Vol. 3, No. 8 ABSTRACTS OF PAPERSTO APPEAR DI J. PHYS. CREM. SOLIDS lxxxv

Incorporated,Murray Hill, New Jersey). (Departmentof ChemistryandChemicalEngineeringandMaterialsResearch

Copperhasbeendiffused into undoped Laboratory,University of flUnois, Urbana,anddopedn-typeGaAs In the range575 - 1000°C, DIlnols).and the Hall effecthasbeenmeasuredfrom roomtemperatureto liquid nitrogentemperature. In The effect of pressureto severalhundredundopedGaAs, the concentrationof acceptors kilobarshasbeenmeasuredon the compress-0. 145 eV abovethe valenceband, dependsupon thility of four carbideshavingthe NaC1 structure.the diffusion temperaturein the form of exp- All four arerelatively incompressiblebut thetB/kT, wherethe valueof ~H is 1.32 eV, and groupW carbides(TiC andZrC) are marKedlyfor diffusion temperaturesabove700°C, the morecompressiblethanthe groupV carbidesacceptorconcentrationcoincideswith the solu- (NbC andTaC). The compressibilityincreasesbility of copperdeterminedby radioactivetracer asone goesdown the periodictable.methods. The solubility of theseacceptorsIn-creasesin dopedn-typeGaAs owing to the (Received6 May 1965)electron-holeequilibrium. Assumingthat copperis singly ionizedduring thediffusion andthat theeffect of otheracceptorlevels introducedduring 41. ADSORPTION SOUS IRRADIATION. Lthe diffusion is negligible, the increasedsolu- ADSORPTIOND’OXYGENE ET D’OXYDEbility hasbeenestimatedtheoretically, result- DE CARBONE SUR ALUMINE.Ing in fairly goodagreementwith that obtained R. Coekelbergs, A. Crucq, J. Decot,from analysisof Hall effect measurement.Some L. Degols,M. Randouxet L. Tlmmerman.of thesecopperdiffusedGaAssampleshave (Ecole RoyaleMiitaire, Institut Interuni-showna drasticdecreasein hole mobility at versitaire DesSciencesNucleaires).low temperatures,especiallyin the sampleginin which the donorsoriginally presentare The presentarticle studiesthe sorptionclosely compensatedby shallow acceptorsintro- phenomenawhenalumina, in the presenceof aducedduring the diffusion. This decreasein gaseousphase(CO or Os), is submittedto irra-mobility is relatedto a non-uniformdistribution diation with X rays (55KV). ~ialitatively, theseof shallow acceptorsin the samples. two gasesgive indenticalresults. The following

observationsare made:(Received3 May 1965) - irradiationalwaysinducesirreversible

adsorption,- alter irradiation is stopped,adsorption

39. FORMATION ENERGIESOF VACANCIES continues(post radiationeffect).AT A (100) SODIUM CHLORIDE SURFACE Threeperiodscanbe distinguishedonJ.M. Blakely andChe-YuLi, (Department the curve of the adsorptionevolutionduringof Materials ScienceandEngineering, irradiation:Cornell University, Ithaca, New York). - an inductionperiod,

- a periodduringwhich the rateremainsThe formation energiesof cationand constant,

anionvacanciesat 0°Kat a (100) surfaceplane a periodduringwhich the rateof adsorptionof sodiumchloridehavebeencalculatedusing decreasesslowly, until final attainmentofthe methodof Mott and Littleton. The valuefor an equilibrium state.a cation, anionvacancypair is foundto be 2. 12eV Theseresultsare qualitatively explainedslightly greaterthanthe correspondingbulk with the aid of a theoreticalmodel which allowsvalue of 1. 90eV. The calculatedvaluefor the both for the chargecarrierscreatedin thesurfacevacancypair energyrepresentsa first courseof the irradiation processandfor theorder approximation. The assumptionsinvolved impurity levelssusceptibleto trapthesecarriers.are discussedin somedetail.

