Light-matter coupling in TMD monolayers and heterostructures
Scanning optical micro-cavities have been used by two collaborating groups to study light-matter coupling phenomena in semiconductor transition metal dichalcogenide (TMD) monolayers and heterostructures. The groups of David Hunger (Karlsruher Institut für Technologie, Karlsruhe, Germany) and Alexander Högele (Ludwig-Maximillians-Universität München, Germany) explored atomically thin TMD semiconductors with scanning-cavity hyperspectral imaging at room and cryogenic temperatures. To this end, WSe&sub2; monolayer and MoSe&sub2;-WSe&sub2; heterobilayer were coupled to a tuneable cavity consisting of a fiber-based micro-mirror at one end and a planar micro-mirror with the sample at the other end, as sketched in figure 1. For room-temperature monolayers in strong-coupling, spatial maps of new half-matter and half-light quasiparticles – so-called exciton polaritons – were correlated to maps of exciton extinctions and fluorescence . Heterobilayers were explored in the weak-coupling regime at 4 K to demonstrate Purcell enhancement of layer-indirect excitons and to determine their oscillator strength . To ensure the required stability, the experiments employed an ECSx3030 and ANPx101 positioner for ambient and cryogenic conditions respectively, to realize the tuneable cavity and align the fiber with respect to the sample
Piezo-based Positioning for Magnetic Field Detection
X-rays, also referred as synchrotron radiation, serve as an important tool to observe the structure and dynamics of matter. The radiation is generated by bending magnets, wigglers or undulators. While bending magnet and wiggler radiation have a broader spectrum of photon energies, undulator generates narrow peaks, i.e. bright and coherent radiation at specific harmonics. This specific peak spectrum and defined photon energy is the main advantage of undulator radiation. Dr Carsten Kuhn and his group at the Helmholz-Zentrum in Berlin (Berlin, Germany) developed the new generation of undulators for the storage ring BESSY II. To detect and specify the magnetic field they designed a measurement slide with six attocube positioners to align a hall probe with respect to the undulators' magnets. With this precise analysing setup, the position accuracy of the Hall-probes is at least 5 μm and 20 μrad.
Life Science: 3D Imaging System Showing Natural Colour
Interesting features in life science and biology often span several orders of magnitude in size. A complete optical study requires to resolve structures from sub-micrometer to centimeter, thus high resolution is a fundamental need. In addition, fast acquisition times are demand, as any movement during the image-taking process will cause blurr.
The group of Prof. Ming Lei at the State Key Laboratory of Transient Optics and Photonics (Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an, China) developed such a 3D microscope with a lateral resolution of 580 nm.
The possibility to obtain full colour 3D images and 3D morphological data in the size range of typical insects opens the door for many different types of entomological investigations. Three attocube ECS positioners actuate a microscopic stage to move and align the sample in all three dimensions. The positioners are perfectly suited for such an application as they provide a travel range of at least 20 mm with a typical step size of less than 100 nm.
This measurement was realized with the ECSx3030/Al/NUM/RT.
Rotating transport measurement setup at 25mK
When designing a setup for mK applications material choice and thermalization is crucial. Titanium becomes superconducting at temperatures below 400 mK consequently, the thermal contact to the sample is not ensure anymore. At Peking University (Beijing, China), Dr. Pengjie Wang from Xi Lin group has chosen the beryllium-copper version of the ANR101 positioner with resistive readout to realize their low-electron-temperature sample rotation system for transport measurements inside a dilution cryostat. The rotator allows to orient the sample in-situ with respect to a high magnetic field of up to 10 T.
The dilution cryostat with a diameter of 81 mm offers the required space for the rotator setup, see picture. The sample holder is designed for the use of up to four sample, each 5 mm x 5 mm large, a red LED is installed to illuminate the samples at 4 K for an easier orientation. The measured electron temperature in the setup is 25 mK, the same as the environmental temperature.The setup is designed for transport measurements and material characterization at ultra-low electron temperatures. A first application shows the tilt-induced localization and delocalization of the second landing level of the two-dimensional electron gas - an experiment for which a pressurized liquid ³He cell had been necessary elsewise.
