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

• de-excitation/excitation of an “impurity” (vibrational mode). The left and right reservoirs defining Hel in Equation 2 are characterized by a structured density of states since we had absorbed the D state in the L terminal, and similarly, the A level in the R metal. These electronic reservoirs are

• temperature T = 300 K. We assumed flat bands with a constant density of states. Linear response behavior of the donor–acceptor junction as a function of gate voltage. (a) Electrical conductance, (b) Seebeck coefficient, (c) electronic thermal conductance, and (d) figure of merit ZT. Parameters are the same as

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

• ascribed to a stronger hybridization with the substrate states as revealed by the increased projected density of states (PDOS) onto the chalcogen atom near EF (Figure 6b,d; more extended atomic orbitals of S than of O) as well as by the larger width of the lowest unoccupied molecular orbital (LUMO

• and (b) projected density of states (PDOS) onto the Cu apex atom as well as onto the atoms in the PhO molecule (adapted from [12]). (c,d) Similar results for the PhS molecule. The tip height was h = 13.9 Å (solid lines) or h = 14.4 Å (dashed lines) and the lateral position was x = 1.4 Å. The

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

• diverging density of states and discontinuities in the transmission function at energies corresponding to band on-sets/channel openings. It is well known that often in order to obtain smooth, well-converged density of states and transmissions as a function of energy, a substantial number of transverse k

• convergence due to its vanishing density of states at the Fermi level. In the remaining parts of the paper we first explain the workings of the interpolation scheme in section Results and Discussion, while we investigate various test cases in section Example cases, and finally discuss limitations to the

• illustrated the method using electron transport through graphene nano-structures and k-point averaging of transmission functions. However, the method is generally applicable also to phonon transport and to other functions such as density of states or other types of interpolation parameters such as

Possibilities and limitations of advanced transmission electron microscopy for carbon-based nanomaterials

• Xiaoxing Ke,
• Carla Bittencourt and
• Gustaaf Van Tendeloo

Beilstein J. Nanotechnol. 2015, 6, 1541–1557, doi:10.3762/bjnano.6.158

• the low-loss or valence region of an EELS spectrum (<50 eV) allows one to study the band structure and in particular the dielectric function of a material. In addition to the collective electron excitation modes marked by characteristic plasmon peaks, the joint density of states above the Fermi level

Current–voltage characteristics of manganite–titanite perovskite junctions

• Benedikt Ifland,
• Patrick Peretzki,
• Birte Kressdorf,
• Philipp Saring,
• Andreas Kelling,
• Michael Seibt and
• Christian Jooss

Beilstein J. Nanotechnol. 2015, 6, 1467–1484, doi:10.3762/bjnano.6.152

• the assumption is made that the current is limited by the rate at which holes can diffuse in the narrow band gap material. X is the fraction of those carriers having sufficient energy to cross the barrier, a is the junction area and NV,2 is the effective density of states of the valence band for the

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

• the high electronegativity of oxygen atoms, charge is transferred from the carbon atoms to the oxygen atoms. Consequently, oxygen-terminated ribbons show p-type doped behaviour [20][21] and their density of states (DOS) is shifted toward positive energies as shown in Figure 3c (dashed line). Figure 3c

• , resulting in mixed AA and AB stacking with graphene. a) HOMO−1, b) HOMO, c) LUMO and d) LUMO+1 state iso-surfaces. Molecular and electronic structure of the EBG electrodes. a) Molecular orbital iso-surfaces, b) band structure of EBG electrodes, c) density of states and number of open channels in the EBG

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

• lowest unoccupied molecular orbital (LUMO), or the next LUMO (LUMO+1), etc.). Then, the total electronic density of states (DOS) is decomposed into the projected density of states (PDOS) associated with each different MO. Finally, by directly comparing the conductance profile, , with the various PDOS

• reason, it is believed that the molecule itself and its electronic structure has a deep influence on the conductance. The interpretation of the conductance profile, , or of the zero-bias conductance, , is often carried out by referring to the projected density of states onto molecular orbitals (see next

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

• for this are changes in the phonon density of states, an increased phonon-boundary scattering and the dispersion of the nanostructures in low dimensional semiconductors [2][4][5][6]. The efficiency of thermoelectric materials and devices is determined by their thermoelectric figure of merit (ZT = S2GT

• /κ) where S is the Seebeck coefficient, which depends on the asymmetry of the density of states around the Fermi level, G is the electrical conductance and T is the temperature [7]. Similarly, the electronic thermoelectric figure of merit also is defined as ZTe = S2GT/κe. Since the efficiency of a

