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A microstructural investigation of a VVER400-type reactor pressure vessel (RPV) steel in the initial state (unirradiated) is presented. Key points include a detailed characterization by electron backscatter diffraction and an analysis of precipitates and inclusions performed by transmission as well as scanning electron microscopy.

The transition from a film to a full magnonic crystal is studied by sequentially ion-milling a periodic stripe pattern into a 40 nm thick Ni$_{80}$Fe$_{20}$ film. The spin-wave resonances of each milling stage are detected by ferromagnetic resonance for both in-plain main field axes, i.e. parallel and perpendicular to the stripe pattern. Theoretical calculations and micromagnetic simulations yield the individual mode profiles, which are analyzed in order to track changes of the mode character. The latter is strongly linked to the evolution of the internal demagnetizing field. It’s role is further studied and imaged by electron holography measurements on a hybrid magnonic crystal, which is made with a 10 nm deep surface modulation. The complex effects of mode coupling, mode localization, and anisotropy-like contributions by the internal field are unraveled. Simple transition rules from the $𝑛^_\mathrm{th}$ film mode to the $𝑚\mathrm{th}$ mode of the full magnonic crystal are formulated. This work has been supported by DFG grant KL2443/5-1.

The transition from a film to a full magnonic crystal is studied by sequentially ion-milling a 40 nm Ni80Fe20 film. The spin-wave resonances of each stage are detected by ferromagnetic resonance for both in-plain field main axes. Theoretical calculations and micromagnetic simulations yield the individual mode profiles, which are analyzed in order to track changes of the mode character. The latter is strongly linked to the evolution of the internal demagnetizing field. It’s role is further studied by electron holography measurements of a hybrid magnonic crystal with 10 nm deep surface modulation. The complex effects of mode coupling, mode localization and anisotropy-like contributions by the internal field are unraveled. Simple transition rules from the 𝑛th film mode to the 𝑚th mode of the full magnonic crystal are formulated.

To date, it has not been possible to combine the high optical quality of silver particles with good chemical stability and synthetic convenience in a fully aqueous system, while simultaneously allowing chemical surface functionalization. We present a synthetic pathway for future developments in information, energy and medical technology where strong optical/electronic properties are crucial. Therefore, the advantages inherent to gold are fused with the plasmonic properties of silver in a fully aqueous Au/Ag/Au core-shell-shell system. These nanoparticles inherit low dispersity from their masked gold cores, yet simultaneously exhibit the strong plasmonic properties of silver. Protecting the silver surface with a sub-skin depth gold layer enables oxidant stability and functionality without altering the Ag-controlled optical properties. This combines both worlds - optical quality and chemical stability - and furthermore it is not limited to a specific particle shape.

Magnonic crystals with locally alternating properties and specific periodicities exhibit interesting effects, such as a multitude of different spin-wave states with adjustable band gaps. This work aims for demonstrating and understanding the key role, which local demagnetizing fields play in such systems. In order to get direct access to this matter, the spin-dynamics of a magnonic crystal were reconstructed from ‘bottom-up’, i.e. the structural shape as well as the internal field landscape of the structure were experimentally reconstructed on the nanoscale using electron holography. Subsequently, both properties were utilized to perform dynamic response calculations. The simulations yield the frequency-field dependence as well as the angular dependence of spin waves in a magnonic crystal and reveal the governing role of the internal field landscape around the backward-volume geometry. Connecting the internal field landscape with the individual spin-wave mode localization, a comprehensive model is presented describing the complex angle-dependent spin-wave behavior around 360◦ rotation of an in-plane external field. A significant spin-wave propagation is reported for a broad angular range around the Damon-Eshbach geometry.

