Highly oriented polytetrafluoroethylene (PTFE) thin films might be useful as substrates for oriented growth of well-organized layers of organic materials. In this study, such PTFE films were deposited onto oxide-covered Si wafers by sliding of a PTFE rod at constant speed under controlled conditions of deposition temperature Td and load W. The morphology of these films was studied down to molecular resolution by atomic force microscopy, and the amount of deposited polymer was measured by nuclear reaction analysis; dependence on Td and W was investigated. For Td > 150 °C these films consist of straight and very long (> 100 μm) ribbons parallel to the sliding direction. Their width and their height, i.e. the amount of PTFE, are increasing with Td and W, so that the substrate can be almost completely covered. These ribbons are crystalline, being bundles of polymer chains with the helix axis parallel to the ribbon length. Known properties of PTFE and our results suggest that the final film formation and the resulting morphology are dependent on crystallization upon cooling and not only on deposition parameters.

Journal of Polymer Science Part B: Polymer PhysicsVolume 31, Issue 1 p. 111-114 Communication Scanning tunneling microscopy of single polyalkylthiophene molecules adsorbed on graphite E. Lacaze, E. Lacaze Groupe de Physique des Solides, Universités Paris VII et Paris VI, 2 Place Jussieu F-75251, Paris Cedex 05, FranceSearch for more papers by this authorK. Uvdal, K. Uvdal Department of Physics, IFM, Linköping University, S-58183 Linköping, SwedenSearch for more papers by this authorP. Bodö, P. Bodö Department of Physics, IFM, Linköping University, S-58183 Linköping, SwedenSearch for more papers by this authorJ. Garbarz, J. Garbarz Groupe de Physique des Solides, Universités Paris VII et Paris VI, 2 Place Jussieu F-75251, Paris Cedex 05, FranceSearch for more papers by this authorW. R. Salaneck, W. R. Salaneck Department of Physics, IFM, Linköping University, S-58183 Linköping, SwedenSearch for more papers by this authorM. Schott, M. Schott Groupe de Physique des Solides, Universités Paris VII et Paris VI, 2 Place Jussieu F-75251, Paris Cedex 05, FranceSearch for more papers by this author E. Lacaze, E. Lacaze Groupe de Physique des Solides, Universités Paris VII et Paris VI, 2 Place Jussieu F-75251, Paris Cedex 05, FranceSearch for more papers by this authorK. Uvdal, K. Uvdal Department of Physics, IFM, Linköping University, S-58183 Linköping, SwedenSearch for more papers by this authorP. Bodö, P. Bodö Department of Physics, IFM, Linköping University, S-58183 Linköping, SwedenSearch for more papers by this authorJ. Garbarz, J. Garbarz Groupe de Physique des Solides, Universités Paris VII et Paris VI, 2 Place Jussieu F-75251, Paris Cedex 05, FranceSearch for more papers by this authorW. R. Salaneck, W. R. Salaneck Department of Physics, IFM, Linköping University, S-58183 Linköping, SwedenSearch for more papers by this authorM. Schott, M. Schott Groupe de Physique des Solides, Universités Paris VII et Paris VI, 2 Place Jussieu F-75251, Paris Cedex 05, FranceSearch for more papers by this author First published: January 1993 https://doi.org/10.1002/polb.1993.090310115Citations: 16AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume31, Issue1January 1993Pages 111-114 RelatedInformation

Highly oriented molecular structures of organic molecules are important in many applications of thin films and interfaces. Recently, it has been shown that poly(tetrafluoroethylene), or PTFE, can be deposited mechanically to form highly oriented thin films on glass substrates. Such oriented PTFE films can in tum be used as substrates for growth of ordered films of organic molecules and polymers, e. g. conjugated polymers. Despite the fact PTFE is electrically insulating, we have been able to use scanning tunneling microscopy (STM) to examine details of oriented ultrathin PTFE films deposited on various substrates, in particularly Pt and highly ordered pyrolytic graphite (HOPG). Ordered structures originating from aligned chains were observed, and reproducible images were obtained at the submicron level. Nanometric molecular details are more difficult to resolve, but indicate interesting features. In particular, we have observed regions of parallel zig-zag shaped molecules, which are separated by approximately 6 angstrom.

l-Cysteine adsorbates and multilayer films on gold and copper surfaces have been investigated by X-ray photoelectron spectroscopy. Both adsorbates, prepared by vapor deposition in UHV and prepared from solution, strongly indicate a dissociative chemisorption through the thiol group (−SH) on the metal surface. We suggest that an organized double layer is formed on gold, for the UHV-prepared layer. In the case of copper, evidence is found for the coordination of both amino and carboxyl groups to the surface, in addition to chemisorption through the thiol group. When l-cysteine is adsorbed from solution on copper, all of the thiol groups interact with copper ions, even in a 25-Å-thick layer. This indicates copper ion diffusion and copper complex formation through the entire layer.

