Surface plasmon polariton propagation length: A direct comparison using photon scanning tunneling microscopy and attenuated total reflection

The propagation of surface plasmon polaritons (SPP's) is studied using a photon scanning tunneling microscope (PSTM) and conventional attenuated total reflection (ATR). The PSTM experiment uses localized (focused beam) launching or SPP's at a wavelength of 632.8 nm. Propagation of the SPP is observed as an exponentially decaying tail beyond the launch site acid the 1/e propagation length is measured directly for a series of Ag films of different thicknesses. The ATR measurements are used to characterize the thin film optical and thickness parameters, revealing, notably, the presence of a contaminating adlayer of Ag2S of typical dielectric function, 8.7 + i2.7, and thickness 1-2 nm. Values of the SPP propagation length, based on the ATR- derived film parameters used in the four-media implicit SPP dispersion relation, show very good agreement with those based on the PSTM images for the case of undercoupled or optimally coupled SPP modes. The observed propagation lengths are quantitatively analyzed taking explicit account of additional intrinsic damping due to the growth of the Ag2S layer and of reradiation of the SPP back into the prism outside the launch site. Finally, the PSTM images show excellent SPP beam confinement in the original propagation direction.

Surface plasmon polariton propagation across a gentle silver step

Surface plasmon polaritons (SPPs) are excited with light of wavelength lambda (1) = 632.8 nm on or near a gentle Ag/Ag step structure using focused beam, prism coupling and detected using a bare, sharpened fibre tip. The tip-sample separation is controlled by means of an evanescent optical field at wavelength lambda (2) = 543.5 nm in a photon scanning tunnelling microscope (PSTM). The SPP propagation properties are first characterised on both the thin and thick sections of the Ag film structure either side of the step, both macroscopically, using attenuated total reflection, and microscopically from the PSTM images; the two techniques yield very good agreement. It is found that the SPP propagation length is similar to 10-11 mum across the step in each direction (thick to thin and vice versa) as observed in the PSTM images. Thus, with reference to the propagation lengths of 14.2 and 11.7 mum for the thick and thin planar parts of the Ag film respectively, it is concluded that the SPPs negotiate the step reasonably successfully. Importantly, also, it is shown that images may be produced, displaying SPPs with either an artificially enhanced (similar to 15-20 mum) or truncated (5-8 mum) propagation length across the step. Consideration of such images leads us to suggest the possibility that the photon tunnelling occurs in a local water environment. (C) 2001 Elsevier Science B.V. All rights reserved.

Measurement and interpretation of the mid-infrared properties of single crystal and polycrystalline gold

The contribution of electron-phonon scattering and grain boundary scattering to the mid-IR (lambda = 3.392 mum) properties of An has been assessed by examining both bulk, single crystal samples-Au(1 1 1) and Au(1 1 0)-and thin film, polycrystalline An samples at 300 K and 100 K by means of surface plasmon polariton excitation. The investigation constitutes a stringent test for the in-vacuo Otto-configuration prism coupler used to perform the measurements, illustrating its strengths and limitations. Analysis of the optical response is guided by a physically based interpretation of the Drude model. Relative to the reference case of single crystal Au at 100 K (epsilon = - 568 + i17.5), raising the temperature to 300 K causes increased electron-phonon scattering that accounts for a reduction of similar to40 nm in the electron mean free path. Comparison of a polycrystalline sample to the reference case determines a mean free path due to grain boundary scattering of similar to 17 nm, corresponding to about half the mean grain size as determined from atomic force microscopy and indicating a high reflectance coefficient for the An grain boundaries. An analysis combining consideration of grain boundary scattering and the inclusion of a small percentage of voids in the polycrystalline film by means of an effective medium model indicates a value for the grain boundary reflection coefficient in the range 0.55-0.71. (C) 2005 Elsevier B.V. All rights reserved.

Molecular Modeling on Inhibitor Complexes and Active-Site Dynamics of Cytochrome P450 C17, a Target for Prostate Cancer Therapy

A molecular model for the P450 enzyme cytochrome P450 C17 (CYP17) is presented based on sequence alignments of multiple template structures and homology modeling. This enzyme plays a central role in the biosynthesis of testosterone and is emerging as a major target in prostate cancer, with the recently developed inhibitor abiraterone currently in advanced clinical trials. The model is described in detail, together with its validation, by providing structural explanations to available site-directed mutagenesis data. The CYP17 molecule in this model is in the form of a triangular prism, with an edge of similar to 55 angstrom and a thickness of similar to 37 angstrom. It is predominantly helical, comprising 13 alpha helices interspersed by six 3(10) helices and 11 beta-sheets. Multinanosecond molecular dynamics simulations in explicit solvent have been carried out, and principal components analysis has been used to reveal the details of dynamics around the active site. Coarse-grained methods have also been used to verify low-frequency motions, which have been correlated with active-site gating. The work also describes the results of docking synthetic inhibitors, including the drug abiraterone and the natural substrate pregnenolone, in the CYP17 active site together with molecular dynamics simulations on the complexes. (C) 2010 Elsevier Ltd. All rights reserved.