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

• techniques can be and have been performed on a wide variety of samples, with each different type of measurement yielding information on distinct properties of the probed sample [2]. The local density of states of a sample (LDOS) provides insight into the electronic and chemical properties of a sample. By

• = ρ(V) is the energy-dependent combined density of states of the tip and the sample, V is the applied tip–sample bias voltage, z is the tip–sample distance, is the tunneling barrier and , with m the rest mass of the electron. The product is sometimes referred to as the inverse decay length and

• * on ζ. In order to make a quantitative analysis possible, a numerical method will have to be developed. As a starting point, Equation 5 will have to be rewritten to eliminate as many unknown parameters as possible. By taking the the derivative dI/dz, the density of states ρ can be eliminated from the

Charge carrier mobility and electronic properties of Al(Op)₃: impact of excimer formation

• Andrea Magri,
• Pascal Friederich,
• Bernhard Schäfer,
• Valeria Fattori,
• Xiangnan Sun,
• Timo Strunk,
• Velimir Meded,
• Luis E. Hueso,
• Wolfgang Wenzel and
• Mario Ruben

Beilstein J. Nanotechnol. 2015, 6, 1107–1115, doi:10.3762/bjnano.6.112

• deviations between the vacuum and matrix dipole moments arise from induction and polarization effects present only in the matrix, which influence the energy disorder. Furthermore, we calculated the width of the local density of states for additional charges (if a Gaussian shape is assumed, this is referred

Statistics of work and orthogonality catastrophe in discrete level systems: an application to fullerene molecules and ultra-cold trapped Fermi gases

• Antonello Sindona,
• Michele Pisarra,
• Mario Gravina,
• Cristian Vacacela Gomez,
• Pierfrancesco Riccardi,
• Giovanni Falcone and
• Francesco Plastina

Beilstein J. Nanotechnol. 2015, 6, 755–766, doi:10.3762/bjnano.6.78

• Fermi level. On the other hand, the lowest- energy unperturbed valence state gets mainly mixed with the first two occupied perturbed valence states (see also Table 1). Energy levels and (broadened) density of states for a trapped gas of spin 1/2 fermions having a number of occupied states (N = 122

Graphene quantum interference photodetector

• Mahbub Alam and
• Paul L. Voss

Beilstein J. Nanotechnol. 2015, 6, 726–735, doi:10.3762/bjnano.6.74

• because the density of states is higher near the resonant energy levels. The external quantum efficiency remains constant with a photon flux of up to approximately 1031 photon/m2/s. The variation of the peak photocurrent with photon flux is shown in Figure 9b and Figure 10b. We should mention here that

• structure as photodetector. In a MZI structure, an electron in the ground, transverse mode goes through the device with a transmittance of one (T = 1) due to constructive interference at energies corresponding to longitudinal resonant modes. At these resonant energies, the electrons have a high density of

• states. In this paper we investigate for the first time the interaction of light in a graphene nanoribbon MZI structure and specifically we study the coupling of light between longitudinal resonant modes for both zigzag and armchair structures. Graphene photodetectors have been studied in detail [2][3

Observation of a photoinduced, resonant tunneling effect in a carbon nanotube–silicon heterojunction

• Carla Aramo,
• Antonio Ambrosio,
• Michelangelo Ambrosio,
• Maurizio Boscardin,
• Paola Castrucci,
• Michele Crivellari,
• Marco Cilmo,
• Maurizio De Crescenzi,
• Francesco De Nicola,
• Emanuele Fiandrini,
• Valentina Grossi,
• Pasqualino Maddalena,
• Maurizio Passacantando,
• Sandro Santucci,
• Manuela Scarselli and
• Antonio Valentini

Beilstein J. Nanotechnol. 2015, 6, 704–710, doi:10.3762/bjnano.6.71

• their density of states shows the same van Hove singularities as the single-walled CNTs. The excitation of electron–hole pairs is the responsible for this effect in each single wall of the multiwall CNT. In the present case, the incident light produces the sizeable absorption band observed around 1.5

Chains of carbon atoms: A vision or a new nanomaterial?