We present results from theoretical studies of diformimide- and methyl-diformimide-on-copper, chosen as a model for the phthalimide- and methyl-phthalimide-on-copper interfaces, respectively. Ab initio Hartree-Fock calculations are performed to derive the geometrical and electronic structure of these systems. Valence band spectra obtained from ultraviolet photo-electron spectroscopy (UPS) are presented for mono- and multi-layers of phthalimide- and methyl-phthalimide-on-copper. The theoretical results are used to interpret these spectra. It is shown that the phthalimide molecules interacting with the copper surface, adhere primarily through reaction at the nitrogen sites, which simultaneously lose their hydrogen atoms. Methyl-diformimide on copper is a model for the interaction at the methyl-phthalimide-on-copper interface. The methyl group in this case is assumed to remain at the original position on the molecule. The ligand-copper inter-action is found to take place primaryly between the nitrogen lone pair and Cu 4s orbitals. This type of interaction is, however, considerably weaker than for phthalimide-on-copper. The different interaction patterns observed for the phthalimide- and methyl-phthalimide-on-copper interfaces are discussed in relation to the polyimide-on-copper interface.

Infrared reflection-absorption spectroscopy and X-ray photoelectron spectroscopy (XPS) are used to characterize adsorbed layers of amino acids on evaporated copper surfaces. Thin layers of glycine, l-alanine, and β-alanine are formed by adsorption from 5 m M aqueous solutions at pH values near their isoelectric points. Glycine is most thoroughly studied, and much attention is paid to a comparison with synthesized complexes of cis-Cu(II)(Gly)2·H2O and trans-Cu(II)(Gly)2·2H2O. A very good agreement is obtained between calculated reflection—absorption spectra based on these model substances and observed spectra of adsorbed glycine on copper. This observation suggests that both the carboxylate oxygens and the amino nitrogens are involved in the bonding to copper and that an ionic lattice (≈10 Å) consisting of Cu ions and glycine is formed on the surface. Further support for an ionic structure is obtained from a preliminary XPS study where differently prepared glycine layers on copper are compared with the cis-Cu(II)(Gly)2·H2O complex. The composition of the ionic lattice is found to vary with the microstructure of the copper surface and with film orientation in particular. Our infrared data indicate that the cis form is more pronounced on copper films with preferred (111) orientation, whereas the trans form appears to dominate on “polycrystalline” copper. l-Alanine and β-alanine also react with copper via the carboxylate-oxygen and amino-nitrogen atoms. However, the layer thicknesses for l- and β-alanine appear to be smaller than those obtained for glycine.

As an approach to a better understanding of adhesion mechanisms between polyimide and copper, we have studied the interaction between a set of model molecules for a polyimide and vapor deposited polycrystalline copper. Thin films and adsorbates of benzene, phthalimide, methyl-phthalimide, benzene-phthalimide, and malonamid, which are representative of separate parts of the polyimide repeat unit, were deposited in situ on clean copper and examined by means of x-ray and Ultraviolet photoelectron spectroscopy (XPS and UPS). In contrast to the previously observed bonding to the carbonyl oxygen in polyimide, as Cu is deposited on polyimide, our results show that most of these polyimide model molecules bond to Cu, through electron transfer, with the imide nitrogen atom as the primary reaction site.

Glycine adsorbed on polycrystalline copper has been studied by angle-dependent X-ray photoelectron spectroscopy, XPS(θ), and infrared reflection absorption spectroscopy, IRAS. At −50°C the molecule adsorbs with its molecular identity intact. Upon heating to 30°C the glycine molecule slowly decomposes on the copper surface. The adsorbate held at −50°C is compared with a thin film of glycine, which is known to be zwitterionic. The binding energy shifts, the intensity ratios in the N(1s), C(1s), and O(1s)XPS(θ) spectra, and the infrared spectra of the adsorbate show that the glycine molecule coordinates with both the nitrogen and the two oxygen atoms to the copper surface. The amino group exists as an −NH2 group in the adsorbate rather than as an −NH3+, which is the case in the zwitterionic form of glycine. This result is in contrast with the molecular orientation of glycine on hydrophilic gold, silicon, and highly oriented pyrolytic graphite (HOPG).

