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Register a new userNano-Fabricated Free-Standing Wire-Scanners with Sub-Micrometer Resolution
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Diagnostics of the beam transverse profile with ever more demanding spatial resolution is required by the progress on novel particle accelerators - such as laser and plasma driven accelerators - and by the stringent beam specifications of the new generation of X-ray facilities. In a linac driven Free-Electron-Laser (FEL), the spatial resolution constraint joins with the further requirement for the diagnostics to be minimally invasive in order to protect radiation sensitive components - such as the undulators - and to preserve the lasing mechanism. As for high resolution measurements of the beam transverse profile in a FEL, wire-scanners (WS) are the top-ranked diagnostics. Nevertheless, conventional WS consisting of a metallic wire (beam-probe) stretched onto a frame (fork) can provide at best a rms spatial resolution at the micrometer scale along with an equivalent surface of impact on the electron beam. In order to improve the spatial resolution of a WS beyond the micrometer scale along with the transparency to the lasing, PSI and FERMI are independently pursuing the technique of the nano-lithography to fabricate a free-standing and sub-micrometer wide WS beam-probe fully integrated into a fork. Free-standing WS with a geometrical resolution of about 250 nm have been successfully tested at SwissFEL where low charge electron beams with a vertical size of 400-500 nm have been characterized. Further experimental tests carried out at SwissFEL at the nominal beam charge of 200 pC confirmed the resilience to the heat-loading of the nano-fabricated WS. In this work, details on the nano-fabrication of free-standing WS as well as results of the electron-beam characterization are presented.
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The wire scanners are used for a measurement of the very small beam size and the emittance in Accelerator Test Facility (ATF). They are installed in the extraction beam line of ATF damping ring. The extracted beam emittance are ex=1.3x10-9 m.rad, ey=1.7x10-11 m.rad with 2x109 electrons/bunch intensity and 1.3GeV energy. The wire scanners scan the beam by a tungsten wire with beam repetition 0.78Hz. The scanning speed is, however, very slow(~500um/sec). Since the extracted beam is quite stable by using the double kicker system, precision of the size measurement is less than 2um for 50 - 150um horizontal beam size and 0.3um for 8 - 16um vertical beam size. The detail of the system and the performance are described.
We demonstrate a neutron tomography technique with sub-micrometer spatial resolution. Our method consists of measuring neutron diffraction spectra using a double crystal diffractometer as a function of sample rotation and then using a phase retrieval algorithm followed by tomographic reconstruction to generate a density map of the sample. In this first demonstration, silicon phase-gratings are used as samples, the periodic structure of which allows the shape of the gratings to be imaged without the need of position sensitive detectors. Topological features found in the reconstructions also appear in scanning electron micrographs. The reconstructions have a resolution of about 300 nm, which is over an order of magnitude smaller than the resolution of radiographic, phase contrast, differential phase contrast, and dark field neutron tomography methods. Further optimization of the underlying phase recovery and tomographic reconstruction algorithm is also considered.
The possible existence of short-channel effects in oxide field-effect transistors is investigated by exploring field-effect transistors with various gate lengths fabricated from LaAlO$_3$-SrTiO$_3$ heterostructures. The studies reveal the existence of channel-length modulation and drain-induced barrier lowering for gate lengths below 1 {mu}m, with a characteristic behavior comparable to semiconducting devices. With the fabrication of field-effect transistors with gate lengths as small as 60 nm the results demonstrate the possibility to fabricate by electron-beam lithography functional devices based on complex oxides with characteristic lengths of several ten nanometers.
In modern high-gain free-electron lasers, ultra-fast photon pulses designed for studying chemical, atomic and biological systems are generated from a serial of behaviors of high-brightness electron beam at the time-scale ranging from several hundred femtoseconds to sub-femtosecond. Currently, radiofrequency transverse deflectors are widely used to provide reliable, single-shot electron beam phase space diagnostics, with a temporal resolution of femtosecond. Here, we show that the time resolution limitations caused by the intrinsic beam size in transverse deflectors, can be compensated with specific transverse-to-longitudinal coupling elements. For the purpose, an undulator with transverse gradient field is introduced before the transverse deflector. With this technique, a resolution of less than 1fs root mean square has been theoretically demonstrated for measuring the longitudinal profile and/or the micro-bunching of the electron bunch.
Nano resonators in which mechanical vibrations and spin waves can be coupled are an intriguing concept that can be used in quantum information processing to transfer information between different states of excitation. Until now, the fabrication of free standing magnetic nanostructures which host long lived spin wave excitatons and may be suitable as mechanical resonators seemed elusive. We demonstrate the fabrication of free standing monocrystalline yttrium iron garnet (YIG) 3D nanoresonators with nearly ideal magnetic properties. The freestanding 3D structures are obtained using a complex lithography process including room temperature deposition and lift-off of amorphous YIG and subsequent crystallization by annealing. The crystallization nucleates from the substrate and propagates across the structure even around bends over distances of several micrometers to form e.g. monocrystalline resonators as shown by transmission electron microscopy. Spin wave excitations in individual nanostructures are imaged by time resolved scanning Kerr microscopy. The narrow linewidth of the magnetic excitations indicates a Gilbert damping constant of only $alpha = 2.6 times 10^{-4}$ rivalling the best values obtained for epitaxial YIG thin film material. The new fabrication process represents a leap forward in magnonics and magnon mechanics as it provides 3D YIG structures of unprecedented quality. At the same time it demonstrates a completely new route towards the fabrication of free standing crystalline nano structures which may be applicable also to other material systems.
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