-
Journal of Nanomaterials 05/2012; · 1.38 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The electric field enhancement associated with detailed structure within novel optical antenna nanostructures is modeled using the surface integral equation technique in the context of surface-enhanced Raman scattering (SERS). The antennae comprise random arrays of vertically aligned, multiwalled carbon nanotubes dressed with highly granular Ag. Different types of "hot-spot" underpinning the SERS are identified, but contrasting characteristics are revealed. Those at the outer edges of the Ag grains are antenna driven with field enhancement amplified in antenna antinodes while intergrain hotspots are largely independent of antenna activity. Hot-spots between the tops of antennae leaning towards each other also appear to benefit from antenna amplification.
Nano Letters 02/2011; 11(2):365-71. · 13.20 Impact Factor
-
P. Legagneux,
N. Le Sech,
P. Guiset,
L. Gangloff,
C. Cojocaru,
J.P. Schnell,
D. Pribat, K.B.K. Teo,
J. Robertson,
W.I. Milne,
F. Andre,
Y. Rozier,
D. Dieumegard
[show abstract]
[hide abstract]
ABSTRACT: We have studied two different kinds of electron tubes using a cold field emission cathode as the electron source. This cathode is an array of vertically aligned multiwall carbon nanotubes. The first device is a triode. With this device, we demonstrated the modulation at 32 GHZ of a 1.4 A/cm2 peak current density with a 82% modulation ratio. The second device is a traveling wave tube. For this device, the objective is to test a cathode delivering a 2 A/cm<sup>2</sup> electron beam.
Vacuum Electronics Conference, 2009. IVEC '09. IEEE International; 05/2009
-
[show abstract]
[hide abstract]
ABSTRACT: A fabrication process for monolithic integration of vertically aligned carbon nanotubes in electrically insulated microfluidic channels is presented. A 150 nm thick amorphous silicon layer could be used both for anodic bonding of a glass lid to hermetically seal the microfluidic glass channels and for de-charging of the wafer during plasma enhanced chemical vapor deposition of the carbon nanotubes. The possibility of operating the device with electroosmotic flow was shown by performing standard electrophoretic separations of 50 microM fluorescein and 50 microM 5-carboxyfluorescein in a 25 mm long column containing vertical aligned carbon nanotubes. This is the first demonstration of electroosmotic pumping and electrokinetic separations in microfluidic channels with a monolithically integrated carbon nanotube forest.
Nanotechnology 04/2009; 20(9):095503. · 3.98 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper describes the growth of Carbon Nanotubes (CNTs) both aligned and non-aligned on fully processed CMOS substrates containing high temperature tungsten metallization. While the growth method has been demonstrated in fabricating CNT gas sensitive layers for high temperatures SOI CMOS sensors, it can be employed in a variety of applications which require the use of CNTs or other nanomaterials with CMOS electronics. In our experiments we have grown CNTs both on SOI CMOS substrates and SOI CMOS microhotplates (suspended on membranes formed by post-CMOS deep RIE etching). The fully processed SOI substrates contain CMOS devices and circuits and additionally, some wafers contained high current LDMOSFETs and bipolar structures such as Lateral Insulated Gate Bipolar Transistors. All these devices were used as test structures to investigate the effect of additional post-CMOS processing such as CNT growth, membrane formation, high temperature annealing, etc. Electrical characterisation of the devices with CNTs were performed along with SEM and Raman spectroscopy. The CNTs were grown both at low and high temperatures, the former being compatible with Aluminium metallization while the latter being possible through the use of the high temperature CMOS metallization (Tungsten). In both cases we have found that there is no change in the electrical behaviour of the CMOS devices, circuits or the high current devices. A slight degradation of the thermal performance of the CMOS microhotplates was observed due to the extra heat dissipation path created by the CNT layers, but this is expected as CNTs exhibit a high thermal conductance. In addition we also observed that in the case of high temperature CNT growth a slight degradation in the manufacturing yield was observed. This is especially the case where large area membranes with a diameter in excess of 500 microns are used.
Journal of Nanoscience and Nanotechnology 12/2008; 8(11):5667-72. · 1.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, the growth and characterisation of both single and multi wall CNTs is described and a realistic appraisal of the future of CNTs in the electronics field will be provided. Although they are very unlikely, in the author's opinion, to take over from silicon for use in the active devices such as transistors and diodes etc. in logic circuits their use in vias and interconnects in next generation integrated circuits is considered as being entirely feasible as is their use in transparent conducting contacts and sensors, thermal interface materials and solder joints.
