Covalent Attachment of Diamondoid Phosphonic Acid Dichlorides to Tungsten Oxide Surfaces

Abstract

Diamondoids (nanometer-sized diamond-like hydrocarbons) are a novel class of carbon nanomaterials that exhibit negative electron affinity (NEA) and strong electron-phonon scattering. Surface-bound diamondoid monolayers exhibit monochromatic photoemission, a unique property that makes them ideal electron sources for electron-beam lithography and high-resolution electron microscopy. However, these applications are limited by the stability of the chemical bonding of diamondoids on surfaces. Here we demonstrate the stable covalent attachment of diamantane phosphonic dichloride on tungsten/tungsten oxide surfaces. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy revealed that diamondoid-functionalized tungsten oxide films were stable up to 300-350 °C, a substantial improvement over conventional diamondoid thiolate monolayers on gold, which dissociate at 100-200 °C. Extreme ultraviolet (EUV) light stimulated photoemission from these diamondoid phosphonate monolayers exhibited a characteristic monochromatic NEA peak with 0.2 eV full width at half-maximum (fwhm) at room temperature, showing that the unique monochromatization property of diamondoids remained intact after attachment. Our results demonstrate that phosphonic dichloride functionality is a promising approach for forming stable diamondoid monolayers for elevated temperature and high-current applications such as electron emission and coatings in micro/nano electromechanical systems (MEMS/NEMS).

Derivatization of diamondoids for functional applications

“…[144][145][146] The inherent photoluminescence [149][150][151] and the tunable electronic properties [152][153][154] have also been applied in a wide range of new optical devices. Initially, the applications of diamondoids focused on taking advantage of the inherent properties of diamondoids, such as excellent mechanical/thermal properties and biocompatibility.…”

“…[140][141][142][143] These binding energies vary with diamondoid monolayer structure and thiol substitution position, consistent with different degrees of steric strain and electronic interaction with the substrate. [144][145][146] But the optical properties of the diamondoids are strongly affected due to a drastic change in the occupied states. 7).…”

Nanotechnology of diamondoids for the fabrication of nanostructured systems

“…It has been found that adamantane-thiol is easily displaced by alkane-thiol [144], indicating the weak bonding strength between the adamantane-thiol and the Au substrate. To solve this problem, Melosh and coworkers [145] have developed a new approach to fabricate the photoemission surface based on the attachment of the diamantane phosphonic dichloride monolayer on tungsten/tungsten oxide. The formation of covalent bonds between the phosphonate and the substrate has been confirmed by high-resolution X-ray photoemission spectroscopy.…”

Transition metal complexes with cage-opened diamondoid tetracyclo[7.3.1.14,12.02,7]tetradeca-6.11-diene

“…Email: Siegfried.Schindler@chemie.uni-giessen.de Downloaded by [New York University] at 10: 27 21 July 2015 and effective electron emitting properties [16,17]. These are characteristic for self-assembled diamondoid derivatives on metal surfaces [18].…”