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Rutherford Backscattering Spectrometry (RBS) is a powerful ion beam analysis technique in frequent use within materials science. The recent emergence of targets incorporating complex features such as ultra-scaled diffusion barriers and isotopically-enriched films has started to push the limits of the technique, necessitating the expanded use of systems with a higher energy resolution. The increased cost and complexity of these systems based on already well-established schemes may present a barrier to their more widespread adoption. Here, we present an RBS detection system specifically designed for simple integration into existing nuclear probe infrastructure, but with a considerably higher energy resolution than a standard passivated planar detector. We employ a modified silicon p–i–n photodiode integrated within an optimised in-vacuum preamplifier to achieve a relative energy resolution of 3 × 10 −3 with 2.2 MeV He + ions. In a glancing angle geometry, this corresponds to a depth resolution of ∼ 1.5 nm and a mass resolution of 1 u from light elements up to Cu. We demonstrate the use of this detector to measure the thermal diffusion of near-surface As implants in a Si substrate, important for the formation of ultra-shallow junctions; and the residual 29Si concentration in an isotopically enriched 28Si specimen, a promising platform for quantum computation.

Nuclear spins were among the first physical platforms to be considered for quantum information processing

In Harbin, the 300 MeV proton microprobe system with long-length quadrupole lenses, as a component of the Space Environment Simulation Research Infrastructure (SESRI), is under development driven by many applications in space science and proton therapy. Significant challenges have previously been addressed including minimization of ion scattering from collimators and the development of promising focusing systems compatible with the large beam magnetic rigidity. Here the intrinsic aberrations contributed by the fringe field regions of quadrupole lenses in the probe forming lens system are investigated with respect to the model used for the fringe field profile. The investigation compares the rectangular model, commonly used with the matrix method, and a more sophisticated model employing a multiphysics code for the full field profile used with a numerical raytracing method. For computational and constructional efficiency the proposed triplet system of long-length quadruple lenses required to achieve strong focusing was split into three pairs of two identical short quadrupole lenses, forming a sextuplet microprobe system. The comparison of the two fringe field models show large variations in the aberration coefficients of this system, however the rectangular model is suitable for a broad survey of possible systems to identify promising configurations for further optimization.

A Maia detector array has been adapted and installed on the CSIRO-MARC Nuclear Microprobe. Maia uses an annular array of 384 silicon detectors to provide a solid-angle of 1.3 sr to improve the collection of X-rays induced by Particle Induced X-ray Emission (PIXE) using a micron focussed MeV proton beam. It features event-by-event data acquisition with dead-time correction and pileup rejection and a total count-rate capacity above 10 M/s, versatile stage and beam scanning modes (coupled to the DAQ-36 system described previously) to cater for a variety of sample configuration and experimental needs, precise measurement of transit time and integration of beam fluence per pixel, and spectral deconvolution of event data in real-time using the Dynamic Analysis method to provide element images during data collection. Here we demonstrate the system on thin sections made from geological samples extracted from active seafloor hydrothermal vents in the PACMANUS hydrothermal field in Papua New Guinea.

Spins in the ``semiconductor vacuum'' of silicon-28 ($^{28}\mathrm{Si}$) are suitable qubit candidates due to their long coherence times. An isotopically purified substrate or epilayer of $^{28}\mathrm{Si}$ is required to limit the decoherence pathway caused by magnetic perturbations from surrounding $^{29}\mathrm{Si}$ nuclear spins ($I=1/2$), present in natural Si ($^{\text{nat}}\mathrm{Si}$) at an abundance of 4.67%. We isotopically enrich surface layers of $^{\text{nat}}\mathrm{Si}$ by sputtering using high fluence ${}^{28}{\text{Si}}^{\ensuremath{-}}$ implantation. Phosphorus (P) donors implanted into one such $^{28}\mathrm{Si}$ layer with $\ensuremath{\sim}3000$ ppm $^{29}\mathrm{Si}$, produced by implanting 30 keV ${}^{28}{\text{Si}}^{\ensuremath{-}}$ ions at a fluence of $4\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$, were measured with pulsed electron spin resonance, confirming successful donor activation upon annealing. The monoexponential decay of the Hahn echo signal indicates a depletion of $^{29}\mathrm{Si}$. A coherence time of ${T}_{2}=285\ifmmode\pm\else\textpm\fi{}14\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$ is extracted, which is longer than that obtained in ${}^{\text{nat}}\text{Si}$ for similar doping concentrations and can be increased by reducing the P concentration in the future. Guided by simulations, the isotopic enrichment was improved by employing one-for-one ion sputtering using 45 keV ${}^{28}{\text{Si}}^{\ensuremath{-}}$ implanted with a fluence of $2.63\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ into ${}^{\text{nat}}\text{Si}$. This resulted in an isotopically enriched surface layer $\ensuremath{\sim}100$ nm thick, suitable for providing a sufficient volume of $^{28}\mathrm{Si}$ for donor qubits implanted into the near-surface region. We observe a depletion of $^{29}\mathrm{Si}$ to 250 ppm as measured by secondary ion mass spectrometry. The impurity content and the crystallization kinetics via solid phase epitaxy are discussed. The $^{28}\mathrm{Si}$ layer is confirmed to be a single crystal using transmission electron microscopy. This method of Si isotopic enrichment shows promise for incorporation into the fabrication process flow of Si spin-qubit devices.

