Abstract
The stability of the molecular self-assembled monolayers (SAMs) is of vital importance to the performance of the molecular electronics and their integration to the future electronics devices. Here we study the effect of electron irradiation-induced cross-linking on the stability of self-assembled monolayer of aromatic 5,5′-bis(mercaptomethyl)-2,2′-bipyridine [BPD; HS-CH2-(C5H3N)2-CH2-SH] on Au (111) single crystal surface. As a refence, we also study the properties of SAMs of electron saturated 1-dodecanethiol [C12; CH3-(CH2)11-SH] molecules. The stability of the considered SAMs before and after electron-irradiation is studied using low energy Ar+ cluster depth profiling monitored by recording the X-ray photoelectron spectroscopy (XPS) core level spectra and the UV-photoelectron spectroscopy (UPS) in the valance band range. The results indicate a stronger mechanical stability of BPD SAMs than the C12 SAMs. The stability of BPD SAMs enhances further after electron irradiation due to intermolecular cross-linking, whereas the electron irradiation results in deterioration of C12 molecules due to the saturated nature of the molecules. The depth profiling time of the cross-linked BPD SAM is more than 4 and 8 times longer than the profiling time obtained for pristine and BPD and C12 SAMs, respectively. The UPS results are supported by density functional theory calculations, which show qualitative agreement with the experiment and enable us to interpret the features in the XPS spectra during the etching process for structural characterization. The obtained results offer helpful options to estimate the structural stability of SAMs which is a key factor for the fabrication of molecular devices.
Highlights
The stability of the molecular self-assembled monolayers (SAMs) is of vital importance to the performance of the molecular electronics and their integration to the future electronics devices
SAMs of both C12 and BPD molecules were characterized by X-ray photoelectron spectroscopy (XPS) before and after the electron irradiation through the S2p and the C1s core level spectra with a particular focus on the deconvolution of the S2p and C1s signals
XPS signals of the non-radiated C12 SAM show well defined splitting of S2p spectrum with the main maximum located at 162.0 eV (Fig. 1a), which corresponds to the thiol sulfur in the S–Au bonding cascade
Summary
The stability of the molecular self-assembled monolayers (SAMs) is of vital importance to the performance of the molecular electronics and their integration to the future electronics devices. Molecular electronics, implementing organic molecules as building blocks, has a great potential to substitute the silicon technology at the nanoscale due to exceptional physical and chemical properties that molecular systems can p rovide[1,2] In this field, the molecular self-assembly is becoming a standard tool in nanofabrication, which enables one to create interface structures with enhanced functionalities. Self-assembled monolayers (SAMs) of thiol-end molecules on noble metal surfaces are promising hybrid systems for practical applications in electronics due to high stability and outstanding electronic and transport properties. Such systems are suitable for large scale production due to easy preparation, materials availability, and large surface coverage at low cost. Berdiyorov and Hamoudi used first-principles calculations to study the effects of molecular backbone and anchoring groups on the transport properties of aromatic molecules sandwiched between metallic electrodes[13,14]
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