Effects of electronic coupling and electrostatic potential on charge transport in carbon-based molecular electronic junctions

• Richard L. McCreery

Beilstein J. Nanotechnol. 2016, 7, 32–46, doi:10.3762/bjnano.7.4

• shows the effect schematically, starting with two separated G9 planes and an AB molecule with its HOMO at −6.16 eV for the free molecule. The −4.7 eV work function observed experimentally is close to the −4.68 eV HOMO calculated for G9, and both G9s have identical HOMO levels. When the G9–AB–G9 system

• is formed, DFT predicts that 0.032 e− are transferred to the AB molecules, as shown in Figure 8B. The local electrostatic potential associated with these electrons shifts all of the orbitals in AB to higher energy, and decreases the transport barrier predicted from the work function and HOMO energy

Large area scanning probe microscope in ultra-high vacuum demonstrated for electrostatic force measurements on high-voltage devices

• Urs Gysin,
• Thilo Glatzel,
• Thomas Schmölzer,
• Adolf Schöner,
• Sergey Reshanov,
• Holger Bartolf and
• Ernst Meyer

Beilstein J. Nanotechnol. 2015, 6, 2485–2497, doi:10.3762/bjnano.6.258

• detection of electrostatic forces and the determination of local work function values was intensively discussed and models combining large scale influences with atomistic simulations have been developed [1][2][3][4]. As early as in the late 1980s H. Wickramasinghe proposed several SPM based methods for the

• . Firstly, we discuss KPFM results from a contact surface of a copper alloy utilized in a power switch. The presence and shape of chromium grains embedded in the copper alloy are clearly visible. The contrast in the measured work function is strongly enhanced by sputtering the sample with argon ions to

• . The grain seems to be covered by a residual layer partly smearing out the CPD contrast. The PtIr-coated tip is most probably contaminated by a metal oxide cluster (CuO or CrO) due to slight tip–sample contacts before the measurements, such that the work function is around Φtip = 5 eV [40]. Also in

Self-organization of gold nanoparticles on silanated surfaces

• Htet H. Kyaw,
• Salim H. Al-Harthi,
• Azzouz Sellai and
• Joydeep Dutta

Beilstein J. Nanotechnol. 2015, 6, 2345–2353, doi:10.3762/bjnano.6.242

• electron emission after APTES was deposited on the glass substrate and AuNPs were deposited on the APTES-functionalized glass substrate. The work function (Φ) can be calculated from the difference in the photon energy of He(I) (21.2 eV) and the energy difference ΔE between the secondary cut-off energy

• (Ecut-off) and the Fermi edge (EF) (as shown in Figure 5a) [28] as The work function is obtained as 4.5 eV for glass and 4.65 eV for the APTES-functionalized glass substrate as well as the substrate with AuNPs deposited on APTES-functionalized glass. The valance band maximum (VBM) of bare glass, APTES

• substrates. The work function also changed from 4.55 eV for sample 1 to 4.62 eV for sample 2 and 4.65 eV for sample 3, respectively. Due to different coverage of AuNPs on APTES-functionalized glass substrates, energy shift in VBM is observed (see Figure 6b). Effects of annealing of AuNPs deposited APTES

Kelvin probe force microscopy for local characterisation of active nanoelectronic devices

• Tino Wagner,
• Hannes Beyer,
• Patrick Reissner,
• Philipp Mensch,
• Heike Riel,
• Bernd Gotsmann and
• Andreas Stemmer

Beilstein J. Nanotechnol. 2015, 6, 2193–2206, doi:10.3762/bjnano.6.225

• electric field by adjusting a bias voltage between tip and sample. Hence, Kelvin probe force microscopy is able to quantify the local contact potential difference (CPD), Ulcpd, which contains contributions, e.g., from the difference in work function between the AFM tip and structures on the sample, dopants

• detection. For an extraction of contact resistances, the voltage profile due to current flow needs to be separated from additional offsets in Ulcpd, such as spatial variations in work function. These are easily obtained from a scan at zero bias. Knowing the potential drop at the contacts, the bias current

The role of low-energy electrons in focused electron beam induced deposition: four case studies of representative precursors

• Rachel M. Thorman,
• Ragesh Kumar T. P.,
• D. Howard Fairbrother and
• Oddur Ingólfsson

Beilstein J. Nanotechnol. 2015, 6, 1904–1926, doi:10.3762/bjnano.6.194

• nature of the substrate (work function, Fermi energy, and Z-value (atomic number)), and to a lesser extent on the PE energy (as long as it is above about 100 eV) [6][7][8]. Conversely, the SE yield depends significantly on both the nature of the substrate and the PE energy. Note that the former

• considerable and the same is true for the errors in the deposition cross section. Furthermore, the exact peak position and the general form of the energy dependence of the calculated SE yield depend strongly on the model used and the Z-number of the respective substrate material, with the work function and

