Natarajan Chandrasekhar | Retired - Academia.edu (original) (raw)

Papers by Natarajan Chandrasekhar

Research paper thumbnail of Switching in organic devices caused by nanoscale Schottky barrier patches

The Journal of Chemical Physics, May 22, 2005

We have identified a possible electronic origin of metal filaments, invoked to explain the switch... more We have identified a possible electronic origin of metal filaments, invoked to explain the switching behavior of organic devices. Interfaces of two representative organics polyparaphenylene (PPP) and poly(2-methoxy-5-2-ethyl-hexyloxy-1,4-phenylenevinylene) with Ag are investigated using ballistic emission microscopy. Nanometer scale spatial nonuniformity of carrier injection is observed in ballistic electron emission microscopy images of both interfaces. The measured Schottky barrier (SB) appears to be consistent with metal states tailing into the gap of the PPP. We find that the SB values exhibit a distribution, even for the diodes with low ideality factors. The implications of this distribution on the measured physical properties of the diode are discussed, in light of work on devices of similar geometry, published in the literature. We also demonstrate that patches of low SB are likely to nucleate current filaments which can cause local ionization and are reported to be responsible for the switching behavior observed in metal-organic, metal-CuS and Ag-AgSe structures.

Research paper thumbnail of The decomposition of single or multiple transition metal cupferron complexes in organic solvents under solvothermal conditions and in the presence of long chain amines yields the corresponding oxide nanoparticles

proportions. The nanoparticles are capped with n-octylamine or n-dodecylamine. The presence of am... more proportions. The nanoparticles are capped with n-octylamine or n-dodecylamine. The presence of amine in the reaction is found to be essential for the formation of the product. The magnetic behavior of pressed pellets of these nanoparticles is presented.

Research paper thumbnail of Comment on ''Temporal response of a high-T c superconducting field-effect transistor'' (Appl. Phys. Lett. 67, 2076 (1995))

Research paper thumbnail of Electrostatic effects of nanoscale dielectric patches in the modification of Schottky contacts

Physical Review B Condensed Matter and Materials Physics, 2009

We study the electrostatic effects of thin organic films in modifying the interface physics of me... more We study the electrostatic effects of thin organic films in modifying the interface physics of metal/semiconductor Schottky contacts. We work out analytically the electrostatic parameter space pointing out where interface state effects exceed space-charge effects and vice versa. This is done by introducing another treatment of the electrostatic problem. We also find that the image force effect on the barrier height due to the insertion of a material with lower dielectric constant than the semiconductor in between the Schottky contact is small but positive. This is in contrast to what might be expected from effective-medium theory. We conclude with an examination of ballistic electron emission microscopy results of pentacene modified Au/n-Si(111) Schottky diodes as a case study. Using the tools fore mentioned, we infer the local charge neutrality level and density of interface gap states (to an area of 500×500nm2 ) from barrier height statistics and pentacene monolayer heights.

Research paper thumbnail of Chain Oxygen Dynamics in YBa2Cu3O7-delta Under Applied Electric Fields and Related Phenomena

Mod Phys Lett B, 1994

Three-terminal field effect devices are widespread in modern electronics due to their versatility... more Three-terminal field effect devices are widespread in modern electronics due to their versatility. The possibility of tuning superconductivity, using electric fields to modulate carrier transport is of great interest. With the high temperature cuprate superconductors, which have fairly low carrier concentrations in comparison to metals, this would permit the study of properties in a systematic manner instead of relying on the stochastic nature of oxygen doping. Demonstrations of the phenomenon in YBa2Cu3O7-δ have been analysed in terms of the conventional metal field effect. In this work, we show that contrary to earlier belief, the field effect in YBa2Cu3O7-δ arises due to changes in the structure. The mechanism is one of ordering induced doping, and is not novel to this oxide, with Fe3O4 exhibiting a similar phenomenon, termed the Verwey transition. Our explanations and results are found to be consistent with experiments, both in terms of the magnitudes of the effects observed as well as their time scales. Also, explicit predictions of this model have recently been confirmed experimentally. Since the effect is omnipresent during the measurement of any physical property in this material, we present a qualitative discussion of its connotations for transport, tunneling, and magnetization. The phenomenon is of importance in a wide variety of device applications.

