Probing the local environment of a single OPE3 molecule using inelastic tunneling electron spectroscopy

• Riccardo Frisenda,
• Mickael L. Perrin and
• Herre S. J. van der Zant

Beilstein J. Nanotechnol. 2015, 6, 2477–2484, doi:10.3762/bjnano.6.257

• become more evident when looking at the differential conductance (dI/dV) or the d2I/dV2, where they show up as steps, or peaks (dips), respectively. In this manuscript, when dealing with experimental data, we call IETS spectra the d2I/dV2/(dI/dV) signals calculated from the IV characteristics. Here, we

• gold wire in the presence of OPE3, a molecule can bridge the freshly broken electrodes, as is schematically illustrated in Figure 1c. When measuring the conductance as a function of electrode displacement (a so-called breaking trace), one can distinguish two types of behavior. The left breaking trace

• in Figure 2a shows the typical signal of an empty junction, in which the conductance after the rupture of the last gold contact decreases exponentially with distance. This is a signature of vacuum tunneling between two metallic electrodes. Once a molecular junction is formed (junction 1, right

Effects of spin–orbit coupling and many-body correlations in STM transport through copper phthalocyanine

• Benjamin Siegert,
• Andrea Donarini and
• Milena Grifoni

Beilstein J. Nanotechnol. 2015, 6, 2452–2462, doi:10.3762/bjnano.6.254

• experimental measurements of 21 meV [8]. Numerical results for the current and the differential conductance, according to Equation 37 and using the full Hamiltonian in Equation 29, are shown in Figure 4. Anionic (cationic) resonances at positive (negative) bias voltages are clearly seen. Notice that, in our

• considerations yielded αT = 0.59 for the tip and αS = −0.16 for the substrate [11]. If given without indices, Vres denotes the bias voltage corresponding to the groundstate-to-groundstate resonance. The negative differential conductance at large negative bias in Figure 4 is caused by blocking due to population

• moment of the LUMOs can be observed, although still blurred by temperature. Again, at finite SOI in Figure 6e there is a much more pronounced dependence on θ. The high conductance areas at θ = 0° and θ = 180° for Vb − Vres ≈ 0.8 meV correspond to the high conductance area in the middle of Figure 5 bottom

High electronic couplings of single mesitylene molecular junctions

• Yuki Komoto,
• Shintaro Fujii,
• Tomoaki Nishino and
• Manabu Kiguchi

Beilstein J. Nanotechnol. 2015, 6, 2431–2437, doi:10.3762/bjnano.6.251

• transport properties of single mesitylene (1,3,5-trimethylbenzene) molecular junctions. The electronic conductance and the current–voltage characteristics of mesitylene molecules wired into Au electrodes were measured by a scanning tunnelling microscopy-based break-junction method at room temperature in a

• liquid environment. We found the molecular junctions exhibited two distinct conductance states with high conductance values of ca. 10−1G0 and of more than 10−3G0 (G0 = 2e2/h) in the electronic conductance measurements. We further performed a statistical analysis of the current–voltage characteristics of

• the molecular junctions in the two states. Within a single channel resonant tunnelling model, we obtained electronic couplings in the molecular junctions by fitting the current–voltage characteristics to the single channel model. The origin of the high conductance was attributed to experimentally

Vibration-mediated Kondo transport in molecular junctions: conductance evolution during mechanical stretching

• David Rakhmilevitch and
• Oren Tal

Beilstein J. Nanotechnol. 2015, 6, 2417–2422, doi:10.3762/bjnano.6.249

• density of states at the Fermi energy, which is expressed as a peak in the conductance at zero voltage (Figure 1a). At a finite voltage and in the absence of inelastic effects, the injected electrons are transmitted off-resonance and the Kondo contribution to the conductance is reduced. However, in the

• the excess energy of the injected electrons at finite voltage is released to activate a vibration mode, allowing the inelastic electrons to participate in the Kondo transport. The effect is manifested as enhanced conductance at a finite bias voltage (Figure 1a) corresponding to the relevant vibration

