Nanodiamonds (NDs) represent a novel nanomaterial applicable from biomedicine to spintronics. Here we study ability of air annealing to further decrease the typical 5 nm NDs produced by detonation synthesis. We use atomic force microscopy (AFM) with sub-nm resolution to directly measure individual detonation nanodiamonds (DNDs) on a flat Si substrate. By means of particle analysis we obtain their accurate and statistically relevant size distributions. Using this approach, we characterize evolution of the size distribution as a function of time and annealing temperature: i) at constant time (25 min) with changing temperature (480, 490, 500°C) and ii) at constant temperature (490°C) with changing time (10, 25, 50 min). We show that the mean size of DNDs can be controllably reduced from 4.5 nm to 1.8 nm without noticeable particle loss and down to 1.3 nm with 36% yield. By air annealing the size distribution changes from Gaussian to lognormal with a steep edge around 1 nm, indicating instability of DNDs below 1 nm.

Atomic force microscopy (AFM) is used to measure local electrical conductivity of HPHT nanodiamonds (NDs) dispersed on Au substrate in the as-received state and after thermal or plasma treatments. Oxygen-treated NDs are highly electrically resistive, whereas on hydrogen-treated NDs electric current around -200 pA at -2 V is detected. The as-received NDs as well as NDs after an underwater radio-frequency (RF) plasma or laser irradiation (LI) treatments contain both electrically conductive (two types: highly and weakly conductive) and highly resistive particles. The higher conductivity is attributed to H-terminated (RF) or graphitized (LI) NDs. The lower conductivity is attributed to NDs with hydrogenated amorphous carbon shell.

Macroscopic and microscopic photovoltage characteristics of detonation nanodiamonds (DNDs) with distinct surface terminations are presented. Organic photodiodes are fabricated based on P3HT+DNDs mixture (50 wt%). We compare effect of hydrogen and oxygen termination of DNDs. Compared to photodiodes without DNDs the current-voltage characteristics of photodiodes with O-DNDs in dark and under AM 1.5 illumination show reduced dark current, and higher photocurrent and open circuit voltage. H-DNDs shunt the photodiodes, which is attributed to their surface conductivity. Kelvin probe force microscopy detects a reproducible photovoltage of around 5 mV generated by a green laser (532 nm) on both types of pristine DNDs. Thus although conductivity of H-DNDs may represent a problem for photodiodes, both types of DNDs alone can function as miniature energy conversion devices.

We employ UV photolithographic and electron beam lithographic patterning of diamond seeding layer on SiO2/Si substrates for the selective growth of micrometer and sub-micrometer diamond patterns. Using bottom-up strategy, thin diamond channels (470 nm in width) are directly grown. Differences between wet chemical and plasma treatment on the patterned diamond growth are studied. We find that the density of parasitic diamond crystals (outside predefined patterns) is lowered for gas mixture CF4/O2 plasma than for rich O2 plasma. After CF4/O2 plasma treatment, the density of parasitic crystals is 106 cm-2 which is comparable to the wet chemical treatment. Introducing sandwich-like structure, i.e. photoresist-seeding layer-photoresist, and its treatment (lift-off and CF4/O2 plasma) further reduces the density of parasitic crystals down to 105 cm-2. The advantage of this novel treatment is short processing time, simplicity, and minimal damage of the substrate surface.

Charge transport in hydrogenated microcrystalline silicon (µc-Si:H) is determined by structure on several size scales: i) local atomic arrangement (<1 nm), ii) crystalline grains and their boundaries (1-10 nm), iii) grain aggregates or columns (0.1-1 µm) and finally iv) features comparable to layer thickness (0.1-10 µm). We first summarize our experimental results concerning these effects: differences of conductivities of grains and amorphous tissue measured locally by conductive AFM, transport anisotropy observed by comparing dark conductivity and ambipolar diffusion length parallel and perpendicular to the substrate, and finally thickness dependence of transport parameters (e.g. dark conductivity activation energy and prefactor). Most of these phenomena can be described by using a novel model of the µc-Si:H growth leading to a structure known as Voronoi adjacency network. The model is based on the nearest neighbor constrained growth. To our knowledge, the Voronoi structure is the first structural model able to predict structure and transport properties of the µc-Si:H and it may become a basis for the future predictive model of µc-Si:H based solar cells.