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Electron emission plays an important role in diverse applications, from cold cathodes to chemical processes (solvated electrons, water purification), energy generation (thermionic or dye-sensitized solar cells), and even cancer treatment. Here we show that by surface treatment using electrochemically grown polypyrrole the secondary-electron emission and photoelectron emission from boron-doped diamond is enhanced even above the intensity of electron emission from the hydrogen-terminated surface with negative electron affinity. This enhancement is stable in air for at least one month and it persists also in vacuum after thermal annealing. Scanning electron microscopy, Kelvin probe force microscopy, total photoelectron yield spectroscopy as well as surface mapping by Auger and secondary ion mass spectroscopies are used to characterize and correlate the surface electronic and chemical properties. A model of the electron emission enhancement is provided.

Recent interest in industrial and medical usage of carbon nanomaterials arises the need for approved testing protocols for characterizing their interaction with living systems. Nanocrystalline diamond (NCD) films were chosen as a promising material for such investigation due to their unique mechanical properties, chemical stability and biocompatibility. In this study, we examined the anti-adhesive properties of differently terminated NCD films deposited by plasma-enhanced CVD on glass or silicon against Escherichia coli bacterium. We focused on the influence of cultivation medium in this process and compared bacterial adhesion to H-, O- and F-terminated NCD films in complex Luria-Bertani (LB) and mineral (M9) cultivation media that substantially differ in the content of organic molecules and thus in the potential of conditioning film formation. We found the properties of NCD films to be independent of the base substrate, as the amount of biofilm was comparable for both NCD films deposited on glass and on silicon. The anti-adhesive effect was observed only in the mineral medium where hydrogen and fluorine terminated NCD films reduced bacterial adhesion by ca. 50%. In complex medium we did not observe the reduction of bacterial adhesion. These differences are attributed to the passivation of the H- or F-terminated NCD films by organic molecules adsorbed from the complex medium. For O-terminated NCD films, no anti-adhesive effect was observed, regardless of the cultivation medium. Our results show that the growth of Escherichia coli in mineral cultivation medium can be affected by the diamond atomic termination.

Samples of a palladium catalyst for direct formic acid fuel cell (DFAFC) applications were prepared on the Elat ® carbon cloth by magnetron sputtering. The quantity of Pd was equal to 3.6, 120 and 720 μg/cm 2 . The samples were tested in a fuel cell for electro-oxidation of formic acid, and were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The XPS measurements revealed a high contribution of PdC x phase formed at the Pd/Elat ® surface interface, with carbon concentration in PdC x from x = 9.9–14.6 at.%, resulting from the C substrate and CO residual gases. Oxygen groups, e.g. hydroxyl (–OH), carbonyl (C O) and carboxyl (COOH), resulted from the synthesis conditions due to the presence of residual gases, electro-oxidation during the reaction and oxidation in the atmosphere. Because of the formation of CO and CO 2 on the catalysts during the reaction, or because of poisoning by impurities containing the –CH 3 group, together with the risk of Pd losses due to dissolution in formic acid, there was a negative effect of catalyst degradation on the active area surface. The effect of different loadings of Pd layers led to increasing catalyst efficiency. Current–voltage curves showed that different amounts of catalyst did not increase the DFAFC power to a great extent. One reason for this was the catalyst structure formed on the carbon cloth. AFM and SEM measurements showed a layer-by-layer growth with no significant variations in morphology. The results for electric power recalculated for the Pd loading per 1 mg of catalyst layers in comparison to carbon substrates decorated by Pd nanoparticles showed that there is potential for applying anodes for formic acid fuel cells prepared by magnetron sputtering.

Diamond is considered as a promising tissue equivalent material in radiation therapies as well as for bio-electronic sensors due to its unique set of properties. These features are combined in this work where effects of gamma irradiation ( 60 Co, up to 300 Gy) on function and stability of microscopic (60 × 20 μm 2 ) hydrogen-terminated diamond (H-diamond) solution-gated field effect transistors (SG-FETs) are studied. The H-diamond SG-FETs were prepared using 300 nm thin diamond films deposited on glass from methane and hydrogen gas mixture by microwave plasma. Prior to gamma irradiation they were interfaced to proteins (fetal bovine serum) and cells (human sarcoma osteogenic cell line — SAOS2) in cell growth medium. Blank H-diamond SG-FETs did not degrade after the irradiation. With adsorbed proteins and cells they showed specific changes in gate current characteristics (about 100% increase) after the irradiation. These current changes are attributed to modified protein layer and cell morphology on the diamond surface. The presented results establish a first step towards real-time electronic monitoring of cell growth during the irradiation by therapeutically relevant doses.