Dopant atoms are ubiquitous in semiconductor technologies, providing the tailored electronic properties that underpin the modern digital information era. Harnessing the quantum nature of these atomic-scale objects represents a new and exciting technological revolution. In this article we describe the use of ion-implanted donor spins in silicon for quantum technologies. We review how to fabricate and operate single-atom spin qubits in silicon, obtaining some of the most coherent solid-state qubits, and we discuss pathways to scale up these qubits to build large quantum processors. Heavier group-V donors with large nuclear spins display electric quadrupole couplings that enable nuclear electric resonance, quantum chaos and strain sensing. Donor ensembles can be coupled to microwave cavities to develop hybrid quantum Turing machines. Counted, deterministic implantation of single donors, combined with novel methods for precision placement, will allow the integration of individual donors spins with industry-standard silicon fabrication processes, making implanted donors a prime physical platform for the second quantum revolution., 18 pages, 11 figures, 134 references. Published in the special issue of Advanced Quantum Technologies "Advancing Quantum Technologies - Chances and Challenges" edited by Rainer Blatt

The quantum coherence and gate fidelity of electron spin qubits in semiconductors is often limited by noise arising from coupling to a bath of nuclear spins. Isotopic enrichment of spin-zero nuclei such as $^{28}$Si has led to spectacular improvements of the dephasing time $T_2^*$ which, surprisingly, can extend two orders of magnitude beyond theoretical expectations. Using a single-atom $^{31}$P qubit in enriched $^{28}$Si, we show that the abnormally long $T_2^*$ is due to the controllable freezing of the dynamics of the residual $^{29}$Si nuclei close to the donor. Our conclusions are supported by a nearly parameter-free modeling of the $^{29}$Si nuclear spin dynamics, which reveals the degree of back-action provided by the electron spin as it interacts with the nuclear bath. This study clarifies the limits of ergodic assumptions in analyzing many-body spin-problems under conditions of strong, frequent measurement, and provides novel strategies for maximizing coherence and gate fidelity of spin qubits in semiconductors., 11 pages, 5 figures

Silicon nanoelectronic devices can host single-qubit quantum logic operations with fidelity better than 99.9%. For the spins of an electron bound to a single donor atom, introduced in the silicon by ion implantation, the quantum information can be stored for nearly 1 second. However, manufacturing a scalable quantum processor with this method is considered challenging, because of the exponential sensitivity of the exchange interaction that mediates the coupling between the qubits. Here we demonstrate the conditional, coherent control of an electron spin qubit in an exchange-coupled pair of $^{31}$P donors implanted in silicon. The coupling strength, $J = 32.06 \pm 0.06$ MHz, is measured spectroscopically with unprecedented precision. Since the coupling is weaker than the electron-nuclear hyperfine coupling $A \approx 90$ MHz which detunes the two electrons, a native two-qubit Controlled-Rotation gate can be obtained via a simple electron spin resonance pulse. This scheme is insensitive to the precise value of $J$, which makes it suitable for the scale-up of donor-based quantum computers in silicon that exploit the Metal-Oxide-Semiconductor fabrication protocols commonly used in the classical electronics industry., 10 pages, 5 figures, plus Supplementary Information. v2 contains additional references, and a simpler explanation of two-qubit CROT gates for donors in silicon

This paper describes the design of a new probe forming lens system consisting of a high excitation magnetic quadrupole lens quadruplet that incorporates a single magnetic octupole lens. This system achieves both a high demagnification and a low spherical aberration compared to conventional high excitation systems and is intended for deployment for the Harbin 300 MeV proton microprobe for applications in space science and ion beam therapy. This relative simplicity of the ion optical design to include a single octupole lens minimizes the risks associated with the constructional and operational precision usually needed for the probe forming lens system and this system could also be deployed in microprobe systems that operate with less magnetically rigid ions. The design of the new system is validated with reference to two independent ion optical computer codes.