Research paper thumbnail of Evidence for surface melting during the growth of high Tc thin films

Physica C: Superconductivity, 1994

We present reflection high energy electron diffraction (RHEED) spot profile analyses, which show ... more We present reflection high energy electron diffraction (RHEED) spot profile analyses, which show anomalous broadening over very short time scales. Our data can only be interpreted in terms of surface melting. The conclusions are consistent with the thermodynamic phase diagrams and with the vapor-liquid-solid (VLS) mechanism of crystal growth. 0921-4534/94/S07.00

Research paper thumbnail of Comment on {open_quote}{open_quote}Mechanism of the electric-field effect in the high-{ital T}{sub {ital c}} cuprates{close_quote}{close_quote}

Phys Rev B, 1996

The electric-field effect in the high-{ital T}{sub {ital c}} cuprates has been claimed to arise f... more The electric-field effect in the high-{ital T}{sub {ital c}} cuprates has been claimed to arise from the field-driven mobility of free charges in the superconductor, a conclusion based on the observation of the field effect in BiâSrâCaCuâO{sub 8+{ital y}} at one sign of the bias. We show that this conclusion is unwarranted.

Research paper thumbnail of Spin Orbit Interaction Induced Spin-Separation In Platinum Nanostructure

NATO Science for Peace and Security Series B: Physics and Biophysics, 2009

Hirsch (1999) proposed a mechanism and geometry for the observation of the spin-Hall effect. In t... more Hirsch (1999) proposed a mechanism and geometry for the observation of the spin-Hall effect. In this work, we present a novel realization of the Hirsch geometry in a platinum (Pt) nanostructure, which is an increasingly important material for spintronics applications. Measurements were made in a non-local geometry to avoid spurious effects. The measurements show the large spin Hall conductivity of Pt. The results are compared with gold (Au) and aluminum (Al). Possible theoretical explanations of our observations are briefly mentioned.

Research paper thumbnail of Charging effects observed in YBa2Cu3O7-x films: Influence of oxygen ordering

Physical review. B, Condensed matter, 1994

... agreement is indeed very satisfactory, when one con-siders the nature of Monte Carlo simulati... more ... agreement is indeed very satisfactory, when one con-siders the nature of Monte Carlo simulation ... the noise is seen at an oxygen 49 6225 6226 N. CHANDRASEKHAR, ORIOL T ... ACKNOWLEDGMENTS One of us (NC) gratefully acknowledges discussions with Dr. SK Kurtz, ...

Research paper thumbnail of Comment on "Mechanism of the electric-field effect in the high-Tc cuprates

Physical review. B, Condensed matter, 1996

ABSTRACT

Research paper thumbnail of Trap Energy Levels in Graphene Oxide Determined by Ballistic Electron Emission Spectroscopy

ECS Solid State Letters, 2012

Research paper thumbnail of Confinement of the field electron emission to atomic sites on ultra sharp tips

Surface Science, 2009

The spatially controlled field assisted etching method for sharpening metallic tips, in a field i... more The spatially controlled field assisted etching method for sharpening metallic tips, in a field ion microscope (FIM), is used to study the evolution of the field emission when the tip apex radius is decreased below 1 nm. Unlike the conventional image formation in a field emission microscope (FEM), we demonstrate that at this scale the field emission is rather confined to atomic sites. A single atom apex fabricated at the end of such tips exhibits an outstanding brightness compared to other atomic tips. The measurements have been repeated for two double atom tips, with different atom-atom separations, and images of atomic field emission localization have also been obtained. We have found that the field emission intensity alternates between adjacent atoms when the applied voltage is gradually increased beyond a threshold value.

