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from Hall measurements. The calculated frequencies are those for which e =0, while the experimental frequencies are those of the reflectivity minima (e =1). Hence, the experimentally determined frequencies are not exactly the calculated frequencies. Table I has also been plotted as Fig. 3, showing a> + and a>_ as functions of the free-carrier concentration.To give a shift of the surface-plasmon frequency from (x) p to (JO P /J~2, the depletion layer must be approximately a wavelength thick or thicker. If it is much less than a wavelength thick, the surface-plasmon frequency lies between oo p and u) p / /2. This shift of the plasmon frequency with thickness of the dielectric overcoat has been used by Stanford 11 to study the thickness of AgS films on Ag. Note that our etching data indicate that the depletion layer is of order 0.1 mm thick, or approximately one wavelength thick.The cutting of the grating also increases the surface roughness and this presumably plays an important role. This is because the incident photon carries less momentum than a surface plasmon of the same energy. However, we are apparently not observing just a change in surface roughness but also a damage layer, because the reflectance minima shift continuously as etching proceeds.In conclusion we have a very simple model of two coupled harmonic oscillators to explain qualitatively the far-infrared reflectivity of w-type InSb. No attempt was made to include retardation effects or to treat rigorously the plasmonphonon coupling. Clearly, both must be done for a complete treatment. Ngai, Economou, and Cohen 5 have done a calculation (including retarda-We report measurements that give for the first time conclusive evidence for the metallic behavior of a square planar organometallic-complex compound. tion) for a semiconductor bounded by a dielectric for the case where the surface-plasma frequency was high enough (-800 cm" 1 ) so that coupling to the phonons could be neglected. It would be interesting to extend this treatment to include coupling to the phonons. Recently Marschall, Fisher, and Oueisser 12 have observed surface plasmons in InSb using the grating technique. The free carrier concentration was an order of magnitude larger than ours, so that the plasma frequency was well removed from the LO phonon frequency and no coupling effects were observed. In addition, their gratings were ruled with a diamond which did not create a damage layer.Single crystals of K2Pt(CN) 4 Br 0#3 * (H 2 0)" show a Drude-type optical reflectivity for light polarized parallel to the crystal axis. The energy of the plasma edge indicates a metallic density of free carriers. The relatively small conductivity at dc and low frequencies and the photoconductivity at 4.2°K can be understood in terms of a simple model assuming metallic strands interrupted by lattice defects.1060

From polarized reflection spectra of TEA(TCNQ), single crystals at room temperature, quantitative values of the complex dielectric function ~( w ) and the optical conductivity a(w) in the range from the far infrared to the ultraviolet have been derived. The polarization of the vibrational bands almost exclusively parallel to the highly conducting direction suggests strong interaction of conduction electrons with intramolecular TCNQ vibrations.An Eirikristallen des hoch anisotropen organischen Halbleiters TEA(TCNQ), wurden bei Zimmertemperatur die polarisierten Reflexionsspektren vom fernen Infrarot bis ins Ultraviolett gemessen. Daraus wurden die kornplexe Dielektrizitatskonstante E ( W ) sonie die optische Leitfahigkeit a(w) bestimnit. Die beobachteten Vibrationsbanden sind fast ausschlieBlich parallel zur Richtung hoher Leitfahigkeit polarisiert. Das ist ein Hinweis dafiir, daI3 die Leitungselektronen ruit den intramolekularen TCNQ-Schningungen stark gekoppelt sind.

The optical absorption spectra of trivalent holmium in single crystals of HoPO, and (I-, Ho)PO, have been measured in the range from 15000 to 29000 em-l including the Zeeman effect of the ground level 51: and the two excited levels 3K; and 5Gk at 85 and 4.2 OK. The splitting factors of the degenerate components of the ground level and the level 3Ki indicate a small mixing of the states Y~J M with different M . With this fact some special features of the transitions between these two levels can be explained qualitatively. Es wurden die Absorptionsspektren des dreiwertigen Holmiums in Einkristallen vonHoPO, und (Y, Ho)PO, zwischen 15000 und 29000 cm-l und der Zeeman-Effekt des Gririidterms 51k und der beiden angeregten Terme 3K; und 5Gk bei 85 und 4,2 OK gemessen. Die Aufspaltungsfaktoren des Grundterms und des Terms 3Ki deuten auf eine geringe Durchmischung der Zustinde yY J M mit unterschiedlichem $1 hin. Damit lassen sich einige Besonderheiten der Ubergange zwischen diesen beiden Termen qualitativ erklaren.

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