(Figure reproduced from Rev. Sci. Instrum. 90, 023905 (2019); doi: 10.1063/1.5083994, with the permission of AIP Publishing)
This measurement was realized with the ANR101/RES/LT - rotator (360° endless).
Micromechanical Testing of Silver Nanowires
The small size of specimens often imposes significant challenges for preparation and testing. To overcome these difficulties, Prof. Horacio Espinosa’s group at the Mechanical Engineering Department in Northwestern University, USA, has developed a microelectromechanical system that allows mechanical testing of nanowires (see left figure). The system is capable of simultaneous four-point electrical measurements, therefore enabling piezoresistivity and -electricity measurements.
In order to mount the silver nanowires, they employed an attocube nanomanipulator, composed of three stacked ECS3030 positioners, one for each axis of movement. The nanomanipulator is ositioned inside an SEM chamber and interfaced to the ECC100 piezo-controller outside the chamber.
This measurement was realized with the ECSx3030/Al/RT.
R.A. Bernal, et al., Small 10, 725 (2014)
Sample positioning in scanning transmission x-ray microscope at SLAC
We use attocube linear stages with optical and resistive encoders for positioning of samples relative to high resolution x-ray optics in a scanning transmission x-ray microscope. The picture shows a magnetic excitation called “soliton” that is the result of a spin polarized current injected into a thin ferromagnetic Co/Pt multilayer. The injected spin causes a localized oscillation of the magnetization at the spot where the current is injected, here a nano contact with a 150 nm diameter in the center of the picture. Time resolved scanning transmission x-ray microscopy using magnetic circular dichroism as a contrast mechanism is used to obtain an image of the magnetic soliton.
(Dr. Hendrik Ohldag, Stanford Synchrotron Radiation Laboratory, SLAC National Accelerator Laboratory.)
Angle-dependent characterizations of materials at mK temperatures
Attocube's rotators offer a way to use the full magnetic field of a 1D magnet for field-angle dependent transport measurements at the sample. This benefit is used by the group of Anne de Visser at the Van der Waals - Zeeman Institute (University of Amsterdam, NL) in two setups with an ANR51 and an ANRv220 both in a closed loop configuration.
Magnetotransport measurements as a function of the angle θ in the trigonal basal plane of the topological superconductor SrxBi2Se3 revealed a large two-fold anisotropy of the upper critical field Bc2. Such a rotational symmetry breaking of Bc2(θ) cannot be explained with standard models, and indicates unconventional superconductivity with an exotic order parameter. More about this work can be found at .
In the second setup a home-built compact dilatometer was mounted on the ANRv220 in a dilution refrigerator. This was used to measure the anisotropy in the ferromagnetic and superconducting phase diagram of a single crystal of UCoGe by applying magnetic fields up to 14 T along the different crystallographic axes .
Lensless Imaging with X-Ray Waveguides
A synchrotron generated X-Ray beam was coupled into an X-Ray waveguide located in the focus of Kirkpatrick-Baez mirrors. The resulting filtered wave was then used to illuminate a sample coherently, yielding a magnified hologram of the sample recorded by a pixel detector. Several linear positioners, goniometers, and rotators were applied for precision alignment of the waveguide with respect to the sample, which in turn was mounted on a high-precision tomographic rotation stage.
This measurement was realized with the ANPx101/UHV - linear x-nanopositioner.
S. Kalbfleisch et al., AIP. Conf. Proc., 1234, 433-436 (2010)
New Stable and Portable X-Ray Microspectroscope at KEK
At the high energy research accelerator KEK in Japan, Dr. Takeichi et al. designed a novel X-Ray microspectroscope for high resolution composition analysis. The setup is comprised of 11 attocube ECS stepping positioners and a dedicated scanner for sample imaging. All the positioners are equipped with optoelectronic sensors and can be digitally controlled. The sample stage is stabilized via attocube’s interferometric FPS3010 sensor with a resolution of 25 pm. The whole four-stack-setup is compact enough to fit into a vacuum chamber of only 220×310×200 mm3. First measurements show the resolution of the new instrument to be approximately 40 nm.
This measurement was realized with the ECSx3030/StSt/HV, and the .