Research paper thumbnail of Chandrasekhar, Valls, and Goldman Reply

Physical Review Letters, 1994

ABSTRACT

Research paper thumbnail of Electrostatic effects of nanoscale dielectric patches in the modification of Schottky contacts

Physical Review B, 2009

We study the electrostatic effects of thin organic films in modifying the interface physics of me... more We study the electrostatic effects of thin organic films in modifying the interface physics of metal/ semiconductor Schottky contacts. We work out analytically the electrostatic parameter space pointing out where interface state effects exceed space-charge effects and vice versa. This is done by introducing another treatment of the electrostatic problem. We also find that the image force effect on the barrier height due to the insertion of a material with lower dielectric constant than the semiconductor in between the Schottky contact is small but positive. This is in contrast to what might be expected from effective-medium theory. We conclude with an examination of ballistic electron emission microscopy results of pentacene modified Au/ n-Si͑111͒ Schottky diodes as a case study. Using the tools fore mentioned, we infer the local charge neutrality level and density of interface gap states ͑to an area of 500ϫ 500 nm 2 ͒ from barrier height statistics and pentacene monolayer heights.

Research paper thumbnail of A mechanism for electric field effects observed in (RE)Ba2Cu3O7−x

Physica B: Condensed Matter, 1994

... N. Chandrasekhar,Oriol T. Valls, and AM Goldman Center for the Science and Application ofSupe... more ... N. Chandrasekhar,Oriol T. Valls, and AM Goldman Center for the Science and Application ofSuperconductivity ... In this Letter we report the results of a Monte Carlo study of the effect of applied electric fields on the dynam-ics of chain oxygen in YBa2Cu307 —„. ...

Research paper thumbnail of A Monte Carlo study of aging effects observed in (RE)Ba2Cu3O7−x films

Physica B: Condensed Matter, 1994

ABSTRACT

Research paper thumbnail of CHAIN OXYGEN DYNAMICS IN YBa 2 Cu 3 O 7− δ UNDER APPLIED ELECTRIC FIELDS AND RELATED PHENOMENA

Modern Physics Letters B, 1994

ABSTRACT Three-terminal field effect devices are widespread in modern electronics due to their ve... more ABSTRACT Three-terminal field effect devices are widespread in modern electronics due to their versatility. The possibility of tuning superconductivity, using electric fields to modulate carrier transport is of great interest. With the high temperature cuprate superconductors, which have fairly low carrier concentrations in comparison to metals, this would permit the study of properties in a systematic manner instead of relying on the stochastic nature of oxygen doping. Demonstrations of the phenomenon in YBa2Cu3O7−δ have been analysed in terms of the conventional metal field effect. In this work, we show that contrary to earlier belief, the field effect in YBa2Cu3O7−δ arises due to changes in the structure. The mechanism is one of ordering induced doping, and is not novel to this oxide, with Fe3O4 exhibiting a similar phenomenon, termed the Verwey transition. Our explanations and results are found to be consistent with experiments, both in terms of the magnitudes of the effects observed as well as their time scales. Also, explicit predictions of this model have recently been confirmed experimentally. Since the effect is omnipresent during the measurement of any physical property in this material, we present a qualitative discussion of its connotations for transport, tunneling, and magnetization. The phenomenon is of importance in a wide variety of device applications.

Research paper thumbnail of Nanotip apex modification with atomic precision and single atom tips restoration

Microelectronic Engineering, 2009

Nanotip technology is increasingly demanded for molecular and atomic characterizations and manipu... more Nanotip technology is increasingly demanded for molecular and atomic characterizations and manipulations. Restoration of the atomic structure of the tip apex in situ is a crucial factor in this work. We demonstrate the modification of the apex structure with atomic precision down to a single atom and introduce a new approach for modelling the arrangement of atoms of the topmost layer. Nanotips with an apex of a single and multiple atoms have been repeatedly fabricated and field emission microscopy has been conducted for various atomic structures. Direct comparisons between field ion and field electron images have revealed that the field electron emission is exclusively confined to protruding apex atoms.