High energy proton irradiation has many applications to the study of radiation effects in semiconductor devices, biological tissues, proton tomography and space science. Many applications could be extended and enhanced by use of a high energy proton microprobe. However the design of a GeV proton microprobe must address significant challenges including beam collimation that minimizes ion scattering and the probe forming lens system for ions of high rigidity. Here we address the probe forming lens system design subject to several practical constraints including the use of non-superconducting normal magnetic quadrupole lenses, the ability to focus 1–5 GeV protons into 5 µm diameter microprobes and compatibility with the beam parameters of GeV proton accelerators. We show that 2, 3 and 4 lens systems of lenses with effective lengths up to 0.63 m can be employed for this purpose with a demagnification up to 58 and investigate the probe size limitations from beam brightness, lens aberrations and machining precision.

In Harbin, a 300 MeV proton microprobe system is under development for many applications in space science studies including upset studies in microelectronic devices, radiation hardness of materials for satellites and radiation effects in human tissues. The microprobe system, as a component of Space Environment Simulation Research Infrastructure (SESRI), will employ a purpose-built synchrotron to provide the proton beam. Our design goal for the 300 MeV proton microprobe is for energy spread 0.1%, emittance 10π mm mrad, intensity 109 per pulse and a probe size of 10 μm. A magnetic quadrupole lens system will be used to focus the microprobe with a demagnification of 50. This paper presents a systematic investigation of the ion beam optics to optimize the design. The feasibility of the design for the Harbin system is evaluated by comparison with existing microprobe systems designed for high energy ions.

The bismuth (Bi) substitutional donor in silicon (Si) is an attractive qubit candidate for quantum computing proposals due to its large Hilbert space, clock transitions, and potential to couple to superconducting flux qubits. Single-qubit control, coupling, and readout by surface nanocircuitry requires a Bi depth of ∼20 nm in Si. This can be achieved using ion implantation of ∼25 keV Bi. This work explores the activation properties of Bi implanted at 26 keV with fluences of 1×1014 and 6×1012cm-2 into both crystalline and preamorphized Si. The Bi electrical activation yield was measured over a broad range of annealing conditions using resistivity and Hall effect measurements, enabling optimal annealing strategies to be proposed for the different implant parameters. For the high and low fluences, the maximum Bi activation yields achieved were 64% and 46%, respectively. Above a critical thermal budget, a substantial fraction of Bi forms electrically inactive complexes in the high fluence sample only. The substitutional fraction and diffusion of high fluence Bi was quantified, with diffusion coefficients D0=4.0±0.5 and 7.5±0.5cm2s-1 found for implantation into crystalline and preamorphized Si, respectively, using Rutherford backscattering spectrometry. To demonstrate the successful activation and quantum control of near-surface implanted Bi, the full hyperfine spectrum of these donors is obtained using continuous-wave electron spin resonance at 25 K, supporting the suitability for Bi donor qubits.

With its large solid angle and an input count rate beyond 10 M/s, the PIXE Maia system, recently commissioned on the CSIRO-MARC NMP at the University of Melbourne, is ideally suited to rapid, large area, high definition mapping of biological materials such as hyperaccumulator plants. These plants possess an unusual ability to accumulate large levels of toxic elements from their local environment. In this paper we summarise results collected on three accumulators, two Ni and one As. Damage issues related to PIXE analysis of materials are briefly discussed in the context of higher beam currents and fluorescence data collected to minimise their influence. Elemental maps for the three samples are then discussed as are the obvious advantages of the Maia system.

We analyze the electron spin relaxation rate $1/T_1$ of individual ion-implanted $^{31}$P donors, in a large set of metal-oxide-semiconductor (MOS) silicon nanoscale devices, with the aim of identifying spin relaxation mechanisms peculiar to the environment of the spins. The measurements are conducted at low temperatures ($T\approx 100$~mK), as a function of external magnetic field $B_0$ and donor electrochemical potential $��_{\rm D}$. We observe a magnetic field dependence of the form $1/T_1\propto B_0^5$ for $B_0\gtrsim 3\,$ T, corresponding to the phonon-induced relaxation typical of donors in the bulk. However, the relaxation rate varies by up to two orders of magnitude between different devices. We attribute these differences to variations in lattice strain at the location of the donor. For $B_0\lesssim 3\,$T, the relaxation rate changes to $1/T_1\propto B_0$ for two devices. This is consistent with relaxation induced by evanescent-wave Johnson noise created by the metal structures fabricated above the donors. At such low fields, where $T_1>1\,$s, we also observe and quantify the spurious increase of $1/T_1$ when the electrochemical potential of the spin excited state $|\uparrow\rangle$ comes in proximity to empty states in the charge reservoir, leading to spin-dependent tunneling that resets the spin to $|\downarrow\rangle$. These results give precious insights into the microscopic phenomena that affect spin relaxation in MOS nanoscale devices, and provide strategies for engineering spin qubits with improved spin lifetimes., 14 pages, 8 figures. Version 2 has extensive text revisions, typo corrections, and two extra authors