• analyze the response of vibration-mediated Kondo transport to mechanical stretching. We characterize the evolution of Kondo transport, background conductance and inelastic contributions due to electron–vibration interaction. In particular, the different contributions of Kondo transport and vibration

Evidence for non-conservative current-induced forces in the breaking of Au and Pt atomic chains

• Carlos Sabater,
• Carlos Untiedt and
• Jan M. van Ruitenbeek

Beilstein J. Nanotechnol. 2015, 6, 2338–2344, doi:10.3762/bjnano.6.241

• applied to any metal. The fine control of the bending and breaking is done by means of a piezo electric element (Figure 1). When gently breaking a small contact in this fashion at the last stages one observes a step-wise decrease in the conductance, which is due to the atom-by-atom break down of the

• contact. The conductance of the last atom bridging the gap depends on the type of metal used in the experiment [12][13]. This conductance is very close to the value of the quantum of conductance, G0 = 2e2/h, for simple monovalent metals, such as Au. When stretching the contact further, once a single atom

• bottom panel of Figure 1. At the start of each experiment for a fresh sample wire the conductance properties of the atomic chain are characterized by recording a conductance histogram: While repeatedly moving the wire ends toward and away from each other a contact is repeatedly formed and broken. During

Negative differential electrical resistance of a rotational organic nanomotor

• Hatef Sadeghi,
• Sara Sangtarash,
• Qusiy Al-Galiby,
• Rachel Sparks,
• Steven Bailey and
• Colin J. Lambert

Beilstein J. Nanotechnol. 2015, 6, 2332–2337, doi:10.3762/bjnano.6.240

• possess a dipole moment aligned along its length such that an applied electric field will cause the rotor to turn relative to the aromatic backbone. Our aim is to examine the response of the device to an external electric field and determine the change in electrical conductance due to the associated

• it is well known that the transmission coefficient is less than unity in asymmetric systems, such as the structure in Figure 1 [47][48][49]. At zero temperature and finite voltage EFL = EF + eV/2 and EFR = EF − eV/2 the current could be calculated as Therefore, the electrical conductance, G = I / V

• , is obtained by averaging T(E) over an energy window of width eV centred upon the Fermi energy. The Fermi functions can then be Taylor expanded over the range eV to give the electrical conductance in the zero-voltage but finite temperature limit by which represents a thermal average of T(E) over an

Thermoelectricity in molecular junctions with harmonic and anharmonic modes

• Bijay Kumar Agarwalla,
• Jian-Hua Jiang and
• Dvira Segal

Beilstein J. Nanotechnol. 2015, 6, 2129–2139, doi:10.3762/bjnano.6.218

• generating function (CGF) of the model, which contains comprehensive information over transport characteristics. Measurements of charge current and electrical conductance in single molecules hand over detailed energetic and dynamical information [16]. Complementing electrical conductance measurements, the

• whether the conductance is HOMO or LUMO dominated. More generally, the thermoelectric performance beyond linear response is of interest, with the two metal leads maintained at (largely) different temperatures and chemical potentials. What information can linear and nonlinear thermoelectric transport

• current by and the heat current by . The resulting expansions are cumbersome thus we write them formally in terms of the coefficients ai,j, (i,j = h,p), For and with Π being the Peltier coefficient [46][47], we identify the electrical conductance the thermopower the electron contribution to the

Controlled switching of single-molecule junctions by mechanical motion of a phenyl ring

• Yuya Kitaguchi,
• Satoru Habuka,
• Hiroshi Okuyama,
• Shinichiro Hatta,
• Tetsuya Aruga,
• Thomas Frederiksen,
• Magnus Paulsson and
• Hiromu Ueba

Beilstein J. Nanotechnol. 2015, 6, 2088–2095, doi:10.3762/bjnano.6.213

• . The switch can be actuated by dual triggers, either by a voltage pulse or by displacement of the electrode, and electronic manipulation of the ring by chemical substitution enables rational control of the on-state conductance. Owing to its simple mechanics, structural robustness, and chemical

• be particularly appealing if device properties (such as switching power, speed, and stability) could be engineered and controlled by chemical design. By optimizing the on-state conductance, a large on/off ratio can be achieved, which is essential for the reliable operation of a molecular switch. In

