We make a distinction between noise and interference. An example of interference is 60 Hz'hum'due... more We make a distinction between noise and interference. An example of interference is 60 Hz'hum'due to ground loops. Both noise and interference may be considered 'unwanted'in an experiment. So if we were to use the definition that 'noise'is whatever is unwanted, we could argue that interference is noise as well. However, sometimes noise is actually the signal that you're interested in! In addition, noise and interference have very distinct characteristics. Interference is not random, but periodic and predictable.
ABSTRACT Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applic... more ABSTRACT Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applications in areas such as environmental protection, exploration, and drug development. We realize atomic scale mass sensing using doubly clamped suspended carbon nanotube nanomechanical resonators, in which their single-electron transistor properties allows self-detection of the nanotube vibration.
Abstract As circuits are made smaller, certain new physical phenomena will appear. When the capac... more Abstract As circuits are made smaller, certain new physical phenomena will appear. When the capacitance of components becomes so small that adding a single electron to that component causes the voltage to jump significantly, then singleelectron effects will have to be included in the device models. This can have important consequences for the conductance through the device and the noise that is observed.
We investigate correlated electronic transport in single-walled carbon nanotubes with two intramo... more We investigate correlated electronic transport in single-walled carbon nanotubes with two intramolecular tunneling barriers. We suggest that below a characteristic temperature the long-range nature of the Coulomb interaction becomes crucial to determine the temperature dependence of the maximum Gmax of the conductance peak. Correlated sequential tunneling dominates transport yielding the power law Gmax/T end-endÿ1, typical for tunneling between the ends of two Luttinger liquids.
We present proof-of-concept all-carbon solar cells. They are made of a photoactive side of predom... more We present proof-of-concept all-carbon solar cells. They are made of a photoactive side of predominantly semiconducting nanotubes for photoconversion and a counter electrode made of a natural mixture of carbon nanotubes or graphite, connected by a liquid electrolyte through a redox reaction. The cells do not require rare source materials such as In or Pt, nor high-grade semiconductor processing equipment, do not rely on dye for photoconversion and therefore do not bleach, and are easy to fabricate using a spray-paint technique. We observe that cells with a lower concentration of carbon nanotubes on the active semiconducting electrode perform better than cells with a higher concentration of nanotubes. This effect is contrary to the expectation that a larger number of nanotubes would lead to more photoconversion and therefore more power generation. We attribute this to the presence of metallic nanotubes that provide a short for photo-excited electrons, bypassing the load. We demonstrate optimization strategies that improve cell efficiency by orders of magnitude. Once it is possible to make semiconducting-only carbon nanotube films, that may provide the greatest efficiency improvement.
We study the patterns that short strands of single-stranded DNA form on the top graphene surface ... more We study the patterns that short strands of single-stranded DNA form on the top graphene surface of graphite. We find that the DNA assembles into two distinct patterns, small spherical particles and elongated networks. Known interaction models based on DNA-graphene binding, hydrophobic interactions, or models based on the purine/pyrimidine nature of the bases do not explain our observed crossover in pattern formation. We argue that the observed assembly behavior is caused by a crossover in the competition between base-base pi stacking and base-graphene pi stacking and we infer a critical crossover energy of eV. The experiments therefore provide a projective measurement of the base-base interaction strength.
I propose a technique for reading the base sequence of a single DNA molecule using a graphene nan... more I propose a technique for reading the base sequence of a single DNA molecule using a graphene nanogap to read the DNA’s transverse conductance. Because graphene is a single atom thick, single-base resolution of the conductance is readily obtained. The nonlinear current−voltage characteristic is used to determine the base type independent of nanogap-width variations that cause the current to change by 5 orders of magnitude. The expected sequencing error rate is 0% up to a nanogap width of 1.6 nm.
Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applications in... more Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applications in areas such as environmental protection, exploration, and drug development. We realize atomic scale mass sensing using doubly clamped suspended carbon nanotube nanomechanical resonators, in which their single-electron transistor properties allows self-detection of the nanotube vibration. We use the detection of shifts in the resonance frequency of the nanotubes to sense and determine the inertial mass of atoms as well as the mass of the nanotube. This highly sensitive mass detection capability may eventually enable applications such as on-chip detection, analysis, and identification of compounds.