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

• tunneling barrier present in these experiments, such as the work function and the presence of an image charge, are determined quantitatively. This opens up the possibility of determining tunneling barriers of both vacuum and molecular systems in an alternative and more detailed manner. Keywords: image

• charge; scanning tunneling spectroscopy (STS); tunneling barrier; work function; z(V); Introduction Although the scanning tunneling microscope (STM) has been used for the topographical imaging of conductive samples since the early 1980s [1], recent times have seen an increasing interest in the

• studies have reported on the possibility of obtaining LDOS information by using closed-loop z(V) measurements [5][6][7][8]. Another field of interest is the determination of the work function of materials, through the use of either STS or mechanical break junction (MBJ) measurements. In the case of STS

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

• −5.83 eV, respectively. As a result of the lower LUMO energy of Al(Op)3 compared to Alq3, the injection of electrons should be not only possible, but enhanced, as a consequence of the reduced mismatch with a cathode such as aluminum with a work function of Φ ≈ 4.3 eV. In addition, considering the

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

• than the noise level. In general, Pt-decorated MWCNTs showed higher response to non-aromatic VOCs than Pd-decorated MWCNTs. The work function of oxygen-plasma-treated MWCNTs ranges from 4.9 to 5.1 eV [41]. This is very close to values of metals such as Pt (4.8 eV) or Pd (4.95 eV) [34], enabling

Raman spectroscopy as a tool to investigate the structure and electronic properties of carbon-atom wires

• Alberto Milani,
• Matteo Tommasini,
• Valeria Russo,
• Andrea Li Bassi,
• Andrea Lucotti,
• Franco Cataldo and
• Carlo S. Casari

Beilstein J. Nanotechnol. 2015, 6, 480–491, doi:10.3762/bjnano.6.49

• polyynes of different chain lengths (N). The following experimental values for the work function and EA have been used in the case of Ag: IP = 4.6 eV and EA = −1.30 eV for EA [34] (b) Modulation of the DFT-computed [39] BLA for phenyl-capped polyynes of different lengths (N) and charge states (0, +1, −1

Kelvin probe force microscopy in liquid using electrochemical force microscopy

• Liam Collins,
• Stephen Jesse,
• Jason I. Kilpatrick,
• Alexander Tselev,
• M. Baris Okatan,
• Sergei V. Kalinin and
• Brian J. Rodriguez

Beilstein J. Nanotechnol. 2015, 6, 201–214, doi:10.3762/bjnano.6.19

• material under investigation and the environment in which the measurement is performed, the CPD can then be related to various electrostatic and electrochemical properties. For example, in the case of a metal probe with known work function in vacuum, the CPD provides a measurement of the work function of

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

• to the vacuum level. For a comparison with the measured values from STS (which are given relative to EF), a constant corresponding to the work function of 5.1 eV has to be added to the calculated values (cf. details in the discussion). Structural analysis For the the structural characterization of as

• additional role of van der Waals forces between neighboring R3 alkyl chains for the self-assembly. (a) Energy and LDOS of calculated orbitals for C1 in the gas phase. Here, a work function of 5.1 eV was assumed. This value results from minimizing the energy differences between calculated and measured

Low cost, p-ZnO/n-Si, rectifying, nano heterojunction diode: Fabrication and electrical characterization

• Vinay Kabra,
• Lubna Aamir and
• M. M. Malik

Beilstein J. Nanotechnol. 2014, 5, 2216–2221, doi:10.3762/bjnano.5.230

• used to eradicate any possibility of rectification through the contacts, as its work function (4.5 eV) is higher than that of p-ZnO (<4 eV). The mercury contacts are assumed to form ohmic contacts [9]. Characterization A Rigaku Minflex-2 X-ray diffractometer was used for determination of the

Electrical contacts to individual SWCNTs: A review

• Wei Liu,
• Christofer Hierold and
• Miroslav Haluska

Beilstein J. Nanotechnol. 2014, 5, 2202–2215, doi:10.3762/bjnano.5.229

• of the Schottky barrier should depend on the work function of the chosen metals. In fact this rule is commonly violated for bulk semiconductors due to the existence of metal induced gap states (MIGS) at the metal–semiconductor interface [11][12]. For bulk semiconductors, MIGS cause a dipole sheet at

• the metal–semiconductor interface and lead to the so-called Fermi level pinning effect, that is, when the Fermi level tends to be fixed at a constant position in the band gap of the semiconductor [13]. The net result is that the Schottky barrier height is less sensitive to the work function difference

• barrier height) was observed for the contacts fabricated with Pd, Ti or Al [15] (Figure 2b). As a result, for a given SWCNT, the height of the Schottky barrier can be adjusted by choosing the proper type of metal for the electrical contact. The work function of SWCNTs has been determined by the thermionic

