15 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
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
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
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
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
Molecular Electronics : Insight from Ab-Initio Transport Simulations
This thesis presents the theoretical studies of electronic transport in molecular electronic devices. Such devices have been proposed and investigated as a promising new approach that complements conventional silicon-based electronics. To design and fabricate future nanoelectronic devices, it is essential to understand the conduction mechanism at a molecular or atomic level. Our approach is based on the non-equilibrium Green's function method (NEGF) combined with density functional theory (DFT). We apply the method to study the electronic transport properties of two-probe systems consisting of molecules or atomic wires sandwiched between leads. A few molecular electronic devices are characterized; namely, conducting molecular wires, molecular switches and molecular recognition sensors. The considered applications are interconnection of different nanoelectronic units with cumulene molecular wires; adding switching functionality to the molecular connectors by applying stress to the CNT-cumulene-CNT junction or by introducing phthalocyanine unit; sensing of individual nucleotides, e.g., for DNA sequencing applications. The obtained results provide useful insights into the electron transport properties of molecules. Several interesting and significant features are analyzed and explained in particular such as, level pinning, negative differential resistance, interfering of conducting channels etc
Molecular Electronics : Insight from Ab-Initio Transport Simulations
This thesis presents the theoretical studies of electronic transport in molecular electronic devices. Such devices have been proposed and investigated as a promising new approach that complements conventional silicon-based electronics. To design and fabricate future nanoelectronic devices, it is essential to understand the conduction mechanism at a molecular or atomic level. Our approach is based on the non-equilibrium Green's function method (NEGF) combined with density functional theory (DFT). We apply the method to study the electronic transport properties of two-probe systems consisting of molecules or atomic wires sandwiched between leads. A few molecular electronic devices are characterized; namely, conducting molecular wires, molecular switches and molecular recognition sensors. The considered applications are interconnection of different nanoelectronic units with cumulene molecular wires; adding switching functionality to the molecular connectors by applying stress to the CNT-cumulene-CNT junction or by introducing phthalocyanine unit; sensing of individual nucleotides, e.g., for DNA sequencing applications. The obtained results provide useful insights into the electron transport properties of molecules. Several interesting and significant features are analyzed and explained in particular such as, level pinning, negative differential resistance, interfering of conducting channels etc
Spin injection and magnetoresistance in MoS2-based tunnel junctions using Fe3Si Heusler alloy electrodes
Recently magnetic tunnel junctions using two-dimensional MoS2 as nonmagnetic spacer have been fabricated, although their magnetoresistance has been reported to be quite low. This may be attributed to the use of permalloy electrodes, injecting current with a relatively small spin polarization. Here we evaluate the performance of MoS2-based tunnel junctions using Fe3Si Heusler alloy electrodes. Density functional theory and the non-equilibrium Green?s function method are used to investigate the spin injection efficiency (SIE) and the magnetoresistance (MR) ratio as a function of the MoS2 thickness. We find a maximum MR of ~300% with a SIE of about 80% for spacers comprising between 3 and 5 MoS2 monolayers. Most importantly, both the SIE and the MR remain robust at finite bias, namely MR?>?100% and SIE?>?50% at 0.7?V. Our proposed materials stack thus demonstrates the possibility of developing a new generation of performing magnetic tunnel junctions with layered two-dimensional compounds as spacer
Single-molecule DNA sequencing using two-dimensional Ti2C(OH)(2) MXene nanopores : A first-principles investigation
Nanopore-based devices have provided exciting opportunities to develop affordable label-free DNA sequencing platforms. Over a decade ago, graphene has been proposed as a two-dimensional (2D) nanopore membrane in order to achieve single-base resolution. However, it was experimentally revealed that clogging of the graphene nanopore can occur due to the hydrophobic nature of graphene, thus hindering the translocation of DNA. To overcome this problem, the exploration of alternative 2D materials has gained considerable interest over the last decade. Here we show that a Ti2C-based MXene nanopore functionalized by hydroxyl groups (-OH) exhibits transverse conductance properties that allow for the distinction between all four naturally occurring DNA bases. We have used a combination of density functional theory and non-equilibrium Green's function method to sample over multiple orientations of the nucleotides in the nanopore, as generated from molecular dynamics simulations. The conductance variation resulting from sweeping an applied gate voltage demonstrates that the Ti2C-based MXene nanopore possesses high potential to rapidly and reliably sequence DNA. Our findings open the door to further theoretical and experimental explorations of MXene nanopores as a promising 2D material for nanopore-based DNA sensing