• this context, π-conjugated species are promising because π orbitals can be manipulated by introducing functional groups, which illustrates a way to control the junction conductance [9] (e.g., via quantum interference effects [10][11]). In a previous study [12], using a scanning tunneling microscope

Simulation of thermal stress and buckling instability in Si/Ge and Ge/Si core/shell nanowires

• Suvankar Das,
• Amitava Moitra,
• Mishreyee Bhattacharya and
• Amlan Dutta

Beilstein J. Nanotechnol. 2015, 6, 1970–1977, doi:10.3762/bjnano.6.201

• and suitability as novel thermoelectric devices [7]. This effect is found to be extremely prominent for ultrathin nanowires with diameters smaller than ≈20 nm [8]. The figure of merit can be further improved by introducing surface disorder without compromising the excellent electronic conductance [9

Conductance through single biphenyl molecules: symmetric and asymmetric coupling to electrodes

• Karthiga Kanthasamy and
• Herbert Pfnür

Beilstein J. Nanotechnol. 2015, 6, 1690–1697, doi:10.3762/bjnano.6.171

• break junction technique (MCBJ), the conductive properties of [1,1’-biphenyl]-4,4’-dithiol (M1) and of 4’-mercapto-[1,1’-biphenyl]-4-carbonitrile (M2) between gold electrodes. As a function of electrode separation, characterized by the conductance close to 0 V, we found several plateaus of relative

• stability, with those close to 0.01G0 being the most pronounced. The overall conductance of symmetric and asymmetric molecules were surprisingly similar, only the range of stability was smaller for M2. While M1 yielded symmetric I–V-curves, only small asymmetries were detected for M2. These are also

• reflected in the comparable values for coupling parameters using the single level resonance model. The high conductance for the asymmetric molecule is interpreted as a result of coherent coupling of electronic states through the whole molecule, so that the outcome cannot be predicted just by adding

Simple and efficient way of speeding up transmission calculations with k-point sampling

• Jesper Toft Falkenberg and
• Mads Brandbyge

Beilstein J. Nanotechnol. 2015, 6, 1603–1608, doi:10.3762/bjnano.6.164

• ” first principles calculations where the leads/electrodes are described by periodic boundary conditions. We show examples of transport in graphene structures where a speed-up of an order of magnitude is easily obtained. Keywords: density functional theory; electronic conductance; interpolation; post

• -processing; shortest-path; Introduction Calculations of electronic conductance based on first principle methods such as density functional theory (DFT) provide a valuable tool in order to gain insights into electronic transport in nano-conductors and comparison to experiments without employing fitting

Electrical properties and mechanical stability of anchoring groups for single-molecule electronics

• Riccardo Frisenda,
• Simge Tarkuç,
• Elena Galán,
• Mickael L. Perrin,
• Rienk Eelkema,
• Ferdinand C. Grozema and
• Herre S. J. van der Zant

Beilstein J. Nanotechnol. 2015, 6, 1558–1567, doi:10.3762/bjnano.6.159

• combined characterization of the electrical and mechanical properties determined by the anchoring groups. From conductance histograms we find that thiol anchored molecules provide the highest conductance; a single-level model fit to current–voltage characteristics suggests that SAc groups exhibit a higher

• -molecule junctions are formed if thiol (SH), methyl sulfide (SMe), pyridyl (Py) and amine (NH2), groups are used as anchoring groups [16][28][29][30]. In a comparative study Hong et al. [20], found that the low-bias conductance follows the trend SH > NH2> Py > CN by comparing a series of tolanes anchored

• anchoring groups. They find that the conductance is such that BT > SH > NH2> Py > CN, and the attenuation factor, β, that describes the length-dependence of the conductance, follows SH = Py > BT > NH2> CN. While SH and Py groups have been extensively studied and compared in single-molecule junctions, SMe

Continuum models of focused electron beam induced processing

• Milos Toth,
• Charlene Lobo,
• Vinzenz Friedli,
• Aleksandra Szkudlarek and
• Ivo Utke

