Effect of treatment temperature on the amination of chlorinated diamond

The amination of a diamond surface was investigated by treatment of chlorinated diamond in an ammonia environment at various temperatures. The chlorinated diamond was prepared by irradiating hydrogenated diamond with ultraviolet (UV) light in the presence of elemental chlorine. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of the chlorinated diamond showed a strong peak corresponding to the C–Cl stretching mode, which has not been reported in previous studies on chlorinated diamonds. The types of amines formed on the diamond surface were strongly affected by the temperature used for the reaction. DRIFT spectra of aminated diamonds indicate that amination at room temperature results in formation of NH₄⁺. Amination at 373 K showed DRIFT peaks corresponding to CN vibration and NH₂ scissoring. At an amination temperature of 573 K, most of the nitrogen on the surface was present as imines.     

Immobilization of horseradish peroxidase via an amino silane on oxidized ultrananocrystalline diamond

We discuss the complete functionalization of nitrogen-doped ultrananocrystalline diamond (UNCD) films, starting from an oxidized surface. First, the presence of hydroxyl groups on oxidized nanocrystalline diamond (NCD) was confirmed by fluorescence microscopy. Next, the grafting of a linker molecule such as 3-aminopropylmethyldiethoxysilane on oxidized NCD was confirmed by fluorescence microscopy and X-ray photoelectron spectroscopy (XPS). Then the horseradish peroxidase (HRP) enzyme was immobilized on silane-modified initially oxidized UNCD. The HRP-modified UNCD was characterized by electrochemical techniques, such as faradaic cyclic voltammetry and the amperometric response to H₂O₂. This response to H₂O₂ is discussed in terms of the layer-by-layer configuration used and the electronic properties of conducting UNCD.     

Plasma amination of ultrananocrystalline diamond/amorphous carbon composite films for the attachment of biomolecules

Ultrananocrystalline diamond/amorphous carbon nanocomposite films (UNCD/a-C) have been deposited by microwave plasma chemical vapour deposition at 600 °C from 17% CH₄/N₂ mixtures. The as-grown films turned out to be hydrogen terminated and very stable. Photochemical amination of H-terminated diamond is a well-established route to attach functional groups to such surfaces for applications in biosensors. Here we report on experiments to aminate UNCD surfaces directly by exposure to ammonia plasmas. Thereafter the surfaces were reacted with the heterobifunctional crosslinker molecule SSMCC bearing a N-hydroxysuccinimide (NHS) ester group which should react with the surface NH₂ groups. By means of X-ray photoelectron spectroscopy (XPS), contact angle measurements and fluorescence microscopy it is shown that both steps, plasma amination and SSMCC attachment lead to the desired aims. On the other hand, experiments to attach a thiol-bearing fluorescein molecule directly to H-terminated UNCD films turned out to be partially successful although according to literature such a reaction should be very unlikely.     

XPS and UPS in situ study of oxygen thermal desorption from nanocrystalline diamond surface oxidized by different process

The chemistry of oxygen bonding on the diamond surface is a rich area of surface science research. It is well known that different surface terminations lead to strong variation of the material work function. This effect in diamond assumes peculiar consequences. In fact the oxidized diamond surface is hydrophilic, due to the high work function it shows a positive electron affinity and it is non conductive. On the contrary hydrogenation completely changes the orientation of the surface dipoles, the surface becomes hydrophobic, the work function lowers leading to a negative electron affinity. In addition hydrogen induces subsurface carriers which render the diamond surface semiconducting. These distinctive electronic properties make the diamond surface very interesting for the fabrication of surface field effect transistors just playing with the oxygen/hydrogen chemistry. Hydrogenation is generally obtained during the diamond synthesis in plasma reactors. Differently, the diamond surface oxidation may be accomplished with different processes (wet chemistry, plasma, UV irradiation).The realization of electronic devices calls for a complete understanding of the carbon-oxygen interactions, their stability and their influence on the electronic properties of diamond. Aim of this work is to explore the properties of diamond surfaces oxidized with piranha mixture, with O₂ plasma and with UV irradiation in a pure O₂ atmosphere. Each of these oxidized surfaces were annealed in situ at different temperatures and analyzed with photoelectron spectroscopies. Decreases of the oxygen concentration obtained via thermal desorption are then correlated with variations of the electronic properties obtained from UPS analyses.     