We present a scalable strategy to manufacture quantum computer devices, by encoding quantum information in the combined electron-nuclear spin state of individual ion-implanted phosphorus dopant atoms in silicon. Our strategy allows a typical pitch between quantum bits of order 200 nm, and retains compatibility with the standard fabrication processes adopted in classical CMOS nanoelectronic devices. We theoretically predict fast and high-fidelity quantum logic operations, and present preliminary experimental progress towards the realization of a “flip-flop” qubit system.

Single crystal isotopically pure 28Si cylindrical Whispering Gallery (WG) mode resonators have been machined from a rod of isotopically pure crystal. Before machining, the rod was loaded into a cavity with the best Bragg confined modes exhibiting Q-factors above a million for frequencies between 10 and 15 GHz. Electron Spin Resonance spectroscopy revealed a very narrow linewidth spin transition, with g-factor of 1.995±0.008. Analysis determined an upper limit to the linewidth of 7 kHz and a concentration of less than 1011 spins/cm3 (10 parts per trillion). After machining into WG mode resonators, the measured frequencies of the fundamental mode families were used to determine the relative permittivity of the material near 4 K and 20 mK to be 11.488±0.024, with the precision limited only by the dimensional accuracy of the resonator. However, the Q-factors were degraded to below 40,000. Raman spectroscopy revealed strain induced broadening on the radial surface of the crystal as a result of the machining. After an acid clean and etch, followed by annealing, the surface damage was repaired. Subsequently, high Q-factors were also restored. The next step will be to purposefully implant ions to try and realise narrow linewidth spin ensembles with clock transitions, which will couple to high-Q WG modes inside the crystal.

Diamond, a wide band-gap semiconductor, can be engineered to exhibit superconductivity when doped heavily with boron. The phenomena has been demonstrated in samples grown by chemical vapor deposition where the boron concentration exceeds the critical concentration for the metal-to-insulator transition of nMIT4×1020/cm3. While the threshold carrier concentration for superconductivity is generally well established in the literature, it is unclear how well correlated higher critical temperatures are with increased boron concentration. Previous studies have generally compared several samples grown under different plasma conditions, or on substrates having different crystallographic orientations, in order to vary the incorporation of boron into the lattice. Here, we present a study of a single sample with unchanging boron concentration, and instead modify the charge-carrier concentration by introducing compensating defects via high-energy ion irradiation. Superconductivity is completely suppressed when the number of defects is sufficient to compensate the hole concentration to below threshold. Furthermore, we show it is possible to recover the superconductivity by annealing the sample in vacuum to remove the compensating defects.

The understanding of weak measurements and interaction-free measurements has greatly expanded the conceptual and experimental toolbox to explore the quantum world. Here we demonstrate single-shot variable-strength weak measurements of the electron and nuclear spin states of a P31 single-atom donor in silicon. We first show how the partial collapse of the nuclear spin due to measurement can be used to coherently rotate the spin to a desired pure state. We explicitly demonstrate that phase coherence is preserved with high fidelity throughout multiple sequential single-shot weak measurements and that the partial state collapse can be reversed. Second, we use the relation between measurement strength and perturbation of the nuclear state as a physical meter to extract the tunnel rates between the P31 donor and a nearby electron reservoir from data conditioned on observing no tunneling events. Our experiments open avenues to measurement-based state preparation, steering and feedback protocols for spin systems in the solid state, and highlight the fundamental connection between information gain and state modification in quantum mechanics.

