A. Persaud

Solid state quantum computer development in silicon with single ion implantation

Spawned by the finding of efficient quantum algorithms, the development of a scalable quantum computer has emerged as a premiere challenge for nanoscience and nanotechnology in the last years. Spins of electrons and nuclei in 31P atoms embedded in silicon are promising quantum bit (qubit) candidates. In this article we describe single atom doping strategies and the status of our development of single atom qubit arrays integrated with control gates and readout structures in a “top down” approach. We discuss requirements for 31P qubit array formation by single ion implantation, and integration with semiconductor processing.

Formation of a few nanometer wide holes in membranes with a dual beam focused ion beam system

When nanometer-scale holes (diameters of 50 to a few hundred nm) are imaged in a scanning electron microscope (SEM) at pressures in the 10−5 to 10−6 Torr range, hydrocarbon deposits build up and result in the closing of holes within minutes of imaging. Additionally, electron or ion beam assisted deposition of material from a gas source allows the closing of holes with films of platinum or tetraethylorthosilicate oxide. In an instrument equipped both with a focused ion beam, and a SEM, holes can be formed and then covered with a thin film to form nanopores with controlled openings, ranging down to only a few nanometers, well below resolution limits of primary beams.

Single atom doping for quantum device development in diamond and silicon

The ability to inject dopant atoms with high spatial resolution, flexibility in dopant species, and high single ion detection fidelity opens opportunities for the study of dopant fluctuation effects and the development of devices in which function is based on the manipulation of quantum states in single atoms, such as proposed quantum computers. The authors describe a single atom injector, in which the imaging and alignment capabilities of a scanning force microscope (SFM) are integrated with ion beams from a series of ion sources and with sensitive detection of current transients induced by incident ions. Ion beams are collimated by a small hole in the SFM tip and current changes induced by single ion impacts in transistor channels enable reliable detection of single ion hits. They discuss resolution limiting factors in ion placement and processing and paths to single atom (and color center) array formation for systematic testing of quantum computer architectures in silicon and diamond.

Single ion implantation for solid state quantum computer development

Several solid state quantum computer schemes are based on the manipulation of electron and/or nuclear spins of single 31P atoms in a solid matrix. The fabrication of qubit arrays requires the placement of individual atoms with nanometer precision and high efficiency. We describe the status of our development of a low energy, single ion implantation scheme for 31Pq+ ions. High ion charge states enable registration of single ion impacts with unity efficiency through the detection of secondary electrons. Imaging contrast in secondary electron emission allows alignment of the implantation and integration with consecutive lithography steps. Critical issues of process integration and resolution limiting factors are discussed.

Extraction of highly charged ions from the electron beam ion trap at LBNL for applications in surface analysis and materials science

We describe results from highly ion extraction experiments at the Electron Beam Ion Trap (EBIT) facility which is now operated at Lawrence Berkeley National Laboratory after transfer from Lawrence Livermore National Laboratory. Requirements on ion source performance for the application of highly charged ions (e. g. Xe{sup 44+}) in surface analysis and materials science are discussed.

Development of a compact neutron source based on field ionization processes

We report on the use of nano-emitters, for example carbon nano-tubes(CNTs), to ionize deuterium atoms and the creation of neutrons in a deuterium-deuterium reaction in a pre-loaded target. Acceleration voltages in the range of 50–80kV are used and the creation of positive and negative deuterium ions is investigated. We discuss optimization of emitters and show preliminary data of first neutron production.

A compact neutron generator using a field ionization source

Field ionization as a means to create ions for compact and rugged neutron sources is pursued. Arrays of carbon nano-fibers promise the high field-enhancement factors required for efficient field ionization. We report on the fabrication of arrays of field emitters with a density up to 10(6) tips∕cm(2) and measure their performance characteristics using electron field emission. The critical issue of uniformity is discussed, as are efforts towards coating the nano-fibers to enhance their lifetime and surface properties.

Novel methods for improvement of a Penning ion source for neutron generator applications.

Penning ion source performance for neutron generator applications is characterized by the atomic ion fraction and beam current density, providing two paths by which source performance can be improved for increased neutron yields. We have fabricated a Penning ion source to investigate novel methods for improving source performance, including optimization of wall materials and electrode geometry, advanced magnetic confinement, and integration of field emitter arrays for electron injection. Effects of several electrode geometries on discharge characteristics and extracted ion current were studied. Additional magnetic confinement resulted in a factor of two increase in beam current density. First results indicate unchanged proton fraction and increased beam current density due to electron injection from carbon nanofiber arrays.

Ion Implantation with Scanning Probe Alignment

We describe a scanning probe instrument which integrates ion beams with the imaging and alignment function of a piezoresistive scanning probe in high vacuum. The beam passes through several apertures and is finally collimated by a hole in the cantilever of the scanning probe. The ion beam spot size is limited by the size of the last aperture. Highly charged ions are used to show hits of single ions in resist, and we discuss the issues for implantation of single ions.

Short intense ion pulses for materials and warm dense matter research

We have commenced experiments with intense short pulses of ion beams on the Neutralized Drift Compression Experiment-II at Lawrence Berkeley National Laboratory, by generating beam spots size with radius r<1 mm within 2 ns FWHM and approximately 1010 ions/pulse. To enable the short pulse durations and mm-scale focal spot radii, the 1.2 MeV Li+ ion beam is neutralized in a 1.6-meter drift compression section located after the last accelerator magnet. An 8-Tesla short focal length solenoid compresses the beam in the presence of the large volume plasma near the end of this section before the target. The scientific topics to be explored are warm dense matter, the dynamics of radiation damage in materials, and intense beam and beam-plasma physics including selected topics of relevance to the development of heavy-ion drivers for inertial fusion energy. Finally, we describe the accelerator commissioning and time-resolved ionoluminescence measurements of yttrium aluminum perovskite using the fully integrated accelerator and neutralized drift compression components.