Trialkylsilanes as reagents for the UV-induced surface modification of polybutadiene

A photochemical process for the modification of polymer surfaces using organosilane compounds has been developed. The process is based upon the UV irradiation of polybutadiene in the presence of liquid ethyldimethylsilane (C₂H₅)(CH₃)₂Si-H and gaseous trimethylsilane (CH₃)₃Si-H. UV irradiation was carried out with a medium pressure Hg lamp and a 193 nm ArF* excimer laser. The modified polymer surfaces were investigated by infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), contact angle measurements and atomic force microscopy (AFM). It is found that the photoassisted surface modification with trialkylsilanes leads to the introduction of trialkylsilyl groups onto the surface of the target polymer. From quantitative XPS data the composition of the modified polymer suface (C, O and Si) was determined. The surface modification with trialkylsilanes results in a significant lowering of surface tension γ of polybutadiene. The silane/UV process was found to be very sensitive to small amounts of oxygen in the process gas. Summing up, it is demonstrated that UV irradiation in the presence of gaseous silane compounds is a convenient way to introduce organosilicon groups onto the surface of technical polymers.     

Characterization of UV irradiated nanocrystalline diamond

The exposure of H-terminated nanocrystalline diamond (NCD) to ultraviolet (UV) light in air and at room temperature modifies the features of the diamond surface, in terms of wettability, electrical conductivity and chemical reactivity. This allows the development of a soft, dry and non invasive method to tailor the surface properties for the development of new chem- or bio-sensors.In this work, we report about the analysis of hydrogen terminated nanocrystalline diamond films grown by hot-filament technique and of their surface modification following UV light exposure. This UV treatment induces an hydrophobic to hydrophilic transformation and an outstanding increase of the electrical resistivity (> 10⁵). X-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy provide insight into the role of chemisorbed oxygen on the modification of the valence band and on the transformation of the electron affinity (from negative to positive) at the diamond surface.     

In situ characterization of interaction of ammonia with carbon surface in oxygen atmosphere

The adsorption and oxidation of ammonia over carbons differing in the chemical structure of surface functional groups have been investigated by FTIR spectroscopy. The reactions of NH₃ with carbons have been studied both in the presence and in the absence of oxygen. As a result of NH₃ chemisorption, in addition to ammonium salts, there are formed surface amide and imide structures. At the higher temperature surface isocyanate species are formed. Thermal stabilities of surface structures, formed as a result of NH₃ chemisorption have been determined by means of FTIR spectroscopy. The activity and selectivity of carbons for the selective catalytic oxidation (SCO) of NH₃ to N₂ with excess O₂ has been shown by microreactor studies at 295-623 K. Carbon catalysts are very active for NH₃ oxidation. Nitrogen is generally the predominant product of ammonia oxidation. The selectivity to N₂, N₂O and NO is determined by the surface oxygen coverage and reaction temperature. The data obtained indicate that the N₂ is formed via selective catalytic reduction (SCR) between NH_x surface species and NO formed from NH₄⁺ oxidation. This implies that ammonia is activated in the form of NH₄⁺ species for both SCR and SCO processes.     

Gas sensing properties of nanocrystalline diamond films

Toxic gas sensing device with metal electrodes built into nanocrystalline diamond (NCD) is investigated. The NCD morphology is controlled via seeding and/or deposition time. The surface properties and morphology of NCD are studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). AFM measurements reveal increase in NCD surface area by up to 13%. Gas sensing properties of H-terminated NCD device show high sensitivity towards oxidizing species where the surface conductivity is increased by an order of magnitude for humid air and by three orders of magnitude for COCl₂. The surface conductivity exhibits a small decrease to reducing spices (CO₂, NH₃).     

