Electrical Nanoprobing of Semiconducting Carbon Nanotubes Using an Atomic Force Microscope

Yaish, Yuval; Park, J.-Y.; Rosenblatt, Sami; Sazonova, V. A.; Brink, Markus; McEuen, Paul L.

doi:10.1103/physrevlett.92.046401

Cited by 147 publications

(128 citation statements)

References 29 publications

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“…[4][5][6][7] In addition, the presence and properties of defects can cause various abnormalities in the conductance properties. To fully understand the overall conductance behavior of a nanostructure with high spatial resolution, various scanning probe microscopy (SPM) techniques have been utilized to locally perturb or electrically contact the target structures.…”

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confidence: 99%

Photocurrent Imaging of p−n Junctions in Ambipolar Carbon Nanotube Transistors

et al. 2007

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We use scanning photocurrent microscopy (SPCM) to investigate the properties of internal p-n junctions as well as local defects in ambipolar carbon nanotube (CNT) transistors. Our SPCM images show strong signals near metal contacts whose polarity and positions change depending on the gate bias. SPCM images analyzed in conjunction with the overall conductance also indicate the existence and gate-dependent evolution of internal p-n junctions near contacts in the n-type operation regime. To determine the p-n junction position and the depletion width with a nanometer scale resolution, a Gaussian fit was used. We also measure the electric potential profile of CNT devices at different gate biases, which shows that both local defects and induced electric fields can be imaged using the SPCM technique. Our experiment clearly demonstrates that SPCM is a valuable tool for imaging and optimizing electrical and optoelectronic properties of CNT based devices.In semiconducting nanostructures, including carbon nanotubes (CNTs) 1, 2 and nanowires (NWs), 3 the electronic properties at various interfaces, especially metal contacts, play a crucial role, often dominating the overall performance of nanostructure-based devices. [4][5][6][7] In addition, the presence and properties of defects can cause various abnormalities in the conductance properties. To fully understand the overall conductance behavior of a nanostructure with high spatial resolution, various scanning probe microscopy (SPM) techniques have been utilized to locally perturb or electrically contact the target structures. 7,8 More recently, scanning photocurrent microscopy (SPCM) has been successfully applied to study electrical and photoelectric properties of a number of linear nanostructures, including carbon nanotubes 9, 10 and semiconducting nanowires. 11,12 The information generated by SPCM includes the band structure near nanostructure/metal interfaces, 12 carrier relaxation dynamics, 13 and detection of local defects. 10 In this paper, we report SPCM measurements of CNT transistors at different gate biases (V G 's) to investigate the electronic band structure. Our measurements reveal that the peak photocurrent (PC) spots near the metal contacts move with gate bias in the n-type regime. We measure with nanoscale resolution the intensity and polarity of these PC spots in conjunction with DC conductance to investigate the dynamics of the internal p-n junctions. We also study the effect of various local potential variations such as naturally existing defects and induced electrical field due to a partial suspension of the CNTs.Our CNT transistors were fabricated using standard photo-and electron beam lithography techniques with CVD-grown semiconducting CNTs. CNTs were first synthesized directly on a 220 nm thick thermal oxide layer on a conducting Si substrate that is also used as a back gate. Metal evaporation and liftoff were used to define drain and source electrodes. We used either Cr/Au (5/45 nm) or Ti (50 nm) for the electrodes.Our SPCM setup uses a diffraction-...

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Photocurrent Imaging of p−n Junctions in Ambipolar Carbon Nanotube Transistors

et al. 2007

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“…Thus, the Schottky barrier formed at the contact is determined mostly by the difference between the metal work function and the electronic affinity of the semiconducting nanotube. [14][15][16] This raises a basic question as to why a gold electrode and CNTs without oxygen atoms frequently result in the FET having n-type transport behaviors. 13 Since the gold surface has a work function ͑ϳ5.3 eV͒ higher than that of the CNT ͑ϳ4.8 eV͒, the Fermi level of the gold surface would be closer to the valence edge and the FET device should show a p-type transport behavior.…”

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Pressure-dependent Schottky barrier at the metal-nanotube contact

Park

Kang

Hong

et al. 2005

Applied Physics Letters

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We carry out first-principles density-functional calculations to investigate the electronic structure of the gold-carbon nanotube contact. It is found that a pressure applied on the gold-nanotube contact shifts the Fermi level from the valence edge to the conduction edge of the carbon nanotube. This can explain the n-type transport behavior frequently observed in the nanotube field-effect transistor using the gold as electrodes. An atomistic model is proposed for a possible origin of the pressure when the nanotube is embedded in the gold electrode.

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“…We can speculate that fabrication of metal-CNT-metal devices should be affected mostly by a symmetry variance; therefore we should expect quite homogeneous conductance properties among equivalent (same metal, same size, same helicity) devices. However a strong distance variance should arise when a contact is represented by a metallised atomic force microscope tip used as scanned electrical nanoprobe in conductance measurements [30]. In this case our results indicate that a careful analysis should be performed in order to understand the experimental results.…”

Section: Discussionmentioning

confidence: 98%

Role of contact bonding on electronic transport in metal–carbon nanotube–metal systems

Deretzis

Magna

2006

Nanotechnology

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Abstract:We have investigated the effects of the interfacial bond arrangement on the electronic transport features of metal-nanotube-metal systems. The transport properties of finite, defect-free armchair and zigzag single-walled carbon nanotubes attached to Au(111) metallic contacts have been calculated by means of the non-equilibrium Green functional formalism with the Tight-Binding and the Extended Hückel Hamiltonians. Our calculations show that the electrode material is not the only factor which rules contact transparency. Indeed, for the same electrode, but changing nanotube helicities, we have observed an overall complex behaviour of the transmission spectra due to band mixing and interference. The comparison of the two models shows that the Tight Binding approach fails to give a satisfactory representation of the transmission function when a more accurate description of the C-C and Au-C chemical bonds has to be considered. We have furthermore examined the effect of interface geometry variance on conduction and found that contact-nanotube distance has a significant impact, while contact-nanotube symmetry plays a marginal, yet evident role.

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Electrical Nanoprobing of Semiconducting Carbon Nanotubes Using an Atomic Force Microscope

Cited by 147 publications

References 29 publications

Photocurrent Imaging of p−n Junctions in Ambipolar Carbon Nanotube Transistors

Photocurrent Imaging of p−n Junctions in Ambipolar Carbon Nanotube Transistors

Pressure-dependent Schottky barrier at the metal-nanotube contact

Role of contact bonding on electronic transport in metal–carbon nanotube–metal systems

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