We present an experiment that systematically probes the basins of attraction of two fixed points ... more We present an experiment that systematically probes the basins of attraction of two fixed points of a nonlinear nanomechanical resonator and maps them out with high resolution. We observe a separatrix which progressively alters shape for varying drive strength and changes the relative areas of the two basins of attraction. The observed separatrix is blurred due to ambient fluctuations, including residual noise in the drive system, which cause uncertainty in the preparation of an initial state close to the separatrix. We find a good agreement between the experimentally mapped and theoretically calculated basins of attraction.
We explore an electrostatic mechanism for tuning the nonlinearity of nanomechanical resonators an... more We explore an electrostatic mechanism for tuning the nonlinearity of nanomechanical resonators and increasing their dynamic range for sensor applications. We also demonstrate tuning the resonant frequency of resonators both upward and downward. A theoretical model is developed that qualitatively explains the experimental results and serves as a simple guide for design of tunable nanomechanical devices.
We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNT... more We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNTs) to realize nanoelectromechanical switches. Our switches consist of two open-ended MWNT segments separated by a nanometer-scale gap. Switching occurs through electrostatically actuated sliding of the inner nanotube shells to close the gap, producing a conducting ON state. For double-walled nanotubes in particular, a gate voltage can restore the insulating OFF state. Acting as a nonvolatile memory element capable of several switching cycles, our devices are straightforward to implement, self-aligned, and do not require complex fabrication or geometries, allowing for convenient scalability.
We report electrical transport experiments, using the phenomenon of electrical breakdown to perfo... more We report electrical transport experiments, using the phenomenon of electrical breakdown to perform thermometry, that probe the thermal properties of individual multiwalled carbon nanotubes. Our results show that nanotubes can readily conduct heat by ballistic phonon propagation. We determine the thermal conductance quantum, the ultimate limit to thermal conductance for a single phonon channel, and find good agreement with theoretical calculations. Moreover, our results suggest a breakdown mechanism of thermally activated C-C bond breaking coupled with the electrical stress of carrying ∼1012 A/m2. We also demonstrate a current-driven self-heating technique to improve the conductance of nanotube devices dramatically.
Nanomechanical resonators with high aspect ratio, such as nanotubes and nanowires are of interest... more Nanomechanical resonators with high aspect ratio, such as nanotubes and nanowires are of interest due to their expected high sensitivity. However, a strongly nonlinear response combined with a high thermomechanical noise level limits the useful linear dynamic range of this type of device. We derive the equations governing this behavior and find a strong dependence [∝d √ (d/L)5 ] of the dynamic range on aspect ratio.
Fabrication and readout of devices with progressively smaller size, ultimately down to the molecu... more Fabrication and readout of devices with progressively smaller size, ultimately down to the molecular scale, is critical for the development of very-high-frequency nanoelectromechanical systems (NEMS). Nanomaterials, such as carbon nanotubes or nanowires, offer immense prospects as active elements for these applications. We report the fabrication and measurement of a platinum nanowire resonator, 43 nm in diameter and 1.3 μm in length. This device, among the smallest NEMS reported, has a fundamental vibration frequency of 105.3 MHz, with a quality factor of 8500 at 4 K. Its resonant motion is transduced by a technique that is well suited to ultrasmall mechanical structures.
We investigate correlated electronic transport in single-walled carbon nanotubes with two intramo... more We investigate correlated electronic transport in single-walled carbon nanotubes with two intramolecular tunneling barriers. We suggest that below a characteristic temperature the long-range nature of the Coulomb interaction becomes crucial to determine the temperature dependence of the maximum Gmax of the conductance peak. Correlated sequential tunneling dominates transport yielding the power law Gmax∝Tαend-end-1, typical for tunneling between the ends of two Luttinger liquids. Our predictions are in agreement with recent measurements.
The low-frequency electronic noise properties of individual single-wall metallic carbon nan- otub... more The low-frequency electronic noise properties of individual single-wall metallic carbon nan- otubes are investigated. The noise exhibits a 1/f frequency dependence and a V 2 voltage dependence. The noise power at 8 K appears to be three orders of magnitude smaller than at 300 K. As a demonstration of how these noise properties affect nanotube devices, a prelimi- nary investigation of the noise characteristics of a fabricated intramolecular carbon nanotube single-electron transistor is presented.
