Aging of Hydrogenated and Oxidized Diamond

Abstract

Effective control of the surface properties of devices becomes more and more important to ensure their prolonged performance, as the size of devices diminishes to the nanoscale. At the nanoscale interfacial properties can differ from the macroscopic properties including conductivity, electron affinity, surface potential, and reactivity.[1] Here, we present a single-molecule sensor to detect molecular adsorption free energies in liquid under variable conditions. Utilizing atomic force microscopy (AFM), this approach provides nanoscale precision and excellent sensitivity to surface properties. This is demonstrated by the investigation of the aging of a diamond that was chemically modified to control its conductivity, surface potential, and wettability.Diamond exhibits extraordinary mechanical properties and is chemically inert as well as biocompatible. It is, therefore, suitable for biomedical applications [2,3] such as cell growth support [4,5] and as a refinement of medical indwelling devices. [6,7] In addition to the exceptional material characteristics, hydrogenated diamond exhibits p-type surface conductivity, whereas oxidized diamond is insulating.[8] These electronic properties have advanced the further development of diamond-based sensor devices, such as electrochemical sensors, [9] biosensors, [10,11] and ion-sensitive field effect transistors (ISFETs) in bioelectronics. [12][13][14] The application of diamond-based devices that take advantage of the unique surface properties of diamond, be it in air, in aqueous solution, or even in blood, necessitates stable surface conditions and interfacial properties in order to ensure the long lasting functionality of the device. Only the limited chemical stability under physiological conditions has hampered the implementation of silicon and other semiconductive materials into similar devices. Implanted medical devices should stay intact for months or even years without the need for removal due to restricted biocompatibility and foreign body reactions.We utilize single-molecule force spectroscopy (SMFS) in order to determine the adsorption free energy of poly(allylamine) (PAAm) on diamond surfaces of different termination and different age (Fig. 1A). In contrast to macroscopic setups, which suffer from bubbles and cavitation effects hampering equilibration, [15] our single-molecule approach allows for equilibration to be achieved on the experimental time scale. The forced desorption under equilibrium conditions is defined by a velocity-independent plateau of constant force over a separation defined by the polymer contour length and, thus, allows for a direct determination of the adsorption free energy per unit length from the area under the plateau curve (Fig. 1B).[16] The distribution of plateau forces for H-and O-terminated diamond are given in Figure 1C. The general observed trend of measuring higher adsorption forces and therefore higher free energies on freshly prepared, hydrophobic diamond compared to hydrophilic diamond is reversed after two months and can be r...

Hydrogen termination of CVD diamond films by high-temperature annealing at atmospheric pressure

“…15 These results show that the H plasma and H 2 -treatment at atmospheric pressure produce surfaces with similar hydrophobicity.…”

In Situ Assembly in Confined Spaces of Coated Particle Scaffolds as Thermal Underfills with Extraordinary Thermal Conductivity

“…26,27 For better observation, spherical silica particles were used to illustrate the filling process. Figure 3a is the assembled silica particle bed via centrifugation.…”

Optical spectroscopy of the surface of nanoporous diamond films

“…2 and 3, after UNC diamond films are oxidized and kept a prolonged time under normal conditions (~(1-3)⋅10 4 h), in the spectra absorption bands of hydride, hydroxyl, and carboxyl groups predominate. Polyfunctionality of the diamond surface is typical for both ultradispersed diamonds made by detonation synthesis [39,48] and for CVD diamonds, for which in- dependently of the initial state of the surface (hydrophobic or hydrophilic after hydrogenation and oxidation respectively), the wetting angle for water after a few months is ~60 o [15]. In order to eliminate the contribution of physically adsorbed molecules, we made measurements before and after evacuating the samples (10 -2 torr, 100 h), which did not change the intensities of the bands for stretching and bending vibrations of CH x groups but led to a sharp decrease in the absorption band with maximum at 1709 cm -1…”

“…Nanocrystalline CVD diamond films, owing to their smooth surface, their suitability for industrial production, their low cost when deposited on a substrate of large surface area and their compatibility with the electronic interface in devices with a planar configuration, are optimal materials for making fast-response gas sensors [12] and biological interfaces [13] operating over a broad temperature range. However, the mechanisms and functional groups responsible for changes under normal conditions in conductivity [14], wettability [15], and coefficient of friction [16] of the diamond surface have been inadequately studied.…”