We report combined studies of the influence of chemical and physical treatments on the properties of indium–tin oxide (ITO) thin films. The ITO films were also used as transparent anodes of polymeric light-emitting diodes (LEDs) incorporating poly(p-phenylene vinylene) (PPV) as the emitter material, with, or without, doped poly(3,4-ethylene dioxythiophene) (PEDOT) as a hole-injection/transport layer. Structures based on a soluble green derivative of PPV, poly(4,4′-diphenylene diphenylvinylene) were also tested. We studied chemical (aquaregia, degreasing, RCA protocol) and physical (oxygen and argon plasmas, Teflon, and paper rubbing) treatments and, in contrast to recently published work, we find that for Balzer Baltracon ITO, oxygen plasma and not aquaregia yields the highest efficiencies and luminances and the lowest drive voltages. For oxygen-plasma-treated anodes, the device efficiency clearly correlates with the value of the ITO surface work function, which in turn depends on the time of treatment. Interestingly, we find that work-function variations induced by our oxygen-plasma treatment are unchanged after long-term storage in air and in the dark. Unexpectedly, we also find that devices incorporating a PEDOT layer benefit from an appropriate treatment of the ITO surface, for both efficiency and lifetime. The results shed light on the physics of conjugated, organic semiconductors and related devices, and in particular on the presence and the role of an anodic energy barrier on the LEDs mechanism of operation. We also discuss the implications of our integrated experimental study in relation to the modification of the ITO sheet resistance, surface and bulk composition, and surface morphology.

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The electronic structure of tris͑8-hydroxyquinoline͒ aluminum (Alq 3 ) has been studied in the pristine molecular solid state as well as upon interaction ͑doping͒ with potassium and lithium. We discuss the results of a joint theoretical and experimental investigation, based on a combination of x-ray and ultraviolet photoelectron spectroscopies with quantum-chemical calculations at the density functional theory level. Upon doping, each electron transferred from an alkali metal atom is stored on one of the three ligands of the Alq 3 molecule, resulting in a new spectral feature ͑peak͒ in the valence band that evolves uniformly when going from a doping level of one to three metal atoms per Alq 3 molecule.

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because the electric field is parallel to the grating grooves. However, a birefringence volume grating can be induced with a weak diffraction efficiency expressed as Z = (pDnh 0 / l) 2 . Assuming h 0 = 1.3 mm, we have Dn » 0.01, which is consistent with previous experiments on azo-silica thin films. [3] In the case of polarization recording, no intensity gradient exists but the polarization gradient can also create a birefringence grating.This polarization dependence of the surface grating definitely excludes thermal effects and clearly suggests that a translation motion of the dye molecules is the main step of the surface deformation (mass transport). This translation probably occurs via the photoisomerization process: the trans±cis photoconversion increases the free volume of the dyes, allowing their motion along the polarization direction during the cis±trans back-conversion. This process is repeated until the dyes are oriented perpendicularly to the p-polarization of the excited light. This molecular translation mechanism had been proposed in organic polymer systems containing azo dyes. [13] Moreover, the crucial role played by the photoisomerization in the thickness deformation process was further confirmed by experiments realized on thin gel films in which dyes that did not exhibit photoisomerization were incorporated. In these samples no surface grating could be inscribed.Finally, the possibility of producing multiple grating azogel films is illustrated in Figure 4c. Two perpendicular gratings were inscribed on the same spot by rotating the sample 90 between two successive inscriptions. This double grating exhibited the same behavior as single gratings: no relaxation under uniform illumination and erasure by heating the sample above 100 C. This result led us to believe that other kind of motifs, such as blazed gratings, could be inscribed on azo-gel films.In conclusion, very stable surface gratings can be inscribed in azo-hybrid thin films prepared by the sol-gel method in appropriate optical and material configurations. This firstly requires a weakly crosslinked network in the gel whose degree of condensation can easily be controlled by heat treatment and also by the functionality of the sol-gel precursor. Concerning this latter point, further improvements of the thin film are expected by using bifunctional precursors. The second requirement to obtain high modulation depths is the simultaneous presence of an intensity gradient and a non-zero component of the resultant optical field along this gradient.Under these conditions, high diffraction efficiencies in three different orders can be obtained, depending on the illumination time. Explanations for the mass transport mechanism have been proposed that consider the photoisomerization process. Complementary experiments are in progress in order to understand the nonlinear behavior of the growth of the thickness profile versus recording energies.The technological prospects of being able to construct electrically pumped lasers based on molecular or polymeric so...

Stocks of finite resources in the technosphere continue to grow due to human activity, at the expense of decreasing in-ground deposits. Human activity, in other words, is changing the prerequisites for mineral extraction. For that reason, mining will probably have to adapt accordingly, with more emphasis on exploitation of previously extracted minerals.This study reviews the prevailing concepts for mining the technosphere as well as actual efforts to do so, the objectives for mining, the scale of the initiatives, and what makes them different from other reuse and recycling concepts. Prevailing concepts such as "urban mining," however, are inadequate guides to the complexity of the technosphere, as these concepts are inconsistently defined and disorganized, often overlapping when it comes to which stocks they address. This review of these efforts and their potential is therefore organized around a new taxonomy based on the umbrella concept technospheric mining, defined as the extraction of technospheric stocks of minerals that have been excluded from ongoing anthropogenic material flows.An analysis on the basis of this taxonomy shows that the prevailing mining initiatives are generally scattered and often driven by environmental factors, in which metal recovery is viewed as an additional source of revenue. However, development of technology, specialized actors and new business models and policy instruments, could lead to technospheric mining operations becoming a profit-driven business.