Anodic refractive index

Refractive index The refractive index of the clear anodic film produced on aluminium of the highest purity in sulphuric acid is 1-59 in the as-formed condition, rising to 1-62 after sealing . 

If measurements are made in thin oxide films (of thickness less than 5 nm), at highly polished Al, within a small acceptance angle (a < 5°), well-defined additional maxima and minima in excitation (PL) and emission (PL and EL) spectra appear.322 This structure has been explained as a result of interference between monochromatic electromagnetic waves passing directly through the oxide film and EM waves reflected from the Al surface. In a series of papers,318-320 this effect has been explored as a means for precise determination of anodic oxide film thickness (or growth rate), refractive index, porosity, mean range of electron avalanches, transport numbers, etc. 

Gradient Refractive Index Anode for High Contrast OLEDs.517... 

FIGURE 6.26 Schematic diagram of a high contrast OLED using a gradient refractive index anode. 

If the properties of anodically grown oxides are compared to those of thermal oxides, distinct differences are observed. Anodic oxides formed in water-rich electrolytes exhibit a lower refraction index (nr< 1.4) than thermal oxides ( =1.46) [Du2]. The density of thick anodic oxides is a weak function of the current density for galvanostatic anodization and increases from 1.8 to about 2.1 g cm-3 (thermal oxide 2.2 g cm4) if... 

The dependence of PS porosity on doping density has been exploited to fabricate optical waveguides. Such structures require only a single variation of refractive index. If a p-type substrate with implanted p+ lines is anodized and partially oxidized, mesoporous lines of high refractive index are embedded in a low refractive index material. An obtained refractive index contrast between core and clad of 30% is promising for future applications [Tal2]. 

The phenomenon known as "microcavity effect" refers to the enhancement or annihilation of the emitted irradiance related to the position of the emitting material relative to this resonance peak of the irradiance. A weak microcavity effect is usually present in conventional OLEDs because internal reflections are caused by the higher refractive index of the ITO anode compared to most organic layers, and the cathode is highly reflective (Bulovic, 1998). This is usually considered a nuisance, but has been exploited in microcavity OLEDs (Jordan, 1996). With Fabry-Perot filters, the phase condition for the appearance of resonance peaks is given by the following equation ... 

The composition of the as-deposited alloy films and anodized films was determined by Auger spectrometry (PHI-660 Perkin Elmer) after five seconds of ion milling of the films. The oxide films were also analyzed with scanning and transmission electron microscopy (TEM). The refractive index of the oxide was measured at A, = 633 nm by ellipsometer LEE - 3M. 

Figure 3.59. Experimental (solid lines) and calculated (dashed lines) IRRAS spectra of porous anodic alumina film 500 nm thick on Al, measured at three different angles of incidence with s-and p-polarized radiation. Calculation was performed using experimentally derived refractive index. Reprinted, by permission, from E. Wackelgard, J. Phys. Condens. Matter 8,4289 (1996), p. 4294, Fig. 2. Copyright 1996 lOP Publishing Ltd.

The very first studies of mesoporous silicon noted the different colors of anodized and so-called stain films (Uhlir 1956 Turner 1958 Archer 1960). Uhlir referred to his surfaces as having a matte black, brown or red deposif (Uhlir 1956). Turner commented that several orders of interference colors can be seen as the film thickens (Turner 1958). The first use of such colored silicon in the late 1950s was in p-n junction delineation (lies and Coppen 1958 Whoriskey 1958 Robbins 1962). Porous silicon, with its lower refractive index than solid silicon, induces optical interference effects as etched films on wafers. A colorimetric analysis for layer thicknesses below 500 nm, at quantified porosities, showed that interference color directly related to the optical thickness of anodized singlelayer structures (Lazarouk et al. 1997). Figure 1 shows examples for stain-etched p + wafers. The visual color of a given layer can be further changed by plasmonic effects of deposited metal nanoparticles (Lublow et al. 2012) or through controlled oxidation of the silicon skeleton. 

Perhaps the first investigation into the chemical composition of the anodic oxide of HgCdTe was reported by Nemirovsky and Finkman in 1979 (50). Anodic oxide films were grown on n-type slush grown (Hg,Cd)Te (Ej = 0.1 eV) in 0.1 N KOH in methanol and various concentrations (< 0.1 N) of KOH in 90% ethylene glycol /10% HjO. The material surface was mechanically polished and etched in 20% Br in methanol prior to anodization. The refractive index and dielectric constant of the oxide were determined to be closer to TeOj than CdO or HgO, so the authors concluded that the... 

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