James M. Burkstrand

Metal‐polymer interfaces: Adhesion and x‐ray photoemission studies

The interfaces formed by evaporating copper, nickel, and chromium layers on polystyrene, polyvinyl alcohol, polyethylene oxide, polyvinyl methyl ether, polyvinyl acetate, and polymethyl methacrylate have been studied with x‐ray photoemission spectroscopy (XPS). The adhesion strengths of the metal films to the polymers were measured by a tensile‐pull test. At submonolayer coverages of the metals, the peak positions and widths of the metallic electron core levels measured with XPS vary significantly from one polymer substrate to another. Most of these variations can be accounted for in terms of changes in the atomic and extra‐atomic relaxation energies during the photoemission process. Much of this change is brought about when the metal atom deposited on an oxygen‐containing polymer interacts with the substrate oxygen and forms a metal‐oxygen‐polymer complex. The presence of this complex is verified by changes in the photoemission lineshapes of the substrate carbon and oxygen atoms. The XPS signatures of th...

Electron spectroscopic study of oxygen‐plasma‐treated polymer surfaces

Oxygen plasma treatment of ABS polymer surfaces has the effect of increasing the adhesion of evaporated metal films on those surfaces. To help understand this, surfaces of commercial ABS and polypropylene were examined with ESCA both before and after oxygen plasma treatment. The plasma treatment was found to change the basic chemical nature of the polymer surface by increasing the number of single and double bonds between carbon and oxygen atoms. It is suspected that these additional carbon–oxygen chemical bonds affect the adhesion between polymers and metals. In addition to the carbon–oxygen bond formation, the plasma treatment removed residual impurities of silicon and increased the residual amounts of other metallic impurities originating in the bulk. The binding energies of these metallic impurities are all indicative of oxides.

Study of the N–Cu(100) system

The reaction of a clean Cu(100) surface with atomic N has been studied with low energy electron diffraction (LEED), Auger electron spectroscopy, ultraviolet photoemission spectroscopy (UPS), and x‐ray photoemission spectroscopy (XPS). Atomic nitrogen, formed by electron dissociation of N2 forms a c(2×2) overlayer on the Cu(100) surface. An analysis of LEED intensity profiles averaged over constant momentum transfer indicates that the N binds in a fourfold symmetric site, 0.145 nm above the first layer of Cu atoms. UPS data reveal small adsorbate‐induced electronic levels at 1.3 and 5.8 eV below the Fermi level, in addition to rather complex changes in the Cu d band. XPS measurements yield 397.3 eV for the binding energy of the N 1s electrons with respect to the Fermi level. Our UPS and Auger data on Cu(100)/N in terms of N‐induced states is shown to be plausible.

Copper–polyvinyl alcohol interface: A study with XPS

It has been known for some time that oxygen treatment of a polymer surface can lead to enhanced adhesion with metals. This has prompted us to investigate the metal–polymer interface of an oxygen‐containing polymer, polyvinyl alcohol. We have vapor‐deposited copper on the clean polymer surface and examined the interface with x‐ray photoemission spectroscopy (XPS). At very low copper coverages, about 0.005 monolayer, the copper 2p3/2 core level binding energy is 1.2 eV larger than the bulk copper value. As the copper coverage increases, this core level shift decreases; at a coverage of one monolayer this shift is sometimes as large as 0.2 eV. At a copper coverage of two monolayers, the 2p3/2 core binding energy is the same as it is in bulk copper, 932.85 eV. In addition to these changes, the carbon 1s and oxygen 1s core levels are observed to change with the addition of copper. The intensity of the C 1s level at 286.6 eV, associated with a C–O group, is observed to decrease faster than that at 285.0 eV whic...

Formation of a copper‐oxygen‐polymer complex on polystyrene

Previous studies have indicated an increase in the adhesion of deposited metal films to commercial polymers when additional carbon‐oxygen bonds were present on the polymer surface. In this work, we report the changes taking place on an oxygen‐treated polystyrene surface following vapor deposition of copper. We first found that atomic oxygen produces a carbon‐oxygen single bond on the polystyrene surface, with the oxygen displacing a hydrogen and either forming an OH group or cross linking two chains. In addition, this bond is strongly perturbed after vapor deposition of copper. The deposition of copper results in the formation of a copper‐oxygen‐polymer complex on the surface, the exact nature of which is still to be determined. The formation of such a complex is consistent with an increased adhesive strength of copper on oxygen‐treated polystyrene.

