| 1. |
- Chayanun, Lert, et al.
(author)
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Combining Nanofocused X-Rays with Electrical Measurements at the NanoMAX Beamline
- 2019
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In: Crystals. - : MDPI AG. - 2073-4352. ; 9:8
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Journal article (peer-reviewed)abstract
- The advent of nanofocused X-ray beams has allowed the study of single nanocrystals and complete nanoscale devices in a nondestructive manner, using techniques such as scanning transmission X-ray microscopy (STXM), X-ray fluorescence (XRF) and X-ray diffraction (XRD). Further insight into semiconductor devices can be achieved by combining these techniques with simultaneous electrical measurements. Here, we present a system for electrical biasing and current measurement of single nanostructure devices, which has been developed for the NanoMAX beamline at the fourth-generation synchrotron, MAX IV, Sweden. The system was tested on single InP nanowire devices. The mechanical stability was sufficient to collect scanning XRD and XRF maps with a 50 nm diameter focus. The dark noise of the current measurement system was about 3 fA, which allowed fly scan measurements of X-ray beam induced current (XBIC) in single nanowire devices.
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| 2. |
- Chayanun, Lert, et al.
(author)
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Direct Three-Dimensional Imaging of an X-ray Nanofocus Using a Single 60 nm Diameter Nanowire Device
- 2020
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 20:11, s. 8326-8331
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Journal article (peer-reviewed)abstract
- Nanoscale X-ray detectors could allow higher resolution in imaging and diffraction experiments than established systems but are difficult to design due to the long absorption length of X-rays. Here, we demonstrate X-ray detection in a single nanowire in which the nanowire axis is parallel to the optical axis. In this geometry, X-ray absorption can occur along the nanowire length, while the spatial resolution is limited by the diameter. We use the device to make a high-resolution 3D image of the 88 nm diameter X-ray nanofocus at the Nanomax beamline, MAX IV synchrotron, by scanning the single pixel device in different planes along the optical axis. The images reveal fine details of the beam that are unattainable with established detectors and show good agreement with ptychography.
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| 3. |
- Chayanun, Lert, et al.
(author)
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Nanoscale mapping of carrier collection in single nanowire solar cells using X-ray beam induced current
- 2019
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In: Journal of Synchrotron Radiation. - 0909-0495.
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Journal article (peer-reviewed)abstract
- Here it is demonstrated how nanofocused X-ray beam induced current (XBIC) can be used to quantitatively map the spatially dependent carrier collection probability within nanostructured solar cells. The photocurrent generated by a 50 nm-diameter X-ray beam was measured as a function of position, bias and flux in single p–i–n doped solar-cell nanowires. The signal gathered mostly from the middle segment decays exponentially toward the p- and n-segments, with a characteristic decay length that varies between 50 nm and 750 nm depending on the flux and the applied bias. The amplitude of the XBIC shows saturation at reverse bias, which indicates that most carriers are collected. At forward bias, the relevant condition for solar cells, the carrier collection is only efficient in a small region. Comparison with finite element modeling suggests that this is due to unintentional p-doping in the middle segment. It is expected that nanofocused XBIC could be used to investigate carrier collection in a wide range of nanostructured solar cells.
