We have investigated the electronic structure of nano-sized iron oxide by scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by photoelectron spectroscopy. Nano particles were produced by thermal treatment of Ferritin molecules containing a self-assembled core of iron oxide. Depending on the thermal treatment we were able to prepare different phases of iron oxide nanoparticles resembling γ-Fe2O3, α-Fe2O3, and a phase which apparently contains both γ-Fe2O3 and α-Fe2O3. Changes to the electronic structure of these materials were studied under reducing conditions. We show that the surface band gap of the electronic excitation spectrum can differ from that of bulk material and is dominated by surface effects.

The low-energy electronic properties of one-dimensional nanowires formed by Pt atoms on Ge(001) are studied with scanning tunneling microscopy down to the millivolt-regime. The chain structure exhibits various dimerized elements at high tunneling bias, indicative of a substrate bonding origin rather than a charge density wave. Unexpectedly, this dimerization becomes vanishingly small when imaging energy windows close to the Fermi level with adequately low tunneling currents. Evenly spaced nanowire atoms emerge which are found to represent conduction states. Implications for the metallicity of the chains are discussed.

We present atomic scale images of a V 2 O 3 single crystal ͑0001͒ surface. Depending on preparation two structural modifications of the surface are observed: ͑i͒ a reconstructed surface due to dimerization of vanadium ions and ͑ii͒ a defect rich vanadium terminated bulklike surface. From scanning tunneling spectroscopy measurements a gap in the electronic density of states at the Fermi energy is inferred for the reconstructed surface, while the bulklike surface shows metallic behavior. The spectral weight of the quasiparticle peak originating from electronic correlations was measured by photoelectron emission and found to be dramatically different for the two surface modifications, in accordance with the scanning tunneling spectroscopy data. The results proof the sensitivity of V 2 O 3 to surface reconstruction. The fact that different surface modifications can be prepared emphasizes the necessity of a thorough surface characterization for photoelectron emission spectroscopy.The electronically correlated compound V 2 O 3 shows a complex phase diagram with paramagnetic metal, paramagnetic insulator, and antiferromagnetic insulator ͑AFI͒ regions as function of temperature and pressure. 1 Over the last decades numerous studies have addressed the role of electronic correlations in V 2 O 3 . 2 Recently, the single particle excitation spectrum of V 2 O 3 has been calculated using dynamical mean-field theory. 3 Input parameters were taken from bandstructure calculations based on the local-density approximation. A sensitive test of agreement between theory and experiment is the comparison of the calculated spectral weight of a quasiparticle peak close to the Fermi energy ⑀ F , which depends strongly on the model parameters, to the spectral function as measured by photoelectron emission spectroscopy ͑PES͒. Due to the surface sensitivity of PES, such experiments should be performed on well characterized surfaces. Only few studies of this kind exist. 4,5 We want to note that V 2 O 3 and, more generally, all the binary vanadium oxides, may be especially prone to surface reconstruction considering the closeness to structural transitions. Recently, PES measurements using high incident photon energies up to 700 eV have been performed. 6 In such experiments the sensitivity to surface effects is reduced. The measurements, performed on cleaved (101 2) surfaces of V 2 O 3 , show a significant higher spectral weight of the quasiparticle peak at the Fermi energy than earlier experiments performed with lowincident photon energies. Such experiments were carried out either on the same surface prepared by cleaving, 7 on scraped single crystal surfaces, 8,9 or on surfaces prepared by heating under vacuum or oxygen atmosphere. 10 The latter technique produces surfaces, which show low-energy electron diffraction ͑LEED͒ pattern of high quality, suggesting the surface is atomically ordered and has trigonal symmetry in accordance with the bulk structure. 5,10 Despite the high quality LEED pattern the PES measurements taken from these surfaces ...