Photoelectron spectroscopy interface studies

High quahty SAMs of alkyltrichlorosilane derivatives are not simple to produce, mainly because of the need to carefully control the amount of water in solution (126,143,144). Whereas incomplete monolayers are formed in the absence of water (127,128), excess water results in facile polymerization in solution and polysiloxane deposition of the surface (133). Extraction of surface moisture, followed by OTS hydrolysis and subsequent surface adsorption, may be the mechanism of SAM formation (145). A moisture quantity of 0.15 mg/100 mL solvent has been suggested as the optimum condition for the formation of closely packed monolayers. X-ray photoelectron spectroscopy (xps) studies confirm the complete surface reaction of the —SiCl groups, upon the formation of a complete SAM (146). Infrared spectroscopy has been used to provide direct evidence for the hiU hydrolysis of methylchlorosilanes to methylsdanoles at the soHd/gas interface, by surface water on a hydrated siUca (147). 

In a carbon-supported metal electrocatalyst, the electronic interaction between metal and carbon support has a significant effect on its electrochemical performance [4], For carbon-supported Pt electrocatalyst, carbon could accelerate the electron transfer at the electrode-electrolyte interface, leading to an accelerated electrode process. Typically, the electrons are transferred from platinum clusters to the oxygen species on the surfece of a carbon support material and the chemical bond formation or the charge transfer process occurs at the contacting phase, which is considered to be beneficial to the enhancement of the catalytic properties in terms of activity and stability of the electrocatalysts. Experimentally, the investigation into the electron interaction between metal catalyst and support materials could be realized by various physical, spectroscopic, and electrochemical approaches. The electron donation behavior of Pt to carbon support materials has been demonstrated by the electron spin resonance (ESR) X-ray photoelectron spectroscopy (XPS) studies, with the conclusion that the electron interaction between Pt and carbon support depends on their Fermi level of electrons. It is considered that the electronic structure change of Pt on carbon support induced by the electron interaction has positive effect toward the enhancement of the catalytic properties and the improvement of the stability of the electrocatalyst system. However, the exact quantitative relationship between electronic interaction of carbon-supported catalyst and its electrocatalytic performance is still not yet fully established [4]. 

In the many reports on photoelectron spectroscopy, studies on the interface formation between PPVs and metals, focus mainly on the two most commonly used top electrode metals in polymer light emitting device structures, namely aluminum [55-62] and calcium [62-67]. Other metals studied include chromium [55, 68], gold [69], nickel [69], sodium [70, 71], and rubidium [72], For the cases of nickel, gold, and chromium deposited on top of the polymer surfaces, interactions with the polymers are reported [55, 68]. In the case of the interface between PPV on top of metallic chromium, however, no interaction with the polymer was detected [55]. The results concerning the interaction between chromium and PPV indicates two different effects, namely the polymer-on-metal versus the metal-on-polymer interface formation. Next, the PPV interface formation with aluminum and calcium will be discussed in more detail. 

T. Mori, H. Fujikawa, S. Tokito, and Y. Taga, Electronic structure of 8-hydroxyquinoline Aluminium/LiF/Al interface for organic electroluminescent device studied by ultraviolet photoelectron spectroscopy, Appl. Phys. Lett., 73 2763-2765 (1998). 

The magnitude of the injection barrier is open to conjecture. Meanwhile there is consensus that energy barriers can deviate significantly from the values estimated from vacuum values of the work-function of the electrode and from the center of the hole and electron transporting states, respectively. The reason is related to the possible formation of interfacial dipole layers that are specific for the kind of material. Photoelectron spectroscopy indicates that injection barriers can differ by more than 1 eV from values that assume vacuum level alignment [176, 177]. Photoemission studies can also delineate band bending close to the interface [178]. 

Dannetun P, Boman M, Stafstrom S, Salaneck WR, Lazzaroni R, Fredriksson C, Bredas JL, Zamboni R, Taliani C (1993) The chemical and electronic structure of the interface between aluminum and polythiophene semiconductors. J Chem Phys 99(l) 664-672 Ahn H, Whitten JE (2003) Vapor-deposition of aluminum on thiophene-terminated self-assembled monolayers on gold. J Phys Chem B 107(27) 6565-6572 Fisher GL, Flooper A, Opila RL, Jung DR, Allara DL, Winograd N (1999) The interaction between vapor-deposited A1 atoms and methylester-terminated self-assembled monolayers studied by time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy and infrared reflectance spectroscopy. J Electron Spectrosc Relat Phenom 98-99 139-148... 

This work continues our initial study concerning the effect of fluorine contamination on PMDA-ODA adhesion [4], In this study we apply APS at the interface. We continue to use the peel test to monitor the adhesion and X-ray photoelectron spectroscopy (XPS) to study the surfaces and loci of failure after the peel test to elucidate the failure mechanisms. 

The substrates used in this study were (0001) sapphire (A1203), (001) magnesia (MgO), and amorphous fused silica (Si02). All substrates were obtained with surface finish to 0.025 / m, and were cleaned with isopropylalcohol (IPA) prior to PA A or APS application. The surfaces and interfaces after peel test were characterized using X-ray photoelectron spectroscopy (XPS). The PMDA-ODA PAA was cast from NMP solution. Figure l shows the structure of the PAA and the thermally imidized PMDA-ODA polyimide. 