The effects of Ar ion bombardment on the polyimide (PI) surface chemistry, Ti film growth, and the Ti/polyimide interface have been studied using x‐ray photoelectron spectroscopy (XPS). The Ti films were grown in an ultrahigh vacuum chamber onto spin coated polyimide substrates and then analyzed in situ by XPS. The substrates were, prior to Ti film deposition, exposed to ion doses of 3.8× and 30×1014 ions/cm2 using 2‐keV Ar ions. By monitoring the chemical shifts in the C 1s level arising from the polyimide molecular structure, a preferential bond breaking of imide carbonyl groups and formation of graphitelike carbons were observed as a consequence of the ion bombardment. As Ti was deposited a C 1s peak corresponding to Ti–C formation was observed for both as‐prepared and ion bombarded samples. The initial Ti film growth was studied by measuring the decrease in the C 1s level as a function of the amount of deposit. As expected for polymers the film growth is three dimensional in its character where islands of depositing atoms are formed in the initial stages. However, on ion bombarded PI substrates the number of nucleation sites is so large that the Ti film growth is comparable with a calculated layer‐by‐layer growth.

As a model molecule for a specific part of a polyimide, pthalimide has been studied adsorbed upon copper substrates at low temperatures using angle-dependent x-ray photoelectron spectroscopy. A stable adsorbate is found to exist in the approximate range −30 °C≤T≤−5 °C. The pthalimide molecule lies approximately flat upon the polycrystalline copper surface. Charge transfer from the copper to the adsorbate is observed. The present results are in contrast with those obtained when copper is vapor deposited upon a polyimide, as reported in the literature.

Titanium films were deposited by electron beam evaporation onto polydimethylsiloxane (PDMS) substrates. Ar+ bombardment as well as O2 plasma pretreatments were found to enhance the adhesion of the titanium films markedly. X-ray photoelectron spectroscopy and scanning electron microscopy were used to study the influence of the pretreatments on the PDMS surface morphology. Both pretreatments resulted in cross-linking and thereby an increased strength of the substrate surface. X-ray photoelectron spectroscopy was also used, together with in situ electron beam evaporation, to study the initial titanium film growth on as-prepared and Ar+-bombarded samples. The C 1s and O 1s peak shifts showed an enhanced film-substrate interaction attributed to formation of Ti-C and Ti-O bonds respectively. The film-substrate interaction was also observed as a change in the titanium film growth mode. If the samples were ion bombarded prior to deposition the film growth changed from a pronounced three-dimensional growth towards a more two-dimensional growth mode.

Auger electron spectroscopy has been used to study the interface between human tissue and implants of titanium and stainless steel. Both the thickness and the nature of the oxide layers on the implant have been found to change during the time of implantation. The stainless steel implants have a surface oxide about 50 Å in thickness prior to implantation. The metal atoms in the oxide are mainly chromium. The changes of the oxide thickness and nature depend on the location of the implant in the body. For implants located in cortical bone, the thickness of the interfacial oxide layer remains unaffected, while it increases by a factor of 3–4 on samples located in bone marrow. In both these cases, calcium and phosphorus are incorporated in the oxides. Implants located in soft tissue have an interfacial oxide with a thickness of about one and a half times that of an unimplanted sample. On these samples, calcium and phosphorus are not incorporated in the oxide layer. Also for titanium an increase in oxide thickness and an incorporation of Ca and P are found. In the cases with titanium implants, it is also demonstrated that the oxidation process occurs over a long period of time, up to several years. For the elements incorporated in these interfacial oxide layers on both stainless-steel and titanium implants, it is found that P is strongly bound to oxygen suggesting the presence of phosphate groups in the oxides. The interaction between the implants and human tissue are discussed in terms oxygen pressure, electron transfer between proteins and implants, metabolic activity, and enzymes producing free radicals.