Whispering Gallery (WG) mode resonators have been machined from a boule of single-crystal isotopically pure silicon-28. Before machining, the as-grown rod was measured in a cavity, with the best Bragg confined modes exhibiting microwave $Q$-factors on the order of a million for frequencies between 10 and 15 GHz. After machining the rod into smaller cylindrical WG mode resonators, the frequencies of the fundamental mode families were used to determine the relative permittivity of the material to be $11.488\pm0.024$ near 4 K, with the precision limited only by the dimensional accuracy of the resonator. However, the Q-factors were degraded by the machining to below $4\times10^4$. Raman spectroscopy was used to optimize post-machining surface treatments to restore high $Q$-factors. This is an enabling step for the use of such resonators for hybrid quantum systems and frequency conversion applications, as silicon-28 also has very low phonon losses, can host very narrow linewidth spin ensembles and is a material commonly used in optical applications., Comment: 7 pages, 6 figures

Hypervelocity dust has a speed of greater than 5 km/s and is a significant problem for equipment deployed in space such as satellites because of impacts that damage vulnerable components. Photovoltaic (PV) arrays are especially vulnerable because of their large surface area and the performance can be degraded owing to the disruption of the structure of the junction in the cells making up the array. Satellite PV arrays returned to Earth after service in orbit reveal a large number of craters larger than 5 μm in diameter arising from hypervelocity dust impacts. Extensive prior work has been done on the analysis of the morphology of craters in PV cells to understand the origin of the micrometeoroid that caused the crater and to study the corresponding mechanical damage to the structure of the cell. Generally, about half the craters arise from natural micrometeoroids, about one third from artificial Al-rich debris, probably from solid rocket exhausts, and the remainder from miscellaneous sources both known and unknown. However to date there has not been a microscopic study of the degradation of the electrical characteristics of PV cells exposed to hypervelocity dust impacts. Here we present an ion beam induced charge (IBIC) pilot study by a 2 MeV He microbeam of craters induced on a Hamamatsu PIN diode exposed to artificial hypervelocity Al dust from a dust accelerator. Numerous 5–30 μm diameter craters were identified and the charge collection efficiency of the crater and surrounds mapped with IBIC with bias voltages between 0 and 20 V. At highest bias, it was found the efficiency of the crater had been degraded by about 20% compared to the surrounding material. The speed distribution achieved in the Al dust accelerator was peaked at about 4 km/s compared to 11–68 km/s for dust encountered in low Earth orbit. We are able to extrapolate the charge collection efficiency degradation rate of unbiased cells in space based on our current measurements and the differences in the structure of the targets.

In a multi-electrode device, the motion of free charge carriers generated by ionizing radiation induces currents on all the electrodes surrounding the active region [1] . The amount of charge induced in each sensitive electrode is a function of the device geometry, the transport parameters and the generation profile. Hence this charge sharing effect allows the signal from each sensitive electrode to provide information about the electrical characteristics of the device, as well as information on the location and the profile of each ionization track. The effectiveness of such approach was recently demonstrated in Ion Beam Induced Charge (IBIC) experiments carried out using a 2 MeV He microbeam scanning over a sub-100 μm scale silicon device, where the ion strike location point was evaluated through a comparative analysis of the charge induced in two independent surface electrodes coupled to independent data acquisition systems [2] . In this report, we show that the Monte Carlo method [3] can be efficiently exploited to simulate this IBIC experiment and to model the experimental data, shedding light on the role played by carrier diffusion, electronic noise and ion beam spot size on the induction of charge in the sensitive electrodes. Moreover, the Monte Carlo method shows that information on the ion strike position can be obtained from the charge signals from the sensitive electrodes.

This paper is dedicated to the characterization of a novel diamond microdosimeter prototype with 3D sensitive volumes produced by high energy boron implantation. Diamond has been chosen in order to further improve solid state based microdosimeter in terms of radiation hardness and tissue equivalency. IBIC measurements were undertaken to determine the charge collection efficiency map of the device. It was demonstrated that the proposed ion implantation technology allows for the formation of an array of well defined 3D SVs. A Geant4 application was developed to explain the effect of Al electrode thickness on observed anomaly in deposited energy. Specifics of the results and an update on the current status of the project is presented.

We investigate the dynamics of a strongly-driven, microwave-dressed, donor-bound electron spin qubit in silicon. A resonant oscillating magnetic field $B_1$ is used to dress the electron spin and create a new quantum system with a level splitting proportional to $B_1$. The dressed two-level system can then be driven by modulating the detuning $\Delta\nu$ between the microwave source frequency $\nu_{\rm MW}$ and the electron spin transition frequency $\nu_e$ at the frequency of the level splitting. The resulting dressed qubit Rabi frequency $\Omega_{R\rho}$ is defined by the modulation amplitude, which can be made comparable to the level splitting using frequency modulation on the microwave source. This allows us to investigate the regime where the rotating wave approximation breaks down, without requiring microwave power levels that would be incompatible with a cryogenic environment. We observe clear deviations from normal Rabi oscillations and can numerically simulate the time evolution of the states in excellent agreement with the experimental data.