Research paper thumbnail of Multiple atomic scale solid surface interconnects for atom circuits and molecule logic gates

Journal of Physics: Condensed Matter, 2010

The scientific and technical challenges involved in building the planar electrical connection of ... more The scientific and technical challenges involved in building the planar electrical connection of an atomic scale circuit to N electrodes (N > 2) are discussed. The practical, laboratory scale approach explored today to assemble a multi-access atomic scale precision interconnection machine is presented. Depending on the surface electronic properties of the targeted substrates, two types of machines are considered: on moderate surface band gap materials, scanning tunneling microscopy can be combined with scanning electron microscopy to provide an efficient navigation system, while on wide surface band gap materials, atomic force microscopy can be used in conjunction with optical microscopy. The size of the planar part of the circuit should be minimized on moderate band gap surfaces to avoid current leakage, while this requirement does not apply to wide band gap surfaces. These constraints impose different methods of connection, which are thoroughly discussed, in particular regarding the recent progress in single atom and molecule manipulations on a surface.

Research paper thumbnail of Charge transport across metal molecule interfaces probed by BEEM

Journal of Physics: Conference Series, 2007

We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky... more We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky barrier distribution over silver /H-T 3 -(CH 2 ) 4 -HS (abbreviated as T3C4SH) self assembled monolayer interface area with nanometer scale spatial resolution. The selfassembled monolayer is absorbed on template stripped gold. BEEM images show spatially non-uniform carrier injection. A Wentzel Kramel Brillouin (WKB) calculation is performed and compared with BEEM spectra. The results show that the measured currents are four orders of magnitude larger than the direct tunnelling contribution, indicating molecular levels being accessed. To further substantiate the findings, characterization by STM distance versus potential spectroscopy is carried out to determine injection barriers at the interface. The results from these two techniques are compared and the implications of which will be discussed.

Research paper thumbnail of Switching in organic devices caused by nanoscale Schottky barrier patches

The Journal of Chemical Physics, May 22, 2005

We have identified a possible electronic origin of metal filaments, invoked to explain the switch... more We have identified a possible electronic origin of metal filaments, invoked to explain the switching behavior of organic devices. Interfaces of two representative organics polyparaphenylene (PPP) and poly(2-methoxy-5-2-ethyl-hexyloxy-1,4-phenylenevinylene) with Ag are investigated using ballistic emission microscopy. Nanometer scale spatial nonuniformity of carrier injection is observed in ballistic electron emission microscopy images of both interfaces. The measured Schottky barrier (SB) appears to be consistent with metal states tailing into the gap of the PPP. We find that the SB values exhibit a distribution, even for the diodes with low ideality factors. The implications of this distribution on the measured physical properties of the diode are discussed, in light of work on devices of similar geometry, published in the literature. We also demonstrate that patches of low SB are likely to nucleate current filaments which can cause local ionization and are reported to be responsible for the switching behavior observed in metal-organic, metal-CuS and Ag-AgSe structures.

Research paper thumbnail of The decomposition of single or multiple transition metal cupferron complexes in organic solvents under solvothermal conditions and in the presence of long chain amines yields the corresponding oxide nanoparticles

proportions. The nanoparticles are capped with n-octylamine or n-dodecylamine. The presence of am... more proportions. The nanoparticles are capped with n-octylamine or n-dodecylamine. The presence of amine in the reaction is found to be essential for the formation of the product. The magnetic behavior of pressed pellets of these nanoparticles is presented.