Room-temperature single-electron transistors are realized within individual metallic single-wall ... more Room-temperature single-electron transistors are realized within individual metallic single-wall carbon nanotube molecules. The devices feature a short (down to ∼20 nanometers) nanotube section that is created by inducing local barriers into the tube with an atomic force microscope. Coulomb charging is observed at room temperature, with an addition energy of 120 millielectron volts, which substantially exceeds the thermal energy. At low temperatures, we resolve the quantum energy levels corresponding to the small island. We observe unconventional power-law dependencies in the measured transport properties for which we suggest a resonant tunneling Luttinger-liquid mechanism.
Using an atomic force microscope we have created nanotube junctions such as buckles and crossings... more Using an atomic force microscope we have created nanotube junctions such as buckles and crossings within individual single-wall metallic carbon nanotubes connected to metallic electrodes. The electronic transport properties of these manipulated structures show that they form electronic tunnel junctions. The conductance shows power-law behavior as a function of bias voltage and temperature, which can be well modeled by a Luttinger liquid model for tunneling between two nanotube segments separated by the manipulated junction.
The tip of an atomic force microscope is used to create carbon nanotube junctions by changing the... more The tip of an atomic force microscope is used to create carbon nanotube junctions by changing the position and shape of individual single-walled carbon nanotubes on a SiO2 surface. With this manipulation technique, we are able to bend, buckle, cross (see Figure), and break nanotubes, and to unravel a nanotube “crop circle” into a single tube. Tapping-mode atomic force microscopy measurements of the height of a carbon nanotube on the surface always yield values smaller than the nanotube diameter. Variation of the scan parameters shows that this is due to a tapping deformation by the tip. The tapping deformation of manipulated nanotube crossings and buckles is discussed as well.
We make a distinction between noise and interference. An example of interference is 60 Hz'hum'due... more We make a distinction between noise and interference. An example of interference is 60 Hz'hum'due to ground loops. Both noise and interference may be considered 'unwanted'in an experiment. So if we were to use the definition that 'noise'is whatever is unwanted, we could argue that interference is noise as well. However, sometimes noise is actually the signal that you're interested in! In addition, noise and interference have very distinct characteristics. Interference is not random, but periodic and predictable.
ABSTRACT Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applic... more ABSTRACT Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applications in areas such as environmental protection, exploration, and drug development. We realize atomic scale mass sensing using doubly clamped suspended carbon nanotube nanomechanical resonators, in which their single-electron transistor properties allows self-detection of the nanotube vibration.
Abstract As circuits are made smaller, certain new physical phenomena will appear. When the capac... more Abstract As circuits are made smaller, certain new physical phenomena will appear. When the capacitance of components becomes so small that adding a single electron to that component causes the voltage to jump significantly, then singleelectron effects will have to be included in the device models. This can have important consequences for the conductance through the device and the noise that is observed.
We investigate correlated electronic transport in single-walled carbon nanotubes with two intramo... more We investigate correlated electronic transport in single-walled carbon nanotubes with two intramolecular tunneling barriers. We suggest that below a characteristic temperature the long-range nature of the Coulomb interaction becomes crucial to determine the temperature dependence of the maximum Gmax of the conductance peak. Correlated sequential tunneling dominates transport yielding the power law Gmax/T end-endÿ1, typical for tunneling between the ends of two Luttinger liquids.
We present proof-of-concept all-carbon solar cells. They are made of a photoactive side of predom... more We present proof-of-concept all-carbon solar cells. They are made of a photoactive side of predominantly semiconducting nanotubes for photoconversion and a counter electrode made of a natural mixture of carbon nanotubes or graphite, connected by a liquid electrolyte through a redox reaction. The cells do not require rare source materials such as In or Pt, nor high-grade semiconductor processing equipment, do not rely on dye for photoconversion and therefore do not bleach, and are easy to fabricate using a spray-paint technique. We observe that cells with a lower concentration of carbon nanotubes on the active semiconducting electrode perform better than cells with a higher concentration of nanotubes. This effect is contrary to the expectation that a larger number of nanotubes would lead to more photoconversion and therefore more power generation. We attribute this to the presence of metallic nanotubes that provide a short for photo-excited electrons, bypassing the load. We demonstrate optimization strategies that improve cell efficiency by orders of magnitude. Once it is possible to make semiconducting-only carbon nanotube films, that may provide the greatest efficiency improvement.