Interconnect Technology Conference, 2008. IITC 2008. International; 07/2008
-
[show abstract]
[hide abstract]
ABSTRACT: The direct deposition of carbon nanotubes on CMOS microhotplates is demonstrated in this paper. Tungsten microhotplates, fabricated on thin SOI membranes aside CMOS control circuitry, are used to locally grow carbon nanotubes by chemical vapour deposition. Unlike bulk heating of the entire chip, which could cause degradation to CMOS devices and interconnects due to high growth temperatures in excess of 500 °C, this novel technique allows carbon nanotubes to be grown on-chip in localized regions. The microfabricated heaters are thermally isolated from the rest of the CMOS chip as they are on the membranes. This allows carbon nanotubes to be grown alongside CMOS circuitry on the same wafer without any external heating, thus enabling new applications (e.g. smart gas sensing) where the integration of CMOS and carbon nanotubes is required.
Nanotechnology 01/2008; 19(2):025607. · 3.98 Impact Factor
-
Advanced Materials 01/2008; 20(2):363 - 366. · 13.88 Impact Factor
-
Journal of Nanoscience and Nanotechnology 01/2008; 8:1-6. · 1.56 Impact Factor
-
Nanotechnology 12/2007; 18(49):495606. · 3.98 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper we demonstrate how secondary ion mass spectrometry (SIMS) can be applied to ZnO nanowire structures for gold catalyst residue determination. Gold plays a significant role in determining the structural properties of such nanowires, with the location of the gold after growth being a strong indicator of the growth mechanism. For the material investigated here, we find that the gold remains at the substrate–nanowire interface. This was not anticipated as the usual growth mechanism associated with catalyst growth is of a vapour–liquid–solid (VLS) type. The results presented here favour a vapour–solid (VS) growth mechanism instead. Copyright © 2007 John Wiley & Sons, Ltd.
Surface and Interface Analysis 10/2007; 39(11):898 - 901. · 1.18 Impact Factor
-
E. Minoux,
L. Hudanski, K.B.K. Teo,
O. Groening,
F. Peauger,
D. Dieumegard,
J.-P. Schnell,
L. Gangloff,
G.A.J. Amaratunga,
W.I. Milne,
J. Robertson,
P. Legagneux
[show abstract]
[hide abstract]
ABSTRACT: Cold cathodes based on carbon nanotubes allow to produce a modulated electron beam. Using an array of vertically aligned CNs that exhibit an aspect ratio of about 200, we demonstrated the modulation of a high current density beam (~ 1 A/cm<sup>2</sup> at 1.5 and 32 GHz frequencies. Such CN cathodes are very promising for their use in a new generation of compact, highly efficient and low cost amplifiers that operate between 10 and 100 GHz.
Nanotechnology, 2007. IEEE-NANO 2007. 7th IEEE Conference on; 09/2007
-
[show abstract]
[hide abstract]
ABSTRACT: We have demonstrated for the first time a beam modulation at 1.5 GHz (Teo, et. al., 2005). However, the use of resonant cavities leads to narrow bandwidth operation. To overcome this limitation we propose an optical control of the electron beam modulation thanks to a novel photocathode, which integrates CNTs with photodiodes.
Vacuum Nanoelectronics Conference, 2007. IVNC. IEEE 20th International; 08/2007
-
[show abstract]
[hide abstract]
ABSTRACT: The effect of temperature on the growth of single-walled carbon nanotubes (SWCNTs) was investigated over the range of 725–900 °C. A cold-wall reactor consisting of a heated stage (on which the substrate for SWCNT growth (Al/Fe/Mo) was placed) and a showerhead (from which C2H2 was introduced vertically into the reactor) was used for the growth. The heating was found to play two roles: (1) it generated complex hydrocarbon radicals during the growth process, as well as (2) promoting catalytic nanoparticles on the substrate during the annealing process. The optimum temperature for the highest SWCNT yield was found to be ~860 °C. For the first time, in situ mass spectroscopy was used to identify the growth precursors generated from thermal pyrolysis of C2H2 within this temperature range. The peak of the radicals found (C6H9, C5H9 and C6H13) and the highest catalyst support particle density (Fe catalyst supported on AlxOy) was correlated to the maximum yield of single walled carbon nanotubes at the optimum growth temperature of ~860 °C. Bottom gate SWCNT-FETs (single-walled carbon nanotube based field effect transistors) were fabricated showing a high transconductance of ~0.12 µS and on/off ratio of ~105 which are both comparable to other state-of-the-art SWCNT-FET.
Nanotechnology 04/2007; 18(18):185709. · 3.98 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents a number of factors which have been found to be important to the growth of carbon nanotubes and nanofibres by plasma enhanced chemical vapour deposition. The effect of the electric field in a plasma discharge on nanotube growth is investigated and shown to be important in achieving nanotube alignment. The use of a plasma discharge also enables deposition to take place at lower temperatures, facilitating the use of substrates which would otherwise be damaged. The effect of varying the ratio of carbon feedstock gas to etchant gas is investigated and the ratio is shown to be important for controlling the shape of deposited nanostructures. The effects of varying plasma power are investigated, showing that greater plasma power results in a lower growth rate. Higher levels of plasma power are also shown to cause the sidewalls of deposited carbon nanotubes to be etched. Finally, the growth rate of carbon nanotubes and nanofibres is shown to depend upon the strength of the local electric field. It is proposed that a higher field causes greater ionization within the plasma, which results in a higher growth rate. This is borne out by comparing simulation results with experimental observations.
