Nonconservative current-driven dynamics: beyond the nanoscale

• Brian Cunningham,
• Tchavdar N. Todorov and
• Daniel Dundas

Beilstein J. Nanotechnol. 2015, 6, 2140–2147, doi:10.3762/bjnano.6.219

• can ruin the degeneracies) is small in these quasi-ballistic systems. Finally, electrons couple strongly to extended phonon modes with the wavevectors needed for momentum conservation under backscattering [14]. Simulations under current indeed show NC dynamics in long atomic wires on a grand scale [13

• spontaneous phonon emission and Joule heating [20]. By contrast with the Landauer method above, the dynamical simulations accommodate departures from steady-state conditions and allow the current to respond to changes in the vibrational amplitudes. To compare the two methods we will further perform a short

• -time Fourier transform on the ion trajectories (t) from the dynamical simulations and examine the evolution of the energy distribution across the phonon band. The Fourier transform uses a Blackman window, effectively suppressing data outside a particular time interval, while ensuring the data remains

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

• coefficients reveal on molecular junctions? Specifically, can they expose the underlying electron–phonon interactions and the characteristics of the vibrational modes participating in the process? Focusing on the challenge of efficient thermoelectric systems, how should we tune molecular parameters to improve

• thermoelectric transport have been developed, e.g., in [50][51][52][53], accounting for many-body effects in a phenomenological manner. Only few studies had considered this problem with explicit electron–phonon interactions, based on the Anderson–Holstein model [54] or Fermi Golden rule expressions [14]. In

• “vibrational instability”. This over-heating effect occurs when (electron-induced) vibrational excitation rates exceed relaxation rates. To cure this physical problem, we allow the particular vibrational mode of frequency ω0 to relax its excess energy to a secondary phonon bath of temperature Tph. This can be

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

• for next generation transistor devices. The radial heterostructure offers the advantage of control of the band gap and charge carrier mobility by tuning their size [5] and selecting suitable impurity doping scheme [3][6]. In addition, they exhibit significantly suppressed phonon thermal conductivity

• motion makes the real temperature, T, different from the classical temperature, TMD, as measured from the simulations. Wang et al. [30] proposed an approximate relation for scaling between the classical and real temperatures based on the phonon frequencies in the solid. Accordingly, this procedure has

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

• or phonon transport in the Landauer transport picture. We suggest a simple and computationally “cheap” post-processing scheme to interpolate transmission functions over k-points to get smooth well-converged average transmission functions. This is relevant for data obtained using typical “expensive

• 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

• , i.e., EDX), all uniquely characterize the studied materials. Chemical compositions, electron fine structures, even the phonon vibrations [31] produced by electron–matter interactions can be acquired, which is quite exciting for a detailed study. Therefore, electron beams are more than an illumination

• electronic scattering and phonon scattering are very likely to be disturbed at the boundary. The fundamental studies on the atomic structure of graphene have a significant impact on the large-scale applications of graphene. Graphene synthesized through chemical vapor deposition (CVD) often exhibits a

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

• hand, the manganite oxide perovskites are strongly correlated electron systems that exhibit a strong electron–phonon interaction. This leads to the formation of small polarons [21]. The polaron-like character of the quasi-particles in perovskite oxides provides at least two exciting issues related to

• electron–phonon interaction across the interface. Under a large electric field, the polaron may even dissociate as indicated by polaron simulations of polymer junctions [33]. On the other hand, the concept of the electrochemical equilibrium at the interface naturally takes into account the spatial

• renormalization of the bandwidth by the electron–phonon interaction further reduces the bandwidth to a few meV [35]. This small bandwidth has strong impact on the matching of electronic states at the interface. Even after establishment of electrochemical equilibrium (which may be hindered by small charge transfer

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

• 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

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

• greater than unity is challenging. The most common material used in thermoelectric applications is bismuth and its alloys, which are toxic, expensive and of limited availability. To improve ZT in new materials, one promising route has been to take advantage of the reduced phonon thermal conductance (κpl

