Vacuum evaporated films

The structure of a CVD material can be classified into three major types which are shown schematically in Fig. 2.13. In Zone (A), the structure consists of columnar grains which are capped by a domelike top. In Zone (B), the structure is also columnar but more faceted and angular. In Zone (C), it consists of fine accost grains. Examples of these structures are shown in Fig. 2.14. " This is the CVD equivalent of the structural model for vacuum-evaporated films first introduced by Movchan and Demshishin.P l... 

J Kalinowski, G Giro, M Cocchi, V Fattori, and P DiMarco, Unusual disparity in electroluminescence and photoluminescence spectra of vacuum-evaporated films of 1,1 -bis ((di-4-tolylamino) phenyl) cyclohexane, Appl. Phys. Lett., 76 2352-2354, 2000. 

In addition to the complexation in solutions, pyridine-appended fulleropyrro-lidines can also form coordination complexes with zinc(II) phthalocyanines in solid-state thin films. Troshin et al. have investigated the photovoltaic behavior of bilayer solar cells fabricated by deposition of solution-processed fulleropy-rrolidines 36-40, which contain chelating pyridyl groups, on vacuum-evaporated films of unsubstituted zinc(II) phthalocyanine (ZnPc) [46], The UV-Vis spectra of these films resemble the spectrum of ZnPc recorded in pyridine, showing a sharp... 

Figure 132 A comparison of the EL and PL spectra of C60. (1) the EL spectrum of a 100 pm-thick single crystal (see Ref. 520a) (2) the EL spectrum of a vacuum-evaporated film of thickness 10 nm < d < 100 nm (see Ref. 521) (3) the PL spectrum of the crystal at low excitation intensity (<1021 quanta cm 2s 1) and (4) the PL spectrum of the crystal at high excitation intensity (>1021 quanta cm-2 s 1) (see Ref. 519). After Ref. 2. Copyright 1999 Institute of Physics (GB).

Figure 11.23 Photo luminescence spectra (Xex = 285nm Xem=545nm) of Tb(tba-PMP)3(TPPO), Tb(tba-PMP)3(H20), and Tb(tba-PMP)3(phen) measured from their 80 nm vacuum evaporated films on quartz substrates [62]. (Reprinted with permission from H. Xin et al., The effect of different neutral ligands on photo luminescence and electroluminescence properties of ternary terbium complexes, The Journal of Physical Chemistry B, 108, 10796-10800, 2004. 2004 American Chemical Society.)...

Cerny and Kovar (241) determined the heat of interaction with vacuum-evaporated films of dysprosium and yttrium at room temperature. These metals yielded high heats of adsorption of 960 and 1060 kj mol", respectively. It was suggested that the oxygen molecules undergo dissociative adsorption on the surface and penetrate into the subsurface, where they form strong bonds to the metal. 

An altemative means to realize well-organized thin films of small molecules is the Langmuir-Blodgett (LB) technique, which allows a fine control of both the stmcture and thickness of the film. We note, however, that this technique is in principle restricted to amphiphilic molecules, composed of a hydrophobic chain and a hydrophobic head-group, which is not the case for most molecules used in OFETs. Nevertheless, LB-grown OFETs have been reported with mixed layers of quinquethiophene (5T) and arachidic acid, which gave well-behaved devices [56]. However, the necessary mixing of the electrically active compound with an inactive compound leads to a substantial decrease in the mobility, as compared to that of a vacuum-evaporated film. 

In UHV conditions two main different substrates are used vacuum-evaporated films and single-crystal or polycrystal bulk samples. 

The Pb(N3)2 films were prepared by exposing vacuum-evaporated films of Pb to the vapor of an aqueous HN3 solution (Chapter 2). Optical measurements were for the most part made at wavelength ranges of high extinction coefficient which are not easily accessible using single crystals and transmission techniques. The measurements are thought to deal mostly with intrinsic optical transitions as differentiated from the optical properties presented elsewhere in this section which deal more directly with imperfections. 

Figure 13.11. X-ray diflfractogram of a vacuum evaporated film of (a) a6T and (b) a,w-dihexyl-a6T. (c) Schematic representation of a a,cu-dihexyl-a6T monolayer on a substrate surface, showing two adjacent rows of oligomers. Reproduced from ref, 69 by kind permission of Pergamon Press.

The corresponding set of spectra obtained by ATR-SEIRAS with a vacuum-evaporated Au(lll) thin-film electrode and 1 mM pyridine-i-0.1 M NaClO. solution in H2O is shown in Fig. 8.8b [55]. The vacuum-evaporated film electrode was subjected to flame annealing before use to give a (111) quasi-single crystal surface. The spectra were recorded with unpolarized radiation and by a simple potential difference tactic with the reference potential of -0.8 V. These spectra are represented in the absorbance units [A=-log(R/i o)]. and thus the up-going bands correspond to pyridine adsorbed on the electrode. Largely different from... 

Most of the light-emitting devices (LEDs) based on conjugated organics are fabricated with spin-cast or vacuum-evaporated films [6]. Several devices based on such layer-by-layer self-assembled films have recently been demonstrated [7]. In this article, we have demonstrated a... 

Silver island vacuum evaporated films are likely the most widely used substrates for the enhancement of fluorescence. With mass thicknesses generally... 

S. Cemy, Adsorption calorimetry on filaments, vacuum-evaporated films and single crystals of metals. Thermochim. Acta 312, 3-16 (1998)... 

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