measured with photoelectron and infrared spectroscopy and in dependency on molecular exposure during SAM formation. The functionality of the SAMs is determined by the performance increase of organic field-effect transistors upon SAM treatment of the source/drain contacts. This combined analytical and device-based approach enables us to minimize the necessary formation times via an optimization of the deposition conditions. Our findings demonstrate that SAMs composed of partially fluorinated alkanethiols can be prepared in ambient atmosphere from ethanol solution using immersion times as short as 5 s and still exhibit almost full charge injection functionality if process parameters are chosen carefully. This renders solution-processed SAMs compatible with high-throughput solution-based deposition techniques.
Electrical properties of end-group functionalised Self-Assembled Monolayers
Microelectronic Engineering, 1997
In a previous study we have demonstrated that a single monolayer of alkyl-trichlorosilane molecules, covalently bonded to the native oxide of a silicon substrate, allows the fabrication of MIS (Metal-Insulator-Semiconductor) devices with excellent electrical properties [C.Boulas et AI., Phys. Rev. Lett. 76, 4797(1996)]. Here we demonstrate that we can ftmctionalise the end-groups of the molecules, once grafted to the substrate, without disturbing the excellent insulating properties of the monolayer. The functionalisation of the monolayer is monitored by FTIR and ellipsometry. Conductivity, photoconductivity and capacitance measurements are performed to study the effect of the chemical functionalisation on the electrical properties of the monolayer. Finally, possible sub-0.1 ttm device applications are presented.
Physical Chemistry Chemical Physics, 2011
Self-assembled organization of functional molecules on solid surfaces has developed into a powerful and sophisticated tool for surface chemistry and nanotechnology. A number of reviews on the topic have been available since the mid 1990s. This perspective article aims to focus on recent development in the investigations of electronic structures and assembling dynamics of electrochemically controlled self-assembled monolayers (SAMs) of thiol containing molecules on gold surfaces. A brief introduction is first given and particularly illustrated by a Table summarizing the molecules studied, the surface lattice structures and the experimental operating conditions. This is followed by discussion of two major high-resolution experimental methods, scanning tunnelling microscopy (STM) and single-crystal electrochemistry. In Section 3, we briefly address choice of supporting electrolytes and substrate surfaces, and their effects on the SAM structures. Section 4 constitutes the major body of the article by offering some details of recent studies for the selected cases, including in situ monitoring of assembling dynamics, molecular electronic structures, and the key external factors determining the SAM packing. In Section 5, we give examples of what can be offered by theoretical computations for the detailed understanding of the SAM electronic structures revealed by STM images. A brief summary of the current applications of SAMs in wiring metalloproteins, design and fabrication of sensors, and single-molecule electronics is described in Section 6. In the final two sections (7 and 8), we discuss the current status in understanding of electronic structures and properties of SAMs in electrochemical environments and what could be expected for future perspectives.