Beilstein J. Nanotechnol. 2015, 6, 1518–1540, doi:10.3762/bjnano.6.157

• the changes that must be made to the above FEBIP models. Adsorbate depletion in high aspect ratio pits [7]: The replenishment rate of precursor molecules consumed in FEBIE can be limited by the gas flow conductance of a growing etch pit. The replenishment rate affects the adsorbate concentration N

• which, in turn, affects the etch rate through equations such as Equation 15. Etch-pit conductance can be the most significant process limiting the FEBIE rate when fabricating high aspect ratio pits. As an etch pit grows during FEBIE, the conductance decreases, causing the etch rate to decrease with time

Atomic force microscopy as analytical tool to study physico-mechanical properties of intestinal cells

• Christa Schimpel,
• Oliver Werzer,
• Eleonore Fröhlich,
• Gerd Leitinger,
• Markus Absenger-Novak,
• Birgit Teubl,
• Andreas Zimmer and
• Eva Roblegg

Beilstein J. Nanotechnol. 2015, 6, 1457–1466, doi:10.3762/bjnano.6.151

• and the removed filter membranes were given a thin coating of gold palladium (Bal-Tec SCD 500) to improve the surface conductance of the sample and thus avoid surface charging of the sample under the beam. The samples were sputtered at 25 mA for 60 s under argon atmosphere and images were acquired

Enhanced fullerene–Au(111) coupling in (2√3 × 2√3)R30° superstructures with intermolecular interactions

• Michael Paßens,
• Rainer Waser and
• Silvia Karthäuser

Beilstein J. Nanotechnol. 2015, 6, 1421–1431, doi:10.3762/bjnano.6.147

• addition, hybrid fullerene–Au(111) surface states suggest partly covalent interactions. Keywords: adatom–vacancy mechanism; differential conductance; fullerene; Ising model; scanning tunnelling microscopy; Introduction Monolayers of close-packed fullerenes on metal surfaces belong to one of the most

• superstructures of C60 on Au(111) surfaces, we investigate in detail the orbital symmetry and thus, the rotational orientation and interface interactions of fullerenes in disordered and uniform (2√3 × 2√3)R30° superstructures. These structural investigations are complemented by conductance measurements sheding

• adatoms. The observed symmetry breaking causes the lifting of the degeneracy of the LUMO and LUMO+1 orbitals in the differential conductance spectra. In addition, hybrid fullerene–metal states are identified and attributed to partly covalent interactions between adatoms on the Au(111) surface and C60

Electron and heat transport in porphyrin-based single-molecule transistors with electro-burnt graphene electrodes

• Hatef Sadeghi,
• Sara Sangtarash and
• Colin J. Lambert

Beilstein J. Nanotechnol. 2015, 6, 1413–1420, doi:10.3762/bjnano.6.146

• ][7]. Transport in single-molecule FETs is mostly dominated by the contacts between the electrodes and molecules, which is an obstacle to achieving reproducibility and stability. Furthermore, in laboratory-based conductance measurements (using, for example, mechanically-controlled break junctions

• order Vds. Figure 7 shows the thermopower, S, and the electronic contribution to the thermal conductance, κ, of the PM–EBG device. The device generated a maximum thermopower of 280 μV/K at 110 K, which then decreased at higher temperatures, as shown in Figure 7a. Furthermore, the thermal conductance of

• small as 10 meV increases the thermopower to 475 μV/K. In contrast, the electronic thermal conductance of the device is quite low and does not change significantly with the small variation of the Fermi energy. The thermoelectric figure-of-merit could be high in this device provided the phonon

Alternative types of molecule-decorated atomic chains in Au–CO–Au single-molecule junctions

• Zoltán Balogh,
• Péter Makk and
• András Halbritter

Beilstein J. Nanotechnol. 2015, 6, 1369–1376, doi:10.3762/bjnano.6.141

• break junctions. The conductance histogram exhibits two distinct molecular configurations, which are further investigated by a combined statistical analysis. According to conditional histogram and correlation analysis these molecular configurations show strong anticorrelations with each other and with

• pure Au monoatomic junctions and atomic chains. We identify molecular precursor configurations with somewhat higher conductance, which are formed prior to single-molecule junctions. According to detailed length analysis two distinct types of molecule-affected chain-formation processes are observed, and

• we compare these results to former theoretical calculations considering bridge- and atop-type molecular configurations where the latter has reduced conductance due to destructive Fano interference. Keywords: atomic chains; break junction; carbon monoxide; correlation analysis; gold; Introduction

Can molecular projected density of states (PDOS) be systematically used in electronic conductance analysis?