Field emission property of arrayed nanocrystalline diamond

Arrays of nanocrystalline diamond (NCD) stripes were fabricated by plasma etching of a NCD film. Electron field emission (EFE) of NCD arrays with 100-μm-wide stripes separated by different spacings was analyzed. The NCD arrays had higher EFE efficacy than the non-patterned blanket NCD film. The turn-on electric field (E_on) decreased from 5.4 V/μm^-1 for the blanket NCD film to 4.2, 4.4 and 4.7 V/μm^− 1 for the NCD arrays with 100, 500 and 1000 μm of spacing, respectively. Both the effective emitting area and the field enhancement factor for the NCD emitters were increased by patterning. The enhanced EFE from arrayed NCD stripes was possibly attributed to the edge effect and reduction of electrostatic screening.     

Author Index to Volume 38

X-ray photoelectron spectroscopy (XPS) is a powerful technique for determining the surface chemical composition of atmospheric particles. In this article, we employed XPS to study atmospheric particles collected from Guangzhou city in typical sites and seasons. The results showed that the weight percentage of carbon, oxygen, nitrogen, and sulfur were about 70.5–87.1%, and these species dominated the surface structure of the particles independent of the collection site and season. Inorganic elements including Si, Na, Ca, Cl, Fe, K, Al, and Cu were also found on the particle surfaces. The high-resolution XPS spectra revealed: (1) High aromatic and aliphatic C-H, and other oxidized carbons were found on the surface of particles. (2) The nitrogen species were characterized by pyridinic, pyrrolic/amide, quaternary type nitrogen functionalities, and nitrate groups, indicating that inorganic and organic N species are both important components of N-containing particles. (3) Sulfate and sulfone groups were also present on the surface and were important components. The oxidized groups of C, N, and S were higher in winter samples, consistent with the monsoon weather of Guangzhou in winter, which is favorable for the formation of oxidized species. A comparison between total and surface analyses showed that the surface of particles was relatively high in organic carbon, NO₃ ^?, and SO₄ ^2?, and the interior of particles was higher in NH₄ ⁺. These results provide information on the formation of aerosols, e.g., NH₄ ⁺ may act as a very important nucleus and organic carbon, NO₃ ^?, and SO₄ ^2? coat the nuclei during particle growth.     

Tribological properties of NCD coated cemented carbides in contact with wood

Cemented carbides coated with diamond layers are promising materials for mills in the wood industry. Therefore, a study of the tribological properties of the contact between this material and wood is interesting and important. Wood is a specific material with a highly anisotropic structure, which causes roughness of its surface. For example, the friction coefficient (μ) of wood in contact with polished steel coated with a smooth DLC layer, has a relatively high value of μ=0.2–0.5. Cemented carbides, as manufactured for tools for wood milling purposes with roughness R_z=0.66 μm, have been modified with a nanocrystalline diamond film (NCD) using the RF PACVD method. The surface of the NCD coating showed ‘sharp hills’ morphology, but the surface roughness of cemented carbide decreased slightly after coating. The friction was very high (μ=0.7–0.8 at v=1 m/s; F_N=60 N) and it depended on the species of wood. When examining oak and poplar using carbides coated with the thickest NCD layer and a DLC film on top, this value decreased by 30% with respect to that of uncoated carbides. For fibreboard against NCD, the value was increased. Comparing the friction of NCD against wood to its friction against steel, titanium and aluminium alloys, we could see that the roughness of wood was the main factor which determined its tribological behaviour. Prime novelty: the tribological properties of a NCD layer deposited on cemented carbides with wood.     

XPS investigation of the reaction of carbon with NO, O2, N2 and H2O plasmas

The interaction of graphite with plasmas of pure gases (O₂, N₂ or H₂O), air or mixtures of gases containing NO has been studied by XPS “in situ” analysis. Depending on the type of plasma, different species of nitrogen, oxygen and carbon have been detected on the surface of graphite. The nitrogen containing species have been attributed to pyridinic, pyrrol, quartenary and oxidized groups adsorbed on the surface. The evolution with the treatment time of the relative intensity of the different nitrogen bands for Ar + NO, N₂ + NO, air or N₂ plasmas has served to propose a model accounting for the reactions of graphite with plasmas of NO containing gases. The model explains why carbon materials (in the form of graphite, soot particles, etc.) can be very effective for the removal of the NO present in exhaust combustion gases excited by a plasma. The analysis of the C1s and O1s photoemission peaks reveals the formation of C/O adsorbed species up to a maximum concentration on the surface of around 10% atomic oxygen. A general evolution is the progressive formation of C/O species where the carbon is sp³ hybridized. This tendency is enhanced when graphite is treated with the plasma of water.     