Focal series wave reconstruction in the Transmission Electron Microscope (TEM) is a well established holographic technique employed in both the medium and atomic resolution regime to study electric, magnetic and strain fields in solids as well as atomic configurations at crystal defects or grain boundaries. Focal series reconstruction does not require an undisturbed reference wave as off-axis holography and may be conducted under relaxed partial coherence provided that the latter is well-behaved and well-known in advance [1]. Moreover, focal series holography may be considered as an instance of the more general quantum state tomography (see Fig. 1) that is successfully employed to study mixed (i.e., incoherent) quantum states of matter (e.g., atoms) and light [2]. These advantages are opposed by ambiguities in the reconstructed wave function, e.g., due to inconsistent and incomplete focal series data. In reality every focal series is inconsistent, e.g., due to the presence of partial coherence, shot and detector noise, as well as geometric and chromatic aberrations depending on the defocus. Similarly, every focal series is incomplete because of a limited number of foci, typically limited to the near field regime, and the restriction to isotropic foci, where astigmatic foci are necessary to provide a dataset allowing for an unabiguous reconstruction of an underlying wave function [3]. For instance, the problematic reconstruction of low spatial frequencies can be traced back to missing focal series data in the far field. Here, we elaborate on focal series reconstruction from the perspective of quantum state tomography and use the obtained results to increase the scope of the technique in terms of convergence and uniqueness in particular for low spatial frequencies. Moreover, we explain a number of previous results by exploiting the above analogy, and open pathways to further improvements. We particularly report on the recording, preprocessing, calibration and reconstruction of a long range focal series ranging from the near to the far field in a TEM. We calibrate the focal series, including the effective defocus and magnification, by a careful calibration of the proportionality between squared current and reziprocal focal length in a magnetic lens. We derive non-linear focal sampling schemes from the phase space analogy. Subsequently, we adapt a modified Gerchberg-Saxton algorithm to the long range focal series by exploiting the link to randomized Kaczmarz (ART) algorithm used in tomography [4]. We use different numerical propagation regimes in the near and far field to take into account the scaling of the wave function and overcome convergence problems by replacing the Kaczmarz iteration with the Landweber (SIRT) iteration as proposed by Allen et al.. [5]. To overcome remaining ambiguities in the reconstruction (e.g, pertaining to a different starting guess in the Gerchberg-Saxton algorithm) resulting from inconsistencies in combination with the non-convex nature of the set of wave functions possessing the same modulus, we discuss several additional constraints such imposed by the topology of the starting guess [6]. To illustrate the above reconstruction principles, we perform a case study on a higher-order vortex beam with topological charge (winding number) 3 truncated by a square aperture (Fig. 2). The beam possesses a non-trivial topology by design, which is nicely suited to discuss the impact of (implicit) topology constraints, rotation alignment as well as other issues. [1] Koch, C. T., Micron, 2014, 63, 69-75 [2] Schleich, W. P., Quantum Optics in Phase Space, Wiley VCH, 2001 [3] Lubk, A. & Röder, F., Phys. Rev. A, 2015, 92, 033844 [4] Natterer, F., Wübbeling, F., Mathematical Methods in Image Reconstruction,SIAM, 2001 [5] Allen, L. J.; McBride, W.; O’Leary, N. L.,Oxley, M. P., Ultramicroscopy, 2004, 100, 91-104 [6] Martin, A. & Allen, L., Optics Communications, 2007, 277, 288-294 [7] Financial support by the DIP programme of the DFG is greatly acknowledged.

In the HIM high fluences of Neon are often used to create structures on the nanoscale. This is not always necessary and certain properties of specific materials systems can be changed using much smaller fluences. The magnetic properties of specific materials as well as the properties connected to the shape of magnets can be influenced.