(Received12 January1965)(Received16 February1965) (Revised U May 1965)(Revised 4 May 1965)

42. THE ENERGYOF DESORPTIONOF40. THE EFFECT OF HIGH PRESSUREON PHOTO-CEEMISORBEDOXYGENA)~D

THE COMPRESSIBILiTY OF FOUR CUBIC NiTROUS OXIDE ON INSULATING CdSCARBIDES. CRYSTALS.A. R. ChampionandH. G. Drickamer, PeterMark, (RCA Laboratories,

lxxxvi ABSTRACTSOF PAPERSTOAPPEAR IN J. PEYS.CHEM. SOLIDS Vol. 3, No. 8

Princeton,New Jersey). for peaks abovethe temperatureat which thecrystalwasX-Irradlated. The effect hasbeen

The energyof desorption of photo-chemi- investigatedIn detail for crystalsdopedwithsorbedoxygen and nitrous oxide on the surfaces variousImpuritiesand under variousconditions.of thin insulatingCdScrystals is obtained in two The results areIn agreementwith the generallyIndependentways: (1) From thermaldesorption acceptedmodelsfor the electronic processesintime measurementswherethe time requiredto QUartz.releaseacertainfraction of the adsorbedionsby thermaldesorptlonis measuredand (2) from (Received22 March 1965)an examinationof the temperaturedependence of (Revised 13 May 1965)the dark current. The two methodsyield theself-consistentresults 0. 91 eV and 0. 74 eV foroxygenandnitrous oxide, respectively. The 45. MAGNETICPROPERTIESOF Cr RICHresults are usedto illustrate certainfeaturesof Fe-Cr ALLOYS AT LOWTEMPERATURESthe model for reversible photo-inducedchemi- Y. Ishikawa, (Institute for Solid Statesorption on insulators. Physics, University of Tokyo, Tokyo, Japan),

andR. Tournier and J. Filippi, (Laboratoire(Received 13 May 1965) d’Electrostatlque et de Physique du Metal

C.N.R.S. Grenoble, France).

43. HEISENBERGMODELWiTH LONGRANGE Magnetic properties of Fe-Cr alloysINTERACTION, containing less than 20 at% Fe were InvestigatedCohn J. Thompson (Department of Physics, in the temperature range between0. 05°K andUniversity of California, San Diego, 600°K. The results confirmed that the iron atomLa JoUa, California). has a localizedmoment of 2 ~ Bat high tempera-

tures. The magneticmoment of iron remainsThe functional Integral methodas used by paramagneticdown to 2°K for 1 at% Fe-Cr,

Siegert in his studyof the Ising Model with long while for the specimencontainingmore thanrange interaction, Is generalizedand applied to 3 at% Fe, the moment of iron is suggested to bethe Heisenbergmodel. Above the Bragg-Williams arranged in an anti-ferromagnetic order atCurie point, the functional Integral expression helium temperature. The analysisof thesus-for the partition function is evaluated by a saddle ceptibility as well as the isothermal magnetiza-point approximation. This gives us an expansion tion curve suggest that the magnetic moment ofin powers of the reciprocal range of the inter- iron at low temperature is about 1.4 ~B oraction which is essentially identical with the smaller. Neutron diffraction measurementsIsthg Model result, in agreement with Brout who showed the existenceof a long range pure anti-used a ring summation approximation. The ex- ferromagnetic order in 4. 7 at% Fe-Cr belowpansion Is not valid through the Curie point, and about260°K with the magneticmoment ofin its present form, our methodseems to be in- 0. 620. 02 ~.i3 at helium temperature. It iscapable of giving spin waves, shown that the magnetic properties of the 4. 7

at% Fe-Cr alloy at low temperatures can be in-(ReceIved6 April 1965) terpreted in terms of superantiferromagnetism(Revised 13 May 1965) andthose of 10 and15 at% Fe-Cr alloys by a

combinationof superpa.ramagnetlsmandsuper-antiferromagnetism.The magnetic contribution

44. OPTICAL STUDIES OF ELECTRON A~T3 to the specificheat at low temperatures wasHOLE TRAPPING LEVELS IN QUARTZ. estimated by usingthe proposedmodel.Mordechay Schlesinger,(DepartmentofPhysics, University of Pittsburgh, (Received14 May 1965)Pittsburgh, Pennsylvania).

Illumination with monochromatic light 46. THE ROLE OF THE IONIZATION OFinto various color-center absorption bands of DEFECTSIN CAUSING SYSTEMATICquartz at liquid nitrogen temperature (LNT) DiFFERENCES IN THE SEMICONDUCTORalter previous X-ray irradiation at room temp- PROPERTIES OF UNDOPED COMPOUNDS.erature (RT) re-excites some glow peaks of the F.A. Kröger, (Department of Electrical“usual” glow-curve in the region between LWr Engineering, University of Southernand RT. Re-excitation can also be performed California, Los Angeles, California, U.S.A).