Y. Takeichi, et al, Rev.Sci.Instr. 87, 013704 (2016)
Detecting vibration propagation and parasitic motions with picometer resolution
Exact sample positioning in synchrotron beamlines requires position detection with highest resolution. A group at the Diamond Light Source designed a sample positioning system with three positioners for x, y, z movements. To determine the error motions, eight axes of three IDS3010 devices were triggered for synchronous data acquisition, controlling the movement with BiSS-C interface. They identified parasitic motions of only 100 pm that were caused in the non orthogonal fixing of the positioners. These smallest amount of deviation can be detected in Ultra-high vacuum only - and with the IDS3010.
(Trevor Bates, Brian Nutter, Diamond Light Source Limited, Oxfordshire, England)
UHV-Compatibility of ANR101/RES/UHV
Experiments in Ultra High Vacuum (UHV) conditions require highest precision and care in manufacturing of the respective equipment. The outgassing behavior is a crucial factor when researchers decide for new instruments in their setups. This application note describes measurements of the outgassing data of an attocube rotator with an integrated resistive encoder ANR101/ RES/UHV.
(The tests were carried out at the BESSY synchrotron facility in Berlin, Germany.)
This measurement was realized with the ANR101/RES/UHV - rotator (360° endless).
Special Micro X-Ray Fluorescence Analysis (micro-XRF) Spectrometer
Confocal micro-XRF is a method to determine the spatial distribution of major, minor and trace elements within a sample in three dimensions. The employed polycapillary x-ray optics need to be aligned precisely to get optimal results. Very compact positioners had to be used inside the vacuum chamber for this purpose. Long-time stability of the alignment is also a major requisite. ANPxyz101 nanopositioners fulfill these requirements very well.
The figure to the left shows a 3D sample measurement of a cross made from 10 µm copper wire which is placed on an x-ray screen and fixed using adhesive tape.
(The data was kindly provided by S. Smolek and C. Streli, Atominstitut of the TU Wien.)
Hypersensitive macroscopic manipulation of quantum many-body states
M. Bartkowiak, S. Gerber and M. Kenzelmann from the Paul Scherrer Institut, Switzerland, have developed a goniometer sample holder for neutron scattering, which permits in-situ tuning of complex quantum states at low temperatures (100 mK) and high magnetic fields (up to 12 T) . The device is based on a purpose-built, non-magnetic ANGt50/LT goniometer of attocube’s cryogenic, open loop positioners. It has an angular range of ±3.6° and is sufficiently compact to fit a dilution refrigerator - cryomagnet environment.
With this device, the magnetic domain population in so-called Ce-115 superconductors could be controlled by altering the alignment of the sample to the magnetic field direction [1,2]. Therewith a binary switching behavior has been found which provides strong evidence for a direct coupling of magnetism and unconventional superconductivity in the vicinity of quantum criticality. Population of the Qh (orange) and Qv (grey) magnetic domains in the so-called Q-phase of the compound CeCoIn5 is shown as a function of the tilt angle with respect to the external magnetic field. For |Ψ| = 0.05° a mono-domain population is found, which can be macroscopically switched (modified from ).
This measurement was realized with the ANGt50/LT - goniometer for "theta" tilting.
The Axion Dark Matter eXperiment - Nano Precision in Extreme Conditions
The Axion Dark Matter eXperiment (ADMX) seeks to prove the existence of the axion and reveal the composition of dark matter by looking for the resonant conversion of dark-matter axions to microwave photons in a strong magnetic field. The new high-frequency Sidecar experiment, developed by Christian Boutan at the University of Washington (now at the Pacific Northwest National Laboratory) is a miniature axion haloscope that fits inside of the ADMX insert and has the capability of searching for axion masses between 16µeV - 30µeV. Two positioners are required for the essential functions of tuning the cavity and adjusting the antenna coupling at mK temperatures in a 8 Tesla field. Attocube's ANR240/RES and ANPz101eXT12/RES were employed in this pathfinder experiment.
Transition from slow Abrikosov to fast moving Josephson vortices
attocube proudly presents his cutting edge application using the ANR31 rotator: They observed the formation of fast moving Josephson vortices, which depends critically on the angular alignment. Using the ANR31, they were able to rotate the sample below 2 K with better than 0.1° precision and could observe no drifts while sweeping temperature and magnetic field.