To increase the efficiency of bulk heterojunctions for organic photovoltaic devices, the complicated photon-to-electron conversion process has to be understood in detail. To this aim, one challenge is to resolve the correlation between processing parameters of organic solar cells (OSC), the resulting nanoscale morphology of the absorber layer, and efficiency of the completed device. Here, we present the effect of substrate heating on the morphology of the OSC where the active layer is a blend of two small molecules; ZnPc (ZnC32H18N8) as donor and C60 as acceptor. Obtaining insights into the morphology of the active layer requires the spatial resolution and a contrast mechanism to discriminate two phases with similar average atomic number. To tackle this challenge, we combine electron microscopy imaging with different analytical techniques; energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) in TEM, as well as Energy selective Backscattered (EsB) imaging in SEM. We imaged different phases of the donor and acceptor, forming ordered and non-ordered regions, depending on the way the heterojunction is fabricated. To this aim, we fabricated samples at substrate temperatures of 110°C and 150°C, each in two different configurations: 1) Focused ion beam prepared ultrathin lamella of a complete solar cell stack with glass substrate, Indium tine oxide (ITO) electrode, ZnPc:C60 blend of the active layer between electron and hole transport layers and aluminum top electrode. 2) Plane view sample as ZnPc:C60 blend deposited on a TEM grid coated with ITO layer. It was shown that at a substrate temperature of 110°C, the solar cell device has high efficiency [1]., so we consider this as the optimum substrate temperature. Since identification of the composition of each phase in the plane view sample is more straight forward, we use the plane view sample to attribute each structure to one component of the blend. SEM images recorded by using secondary electron detector show that, the high temperature sample consists of rod-like features and cube-shaped material in between the rods. By combination of analytical microscopy techniques, we can attribute the rod-like structures to ZnPc. An energy-selective backscatter (EsB) electron detector in a SEM is used to obtain backscattered contrast of the plane view sample. Due to the atomic number difference between the donor phase and the acceptor phase, (the average atomic number of 8.6 for ZnPc and 6 for the C60) sufficient contrast can be achieved [2]. A clear confirmation for the attribution of the ZnPc phase to the rod-like features and the attribution of C60 to the granular structure in between can be drawn from the investigation of the sample in SEM using EDX and with even higher precision in TEM using an improved EDX system. The chemical mapping of zinc and carbon, proves the correct phase assignment, in both plane view and ultrathin samples, prepared at high temperature. For the sample produced at optimum temperature, a much smaller roughness was observed because of the absence of large ordered regions. Even in the plane view sample, the imaging contrast is low due to less separated phases and smaller domains. To conclude, we clearly resolved the phase morphology of the interpenetrating network of ZnPc:C60 blends for high and optimum temperature samples in plane view and furthermore we were even able to reveal the morphology from TEM images of cross-section lamellas of the real solar cell stacks. Since the ideal active layer should have domain sizes at the range of the exciton diffusion length (10-20nm), the sample produced at high temperature does not show the desired microstructure. Due to the domain sizes of ~100 nm there is no closed path for exciton dissociation. In addition to that, the sample shows a quite high roughness. Acknowledgement: Authors thank A. G. Cid for SEM images. This work was supported by the German Science Council Center of Advancing Electronics Dresden (cfaed). TEM-EDX results were achieved by funding (support code 03SF0451) through the Helmholtz Energy Materials Characterization Platform (HEMCP) initiated by the Helmholtz Association and the German Federal Ministry of Education and Research (BMBF). References: [1] S. Pfuetzner, C. Mickel, J. Jankowski, M. Hein, J. Meiss, C. Schuenemann, C. Elschner, A.A. Levin, B. Rellinghaus, K. Leo and M. Riede, “The influence of substrate heating on morphology and layer growth in C60:ZnPc bulk heterojunction solar cells” Org. Electron., 12 (2010), pp. 435–441 [2] A. G. Cid, M. Sedighi, M. Löffler, W. F. van Dorp and E. Zschech, “Energy-Filtered Backscattered Imaging Using Low-Voltage Scanning Electron Microscopy: Characterizing Blends of C60:ZnPc for Organic Solar Cells”. (DOI: 10.1002/adem.201600063)

