In situ spectroscopy of intrinsic Bi2Te3 topological insulator thin films and impact of extrinsic defects Ngabonziza, P.; Heimbuch, R.; de Jong, N.; Klaassen, R.A.; Stehno, M.P.; Snelder, M.; Solmaz, A.; Ramankutty, S.V.; Frantzeskakis, E.; van Heumen, E.; Koster, G.; Golden, M.S.; Zandvliet, H.J.W.; Brinkman, A. Published in:Physical Review B DOI:10.1103/PhysRevB.92.035405 Link to publicationCitation for published version (APA): Ngabonziza, P., Heimbuch, R., de Jong, N., Klaassen, R. A., Stehno, M. P., Snelder, M., ... Brinkman, A. (2015). In situ spectroscopy of intrinsic Bi2Te3 topological insulator thin films and impact of extrinsic defects. Physical Review B, 92(3), [035405]. https://doi.org/10.1103/PhysRevB.92.035405 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Combined in situ x-ray photoemission spectroscopy, scanning tunneling spectroscopy, and angle resolved photoemission spectroscopy of molecular beam epitaxy grown Bi 2 Te 3 on lattice mismatched substrates reveal high quality stoichiometric thin films with topological surface states without a contribution from the bulk bands at the Fermi energy. The absence of bulk states at the Fermi energy is achieved without counterdoping. We observe that the surface morphology and electronic band structure of Bi 2 Te 3 are not affected by in vacuo storage and exposure to oxygen, whereas major changes are observed when exposed to ambient conditions. These films help define a pathway towards intrinsic topological devices.

In order to design and realize single-molecule devices it is essential to have a good understanding of the properties of an individual molecule. For electronic applications, the most important property of a molecule is its conductance. Here we show how a single octanethiol molecule can be connected to macroscopic leads and how the transport properties of the molecule can be measured. Based on this knowledge we have realized two single-molecule devices: a molecular switch and a molecular transistor. The switch can be opened and closed at will by carefully adjusting the separation between the electrical contacts and the voltage drop across the contacts. This single-molecular switch operates in a broad temperature range from cryogenic temperatures all the way up to room temperature. Via mechanical gating, i.e., compressing or stretching of the octanethiol molecule, by varying the contact's interspace, we are able to systematically adjust the conductance of the electrode-octanethiol-electrode junction. This two-terminal single-molecule transistor is very robust, but the amplification factor is rather limited.

Atomic nanowires on semiconductor surfaces induced by the adsorption of metallic atoms have attracted a lot of attention as possible hosts of the elusive, one-dimensional Tomonaga-Luttinger liquid. The Au/Ge(100) system in particular is the subject of controversy as to whether the Au-induced nanowires do indeed host exotic, 1D metallic states. In light of this debate, we report here a thorough study of the electronic properties of high quality nanowires formed at the Au/Ge(100) surface. The high resolution ARPES data show the low-lying Auinduced electronic states to possess a dispersion relation that depends on two orthogonal directions in k-space. Comparison of the E(kx,ky) surface measured using high-resolution ARPES to tight-binding calculations yields hopping parameters in the two different directions that differ by a factor of two. Additionally, by pinpointing the Au-induced surface states in the first, second and third surface Brillouin zones, and analysing their periodicity in k || , the nanowire propagation direction seen clearly in STM can be imported into the ARPES data. We find that the larger of the two hopping parameters corresponds, in fact, to the direction perpendicular to the nanowires (tperp). This, the topology of the E=EF contour in k || , and the fact that t || /tperp∼0.5 proves that the Au-induced electron pockets possess a two-dimensional, closed Fermi surface, and this firmly places the Au/Ge(100) nanowire system outside potential hosts of a Tomonaga-Luttinger liquid. We combine these ARPES data with scanning tunneling spectroscopic measurements of the spatially-resolved electronic structure and find that the spatially straight -wire-like -conduction channels observed up to energies of order one electron volt below the Fermi level do not originate from the Au-induced states seen in the ARPES data. The former are rather more likely to be associated with bulk Ge states that are localized to the subsurface region. Despite our proof of the 2D nature of the Au-induced nanowire and sub-surface Ge-related states, an anomalous suppression of the density of states at the Fermi level is observed in both the STS and ARPES data, and this phenomenon is discussed in the light of the effects of disorder.

Working on a true molecular level is essential for advances in the field of molecular electronics. Techniques have to be perfected and new approaches have to be developed in order to characterize the properties of a single molecule. In this work we report temperature-dependent transport studies of a single octanethiol molecule trapped between the apex of a scanning tunneling microscope tip and a substrate. At each temperature the molecule is brought into contact by decreasing the gap between tip and substrate in a controlled way. At a positive sample bias the molecule jumps into contact upon approaching the substrate by 0.16 ± 0.01 nm with respect to a fixed reference point defined by a sample bias of +1.5 V and a tunneling current of 0.5 nA. The conductance of octanethiol is temperature independent, demonstrating that either tunneling or ballistic transport is the main transport mechanism.

correspondenceKob et al. reply -In their Correspondence, Flenner and Szamel 1 compare the temperature dependence of an alternative dynamic length scale, ξ 4 , with that of ξ dyn , which we studied 2 . Using computer simulations of the same system, they conclude that these two length scales have a different temperature dependence. In particular, ξ 4 does not follow the striking non-monotonic temperature dependence we reported for ξ dyn . Although both types of measurements aim at quantifying the spatial extent of dynamic correlations in supercooled liquids, the two procedures differ on essential points, which we now discuss.Whereas we measured up to the distance at which the value of the relaxation time is affected by the presence of an amorphous wall 2 , Flenner and Szamel quantify instead the spatial extent of spontaneous dynamic fluctuations at low wavevectors for a fixed timescale (the bulk relaxation time). These two measurements need not be directly related, although they seem to coincide at moderate temperatures ( Fig. 1a of ref. 1). Although four-point functions as measured by Flenner and Szamel have played a pivotal role in previous analysis of dynamic heterogeneity, theoretical work has also revealed a number of shortcomings. Most notably, four-point functions display a strong dependence on the statistical ensemble chosen to perform measurements. As a result, they receive distinct contributions from density and energy fluctuations and show, even in idealized cases, complex scaling properties 3 , which complicates the direct extraction of a correlation length. A second difficulty lies in the fact that these various contributions have different temperature dependences, with a crossover taking place very close to the modecoupling temperature where the subtle effects we reported 2 occur. We remark that this corresponds to the temperature scale where ξ 4 and ξ dyn start to differ. These known weaknesses of four-point functions had in fact motivated our study of an alternative correlation length scale that is free of such ambiguities.Given these important differences, it is not clear how a non-monotonic temperature evolution of dynamic correlations will manifest itself in the numerical data of Flenner and Szamel. Although the authors argue that the evolution of ξ 4 with the relaxation time shows a crossover (Fig.1c in ref. 1), we point out that the presented data does not clearly show such a change in behaviour. Another possibility, not explored by Flenner and Szamel, could be that the functional form of the four-point correlation function S 4 (q,t) as investigated by these authors changes with temperature, in agreement with the idea that the geometry of the relaxing entities changes with temperature, as we argued 2 . As the reported effect is small (Fig. 2b in ref. 2), one would presumably need a relative accuracy of S 4 (q,t) of better than 1% at low wavevectors. The data shown by Flenner and Szamel demonstrate that at present this remains technically difficult.Finally, the crossover we report also coincides...