The study of the chemical composition of buried interfaces by X-ray photoelectron spectroscopy (XPS) is limited by the inelastic mean free path of emitted photoelectrons (PE). Soft X-ray sources (AlKα) are generally suitable for careful probing of surfaces or very thin films. Here we applied gas cluster ion beam sputtering in combination with in-situ XPS (GCIB-XPS) to analyze buried GaP/Si(0 0 1) heterointerfaces. The GCIB method was used to dig a crater into the 20 nm thick GaP(0 0 1) film. We found optimal parameters for GCIB sputtering and achieved interface layers without severe damage. Destructive effects, i.e. broadening of core level peaks, could not be completely avoided, however, and the formation of metallic Ga on the GaP surface was observed. PE spectra of the sputtered heterostructures were compared with corresponding reference spectra of sputtered bulk crystals. Interface contributions to the intensity of phosphorus and sillicon core level peaks were revealed: interface components are shifted to high binding energies of P 2p Si 2p core levels. Similar results were obtained on 4 nm thick GaP/Si(0 0 1) by XPS. Finally, a top-to-bottom concept for buried semiconductor interfaces studies by GCIB-XPS is demonstrated.

The work presented here aimed to synthesize the non-conducting form of PANI nanofibrils and to study their properties, which are determined by their chemical structure and morphology. Non-conducting PANI nanofibrils were synthesized by an alkali-based treatment process. Raman measurements revealed that synthesized PANI nanofibrils consist mainly of benzenoid units with a small number of quinoid units. Calculations based on Raman spectra show that ratio of benzenoid to quinoid units is 3:1. This ratio is 3 times higher than the characteristic/typical value for synthesized non-conducting PANI, as reported in the literature. Moreover, the photoluminescence of these non-conducting PANI nanofibrils (measured with excitation of 442 nm) possesses two maxima, with wavelengths of 550 nm and 1110 nm. These wavelengths correspond to photon energies of 2.25 eV and 1.12 eV, which resemble very long Stokes shifts of 108 nm and 658 nm, respectively. This finding has not been presented previously. However, when the excitation is performed with a 785 nm red laser, the emission spectra of non-conducting PANI nanofibrils exhibit numerous sharp emission peaks. We attribute these transitions to the chemical structure of the synthesized polymer chains and to its nanofibril morphology.

Tailorable surface termination of nanocrystalline diamond (NCD) and diamond-like carbon (DLC) films significantly contribute to their wide potential applications in biomedicine which require defined and stable surface towards aging. Here, we present a comparative study on the surface termination stability of NCD and DLC films in terms of XPS and water contact angle (WCA) measurements. The samples were plasma-treated with hydrogen, oxygen or nitrogen containing functional groups employing low temperature radio frequency (RF) or high temperature microwave (MW) plasma. The samples were exposed to air up to 30 days, during which the termination stability was analyzed by XPS, WCA, AFM, Raman spectroscopy and SEM measurements. It was shown that NCD films were more efficiently hydrogenated in the high temperature MW plasma than in RF plasma, and also the surface stability was better. However, the MW plasma deteriorated the surface of the DLC film. In RF plasma treatment, a contrast between WCA and XPS data was observed. Surprisingly, while the XPS measurements showed relatively stable surface termination for all cases (H-, O- and NH2-terminated surfaces), the WCA values for O- and NH2-treated samples increased by ~200 ÷ 300%. Generally, the NCD film showed more stable surface termination than DLC. The possible reasons of the different behavior of WCA and XPS results, as well as complex characterization of the surface properties of H-, O- and NH2-terminated NCD and DLC film regarding to the aging and surface termination stability are discussed in the article.

Diamond exhibits good biocompatibility and a large electrochemical potential window, and thus, it is particularly suitable for bio-functionalization and bio-sensing. Modification of the diamond surface can be achieved through mussel-inspired surface chemistry based on polydopamine (PDA) while maintaining the intrinsic properties of the surface. We present a comparative study on the polymerization/deposition of PDA from an aqueous solution of dopamine on hydrogen- (H) and oxygen- (O) terminated nanocrystalline diamond films (NCD). The dopamine polymerization/deposition was performed under mild conditions, which resulted in a confluent PDA layer. A detailed investigation of the growth kinetics of the PDA film on H- and O-terminated NCD substrates was performed using spectroscopic ellipsometry. The chemical composition, the functional group distribution, the surface topography and the wetting properties of the adherent PDA films were evaluated using X-ray photoelectron spectroscopy, atomic force microscopy and water contact angle goniometry, respectively. According to the results, a PDA layer can be used as a platform for future bio-functionalization and/or optical bio-sensing applications.