• Tonatiuh Rangel,
• Gian-Marco Rignanese and
• Valerio Olevano

Beilstein J. Nanotechnol. 2015, 6, 1247–1259, doi:10.3762/bjnano.6.128

• the quantum transport conductance in terms of the projected density of states (PDOS) onto molecular orbitals (MOs). We first consider two different methods for identifying the relevant MOs: (1) diagonalization of the Hamiltonian of the isolated molecule and (2) diagonalization of a submatrix of the

• junction (e.g., with or without dangling bonds); within Method 2, the PDOS depends on the chosen basis set. We show that these differences can be critical when the PDOS is used to provide a physical interpretation of the conductance (especially when its value is small, as it happens typically at zero bias

• ). In this work, we propose a new approach in an attempt to reconcile the two traditional methods. Although some improvements were achieved, the main problems remain unsolved. Our results raise more general questions and doubts on a PDOS-based analysis of the conductance. Keywords: benzene-diamine

Enhancing the thermoelectric figure of merit in engineered graphene nanoribbons

• Hatef Sadeghi,
• Sara Sangtarash and
• Colin J. Lambert

Beilstein J. Nanotechnol. 2015, 6, 1176–1182, doi:10.3762/bjnano.6.119

• values as high as ZTe = 2.45 are obtained. All thermoelectric properties can be further enhanced by tuning the Fermi energy of the leads. Keywords: graphene nanoribbons; quantum transport; thermal conductance; thermoelectric figure of merit; thermopower; Introduction Nowadays, the performance of

• thermoelectricity requires a strongly suppressed thermal conductivity (κ) since the performance of thermoelectric devices is inversely proportional to the thermal conductivity. On the other hand, the cooling of local hot spots requires a high thermal conductivity [3]. Thermal conductance in a solid is defined by

• Fourier’s law, where q is the heat flux, κ = κpl + κe is the thermal conductance due to phonons (κpl) and electrons (κe) and is the temperature gradient [1]. Nanostructures show significantly different thermal properties than bulk crystals in which acoustic phonons are the main heat carriers. The reasons

Electrical characterization of single molecule and Langmuir–Blodgett monomolecular films of a pyridine-terminated oligo(phenylene-ethynylene) derivative

• Henrry M. Osorio,
• Santiago Martín,
• María Carmen López,
• Santiago Marqués-González,
• Simon J. Higgins,
• Richard J. Nichols,
• Paul J. Low and
• Pilar Cea

Beilstein J. Nanotechnol. 2015, 6, 1145–1157, doi:10.3762/bjnano.6.116

• -aggregates. Scanning tunneling microscopy (STM), in particular the “STM touch-to-contact” method, was used to determine the electrical properties of LB films of 1. From these STM studies symmetrical I–V curves were obtained. A junction conductance of 5.17 × 10−5 G0 results from the analysis of the

• pseudolinear (ohmic) region of the I–V curves. This value is higher than that of the conductance values of LB films of phenylene-ethynylene derivatives contacted by amines, thiols, carboxylate, trimethylsilylethynyl or acetylide groups. In addition, the single molecule I–V curve of 1 determined using the I(s

• molecules within the LB film do not strongly influence the molecule conductance. The results presented here complement earlier studies of single molecule conductance of 1 using STM-BJ methods, and support the growing evidence that the pyridyl group is an efficient and effective anchoring group in sandwiched

Closed-loop conductance scanning tunneling spectroscopy: demonstrating the equivalence to the open-loop alternative