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| 4. |
- Chayanun, Lert
(author)
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Nanowire devices for X-ray detection
- 2020
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Doctoral thesis (other academic/artistic)abstract
- High spatial resolution X-ray microscopy has become a dedicated tool to study nanocrystals and nanostructure devices in recent years. In general, the spatial resolution of X-ray microscopy depends on the spot size of the X-ray beam and the pixel size of X-ray detectors. High-resolution X-ray detection ideally requires a minimal active region with a sufficient thickness for the X-ray absorption, which leads to nanowire-shaped structures. This thesis made use of semiconductor nanowires to create a single-pixel X-ray detector at nanoscale resolution. The basic interaction between X-rays and nanowire devices can best be investigated by choosing a sample geometry where the nanowire is oriented in-plane with the substrate and orthogonal to the beam. X-ray beam induced current (XBIC), which is the physical process used in X-ray detectors, was used as the primary method to investigate the electrical response from nanowire devices. Different aspects of the XBIC process were investigated in two nanowire materials, InP and InGaP, with two types of doping profiles, n-i-n and p-i-n.The spectrally resolved XBIC measurements shed light on the underlying XBIC signal generation process in nanowire devices, showing that the XBIC signal originates at the atomic level with photoelectric absorption. Then, the X-ray flux variation revealed that the n+-i-n+ doped InGaP nanowire devices were affected by charge trapping leading to photogating and photodoping effects. In contrast, both kinds of p-i-n doped nanowire devices illustrated a linear response as function of the X-ray photon flux, which makes this doping profile more suitable for X-ray detectors. The XBIC measurements of this thesis could reveal the spatially resolved charge collection efficiency (CCE) or internal quantum efficiency (IQE) of the nanowire device. This result emphasizes the key ability of XBIC to be used in the development of nanowire solar cells. Furthermore, calculations based on the finite element method (FEM) was used to get a better understanding of the XBIC results.Although the in-plane nanowire devices can be used for understanding of the XBIC process at the nanoscale, they are not ideal for X-ray detection. The spatial resolution is still limited by the length of the active region, and the diameter of the nanowire limits the absorbing length. A novel fabrication process was therefore developed for a single vertical nanowire device where standing as-grown nanowires were turned into single pixel devices. With this configuration, the incident X-rays can be absorbed along the nanowire axis instead of the diameter. The nanowire used for this device is a p-i-n doped InP nanowire with a diameter of 60 nm as pixel size. Unlike the horizontal NW devices, the flux variation XBIC measurement reveals a sub-linear behaviour.The vertical nanowire device was used to make a high-resolution 3D image of a 90 nm nanofocused X-ray beam by scanning the device in different planes along the beam. The measurements reveal details of the intensity distribution that agree well with calculations based on ptychography. Instead of the nanowire diameter, the spatial detection was limited to about 100 nm due to the stability of the measurement system and X-ray absorption in the top contact. In the future, the device design with as-grown nanowires could scale up into multi-pixel array detectors operating much like conventional X-ray detectors.
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| 5. |
- Chayanun, Lert, et al.
(author)
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Optical demonstration of crystallography and reciprocal space using laser diffraction from Au microdisc arrays
- 2022
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In: Journal of Applied Crystallography. - 0021-8898. ; 55, s. 168-171
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Journal article (peer-reviewed)abstract
- Crystallography is an invaluable tool in materials science, solid state physics and protein science. Understanding crystallography requires grasping the powerful but abstract concept of reciprocal space. Here a simple but insightful experiment using a laser pointer and Au microdisc arrays to explore and illustrate Bragg diffraction and reciprocal space is demonstrated. The Au microdisc arrays were manufactured using standard semiconductor fabrication techniques. The flexibility of the array design allows the demonstration of basic concepts such as lattice and atomic form factor, but also more advanced ones such as quasicrystal and shape function.
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| 6. |
- Chayanun, Lert, et al.
(author)
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Spectrally resolved x-ray beam induced current in a single InGaP nanowire
- 2018
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 29:45
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Journal article (peer-reviewed)abstract
- We demonstrate x-ray absorption fine structure spectroscopy (XAFS) detected by x-ray beam induced current (XBIC) in single n + -i-n + doped nanowire devices. Spatial scans with the 65 nm diameter beam show a peak of the XBIC signal in the middle segment of the nanowire. The XBIC and the x-ray fluorescence signals were detected simultaneously as a function of the excitation energy near the Ga K absorption edge at 10.37 keV. The spectra show similar oscillations around the edge, which shows that the XBIC is limited by the primary absorption. Our results reveal the feasibility of the XBIC detection mode for the XAFS investigation in nanostructured devices.
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| 7. |
- Hammarberg, Susanna, et al.
(author)
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High resolution strain mapping of a single axially heterostructured nanowire using scanning X-ray diffraction
- 2020
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In: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 13:9, s. 2460-2468
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Journal article (peer-reviewed)abstract
- Axially heterostructured nanowires are a promising platform for next generation electronic and optoelectronic devices. Reports based on theoretical modeling have predicted more complex strain distributions and increased critical layer thicknesses than in thin films, due to lateral strain relaxation at the surface, but the understanding of the growth and strain distributions in these complex structures is hampered by the lack of high-resolution characterization techniques. Here, we demonstrate strain mapping of an axially segmented GaInP-InP 190 nm diameter nanowire heterostructure using scanning X-ray diffraction. We systematically investigate the strain distribution and lattice tilt in three different segment lengths from 45 to 170 nm, obtaining strain maps with about 10−4 relative strain sensitivity. The experiments were performed using the 90 nm diameter nanofocus at the NanoMAX beamline, taking advantage of the high coherent flux from the first diffraction limited storage ring MAX IV. The experimental results are in good agreement with a full simulation of the experiment based on a three-dimensional (3D) finite element model. The largest segments show a complex profile, where the lateral strain relaxation at the surface leads to a dome-shaped strain distribution from the mismatched interfaces, and a change from tensile to compressive strain within a single segment. The lattice tilt maps show a cross-shaped profile with excellent qualitative and quantitative agreement with the simulations. In contrast, the shortest measured InP segment is almost fully adapted to the surrounding GaInP segments. [Figure not available: see fulltext.].