We study the patterns that short strands of single-stranded DNA form on the top graphene surface ... more We study the patterns that short strands of single-stranded DNA form on the top graphene surface of graphite. We find that the DNA assembles into two distinct patterns, small spherical particles and elongated networks. Known interaction models based on DNA-graphene binding, hydrophobic interactions, or models based on the purine/pyrimidine nature of the bases do not explain our observed crossover in pattern formation. We argue that the observed assembly behavior is caused by a crossover in the competition between base-base pi stacking and base-graphene pi stacking and we infer a critical crossover energy of eV. The experiments therefore provide a projective measurement of the base-base interaction strength.
I propose a technique for reading the base sequence of a single DNA molecule using a graphene nan... more I propose a technique for reading the base sequence of a single DNA molecule using a graphene nanogap to read the DNA’s transverse conductance. Because graphene is a single atom thick, single-base resolution of the conductance is readily obtained. The nonlinear current−voltage characteristic is used to determine the base type independent of nanogap-width variations that cause the current to change by 5 orders of magnitude. The expected sequencing error rate is 0% up to a nanogap width of 1.6 nm.
Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applications in... more Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applications in areas such as environmental protection, exploration, and drug development. We realize atomic scale mass sensing using doubly clamped suspended carbon nanotube nanomechanical resonators, in which their single-electron transistor properties allows self-detection of the nanotube vibration. We use the detection of shifts in the resonance frequency of the nanotubes to sense and determine the inertial mass of atoms as well as the mass of the nanotube. This highly sensitive mass detection capability may eventually enable applications such as on-chip detection, analysis, and identification of compounds.
We present an experiment that systematically probes the basins of attraction of two fixed points ... more We present an experiment that systematically probes the basins of attraction of two fixed points of a nonlinear nanomechanical resonator and maps them out with high resolution. We observe a separatrix which progressively alters shape for varying drive strength and changes the relative areas of the two basins of attraction. The observed separatrix is blurred due to ambient fluctuations, including residual noise in the drive system, which cause uncertainty in the preparation of an initial state close to the separatrix. We find a good agreement between the experimentally mapped and theoretically calculated basins of attraction.
We explore an electrostatic mechanism for tuning the nonlinearity of nanomechanical resonators an... more We explore an electrostatic mechanism for tuning the nonlinearity of nanomechanical resonators and increasing their dynamic range for sensor applications. We also demonstrate tuning the resonant frequency of resonators both upward and downward. A theoretical model is developed that qualitatively explains the experimental results and serves as a simple guide for design of tunable nanomechanical devices.
We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNT... more We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNTs) to realize nanoelectromechanical switches. Our switches consist of two open-ended MWNT segments separated by a nanometer-scale gap. Switching occurs through electrostatically actuated sliding of the inner nanotube shells to close the gap, producing a conducting ON state. For double-walled nanotubes in particular, a gate voltage can restore the insulating OFF state. Acting as a nonvolatile memory element capable of several switching cycles, our devices are straightforward to implement, self-aligned, and do not require complex fabrication or geometries, allowing for convenient scalability.
We report electrical transport experiments, using the phenomenon of electrical breakdown to perfo... more We report electrical transport experiments, using the phenomenon of electrical breakdown to perform thermometry, that probe the thermal properties of individual multiwalled carbon nanotubes. Our results show that nanotubes can readily conduct heat by ballistic phonon propagation. We determine the thermal conductance quantum, the ultimate limit to thermal conductance for a single phonon channel, and find good agreement with theoretical calculations. Moreover, our results suggest a breakdown mechanism of thermally activated C-C bond breaking coupled with the electrical stress of carrying ∼1012 A/m2. We also demonstrate a current-driven self-heating technique to improve the conductance of nanotube devices dramatically.