Advances in NO₂ sensing with individual single-walled carbon nanotube transistors

• Kiran Chikkadi,
• Matthias Muoth,
• Cosmin Roman,
• Miroslav Haluska and
• Christofer Hierold

Beilstein J. Nanotechnol. 2014, 5, 2179–2191, doi:10.3762/bjnano.5.227

• work function difference between the metal and the nanotube, a Schottky barrier is commonly formed at both contacts. The channel conductivity is controlled by a gate electrode that is separated from the nanotube channel by a gate dielectric. In Schottky barrier field-effect transistors, the effect of

• , the different sensing mechanisms which may be present in a CNFET sensor are discussed in detail. Adsorption on the metal The work function of a metal is known to be sensitive to the adsorption of gaseous surface species. Methods such as Kelvin probe [31], scanning tunneling spectroscopy, X-ray and

• ultraviolet photoelectron spectroscopy [32] (XPS and UPS) have been used to understand the mechanism of this work function change. For polar molecules such as NO2, a dipole layer is expected to be formed at the surface of the metal, thereby modifying the metal work function [33][34]. In Schottky barrier

Effect of channel length on the electrical response of carbon nanotube field-effect transistors to deoxyribonucleic acid hybridization

• Hari Krishna Salila Vijayalal Mohan,
• Jianing An,
• Yani Zhang,
• Chee How Wong and
• Lianxi Zheng

Beilstein J. Nanotechnol. 2014, 5, 2081–2091, doi:10.3762/bjnano.5.217

• region is low, which indicates that the modulation in the CNT–metal work function also influences the response, in addition to the aforementioned mechanisms [18]. With increasing L, the number of additional charges present on the CNT surface in the form of ds-DNA hybrids increases, thereby ΔVth increases

• contribution of each mechanism for different L, thereby resulting in the observed trend with L. These mechanisms include the effect of electron transfer, CNT contact work function modulation, DNA–DNA duplex affinity on the SWCNT, hopping conduction, etc. on the response [27][28][33]. Therefore, it is necessary

• consequently, K ≠ φ. For short channel lengths, after hybridization, ΔRc also contributed significantly to ΔRon, and the CNT–metal work function is altered, which affects the mobility. Phonon scattering is prominent for all VG and increases with L [38]. The degrading effect of phonon scattering on the mobility

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

• microscopy (MEM) regime. This MEM–LEEM transition marks the onset for the total reflection of incident electrons as the electron energy is lowered. The threshold energy predominantly depends on the surface work function and on the angle of incidence of the electrons. Therefore, imaging at or near the MEM

• transition allows to map the local work function as well as the variations in the surface topography. The effect of the work function is clear in the inset of Figure 2, in which the adsorption of oxygen on W(110) results in a work function more than 1.2 eV higher than that of the clean surface, with a

• corresponding shift in the MEM–LEEM transition. Fe adsorption, instead, induces a less pronounced shift towards a lower work function. The diffraction contrast is also exploited in the dark field mode, obtained by imaging with higher order LEED beams. The diffraction order is selected by placing the contrast

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

• reaction proceed at room temperature. The total Gibbs free energy change is given by ΔG + W for p-doping and ΔG − W for n-doping, where ΔG is the free energy for the molecular reaction and W is the work function of graphene. The work function of graphene is expected to be similar to that of graphite, about

• graphene was studied by synchrotron-based high resolution photoemission spectroscopy (PES) [35]. The increase of the graphene work function due to the deposition of F4-TCNQ (Figure 5) suggests that there is an electron transfer from graphene to the molecule. In agreement with PES measurements DFT

Highly NO₂ sensitive caesium doped graphene oxide conductometric sensors

• Carlo Piloto,
• Marco Notarianni,
• Mahnaz Shafiei,
• Elena Taran,
• Dilini Galpaya,
• Cheng Yan and
• Nunzio Motta

Beilstein J. Nanotechnol. 2014, 5, 1073–1081, doi:10.3762/bjnano.5.120

• . We attribute this drop to the chemical reduction of the GO caused by the Cs2CO3 that tends to decrease the work function as observed by [55][59][60][61]. This result suggests that doped GO may have good performance as a gas sensing material. XPS survey analysis of the GO (Figure 3a, blue line

The study of surface wetting, nanobubbles and boundary slip with an applied voltage: A review

• Yunlu Pan,
• Bharat Bhushan and
• Xuezeng Zhao

Beilstein J. Nanotechnol. 2014, 5, 1042–1065, doi:10.3762/bjnano.5.117

• , The electrowetting coefficient k describes the sensitivity of the system to the applied voltage, and a larger value of k means that the CA will change more with same applied voltage. In this work, the interface of silicon and PS film will be charged due to the different work function. The charge layer