We describe an approach to quantum computer technology based on engineered single donor atoms implanted into silicon. We exploit quantum superposition and entanglement in potentially scalable nanoscale quantum devices engineered with just a single phosphorus donor atom in a silicon nano-scale complementary metal-oxide-semiconductor device. The devices are sensitive to the variation in the position of the donor atoms and also, when cooled to 100 mK, to the quantum state of single donors. Over the past two years we have fabricated devices incorporating 31P donor atoms implanted 20 nm deep into isotopically enriched 28Si followed by rapid thermal annealing at 1000oC for 5 s to activate the donors and minimise diffusion. Measurement of a single ionized donor gives the 31P nuclear spin (I=1/2) coherence time greater than 30 seconds showing exceptional promise and the robustness of this quantum system despite the influence of the nearby gate oxide and electrode metals. To implant donor atoms in a large-scale device we have developed a deterministic ion implantation method that is cited by the 2011 International Semiconductor Roadmap. We exploit signals arising from the ion induced charge from single implants in the substrate detected by on-chip detector electrodes. We describe our approach to take this technology to the next stage by building deterministic arrays of single atoms with the goal of sub-10 nm positioning precision as a pathway to a large scale device that could form the building block of a future CMOS quantum computer fabricated with the standard tools of the industry.

Coherent dressing of a quantum two-level system provides access to a new quantum system with improved properties—a different and easily tunable level splitting, faster control and longer coherence times. In our work we investigate the properties of the dressed, donor-bound electron spin in silicon, and assess its potential as a quantum bit in scalable architectures. The two dressed spin-polariton levels constitute a quantum bit that can be coherently driven with an oscillating magnetic field, an oscillating electric field, frequency modulation of the driving field or a simple detuning pulse. We measure coherence times of and , one order of magnitude longer than those of the undressed spin. Furthermore, the use of the dressed states enables coherent coupling of the solid-state spins to electric fields and mechanical oscillations. A single electron spin in silicon is dressed by a microwave field to create a new qubit with tangible advantages for quantum computation and nanoscale research.

In Harbin, we are developing a 300 MeV proton microbeam for many applications in space science including upset studies in microelectronic devices, radiation hardness of materials for satellites and radiation effects in human tissues. There are also applications of this facility proposed for proton therapy. The microbeam system will employ a purpose-built proton synchrotron to provide the beam. However there are many challenges to be addressed in the design, construction and operation of this facility. Here we address two important design aspects for which we apply GEANT4 modeling. First, the high energy proton beam interacts strongly with beam line materials, especially the collimation slits, to produce showers of secondary particles which could introduce significant background signals and degrade the resolution of the proton microbeam. Second, the beam transport within the residual vacuum of the beam line may also introduce undesirable background radiation. In both cases mitigation strategies need to be incorporated during the design phase of the new system. We study the use of a dipole magnet following the aperture collimator to reduce the flux of secondary particles incident on the analysis chamber. Monte Carlo simulations are performed using GEANT4 and SRIM. By inserting the dipole magnet, we find as expected a significant reduction in the scattering of protons and other particles, such as neutrons and gamma rays, at the collimation system exit position. Secondary radiation from the residual gas pressure within the beam line vacuum system are also modelled and found to be negligible under the standard operating conditions.

We demonstrate the fabrication of sub-micron layers of single-crystal diamond suitable for subsequent processing as demonstrated by this test ring structure. This method is a significant enabling technology for nanomechanical and photonic structures incorporating colour-centres. The process uses a novel double implant process, annealing and chemical etching to produce membranes of diamond from single-crystal starting material, the thinnest layers achieved to date are 210 nm thick., Comment: 21 pages, 4 figures

We demonstrate a novel nuclear microprobe imaging and analysis modality for micrometre-scale field effect transistor devices probed with focused beams of MeV ions. By recording the drain current as a function of time during ion irradiation it is possible to identify current transients induced by the passage of single ions through the sensitive structures of the device. This modality takes advantage of the fact that the ionization produced by the passage of a single ion acts in an equivalent way to a transient change in the gate bias which therefore modulates the drain current as a function of time. This differs from the traditional ion beam induced charge technique where the ionization drifts in an internal electric field and induces a single charge pulse in an electrode applied to the device. Instead a richer variety of phenomena are observed, with different time constants which depend on the proximity of the ion strike to the channel of the device. The signals may be used to examine device function, radiation sensitivity or to count ion impacts within the channel.

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 μm 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.