Nanomechanical resonators with high aspect ratio, such as nanotubes and nanowires are of interest... more Nanomechanical resonators with high aspect ratio, such as nanotubes and nanowires are of interest due to their expected high sensitivity. However, a strongly nonlinear response combined with a high thermomechanical noise level limits the useful linear dynamic range of this type of device. We derive the equations governing this behavior and find a strong dependence [∝d √ (d/L)5 ] of the dynamic range on aspect ratio.
Fabrication and readout of devices with progressively smaller size, ultimately down to the molecu... more Fabrication and readout of devices with progressively smaller size, ultimately down to the molecular scale, is critical for the development of very-high-frequency nanoelectromechanical systems (NEMS). Nanomaterials, such as carbon nanotubes or nanowires, offer immense prospects as active elements for these applications. We report the fabrication and measurement of a platinum nanowire resonator, 43 nm in diameter and 1.3 μm in length. This device, among the smallest NEMS reported, has a fundamental vibration frequency of 105.3 MHz, with a quality factor of 8500 at 4 K. Its resonant motion is transduced by a technique that is well suited to ultrasmall mechanical structures.
We investigate correlated electronic transport in single-walled carbon nanotubes with two intramo... more We investigate correlated electronic transport in single-walled carbon nanotubes with two intramolecular tunneling barriers. We suggest that below a characteristic temperature the long-range nature of the Coulomb interaction becomes crucial to determine the temperature dependence of the maximum Gmax of the conductance peak. Correlated sequential tunneling dominates transport yielding the power law Gmax∝Tαend-end-1, typical for tunneling between the ends of two Luttinger liquids. Our predictions are in agreement with recent measurements.
The low-frequency electronic noise properties of individual single-wall metallic carbon nan- otub... more The low-frequency electronic noise properties of individual single-wall metallic carbon nan- otubes are investigated. The noise exhibits a 1/f frequency dependence and a V 2 voltage dependence. The noise power at 8 K appears to be three orders of magnitude smaller than at 300 K. As a demonstration of how these noise properties affect nanotube devices, a prelimi- nary investigation of the noise characteristics of a fabricated intramolecular carbon nanotube single-electron transistor is presented.
Room-temperature single-electron transistors are realized within individual metallic single-wall ... more Room-temperature single-electron transistors are realized within individual metallic single-wall carbon nanotube molecules. The devices feature a short (down to ∼20 nanometers) nanotube section that is created by inducing local barriers into the tube with an atomic force microscope. Coulomb charging is observed at room temperature, with an addition energy of 120 millielectron volts, which substantially exceeds the thermal energy. At low temperatures, we resolve the quantum energy levels corresponding to the small island. We observe unconventional power-law dependencies in the measured transport properties for which we suggest a resonant tunneling Luttinger-liquid mechanism.
Using an atomic force microscope we have created nanotube junctions such as buckles and crossings... more Using an atomic force microscope we have created nanotube junctions such as buckles and crossings within individual single-wall metallic carbon nanotubes connected to metallic electrodes. The electronic transport properties of these manipulated structures show that they form electronic tunnel junctions. The conductance shows power-law behavior as a function of bias voltage and temperature, which can be well modeled by a Luttinger liquid model for tunneling between two nanotube segments separated by the manipulated junction.
The tip of an atomic force microscope is used to create carbon nanotube junctions by changing the... more The tip of an atomic force microscope is used to create carbon nanotube junctions by changing the position and shape of individual single-walled carbon nanotubes on a SiO2 surface. With this manipulation technique, we are able to bend, buckle, cross (see Figure), and break nanotubes, and to unravel a nanotube “crop circle” into a single tube. Tapping-mode atomic force microscopy measurements of the height of a carbon nanotube on the surface always yield values smaller than the nanotube diameter. Variation of the scan parameters shows that this is due to a tapping deformation by the tip. The tapping deformation of manipulated nanotube crossings and buckles is discussed as well.
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Papers by Henk Postma
[∝d
√ (d/L)5
]
of the dynamic range on aspect ratio.
[∝d
√ (d/L)5
]
of the dynamic range on aspect ratio.