• Florian Banhart

Beilstein J. Nanotechnol. 2015, 6, 559–569, doi:10.3762/bjnano.6.58

• carbon atoms [49]. By considering cumulene chains between two metal electrodes, Lang and Avouris [46] have found that even-number chains have a lower density of states (DOS) at the Fermi level than odd-number chains. In free chains (no contacts), the highest occupied molecular orbital (HOMO) is half

• of states in the contacting material at low energy is small. Another aspect is the local hybridization of the carbon atoms at the contact. A sp3-hybridized carbon atom (e.g., when the chain is connected to the middle of a graphenic sheet or the wall of a carbon nanotube as shown in Figure 5) leads to

• states in the chain, due to reflections at the interface to the contacts [50]. Close to the Fermi energy of perfect graphene, the transmission T decreases linearly with electron energy. The low transmission results from the vanishing of the DOS in undoped graphene. The reflection is high if the density

Inorganic Janus particles for biomedical applications

• Isabel Schick,
• Steffen Lorenz,
• Dominik Gehrig,
• Stefan Tenzer,
• Wiebke Storck,
• Karl Fischer,
• Dennis Strand,
• Frédéric Laquai and
• Wolfgang Tremel

Beilstein J. Nanotechnol. 2014, 5, 2346–2362, doi:10.3762/bjnano.5.244

• . attributed this broadening and damping to the tunnelling of conduction band electrons of the Au nanoparticles into the projected density of states of the Fe3O4 domains, the so-called “interface decay channel” [56]. As a metal oxide starts to nucleate heterogeneously on the gold nanoparticles, the induced

Spectroscopic mapping and selective electronic tuning of molecular orbitals in phosphorescent organometallic complexes – a new strategy for OLED materials

• Pascal R. Ewen,
• Jan Sanning,
• Tobias Koch,
• Nikos L. Doltsinis,
• Cristian A. Strassert and
• Daniel Wegner

Beilstein J. Nanotechnol. 2014, 5, 2248–2258, doi:10.3762/bjnano.5.234

• the local density of states of the sample. Energy-resolved spectral maps (that visualize the spatial distribution of molecular orbitals) were acquired by measuring dI/dV at a fixed bias as a function of lateral position in constant-current mode. For the DFT calculations shown here, Kohn–Sham molecular

• given MOs exhibit a significant contribution at the ligands. We first focus our discussion on the ligands (i.e., excluding the Pt site). The depicted seven dI/dV maps in Figure 3b reveal the local density of states (LDOS) of several MOs between −3.2 V and +3.2 V. Below −3.0 V the dI/dV intensity is most

Hybrid spin-crossover nanostructures

• Carlos M. Quintero,
• Gautier Félix,
• Iurii Suleimanov,
• José Sánchez Costa,
• Gábor Molnár,
• Lionel Salmon,
• William Nicolazzi and
• Azzedine Bousseksou

Beilstein J. Nanotechnol. 2014, 5, 2230–2239, doi:10.3762/bjnano.5.232

• onto gold substrates as control samples. It was found that there was a shift in the density of unoccupied states during the spin transition that leads to a significant loss in the density of states just above the Fermi energy level in a HS to LS transition. This situation was observed in SCO films

Two-dimensional and tubular structures of misfit compounds: Structural and electronic properties

• Tommy Lorenz,
• Jan-Ole Joswig and
• Gotthard Seifert

Beilstein J. Nanotechnol. 2014, 5, 2171–2178, doi:10.3762/bjnano.5.226

• ” [36]. In Figure 5 the density of states of the electronic bands of PbSe and NbSe2 near the Fermi level are displayed schematically. The overlap of the Se(PbSe) 4p states with the Nb dz² states can be seen clearly, which is used as an argument for potential charge transfer. Additionally, the dependence

• recent theoretical study performed with density functional-based tight-binding calculations investigated a possible charge transfer between the SnS and SnS2 layers. By comparing the density of states (DOS) for a hypothetical SnS–SnS2 misfit system with the sum of the DOSs of the two isolated monolayers

• positions in space: black atoms above the paper-plane and red ones beneath it. Adapted with permission from [3]. Copyright 1995 Elsevier. Schematic representation of the density of states of a PbSe layer (left) and a NbSe2 layer (right). The electron transfer takes place from the PbSe valance band to the

UHV deposition and characterization of a mononuclear iron(III) β-diketonate complex on Au(111)

• Irene Cimatti,
• Silviya Ninova,
• Valeria Lanzilotto,
• Luigi Malavolti,
• Luca Rigamonti,
• Brunetto Cortigiani,
• Matteo Mannini,
• Elena Magnano,
• Federica Bondino,
• Federico Totti,
• Andrea Cornia and
• Roberta Sessoli

Beilstein J. Nanotechnol. 2014, 5, 2139–2148, doi:10.3762/bjnano.5.223

• , the density of states (DOS) for the Fe(dpm)3@Au(111) system was computed through a periodic density functional approach (see details in Experimental section). The comparison between the experimental and computed DOS spectra (Figure 2) shows a good correlation between the main features. The DOS region

