Helium ion beam milling to create a nano-structured domain wall magnetoresistance spin valve

Quantitative investigation of surface structure and interatomic potential with impact-collision ion scattering spectroscopy

Helium ion beam interactions with materials have important implications for magnetic confinement fusion, material modification, and helium ion microscopy. These interactions depend on the precise physics of how helium ions channel into the materials, which can vary greatly based on the local crystalline orientation. In this work, we performed a dedicated experiment to investigate helium ion channeling in a well-characterized tungsten single crystal. Time-of-flight impact-collision ion scattering spectroscopy was used to obtain multi-angle maps of the backscattering intensity for 3 keV He⁺ → W(111). We found that the backscattering intensity profile arising from helium ion channeling could be well described by a shadow cone analysis. This analysis revealed that subsurface W atoms as deep as the ninth monolayer contributed to the backscattering intensity profile. Binary collision approximation simulations were performed with MARLOWE to model the experimental maps with sufficient accuracy to allow for quantitative comparisons using reliability factors. These quantitative comparisons were applied to investigate how the W lattice structure and He-W interatomic potential affect the multi-angle maps.

An atomic force microscope integrated with a helium ion microscope for correlative nanoscale characterization

In this work, we report on the integration of an atomic force microscope (AFM) into a helium ion microscope (HIM). The HIM is a powerful instrument, capable of imaging and machining of nanoscale structures with sub-nanometer resolution, while the AFM is a well-established versatile tool for multiparametric nanoscale characterization. Combining the two techniques opens the way for unprecedented in situ correlative analysis at the nanoscale. Nanomachining and analysis can be performed without contamination of the sample and environmental changes between processing steps. The practicality of the resulting tool lies in the complementarity of the two techniques. The AFM offers not only true 3D topography maps, something the HIM can only provide in an indirect way, but also allows for nanomechanical property mapping, as well as for electrical and magnetic characterization of the sample after focused ion beam materials modification with the HIM. The experimental setup is described and evaluated through a series of correlative experiments, demonstrating the feasibility of the integration.

Defect Control and n-Doping of Encapsulated Graphene by Helium-Ion-Beam Irradiation

We study with Raman spectroscopy the influences of He(+) bombardment and the environment on beam-induced defects in graphene encapsulated in hexagonal boron nitride (h-BN). We show for the first time experimentally the autonomous behavior of the D' defect Raman peak: in contrast to the D defect peak, the D' defect peak is sensitive to the local environment. In particular, it saturates with ion dose in the encapsulated graphene. Electrical measurements reveal n-type conduction in the BN-encapsulated graphene. We conclude that unbound atoms ("interfacials") between the sp(2)-layers of graphene and h-BN promote self-healing of the beam-induced lattice damage and that nitrogen-carbon exchange leads to n-doping of graphene.

Ultrafast nonlinear control of progressively loaded, single plasmonic nanoantennas fabricated using helium ion milling

We demonstrate milling of partial antenna gaps and narrow conducting bridges with nanometer precision using a helium ion beam microscope. Single particle spectroscopy shows large shifts in the plasmonic mode spectrum of the milled antennas, associated with the transition from capacitive to conductive gap loading. A conducting bridge of nanometer height is found sufficient to shift the antenna from the capacitive to the conductive coupling regime, in agreement with circuit theory. Picosecond pump-probe spectroscopy reveals an enhanced nonlinear response for partially milled antennas, reaching an optimum value for an intermediate bridge height. Our results show that manipulation of the antenna load can be used to increase the nonlinear response of plasmonic antennas.