Carbon nitride films deposited by three different methods have been analyzed using in situ Auger electron spectroscopy and ex situ x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry.The XPS data for all 27 samples indicate that these films have a similar composition consisting of two phases. One phase has a stoichiometry near C3N4 and is identified as a tetrahedral component.The other phase has a variable stoichiometry from C5N to C2N and is identified as predominantly an sp' bonded structure. For a film composition of [N]/ [C] ( 1, the tetrahedrally bonded component grows only moderately as the nitrogen content of the films is increased. PACS numbers: 68.55.Nq, 81.15. -z, 82.80.PvIn 1990, Liu and Cohen presented a pseudopotential study [1] of the structural and electronic properties of P-C&N4, a hypothetical compound, and of P-Si3N4, a compound with well-known properties. The good agreement between calculated and experimental data for the latter compound lends credibility to the findings of this study concerning the exciting properties of the unknown C-N compound. The calculated bulk modulus of P-C3N4 was found to be comparable to that of diamond. In addition, the velocity of sound in the C-N compound was predicted to be about 1.1 X 106 cm/s, suggesting a high thermal conductivity. It was suggested that P-C,N4 may be metastable because of its moderately large cohesive energy. Synthesis of P-C3N4 has recently been claimed [2] on the basis of electron diffraction data but the overall composition of the films in this, as in most other experiments [3 -6], is not stoichiometric: the ¹o-Cconcentration ratio attained in most cases is about [N]/[C] = 0.7.We propose that the reason for this discrepancy, which may raise questions about the results of Niu, Lu, and Lieber [2], is that for the deposition methods investigated, P-CsN4 forms only in very small crystallites that are embedded in amorphous sp2 bonded C"N, where y /x is typically between 0.2 and 0.5, depending on deposition conditions. Furthermore, we present x-ray photoelectron spectroscopic (XPS) data which shows that these two carbon nitride phases can be distinguished by their binding energies. Such a distinction provides researchers with a tool to assess quickly and effectively the quality of their films not simply on the basis of the overall nitrogen content, but rather based on the nitrogen and carbon that

Methyl- and hydroxyl-terminated phosphonic acid self-assembled monolayers (SAMs) were coated on Ti from aqueous solution. Dodecyl phosphate and dodecyltrichlorosilane SAMs were also coated on Ti using solution-phase deposition. The stability of SAMs on Ti was investigated in Tris-buffered saline (TBS) at 37 degrees C using X-ray photoelectron spectroscopy, contact angle goniometry, and atomic force microscopy. For comparison purposes, a hydroxyl-terminated thiol SAM was coated on Au, and its stability was also investigated under similar conditions. In TBS, a significant proportion of phosphonic acid or phosphate molecules were desorbed from the Ti surface within 1 day, while the trichlorosilane SAM on Ti or thiol SAM on Au was stable for up to 7 days under similar conditions. The stability of hydroxyl-terminated phosphonic acid SAM coated Ti and thiol SAM coated Au was investigated in ambient air and ultraviolet (UV) light. In ambient air, the phosphonic acid SAM on Ti was stable for up to 14 days, while the thiol SAM on Au was not stable for 1 day. Under UV-radiation exposure, the alkyl chains of the phosphonic acid SAM were decomposed, leaving only the phosphonate groups on the Ti surface after 12 h. Under similar conditions, decomposition of alkyl chains of the thiol SAM was observed on the Au surface accompanied by oxidation of thiolates.

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Thin carbon–nitrogen films have been formed by direct impingement of 5–100 eV C+ and N+ or N+2 ions upon solid surfaces, as well as by 5–350 eV N+ bombardment of graphite surfaces. The influences of ion energy, N+/C+ arrival rate, and type of substrate have been studied. The films deposited in this manner are found to be essentially amorphous, with some graphitic regions on the scale of a few nm. Two distinct types of C–N bonding, one attributed to graphitelike local structure (C–N π bonds) and one attributed to C3N4-like local structure (C–N σ bonds), have been detected by x-ray photoelectron spectroscopy. Films deposited by dual-beam deposition and single-beam nitridation at 75 eV or less exhibit differences in the single-bonded structure. Total nitrogen concentrations of up to 47 at. % have been measured by Auger electron spectroscopy (AES) and Rutherford backscattering spectrometry. The C KVV Auger line shapes of the two phases have been determined by factor analysis. These line shapes are consistent with the expected band structures for the two phases. Film growth is consistent with a combined surface deposition/subplantation model, with high incident energies resulting preferentially in damage to the C3N4-like phase. A significant amount of disorder is present in all of the films, as indicated by AES line shapes and transmission electron microscopy analysis. Preferential sputtering of N is observed during AES depth profiling with a 1 keV Ar+ beam. Implications of this work for deposition of C–N films by energetic particle bombardment are discussed.