• graphene [20]. This means that 2D graphene and its multilayer counterparts are useful for thermal management applications [21]. The high thermal conductivity of the graphene is mainly due to the high phonon contribution to heat transport. Therefore, for thermoelectricity applications, one needs to engineer

Electronic interaction in composites of a conjugated polymer and carbon nanotubes: first-principles calculation and photophysical approaches

• Florian Massuyeau,
• Jany Wéry,
• Jean-Luc Duvail,
• Serge Lefrant,
• Abu Yaya,
• Chris Ewels and
• Eric Faulques

Beilstein J. Nanotechnol. 2015, 6, 1138–1144, doi:10.3762/bjnano.6.115

• without hopping to the SWNTs. This implies that they survive longer with a slower time constant τ2. Therefore, we suggest associating the fast decay component to the PL of PPV, which is quenched by a non-radiative transfer of energy to the polymer network via phonon emission. This process results from the

• approach assumes that the radiative and non-radiative lifetimes τr, τnr can be expressed as a function of the PL quantum yield Q, , . τnr accounts for phonon emission, intersystem crossing to triplet states, trapping at chemical defects and exciton migration/dissociation. For standard PPV (x = 0%) we find

Effects of swift heavy ion irradiation on structural, optical and photocatalytic properties of ZnO–CuO nanocomposites prepared by carbothermal evaporation method

• Sini Kuriakose,
• D. K. Avasthi and
• Satyabrata Mohapatra

Beilstein J. Nanotechnol. 2015, 6, 928–937, doi:10.3762/bjnano.6.96

• that wurtzite ZnO has an irreducible representation A1 + 2B1 + E1 + 2E2. Since the modes A1 and E1 are polar they exhibit two frequencies corresponding to the transverse optical (TO) and the longitudinal optical (LO) phonon modes. The non-polar E2 mode has two frequencies E2(high) originating from the

Combination of surface- and interference-enhanced Raman scattering by CuS nanocrystals on nanopatterned Au structures

• Alexander G. Milekhin,
• Nikolay A. Yeryukov,
• Larisa L. Sveshnikova,
• Tatyana A. Duda,
• Ekaterina E. Rodyakina,
• Victor A. Gridchin,
• Evgeniya S. Sheremet and
• Dietrich R. T. Zahn

Beilstein J. Nanotechnol. 2015, 6, 749–754, doi:10.3762/bjnano.6.77

• substrate reveal only features corresponding to crystalline Si. However, a new relatively strong peak occurs in the Raman spectrum of CuS NCs on Au nanocluster arrays at 474 cm−1. This feature is related to the optical phonon mode in CuS NCs and manifests the SERS effect. For CuS NCs deposited on a SiO2

• layer this phonon mode is also observed due to the IERS effect. Its intensity changes periodically with increasing SiO2 layer thickness for different laser excitation lines and is enhanced by a factor of about 30. CuS NCs formed on Au nanocluster arrays fabricated on IERS substrates combine the

• optical (SO) and LO phonon modes in a CdSe core and the transverse optical (TO) phonon mode in a ZnS shell of core–shell CdSe/ZnS NCs attached to the surface of a Au nanowire. The spectrum of optical and interface phonons was obtained from the analysis of SERS spectra of pure CdSe NCs, core–shell CdSe/CdS

Graphene quantum interference photodetector

• Mahbub Alam and
• Paul L. Voss

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

• generation mechanisms in graphene photodetectors include the photovoltaic effect, photothermoelectric effect, bolometric effect and phonon drag effect [3]. In the photovoltaic effect, the built-in electric field generated in the junction of p- and n-type graphene is utilized for separation of photogenerated

• volume of V, c is the speed of light, εr is the relative permittivity, μr is the relative permeability and ε is the absolute permittivity. The photon scattering functions, and , are calculated assuming monochromatic light and two energy levels for excitation. Both the acoustic phonon and optical phonon