New and Alternative Social Movements in Spain: The Left, Identity and Globalizing Processes

This collection offers a diachronic analytical study of new and alternative social movements in Spain from the democratic transition to the first decade of the 21st century, paying attention to anti-war mobilizations and the use of new technologies as a mobilizing resource. New and alternative social movements are studied through the prism of identified linkages among the left, movement identities and global processes in the Spanish context. Weight is given to certain important historical aspects, like Spain’s relatively recent authoritarian past, and certain value-added factors, such as the weak associationalism and materialism exhibited by the Spanish public. These are complemented by exploring insights offered by key theoretical approaches on social movements (political opportunities structures, resource mobilization). The volume covers established social movement cases (gender, peace, environmental movements) as well as those with a more explicit connection to the current context of global contestation (squatters’ and anti-globalization movements).

Challenging the SD benefits attributed to sport Mega-Events hosting

Sport Mega-event hosting faces opposition that is manifested with different intensity during the different phases of the event, from its inception as an idea to its delivery and legacy. Some Social Movements Organisations (SMOs) have acted as indefatigable monitors of the Sustainable Development (SD) dimension of sporting events in general and, in some of the most recent sport mega-events, in particular the Olympics, they have served as important advisors and facilitators. Nevertheless, in many cases we see enthusiastic supporters turning to vehemently challenging whatever positives have been associated with hosting the event. In addition, there is opposition to sport Mega-events in their entirety. That type of opposition tends to employ a holistic prism that manages to identify multiple interconnected negative aspects of hosting a sport mega-event and incorporate them into an anti-systemic discourse. It is important to bear in mind that irrespective of many proclamations to the opposite as far as megas are concerned (projects and/or events), a number of studies have demonstrated that citizen participation and democratic accountability in decision-making have been notoriously absent. After all, the idea of citizen participation in the planning of sport mega-event is essentially the public response to a plan conceived by others. There were, of course, some notable cases of democratic consultation at the early stages of bidding to host a sport mega-event but these more democratic approaches resulted in the failure of the bid (for e.g. Toronto 1996). The knowledge of this by the groups that initiated the hosting idea and the bidding process has led to discouraging in depth public consultation that may fit perfectly to the democratic process but not to the tight schedules of associated projects completion. That produces ‘autocracy against which opposition may arise’ (Hiller, 2000, p. 198). It is this democratic deficit that has led to important instances of social contestation and protest mobilizations by citizen groups as well as the more regular corps of social activists. From a perspective borrowed from the sociology of protest and social movements, sport mega-events hosting can operate as an issue that stimulates protest activities by an existing protest milieu and new actors as well as an important mobilizing resource. In fact, some scholars have also argued that the Olympic Games were an important frame for the transnational activism that was marked by anti-globalization protest in Seattle in 1999 (Cottrell & Nelson, 201; Lenskyj, 2008). In addition, it’s important not to lose sight of other acts dissent that take place in relatively close proximity, about a year before the event when most infrastructural and societal changes brought by hosting the event and impact start to become apparent by the host communities, like the rioting of August 2011 in the London Olympic Boroughs and the 2012 riots of June 2013 in Sao Paulo and other Brazilian cities. This paper starts by outlining the SD claims made in the bidding to host the summer Olympic Games by five prospective hosts (Sydney; Athens; Beijing; London and Rio) proceeds towards examining the opposition and challenges that was manifested in relation to these claims. In Particular it provides an assessment of protest-events over the aforementioned different phases of sport mega-events hosting. A different picture emerges for each of the host nation that is partly explained by local, national and global configuration of protest politics. Whereas the post-event legacy of the first two hosts of the Games can be assessed and that way see the validity of claims made by challengers in the other phases, in the other three cases, the implementation of Olympic Games Impact (OGI) studies offers the tool for discussing the post-event phase for Beijing and London and engage in a speculative exercise for the case of Rio. Judging by available findings, the paper concludes that the SD aspiration made in the bid documents are unlikely to be met and social contestation based on the same issues is likely to increase due to the current global economic crisis and BRICS, like China and Brazil, having entered the process of becoming global economic hegemons.

