Nanoscale work function contrast induced by decanethiol self-assembled monolayers on Au(111)

In this paper, we obtain maps of the spatial tunnel barrier variations in self-assembled monolayers of organosulfurs on Au(111). Maps down to the sub-nanometer scale are obtained by combining topographic scanning tunneling microscopy images with dI/dz spectroscopy. The square root of the tunnel barrier height is directly proportional to the local work function and the dI/dz signal. We use ratios of the tunnel barriers to study the work function contrast in various decanethiol phases: the lying-down striped β phase, the dense standing-up φ phase, and the oxidized decanesulfonate λ phase. We compare the induced work function variations too: the work function contrast induced by a lying-down striped phase in comparison to the modulation induced by the standing-up φ phase, as well as the oxidized λ phase. By performing these comparisons, we can account for the similarities and differences in the effects of the mechanisms acting on the surface and extract valuable insights into molecular binding to the substrate. The pillow effect, governing the lowering of the work function due to lying-down molecular tails in the striped low density phases, seems to have quite a similar contribution as the surface dipole effect emerging in the dense standing-up decanethiol phases. The dI/dz spectroscopy map of the nonoxidized β phase compared to the map of the oxidized λ phase indicates that the strong binding of molecules to the substrate is no longer present in the latter.Fil: Tsvetanova, Martina. University of Twente; Países BajosFil: Oldenkotte, Valent J. S.. University of Twente; Países BajosFil: Bertolino, María Candelaria. University of Twente; Países Bajos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Gao, Yuqiang. University of Twente; Países BajosFil: Siekman, Martin H.. University of Twente; Países BajosFil: Huskens, Jurriaan. University of Twente; Países BajosFil: Zandvliet, Harold J. W.. University of Twente; Países BajosFil: Sotthewes, Kai. University of Twente; Países Bajo

Les versions catalanes de la 'vida de santa caterina de siena'. Notes sobre el text i el paratext

S'analitzen les traduccions catalanes de la Vida de Caterina de Siena, amb especial atenció les dedicatòries i pròlegs de les diferents versions per tal de valorar la importància de la seva recepció en català. La vida de la santa de Siena era coneguda des de mitjans del segle XV, almenys per la reina Maria d'Aragó que en tingué un exemplar. Però el focus inicial d'aquest interès es trobava a València, ciutat on es varen imprimir dues importants traduccions els anys 1499 i 1511 impulsades per intel·lectuals i sobretot pels dominics amb l'objectiu de reforçar els lligams religiosos amb Roma després del Cisma d'Occident i d'impulsar la renovació dels costums de la burgesia amb nous models de santedat. La popularitat de santa Caterina va arribar a través del Flos Sanctorum que inclou la seva vida almenys des de l'edició de l'any 1494 impresa a Barcelona per Joan Rosembac

Local Conduction in MoxW1- xSe2: The Role of Stacking Faults, Defects, and Alloying

Here, we report on the surface conductivity of WSe2 and MoxW1-xSe2 (0 ≤ x ≤ 1) crystals investigated with conductive atomic force microscopy. We found that stacking faults, defects, and chemical heterogeneities form distinct two-dimensional and one-dimensional conduction paths on the transition metal dichalcogenide surface. In the case of WSe2, in addition to step edges, we find a significant amount of stacking faults (formed during the cleaving process) that strongly influence the surface conductivity. These regions are attributed to the alternation of the 2H and 3R polytypism. The stacking faults form regular 2D patterns by alternation of the underlying stacking order, with a periodicity that varies significantly between different regions and samples. In the case of MoxW1-xSe2, its conductivity has a localized nature, which depends on the underlying chemical composition and the Mo/W ratio. Segregation to W-rich and Mo-rich regions during the growth process leads to nonuniform conduction paths on the surface of the alloy. We found a gradual change of the conductivity moving from one region to the other, reminiscent of lateral band bending. Our results demonstrate the use of C-AFM as a nanoscopic tool to probe the electrical properties of largely inhomogeneous samples and show the complicated nature of the surface conductivity of TMDC alloys

A novel electrostatically actuated AFM probe for vibro-flexural mode operation

A successful approach to drastically reduce or even completely eliminate friction and wear in scanning force microscopy is the use of electrostatic modulation of the normal force acting on the tip-sample contact. In this paper we have devised, fabricated and experimentally characterized a novel electrostatically actuated AFM probe. The probe consists of a flexible cantilever that has an electrostatic circular plate actuator with a built-in sharp tip monolithically integrated at its free end. This unique probe configuration will allow for the vibro-flexural mode operation in which vibration of the tip relative to the cantilever is generated and controlled by the integrated plate actuator, while the tip-sample interaction is resolved by deflection of the cantilever. We envision that this new operation mode will result in an efficient electrostatic force modulation, which in the end will enable us to control friction and wear during AFM imaging

Combined I(V) and dI(V)/dz scanning tunneling spectroscopy

We present a method to simultaneously record I(V) and dI(V)dz spectra in a scanning tunneling microscopy measurement, where I, V and z refer to the tunnel current, sample bias and tip-substrate separation, respectively. The I(V) spectrum is recorded by ramping the bias voltage, while the feedback loop of the scanning tunneling microscope is disabled. Simultaneously the z-piezo is modulated with a small sinusoidal high frequency signal. The dI(V)dz signal is recorded using a lock-in amplifier. This method allows to simultaneously record the topography, I(V), dI(V)dV and dI(V)dz in a single scanning tunneling microscopy measurement

Tuning the Friction of Graphene on Mica by Alcohol Intercalation

The friction of graphene on mica was studied using lateral force microscopy. We observed that intercalation of alcohol molecules significantly increases the friction of graphene, as compared to water. An increase of 1.8, 2.4, and 5.9 times in friction between the atomic force microscopy tip and single-layer graphene was observed for methanol, ethanol, and 2-propanol, respectively. Moreover, the friction of graphene is found to be higher for single-layer graphene than for multilayer graphene. We attribute the increase in friction to the additional vibrational modes of alcohol molecules. The significant variation of the frictional characteristics of graphene at the nanoscale by altering the intercalant could open up applications for the next-generation nanolubricants and nanodevices

Batch fabrication of scanning microscopy probes for thermal and magnetic imaging using standard micromachining

We present a process for batch fabrication of a novel scanning microscopy probe for thermal and magnetic imaging using standard micromachining and conventional optical contact lithography. The probe features an AFM-type cantilever with a sharp pyramidal tip composed of four freestanding silicon nitride nanowires coated by conductive material. The nanowires form an electrical cross junction at the apex of the tip, addressable through the electrodes integrated on the cantilever. The cross junction on the tip apex can be utilized to produce heat and detect local temperature changes or to serve as a miniaturized Hall magnetometer enabling, in principle, thermal and magnetic imaging by scanning the probe tip over a surface. We have successfully fabricated a first probe prototype with a nanowire tip composed of 140 nm thick and 11 μ m long silicon nitride wires metallized by 6 nm titan and 30 nm gold layers. We have experimentally characterized electrical and thermal properties of the probe demonstrating its proper functioning. ©2010 IEEE