Comparison of different oxidation techniques on single-crystal and nanocrystalline diamond surfaces

Various oxidation techniques (plasma-beam, sulfo-chromic acid, UV-ozone, heating in air) were applied to single-crystalline (111) and (100) diamond surfaces as well as nanocrystalline diamond (NCD) films and analyzed by X-ray photoelectron spectroscopy (XPS) with respect to oxygen content and type of carbon–oxygen groups formed upon oxidation. Due to their increased surface, NCD films show a significantly higher oxygen uptake as compared to their single-crystal counterparts. No marked differences were observed between the different oxidation techniques. For all oxidation techniques used, several carbon–oxygen groups are simultaneously present on the surface. The relative fraction of singly-oxidized carbon atoms (attributed to isolated ether or epoxy-like groups) generally decreases slightly with increasing oxygen content, but always remains the dominating species.     

The pH response of the InP/liquid ammonia interface at 223 K: A pure nernstian behavior

Liquid ammonia (NH₃liq.) provides an original electrochemical environment onto semiconductors electrodes (SC). Its particular interest is that water influences can be neglected in opposition to a lot of non-aqueous other solvents. Fundamentals electrochemistries of the SC are related to the energy diagram of the interface. In this paper it is established into NH₃liq., on both types, on p- and n-InP by flat band potential (V_fb) measurements. The V_fb are determined over the whole range of pH that reaches 33 pH units in this non-aqueous solvent. InP exhibits a pure nernstian behavior with a specific 44 mV/pH slope at 223 K. This is particular compare to the “under nernstian” dependency, observed in water onto InP. The actual band positions are related to the initial chemical state of the InP surface, since oxide free surfaces and thin native oxide covered surfaces differ slightly. Reproducible contrasted results from the acid-base equilibrium, which is supported by the V_fb according to the pH, for singular interfacial chemistry. This aspect is confirmed by XPS measurements performed before and after InP immersion into NH₃liq. They establish the perfect stability of the initial chemical composition of the semiconducting surface in contact with NH₃liq. whatever its pH conditions. NH₃liq. appears as an inert solvent which is able to create an acid-base equilibrium onto InP surfaces. Each InP surface chemistry support its own linear V_fbvs. pH variation. In NH₃liq., the poor water control on the building of the Helmholtz layer is well shown by the perfect V_fb alignment position from the intermediated pH buffered solution obtained from the addition of tetraethyl ammonium hydroxide ((Et)₄N⁺,OH⁻) dissolved in water (20%).     

A new regime for high rate growth of nanocrystalline diamond films using high power and CH4/H2/N2/O2 plasma

In this work, we report high growth rate of nanocrystalline diamond (NCD) films on silicon wafers of 2 inches in diameter using a new growth regime, which employs high power and CH₄/H₂/N₂/O₂ plasma using a 5 kW MPCVD system. This is distinct from the commonly used hydrogen-poor Ar/CH₄ chemistries for NCD growth. Upon rising microwave power from 2000 W to 3200 W, the growth rate of the NCD films increases from 0.3 to 3.4 μm/h, namely one order of magnitude enhancement on the growth rate was achieved at high microwave power. The morphology, grain size, microstructure, orientation or texture, and crystalline quality of the NCD samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction, and micro-Raman spectroscopy. The combined effect of nitrogen addition, microwave power, and temperature on NCD growth is discussed from the point view of gas phase chemistry and surface reactions.     

Influence of the substrate nature on the properties of nanocrystalline diamond films

Nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films have been deposited by microwave plasma CVD from CH₄/N₂ mixtures on a variety of substrates such as polycrystalline diamond, cubic boron nitride, silicon, titanium nitride, and Ti–6Al–4V. The study aimed to investigate the influence of the chemical nature of the substrate, the surface roughness, and the pretreatment of the substrate on the nucleation, the bulk structure, and the mechanical and tribological properties of the NCD/a-C films. The present paper is especially devoted to the bulk structure of the films. By means of X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) it is shown that the bulk properties of the films are not affected by the properties of the substrate although these have a strong influence on the nucleation behaviour. XRD measurements show that – irrespective of the substrate used – the films contain diamond nanocrystallites of 3–5 nm diameter. From the Raman spectra it can be inferred that the crystallite/matrix ratio does not vary. The XPS measurements, finally, show that there are no great changes in the sp²/sp³ ratio of the matrix. These findings are discussed in view of possible growth mechanisms of NCD/a-C nanocomposite films.     

