107 research outputs found
Interference effects in phtalocyanine controlled by H-H tautomerization: a potential two-terminal unimolecular electronic switch
We investigate the electrical transport properties of two hydrogen tautomer
configurations of phthalocyanine (H2Pc) connected to cumulene and gold leads.
Hydrogen tautomerization affects the electronic state of H2Pc by switching the
character of molecular orbitals with the same symmetry close to the Fermi
level. The near degeneracy between the HOMO and HOMO-1 leads to pronounced
interference effects, causing a large change in current for the two tautomer
configuratons, especially in the low-bias regime. Two types of planar junctions
are considered: cumulene-H2Pc-cumulene and gold-H2Pc-gold. Both demonstrate
prominent difference in molecular conductance between ON and OFF states. In
addition, junctions with gold leads show pronounced negative differential
resistance (NDR) at high bias voltage, as well as weak NDR at intermediate
bias.Comment: 10 pages, 7 figures, accepted for publication in Physical Review
Cumulene Molecular Wire Conductance from First Principles
We present first principles calculations of current-voltage characteristics
(IVC) and conductance of Au(111):S2-cumulene-S2:Au(111) molecular wire
junctions with realistic contacts. The transport properties are calculated
using full self-consistent ab initio NEGF-DFT methods under external bias. The
conductance of the cumulene wires shows oscillatory behavior depending on the
number of carbon atoms (double bonds). Among all conjugated oligomers, we find
that cumulene wires with odd number of carbon atoms yield the highest
conductance with metallic-like ballistic transport behavior. The reason is the
high density of states in broad LUMO levels spanning the Fermi level of the
electrodes. The transmission spectrum and the conductance depend only weakly on
applied bias, and the IVC is nearly linear over a bias region from +1 to -1 V.
Cumulene wires are therefore potential candidates for metallic connections in
nanoelectronic applications.Comment: Accepted in Phys. Rev. B; 5 pages and 6 figure
Mechano-switching devices from carbon wire-carbon nanotube junctions
Well-known conductive molecular wires, like cumulene or polyyne, provide a
model for interconnecting molecular electronics circuit. In the recent
experiment, the appearance of carbon wire bridging two-dimensional electrodes -
graphene sheets - was observed [PRL 102, 205501 (2009)], thus demonstrating a
mechanical way of producing the cumulene. In this work, we study the structure
and conductance properties of the carbon wire suspended between carbon
nanotubes (CNTs) of different chiralities (zigzag and armchair), and
corresponding conductance variation upon stretching. We find the geometrical
structure of the carbon wire bridging CNTs similar to the experimentally
observed structures in the carbon wire obtained between graphene electrodes. We
show a capability to modulate the conductance by changing bridging sites
between the carbon wire and CNTs without breaking the wire. Observed current
modulation via cumulene wire stretching/elongation together with CNT junction
stability makes it a promising candidate for mechano-switching device for
molecular nanoelectronics.Comment: 8 pages, 8 figure
Topological Line Defects around Graphene Nanopores for DNA Sequencing
Topological line defects in graphene represent an ideal way to produce highly
controlled structures with reduced dimensionality that can be used in
electronic devices. In this work we propose using extended line defects in
graphene to improve nucleobase selectivity in nanopore-based DNA sequencing
devices. We use a combination of QM/MM and non-equilibrium Green's functions
methods to investigate the conductance modulation, fully accounting for solvent
effects. By sampling over a large number of different orientations generated
from molecular dynamics simulations, we theoretically demonstrate that
distinguishing between the four nucleobases using line defects in a
graphene-based electronic device appears possible. The changes in conductance
are associated with transport across specific molecular states near the Fermi
level and their coupling to the pore. Through the application of a specifically
tuned gate voltage, such a device would be able to discriminate the four types
of nucleobases more reliably than that of graphene sensors without topological
line defects.Comment: 6 figures and 6 page
Search for alternative magnetic tunnel junctions based on all-Heusler stacks
By imposing the constraints of structural compatibility, stability and a
large tunneling magneto-resistance, we have identified the
FeAl/BiF/FeAl stack as a possible alternative to the
well-established FeCoB/MgO/FeCoB in the search for a novel materials platform
for high-performance magnetic tunnel junctions. Various geometries of the
FeAl/BiF/FeAl structure have been analyzed, demonstrating that a
barrier of less than 2~nm yields a tunneling magneto-resistance in excess of
25,000~\% at low bias, without the need for the electrodes to be half-metallic.