• time of the electron through the device. Since we are assuming that the device length is less than the mean free path of the electron, we are neglecting all phonon interactions here. The photocurrent flows through the leads because one of the leads (drain) cannot supply the electrons to fill up the

Morphological and structural characterization of single-crystal ZnO nanorod arrays on flexible and non-flexible substrates

• Omar F. Farhat,
• Mohd M. Halim,
• Mat J. Abdullah,
• Mohammed K. M. Ali and
• Nageh K. Allam

Beilstein J. Nanotechnol. 2015, 6, 720–725, doi:10.3762/bjnano.6.73

• strain. Wurtzite ZnO belongs to the C6v4 (P63mc) space group, having two formula units in the primitive cell with all atoms occupying C3v. Also, wurtzite ZnO has eight sets of optical phonon modes at the Brillion zone center (q = 0). These include the Raman active Г = 2 × (A1 + B1 + E1 + E2) phonon modes

• active, while the E and TO are forbidden. Due to the long-range electrostatic forces, the phonons with A1 and E symmetry are polar and hence exhibit different frequencies for the TO and LO phonons. Every mode corresponds to a band in the Raman spectrum, with the A1 phonon vibration polarized parallel to

• the c-axis and the E phonon polarized perpendicular to the c-axis. The intensities of these bands depend on the scattering cross section of these modes [20]. Figure 4a–c shows the obtained Raman spectra of the single-crystal ZnO nanorod arrays grown on Si, PET and glass substrates, respectively. All

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

• 0.3–1.3 eV) and log(fB0) (in the range from 1010 to 1024 Hz). The latter apparent prefactor values exceed typical phonon frequencies (1013 Hz) by more than ten decades. This "compensation law" observed for solid-state phenomena with a large activation energy in many areas (physics, mechanics

Structural, optical, opto-thermal and thermal properties of ZnS–PVA nanofluids synthesized through a radiolytic approach

• Alireza Kharazmi,
• Nastaran Faraji,
• Roslina Mat Hussin,
• Elias Saion,
• W. Mahmood Mat Yunus and
• Kasra Behzad

Beilstein J. Nanotechnol. 2015, 6, 529–536, doi:10.3762/bjnano.6.55

• at constant pressure, υ is the phonon velocity and l is the phonon mean free path. Therefore, changes in the phonon mean free path proportionally change the thermal conductivity. Figure 8 shows the typical PA signal as a function of frequency for (a) distilled water and ethylene glycol and (b) ZnS

• and ZnS–PVA nanofluids are given in Table 2. The value of thermal effusivity decreased upon the increase of the radiation dose, as illustrated in Figure 7b. The decrement of thermal effusivity can be also explained by a decreasing chain length of PVA and, consequently, a shorter phonon mean free path

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

• -large) which can display either semiconducting or metallic properties due to the conjugation and electron–phonon coupling effects of their delocalized π electrons. In addition to many examples in organic chemistry, the occurrence of sp-hybridized carbon has been observed in many carbon-based materials

• powerful tool for the characterization of carbon materials and nanostructures due to its sensitivity to the vibration of C–C bonds. For instance, strong electron–phonon coupling and resonance effects allow for the measurement of single carbon nanostructures and together with confinement effects, provides

• atom per unit cell, providing one electron from each 2pz orbital, thus forming a half-filled band of a 1D metal. As a consequence of Peierls distortion (driven by electron–phonon coupling and dimerization of the structure), an energy gap opens and the metallic character of cumulenes changes into the

Carrier multiplication in silicon nanocrystals: ab initio results

• Ivan Marri,
• Marco Govoni and
• Stefano Ossicini

Beilstein J. Nanotechnol. 2015, 6, 343–352, doi:10.3762/bjnano.6.33

• momentum conservation and by fast phonon relaxation processes, CM is often inefficient in bulk semiconductors. On the nanoscale, CM is favored (a) by quantum confinement that enhances the carrier–carrier Coulomb interaction [7], (b) by the lack of restrictions imposed by the conservation of momentum [8