• Chris Hellenthal,
• Kai Sotthewes,
• Martin H. Siekman,
• E. Stefan Kooij and
• Harold J. W. Zandvliet

Beilstein J. Nanotechnol. 2015, 6, 1116–1124, doi:10.3762/bjnano.6.113

• using closed-loop z(V) conductance scanning tunneling spectroscopy (STS) measurements for the determination of the effective tunneling barrier by comparing them to more conventional open-loop I(z) measurements. Through the development of a numerical model, the individual contributions to the effective

• measurements, perhaps the most simple method of determining the work function is performing I(z) spectroscopy and plotting the natural logarithm of the measured tunneling conductance G as function of the tip–sample distance. The slope of the obtained line is equal to the inverse decay length κ which, for low

• conductance measurements performed in I(z) and z(V) spectroscopy mode. The equivalence of both methods is demonstrated by comparing the obtained results and plotting them in a single graph. Additionally, an alternative numerical method of determining the work function of a sample through I(z) and z(V

Tunable magnetism on the lateral mesoscale by post-processing of Co/Pt heterostructures

• Oleksandr V. Dobrovolskiy,
• Maksym Kompaniiets,
• Roland Sachser,
• Fabrizio Porrati,
• Christian Gspan,
• Harald Plank and
• Michael Huth

Beilstein J. Nanotechnol. 2015, 6, 1082–1090, doi:10.3762/bjnano.6.109

• °C, and dropped to 70–90 μΩ·cm after 10 oxygen pulses. Figure 3 depicts the time-dependent normalized conductance of the Pt layer of sample C during the purification process. The post-processed Pt layers exhibited a nano-porous structure and a reduction of height from 50 ± 1.5 nm to 11 ± 1.5 nm, as

• conductance of the Pt layer of sample C normalized to its saturation value after the purification process at 150 °C consisting of 12 cycles with a total duration of 120 min. The filled areas under the curve show the time intervals with the oxygen flux switched on. Hall voltage cycling at 10 K for all samples

Pt- and Pd-decorated MWCNTs for vapour and gas detection at room temperature

• Hamdi Baccar,
• Atef Thamri,
• Pierrick Clément,
• Eduard Llobet and
• Adnane Abdelghani

Beilstein J. Nanotechnol. 2015, 6, 919–927, doi:10.3762/bjnano.6.95

• molecule to the metal nanoparticle–MWCNT system, which results in a decrease in the conductance of the nanotube. The lower concentrations shown in Figure 3 and Figure 4 are far from the limit of detection for these compounds, considering that a clear response signal should be at least three times higher

Electroburning of few-layer graphene flakes, epitaxial graphene, and turbostratic graphene discs in air and under vacuum

• Andrea Candini,
• Nils Richter,
• Domenica Convertino,
• Camilla Coletti,
• Franck Balestro,
• Wolfgang Wernsdorfer,
• Mathias Kläui and
• Marco Affronte

Beilstein J. Nanotechnol. 2015, 6, 711–719, doi:10.3762/bjnano.6.72

• suppression of conductance fluctuations [14]. Recent works have successfully made use of graphene for the realization of electrodes in molecular devices [10][17]. Specifically, parallel multi-junctions devices have been fabricated in chemical vapor deposition (CVD) graphene by electron beam lithography and

• the contacts to the pads) were obtained by the evaporation of 10 nm Cr/100 nm Au and lift-off. For mechanically exfoliated and epitaxial graphene the electroburning process was performed by applying an increasing voltage ramp (20 mV/s) while continuously measuring the conductance of a junction. The

Entropy effects in the collective dynamic behavior of alkyl monolayers tethered to Si(111)

• Christian Godet

Beilstein J. Nanotechnol. 2015, 6, 583–594, doi:10.3762/bjnano.6.60

• to 1 × 107 Hz). To observe dipolar relaxation mechanisms, low temperature and reverse bias were imposed to obtain low dc conductance and a relaxation frequency of the space-charge layer below 1 Hz [32]. The complex admittance, Y*(VDC,T,ω) = Gm + jω Cm, can be analyzed by using either the capacitance