Theory and experimental methods. Since the combined experimental-theoretical approach is stressed, both the underlying theoretical and experimental aspects receive considerable attention in chapters 2 and 3. Computational methods are presented in order to introduce the nomenclature, discuss the input into the models, and the other approximations used. Thereafter, a brief survey of possible surface science experimental techniques is provided, with a critical view towards the application of these techniques to studies of conjugated polymer surfaces and interfaces. Next, some of the relevant details of the most common, and singly most useful, measurement employed in the studies of polymer surfaces and interfaces, photoelectron spectroscopy, are pointed out, to provide the reader with a familiarity of certain concepts used in data interpretation in the Examples chapter (chapter 7). Finally, the use of the output of the computational modelling in interpreting experimental electronic and chemical structural data, the combined experimental-theoretical approach, is illustrated. 

X-ray photoelectron spectroscopy of atomic core levels (XPS or ESCA) is a very powerful tool for characterization of the chemical surrounding of atoms in molecules. In particular, since the method is very surface sensitive, it is possible to monitor the first stages of the interface formation, i.e., in our case the interaction between individual metal atoms and the polymer. Standard core level bonding energies are well known for common materials. However, in our case, we are studying new combinations of atoms and new types of structures for which there are no reference data available. In order to interpret the experimental chemical shifts it is useful to compare with theoretical estimates of the shifts. 

Here we survey a series of possible surface-sensitive measurements which in principle can be used to study the surfaces of conjugated polymers and the early stages of metal interface formation. We then motivate the use of photoelectron spectroscopy. 

Angle-resolved UPS studies of polymers and interfaces Although few polymer systems exist in the form of single crystals, it can be expected that in the future, polymer systems will be prepared which are more ordered. The studies reviewed here are prototypical of what can be done on ordered polymer systems, and lay the basis for future work on ordered systems using photoelectron spectroscopies. 

K. C. Pillai and V.Y. Young,/. Colloid Interface Sci 103 103 (1985). X-ray photoelectron spectroscopy study of xanthate adsorption on pyrite mineral surfaces. 

Experimental determinations of barrier heights on oxide semiconductor interfaces using photoelectron spectroscopy are rarely found in literature and no systematic data on interface chemistry and barrier formation on any oxide are available. So far, most of the semiconductor interface studies by photoelectron spectroscopy deal with interfaces with well-defined substrate surfaces and film structures. Mostly single crystal substrates and, in the case of semiconductor heterojunctions, lattice matched interfaces are investigated. Furthermore, highly controllable deposition techniques (typically molecular beam epitaxy) are applied, which lead to films and interfaces with well-known structure and composition. The results described in the following therefore, for the first time, provide information about interfaces with oxide semiconductors and about interfaces with sputter-deposited materials. Despite the rather complex situation, photoelectron spectroscopy studies of sputter-deposited... 

Bluhm H, Havecker M, Knop-Gericke A, Kiskinova M, Schlogl R, Salmeron M. In situ X-ray photoelectron spectroscopy studies of gas-solid interfaces at near-ambient conditions. MRS Bull. 2007 32 1022. 

The application of photoelectron spectroscopy (PES) for the investigation of polymer-metal interfaces is discussed in this chapter. The information obtainable from both core-level spectra and valence-band spectra is briefly described. The approach of model compounds to study specific interactions is shown to be a useful aid to the understanding of polymer-metal reactivity. Emphasis is given to a number of experimental aspects relevant to polymer-metal interface studies, such as sample preparation and problems such as beam induced dam ge. 

Photoelectron spectroscopy (PES) has become an important and widely used tool in material science (1-3). It has been a particularly fruitful technique for the investigation of polymers (4-9). In this review, we will focus on the application of photoelectron spectroscopy to the investigation of the interfaces between metals and polymers. These studies are directed primarily to understand the role of Interfacial chemistry in the adhesion between metals and polymers. Two aspects, which will be emphasized here, are the experimental approaches in PES studies of polymer/metal interfaces and the types of information accessible from the PES experiments. The experimental emphasis will be on preparation of appropriate samples for polymer/metal interface studies, practical problems... 

This paper will discuss the use of Near-Edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy to study the unoccupied n molecular orbital (MO) structures of polymers and polymer-metal interfaces. A collection of systematic NEXAFS and EELS studies of simple organic compounds by J. Stohr and others (1-10) has led to recent advances in the understanding and interpretation of this technique. It s application to complicated polymers and polymer-metal interactions has only begun, but NEXAFS spectroscopy promises to be an important complement to other photoelectron spectroscopies. 

X-ray photoelectron spectroscopy has been used to study the metal polyimide interface formed during room temperature metal deposition. Several mono-layers of Al, Au and Cu were sputter-deposited onto cured polyimide, to a thickness which permitted the observation of both polyimide and metal peaks. Deconvolution of core-level Cls, Nls and Ols polyimide peaks and A12p, Au4f and Cu2p3/2 metal overlayer peaks has demonstrated that chemical reaction occurs at the carbonyl sites for all these metals under the conditions used. In addition, the aromatic nature of the molecular structure at the interface is believed to decrease while the percentage of an isoimide-like component increases. 

---