Research paper thumbnail of Comment on ''Temporal response of a high-T c superconducting field-effect transistor'' (Appl. Phys. Lett. 67, 2076 (1995))

Research paper thumbnail of Electrostatic effects of nanoscale dielectric patches in the modification of Schottky contacts

Physical Review B Condensed Matter and Materials Physics, 2009

We study the electrostatic effects of thin organic films in modifying the interface physics of me... more We study the electrostatic effects of thin organic films in modifying the interface physics of metal/semiconductor Schottky contacts. We work out analytically the electrostatic parameter space pointing out where interface state effects exceed space-charge effects and vice versa. This is done by introducing another treatment of the electrostatic problem. We also find that the image force effect on the barrier height due to the insertion of a material with lower dielectric constant than the semiconductor in between the Schottky contact is small but positive. This is in contrast to what might be expected from effective-medium theory. We conclude with an examination of ballistic electron emission microscopy results of pentacene modified Au/n-Si(111) Schottky diodes as a case study. Using the tools fore mentioned, we infer the local charge neutrality level and density of interface gap states (to an area of 500×500nm2 ) from barrier height statistics and pentacene monolayer heights.

Research paper thumbnail of Chain Oxygen Dynamics in YBa2Cu3O7-delta Under Applied Electric Fields and Related Phenomena

Mod Phys Lett B, 1994

Three-terminal field effect devices are widespread in modern electronics due to their versatility... more Three-terminal field effect devices are widespread in modern electronics due to their versatility. The possibility of tuning superconductivity, using electric fields to modulate carrier transport is of great interest. With the high temperature cuprate superconductors, which have fairly low carrier concentrations in comparison to metals, this would permit the study of properties in a systematic manner instead of relying on the stochastic nature of oxygen doping. Demonstrations of the phenomenon in YBa2Cu3O7-δ have been analysed in terms of the conventional metal field effect. In this work, we show that contrary to earlier belief, the field effect in YBa2Cu3O7-δ arises due to changes in the structure. The mechanism is one of ordering induced doping, and is not novel to this oxide, with Fe3O4 exhibiting a similar phenomenon, termed the Verwey transition. Our explanations and results are found to be consistent with experiments, both in terms of the magnitudes of the effects observed as well as their time scales. Also, explicit predictions of this model have recently been confirmed experimentally. Since the effect is omnipresent during the measurement of any physical property in this material, we present a qualitative discussion of its connotations for transport, tunneling, and magnetization. The phenomenon is of importance in a wide variety of device applications.

Research paper thumbnail of Evidence for surface melting during the growth of high Tc thin films

Physica C: Superconductivity, 1994

We present reflection high energy electron diffraction (RHEED) spot profile analyses, which show ... more We present reflection high energy electron diffraction (RHEED) spot profile analyses, which show anomalous broadening over very short time scales. Our data can only be interpreted in terms of surface melting. The conclusions are consistent with the thermodynamic phase diagrams and with the vapor-liquid-solid (VLS) mechanism of crystal growth. 0921-4534/94/S07.00

Research paper thumbnail of Comment on {open_quote}{open_quote}Mechanism of the electric-field effect in the high-{ital T}{sub {ital c}} cuprates{close_quote}{close_quote}

Phys Rev B, 1996

The electric-field effect in the high-{ital T}{sub {ital c}} cuprates has been claimed to arise f... more The electric-field effect in the high-{ital T}{sub {ital c}} cuprates has been claimed to arise from the field-driven mobility of free charges in the superconductor, a conclusion based on the observation of the field effect in BiâSrâCaCuâO{sub 8+{ital y}} at one sign of the bias. We show that this conclusion is unwarranted.

Research paper thumbnail of Spin Orbit Interaction Induced Spin-Separation In Platinum Nanostructure

NATO Science for Peace and Security Series B: Physics and Biophysics, 2009

Hirsch (1999) proposed a mechanism and geometry for the observation of the spin-Hall effect. In t... more Hirsch (1999) proposed a mechanism and geometry for the observation of the spin-Hall effect. In this work, we present a novel realization of the Hirsch geometry in a platinum (Pt) nanostructure, which is an increasingly important material for spintronics applications. Measurements were made in a non-local geometry to avoid spurious effects. The measurements show the large spin Hall conductivity of Pt. The results are compared with gold (Au) and aluminum (Al). Possible theoretical explanations of our observations are briefly mentioned.