We present a spatial analysis of biased polycrystalline silicon solar cell samples at cryogenic temperatures by the ion beam-induced charge technique. Performing the measurements at cryogenic temperatures leads to freezing out of deep trapping centers, a reduction of the specimen’s capacitance, an increase in the mobility of carriers, and an improvement in the signal to noise ratio and charge collection efficiency. At this low temperature, it permits a higher sensitivity analysis when compared to room temperature measurements, which are limited to zero bias due to leakage current that occurs via surface carrier trapping and detrapping along the grain boundaries. As a result we find the images are significantly more sensitive to subtle differences in charge collection efficiency arising from intra-grain defects.

Colour centres in diamond are important for potential applications in quantum information technology. Centres based on Ni have attractive properties but the structures are still not fully understood. One interesting colour centre is NIRIM-2 which emits around 884 nn and is based on Ni preferentially incorporated into the growth sector during high-pressure high-temperature diamond growth in the presence of a Ni catalyst. To help understand the structure of this colour centre a combination of Rutherford backscattering spectrometry (RBS) with ion channelling and particle induced X-ray emission (PIXE) with 2 MeV H and He ions has been used to study the location of the Ni atoms in the diamond lattice. The Ni concentration, typically below 25 ppm, is well below the detection threshold for RBS, but the yield of characteristic Ni K α , X-rays shows a decrease when the ion beam is channelled into the growth sector of the diamond. This suggests a significant fraction of Ni is incorporated substitutionally in the diamond lattice. Correlation of Ni location in the diamond host with optical properties of Ni-related centres in the same growth sector of the diamond offers the possibility of advancing our understanding of the structure of these important optical centres.

Avalanche silicon photodiodes have potential applications to detect low energy single ions for counting single ion impacts in shallow implant depths for the deterministic doping of nanoscale electronic devices. This paper reports the investigation of avalanche photodiode detectors in the linear operation mode for detection of 0.5–2 MeV helium ions. The measured charge gain was found to be up to 100 depending on bias voltage. The charge gain was found to saturate at a level that correlated with the ion stopping depth in silicon. The measured charge gain for energetic ions, which have a well-defined depth in a silicon substrate for the deposition of ionization energy, is compared with that of X-rays and photons, which deposit the ionization energy over a wider range of depth. This allowed the identification of a suitable structure for an avalanche photodiode optimised for the detection of sub-10 keV heavy ions with an internal charge gain above 10 achievable. This offers significant advantages over conventional PIN devices where the signals from such ions would be lost in the noise.

Scanning vibrating electrode (SVE), particle induced X-ray emission spectroscopy (PIXE) and standard electrochemical measurements were used to study the establishment of stable pits on AA2024-T3 in neutral sodium chloride solution (0.1 M NaCl). Pits were allowed to develop until hydrogen evolution was observed. Typical current at the mouth of the pits were in the vicinity of 1 mA. PIXE maps revealed the intermetallic (IM) particle distributions in the surface as well as significant chloride buildup around the pits. A significant fraction of the small selection of pits examined here appeared to have an S-phase particle (or remnant) within 20 μm of a AlCuFeMn type IM particle suggesting a coupling between the two. The electrochemistry of the coupling between different IM particle types was further investigated using potentiodynamic scans in 0.1 M aqueous NaCl solution of macroscopic electrodes made according to the IM particle compositions. Current densities at the open circuit potential of AA2024-T3 were largest, typically (0.2 up to 1 mA/cm2) for phases that were anodic with respect to AA2024-T3. Coupling of the IM particles was examined by comparing the degree of clustering around chloride attack sites to the average particle density for each map. There were significantly higher number of IM particles surrounding pit sites than the average IM particle densities indicating that local clustering played an important role in pit initiation.

We have developed nanoscale double-gated field-effect-transistors for the study of electron states and transport properties of single deliberately implanted phosphorus donors. The devices provide a high-level of control of key parameters required for potential applications in nanoelectronics. For the donors, we resolve transitions corresponding to two charge states successively occupied by spin down and spin up electrons. The charging energies and the Lande g-factors are consistent with expectations for donors in gated nanostructures.

The mechanism of corrosion inhibition by cerium(III) dibutylphosphate [Ce(dbp)3] on aluminium alloy 2024-T3 (AA2024-T3) has been investigated using macroscopic models of the intermetallic (IM) phases in the alloy. Polished specimens of pure Al (99·999%) and the macroscopic IM phases Al2CuMg, Al7Cu2Fe and Al3Fe were each coupled to a large surface area of AA2024-T3 to simulate the interaction they experience in the alloy. Samples were immersed in 0·1M NaCl with 200 ppm Ce(dbp)3 for 24 h, and the resulting surfaces characterised by scanning electron microscopy, X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy and Raman spectroscopy. Ce(dbp)3 was found to interact differently with each of the different phases examined, providing evidence for a multifunctional corrosion inhibition mechanism.