Importantly, the presence of a significant spin gap in FeAl for states with
symmetry along the stack direction makes the TMR very resilient to
high voltages
Transverse Electronic Transport through DNA Nucleotides with Functionalized Graphene Electrodes
Graphene nanogaps and nanopores show potential for the purpose of electrical
DNA sequencing, in particular because single-base resolution appears to be
readily achievable. Here, we evaluated from first principles the advantages of
a nanogap setup with functionalized graphene edges. To this end, we employed
density functional theory and the non-equilibrium Green's function method to
investigate the transverse conductance properties of the four nucleotides
occurring in DNA when located between the opposing functionalized graphene
electrodes. In particular, we determined the electrical tunneling current
variation as a function of the applied bias and the associated differential
conductance at a voltage which appears suitable to distinguish between the four
nucleotides. Intriguingly, we observe for one of the nucleotides a negative
differential resistance effect.Comment: 19 pages, 7 figure
DNA nucleotide-specific modulation of \mu A transverse edge currents through a metallic graphene nanoribbon with a nanopore
We propose two-terminal devices for DNA sequencing which consist of a
metallic graphene nanoribbon with zigzag edges (ZGNR) and a nanopore in its
interior through which the DNA molecule is translocated. Using the
nonequilibrium Green functions combined with density functional theory, we
demonstrate that each of the four DNA nucleotides inserted into the nanopore,
whose edge carbon atoms are passivated by either hydrogen or nitrogen, will
lead to a unique change in the device conductance. Unlike other recent
biosensors based on transverse electronic transport through DNA nucleotides,
which utilize small (of the order of pA) tunneling current across a nanogap or
a nanopore yielding a poor signal-to-noise ratio, our device concept relies on
the fact that in ZGNRs local current density is peaked around the edges so that
drilling a nanopore away from the edges will not diminish the conductance.
Inserting a DNA nucleotide into the nanopore affects the charge density in the
surrounding area, thereby modulating edge conduction currents whose magnitude
is of the order of \mu A at bias voltage ~ 0.1 V. The proposed biosensor is not
limited to ZGNRs and it could be realized with other nanowires supporting
