Publications (93) View all
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Article: Controlled deterministic implantation by nanostencil lithography at the limit of ion-aperture straggling.
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ABSTRACT: Solid state electronic devices fabricated in silicon employ many ion implantation steps in their fabrication. In nanoscale devices deterministic implants of dopant atoms with high spatial precision will be needed to overcome problems with statistical variations in device characteristics and to open new functionalities based on controlled quantum states of single atoms. However, to deterministically place a dopant atom with the required precision is a significant technological challenge. Here we address this challenge with a strategy based on stepped nanostencil lithography for the construction of arrays of single implanted atoms. We address the limit on spatial precision imposed by ion straggling in the nanostencil-fabricated with the readily available focused ion beam milling technique followed by Pt deposition. Two nanostencils have been fabricated; a 60 nm wide aperture in a 3 μm thick Si cantilever and a 30 nm wide aperture in a 200 nm thick Si3N4 membrane. The 30 nm wide aperture demonstrates the fabricating process for sub-50 nm apertures while the 60 nm aperture was characterized with 500 keV He(+) ion forward scattering to measure the effect of ion straggling in the collimator and deduce a model for its internal structure using the GEANT4 ion transport code. This model is then applied to simulate collimation of a 14 keV P(+) ion beam in a 200 nm thick Si3N4 membrane nanostencil suitable for the implantation of donors in silicon. We simulate collimating apertures with widths in the range of 10-50 nm because we expect the onset of J-coupling in a device with 30 nm donor spacing. We find that straggling in the nanostencil produces mis-located implanted ions with a probability between 0.001 and 0.08 depending on the internal collimator profile and the alignment with the beam direction. This result is favourable for the rapid prototyping of a proof-of-principle device containing multiple deterministically implanted dopants.Nanotechnology 03/2013; 24(14):145304. · 3.98 Impact Factor -
Article: Charge sharing in multi-electrode devices for deterministic doping studied by IBIC
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ABSTRACT: Following a single ion strike in a semiconductor device the induced charge distribution changes rapidly with time and space. This phenomenon has important applications to the sensing of ionizing radiation with applications as diverse as deterministic doping in semiconductor devices to radiation dosimetry. We have developed a new method for the investigation of this phenomenon by using a nuclear microprobe and the technique of Ion Beam Induced Charge (IBIC) applied to a specially configured sub-100 mu m scale silicon device fitted with two independent surface electrodes coupled to independent data acquisition systems. The separation between the electrodes is comparable to the range of the 2 Mev He ions used in our experiments. This system allows us to integrate the total charge induced in the device by summing the signals from the independent electrodes and to measure the sharing of charge between the electrodes as a function of the ion strike location as a nuclear microprobe beam is scanned over the sensitive region of the device. It was found that for a given ion strike location the charge sharing between the electrodes allowed the beam-strike location to be determined to higher precision than the probe resolution. This result has potential application to the development of a deterministic doping technique where counted ion implantation is used to fabricate devices that exploit the quantum mechanical attributes of the implanted ions.Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 10/2011; 269(20):2336. · 1.21 Impact Factor -
Article: Surface damage on diamond membranes fabricated by ion implantation and lift-off
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ABSTRACT: Thin membranes with excellent optical properties are essential elements in diamond based photonic systems. Due to the chemical inertness of diamond, ion beam processing must be employed to carve photonic structures. One method to realize such membranes is ion-implantation graphitization followed by chemical removal of the sacrificial graphite. The interface revealed when the sacrificial layer is removed has interesting properties. To investigate this interface, we employed the surface sensitive technique of grazing angle channeled Rutherford backscattering spectroscopy. Even after high temperature annealing and chemical etching a thin layer of damaged diamond remains, however, it is removed by hydrogen plasma exposure.Applied Physics Letters 06/2011; 98(23):231904-231904-3. · 3.84 Impact Factor -
Article: Drain current modulation in a nanoscale field-effect-transistor channel by single dopant implantation
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ABSTRACT: We demonstrate single dopant implantation into the channel of a silicon nanoscale metal-oxide-semiconductor field-effect-transistor. This is achieved by monitoring the drain current modulation during ion irradiation. Deterministic doping is crucial for overcoming dopant number variability in present nanoscale devices and for exploiting single atom degrees of freedom. The two main ion stopping processes that induce drain current modulation are examined. We employ 500~keV He ions, in which electronic stopping is dominant, leading to discrete increases in drain current and 14~keV P dopants for which nuclear stopping is dominant leading to discrete decreases in drain current. Comment: 13 pages, 3 figures, 1 table, accepted for Applied Physics Letters07/2010; -
Article: Microstructure evolution in carbon-ion implanted sapphire
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ABSTRACT: Carbon ions of MeV energy were implanted into sapphire to fluences of 1×10<sup>17</sup> or 2×10<sup>17</sup> cm <sup>-2</sup> and thermally annealed in forming gas (4% H in Ar) for 1 h . Secondary ion mass spectroscopy results obtained from the lower dose implant showed retention of implanted carbon and accumulation of H near the end of range in the C implanted and annealed sample. Three distinct regions were identified by transmission electron microscopy of the implanted region in the higher dose implant. First, in the near surface region, was a low damage region ( L <sub>1</sub>) composed of crystalline sapphire and a high density of plateletlike defects. Underneath this was a thin, highly damaged and amorphized region ( L <sub>2</sub>) near the end of range in which a mixture of i-carbon and nanodiamond phases are present. Finally, there was a pristine, undamaged sapphire region ( L <sub>3</sub>) beyond the end of range. In the annealed sample some evidence of the presence of diamond nanoclusters was found deep within the implanted layer near the projected range of the C ions. These results are compared with our previous work on carbon implanted quartz in which nanodiamond phases were formed only a few tens of nanometers from the surface, a considerable distance from the projected range of the ions, suggesting that significant out diffusion of the implanted carbon had occurred.Journal of Applied Physics 02/2010; · 2.17 Impact Factor