Research paper thumbnail of Charging effects observed in YBa2Cu3O7-x films: Influence of oxygen ordering

Physical review. B, Condensed matter, 1994

... agreement is indeed very satisfactory, when one con-siders the nature of Monte Carlo simulati... more ... agreement is indeed very satisfactory, when one con-siders the nature of Monte Carlo simulation ... the noise is seen at an oxygen 49 6225 6226 N. CHANDRASEKHAR, ORIOL T ... ACKNOWLEDGMENTS One of us (NC) gratefully acknowledges discussions with Dr. SK Kurtz, ...

Research paper thumbnail of Comment on "Mechanism of the electric-field effect in the high-Tc cuprates

Physical review. B, Condensed matter, 1996

ABSTRACT

Research paper thumbnail of Trap Energy Levels in Graphene Oxide Determined by Ballistic Electron Emission Spectroscopy

ECS Solid State Letters, 2012

Research paper thumbnail of Confinement of the field electron emission to atomic sites on ultra sharp tips

Surface Science, 2009

The spatially controlled field assisted etching method for sharpening metallic tips, in a field i... more The spatially controlled field assisted etching method for sharpening metallic tips, in a field ion microscope (FIM), is used to study the evolution of the field emission when the tip apex radius is decreased below 1 nm. Unlike the conventional image formation in a field emission microscope (FEM), we demonstrate that at this scale the field emission is rather confined to atomic sites. A single atom apex fabricated at the end of such tips exhibits an outstanding brightness compared to other atomic tips. The measurements have been repeated for two double atom tips, with different atom-atom separations, and images of atomic field emission localization have also been obtained. We have found that the field emission intensity alternates between adjacent atoms when the applied voltage is gradually increased beyond a threshold value.

Research paper thumbnail of Chandrasekhar, Valls, and Goldman Reply

Physical Review Letters, 1994

ABSTRACT

Research paper thumbnail of Electrostatic effects of nanoscale dielectric patches in the modification of Schottky contacts

Physical Review B, 2009

We study the electrostatic effects of thin organic films in modifying the interface physics of me... more We study the electrostatic effects of thin organic films in modifying the interface physics of metal/ semiconductor Schottky contacts. We work out analytically the electrostatic parameter space pointing out where interface state effects exceed space-charge effects and vice versa. This is done by introducing another treatment of the electrostatic problem. We also find that the image force effect on the barrier height due to the insertion of a material with lower dielectric constant than the semiconductor in between the Schottky contact is small but positive. This is in contrast to what might be expected from effective-medium theory. We conclude with an examination of ballistic electron emission microscopy results of pentacene modified Au/ n-Si͑111͒ Schottky diodes as a case study. Using the tools fore mentioned, we infer the local charge neutrality level and density of interface gap states ͑to an area of 500ϫ 500 nm 2 ͒ from barrier height statistics and pentacene monolayer heights.

Research paper thumbnail of A mechanism for electric field effects observed in (RE)Ba2Cu3O7−x

Physica B: Condensed Matter, 1994

... N. Chandrasekhar,Oriol T. Valls, and AM Goldman Center for the Science and Application ofSupe... more ... N. Chandrasekhar,Oriol T. Valls, and AM Goldman Center for the Science and Application ofSuperconductivity ... In this Letter we report the results of a Monte Carlo study of the effect of applied electric fields on the dynam-ics of chain oxygen in YBa2Cu307 —„. ...