Antibacterial properties of polycrystalline diamond films

Electronic and mechanical properties, and their biocompatibility, make diamond-based materials promising biomedical applications. The cost required to produce high quality single crystalline diamond films is still a hurdle to prevent them from commercial applications, but the emergence of polycrystalline diamond (PCD) films grown by chemical vapour deposition (CVD) method has provided an affordable strategy. PCD films grown on silicon wafer have been used throughout and were fully characterised by SEM, XPS, Raman spectroscopy and FTIR. The samples contain nearly pure carbon, with impurities originated from the CVD growth and the silicon etching process. Raman spectroscopy revealed it contained tetrahedral amorphous carbon with small tensile stress. The sp² carbon content, comprised between 16.1 and 18.8%, is attributed to the diamond grain boundaries and iron-catalysed graphitisation. Antibacterial properties of PCD films were performed with two model bacteria, i.e. Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) using direct contact and shaking flask methods. The samples showed strong bacteriostatic properties against S. aureus and E. coli with the direct contact method and no influence on planktonic bacterial growth. These results suggest that the bacteriostatic mechanism of PCD films is linked to their surface functional groups (carbon radicals and –NH₂ and –COOH groups) and that no diffusible molecules or components were involved.     

Functionalisation and chemical characterisation of cellulose-derived carbon aerogels

A series of nitrogen- and oxygen-functionalised carbon aerogels was produced from a carbon aerogel derived from cellulose acetate. Samples were oxidised by H₂O₂ or HNO₃ and/or enriched in nitrogen by reaction with gaseous ammonia or co-heating of the carbon aerogel and melamine. Porosity variations and morphology were monitored using N₂ adsorption and helium pycnometry. The surface chemistry was characterised by elemental analysis, FTIR and XPS spectroscopy, pH of the point of zero charge and acid/base titration. The prepared carbons are mainly mesoporous and show a moderate porosity development (S_BET between 160 and 300 m²/g). The applied chemical methods allow producing a wide range of functionalised carbon aerogels differing in terms of oxygen and nitrogen groups, their distribution and basicity. Both oxidation methods introduce a similar amount of oxygen, while the produced carbons differ in term of their acid/base character. Treatment with ammonia produces the most basic materials, which is partly due to the introduction of basic nitrogen groups, but also to the reduction of the acidic oxygen functionalities.     

Superconductivity in heavily B-doped diamond layers deposited on highly oriented diamond films

We deposited a [100]-oriented B-doped diamond layer by three methods to clarify the effects of film morphology on the transition from metallic to superconducting diamond. Heavily B-doped [100]-oriented diamond layers were deposited on [first method] undoped polycrystalline diamond films with [111] faces, [second method] highly oriented undoped diamond (HOD) thin films with a pyramidal surface, and [third method] thick undoped HOD films with a pyramidal surface. We confirmed that the B-doped layer in the third method was oriented in the [100] direction by scanning electron microscopy (SEM). The highest transition temperatures were T_c(onset) = 5.0 K and T_c(zero) = 3.1 K for the B-doped layer deposited on a thick HOD film with a pyramidal surface under a zero magnetic field. By contrast, T_c(onset) was 4.1 K for a heavily B-doped diamond layer deposited on a thin HOD film with a pyramidal surface, and was 3.9 K for a heavily B-doped diamond layer deposited on an undoped polycrystalline diamond film. These differences in T_c for our samples are affected by disorder and effective hole-carrier doping in each sample. Using the third method, we successfully deposited a high-quality B-doped [100] layer in three steps: (first step) depositing a [100] HOD film on a Si [100] substrate, (second step) depositing an HOD film with a pyramidal surface, and (third step) depositing a [100]-oriented B-doped layer. The change in the electronic states due to the B-doping of diamond films and the film morphology were investigated by x-ray photoelectron spectroscopy (XPS) measurements and band calculations.