The ability of gas field ion sources (GFIS) to produce controllable inert gas ion beams with atomic level precision opens up new applications in nanoscale direct-write material modification. Two areas where this has recently been demonstrated is focused helium ion beam production of high-transition temperature (high-TC) superconductor electronics and magnetic spin transport devices. The enabling advance in the case of superconducting electronics is the ability to use the GFIS to make features on the small length-scale of quantum mechanical tunnel barriers. Because the tunneling probability depends exponentially on distance, tunnel barriers must be less than a few nanometers wide, which is beyond the limits of other nanofabrication techniques such as electron beam lithography. In magnetism, the GFIS has recently been used to generate chemical disordering and modify magnetic properties at the nanoscale. The strongest effect is observed in materials where ion-induced chemical disordering leads to increased saturation magnetization, enabling positive magnetic patterning. In this chapter, we review the latest results and progress in GFIS ion beam modification of (high-TC) superconductors and magnetic materials.

Magnetic data-storage, spintronic and magnonic devices have driven the need for producing well-defined nanoscale magnets of complex geometries. We show how ion-beams can be used to generate nanomagnets in thin films of certain alloys such as B2 ordered Fe60Al40 and Fe50Rh50.[1,2] In these materials a large increase of the saturation magnetization is achieved by inducing subtle atomic displacements caused by collision cascades of penetrating light ions. The ions knock atoms from their ordered sites, generating antisite defects and causing an increase of the Fe-Fe nearest-neighbour interactions which are linked to the increasing magnetization. For instance, a weak magnetization of 0.04 μB per Fe-atom in B2-Fe60Al40 can be increased to 1.67 μB per Fe-atom by the irradiation of light noble gas ions such as He+ or Ne+. The above ion-induced increase of magnetization can be manifested at the local scale and is termed positive magnetic patterning. Patterning can be performed either by irradiation through lithographed masks,[1] or by a direct writing process using the highly focused ion-beam of a Gas Field Ion-Source.[3] Lateral magneto-resistive devices and magnetic arrays produced by ion-irradiation will be described. The application of ion-assisted magnetic writing opens vast opportunities not only in the field of nanomagnetism and devices, but also in the study of disorder-induced magnetic phase transitions at the nanoscale. [1] R. Bali et al., Nano Letters (2014) 14 435. [2] A. Heidarian et al., Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms (2015) 358 251. [3] F. Röder et al., Scientific Reports (2015) 5 16786.

Writing nanoscale magnets with neon using a gas field ion source microscope

Electron interferometric techniques have progressed in the last years thanks to the development of multiple biprisms microscopes. Here, we will discuss some recent developments in the field of strain measurement carried out with the I2TEM microscope (In-situ Interferometry Transmission Electron Microscope) installed in Toulouse in 2012. The I2TEM is a Hitachi HF-3300 equipped with one pre-specimen electrostatic biprism, three post-specimen biprisms, an image corrector (CEOS B-COR for correcting off-axial aberrations) and two stages (objective stage and Lorentz stage above the objective lens). In the dark-field off-axis scheme [1], electron beams diffracted by an epitaxially grown region are interfered with beams diffracted by the substrate thanks to a post-specimen biprism (Fig. 1(a)). Fig. 1(b-d) is an example obtained on a p-MOSFET like transistor with SiGe source/drain. The deformation is recorded as a frequency modulation (FM) in the hologram (Fig. 1(c)) and it can be calculated from the gradient of the reconstructed phase image (Fig 1(d)). In a recently proposed variant called differential phase contrast dark-field holography (DPCDFEH) [2], a pre-specimen biprism is used to create two overlapping waves on the sample (Fig. 1(e)). The interference of beams diffracted by slightly distant regions is acquired in a defocused plane. The deformation is recorded as a phase modulation (PM) in the hologram (Fig. 1(f)) and the DPC phase is directly proportional to the deformation (Fig. 1(g)). Another option is the 4-wave dark-field setup where two biprisms oriented perpendicularly are used to interfere three reference waves and one object wave (Fig. 1(h-j)). The holographic fringes are modulated in amplitude (AM) and each amplitude contour corresponds to a given displacement of the lattice planes. It can provide live information if a sufficient fringe contrast is achieved. In any case, strain measurement requires a reference wave diffracted by a region of known lattice parameter (usually the substrate). One solution is the “tilted reference wave” (TRW) where a pre-specimen biprism and the condenser system are used to create an object-independent reference wave with an adjustable tilt angle [3]. Fig 2(a,b) is an example acquired in the vacuum and Fig. 2(c,d) shows the dark-field configuration for strain measurement. Finally, a pre-specimen biprism can also be useful for electron diffraction techniques. For instance, one can create two parallel half cones on a specimen (SCBED) with a controllable distance (Fig. 3(a)) [4]. Each spot in the diffraction pattern contains two lobes related to the regions crossed by the two probes. Fig. 1(b) shows an example of SCBED pattern series where the left and right lobes are related to unstrained and increasingly strained regions respectively. [1] MJ Hÿtch et al, Nature 453 (2008), 1086–1089. [2] T Denneulin et al, Ultramicroscopy 160 (2016), 98–109. [3] F Röder et al, Ultramicroscopy 161 (2016), 23–40. [4] F Houdellier et al, Ultramicroscopy 159, Part 1 (2015), 59–66. Acknowledgments This work was funded through the European Metrology Research Programme (EMRP) Project IND54 Nanostrain. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. The authors acknowledge the European Union under the Seventh Framework Programme under a contract for an Integrated Infrastructure Initiative Reference 312483-ESTEEM2.

