Photon-surface interaction

The reaction mechanisms of plasma polymerization processes are not understood in detail. Poll et al [34] (figure C2.13.6) proposed a possible generic reaction sequence. Plasma-initiated polymerization can lead to the polymerization of a suitable monomer directly at the surface. The reaction is probably triggered by collisions of energetic ions or electrons, energetic photons or interactions of metastables or free radicals produced in the plasma with the surface. Activation processes in the plasma and the film fonnation at the surface may also result in the fonnation of non-reactive products. 

PHOTONUCLEAR REACTION. A nuclear reaction induced by a photon. In some cases the reaction probably takes place via a compound nucleus formed by absorption of the photon followed by distribution of its energy among the nuclear constituents. One or more nuclear particles then "evaporate from the nuclear surface, or occasionally the nucleus undergoes pliotofissioii. In other cases the photon apparently interacts directly with a single nucleon, which is ejected as a photoneutron or photoproton without appreciable excitation of the rest of the nucleus. 

Electron microprobes permit chemical microanalysis as well as SEM and BSE detection, often referred to as analytical electron microscopy (AEM), or electron probe microanalysis (EPMA)56 57. This is because another product of the surface interaction with an incident electron beam is X-ray photons which have wavelengths and energies dependent on element identity and on the electron shell causing the emission. Analysis of these photons can give a local chemical analysis of the surface. Resolution of 1 pm is attainable. Two types of X-ray spectrometer can be employed ... 

Laser-induced reaction has been widely used to stimulate gas-surface interaction. Lasers are also used to probe molecular dynamics in heterogeneous systems as well. In the applied area, the laser photochemical techniques are successfully applied to produce well defined microstructures and new materials for microelectronic devices (1). Enhanced adsorption and chemical reaction on surfaces can be achieved by a photoexcitation of gaseous molecules, adsorbed species as well as solid substrates. The modes of the excitation include vibrational and electronic states of the gaseous species and of the adsorbates surface complexes. Both a single and a multiple photon absorption may be involved in the excitation process. 

The photon-stimulated surface interactions are often divided... 

Other applications involved photon adsorption or emission. An FTIR spectroscopic study of the adsorption of pyrimidine on loughlinite was conducted to characterize the surface interaction <04JMS147>, and new mono-, poly-, and macrocyclic mesoionic pyrimidinium-olates were prepared and their propensity toward photochemical rearrangement to his(P-lactam) derivatives was studied <04710011>. Sequential nucleophilic addition of aryl anions to 2-methylthiopyrimidine 76 followed hy DDQ oxidation gave 4-aryl-2-methylthiopyrimidines, then... 

The solution, proposed by Einstein, was that the discrete energy units, identified by Planck, correspond to quanta of light, called photons, which interact with electrons in the metal surface during direct collision. This dual wave/particle nature of light inspired de Broglie to postulate a similar behaviour for electrons. Experimental observation of electron diffraction confirmed the wave nature of electrons and firmly estabUshed the dual character of all quantum objects as mysterious reality. As the logical pictme of an entity, which is wave as well as particle, is hard to swallow, it has become fashionable to avoid all physical models of quantum events it is considered poor taste to contaminate the quantmn world with classical concepts. This noble idea of the so-called Copenhagen interpretation of quantmn theory has resulted in a probabilistic computational model that, not only defies, but denies comprehension. 

The energy loss of photons in matter can be characterized by the cross section of the process and also by the mean free path of photons between interactions. The latter can be expressed in units of surface density, and then it is called mass attenuation length. Photon attenuation lengths for various elements are shown inO Fig. 8.13 as taken from Bichsel et al. (2002). 

This expression may be interpreted in a very similar spirit to tliat given above for one-photon processes. Now there is a second interaction with the electric field and the subsequent evolution is taken to be on a third surface, with Hamiltonian H. In general, there is also a second-order interaction with the electric field through which returns a portion of the excited-state amplitude to surface a, with subsequent evolution on surface a. The Feymnan diagram for this second-order interaction is shown in figure Al.6.9. 

With the exception of the scanning probe microscopies, most surface analysis teclmiques involve scattering of one type or another, as illustrated in figure A1.7.11. A particle is incident onto a surface, and its interaction with the surface either causes a change to the particles energy and/or trajectory, or the interaction induces the emission of a secondary particle(s). The particles that interact with the surface can be electrons, ions, photons or even heat. An analysis of the mass, energy and/or trajectory of the emitted particles, or the dependence of the emitted particle yield on a property of the incident particles, is used to infer infomiation about the surface. Although these probes are indirect, they do provide reliable infomiation about the surface composition and structure. 

The chemical, stmctural, and electronic characteristics of surfaces and interfaces are usually different from those of the bulkphase(s). Thus, methods to be used for the analysis of surfaces must be selective in response to the surface or interfacial region relative to the bulk. Surfaces and interfaces are most commonly explored using techniques based on the interaction of photons, electrons, or ions with the surface or using a force such as electric field or van der Waals attraction. These excitations generate a response involving the production of photons, electrons, ions or the alteration of a force that is then sensed in the analysis. 

Depth sensitivity is an equally important consideration in the analysis of surfaces. Techniques based on the detection of electrons or ions derive their surface sensitivity from the fact that these species cannot travel long distances in soflds without undergoing interactions which cause energy loss. If electrons are used as the basis of an analysis, the depth resolution will be relatively shallow and depend on both the energy of the incident and detected electrons and on characteristics of the material. In contrast, techniques based on high energy photons such as x-rays will sample a much greater depth due... 

The physical techniques used in IC analysis all employ some type of primary analytical beam to irradiate a substrate and interact with the substrate s physical or chemical properties, producing a secondary effect that is measured and interpreted. The three most commonly used analytical beams are electron, ion, and photon x-ray beams. Each combination of primary irradiation and secondary effect defines a specific analytical technique. The IC substrate properties that are most frequendy analyzed include size, elemental and compositional identification, topology, morphology, lateral and depth resolution of surface features or implantation profiles, and film thickness and conformance. A summary of commonly used analytical techniques for VLSI technology can be found in Table 3. 

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