The Experts below are selected from a list of 141 Experts worldwide ranked by ideXlab platform
Jean-pierre Leburton - One of the best experts on this subject based on the ideXlab platform.
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Single-Site Resolution Detection of Methylation in DNA with Graphene Nanopores
Biophysical Journal, 2016Co-Authors: Aditya Sarathy, Klaus Schulten, Hu Qiu, Jean-pierre LeburtonAbstract:Epigenetic modification of DNA where methyl groups are added at the 5-carbon position of cytosine is known as DNA methylation. It is associated with carcinogenesis, thus capable of serving as markers for detection of cancer. Nanopore analytics provides an easier and quicker route to detect methylated sites by avoiding complicated bisulfite treatment and polymerase chain reaction amplification. Graphene has a thickness of a single atom, thereby holding the potential to detect the methylation at single-site resolution. In this work, we use a self-consistent Poisson-Boltzmann formalism to simulate the translocation of methyl-CpG (MBD) proteins bound to a DNA molecule in a graphene nanopore, and detect the methylated sites along the DNA strand by computing both ionic current using molecular dynamics simulations and transverse sheet current via tight binding Hamiltonian based none-equilibrium Green's function approach.1 Evident dips are recorded in the ionic current trace through the nanopore for each methylation site, as expected, suggesting a single-site resolution. The graphene membrane with added quantum point contacts, by means of transverse sheet currents, can also detect the methylated site through local jumps in the variance of the measured transverse current. The proposed measurement strategy allows for real time, fast and high resolution DNA methylation detection.21. Girdhar, A., Sathe, C., Schulten, K., & Leburton, J. P. (2013). Graphene quantum point contact Transistor for DNA sensing. Proceedings of the National Academy of Sciences, 110(42), 16748-16753.2. Sarathy, A., Qiu, H., Schulten, K., & Leburton, J. P. Single-site detection of methylation in DNA with graphene nanopores. To be published.
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Tunable graphene quantum point contact Transistor for DNA detection and characterization
Nanotechnology, 2015Co-Authors: Anuj Girdhar, Chaitanya Sathe, Klaus Schulten, Jean-pierre LeburtonAbstract:A graphene membrane conductor containing a nanopore in a quantum point contact geometry is a promising candidate to sense, and potentially sequence, DNA molecules translocating through the nanopore. Within this geometry, the shape, size, and position of the nanopore as well as the edge configuration influences the membrane conductance caused by the electrostatic interaction between the DNA nucleotides and the nanopore edge. It is shown that the graphene conductance variations resulting from DNA translocation can be enhanced by choosing a particular geometry as well as by modulating the graphene Fermi energy, which demonstrates the ability to detect conformational transformations of a double-stranded DNA, as well as the passage of individual base pairs of a single-stranded DNA molecule through the nanopore.
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Graphene quantum point contact Transistor for DNA sensing
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Anuj Girdhar, Chaitanya Sathe, Klaus Schulten, Jean-pierre LeburtonAbstract:By using the nonequilibrium Green’s function technique, we show that the shape of the edge, the carrier concentration, and the position and size of a nanopore in graphene nanoribbons can strongly affect its electronic conductance as well as its sensitivity to external charges. This technique, combined with a self-consistent Poisson–Boltzmann formalism to account for ion charge screening in solution, is able to detect the rotational and positional conformation of a DNA strand inside the nanopore. In particular, we show that a graphene membrane with quantum point contact geometry exhibits greater electrical sensitivity than a uniform armchair geometry provided that the carrier concentration is tuned to enhance charge detection. We propose a membrane design that contains an electrical gate in a configuration similar to a field-effect Transistor for a graphene-based DNA sensing device.
Klaus Schulten - One of the best experts on this subject based on the ideXlab platform.