Angle-dependent transport measurements at 40 mK
Based on an attocube systems rotator ANR30/LT a rotation stage for angle-dependent transport measurements in magnetic fields up to 33 T and temperatures down to 40 mK was built at the user facility of the High Field Magnet Laboratory in Nijmegen.
The mixing chamber of the commercially available dilution refrigerator from Leiden Cryogenics offers only a limited space of 17 mm in diameter. Hence, the ultra compact attocube rotator ANR30/LT is the positioner of choice for this task. The rotator is fixed on a plastic (Hysol) dilution refrigerator insert.
Scanning Microwave Impedance Microscopy at 4 K and 9 T
A set of linear positioners and scanners made for cryogenic application was implemented into a microwave impedance microscope located inside a liquid Helium flow cryostat equipped with a 9 T superconducting magnet. The 1 GHz microwave signal was guided to the cantilever probe, which detected the dielectric constant and conductivity contrast of the sample during scanning. The system is a versatile tool for fundamental research on complex materials and phase transitions under various conditions.
Performance Test of the ANPz30/LT at 35 mK and 15 Tesla
The precise performance of nanopositioning elements is of great importance in order to realize instrumental setups which work reliably under extreme environmental conditions. Although attocube systems’ positioners have been tested at low temperatures down to 10 mK and at high magnetic fields up to 28 Tesla, their successful performance has never been demonstrated when both environmental conditions were simultaneously applied. A real challenge, furthermore, is to carry out such a test in a 3He/4He environment due to the fact that 3He carries a magnetic spin which becomes polarized in magnetic fields. This influence on the positioner’s operation was investigated for the first time in this application.
Magnetic Resonance Imaging of Nanoscale Virus at 300 mK
attocube’s ANPx51 positioners were used in an MRFM setup with the task to precisely and reliably position a magnetic tip and a copper nanowire to close proximity of an ultra-sensitive cantilever. The MRFM setup was applied to investigate and reconstruct the 1H spin distribution of Tobacco Mosaic Virus particles, representing a 100-million fold improvement in volume resolution over conventional MRI.
Photoluminescence measurements in fields up to 28 T
The attocube systems positioners ANPxyz100/LT have been used in a setup for optical measurements in liquid 4He temperature and magnetic fields up to 28 T at the Grenoble High Magnetic Field Laboratory. In the setup laser excitation is delivered using a single-mode fiber and is focused onto the sample with two microlenses. A multimode fiber is used for photoluminescence (PL) collection.
Scanning Hall Probe Microscopy at 300 mK with ANP positioners
The magnetic properties of superconducting and ferromagnetic materials at ultra-low temperatures represent some of the most interesting contemporary problems in condensed matter physics. These properties are typically investigated using a magnetic force microscope or a scanning Hall probe microscope (SHPM). In this note, we report on a self-built SHPM capable of working at temperatures as low as 300 mK and magnetic fields of up to 10 T, while still having sub-micron lateral spatial resolution.
Piezo-Controlled Exfoliation of Graphene
In the group of Prof. Gosh at the IIS in Bangalore, researcher Kinikar and his coworkers managed to measure the conductance of narrow stripes of graphene during their exfoliation. A metal tip is crashed into a graphite HOPG crystal using an attocube positioner for vacuum application, namely the ANPz101, and slowly retracted via a piezo tube. Conductance is measured from the tip through the HOPG crystal. The setup situated inside a SEM is shown in picture 1. The graphite piece sticking on the tip will thereby be torn to a single layer of graphene. Mechanically torn graphene has highly crystalline edges, leading to quantized conductance. This is due to one-dimensional channels forming at the edges each with a conductance of 2e2/h (graph 2). A similar setup was used in a cryostat for high magnetic field measurements.
Kinikar: “The attocubes have been with us for over a decade, and they still work perfectly!”
This measurement was realized with the ANPz101/HV - linear z-nanopositioner.