• ] and, in some cases, (c) by the so-called “phonon bottleneck” effect [9][10] that reduces the probability of exciton relaxation by phonon emission. These conditions make the formation of multiple e–h pairs after absorption of high energy photons more likely to occur in low-dimensional nanostructures

• . Consequently, at the nanoscale CM can be as fast as (or faster than) phonon scattering processes and Auger cooling mechanisms [11]. Therefore, CM represents an effective way to minimize energy loss factors and constitutes a possible route for increasing solar cell photocurrent, and hence, to increase solar

Nanoporous Ge thin film production combining Ge sputtering and dopant implantation

• Jacques Perrin Toinin,
• Alain Portavoce,
• Khalid Hoummada,
• Michaël Texier,
• Maxime Bertoglio,
• Sandrine Bernardini,
• Marco Abbarchi and
• Lee Chow

Beilstein J. Nanotechnol. 2015, 6, 336–342, doi:10.3762/bjnano.6.32

• wavelengths (red–green). Si and Ge are indirect gap materials, requiring phonon scattering for optical absorption/emission to take place. However, Q-size effects present in porous semiconductors can promote optical transitions without the need of phonons by breaking the momentum conservation rules and/or by

• making the material quasi-direct through the process of Brillouin zone folding [3]. For example, non-phonon processes were shown to dominate in the case of porous Si under strong confinement potential [4][5][6]. In addition, Q-effects in porous semiconductors can be interesting for photovoltaic

• observed in Ge for the case of strained [11] and doped [12] Ge layers. Furthermore, in addition to its small indirect band gap (≈0.66 eV), Ge exhibits a larger direct band gap (≈0.80 eV) that could promote non-phonon optical transitions if n-type doping of about 1020 cm−3 could be achieved in Ge. Since Ge

X-ray photoelectron spectroscopy of graphitic carbon nanomaterials doped with heteroatoms

• Toma Susi,
• Thomas Pichler and
• Paola Ayala

Beilstein J. Nanotechnol. 2015, 6, 177–192, doi:10.3762/bjnano.6.17

• -monochromatic X-ray sources are used, as is often the case. In addition, a finite sample temperature causes thermal broadening due to phonon vibrations, but this is usually negligible compared to the other factors (since the thermal energy is only approx. 25 meV at 300 K). Finally, each peak has a natural

Bright photoluminescence from ordered arrays of SiGe nanowires grown on Si(111)

• D. J. Lockwood,
• N. L. Rowell,
• A. Benkouider,
• A. Ronda,
• L. Favre and
• I. Berbezier

Beilstein J. Nanotechnol. 2014, 5, 2498–2504, doi:10.3762/bjnano.5.259

• to 25 K) with excitation at 405 and 458 nm. There are four major features in the energy range of interest (980–1120 meV) at energies of 1040.7, 1082.8, 1092.5, and 1098.5 meV, which are assigned to the NW-transverse optic (TO) Si–Si mode, NW-transverse acoustic (TA), Si–substrate–TO and NW-no-phonon

• (NP) lines, respectively. From these results the NW TA and TO phonon energies are found to be 15.7 and 57.8 meV, respectively, which agree very well with the values expected for bulk Si1−xGex with x = 0.15, while the measured NW NP energy of 1099 meV would indicate a bulk-like Ge concentration of x

• were obtained from the other samples. Figure 4 shows that the NW spectral region of interest (from approximately 950 to 1050 meV) is dominated by the boron (≈1017 cm−3)-doped Si substrate phonon-replica spectrum at the lowest temperatures (6 and 10 K). On increasing the sample temperature up to 20 K

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

• plausible reasons for the observed behavior are discussed subsequently. Ideally, Δφ should be close to 0, however, in reality, φ could be influenced by contact resistance [35][36], optical/acoustic phonon scattering [33], and trapped charges [37] depending on L and VG, which leads to Δφ ≠ 0, and