The interaction of proteins with nonbiological surfaces is important because of its possible involvement in the biological acceptance or rejection of artificial implants. In this paper, we report on the adsorption of fibrinogen onto titanium and gold metal surfaces. Results both from X-ray photoelectron spectroscopy (ESCA) studies performed in high vacuum and from ellipsometric measurements performed with the protein layer in buffer solutions are reported. Both techniques show that there is a difference in the adsorption behavior and the conformation of the protein on titanium and gold surfaces, respectively. While the fibrinogen adsorbs in more or less a native form on the titanium surface, it changes its conformation and adsorbs in a thin dense layer on the gold surface. The comparison between the ESCA and the ellipsometry measurements shows a relative change in the conformation of the protein molecules on the titanium surface due to dehydration during high vacuum conditions. Despite this, the protein molecules on the titanium surface seem to retain much of their structure also under UHV conditions. This was concluded by comparing mainly the shape of the C 1 s peak with that from thick bulk protein layers. The results obtained are discussed in terms of electrostatic and hydrophobic interactions during the adsorption processes.

Ti films were deposited onto high-density polyethylene (HDPE) samples by electron-beam evaporation. Prior to film deposition the samples were in situ pretreated by Ar ion bombardment using a sputter ion gun. The adhesion of the films, determined as the pull strength required for film failure, was measured as a function of ion dose. HDPE substrates processed at two different temperatures were examined. The adhesion of the Ti films to HDPE samples processed at ≊150 °C increased with the ion dose to a steady-state value corresponding to the cohesive strength of the HDPE substrate. The adhesion to the samples processed at ≊200 °C increased to a maximum and then decreased for further ion bombardment to a level of the same order as that for films deposited onto as-prepared samples. The effects of the ion bombardment upon the HDPE surface chemistry were examined by means of x-ray photoelectron spectroscopy (XPS). The ion bombardment resulted in dehydrogenation and cross linking of the surface region and for prolonged ion bombardment, a graphitelike surface was obtained. The film/substrate interface as well as the initial Ti film growth were examined by XPS analysis. A chemical interaction which resulted in Ti–C bonds was observed at the interface. The Ti film growth followed a pronounced three-dimensional growth mode on as-prepared surfaces whereas the ion bombardment resulted in a change toward a more two-dimensional growth mode. The difference in adhesion behavior for the two types of HDPE substrates was found to be due to a difference in the amounts of low molecular weight products present within the substrates. The HDPE substrates processed at ≊200 °C contained larger amounts of low molecular weight products and also had a lower degree of crystallinity and a less closely packed structure compared to those substrates processed at ≊150 °C. This resulted in a segregation of low molecular weight products towards the surface of substrates processed at ∼200 °C. This segregation in turn is suggested to lead to a weak boundary layer, reducing the adhesion to as-prepared samples and to substrates exposed to a high ion dose.

Auger electron spectroscopy together with scanning electron microscopy has been used to study the interface between stainless-steel implants and human tissue. The thickness and nature of the oxide layer on the implants have been found to depend on the location of the implants in the body. Before implantation, the oxide layer is about 50 A thick, consisting mainly of chromium oxide. For implants located in cortical bone the thickness of the interfacial oxide layer remains unaffected, while it increases by a factor of three to four on samples located in bone marrow. In both these cases calcium and phosphorus are incorporated in the oxides. Implants located in soft tissue have an interfacial oxide layer with a thickness of about one and one-half times that on an unimplanted sample. On these samples, calcium and phosphorus are not found, but occasionally sulfur is found in the oxide layer. All these samples originated from the oral region of the body; the reason for this finding, however, is not known at present time. The interactions between the implants and human tissues resulting in the observed changes of the implant surfaces are discussed in terms of oxygen pressures and metabolic activity.

Titanium films, 1 μm thick were electron-beam evaporated onto polyethylene (PE) that had been pretreated in situ by 2 keV Ar+ bombardment. A measure of the film adhesion was obtained by measuring the pull strength required to remove the Ti films. A strong dependence of the adhesion on the ion dose was found. The pull strength had a maximum of approximately 20 MPa after a dose of 6×1014 ions/cm2 but decreased for higher ion doses. Without any ion bombardment prior to deposition, the adhesion was very poor with a pull strength of approximately 2 MPa. XPS analysis was used to examine the effect of the ion bombardment on the chemistry of the PE substrate and the Ti/PE interface. Untreated PE samples were contaminated with surface impurities and probably also with low molecular weight hydrocarbons. As the adhesion is maximized, most of the impurities are removed by the ion bombardment. The strong adhesion is suggested to be due to formation of a carbidelike Ti–C interfacial layer, detected by XPS.