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Single-Site Resolution Detection of Methylation in DNA with Graphene Nanopores
Biophysical Journal, 2016Co-Authors: Aditya Sarathy, Klaus Schulten, Hu Qiu, Jean-pierre LeburtonAbstract:Epigenetic modification of DNA where methyl groups are added at the 5-carbon position of cytosine is known as DNA methylation. It is associated with carcinogenesis, thus capable of serving as markers for detection of cancer. Nanopore analytics provides an easier and quicker route to detect methylated sites by avoiding complicated bisulfite treatment and polymerase chain reaction amplification. Graphene has a thickness of a single atom, thereby holding the potential to detect the methylation at single-site resolution. In this work, we use a self-consistent Poisson-Boltzmann formalism to simulate the translocation of methyl-CpG (MBD) proteins bound to a DNA molecule in a graphene nanopore, and detect the methylated sites along the DNA strand by computing both ionic current using molecular dynamics simulations and transverse sheet current via tight binding Hamiltonian based none-equilibrium Green's function approach.1 Evident dips are recorded in the ionic current trace through the nanopore for each methylation site, as expected, suggesting a single-site resolution. The graphene membrane with added quantum point contacts, by means of transverse sheet currents, can also detect the methylated site through local jumps in the variance of the measured transverse current. The proposed measurement strategy allows for real time, fast and high resolution DNA methylation detection.21. Girdhar, A., Sathe, C., Schulten, K., & Leburton, J. P. (2013). Graphene quantum point contact Transistor for DNA sensing. Proceedings of the National Academy of Sciences, 110(42), 16748-16753.2. Sarathy, A., Qiu, H., Schulten, K., & Leburton, J. P. Single-site detection of methylation in DNA with graphene nanopores. To be published.
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Tunable graphene quantum point contact Transistor for DNA detection and characterization
Nanotechnology, 2015Co-Authors: Anuj Girdhar, Chaitanya Sathe, Klaus Schulten, Jean-pierre LeburtonAbstract:A graphene membrane conductor containing a nanopore in a quantum point contact geometry is a promising candidate to sense, and potentially sequence, DNA molecules translocating through the nanopore. Within this geometry, the shape, size, and position of the nanopore as well as the edge configuration influences the membrane conductance caused by the electrostatic interaction between the DNA nucleotides and the nanopore edge. It is shown that the graphene conductance variations resulting from DNA translocation can be enhanced by choosing a particular geometry as well as by modulating the graphene Fermi energy, which demonstrates the ability to detect conformational transformations of a double-stranded DNA, as well as the passage of individual base pairs of a single-stranded DNA molecule through the nanopore.
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Graphene quantum point contact Transistor for DNA sensing
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Anuj Girdhar, Chaitanya Sathe, Klaus Schulten, Jean-pierre LeburtonAbstract:By using the nonequilibrium Green’s function technique, we show that the shape of the edge, the carrier concentration, and the position and size of a nanopore in graphene nanoribbons can strongly affect its electronic conductance as well as its sensitivity to external charges. This technique, combined with a self-consistent Poisson–Boltzmann formalism to account for ion charge screening in solution, is able to detect the rotational and positional conformation of a DNA strand inside the nanopore. In particular, we show that a graphene membrane with quantum point contact geometry exhibits greater electrical sensitivity than a uniform armchair geometry provided that the carrier concentration is tuned to enhance charge detection. We propose a membrane design that contains an electrical gate in a configuration similar to a field-effect Transistor for a graphene-based DNA sensing device.
Anuj Girdhar - One of the best experts on this subject based on the ideXlab platform.
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Tunable graphene quantum point contact Transistor for DNA detection and characterization
Nanotechnology, 2015Co-Authors: Anuj Girdhar, Chaitanya Sathe, Klaus Schulten, Jean-pierre LeburtonAbstract:A graphene membrane conductor containing a nanopore in a quantum point contact geometry is a promising candidate to sense, and potentially sequence, DNA molecules translocating through the nanopore. Within this geometry, the shape, size, and position of the nanopore as well as the edge configuration influences the membrane conductance caused by the electrostatic interaction between the DNA nucleotides and the nanopore edge. It is shown that the graphene conductance variations resulting from DNA translocation can be enhanced by choosing a particular geometry as well as by modulating the graphene Fermi energy, which demonstrates the ability to detect conformational transformations of a double-stranded DNA, as well as the passage of individual base pairs of a single-stranded DNA molecule through the nanopore.