We employ nanocrystalline diamond (NCD) thin films with average grain sizes of 250 and 80 nm to resolve influence of grain boundaries and sp 2 phase on protein adsorption and electronic function of solution-gated field-effect transistors (SGFET). Microscopic (20 μm × 60 μm) SGFETs are fabricated without gate oxides based on hydrogen-terminated NCD films on glass substrates. We show that NCD with grain sizes down to 80 nm and film thickness of 100 nm is fully operational as SGFET. We find that inherent hysteresis of SGFET transfer characteristics, their reaction time, their negative shift after protein adsorption and cell culturing process, low gate leakage currents and no influence of UV sterilization or rinsing are all independent of the NCD grain size. Thus we propose a microscopic model where the function of NCD SGFET is determined by the H-terminated surface of diamond nanocrystals and its interaction with proteins, not by grain boundaries or sp 2 phase in general.

The nanocrystalline diamond (NCD) layers were grown by the large area (linear plasma) MWCVD on polished silicon substrates with and without intermediate mirror-like metallic coatings. The optical reflectance and Raman spectroscopy in the ultraviolet, visible and near infrared region (UV–VIS–NIR) reveals the thickness and the optical quality of NCD layers. The modified grazing angle reflectance (GAR) spectroscopy is applied in the mid infrared region 800–4000/cm to detect the molecular vibrations (functional groups) at the functionalized NCD surface. The optical absorbance of functionalized NCD surface is evaluated from p-polarized reflectance spectra measured at Brewster angle of incidence (BAR) to eliminate the interference fringes. We report a significant enhancement of sensitivity of BAR using NCD growth on metal mirrors.

We investigate the role of fetal bovine serum (FBS) proteins in the assembly of osteoblastic cells (SAOS-2) in McCoy's 5A medium on synthetic monocrystalline and nanocrystalline diamonds having H- and O-terminated array patterns. We characterize i) adhesion of proteins and cells to diamond by shaking experiments (1000 rpm), fluorescence, and atomic force microscopy, ii) distribution of FBS proteins by micro-Raman spectroscopy, and iii) influence of pre-adsorbed specific FBS proteins (albumin, fibronectin, vitronectin) on the cell assembly. There is 40% lower adhesion of cells on H-terminated diamond with adsorbed FBS compared to this surface without FBS as well as to O-terminated surfaces. Spatially resolved Raman spectroscopy of C―H stretching bands around 2900 cm− 1 showed uniform coverage of H/O-diamond by the albumin in more than 50 nm thick FBS layers. The other FBS proteins were not detectable by Raman. Pre-adsorption of the specific proteins prior to cell plating indicated that the cell preference to O-terminated diamond is controlled by the fibronectin rather than by the albumin. We discuss the data with a view to the cell preferential assembly on H/O-diamond micro-arrays.

article i nfo We investigate adsorption of fetal bovine serum (FBS), a crucial component for cell growth, on intrinsic CVD mono-crystalline diamond with hydrogen and oxygen surface terminations. The surface terminations are prepared by oxygen and hydrogen plasma process. The FBS adsorption is done by immersing diamond into McCoy's 5A medium supplemented with 15% FBS for 10 s-24 h. After rinsing the samples are characterized in the McCoy's medium and for comparison also in air by atomic force microscopy (AFM). By optimized measurements of AFM topography in oscillating regime and by using advanced AFM regimes such as phase imaging, nanoshaving, and force spectroscopy we characterize FBS thickness, adhesion, conformation and selectivity on the H/O-diamond surfaces. We find that FBS is adsorbed in about the same monolayer thickness (2-4 nm) on both H/O-diamond surfaces, yet the protein conformation is different. We present a schematic model.

We show correlation of microscopic surface quality and morphology of nanocrystalline diamond films as a function of deposition temperature and post-growth acid treatment detected by atomic force microscopy in phase detection regime, X-ray photoelectron spectroscopy, X-ray induced Auger electron spectroscopy, Scanning Electron Microscopy, Raman spectroscopy, and the electrical conductivity of H-terminated diamond surfaces. The correlation reflects the decrease in sp 2 amount and enhanced surface conductivity of the diamond surface after the chemical treatment. These results indicate that the AFM phase can detect clearly and microscopically carbon sp 2 phase on facets and grain boundaries of nanocrystalline diamond films.