Volcano plots in hydrogen electrocatalysis – uses and abuses

• Paola Quaino,
• Fernanda Juarez,
• Elizabeth Santos and
• Wolfgang Schmickler

Beilstein J. Nanotechnol. 2014, 5, 846–854, doi:10.3762/bjnano.5.96

• proposed with a host of other metal characteristics: work function, latent heat of melting, lattice constants, etc. A fairly complete list has been given by Petrii and Tsirlina [11] and makes for an amusing read. They are not based on any sound principle like Sabatier’s, and it is not surprising that none

CoPc and CoPcF₁₆ on gold: Site-specific charge-transfer processes

• Fotini Petraki,
• Heiko Peisert,
• Johannes Uihlein,
• Umut Aygül and
• Thomas Chassé

Beilstein J. Nanotechnol. 2014, 5, 524–531, doi:10.3762/bjnano.5.61

• of transferred charges may sufficiently explain “macroscopic” electronic interface properties such as the size of dipoles. The formation of interface dipoles can be monitored by work function (Φ) measurements, where a change of Φ at the interface indicates the formation of an interface dipole. Figure

•  6 displays the development of the work function determined by using UPS as a function of the CoPcF16 thickness on gold. The corresponding values for the CoPc–Au interface studied previously [6] were added for comparison. A strong decrease of the work function occurs for the very first steps of the

• deposition on both interfaces, relating to coverage in the monolayer range. Such potential drops at the interface can be attributed to a modification of the work function of gold upon adsorption of molecules due to the push back of the electron cloud of the metallic substrate. The extent of the changes of

Effect of contaminations and surface preparation on the work function of single layer MoS₂

• Oliver Ochedowski,
• Kolyo Marinov,
• Nils Scheuschner,
• Artur Poloczek,
• Benedict Kleine Bussmann,
• Janina Maultzsch and
• Marika Schleberger

Beilstein J. Nanotechnol. 2014, 5, 291–297, doi:10.3762/bjnano.5.32

• caused by the processing on the surface potential of MoS2. It is shown that the charge transfer from the substrate is able to change the work function of MoS2 by about 40 meV. Our findings suggest two things. First, the necessity to properly clean devices after processing as contaminations have a great

• impact on the surface potential. Second, that by choosing appropriate materials the work function can be modified to reduce contact resistance. Keywords: KPFM; MoS2; NC-AFM; surface potential; work function; Introduction Due to their unique properties which can differ a lot compared to bulk materials

• that the performance of these devices can greatly vary due to the choice of the material of the contacts, the cleanliness of the SLM surface and a top gated structure with a high κ dielectric [22][23][24][25][26][27]. By choosing appropriate materials in 2D-devices the work function can be tuned to

Change of the work function of platinum electrodes induced by halide adsorption

• Florian Gossenberger,
• Tanglaw Roman,
• Katrin Forster-Tonigold and
• Axel Groß

Beilstein J. Nanotechnol. 2014, 5, 152–161, doi:10.3762/bjnano.5.15

• platinum(111) surface have been studied by using density functional theory (DFT), because halides are often present at electrochemical electrode/electrolyte interfaces. We focused in particular on the halogen-induced work function change as a function of the coverage of fluorine, chlorine, bromine and

• iodine. For electronegative adsorbates, an adsorption-induced increase of the work function is usually expected, yet we find a decrease of the work function for Cl, Br and I, which is most prominent at a coverage of approximately 0.25 ML. This coverage-dependent behavior can be explained by assuming a

• combination of charge transfer and polarization effects on the adsorbate layer. The results are contrasted to the adsorption of fluorine on calcium, a system in which a decrease in the work function is also observed despite a large charge transfer to the halogen adatom. Keywords: density functional theory

Noise performance of frequency modulation Kelvin force microscopy

• Heinrich Diesinger,
• Dominique Deresmes and
• Thierry Mélin

Beilstein J. Nanotechnol. 2014, 5, 1–18, doi:10.3762/bjnano.5.1

• cutoff frequency of the distance controller, but below the cutoff frequency of the PLL. The contact potential difference (CPD) between tip and sample is indicated by a voltage applied to the sample. It may be due to a work function difference between the sample and the tip or due to a sample to which a

Ellipsometry and XPS comparative studies of thermal and plasma enhanced atomic layer deposited Al₂O₃-films

• Jörg Haeberle,
• Karsten Henkel,
• Hassan Gargouri,
• Franziska Naumann,
• Bernd Gruska,
• Michael Arens,
• Massimo Tallarida and
• Dieter Schmeißer

Beilstein J. Nanotechnol. 2013, 4, 732–742, doi:10.3762/bjnano.4.83

• been investigated for several applications like surface passivation or encapsulation in organic and inorganic photovoltaic devices [1][2], interfacial buffering for high-k dielectrics [3][4], organic memories [5], and nano-laminates [6] as well as work function modification [7], gas diffusion barrier