Research paper thumbnail of A Monte Carlo study of aging effects observed in (RE)Ba2Cu3O7−x films

Physica B: Condensed Matter, 1994

ABSTRACT

Research paper thumbnail of CHAIN OXYGEN DYNAMICS IN YBa 2 Cu 3 O 7− δ UNDER APPLIED ELECTRIC FIELDS AND RELATED PHENOMENA

Modern Physics Letters B, 1994

ABSTRACT Three-terminal field effect devices are widespread in modern electronics due to their ve... more ABSTRACT Three-terminal field effect devices are widespread in modern electronics due to their versatility. The possibility of tuning superconductivity, using electric fields to modulate carrier transport is of great interest. With the high temperature cuprate superconductors, which have fairly low carrier concentrations in comparison to metals, this would permit the study of properties in a systematic manner instead of relying on the stochastic nature of oxygen doping. Demonstrations of the phenomenon in YBa2Cu3O7−δ have been analysed in terms of the conventional metal field effect. In this work, we show that contrary to earlier belief, the field effect in YBa2Cu3O7−δ arises due to changes in the structure. The mechanism is one of ordering induced doping, and is not novel to this oxide, with Fe3O4 exhibiting a similar phenomenon, termed the Verwey transition. Our explanations and results are found to be consistent with experiments, both in terms of the magnitudes of the effects observed as well as their time scales. Also, explicit predictions of this model have recently been confirmed experimentally. Since the effect is omnipresent during the measurement of any physical property in this material, we present a qualitative discussion of its connotations for transport, tunneling, and magnetization. The phenomenon is of importance in a wide variety of device applications.

Research paper thumbnail of Nanotip apex modification with atomic precision and single atom tips restoration

Microelectronic Engineering, 2009

Nanotip technology is increasingly demanded for molecular and atomic characterizations and manipu... more Nanotip technology is increasingly demanded for molecular and atomic characterizations and manipulations. Restoration of the atomic structure of the tip apex in situ is a crucial factor in this work. We demonstrate the modification of the apex structure with atomic precision down to a single atom and introduce a new approach for modelling the arrangement of atoms of the topmost layer. Nanotips with an apex of a single and multiple atoms have been repeatedly fabricated and field emission microscopy has been conducted for various atomic structures. Direct comparisons between field ion and field electron images have revealed that the field electron emission is exclusively confined to protruding apex atoms.

Research paper thumbnail of Multiple atomic scale solid surface interconnects for atom circuits and molecule logic gates

Journal of Physics: Condensed Matter, 2010

The scientific and technical challenges involved in building the planar electrical connection of ... more The scientific and technical challenges involved in building the planar electrical connection of an atomic scale circuit to N electrodes (N > 2) are discussed. The practical, laboratory scale approach explored today to assemble a multi-access atomic scale precision interconnection machine is presented. Depending on the surface electronic properties of the targeted substrates, two types of machines are considered: on moderate surface band gap materials, scanning tunneling microscopy can be combined with scanning electron microscopy to provide an efficient navigation system, while on wide surface band gap materials, atomic force microscopy can be used in conjunction with optical microscopy. The size of the planar part of the circuit should be minimized on moderate band gap surfaces to avoid current leakage, while this requirement does not apply to wide band gap surfaces. These constraints impose different methods of connection, which are thoroughly discussed, in particular regarding the recent progress in single atom and molecule manipulations on a surface.

Research paper thumbnail of Charge transport across metal molecule interfaces probed by BEEM

Journal of Physics: Conference Series, 2007

We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky... more We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky barrier distribution over silver /H-T 3 -(CH 2 ) 4 -HS (abbreviated as T3C4SH) self assembled monolayer interface area with nanometer scale spatial resolution. The selfassembled monolayer is absorbed on template stripped gold. BEEM images show spatially non-uniform carrier injection. A Wentzel Kramel Brillouin (WKB) calculation is performed and compared with BEEM spectra. The results show that the measured currents are four orders of magnitude larger than the direct tunnelling contribution, indicating molecular levels being accessed. To further substantiate the findings, characterization by STM distance versus potential spectroscopy is carried out to determine injection barriers at the interface. The results from these two techniques are compared and the implications of which will be discussed.