Journal of Physics D Applied Physics 04/2007; 40(8):2285. · 2.54 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The controllable growth of vertically aligned ZnO nanowires using a simple vapour deposition method system is reported. The growth properties are studied as a function of the thickness of the Au catalyst layer, total pressure, deposition temperature and oxygen partial pressure. The experiments indicate the existence of five main zones of growth. The zone in which the aligned wires grow varies according to the pressure, temperature and oxygen partial pressure. A specific level of low supersaturation of Zn and oxygen vapour are both necessary to ensure the correct rate of growth, which then leads to having thin and densely aligned wires. The growth kinetics are discussed in terms of the interdependent variables. It was found that the diameter and density of the nanowires is controlled mostly by the growth temperature and pressure. The zone with the most aligned nanowires with the highest aspect ratio was found to be at 5 mbar in a temperature range of 860–800 °C with a flow of 27 sccm of a N2/O2 mixture.
Nanotechnology 09/2006; 17(19):4811. · 3.98 Impact Factor
-
W. I. Milne, K. B. K. Teo,
M. Mann,
I. Y. Y. Bu,
G. A. J. Amaratunga,
N. De Jonge,
M. Allioux,
J. T. Oostveen,
P. Legagneux,
E. Minoux,
L. Gangloff,
L. Hudanski,
J.-P. Schnell,
L. D. Dieumegard,
F. Peauger,
T. Wells,
M. El-Gomati
[show abstract]
[hide abstract]
ABSTRACT: Carbon nanotubes (CNTs) are a unique form of carbon filament/fiber in which the graphene walls roll up to form tubes. They can exhibit either metallic-like or semiconductor-like properties. With the graphene walls parallel to the filament axis, nanotubes (single wall metallic-type or multi-wall) exhibit high electrical conductivity at room temperature. This high electrical conductivity allied to their remarkable thermal stability has made CNTs one of the most intensely studied material systems for field emission (FE) applications. In this paper we will describe the growth of multiwall CNTs and their application in a range of field emission based systems including their use in SEM sources, emitters for use in microwave amplifiers and as emitters in field emission based displays (FEDs). (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Physica Status Solidi (A) Applications and Materials 04/2006; 203(6):1058 - 1063. · 1.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The subthreshold slope, transconductance, threshold voltage, and hysteresis of a carbon nanotube field-effect transistor (CNT FET) were examined as its configuration was changed from bottom-gate exposed channel, bottom-gate covered channel to top-gate FET. An individual single wall CNT was grown by chemical vapor deposition and its gate configuration was changed while determining its transistor characteristics to ensure that the measurements were not a function of different chirality or diameter CNTs. The bottom-gate exposed CNT FET utilized 900 nm SiO2 as the gate insulator. This CNT FET was then covered with TiO2 to form the bottom-gate covered channel CNT FET. Finally, the top-gate CNT FET was fabricated and the device utilized TiO2 (κ ∼ 80, equivalent oxide thickness = 0.25 nm) as the gate insulator. Of the three configurations investigated, the top-gate device exhibited best subthreshold slope (67–70 mV/dec), highest transconductance (1.3 μS), and negligible hysteresis in terms of threshold voltage shift.
Applied Physics Letters 03/2006; 88(11):113507-113507-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate the fabrication and operation of a carbon nanotube (CNT) based Schottky diode by using a Pd contact (high-work-function metal) and an Al contact (low-work-function metal) at the two ends of a single-wall CNT. We show that it is possible to tune the rectification current-voltage (I-V) characteristics of the CNT through the use of a back gate. In contrast to standard back gate field-effect transistors (FET) using same-metal source drain contacts, the asymmetrically contacted CNT operates as a directionally dependent CNT FET when gated. While measuring at source-drain reverse bias, the device displays semiconducting characteristics whereas at forward bias, the device is nonsemiconducting.
Applied Physics Letters 12/2005; 87(25):253116-253116-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Here we report the reversible change in the nonlinear conductance of a multiwall carbon nanotube (MWNT) when it is bent longitudinally. As the nanotube is compressed and bent, its resistance decreases dramatically. This behavior is fully recoverable. The observed drop in resistance during bending must be the result of increasing number of conduction channels in the nanotube and parallel transport through them. Using this concept of parallel transport, we show that it is indeed possible to electrically model the behavior of the MWNT under compression. The reversible electrical characteristics of a MWNT under bending opens new possibilities for these structures to be applied as nanoscale displacement sensors.
Applied Physics Letters 11/2005; 87(22):223103-223103-3. · 3.84 Impact Factor