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| 8. |
- Kalbfleisch, Sebastian, et al.
(author)
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X-ray in-line holography and holotomography at the NanoMAX beamline
- 2022
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In: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 29, s. 224-229
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Journal article (peer-reviewed)abstract
- Coherent X-ray imaging techniques, such as in-line holography, exploit the high brilliance provided by diffraction-limited storage rings to perform imaging sensitive to the electron density through contrast due to the phase shift, rather than conventional attenuation contrast. Thus, coherent X-ray imaging techniques enable high-sensitivity and low-dose imaging, especially for low-atomic-number (Z) chemical elements and materials with similar attenuation contrast. Here, the first implementation of in-line holography at the NanoMAX beamline is presented, which benefits from the exceptional focusing capabilities and the high brilliance provided by MAX IV, the first operational diffractionlimited storage ring up to approximately 300 eV. It is demonstrated that in-line holography at NanoMAX can provide 2D diffraction-limited images, where the achievable resolution is only limited by the 70 nm focal spot at 13 keV X-ray energy. Also, the 3D capabilities of this instrument are demonstrated by performing holotomography on a chalk sample at a mesoscale resolution of around 155 nm. It is foreseen that in-line holography will broaden the spectra of capabilities of MAX IV by providing fast 2D and 3D electron density images from mesoscale down to nanoscale resolution.
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| 9. |
- Li, Hangxi, 1994, et al.
(author)
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Experimentally Verified, Fast Analytic, and Numerical Design of Superconducting Resonators in Flip-Chip Architectures
- 2023
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In: IEEE Transactions on Quantum Engineering. ; 4
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Journal article (peer-reviewed)abstract
- In superconducting quantum processors, the predictability of device parameters is of increasing importance as many laboratories scale up their systems to larger sizes in a 3-D-integrated architecture. In particular, the properties of superconducting resonators must be controlled well to ensure high-fidelity multiplexed readout of qubits. Here, we present a method, based on conformal mapping techniques, to predict a resonator's parameters directly from its 2-D cross-section, without computationally heavy and time-consuming 3-D simulation. We demonstrate the method's validity by comparing the calculated resonator frequency and coupling quality factor with those obtained through 3-D finite-element-method simulation and by measurement of 15 resonators in a flip-chip-integrated architecture. We achieve a discrepancy of less than 2% between designed and measured frequencies for 6-GHz resonators. We also propose a design method that reduces the sensitivity of the resonant frequency to variations in the interchip spacing.
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| 10. |
- Soltau, Jakob, et al.
(author)
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Off-axis multilayer zone plate with 16 nm × 28 nm focus for high-resolution X-ray beam induced current imaging
- 2021
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In: Journal of Synchrotron Radiation. - 0909-0495. ; 28, s. 1573-1582
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Journal article (peer-reviewed)abstract
- Using multilayer zone plates (MZPs) as two-dimensional optics, focal spot sizes of less than 10 nm can be achieved, as we show here with a focus of 8.4 nm × 9.6 nm, but the need for order-sorting apertures prohibits practical working distances. To overcome this issue, here an off-axis illumination of a circular MZP is introduced to trade off between working distance and focal spot size. By this, the working distance between order-sorting aperture and sample can be more than doubled. Exploiting a 2D focus of 16 nm × 28 nm, real-space 2D mapping of local electric fields and charge carrier recombination using X-ray beam induced current in a single InP nanowire is demonstrated. Simulations show that a dedicated off-axis MZP can reach sub-10 nm focusing combined with reasonable working distances and low background, which could be used for in operando imaging of composition, carrier collection and strain in nanostructured devices.
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