• larger discrepancies observed at higher binding energies. By plotting the projected density of states (PDOS) on the ligands and the iron ion (see Figure 3a), it is evident that dpm− ligands provide the main orbital contributions to the energy region where the molecular peaks (a, b, c, d) can be

• coverage (grey curve) and the clean substrate (red curve). (Bottom panel) Theoretical density of states for the system Fe(dpm)3@Au(111) (grey curve) and decomposition into Au and Fe(dpm)3 contributions. Projected DOS of the molecules in Fe(dpm)3@Au(111) (a), FeOH(dpm)2@Au(111) (b), and Fe(dpm)2@Au(111) (c

Cathode lens spectromicroscopy: methodology and applications

• T. O. Menteş,
• G. Zamborlini,
• A. Sala and
• A. Locatelli

Beilstein J. Nanotechnol. 2014, 5, 1873–1886, doi:10.3762/bjnano.5.198

• ideally suited to compare the density of states (DOS) of different, adjacent types of graphene exhibiting distinct electronic structure properties. Laterally resolved XAS was also utilized in an isolated study on exfoliated graphene, in which selected features in the K-edge spectrum of C were studied as a

Electronic and electrochemical doping of graphene by surface adsorbates

• Hugo Pinto and
• Alexander Markevich

Beilstein J. Nanotechnol. 2014, 5, 1842–1848, doi:10.3762/bjnano.5.195

• (marked B in Figure 3a) are delocalized over the carbon atoms of graphene (Figure 3c) indicating the presence of free electrons. These results confirm that n-type doping of graphene occurs due to the transfer of electrons from K atoms to graphene. Integration of the graphene density of states between the

Quasi-1D physics in metal-organic frameworks: MIL-47(V) from first principles

• Danny E. P. Vanpoucke,
• Jan W. Jaeken,
• Stijn De Baerdemacker,
• Kurt Lejaeghere and
• Veronique Van Speybroeck

Beilstein J. Nanotechnol. 2014, 5, 1738–1748, doi:10.3762/bjnano.5.184

• positions and cell shape. The convergence criterion is set to a difference in energy of less than 1.0 × 10−7 eV between subsequent ionic steps. After full relaxation, the forces on the ions are then found to be below 1.2 meV/Å. The density of states (DOS) was obtained by using a denser k-point grid of 3 × 3

• an antiferromagnetic spin configuration, while the lower chain has a ferromagnetic spin configuration. The iso-surface is taken at 0.00125, with majority spin shown in blue, and minority in red. The black rectangle indicates a single unit cell. Band structure and density of states (DOS) near the

Numerical investigation of the effect of substrate surface roughness on the performance of zigzag graphene nanoribbon field effect transistors symmetrically doped with BN

• Majid Sanaeepur,
• Arash Yazdanpanah Goharrizi and
• Mohammad Javad Sharifi

Beilstein J. Nanotechnol. 2014, 5, 1569–1574, doi:10.3762/bjnano.5.168

• to the width of the GNR [7][8][9][10][11]. Armchair graphene nanoribbons (AGNRs) are non-magnetic. Zigzag graphene nanoribbons (ZGNRs), however, have a spin-polarized ground state and a high density of states localized at the zigzag edges of the ribbon [8][12][13][14]. Nonetheless, the energy of the

Review of nanostructured devices for thermoelectric applications

• Giovanni Pennelli

Beilstein J. Nanotechnol. 2014, 5, 1268–1284, doi:10.3762/bjnano.5.141

• particular it increases when the average difference between the carrier energies and the Fermi energy increases. In low dimensional systems, the density of states is reshaped with respect to bulk systems, in such a way that charge carriers are spread to higher energies. This produces an increase not only of

DFT study of binding and electron transfer from colorless aromatic pollutants to a TiO₂ nanocluster: Application to photocatalytic degradation under visible light irradiation

• Corneliu I. Oprea,
• Petre Panait and
• Mihai A. Gîrţu

Beilstein J. Nanotechnol. 2014, 5, 1016–1030, doi:10.3762/bjnano.5.115

• wavelength electronic transitions and the absorption in the visible range. Although taken separately both the pollutants and the catalyst absorb in the UV, the states with mixed character lead to allowed optical transitions. We can even better understand these concepts looking at the density of states (DOS

• , BA, pHBA, and SA, respectively. In line with the previous discussion, important to note is the mixed character of the states involved in the optical transitions. Looking carefully at the density of states, we can observe that the HOMOs have some small contribution from the catalyst and, similarly

• displayed schematically in Figure 10. The left panel shows the density of states and reveals the mixed character of the key orbitals, such that, due to charge delocalization optical transitions in the visible become possible. The diagram in the central panel illustrates the energy level alignment and the