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The authors report the direct-write growth of hammerhead atomic force microscope(AFM) probes by He+beam induced deposition of platinum-carbon. In order to grow a thin nanoneedle on top of a conventional AFM probe, the authors move a focused He+beam during exposure to a PtC precursor gas. In the final growth stage, a perpendicular movement of the beam results in the required three-dimensional (hammerhead) shape. The diameter of the needle depends on the ion beam dose, beam dwell time, and speed of the beam movement. A nanoneedle radius below 10?nm and a hammerhead smaller than 35?nm have been achieved. This fabrication process is robust and enables precise control over the three-dimensions of the hammerhead AFM probe. Finally, the authors test the capabilities of the fabricated AFM probes for two-dimensional metrology of sidewall angles and line-edge roughness of trenches and shark-fins in silicon., QN/Quantum Nanoscience, Applied Sciences

In this article, we present novel sample preparation methods using a helium ion microscope (HIM). We report the possibility of reshaping, at room temperature, thin metal lines on an electron-transparent membrane: A set of platinum bridges with standard geometry (300X200X15 nm) was modified at room temperature into different shapes using focused helium (He)-ion beam. Also the applicability of the HIM as a tool for precise modification of silicon (Si) and strontium titanate (SrTiO3) lamellae is shown and discussed. We demonstrated that in situ heating (e.g., at 600°C) of the samples during He-beam illumination by use of a specially developed heating stage enables production of thin Si and SrTiO3 samples without significant artifacts. The quality of such cuts was inspected by transmission electron microscopy with high-resolution imaging, and the diffraction patterns were analyzed., Kavli Insitute of Nanoscience, Applied Sciences

In recent years, novel ion sources have been designed and developed that have enabled focused ion beam machines to go beyond their use as nano-fabrication tools. Secondary electrons are usually taken to form images, for their yield is high and strongly dependent on the surface characteristics, in terms of chemical composition and topography. In particular, the secondary electron yield varies characteristically with the angle formed by the beam and the direction normal to the sample surface in the point of impact. Knowledge of this dependence, for different ion/atom pairs, is thus the first step toward a complete understanding of the contrast mechanism in scanning ion microscopy. In this article, experimentally obtained ion-induced secondary electron yields as a function of the incidence angle of the beam on flat surfaces of Al and Cr are reported, for usual conditions in Ga+ and He+ microscopes. The curves have been compared with models and simulations, showing a good agreement for most of the angle range; deviations from the expected behavior are addressed and explanations are suggested. It appears that the maximum value of the ion-induced secondary electron yield is very similar in all the studied cases; the yield range, however, is consistently larger for helium than for gallium, which partially explains the enhanced topographical contrast of helium microscopes over the gallium focused ion beams., IST/Imaging Science and Technology, Applied Sciences

The sub-nanometer beam of a helium ion microscope was used to study and optimize helium-ion beam induced deposition of PtC nanopillars with the (CH3)3Pt(CPCH3) precursor. The beam current, beam dwell time, precursor refresh time, and beam focus have been independently varied. Continuous beam exposure resulted in narrow but short pillars, while pulsed exposure resulted in thinner and higher ones. Furthermore, at short dwell times the deposition efficiency was very high, especially for a defocused beam. Efficiencies were measured up to 20 times the value for continuous exposure conditions. The interpretation of the experimental data was aided by a Monte Carlo simulation of the deposition. The results indicate that two regimes are operational in ion beam induced deposition (IBID). In the first one, the adsorbed precursor molecules originally present in the beam interaction region decompose. After the original precursor layer is consumed, further depletion is averted and growth continues by the supply of molecules via adsorption and surface diffusion. Depletion around the beam impact site can be distinguished from depletion on the flanges of the growing pillars. The Monte Carlo simulations for low precursor surface coverage reproduce measured growth rates, but predict considerably narrower pillars, especially at short dwell times. Both the experiments and the simulations show that the pillar width rapidly increases with increasing beam diameter. Optimal writing strategy, good beam focusing, and rapid beam positioning are needed for efficient and precise fabrication of extended and complex nanostructures by He-IBID., QN/Quantum Nanoscience, Applied Sciences

In experiments on current-driven domain wall (DW) motion in nanostrips with perpendicular magnetic anisotropy (PMA), the initial DW preparation is usually not well controlled. We demonstrate precise control of DW injection using Ga and novel He focused ion beam (FIB) irradiation to locally reduce the anisotropy in part of a Pt/Co/Pt strip. DWs experience pinning at the boundary of the irradiated area. This DW pinning is more pronounced at the He irradiation boundary compared to Ga. This is attributed to a better He beam resolution, causing an anisotropy gradient over a much smaller length scale and hence, a steeper energy barrier for the DW. The results indicate that He FIB is a useful tool for anisotropy engineering of magnetic devices in the nanometer range.

A 25 keV focused helium ion beam has been used to grow PtC nanopillars on a silicon substrate by beam-induced decomposition of a (CH3)3Pt(CPCH3) 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., QN/Quantum Nanoscience, Applied Sciences

An analytical model for the growth of nanopillars by helium ion-beam-induced deposition is presented and compared to experimental data. This model describes the competition between pillar growth in vertical and lateral directions. It assumes that vertical growth is induced by incident primary ions and type-1 secondary electrons, whereas lateral growth is induced by scattered ions and type-2 secondary ions. An essential element of the model is the notion that depletion of adsorbed precursor molecules occurs only at the pillars’ apex. Depletion impedes vertical growth at the apex, allowing more time for lateral outgrowth of the pillar’s sidewalls. The model describes qualitatively the trends in measured vertical, lateral, and volumetric growth rates of PtC pillars as functions of the ion-beam current. It can be used to design growth experiments and Monte Carlo simulations., QN/Quantum Nanoscience, Applied Sciences

Quantum Nanoscience, Applied Sciences

The recently introduced helium ion microscope (HIM) is capable of imaging and fabrication of nanostructures thanks to its sub-nanometer sized ion probe [1,2]. 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 [3]. 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., Kavli Institute of Nanoscience, Applied Sciences

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., QN/Quantum Nanoscience, Applied Sciences

The recently introduced helium ion microscope (HIM) is capable of imaging and fabrication of nanostructures thanks to its sub-nanometer sized ion probe [1,2]. 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 [3]. 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., Kavli Institute of Nanoscience, Applied Sciences

The determination of the quality of an imaging system is not an easy task for, in general, at least three parameters, strictly interdependent, concur in defining it: resolution, contrast, and signal-to-noise ratio. The definition of resolution itself in scanning microscopy is elusive and the case of scanning ion microscopy is complicated by the damage of the sample under the ion beam, which, especially for small features, can be the limiting factor. This is indeed the case for most focused ion beam systems, which exploit beams of Ga+. The only way to overcome this limit is to exploit sources of low mass ions, such as H+ and He+. In this article the authors analyze the way the sputtering may affect the resolution, defined as smallest detectable feature in an image, of a scanning ion microscope, for heavy and light ions, in the case of spherical features. It appears that the fundamental limit to the resolution in scanning microscopy is not given by the spot size, but by the dynamics of the interaction of the beam with the sample and the consequent modification of the sample’s geometry, even for beams of light ions. For example, in the case of Sn nanospheres under a He+ beam, the authors found a minimum theoretical detectable particle size limit of ? 1?nm and an experimental limit of ? 5?nm., IST/Imaging Science and Technology, Applied Sciences