transverse edge currents, such as chiral GNRs or wires made of two-dimensional
topological insulators.Comment: 6 pages, 6 figures, PDFLaTe
ΠΠ΅Ρ Π°Π½ΠΈΠ·ΠΌΡ ΡΠΎΡΠΌΠΎΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡ ΠΊΠ»ΠΈΠ½ΠΎΠ²ΠΈΠ΄Π½ΡΡ Π΄Π²ΠΎΠΉΠ½ΠΈΠΊΠΎΠ² Π² Π»ΠΎΠΊΠ°Π»ΡΠ½ΠΎ-Π΄Π΅ΡΠΎΡΠΌΠΈΡΡΠ΅ΠΌΡΡ ΠΈΠΎΠ½Π½ΠΎΠΈΠΌΠΏΠ»Π°Π½ΡΠΈΡΠΎΠ²Π°Π½Π½ΡΡ ΠΌΠΎΠ½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»Π°Ρ Π²ΠΈΡΠΌΡΡΠ°
ΠΠ·ΡΡΠ΅Π½ΠΎ Π²Π»ΠΈΡΠ½ΠΈΠ΅ ΠΈΠΌΠΏΠ»Π°Π½ΡΠ°ΡΠΈΠΈ ΠΈΠΎΠ½ΠΎΠ² Π±ΠΎΡΠ°, Π°Π·ΠΎΡΠ°, ΡΠ³Π»Π΅ΡΠΎΠ΄Π°, Π°ΡΠ³ΠΎΠ½Π°, ΡΠΈΡΠΊΠΎΠ½ΠΈΡ ΠΈ ΡΠ°Π½ΡΠ°Π»Π° ΡΠ½Π΅ΡΠ³ΠΈΠ΅ΠΉ 25 ΠΊΡΠ, Π΄ΠΎΠ·ΠΎΠΉ 10 17 ΠΈΠΎΠ½/ΡΠΌ 2 Π½Π° Π·Π°ΠΊΠΎΠ½ΠΎΠΌΠ΅ΡΠ½ΠΎΡΡΠΈ ΠΈΡΠΊΡΠΈΠ²Π»Π΅Π½ΠΈΡ, Π²Π΅ΡΠ²Π»Π΅Π½ΠΈΡ ΠΈ
Π·Π°ΡΠΎΠΆΠ΄Π΅Π½ΠΈΡ Π²Π΄Π°Π»ΠΈ ΠΎΡ ΠΎΡΠΏΠ΅ΡΠ°ΡΠΊΠ° ΠΈΠ½Π΄Π΅Π½ΡΠΎΡΠ° ΠΊΠ»ΠΈΠ½ΠΎΠ²ΠΈΠ΄Π½ΡΡ
Π΄Π²ΠΎΠΉΠ½ΠΈΠΊΠΎΠ² Π² ΠΌΠΎΠ½ΠΎΠΊΡΠΈΡΡΠ°Π»Π»Π°Ρ
Π²ΠΈΡΠΌΡΡΠ°. Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½Ρ ΠΌΠ΅Ρ
Π°Π½ΠΈΠ·ΠΌΡ ΡΠΎΡΠΌΠΎΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡ ΠΊΠ»ΠΈΠ½ΠΎΠ²ΠΈΠ΄Π½ΡΡ
Π΄Π²ΠΎΠΉΠ½ΠΈΠΊΠΎΠ²ΡΡ
Π»Π°ΠΌΠ΅Π»Π΅ΠΉ.
ΠΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½ ΠΌΠ΅Ρ
Π°Π½ΠΈΠ·ΠΌ Π·Π°ΡΠΎΠΆΠ΄Π΅Π½ΠΈΡ Π΄ΠΈΡΠ»ΠΎΠΊΠ°ΡΠΈΠΎΠ½Π½ΡΡ
ΡΡΠΎΠΏΠΎΡΠΎΠ² ΠΈ ΠΈΡΡΠΎΡΠ½ΠΈΠΊΠΎΠ² Π΄Π²ΠΎΠΉΠ½ΠΈΠΊΡΡΡΠΈΡ
Π΄ΠΈΡΠ»ΠΎΠΊΠ°ΡΠΈΠΉ Π² Ρ
ΠΎΠ΄Π΅ ΠΈΠΎΠ½Π½ΠΎΠΉ ΠΈΠΌΠΏΠ»Π°Π½ΡΠ°ΡΠΈΠΈ ΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ². Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½ΠΎ Π²Π·Π°ΠΈΠΌΠΎΠ΄Π΅ΠΉΡΡΠ²ΠΈΠ΅
Π½Π°Π½ΠΎΠ΄Π²ΠΎΠΉΠ½ΠΈΠΊΠΎΠ², ΡΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π²ΡΠΈΡ
ΡΡ ΠΏΡΠΈ ΠΈΠΎΠ½Π½ΠΎΠΉ ΠΈΠΌΠΏΠ»Π°Π½ΡΠ°ΡΠΈΠΈ, Ρ Π΄Π²ΠΎΠΉΠ½ΠΈΠΊΠ°ΠΌΠΈ, ΠΎΠ±ΡΠ°Π·ΡΡΡΠΈΠΌΠΈΡΡ ΠΏΡΠΈ Π»ΠΎΠΊΠ°Π»ΡΠ½ΠΎΠΌ Π΄Π΅ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠΈ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠΈ.The influence of implantation of boron, nitrogen, carbon, argon, zirconium and tantalum
ions of energy of 25 keV, dose of 10 17 ion/cm 2 on the mechanism of distortion, branching and
origination far from indentation of wedge-shaped twins in monocrystals of bismuth have been
studied The mechanisms of lamella wedge-shaped twin deformation are considered. A mechanism is proposed for origination of dislocation stop and the sources of twinning dislocation in
the process of crystal ion implantation. The interaction of nano-twins formed at ion implantation with the twins formed at local deformation of the surface is considered
Single molecule detection with graphene and other two-dimensional materials: nanopores and beyond
Supramolecular & Biomaterials Chemistr
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