In situ Measurements of Irradiation-Induced Creep on Amorphous Micropillars
S. Özerinç and his colleagues at the University of Illinois at Urbana-Champaign have developed an apparatus for measuring irradiation induced damage and stress on the nanometer scale. Using attocube's ECS3030 as well as the FPS3010 interferometer, the system can measure in situ the deformation of mechanically stressed micro-pillars, during which the pillars are irradiated with heavy MeV ions. The apparatus provides a new and effective approach to accelerate the evaluation of promising materials for future nuclear power plant applications.
Mapping and Manipulation of Leakage Currents in a Nanostructure
In this application note, attocube’s smallest titanium positioners (ANPx51/RES and ANPz51/RES) are used as part of an atomic force microscope (AFM) inside a Janis ³He cryostat with a base temperature of 280 mK. The setup is a combined low temperature AFM and scanning tunneling microscope (STM), which is emploied to carry out scanning gate microscopy experiments on various nanostructures. In these measurements the positioners are used to move the metallic tip directly above the nanostructure predominantly at 4.2 K but also as low as 280 mK.
Mechanically Controlled Multi-Contact Break Junctions
In this application, small tips made from either glass or graphite were used to locally deform a silicon membrane, creating break junctions in a very controlled fashion. The tips with a typical radius between 50 and 200 microns were precisely controlled using attocube’s nanopositioning technology. The approach of locally creating and controlling individual break junctions can be used to study the influence of optical excitations on the conductance of individual molecules and for controllable metallic single-electron transistors.
Automatic Mapping of Semiconductor QDs
Returning to interesting sample positions has never been easier: Yves Delley from the Quantum Photonics Group (QPG) at the ETH Zurich have - based on attocube positioners with resistive encoders made for cryogenics - built a micro-photoluminescence (PL) setup and automated it to a great extent. They programmed a fully automated routine for raster-imaging a full sample of up to 4 x 4 mm2 as well as implemented an auto-focus routine. Once initiated, the positioners are moved frame-by-frame and a CCD camera takes images of the PL of their semiconductor quantum dot samples. Knowing the coordinates of all individual images, it is easy to put together a complete map of the sample (see figure ).
“Now, we have to select the interesting dots, at which we want to take a closer look”, says Yves Delley, the responsible project researcher at QPG and gags: “Yet, in order to find the shortest route between all these quantum dots, we would need a quantum computer to solve this problem.”
(Image kindly provided by Yves Delley, Quantum Photonics Group, ETH Zurich, Switzerland)
3D g-Factor Mapping of Single Quantum Dots
A xyz linear positioning stack combined with a rotator was used in a novel fiber-based confocal microscope, dedicated for the investigation of certain nanostructures such as InGaAs quantum dots (QDs) using magneto-photoluminescence (PL). The specific arrangement of positioners enabled scientists in this experiment to tilt and rotate samples at low temperature with respect to a magnetic field of up to 10 T while maintaining focus on a single QD.
Vectorial Scanning Force Microscopy Using a Nanowire Sensor
Using a GaAs/AlGaAs nanowire and its two distinct flexural modes the group of Martino Poggio in Basel was able to detect lateral 2D forces in a novel type of low temperature AFM system. An XYZ set of attocube’s ultra stable ANPx311/HL/LT/UHV cryogentic positioners helped in positioning the nanowire in the focus point of an interferometer detecting its motion. A second 3D set of attocube positioners was used to position and image the sample. Detection of both eigenmodes is possible due to their distinct resonance frequency. Interaction with an in-plane field lead to a rotation of the eigenmodes the angle of which yields the force field.
This measurement was realized with the ANPx311/HL/LT/UHV - linear x-nanopositioner.
Nanomanipulation of 1-D nanostructures using ECSx3030 positioners inside an electron microscope
The group of Horacio Espinosa at Northwestern University has employed attocube‘s ECS3030 positioners (controlled by an ECC100 piezo-controller) to accomplish nanometer precise manipulation of various nanotubes inside a SEM chamber. Once a nanowire is picked up, the manipulator is used to position it on top of a MEMS device for testing elastic strength as well as for four-point electrical measurements.
