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The .v0lta~e ?istribution of br~akdown spots in p-n junctions was measured. A junction in silicon which w~s umform m lts crystallographlc properties, and had an impurity gradient of 10 22 cm-4 showed two kinds of mlcroplasmas. One type is characterized by bright light emission and low breakdown v~1tage and the other has less light emission and higher breakdo~~ voltage: Both have broad distribution of breakdown voltages of t~e.order of se.veral volts. Samples contammg a.gram b?unda~y show a line of light emitting spots having a Ill1mmum spacmg of 7000 A versus a 4O-A spacmg of dislocatlOns along the grain boundary.

Water adsorption on Si(100) and Si(ll1) surfaces at room temperature has been investigated by angle-resolved ultraviolet photo-electron spectroscopy (ARUPS) using synchrotron radiation. Earlier angle-integrated UPS studies have suggested that the adsorption is non-dissociative on (100) and dissociative on (111). The ARUPS data indicate that the adsorptionis dissociative on both surfaces; the adsorbate-related valence features are similar and their binding energies agree closely with a self-consistent calculation of quasi-molecular SiOH. In this common dissociative-adsorption scheme there is no conflict between UPS and other techniques. The calculation provides an assignment of features which may allow the adsorption geometry to be probed by the application of photo-emission selection rules.

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SynopsisAn infrared and NMR study was made of the microstructural changes produced in thin films of purified cis-and trans-1,4-polyi~prene when irradiated with ultraviolet light in uacuo a t room temperature. The major photochemical processes observed were cis-trans isomerization and loss of 1,4 double bonds, the latter process being accompanied by the formation of vinylidene and vinyl double bonds as well as some endlinking.Very surprisingly, the loss of original double bonds contributed also to a novel photocyclization which gave rise to cyclopropyl groups in the polyisoprene chain. The isomerization and the formation of cyclopropyl groups are presumed to proceed through triplet and biradical states of the 1,4 double bonds, while the vinylidene and vinyl double bonds must result from chain rupture a t the carbon-carbon bond joining successive isoprene units. Hydrogen abstraction and double-bond migration are of negligible importance in the overall photochemistry of polyisoprene. INTRODUCTIONConsiderable interest has been shown for many years in the light aging or weathering of rubber products, but mainly from a technological standpoint. Very little fundamental work has been done on the photooxidation of 1,4-polyisoprene and even less on its photolysis in the absence of oxygen. The lack of attention to the latter topic is surprising in view of the many recent papers dealing with the radiolysis of 1,4polyisoprene in ziacuo.l A survey of prior work on the photodegradation of rubber has appeared recently,2 and it is evident that there is a need for a detailed study (using modern tools like infrared and NMR spectroscopy) of the microstructural changes produced in thin films of purified 1,4-polyisoprene when exposed to ultraviolet radiation in vacuo. Such a study has never been carried out, although infrared spectroscopy has been used to examine the photooxidation of 1,4-polyisoprene3 and also the photolysis of high-l,2-polybutadiene4 and 1,4polybutadiene.SThe only fundamental work reported on the photolysis of 1,4-polyisoprene dates back over twenty years; Bateman6B7 showed that irradiation of thoroughly degassed, purified hevea rubber films with ultraviolet light in the wavelength range 2300-3650 A. resulted in gas evolution, mostly hydrogen, with a quantum yield of the order of 4 X The largest relative yield, observed for the range 2350-2850 A., was about 2.5 times this value, so that an upper limit of could be set for the efficiency of noncondensable gas formation. The hydrogen was assumed to arise from photoinduced rupture of a-methylenic carbon-hydrogen bonds, followed by the exothermic reaction, H + R H + H a + Rwhere R is an dlylic radical, while the resulting polymeric radicals R then combine to produce crosslinks. The attendant insolubilization of the ultraviolet-irradiated polyisoprene restricted its chemical examination, but there was tentative indication of a decrease in the unsaturation with a quantum yield that could be as high as 0.1.6v8 Since quantum yields approaching this order of magnitude were o...