Field effect enhancement in buffered quantum nanowire networks

III-V semiconductor nanowires have shown great potential in various quantum transport experiments. However, realizing a scalable high-quality nanowire-based platform that could lead to quantum information applications has been challenging. Here, we study the potential of selective area growth by molecular beam epitaxy of InAs nanowire networks grown on GaAs-based buffer layers. The buffered geometry allows for substantial elastic strain relaxation and a strong enhancement of field effect mobility. We show that the networks possess strong spin-orbit interaction and long phase coherence lengths with a temperature dependence indicating ballistic transport. With these findings, and the compatibility of the growth method with hybrid epitaxy, we conclude that the material platform fulfills the requirements for a wide range of quantum experiments and applications

Structural investigations of nanowires using X-ray diffraction

Advancements in growth of the nanowire-based devices opened another dimension of possible structures and material combinations, which find their applications in a wide variety of fields, including everyday life. Characterization of such devices brings its own challenges and here we show that X-rays offer large possibilities to analyze the structural properties.In the present work we used three different techniques to characterize a large spectrum of different nanowire heterostructures from the structural point of view:(i) First, we measured high resolution three dimensional reciprocal space maps averaged over large number of nanowires. Knowing the precise positions of multiple Bragg peaks in reciprocal space we could calculate the average strain and composition.(ii) In the second technique we used a nanofocused X-ray beam of ≈ 100 nm in diameter to measure the local variation of strain and tilt on a scale of a few nanowires with high spatial resolution. Next, we combined it with three dimensional reciprocal space mapping and while scanning across a single nanowire with the nanofocused beam, we measured three dimensional intensity distributions around the Bragg peaks at every step. This allowed a very accurate measurements of strain at every point of the single nanowire. We showed that in critical heterostructures the strain distribution can be very inhomogeneous.(iii) Lastly, we have studied in-situ the nanowire growth by molecular beam epitaxy at the synchrotron beamline. With this, we could grow the nanowires and measure X-ray diffraction in real time. We studied the initial stage of pure WZ InAs nanowire growth. By measuring the interference fringes in the scattering signal, raising from the finite length of the NWs it was possible to precisely determine the nanowire length evolution at each time step. Next, we formed a hybrid axial and radial heterostructure with InAsSb and observed how bending of the nanowires takes place in real time

Structural Investigations of Nanowires Using X-Ray Diffraction

Advancements in growth of the nanowire-based devices opened another dimension of possible structures and material combinations, which find their applications in a wide variety of fields, including everyday life. Characterization of such devices brings its own challenges and here we show that X-rays offer large possibilities to analyze the structural properties.In the present work we used three different techniques to characterize a large spectrum of different nanowire heterostructures from the structural point of view:(i) First, we measured high resolution three dimensional reciprocal space maps averaged over large number of nanowires. Knowing the precise positions of multiple Bragg peaks in reciprocal space we could calculate the average strain and composition.(ii) In the second technique we used a nanofocused X-ray beam of ≈ 100 nm in diameter to measure the local variation of strain and tilt on a scale of a few nanowires with high spatial resolution. Next, we combined it with three dimensional reciprocal space mapping and while scanning across a single nanowire with the nanofocused beam, we measured three dimensional intensity distributions around the Bragg peaks at every step. This allowed a very accurate measurements of strain at every point of the single nanowire. We showed that in critical heterostructures the strain distribution can be very inhomogeneous.(iii) Lastly, we have studied in-situ the nanowire growth by molecular beam epitaxy at the synchrotron beamline. With this, we could grow the nanowires and measure X-ray diffraction in real time. We studied the initial stage of pure WZ InAs nanowire growth. By measuring the interference fringes in the scattering signal, raising from the finite length of the NWs it was possible to precisely determine the nanowire length evolution at each time step. Next, we formed a hybrid axial and radial heterostructure with InAsSb and observed how bending of the nanowires takes place in real time

Interferometric characterization of rotation stages for X-ray nanotomography

The field of three-dimensional multi-modal X-ray nanoimaging relies not only on high-brilliance X-rays but also on high-precision mechanics and position metrology. Currently available state-of-the-art linear and rotary drives can provide 3D position accuracy within tens to hundreds of nm, which is often insufficient for high resolution imaging with nanofocused X-ray beams. Motion errors are especially troublesome in the case of rotation drives and their correction is more complicated and relies on the metrology grade reference objects. Here we present a method which allows the characterisation and correction of the radial and angular errors of the rotary drives without the need for a highly accurate metrology object. The method is based on multi-probe error separation using fiber-laser interferometry and uses a standard cylindrical sample holder as a reference. The obtained runout and shape measurements are then used to perform the position corrections using additional drives. We demonstrate the results of the characterization for a piezo-driven small rotation stage. The error separation allowed us to measure the axis runout to be approximately ±1.25 μm, and with active runout compensation this could be reduced down to ±42 nm

Moiré method for nanometer instability investigation of scanning hard x-ray microscopes

We present a Moiré method that can be used to investigate positional instabilities in a scanning hard x-ray microscope with nanometer precision. The development of diffractionlimited storage rings offering highly-brilliant synchrotron radiation and improvements of nanofocusing x-ray optics paves the way towards 3D nanotomography with 10 nm resolution or below. However, this trend demands improved designs of x-ray microscope instruments which should offer few-nm beam stabilities with respect to the sample. Our technique can measure the position of optics and sample stage relative to each other in the two directions perpendicular to the beam propagation in a scanning x-ray microscope using simple optical components and visible light. The usefulness of the method was proven by measuring short and long term instabilities of a zone-plate-optics-based prototype microscope. We think it can become an important tool for the characterization of scanning x-ray microscopes, especially prior to experiments with an actual x-ray beam

Extraordinary Renditions (Stockholm): The Cultural Negotiation of Science

Christine Borland, Fiona Crisp, Chris Dorsett, Rona Lee The Cultural Negotiation of Science is a research group based at Northumbria University, Newcastle, UK that brings together several artists and academics whose practices engage with expert cultures across a broad spectrum of science and technology. Collectively, the group is characterised by a performative approach to the production of knowledge that actively challenges the use of art as an instrumental or illustrative device to interpret science.Here at the Royal Institue of Art, four artists from the Cultural Negotiation of Science group, Christine Borland, Fiona Crisp, Chris Dorsett and Rona Lee, will talk about their work across bio-medical ethics, fundamental science, genetics & museum holdings and physical geography respectively

Nanofocused x-ray beams applied for mapping strain in core-shell nanowires

The core-shell nanowires have the promise to become the future building blocks of light emitting diodes, solarcells and quantum computers. The high surface to volume ratio allows ecient elastic strain relaxation, makingit possible to combine a wider range of materials into the heterostructures as compared to the traditional, planargeometry. As a result, the strain elds appear in both the core and the shell of the nanowires, which can aectthe device properties. The hard x-ray nanoprobe is a tool that enables a nondestructive mapping of the strainand tilt distributions where other techniques cannot be applied. By measuring the positions of the Bragg peaksfor each point on the sample we can evaluate the values of local tilt and strain. In this paper we demonstratethe detailed strain mapping of the strained InGaN/GaN core-shell nanowire. We observe an asymmetric straindistribution in the GaN core caused by an uneven shell relaxation. Additionally, we analyzed the local micro-tiltdistribution, which shows the edge eects at the top and bottom of the nanowire. The measurements werecompared to the nite element modelling and show a good agreement