Cavity Enhanced Raman Microscopy
level signals remain intrinsically small. Recently Th. Hümmer et al from the group of Prof. Hänsch achieved a more than sixfold amplification by putting the sample inside a tiny cavity. The cavity formed by the sample and a micro mirror on the tip of an optical fiber (1) can be scanned by a set of attocube’s ECSx3030 positioners to obtain images with close to optical resolution. The micro cavity is adjusted with some tens of pm resolution using another ECS positioner and an additional piezo. The signal is enhanced due to the Purcell effect stemming from the enhanced photon lifetime in a small cavity volume (2).
The group around Dr. Hunger at the LMU Munich applied the new method to some carbon nanotubes leading to clear pictures showing (3) the extinction cross-section and (4) the Raman signal of the G’ mode. “The cavity amplifies both the Raman scattering process as well as absorption from the sample. This allows one to combine ultrasensitive absorption microscopy with Raman imaging within a single measurement.”, explains Dr. Hunger. The group is confident to improve the method further boosting the signal enhancement by several orders of magnitude in the future.
(*Pictures are under Creative Commons Attribution 4.0 international license)
Haptic 3D micromanipulation with positioners
M. A. Srinivasan of MIT, USA and UCL, London, with support from TUM-IAS, Munich, has developed a micromanipulator with an haptic interface to enable manual exploration, manipulation, and assembly of micro-structures. In collaboration with A. Schmid of UCL, London, S. Thalhammer of Helmholtz Zentrum, Munich, and R. Yechangunja of Yantric, Inc., USA, he has demonstrated manual grasping and moving of 10 to 100 µm sized objects with direct haptic feedback of the gripping force in real-time, so that the objects can be placed in three dimensions with nanometer precision.
A force-sensing microgripper with 100 µm opening is mounted on an ANPxyz101/NUM stack of attocube’s closed loop positioners. Measured forces by the microgripper in the micro-Newton range are scaled up and exerted on the operator’s fingers through a haptic interface.
Tuning of a Fabry-Pérot Resonator for High Field
P. Neugebauer and his team have integrated attocube's ANPz51 in a new cavity design to measure high-frequency electron paramagnetic resonances (HF-EPR).
Among other advantages, the group was able to move a mirror in-situ within the resonator, to find the right mode and precisely fine-tune its position.
This measurement was realized with the ANPz51/RT - linear z-nanopositioner.
Controlling Electron Emission in Space and Time
The dynamics of electrons emitted from a sharp tungsten tip triggered by femtosecond laser pulses have been investigated. The setup shown to the left is situated in an UHV chamber at p = E-10 mbar pressure. A xyz positioning stack enables precision alignment of the tip. Photoelectron spectra are recorded while the phase between carrier wave and intensity envelope is varied in small steps. The lower figure shows two electron spectra, recorded with a phase difference of 180°. In a), pronounced peaks are visible caused by interference of two electron wave packets emitted during subsequent optical cycles. In b), no peak structure is visible; only one electron wave packet contributes. This energy domain effect allows conclusions about the time dynamics of the electrons. By shaping the laser electric field with the carrier-envelope phase, the dynamics of the electrons can be controlled with attosecond precision. The presented system enables control over photoelectrons from a metal tip in space (nanometer scale) and time (attosecond scale).
(The data was kindly provided by M. Krüger, M. Schenk, and P. Hommelhoff, Max Planck Institute of Quantum Optics, Garching, Germany.)
HF-SPM using attocube nano-positioners in magnetic fields above 30 T
In an outstanding setup, Benjamin Bryant and Lisa Rossi (High Field Magnet Laboratory, Radboud University, Nijmegen, NL), together with the SPM group of Alex Khajetoorians (Radboud University), designed a high field scanning probe microscope (HF-SPM) for operation at cryogenic temperatures and in extreme magnetic fields up to 38 T. The high magnetic field is provided using a water-cooled Bitter magnet: noise from the cooling water creates a highly challenging vibration environment for SPM. An ANPz30 nanopositioner controls the coarse approach of an atomic force microscope cantilever to a scanned sample. The attocube positioner provides for a modular design that makes it easy not only to change the components if needed but also allows the flexibility to employ different cantilever or sample holders. Due to the compactness and rigid design of the positioner the sensitivity to vibrational noise is reduced, which is critical for SPM in the extreme environment of the Bitter magnet.