The interaction of surface plasmon polaritons with a silver film edge

A prism coupling arrangement is used to excite surface plasmons at the surface of a thin silver aim and a photon scanning tunnelling microscope is used to detect the evanescent field above the silver surface. Excitation of the silver/ air mode of interest is performed at lambda(1) = 632 . 8 nm using a tightly focused beam, while the control of the tip is effected by exciting a counter-propagating surface plasmon field at a different wavelength. lambda(2) = 543 . 5 nm, using an unfocused beam covering a macroscopic area. Propagation of the red surface plasmon is evidenced by an exponential tail extending away from the launch site, but this feature is abruptly truncated if the surface plasmon encounters the edge of the silver film - there is no specularly reflected 'beam'. Importantly, the radiative decay of the surface mode at the film edge is observable only at larger tip-sample separations, emphasizing the importance of accessing the mesoscopic regime.

Application of surface plasmon polaritons in the laser ablation and characterisation of thin aluminium films

Surface modification of thin aluminium films is both produced and characterised by exciting surface plasmon polaritons in an attenuated total reflection geometry: silica prism/aluminium/aluminium oxide system. The modification is performed, under ambient conditions, by exposure to a low fluence (

Characterization of optical properties of PtSi at 3.392 mu m from 300 K to 85 K and relation of morphological effects

PtSi/Si Schottky junctions, fabricated using a conventional technique of Pt deposition with a subsequent thermal anneal, are examined using X-ray diffraction, atomic force microscopy and a novel prism/gap/sample optical coupling system. With the aid of X-ray diffraction and atomic farce microscopy it is shown that a post-anneal etch in aqua regia is essential for the removal of an unreacted, rough surface layer of Pt, to leave a much smoother PtSi film. The prism/gap/sample or Otto coupling rig is mounted in a small UHV chamber and has facilities for remote variation of the gap (by virtue of a piezoactuator system) and variation of the temperature in the range of similar to 300 K - 85 K. The system is used to excite surface plasmon polaritons on the outer surface of the PtSi and thus produce sensitive optical characterisation as a function of temperature. This is performed in order to yield an understanding of the temperature dependence of phonon and interface scattering of carriers in the PtSi.

Contrasting damage characteristics in direct incidence and surface plasmon mediated single-shot laser ablation of aluminium films

Thin, oxidised Al films grown an one face of fused silica prisms are exposed. tinder ambient conditions, to single shots from an excimer laser operating at wavelength 248 nm. Preliminary characterisation of the films using attenuated total reflection yields optical and thickness data for the Al and Al oxide layers; this step facilitates the subsequent, accurate tuning of the excimer laser pulse to the: surface plasmon resonance at the Al/(oxide)/air interface and the calculation of the fluence actually absorbed by the thin film system. Ablation damage is characterised using scanning electron, and atomic force microscopy. When the laser pulse is incident, through the prism on the sample at less than critical angle, the damage features are molten in nature with small islands of sub-micrometer dimension much in evidence, a mechanism of film melt-through and subsegment blow-off due to the build up of vapour pressure at the substrate/film interface is appropriate. By contrast, when the optical input is surface plasmon mediated, predominately mechanical damage results with the film fragmenting into large flakes of dimensions on the order of 10 mu m. It is suggested that the ability of surface plasmons to transport energy leads to enhanced, preferential absorption of energy at defect sites causing stress throughout the film which exceeds the ultimate tensile stress for the film: this in turn leads to film break-up before melting can onset. (C) 1998 Elsevier Science B.V.

IMAGING OF SURFACE-PLASMON LAUNCH AND PROPAGATION USING A PHOTON SCANNING TUNNELING MICROSCOPE

The spectroscopic capability of the photon scanning tunneling microscope is exploited to study directly the launch and propagation of surface plasmons on thin silver films. Two input beams, of different wavelength, are incident through the prism in a prism-Ag film-air-fibre tip system. Both excite surface plasmons at the Ag-air interface and light of both wavelengths is coupled into the fibre probe via the respective surface plasmon evanescent fields. One laser beam is used for instrument control. The second, or probe beam is tightly focused on the sample, within the area of the unfocused or control beam, giving a well-defined and symmetrical, confined surface plasmon launch site. However, the image at the probe wavelength is highly asymmetrical in section with an exponential tail extending beyond one side of the launch site. This demonstrates in a very direct fashion;the propagation of surface plasmons; a propagation length of similar to 11.7 mu m is measured at a probe wavelength of 543.5 nm. On rough Ag films the excitation of localised scattering centres is also observed in addition to the launch of delocalised surface plasmons.