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Graphene quantum point contact Transistor for DNA sensing
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Anuj Girdhar, Chaitanya Sathe, Klaus Schulten, Jean-pierre LeburtonAbstract:By using the nonequilibrium Green’s function technique, we show that the shape of the edge, the carrier concentration, and the position and size of a nanopore in graphene nanoribbons can strongly affect its electronic conductance as well as its sensitivity to external charges. This technique, combined with a self-consistent Poisson–Boltzmann formalism to account for ion charge screening in solution, is able to detect the rotational and positional conformation of a DNA strand inside the nanopore. In particular, we show that a graphene membrane with quantum point contact geometry exhibits greater electrical sensitivity than a uniform armchair geometry provided that the carrier concentration is tuned to enhance charge detection. We propose a membrane design that contains an electrical gate in a configuration similar to a field-effect Transistor for a graphene-based DNA sensing device.
Haroon Ahmed - One of the best experts on this subject based on the ideXlab platform.
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Inter-grain coupling effects on Coulomb oscillations in dual-gated nanocrystalline silicon Point-Contact Transistors
Thin Solid Films, 2005Co-Authors: M. A. H. Khalafalla, Zahid A. K. Durrani, Haroon Ahmed, Hiroshi Mizuta, Shunri OdaAbstract:Abstract Inter-grain electron-coupling effects are investigated at 4.2 K in dual-gated, Point-Contact, single-electron Transistors fabricated in nanocrystalline silicon. The nanocrystalline silicon film is ∼40 nm thick, with grains ∼10–30 nm in size. The Point-Contact Transistor channel is ∼30 nm×30 nm×40 nm in size, with two side-gates. Only a few grains exist within the channel and different grains contribute in varying degrees to the device conduction. By modifying the inter-grain coupling using selective oxidation of the grain boundaries, both electrostatic and wavefunction-coupling effects can be observed in the Coulomb oscillations vs. the two gate voltages.
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Nanosilicon for single-electron devices
Current Applied Physics, 2003Co-Authors: Hiroshi Mizuta, Zahid A. K. Durrani, Kazuo Nakazato, Y. Furuta, Toshio Kamiya, Y. T. Tan, Shuhei Amakawa, Haroon AhmedAbstract:This paper presents a brief overview of the physics of nanosilicon materials for single-electron device applications. We study how a nanosilicon grain and a discrete grain boundary work as a charging island and a tunnel barrier by using a Point-Contact Transistor, which features an extremely short and narrow channel. Single-electron charging phenomena are investigated by comparing asprepared devices and various oxidized devices. The optimization of grain and grain-boundary structural parameters is discussed for improving the Coulomb blockade characteristics and realizing room temperature device operation. � 2003 Published by Elsevier B.V. PACS: 81.07.Bc; 73.23.Hk; 85.35.Gv
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Single-electron charging phenomena in nano/polycrystalline silicon Point-Contact Transistors
Solid State Phenomena, 2003Co-Authors: Hiroshi Mizuta, Zahid A. K. Durrani, Y. Furuta, Y. T. Tan, T. Kamiya, K. Nakazato, Haroon AhmedAbstract:This paper gives a review of our recent work investigating the physics of single-electron charging phenomena in nano/polycrystalline silicon nanostructures. We first provide a short overview on the research of silicon-based single-electron devices from the last decade. Various single-electron Transistor structures are compared in terms of control of electron islands and tunnel barriers. We then study the single-electron charging phenomena in nano/polycrystalline silicon nanostructures. A novel Point-Contact Transistor is introduced, which features an extremely short and narrow nano/poly-Si nanowire as the Transistor’s channel. This structure is suitable for studying how a grain smaller than 10 nm in size and a discrete grain boundary work as a charging island and a tunnel barrier, respectively. The relationships between structural and electrical parameters of grains/grain-boundaries and the resulting Coulomb blockade characteristics for the point contact Transistors are investigated by applying various passivation processes. Finally, optimisation of grain and grain-boundary structures is discussed for improving the Coulomb blockade characteristics and realizing nano/poly-Si single-electron Transistors operating at room temperature. Introduction Over the last few decades, the performance of VLSI circuits has been improved steadily by scaling down device dimensions. In dynamic random access memories (DRAMs), for instance, the amount of charge stored per memory cell has been decreased with reduction of the cell area. After the 1 Mbit generation, however, it has become increasingly difficult to keep up such a continuous decrease in the stored charge per bit because the signal becomes less immune to leakage current, internal noise, and soft errors. In microprocessors, power consumption per one MOS Transistor has also been reduced due