Formation of metal–oxygen–polymer complexes on polystyrene with nickel and chromium

The microscopic interactions between vapor‐deposited nickel and chromium atoms and oxygen‐treated polystyrene surfaces were investigated using x‐ray photoemission spectroscopy. Exposure to atomic oxygen created single bonds between carbon and oxygen atoms in both C–O–H and C–O–C groups. The resulting O 1s core lineshape shifted from 533.2 to 532.7 eV after deposition of Ni and from 533.6 to 531.9 eV after deposition of Cr. These changes indicate the formation of metal–oxygen–polymer complexes at the interface. The presence of these complexes correlated with an increase in the adhesion of these metal films to the oxygen‐treated substrate compared to the clean polystyrene substrate.

Auger and photoelectron study of codeposited sulfur and oxygen layers on silver (111)

When oxygen and sulfur are codeposited on a silver surface, the sulfur L2,3MM Auger spectrum is altered significantly from that obtained when sulfur alone is deposited. Besides a chemical shift due to the observed 6.6‐eV sulfur L2,3 binding energy increase on coadsorption with oxygen, the oxygen L1 core level and a hybridized sulfur level in the valence band participate in the sulfur Auger process, introducing new Auger peaks similar to those present in surfaces containing SO4= groups. Electron bombardment of this film preferentially desorbs oxygen and alters the Auger spectrum back to one characteristic of films of sulfur alone on silver. These Auger spectra are analyzed on the basis of a model which uses experimentally determined initial states and small final‐state effects.

Structure of Cu(100) from low energy electron diffraction

Abstract A large number of nonspecular LEED intensity profiles from the clean (100) surface of copper have been measured. The geometrical structures resulting from application of data averaging methods to both experimental and theoretical intensity profiles are presented and compared with earlier work. The present results indicate that the upper layer spacing of the Cu (100) surface is within 1% of the bulk layer spacing, but that the surface registry vector of the layer is 8% larger in magnitude than the bulk registry vector. The results obtained from grand-averaged model calculations indicate that averaging does not give accurate results for surface layer registries. In general, it seems that the data-averaging technique is much more useful for determination of surface layer spacing (which is most sensitive to the momentum spacing between kinematic peaks) than for finding surface registry (which is most dependent upon absolute peak positions).

Core‐level spectra of chromium and nickel atoms on polystyrene

Nickel and chromium atoms which were vapor deposited on clean surfaces of polystyrene were characterized with x‐ray photoemission spectroscopy. For nickel coverages less than 0.01 monolayer the nickel atoms form isolated clusters. As the nickel coverage increases, these islands gradually coalesce into larger islands. The chromium undergoes the same coverage‐dependent behavior beginning at about 0.02 monolayer. A comparison of the nickel and chromium data with the corresponding data for copper indicates that the mobility of copper on the polystyrene is less than that of either nickel or chromium. Finally, we did not find a nickel or chromium surface site with an unusually low core‐electron binding energy similar to the copper site previously observed.

Unusual core level spectra of copper on polystyrene

X-ray photoemission spectroscopy was used to examine the surfaces of atactic polystyrene before and after vapor deposition of copper. At copper coverages of less than 0.01 monolayer the copper 2p32 core electron binding energy was measured at 931.5 eV, 1.5 eV less than the value for bulk copper. At larger copper coverages, the core lineshape split into a doublet, with a new peak at 934.1 eV. This new peak is indicative of isolated small clusters of copper atoms whose binding energy approaches the bulk value of 933.0 eV as the copper coverage approaches a monolayer. However the first peak at 931.5 eV indicates that an unusual site for copper exists on the surface. The measured binding energy is indicative of a copper atom in a region of high electron density where the electronic relaxation energy is greater than in bulk copper or of a copper atom that has undergone significant charge rearrangement.