Paul F. A. Alkemade

High-fidelity projective read-out of a solid-state spin quantum register

Initialization and read-out of coupled quantum systems are essential ingredients for the implementation of quantum algorithms. Single-shot read-out of the state of a multi-quantum-bit (multi-qubit) register would allow direct investigation of quantum correlations (entanglement), and would give access to further key resources such as quantum error correction and deterministic quantum teleportation. Although spins in solids are attractive candidates for scalable quantum information processing, their single-shot detection has been achieved only for isolated qubits. Here we demonstrate the preparation and measurement of a multi-spin quantum register in a low-temperature solid-state system by implementing resonant optical excitation techniques originally developed in atomic physics. We achieve high-fidelity read-out of the electronic spin associated with a single nitrogen–vacancy centre in diamond, and use this read-out to project up to three nearby nuclear spin qubits onto a well-defined state. Conversely, we can distinguish the state of the nuclear spins in a single shot by mapping it onto, and subsequently measuring, the electronic spin. Finally, we show compatibility with qubit control: we demonstrate initialization, coherent manipulation and single-shot read-out in a single experiment on a two-qubit register, using techniques suitable for extension to larger registers. These results pave the way for a test of Bell’s inequalities on solid-state spins and the implementation of measurement-based quantum information protocols.

Sub-10-nm nanolithography with a scanning helium beam

Scanning helium ion beam lithography is presented as a promising pattern definition technique for dense sub-10-nm structures. The powerful performance in terms of high resolution, high sensitivity, and a low proximity effect is demonstrated in a hydrogen silsesquioxane resist.

THE COMPLEX FORMATION OF RIPPLES DURING DEPTH PROFILING OF SI WITH LOW ENERGY, GRAZING OXYGEN BEAMS

Surface roughening of Si under low-energy (0.5–2.0 keV) O2+ bombardment at incidence angles between 45° and 80° has been studied. Surface roughening occurred already at an erosion depth of only a few tens of nanometers. It was found that there were distinctly two angular ranges for sub-keV beams where roughening was strong, and two ranges where it was insignificant. The transition between the different ranges can be very sharp. These observations cannot be explained by the current models for surface roughening. Instead, it is believed that it is the combined sputtering rate dependence on both the surface topography and the oxygen content that determines the occurrence of roughening.

Nanofabrication with a helium ion microscope

The recently introduced helium ion microscope (HIM) is capable of imaging and fabrication of nanostructures thanks to its sub-nanometer sized ion probe. The unique interaction of the helium ions with the sample material provides very localized secondary electron emission, thus providing a valuable signal for high-resolution imaging as well as a mechanism for very precise nanofabrication. The low proximity effects, due to the low yield of backscattered ions and the confinement of the forward scattered ions into a narrow cone, enable patterning of ultra-dense sub-10 nm structures. This paper presents various nanofabrication results obtained with direct-write, with scanning helium ion beam lithography, and with helium ion beam induced deposition.

Beam induced deposition of platinum using a helium ion microscope

Helium ion microscopy is now a demonstrated practical technology that possesses the resolution and beam currents necessary to perform nanofabrication tasks, such as circuit edit applications. Due to helium’s electrical properties and sample interaction characteristics relative to gallium, it is likely that the properties and deposition characteristics of beam induced deposited films will be different than those produced using gallium focused ion beam technology. However, there is at this date very little literature discussing the use of helium beams for beam induced chemistry or characterization of the resulting films. In this article, the authors present initial results regarding the deposition of platinum using a helium ion microscope and a gaseous organometallic precursor. Within this work a Carl Zeiss ORION™ helium ion microscope was used along with an OmniGIS unit to deposit platinum while exploring a variety of controllable parameters such as beam current, beam overlap, and size of deposition.

Polarization tomography of metallic nanohole arrays.

We report polarization tomography experiments on metallic nanohole arrays with square and hexagonal symmetry. As a main result we find that a fully polarized input beam is partly depolarized after transmission through a nanohole array. This loss of polarization coherence is found to be anisotropic; i.e., it depends on the polarization state of the input beam. The depolarization is ascribed to a combination of two factors: (i) the nonlocal response of the array as a result of surface-plasmon propagation and (ii) the non-plane-wave nature of a practical input beam.

