C. D. Weis

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.

Detection of low energy single ion impacts in micron scale transistors at room temperature

We report the detection of single ion impacts through monitoring of changes in the source-drain currents of field effect transistors at room temperature. Implant apertures are formed in the interlayer dielectrics and gate electrodes of planar, microscale transistors by electron beam assisted etching. Device currents increase due to the generation of positively charged defects in gate oxides when ions (Sb12+,14+121 and Xe6+; 50–70keV) impinge into channel regions. Implant damage is repaired by rapid thermal annealing, enabling iterative cycles of device doping and electrical characterization for the development of single atom devices and studies of dopant fluctuation effects.

Electrical activation and electron spin resonance measurements of implanted bismuth in isotopically enriched silicon-28

We have performed continuous wave and pulsed electron spin resonance measurements of implanted bismuth donors in isotopically enriched silicon-28. Donors are electrically activated via thermal annealing with minimal diffusion. Damage from bismuth ion implantation is repaired during thermal annealing as evidenced by narrow spin resonance linewidths (Bpp=12μT) and long spin coherence times (T2=0.7 ms, at temperature T=8 K). The results qualify ion implanted bismuth as a promising candidate for spin qubit integration in silicon.

In situ optimization of co-implantation and substrate temperature conditions for nitrogen-vacancy center formation in single-crystal diamonds

In this paper, we present first results of in situ characterization of nitrogen vacancy (NV)-center formation in single-crystal diamonds after implantation of low-energy nitrogen ions (7.7u2009keV), co-implantation of hydrogen, helium and carbon ions and in situ annealing. Diamond samples were implanted either at room temperature or at 780u2009°C. We found that dynamic annealing during co-implantation enhances NV-center formation by up to 25%.

Possible Diamond-Like Nanoscale Structures Induced by Slow Highly-Charged Ions on Graphite (HOPG)

The interaction between slow highly-charged ions (SHCI) of different charge states from an electron-beam ion trap and highly oriented pyrolytic graphite (HOPG) surfaces is studied in terms of modification of electronic states at single-ion impact nanosizeareas. Results are presented from AFM/STM analysis of the induced-surface topological features combined with Raman spectroscopy. I-V characteristics for a number of different impact regions were measured with STM and the results argue for possible formation of diamond-like nanoscale structures at the impact sites.

Spin coherence and 14N ESEEM effects of nitrogen-vacancy centers in diamond with X-band pulsed ESR

Abstract Pulsed ESR experiments are reported for ensembles of negatively-charged nitrogen-vacancy centers (NV xa0− ) in diamonds at X-band magnetic fields (280–400xa0mT) and low temperatures (2–70xa0K). The NV xa0− centers in synthetic type IIa diamonds (nitrogen impurity concentration 13 cm xa0−3 to 4 ⋅ 10 14 cm xa0−3 by high-energy electron irradiation and subsequent annealing. We find that a proper post-radiation anneal (1000°C for 60xa0min) is critically important to repair the radiation damage and to recover long electron spin coherence times for NV xa0− s. After the annealing, spin coherence times of T 2 xa0=xa00.74ms at 5xa0K are achieved, being only limited by 13 C nuclear spectral diffusion in natural abundance diamonds. By measuring the temperature dependence of T 2 in the under-annealed diamonds (900°C) we directly extract the density (10 14xa0−16 cm xa0−3 ) and activation energy (2.5xa0meV) of unannealed defects responsible for the faster NV xa0− decoherence. At X-band magnetic fields, strong electron spin echo envelope modulation (ESEEM) is observed originating from the central 14 N nucleus, and we extract accurate 14 N nuclear hypefine and quadrupole tensors. In addition, the ESEEM effects from two proximal 13 C sites (second-nearest neighbor and fourth-nearest neighbor) are resolved and the respective 13 C hyperfine coupling constants are extracted.