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We have studied the influence of oxygen radio frequency glow discharge (RfGD) on the surface and bulk properties of poly(D,L-lactic acid) (PDLLA) and the effect of this surface modification on both protein adsorption and bone cell behavior. PDLLA films were characterized before and after plasma surface modification by water contact angle, surface energy, and adhesion tension of water as well as by scanning electron microscopy (SEM), X-ray electron spectroscopy (XPS), and Fourier transform infra-red (FTIR) spectroscopy. RfGD-films showed an increase in hydrophilicity and surface energy when compared with untreated films. Surface morphological changes were observed by SEM. Chemical analysis indicated significant differences in both atomic percentages and oxygen functional group. Protein adsorption was evaluated by combining solute depletion and spectroscopic techniques. Bovine serum albumin (BSA), fibronectin (FN), vitronectin (VN), and fetal bovine serum (FBS) were used in this study. RfGD-treated surfaces adsorbed more BSA and FN from single specie solutions than FBS that is a more complex, multi-specie solution. MG63 osteoblast-like cells and primary cultures of fetal rat calvarial (FRC) cells were used to assess both the effect of RfGD treatment and protein adsorption on cell attachment and proliferation. In the absence of preadsorbed proteins, cells could not distinguish between treated and untreated surfaces, with the exception of MG63 cells cultured for longer periods of time. In contrast, the adsorption of proteins increased the cells' preference for treated surfaces, thus indicating a crucial role for adsorbed proteins in mediating the response of osteogenic cells to the RfGD-treated PDLLA surface.

Although intravascular stents have received widespread application, significant limitations remain. In stent restenosis, the most pervasive problem affecting stents, is related in part to technical aspects of the device. Design features of the stent that influence outcome have been identified and optimized for improved performance. The influence of stent materials on critical aspects of healing, such as thrombotic, inflammatory, and hyperplastic responses, are less well understood. For this reason, significant progress in this area is lacking. Current stents have significant contamination with industrial impurities on the surface and in the bulk. This fact adds to the difficulties in interpreting the biologic reaction of the host to the device. Better understanding of the basic biologic interactions is the path to significant improvement.

Polymer-based carriers are commonly used to deliver drugs from stents. However, adverse responses to polymer coatings have raised serious concerns. This research is focused on delivering drugs from stents without using polymers or any carriers. Paclitaxel (PAT), an anti-restenotic drug, has strong adhesion towards a variety of material surfaces. In this study, we have utilized such natural adhesion property of PAT to attach these molecules directly to cobalt–chromium (Co–Cr) alloy, an ultra-thin stent strut material. Four different groups of drug coated specimens were prepared by directly adding PAT to Co–Cr alloy surfaces: Group-A (PAT coated, unheated, and ethanol cleaned); Group-B (PAT coated, heat treated, and ethanol cleaned); Group-C (PAT coated, unheated, and not ethanol cleaned); and Group-D (PAT coated, heat treated and not ethanol cleaned). In vitro drug release of these specimens was investigated using high performance liquid chromatography. Groups A and B showed sustained PAT release for up to 56 days. A simple ethanol cleaning procedure after PAT deposition can remove the loosely bound drug crystals from the alloy surfaces and thereby allowing the remaining strongly bound drug molecules to be released at a sustained rate. The heat treatment after PAT coating further improved the stability of PAT on Co–Cr alloy and allowed the drug to be delivered at a much slower rate, especially during the initial 7 days. The specimens which were not cleaned in ethanol, Groups C and D, showed burst release. PAT coated Co–Cr alloy specimens were thoroughly characterized using scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. These techniques were collectively useful in studying the morphology, distribution, and attachment of PAT molecules on Co–Cr alloy surfaces. Thus, this study suggests the potential for delivering paclitaxel from Co–Cr alloy surfaces without using any carriers.