SURFACE-PLASMON ENHANCED LASER-ABLATION OF THIN METAL-FILMS

Surface plasmon enhancement of laser ablation of thin Al films is examined with a view to its application in metal film patterning and nano-structuring. Al films, deposited on silica prisms, are first characterized by attenuated total reflection using a broadband UV source and appropriate interference filter. The films are subsequently subjected to excimer laser radiation of wavelength 248 nm under conditions both of direct incidence from the air side of the film, and of surface plasmon excitation in which light is incident through the prism at greater than critical angle. For a given level of ablation damage in a particular film the fluence required using the surface plasmon technique is 3-5 times less than that needed when direct incidence is used. This is roughly in line with the energy absorbed in the film. From a practical standpoint it is clear that ablation of metal films can be achieved with much lower fluences than has hitherto been possible, thus reducing the requirements on laser output and relaxing the power handling constraints on any input optical elements.

PHOTOSIGNAL ENHANCEMENT IN AL-GAAS DIODES DUE TO SURFACE-PLASMONS AND GUIDED-WAVE MODES

Light of wavelength 632.8 nm and p-polarization is incident on a prism-air gap (varied from 0.7 to 7 mum)-Al-GaAs arrangement. Both the photosignal generated by the Schottky diode and the reflectance are measured as a function of the internal angle of incidence in the prism. There is significant, well-defined enhancement of the photosignal, up to a factor of approximately 7.5, associated with two different types of enhanced absorption modes. For air gaps <1.5 mum there is photosignal enhancement due to an enhanced absorption feature (reflectance dip) that occurs at an angle of incidence just above critical angle in the prism; this feature corresponds to the excitation of a surface plasmon polariton at the Al-air interface. For air gaps > 1 mum there are between one and ten photoresponse peaks at input angles less than the critical angle. The corresponding enhanced absorption features are due to leaky guided wave modes set up in the air gap.

ANALYSIS OF SURFACE-PLASMON POLARITON ENHANCEMENT IN PHOTODETECTION BY AL-GAAS SCHOTTKY DIODES

The surface plasmon polariton mediated photoresponse from Al-GaAs diodes is examined in a prism-air gap-diode configuration as a function of both the wavelength of the incident light and thickness of the Al electrode. The experimental data shows a pronounced dip in reflectance as a function of internal angle of incidence in the prism, due to the excitation of the surface plasmon polariton at the Al-air interface, and a corresponding peak in device photosignal. Careful modelling of reflectance and quantum efficiency data shows that the bulk of the signal is generated by light which is re-radiated from this surface mode into the semiconductor substrate where it is absorbed by the creation of electron-hole pairs in the depletion region. This holds for all the wavelengths used here (all are shorter than the GaAs absorption edge) and across the thickness range of the Al electrodes (20-50 nm). Quantum efficiencies in the range 0.5-22% and enhancement factors of typically 7.5 were recorded in this investigation.

INTERPLAY OF CAF2 SUBSTRATE ROUGHENING AND FILM DEPOSITION RATE ON RADIATIVE SCATTERING OF SURFACE-PLASMON POLARITONS FROM AG FILMS

The radiative decay of surface plasmon polaritons has been investigated in an attempt to characterize the surface roughness of Ag films prepared under different conditions. The polaritons were excited by the method of attenuated total reflection of light. The films were deposited on the face of a 60-degrees BK-7 glass prism at a rate that was deliberately fixed in two different ranges (centred on 0.1 and 10 nm s-1) and in some cases a CaF2 underlayer was used to roughen the film surfaces. The intensity of the scattered light emitted from the opposite face of the films was measured as a function of direction for each using the same sensitivity scale and was correlated with the preparation of the film. It was found that on nominally smooth substrates fast-deposited thinner films give out more light and are deduced to have greater short wavelength (300-600 nm) roughness amplitude. There is also evidence for long wavelenth (7 mum) periodic roughness due to the prism substrate itself. On CaF2 roughened surfaces the light output from the films is further increased and the peak intensity is backward directed with respect to the exciting laser beam direction. Here roughness on a lateral scale of 350 nm is responsible. Also, elastic scattering of surface plasmon polaritons at grain boundaries reduces the light output from fast deposited, small grain, films on CaF2 roughened surfaces. Overall, a consistent picture of roughness induced radiative polariton decay emerges for all cases studied.