High-temperature superconductors studied by electron tunneling and surface analysis techniques

Miscellaneous · Fri Jan 01 00:00:00 EST 1993

OSTI ID:6916500

Lu, F

Part I focuses on the study of superconductivity of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] by a conventional planar tunneling method. The tunnel junctions were made on cleaved ab planes of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] single crystals with Pb counterelectrodes. A second gap inside the main gap has been observed for fresh junctions. The inner gap [Delta][sub i] (T) is BCS-like, the outer gap [Delta](T) is not BCS-like. The fitted outer gap [Delta](0) = 26 meV, or 2[Delta](0)/kT[sub c] = 6.7. Tunneling conductances G(V,T) near T[sub c] reveal a broadening [Gamma](T) such that [Delta](T[sub c]) [approx] [Gamma](T[sub c]) [approx] 2kT[sub c]. G(V,T > T[sub c]) has a minimum at V = 0, suggestive of known c-direction localization. G(V,T) also reveals the expected fluctuation superconductivity above T[sub c]. In part II, the author concentrates on the studies of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] surfaces, Ag adatoms, and iodine intercalation with UHV, STM, AES, and XPS. Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] crystals were cleaved in situ and examined by AES. The Bi atomic structure and b-axis superstructure were observed by the STM. The DOS measured by the STM shows a weakly metallic property of the BiO layer. STM topography of Ag adatoms on the BSCCO surface revealed that the Ag atoms form clusters. Iodine was used to intercalate the Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] compound to form stage-1 IBi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y]. The XPS spectrum confirms that iodine is bonded in the crystal. The iodine 3d[sub 5.2] and 3d[sub 3/2] core level XPS peaks indicate that iodine is in the I[sup [minus]] oxidation state. The O 1s peak was broadened and shifted about 0.8 eV toward higher binding energy, consistent with electrons transferring to the iodine intercalated between the oxygen atoms in the Bi-O bilayers. The Bi 4f and Cu 2p[sub 3/2] peaks exhibit relatively small shifts toward lower binding energy.

• Research Organization: Polytechnic Univ., Brooklyn, NY (United States)
• OSTI ID: 6916500
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
HIGH-TC SUPERCONDUCTORS
SURFACE PROPERTIES
TUNNEL EFFECT
BISMUTH OXIDES
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INTERMETALLIC COMPOUNDS
STRONTIUM OXIDES
TUNNEL DIODES
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
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COPPER COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
SEMICONDUCTOR DEVICES
SEMICONDUCTOR DIODES
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