42 research outputs found
Pentacene islands grown on ultra-thin SiO2
Ultra-thin oxide (UTO) films were grown on Si(111) in ultrahigh vacuum at
room temperature and characterized by scanning tunneling microscopy. The
ultra-thin oxide films were then used as substrates for room temperature growth
of pentacene. The apparent height of the first layer is 1.57 +/- 0.05 nm,
indicating standing up pentacene grains in the thin-film phase were formed.
Pentacene is molecularly resolved in the second and subsequent molecular
layers. The measured in-plane unit cell for the pentacene (001) plane (ab
plane) is a=0.76+/-0.01 nm, b=0.59+/-0.01 nm, and gamma=87.5+/-0.4 degrees. The
films are unperturbed by the UTO's short-range spatial variation in tunneling
probability, and reduce its corresponding effective roughness and correlation
exponent with increasing thickness. The pentacene surface morphology follows
that of the UTO substrate, preserving step structure, the long range surface
rms roughness of ~0.1 nm, and the structural correlation exponent of ~1.Comment: 15 pages, 4 figure
Influence of steps on the tilting and adsorption dynamics of ordered Pn films on vicinal Ag(111) surfaces
Here we present a structural study of pentacene (Pn) thin films on vicinal
Ag(111) surfaces by He atom diffraction measurements and density functional
theory (DFT) calculations supplemented with van der Waals (vdW) interactions.
Our He atom diffraction results suggest initial adsorption at the step edges
evidenced by initial slow specular reflection intensity decay rate as a
function of Pn deposition time. In parallel with the experimental findings, our
DFT+vdW calculations predict the step edges as the most stable adsorption site
on the surface. An isolated molecule adsorbs as tilted on the step edge with a
binding energy of 1.4 eV. In addition, a complete monolayer (ML) with
pentacenes flat on the terraces and tilted only at the step edges is found to
be more stable than one with all lying flat or tilted molecules, which in turn
influences multilayers. Hence our results suggest that step edges can trap Pn
molecules and act as nucleation sites for the growth of ordered thin films with
a crystal structure similar to that of bulk Pn.Comment: 4 pages, 4 figures, 1 tabl
Du rôle de la surface dans l'émission de lumière induite par STM
AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF
L'étrange renoncement / Henri Guaino
Contient une table des matièresAvec mode text
Large white organic light-emitting diode lighting panel on metal foils
Large-area top-emitting PIN structure (highly p- and n- type doped transport layers for electrons and holes and an undoped emitter layer)–organic light-emitting diode (OLED) on advanced metal foils were fabricated for lighting applications. ArcelorMittal has developed a new surface treatment on metal foils, suitable for roll-to-roll production and dedicated to large-area device integration. Both monochromatic and white devices are realized on advanced metal foils. Power efficiencies at 1000 cd/m2 of >70 lm/W (green), moreover, power efficiency of white devices of >22 lm/W are achieved. Furthermore, first large-area 60 × 60 cm white OLED sources on metal foils are presented
OLED Light extraction improvement with surface nano-micro texturation based on speckle lithography.
Part of the light rays generated within a luminescent medium with a higher refractive index than that of the exit medium, typically air, undergo total internal reflection phenomenon (TIR); these rays will be trapped and guided into the emissive material and will not be extracted out of an OLED device for instance. Trapped light is reabsorbed and eventually converted into heat that will be detrimental to the device performance and lifetime. The amount of trapped energy is highly dependent on the values of the refractive indices involved in the multilayer stack constituting the light emitting device. The amount of trapped energy can be extensive and can even reach as much as 75% in certain cases. Solutions to improve the outcoupling efficiency are therefore attractive. In this paper we propose to use laser speckle to produce a random surface with controlled parameters to enhance the OLED outcoupling. A laser speckle pattern is transferred onto a photoresist which will be subsequently converted into a surface relief profile. The optical setup parameters drive the properties of such surface and thus the outcoupling properties. The resulting surface has a quasi-random shape which could be assimilated to a corrugated surface. We will show that these typical surfaces exhibit light extraction enhancement properties. The generated pattern is then transferred onto the exit interfaces of the emitting device. An extraction improvement close to a factor 3 is measured. We finally discuss a practical case for which the laser speckle shape is applied to texture the surface of encapsulating cover glasses in a top-emitting OLED on steel substrates