both to miniaturisation and to improved operation conditions. Nevertheless, the total power consumption per microprocessor has gradually been increasing as the number of MOS Transistors per chip increases, and the number of electrons used to switch one MOS Transistor on and off needs to be reduced further to counter this trend. However, when the number of electrons becomes less than 1000, inherent charge fluctuations cause unacceptable statistical variations in the subthreshold characteristics of the MOS Transistors. For both memory and logic applications, how to guarantee future ‘scalability’ of the devices is a key issue, along with a reduction of the number of electrons. Singleand few-electron devices are expected to overcome these issues by introducing the Coulomb blockade (CB) effect [1],[2] as a new principle for the controlled transfer of a small number of electrons. A key building block for singleand fewelectron devices are the double tunnel junction (DTJ) and multiple tunnel junction (MTJ) structures shown in Figs. 1(a) and (b), which are composed of a series of islands with tunnel barriers between them. When a single electron enters onto the island, the charging energy EC of the island increases, and the transfer of even one electron is strongly suppressed (Coulomb blockade) if the charging energy is higher than the thermal energy kBT. From the device-engineering point of view, the MTJ is more preferable than the simple DTJ since it reduces co-tunnelling [3], which generally leads to unfavourable leakage current. Also the MTJ structure is robust against offset charge effects [4][5], which vary the Coulomb gap and even may break the CB. In general, the tunnel junction (TJ) should meet the following two requirements to show the CB effects at a temperature T: (a) (b) conductor island Fig.1: (a) Double tunnel junction and (b) multiple tunnel junction. Rt ≫ RQ = h/e = 25.6 kΩ (1) EC = e/2CΣ ≫ kBT (2) to avoid quantum and thermal smearing of the electronic states confined in the islands. In Eqs. (1) and (2) RQ is the quantum resistance (≡ h/e), and Rt and CΣ are the total tunnel resistance of the TJ and total capacitance of the electron islands, respectively. A number of fabrication methods for DTJs and MTJs have been reported. These structures may be classified into two groups in terms of the manner of formation of nanoscale electron islands: patterned electron islands and naturally formed ones. A silicon-based patterned island structure has been realized by using a pattern-dependent oxidation (PADOX) technique [6]. This technique utilizes faster oxidation caused by stress at the pattern edge, and a DTJ is formed at the both ends of a Si nanowire (NW). This technique has achieved a single electron island with a lateral size of less than 10 nm. An alternative approach is to use an AFM-based oxidation technique [7]. A NbO2 DTJ was defined on a Nb NW resulting in a Nb single island with a lateral dimension of a few nm. A step edge cut off (SECO) technique [8] has also been reported to form a metallic MTJ structure. Table Naturally formed structures exploit various kinds of local disorder in nanometer-scale structures to form the DTJ or MTJ. In a heavily doped Si NW [9] with a few tens of nanometers in width, randomly distributed dopant atoms cause potential fluctuations, and a linear chain of electron islands are formed when a negative gate bias is applied to a gate electrode placed adjacent to the NW [10]. This is a fairly simple structure and has often been used for making CB memory [11][12] and logic [13] devices. However, the CB oscillation can usually be observed Naturally-formed Patterned Controllability of dot size Controllability of dot position Controllability of tunnel barrier thickness Compatibility with Si-ULSI Controllability of tunnel barrier height Random dopant induced Roughness induced Defect induced
Kim M. Lewis - One of the best experts on this subject based on the ideXlab platform.
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Quantum point contact Transistor with high gain and charge sensitivity
Journal of Applied Physics, 2001Co-Authors: Cagliyan Kurdak, L. Farina, Kim M. LewisAbstract:We analyze the potential performance of quantum point contact (QPC) devices in charge detection applications. For the standard QPC structure we show that the charge sensitivity is strongly dependent on gate geometry and can be close to the quantum limit, and that the gain parameter is less than one under bias conditions where the charge sensitivity is optimized. We propose a novel QPC device consisting of two split gates for defining the QPC and a third gate which can be used to filter out hot electrons that are emitted from the QPC. We show that this proposed device can have a high gain and a charge sensitivity close to that of single electron Transistors. The device can be realized using high quality GaAs/AlGaAs with a two-dimensional electron gas and standard nanofabrication techniques. Unlike single electron Transistors, the gain of the proposed device does not depend on the charge configuration near the active region of the device. Therefore the device can be used as an electrometer without a feedback charged locked loop and multiple devices can easily be integrated.