Scanning Kelvin-probe microscopy is applied in ultra-high vacuum to characterise local changes in the work function of the hydrogen-terminated diamond surface following modification by thermal annealing and ion-implantation. The effect on the work function of hydrogen desorption was monitored during annealing. Ion irradiation was found to give rise to a different response, inconsistent with hydrogen removal. Increased ion fluence causes a rapid enhancement in the work function, each impinging ion causing band structure modification which extends over length scales of at least 20 nm beyond the impact site, considerably larger than the damage cylinder in the vicinity of each ion impact.

Nitrogen vacancy (NV) centers in diamond have distinct promise as solid-state qubits. This is because of their large dipole moment, convenient level structure and very long room-temperature coherence times. In general, a combination of ion irradiation and subsequent annealing is used to create the centers, however for the rigorous demands of quantum computing all processes need to be optimized, and decoherence due to the residual damage caused by the implantation process itself must be mitigated. To that end we have studied photoluminescence (PL) from NV$^-$, NV$^0$ and GR1 centers formed by ion implantation of 2MeV He ions over a wide range of fluences. The sample was annealed at $600^{\circ}$C to minimize residual vacancy diffusion, allowing for the concurrent analysis of PL from NV centers and irradiation induced vacancies (GR1). We find non-monotic PL intensities with increasing ion fluence, monotonic increasing PL in NV$^0$/NV$^-$ and GR1/(NV$^0$ + NV$^1$) ratios, and increasing inhomogeneous broadening of the zero-phonon lines with increasing ion fluence. All these results shed important light on the optimal formation conditions for NV qubits. We apply our findings to an off-resonant photonic quantum memory scheme using vibronic sidebands.

A high aspect ratio nano-aperture mask was used to perform sub-micrometre lithography with MeV ions. Such a mask can localise ion placement in ion machining or doping, including the fabrication of high aspect ratio structures from ion beam damaged regions by subsequent etching. Ion scattering and straggling is the main limiting factor for the transmission with respect to transmitted energy, lateral intensity and angular intensity distribution of the ions. These limits are investigated by a 3D Monte Carlo modelling program based on the SRIM code; simulation of 1.5 MeV He incident on nano-scale apertures of various diameters indicates that the masking is highly effective. The simulation results were tested by experiments on the transmission of 1.5 MeV He ions through apertures that were machined using a focused ion beam of keV Ga ions in a 10 μm thick Si-cantilever. Firstly, the aperture was placed in front of a 50 nm thick polymethyl methacrylate (PMMA) coated photodiode and scanned by a microprobe. The photodiode gives an energy spectrum of the transmitted ions. Secondly, a nano-scale pattern was produced in an 800 nm thick PMMA sample by the step-and-repeat process, implementing a nanonics stage that facilitates precise three-dimensional orientation of the mask. The damaged PMMA was developed and the lateral distribution of ion impacts was imaged using non contact AFM.

We present a computational and experimental study investigating the optical properties of nanoscale silver composite metamaterials fabricated by ion beam lithography. Both simulations and experimental results demonstrate high transmission efficiencies in the near infra-red through these devices. Implications for experimentally verifying the calculated near-field distributions of these materials are also discussed.

Bell's theorem sets a boundary between the classical and quantum realms, by providing a strict proof of the existence of entangled quantum states with no classical counterpart. An experimental violation of Bell's inequality demands simultaneously high fidelities in the preparation, manipulation and measurement of multipartite quantum entangled states. For this reason the Bell signal has been tagged as a single-number benchmark for the performance of quantum computing devices. Here we demonstrate deterministic, on-demand generation of two-qubit entangled states of the electron and the nuclear spin of a single phosphorus atom embedded in a silicon nanoelectronic device. By sequentially reading the electron and the nucleus, we show that these entangled states violate the Bell/CHSH inequality with a Bell signal of 2.50(10). An even higher value of 2.70(9) is obtained by mapping the parity of the two-qubit state onto the nuclear spin, which allows for high-fidelity quantum non-demolition measurement (QND) of the parity. Furthermore, we complement the Bell inequality entanglement witness with full two-qubit state tomography exploiting QND measurement, which reveals that our prepared states match the target maximally entangled Bell states with $>$96\% fidelity. These experiments demonstrate complete control of the two-qubit Hilbert space of a phosphorus atom, and show that this system is able to maintain its simultaneously high initialization, manipulation and measurement fidelities past the single-qubit regime., 10 pages, 3 figures, 1 table, 4 extended data figures