Alloing, B.; Zinoni, C.; Zwiller, V.; Li, L.; Monat, C.; Gobet, M.; Buchs, G.; Fiore, A.; Pelucchi, E.; Kapon, E.

Intratube quantum dots showing particle-in-a-box-like states with level spacings up to 200 meV are realized in metallic single-walled carbon nanotubes by means of low dose medium energy Ar + irradiation. Fourier transform scanning tunneling spectroscopy compared to results of a Fabry-Pérot electron resonator model yields clear signatures for inter-and intra-valley scattering of electrons confined between consecutive irradiation-induced defects (inter-defects distance ≤ 10 nm). Effects arising from lifting the degeneracy of the Dirac cones within the first Brillouin zone are also observed.PACS numbers: 81.07. Ta,73.20.At,68.37.Ef The experimental realization of quantum dots (QDs) [1], sometimes called "artificial atoms", has led to a variety of new concepts in nanotechnology underlying advanced QD-based devices for applications in promising fields like nanoelectronics, nanophotonics and quantum information/computation [2,3,4]. Frequently, for these applications a QD needs to be contacted by source, drain, and gate electrodes. In the field of semiconductor heterostructures the excitation energies of contacted QDs are usually so small that the devices can only be operated at cryogenic temperatures. A promising candidate for room temperature active dots are intra-nanotube QDs formed within a single-walled carbon nanotube (SWNT) by means of two local defects [5]. For defect separations of order 10 nm the dot excitation energies are well above 100 meV and thus large compared with k B T at room temperature. Furthermore, the remaining sections of the SWNT to either side of the confining defects provide natural source and drain electrodes. So far, SWNT-based QD prototypes have been realized by tunneling barriers at metal-nanotube interfaces and/or by gate electrodes [6]. Several authors have analyzed defect-induced standing waves by means of scanning tunneling microscopy (STM) [7,8,9]. However, a detailed description of the scattering dynamics of electrons in and out of the QD is absent. Elaborate studies have only been reported for epitaxial graphene with defects, where an analysis of standing waves in Fourier space has permitted to distinguish between contributions to the wave modulation due to inter-and intra-valley scattering [10]. In this Letter we investigate electron standing waves in intra-tube QDs created in SWNTs irradiated with medium energy Ar + ions. This promising alternative to build intra-tube QDs has been suggested by observations of electronic confinement in metallic SWNTs due to intrinsic defects [11]. We first show that by virtue of this technique it is indeed possible to realize QDs with a level spacing considerably larger than the thermal broadening at room temperature. Then, by means of Fourier-transform scanning tunneling spectroscopy (FTSTS) combined with a Fabry-Pérot electron resonator model we are able to describe the dominant scattering mechanisms and to identify contributions from inter-and intra-valley scattering.Our measurements were performed in a commercial (Omicron), ultrahigh vacuum...

We report on a photodetector in which colloidal quantum-dots directly bridge nanometer-spaced electrodes. Unlike in conventional quantum-dot thin film photodetectors, charge mobility no longer plays a role in our quantum-dot junctions as charge extraction requires only two individual tunnel events. We find an efficient photoconductive gain mechanism with external quantum-efficiencies of 38 electrons-per-photon in combination with response times faster than 300 ns. This compact device-architecture may open up new routes for improved photodetector performance in which efficiency and bandwidth do not go at the cost of one another.

No abstract

We present a detailed comparison between theoretical predictions on electron scattering processes in metallic single-walled carbon nanotubes with defects and experimental data obtained by scanning tunneling spectroscopy of Ar + irradiated nanotubes. To this purpose we first develop a formalism for studying quantum transport properties of defected nanotubes in presence of source and drain contacts and an STM tip. The formalism is based on a field theoretical approach describing lowenergy electrons. We account for the lack of translational invariance induced by defects within the so called extended k ·p approximation. The theoretical model reproduces the features of the particle-in-a-box-like states observed experimentally. Further, the comparison between theoretical and experimental Fourier-transformed local density of state maps yields clear signatures for interand intra-valley electron scattering processes depending on the tube chirality.

No abstract

Local controllable modification of the electronic structure of carbon nanomaterials is important for the development of carbon-based nanoelectronics. By combining density-functional theory simulations with Arion-irradiation experiments and low-temperature scanning tunneling microscopy and spectroscopy ͑STM/STS͒ characterization of the irradiated samples, we study the changes in the electronic structure of single-walled carbon nanotubes due to the impacts of energetic ions. As nearly all irradiation-induced defects look as nondistinctive hillocklike features in the STM images, we compare the experimentally measured STS spectra to the computed local density of states of the most typical defects with an aim to identify the type of defects and assess their abundance and effects on the local electronic structure. We show that individual irradiationinduced defects can give rise to single and multiple peaks in the band gap of the semiconducting nanotubes and that a similar effect can be achieved when several defects are close to each other. We further study the stability of defects and their evolution during STM measurements. Our results not only shed light on the abundance of the irradiation-induced defects in carbon nanotubes and their signatures in STS spectra but also suggest a way the STM can be used for engineering the local electronic structure of defected carbon nanotubes.

The authors report on the generation of localized defects on single-walled carbon nanotubes by means of a hydrogen electron cyclotron resonance plasma. The defects have been investigated using scanning tunneling microscopy (STM) and show an apparent topographic height in the STM of 1–3Å. In the vicinity of defects, characteristic superstructures could be observed and the patterns could be simulated using a simple model based on large momentum scattering of the valence electrons. The combination of low structural damage and high electronic activity opens the possibility to tune the electronic transport properties using such defects.