• 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

• and reverse gate voltage sweeps, which is responsible for the hysteresis behavior [39]. These charge traps could participate in Coulombic scattering [40], and thereby influence mobility. If Δφc, Δφs and Δφh represent the influence of contact resistance, phonon scattering, and charge traps respectively

Synthesis of Pt nanoparticles and their burrowing into Si due to synergistic effects of ion beam energy losses

• Pravin Kumar,
• Udai Bhan Singh,
• Kedar Mal,
• Sunil Ojha,
• Indra Sulania,
• Dinakar Kanjilal,
• Dinesh Singh and
• Vidya Nand Singh

Beilstein J. Nanotechnol. 2014, 5, 1864–1872, doi:10.3762/bjnano.5.197

• local melting (thermal spike) [29] occurs along the ion trajectory due to the energy deposition into the electronic subsystem (within 10−16 s). The local thermalization of the electronic sub-system takes place within 10−14 s. The deposited energy is transferred to the atomic subsystem by electron–phonon

• ]. The melting point of silicon is ≈1400 K and transient molten zones (giving rise to viscous flow of Pt atoms) in silicon are possible by ion irradiation. Since the temperature spike quenches via electron–phonon coupling within 10−11 s, a very small contribution by the viscous flow in Pt diffusion is

Experimental techniques for the characterization of carbon nanoparticles – a brief overview

• Wojciech Kempiński,
• Szymon Łoś,
• Mateusz Kempiński and
• Damian Markowski

Beilstein J. Nanotechnol. 2014, 5, 1760–1766, doi:10.3762/bjnano.5.186

• on the phonon scattering phenomena and much valuable information can be obtained from the relative intensities of the spectral components. It was shown by Tuinstra and Koenig in 1970 [22][23] and recently by Ferrari et al. [14][24] and Cançado et al. [25] that the D to G peak intensity ratio in the

A study on the consequence of swift heavy ion irradiation of Zn–silica nanocomposite thin films: electronic sputtering

• Compesh Pannu,
• Udai B. Singh,
• Dinesh. C. Agarwal,
• Saif A. Khan,
• Sunil Ojha,
• Ramesh Chandra,
• Hiro Amekura,
• Debdulal Kabiraj and
• Devesh. K. Avasthi

Beilstein J. Nanotechnol. 2014, 5, 1691–1698, doi:10.3762/bjnano.5.179

• target due to electronic excitations and ionizations. First, this energy is shared between the electrons of the target leading to the thermalization of the energy at a time scale of 10−15 to 10−14 s. Then the deposited energy is transferred from the electrons to the lattice through electron–phonon

• coupling. This coupling causes an increase in the lattice temperature of the target at a time scale of 10−13 to 10−12 s. The transient local temperature of the thermal spike depends on the volume, in which the energy is deposited and on the strength of the electron–phonon coupling. The electron phonon

• , the incoming ion transfers its energy to electrons of the target. Due to the high thermal conductivity, the deposited energy is quickly transferred to other electrons and the heat transferred to the metal lattice through electron–phonon coupling is not sufficient to cause the melting of the metal

Review of nanostructured devices for thermoelectric applications

• Giovanni Pennelli

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

• measured in nanostructured bismuth antimony telluride alloys, because phonon scattering at nanocrystal boundaries gives a reduced thermal conductivity [26]. Hovewer, TEGs based on bismuth telluride compounds have a small operating temperature range, because the Z factor rapidly decreases well below 2 × 10

• distribution of filling ions as well as their “rattling” effect increases the phonon scattering on a large spectrum, so that the thermal conductivity is strongly reduced and Z is quite high. Several filling elements, such as La [32], Co [33], Ta [34], and others, have been experimented. Recently, filled [35

• ). The first term ke takes into account the heat brought by the charge carriers (electrons or holes) that diffuse from the hot part TH to the cold part TC. The second term kph takes into account the heat conduction through the material crystalline lattice, due to phonon propagation. ke (e for electrons