The use of focussed beams of ions to induce strong saturation magnetization (Ms) can lead to unprecedented flexibility in rapidly producing modulated magnetic materials of desired geometry. True flexibility is achieved if the process is non-destructive i.e., Ms is activated at the point of ion impact. Furthermore, the ion is ideally chemically inert and of low mass, such that it escapes the lattice after undergoing the collision process with host atoms and coming to rest. Here we describe the possibility of using a nano-focussed beam of Ne+ ions to generate ferromagnetic phases within initially non-ferromagnetic B2 materials such as Fe60Al40 and Fe50Rh50. The transition occurs as the penetrating ions displace atoms, and the subsequent vacancy creation and recombination leading to the formation of the chemically disordered A2 structure, which is ferromagnetic. The beam has a diameter of ≈ 2 nm and the transformed region is confined to the interaction volume of the ions with the host atoms, with a diameter < 50 nm. Such an ion-beam is readily available in a He+-ion microscope (where Ne+ can also be loaded). The locally formed ferromagnetic nanostructures are embedded within the electrically conducting B2 precursor material. In the case of Fe60Al40 ferromagnetic regions of Ms = 780 kAm-1 [1] are embedded within a non-ferromagnetic matrix. For Fe50Rh50, ferromagnetic regions of Ms = 1000 kAm-1 [2] can be embedded within an antiferromagnetic matrix. The ion-induced B2 → A2 phase transition is the most viable route to achieving well-defined ferromagnetic nanostructures of desired geometry within non-ferromagnetic metallic matrices. We describe our recent direct nanoscale imaging of ion-induced magnetic regions [3] and our attempts to demonstrate possible applications in spin-transport and magnonic devices. References: [1] R. Bali, S. Wintz, F. Meutzner, R. Hübner, R Boucher, A. A. Ünal, S Valencia, A. Neudert, K. Potzger, J. Bauch, F. Kronast, S. Facsko, J. Lindner, and J. Fassbender, Nano Letters 14, 2, 435 (2014). [2] Alireza Heidarian, Rantej Bali, Jörg Grenzer, Richard A. Wilhelm, Rene Heller, Oguz Yildirim, Jürgen Lindner and Kay Potzger, Nucl. Instrum. Methods Phys. Res. B 358, 251-254 (2015). [3] Falk Röder, Gregor Hlawacek, Sebastian Wintz, René Hübner, Lothar Bischoff, Hannes Lichte, Kay Potzger, Jürgen Lindner, Jürgen Fassbender, and Rantej Bali, under review, Scientific Reports (2015).