Nanopillar growth by focused helium ion-beam-induced deposition

A 25 keV focused helium ion beam has been used to grow PtC nanopillars on a silicon substrate by beam-induced decomposition of a (CH(3))(3)Pt(C(P)CH(3)) precursor gas. The ion beam diameter was about 1 nm. The observed relatively high growth rates suggest that electronic excitation is the dominant mechanism in helium ion-beam-induced deposition. Pillars grown at low beam currents are narrow and have sharp tips. For a constant dose, the pillar height decreases with increasing current, pointing to depletion of precursor molecules at the beam impact site. Furthermore, the diameter increases rapidly and the total pillar volume decreases slowly with increasing current. Monte Carlo simulations have been performed with realistic values for the fundamental deposition processes. The simulation results are in good agreement with experimental observations. In particular, they reproduce the current dependences of the vertical and lateral growth rates and of the volumetric deposition efficiency. Furthermore, the simulations reveal that the vertical pillar growth is due to type-1 secondary electrons and primary ions, while the lateral outgrowth is due to type-2 secondary electrons and scattered ions.

Location-Control of Large Si Grains by Dual-Beam Excimer-Laser and Thick Oxide Portion

An array of large Si grains was placed at a predetermined position by dual excimer-laser irradiation of a multi-layer structure of silicon (Si), silicon dioxide (SiO2) with an array of bumps and metal on a glass substrate. We have investigated the effects of irradiating energy density and the topology of the structure on the grain size and crystallographic structure by scanning electron microscopy (SEM) and electron back-scattering pattern (EBSP) analysis. In the low-energy-density regime, numerous small grains and petal shaped grains formed on top of the SiO2 bumps. The number of small grains on the bumps decreased with increasing irradiating energy density. At sufficiently high energy densities, one single Si grain as large as 3.5 µm was positioned at the center of the bumps. Although most of the area of the large Si grain has a single crystallographic orientation, twins and low-angle grain boundaries are often formed at the periphery of the grain. There was no preferred crystallographic orientation in the center of the location-controlled Si grain. Numerical analysis of the temperature profile showed that a temperature drop occurs at the center of the bump, during and immediately after laser irradiation. The diameter of the location-controlled Si grain increased with total thickness of the intermediate SiO2 layer, and took the maximum value of 6.2 µm.

Imaging and nanofabrication with the helium ion microscope of the Van Leeuwenhoek Laboratory in Delft

Although helium ion microscopy (HIM) was introduced only a few years ago, many new application fields are emerging. The connecting factor between these novel applications is the unique interaction of the primary helium ion beam with the sample material at and just below its surface. In particular, the HIM secondary electron signal stems from an area that is extremely well localized around the point of incidence of the primary beam. This makes the HIM well suited for both high-resolution imaging and high-resolution nanofabrication. Another advantage in nanofabrication is the low ion backscattering fraction, which leads to a weak proximity effect. The subnanometer probe size and the unique beam-materials interactions have opened new areas of research. This review presents a selection of studies conducted on a single instrument. The selection encompasses applications ranging from imaging to nanofabrication and from fundamental academic research to applied industrial developments.

High Depth Resolution SIMS Analysis with Low‐energy Grazing O2+ Beams

By the use of a deceleration electrode in the primary beam line of a magnetic sector SIMS instrument, an O 2 + primary beam of variable energy and angle has been produced. The SIMS measurements of ultrathin Ge and B layers in Si were performed with low-energy (0.7-2 keV) and grazingly incident (50-75°) O 2 + ions. Consequently, ultrahigh depth resolution with characteristic exponential leading and decay lengths of 0.25 and 0.9 nm, respectively, and 1.6 nm full width at half-maximum for a Ge delta layer was obtained. A depth profile analysis without any appreciable loss in depth resolution was achieved down to a depth of 1 μm with a 1 keV 60° O 2 + beam. Furthermore, good dynamic range, acceptable detection limit and moderate sputtering rates were achieved in this ultrahigh depth resolution mode.