M. Knupfer

Full characterization of the interface between the organic semiconductor copper phthalocyanine and gold

We present a study of the interface properties of the molecular organic semiconductor copper phthalocyanine (CuPC) on single crystalline as well as polycrystalline Au using photoemission spectroscopy. Despite the different orientation of the molecules on the two substrates, the observed energy level alignment is identical. We observe the formation of an interface dipole while band bending is very small. In addition, we have carried out complementary studies of the CuPC/GeS(001) interface to pin down photoemission final state effect contributions to the observed energy level shifts.

Detailed analysis of the mean diameter and diameter distribution of single-wall carbonnanotubes from their optical response

We report a detailed analysis of the optical properties of single-wall carbon nanotubes (SWCNTs) with different mean diameters as produced by laser ablation. From a combined study of optical absorption, high-resolution electron energy-loss spectroscopy in transmission, and tight-binding calculations we were able to accurately determine the mean diameter and diameter distribution in bulk SWCNT samples. In general, the absorption response can be well described assuming a Gaussian distribution of nanotube diameters and the predicted inverse proportionality between the nanotube diameter and the energy of the absorption features. A detailed simulation enabled not only a determination of the mean diameter of the nanotubes, but also gives insight into the chirality distribution of the nanotubes. The best agreement between the simulation and experiment is observed when only nanotubes within

Transition from a Tomonaga-Luttinger Liquid to a Fermi Liquid in Potassium-Intercalated Bundles of Single-Wall Carbon Nanotubes

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(pi-pi) electronic order in iron arsenide superconductors

of the armchair axis are considered. The mean diameters and diameter distributions from the optical simulations are in very good agreement with the values derived from other bulk sensitive methods such as electron diffraction, x-ray diffraction, and Raman scattering.

Reduced diameter distribution of single-wall carbon nanotubes by selective oxidation

We report on the first direct observation of a transition from a Tomonaga-Luttinger liquid to a Fermi-liquid behavior in potassium-intercalated mats of single-wall carbon nanotubes. Using high resolution photoemission spectroscopy, an analysis of the spectral shape near the Fermi level reveals a Tomonaga-Luttinger liquid power law scaling in the density of states for the pristine sample and for low dopant concentration. As soon as the doping is high enough to achieve a filling of the conduction bands of the semiconducting tubes, a distinct transition to metallic single-wall carbon nanotube bundles with the scaling behavior of a normal Fermi liquid occurs.

Electronic properties of the organic semiconductor interfaces CuPc∕C60 and C60∕CuPc

The distribution of valence electrons in metals usually follows the symmetry of the underlying ionic lattice. Modulations of this distribution often occur when those electrons are not stable with respect to a new electronic order, such as spin or charge density waves. Electron density waves have been observed in many families of superconductors, and are often considered to be essential for superconductivity to exist. Recent measurements seem to show that the properties of the iron pnictides are in good agreement with band structure calculations that do not include additional ordering, implying no relation between density waves and superconductivity in these materials. Here we report that the electronic structure of Ba1-xKxFe2As2 is in sharp disagreement with those band structure calculations, and instead reveals a reconstruction characterized by a (π, π) wavevector. This electronic order coexists with superconductivity and persists up to room temperature (300 K).

The joys and pitfalls of Fermi surface mapping in Bi2Sr2CaCu2O8+d using angle resolved photoemission

We report an easy way to narrow the diameter distribution of single-walled carbon nanotubes (SWNT) by oxidization treatments. Both a chemical treatment in 2 M HNO3 as well as oxidation in a reduced O2 atmosphere lead to a selective burning of the narrower SWNT in bulk samples and to a diameter distribution which is smaller by a factor of two. This is a first important step towards a selective production of SWNT with a defined diameter on a bulk scale.

Momentum dependence of the superconducting gap in Ba 1 − x K x Fe 2 As 2

We report on the electronic properties of the organic heterointerfaces between C60 and copper phthalocyanine (CuPc), studied by means of photoemission spectroscopy and the Kelvin-probe method. We found both interfaces, CuPc∕C60 and C60∕CuPc, to be nonreactive with pronounced shifts of the vacuum level pointing to the formation of an interfacial dipole mainly on the CuPc side of the heterojunctions. The dipole values are close to the difference of the work functions of the two materials. Important interface parameters and hole-injection barriers were obtained. It is shown that the sequence of deposition does not influence the electronic properties of the interfaces.

Transition metal phthalocyanines: Insight into the electronic structure from soft x-ray spectroscopy

: On the basis of angle-scanned photoemission data recorded using unpolarized radiation, with high (E,k) resolution, and an extremely dense sampling of k space, we resolve the current controversy regarding the normal state Fermi surface (FS) in Bi(2)Sr(2)CaCu(2)O(8+delta). The true picture is simple, self-consistent, and robust: the FS is holelike, with the form of rounded tubes centered on the corners of the Brillouin zone. Two further types of features are also clearly observed: shadow FSs, which are most likely to be due to short range antiferromagnetic spin correlations, and diffraction replicas of the main FS caused by passage of the photoelectrons through the modulated Bi-O planes.

Spin and Orbital Ground State of Co in Cobalt Phthalocyanine

D. V. Evtushinsky,1 D. S. Inosov,1,2 V. B. Zabolotnyy,1 A. Koitzsch,1 M. Knupfer,1 B. Buchner,1 M. S. Viazovska,3 G. L. Sun,2 V. Hinkov,2 A. V. Boris,2,4 C. T. Lin,2 B. Keimer,2 A. Varykhalov,5 A. A. Kordyuk,1,6 and S. V. Borisenko1 1Institute for Solid State Research, IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany 2Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany 3Max-Planck-Institute for Mathematics, Vivatsgasse 7, 53111 Bonn, Germany 4Department of Physics, Loughborough University, Loughborough, LE11 3TU. United Kingdom 5BESSY GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany 6Institute of Metal Physics, National Academy of Sciences of Ukraine, 03142 Kyiv, Ukraine Received 24 September 2008; revised manuscript received 30 December 2008; published 17 February 2009