Introduction to Surface Physical Chemistry

Christmann, K.

doi:10.1007/978-3-662-08009-2

Cited by 241 publications

(228 citation statements)

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“…59 Typically the defect site can be considered the most reactive but dissociation energies and activation energies can differ substantially just by surface and site dependences. 18 The solution to this would be again abandoning the rate equation approach and using a CTRW Monte Carlo technique to track the adsorbate on the grain surface. For dissociation energies and activation energies we used some less then ideal techniques to estimate barriers.…”

Section: Discussionmentioning

confidence: 99%

“…If a diatomic comes into contact with the surface at the crossover point spontaneous dissociation will occur (dissociative adsorption). [17][18] For this to occur the chemisorption site needs to be at a lower energy then the physisorption site and the barrier needs to lie below the energy of the incoming molecule. In this case dissociative adsorption will occur upon almost every collision.…”

Section: Chemistry On Bare Grainsmentioning

confidence: 99%

“…Dissociation is more efficient for smaller systems; more atoms leads to more vibrations in the complex in which energy can 18 be distributed which leads to slower re-dissociation. In interstellar environments radiative association is only a competitive process when the complex is large (>10 atoms) or one of the reactants is the relatively abundant molecular hydrogen, in such cases k diss ≤ k rad and radiative association occurs at the collisional rate.…”

Section: Radiative Associationmentioning

confidence: 99%

“…However, for chemisorption the adsorbate needs a free site to bind to due to electron sharing between the surface and adsorbate and short range interactions, if it hits a filled site the species is assumed to scatter. 18 Equation 2.16 below was implemented to account for coverage dependence of the sticking coefficient:…”

Section: Proton and Charge Exchange Reactionsmentioning

confidence: 99%

“…18 These forces are very weak (binding energies of roughly .1 eV) and dominate the chemistry in low temperature regimes. They are also responsible for adsorption of noble gases and other closed shell species (CH 4 or H 2 ) even at higher temperatures.…”

Section: Chemisorption Vs Physisorption Processesmentioning

confidence: 99%

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Computational Modeling of High Temperature Gas-Grain Chemistry in Interstellar Medium (ISM)

Schulte¹

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Section: Discussionmentioning

confidence: 99%

Section: Chemistry On Bare Grainsmentioning

confidence: 99%

Section: Radiative Associationmentioning

confidence: 99%

Section: Proton and Charge Exchange Reactionsmentioning

confidence: 99%

Section: Chemisorption Vs Physisorption Processesmentioning

confidence: 99%

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Computational Modeling of High Temperature Gas-Grain Chemistry in Interstellar Medium (ISM)

Schulte¹

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X‐Ray Photoelectron Spectroscopy

Weimer¹

2002

Characterization of Materials

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X‐ray photoelectron spectroscopy (XPS) uses x rays of a characteristic energy (wavelength) to excite electrons from orbitals in atoms. The photoelectrons emitted from the material are collected as a function of their kinetic energy, and the number of photoelectrons collected in a defined time interval is plotted versus kinetic energy. This results in a spectrum of electron counts (number per second) versus electron kinetic energy (eV). Peaks appear in the spectrum at discrete energies due to emission of electrons from states of specific binding energies (orbitals) in the material. The positions of the peaks identify the chemical elements in the material. Peak areas are proportional to the number of orbitals in the analysis volume and are used to quantify elemental composition. The positions and shapes of the peaks in an XPS spectrum can also be analyzed in greater detail to determine the chemical state of the constituent elements in the material, including oxidation state, partial charge, and hybridization. This article details the overall protocal for XPS analysis. X‐ray photoelectron spectroscopy is widely applied to all types of solids, including metals, ceramics, semiconductors, and polymers, in many forms, including foils, fibers, and powders. It has also been used to obtain spectra of gas‐phase compounds. In general, it is a nondestructive method of analysis. When applied to solids, XPS is a surface‐sensitive technique. The best sensitivity of XPS for quantifying elemental composition in solids is on the order of 0.1 at. %. All elements with atomic number greater than three can be detected. The detection sensitivity varies for each element, with some elements requiring greater concentrations to reach a nominal detection threshold in a reasonable analysis time. Thin film samples can be analyzed with XPS to determine film thickness. Typical methods of analysis involve measuring composition either as a function of sputter depth into the sample (sputter profiling) or as a function of electron emission angle (angle‐resolved XPS). The chemical state information obtained with XPS includes oxidation states or hybridization states for chemical bonds of the elements. Assignment of chemical state using XPS is not without ambiguities, because other factors besides chemical environment shift the peaks in an XPS spectrum. The use of references with known composition and chemistry can usually help resolve these ambiguities. The primary limitation of XPS is the need for ultrahigh vacuum conditions during analysis. This generally limits the type of material to those with a low vapor pressure (<10 −8 mbar) at room temperature and limits the sample size to that which will fit through the introduction ports on the vacuum chamber. Some compounds, such as polymers, can also degrade under the x‐ray flux. Another limitation in interpretation of spectra from insulator and semiconductor samples arises from sample charging. This is an artifact that can be corrected either during or after data acquisition, although the extent of the correction is often not straightforward to determine.

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X‐Ray Photoelectron Spectroscopy

Weimer

2012

Characterization of Materials

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X‐ray photoelectron spectroscopy (XPS) uses x‐rays of a characteristic energy (wavelength) to excite electrons from orbitals in atoms. Photoelectrons are emitted from the material and collected as a function of their exiting kinetic energy. For single‐step excitation processes, the initial binding energy of the photoelectron is related through energy conservation to its kinetic energy and the x‐ray energy. A typical XPS spectrum shows intensity of electrons as number of electrons per time versus electron binding energy. Features appear in the spectrum due to photoemission from specific binding energy states (excitation from orbitals) in the material and to interactions of the escaping photoelectrons within the material. Chemical elements give rise to peaks at defined binding energies that are from their core levels. The total, integrated photoelectron emission from a core level peak is proportional to the number of orbitals in the analysis volume. This relationship is used to quantify the relative elemental composition of the material in atom percent ( at %). The binding energy positions and shapes of the core level peaks and of other excitation features can also be analyzed in detail to determine chemical state information, including oxidation states, partial charges, or hybridization of the elements. The ability to provide both quantitative elemental composition and orbital bonding state information makes XPS unique and gives rise to the additional name as electron spectroscopy for chemical analysis (ESCA).

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Introduction to Surface Physical Chemistry

Cited by 241 publications

References 0 publications

Computational Modeling of High Temperature Gas-Grain Chemistry in Interstellar Medium (ISM)

Computational Modeling of High Temperature Gas-Grain Chemistry in Interstellar Medium (ISM)

X‐Ray Photoelectron Spectroscopy

X‐Ray Photoelectron Spectroscopy

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