Ian Mcnulty

• Lund University

Nanoporous metals fabricated by dealloying have a unique bi-continuous, sponge-like porous structure with ultra-high surface area. The unique properties of these materials, especially nanoporous gold, have numerous potential applications in sensors and actuators and in energy-related applications as catalytic materials, super-capacitors and battery...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Atomic-level understanding of the active sites and transformation mechanisms under realistic working conditions is a prerequisite for rational design of high-performance photocatalysts. Here, by using correlated scanning fluorescence X-ray microscopy and environmental transmission electron microscopy at atmospheric pressure, in operando, we directl...

Crystallization from an amorphous precursor presents a new route to control the properties of complex oxides by selecting their nanoscale morphology. A key challenge in crystal growth from the amorphous form is to select the locations of nucleation and the crystallographic orientation of the resulting crystals. Nucleation sites for crystallization...

Pygmi: Guided Microscope Control Interface with Workflow Manager - Volume 24 Supplement - Mirna Lerotic, Ian McNulty, Martin V. Holt

Precise management of soil phosphorus (P) to meet competing demands of agriculture and environmental protection can benefit from more comprehensive characterization of P speciation in soils. Our objectives were to provide spatial context for spectroscopic analyses of soil P speciation in relation to molecular‐scale species and landscape‐scale manag...

Visualizing the dynamical response of material hetero-interfaces is increasingly important for design of hybrid materials and structures with tailored properties for use in functional devices. In-situ characterization of nanoscale hetero-interfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, ele...

We report evidence of spontaneous formation of a heterogeneous network of superdomains in two-dimensional square artificial spin ice nanostructures in externally applied magnetic fields. The magnetic heterogeneity is locally disordered but has a zig-zag texture at longer length scales. Resonant coherent soft-x-ray scattering off such textures give...

We report evidence of spontaneous formation of a heterogeneous network of superdomains in two-dimensional square artificial spin ice nanostructures in externally applied magnetic fields. The magnetic heterogeneity is locally disordered but has a zig-zag texture at longer length scales. Resonant coherent soft-x-ray scattering off such textures give...

The rational design of novel catalysts for CO 2 reduction has attracted considerable attention, owing to the increasing global fuel demand and greenhouse gas emission. Cu 2 O has been suggested to be thermodynamically capable of photocatalytically reducing CO 2 to methanol. ¹ However, due to the inertness of CO 2 molecules, it is relatively hard fo...

We studied the evolution of dealloying-induced strain along the {111} in a Ag-Au nano-crystal in situ, during formation of nanoporous gold at the initial stage of dealloying using Bragg coherent x-ray diffractive imaging. The maximum strain magnitude in the crystal doubled in 10 s of dealloying. Although formation of nano-pores just began at the su...

Multi-keV X-ray microscopy has been particularly successful in bridging the resolution gap between optical and electron microscopy. However, resolutions below 20 nm are still considered challenging, as high throughput direct imaging methods are limited by the availability of suitable optical elements. In order to bridge this gap, we present a new t...

Imaging the dynamical response of materials following ultrafast excitation can reveal energy transduction mechanisms and their dissipation pathways, as well as material stability under conditions far from equilibrium. Such dynamical behaviour is challenging to characterize, especially operando at nanoscopic spatiotemporal scales. In this letter, we...

We propose a new approach to robustly retrieve the exit wave of an extended sample from its coherent diffraction pattern by exploiting sparsity of the sample’s edges. This approach enables imaging of an extended sample with a single view, without ptychography. We introduce nonlinear optimization methods that promote sparsity, and we derive update r...

We report direct evidence that magnetically charged superdomain walls form spontaneously in two dimensional square artificial spin ice nanostructures in response to external magnetic fields. These extended magnetic defects were revealed by the development of internal structure, which varies as a function of applied magnetic field, within the Bragg...

Recent progress in the development of dichroic Bragg coherent diffractive imaging, a new technique for simultaneous three-dimensional imaging of strain and magnetization at the nanoscale, is reported. This progress includes the installation of a diamond X-ray phase retarder at beamline 34-ID-C of the Advanced Photon Source. The performance of the p...

Abstract Scientific studies of magnetic systems have been limited to surface domain analysis of bulk samples, or thin magnetic films; however the properties of magnetic materials are dominated by their three-dimensional magnetic domain structures. The arrangement and interaction of microscopic magnetic domains determines macroscopic properties, and...

Many organisms in nature have evolved sophisticated cellular mechanisms to produce photonic nanostructures and, in recent years, diverse crystalline symmetries have been identified and related to macroscopic optical properties. However, because we know little about the distributions of domain sizes, the orientations of photonic crystals, and the na...

The human connectome contains ~1x10^8 neurons and ~1x10^13 synapses. Serial electron microscopy (transmission and scanning) methods for 3D brain imaging are rapidly advancing and have delivered compelling results. Yet, the largest volume studied to date is less than ~100 µm3. X-ray microscopy offers the potential for mapping much larger volumes of...

Operando characterization of gas-solid reactions at the atomic scale is of great importance for determining the mechanism of catalysis. This is especially true in the study of heterostructures because of structural correlation between the different parts. However, such experiments are challenging and have rarely been accomplished. In this work, ato...

X-ray tomography can be used to study the structure of whole cells in close to their native state. Ptychographic Fresnel coherent diffractive imaging (FCDI) holds particular promise for high-resolution tomographic imaging with quantitative phase sensitivity. To avoid the common missing wedge problem in tomography, cells can be mounted in thin glass...

Biological productivity in many ocean regions is controlled by the availability of the nutrient phosphorus. In the Mediterranean Sea, aerosol deposition is a key source of phosphorus and understanding its composition is critical for determining its potential bioavailability. Aerosol phosphorus was investigated in European and North African air mass...

We report quantitative determination of elemental distribution in binary compounds with nano meter scale spatial resolution using x-ray Fresnel coherent diffractive imaging (FCDI). We show that the quantitative magnitude and phase values of the x-ray wave exiting an object determined by FCDI can be utilized to obtain full-field atomic density maps...

Ptychographic coherent x-ray diffractive imaging is a form of scanning microscopy that does not require optics to image a sample. A series of scanned coherent diffraction patterns recorded from multiple overlapping illuminated regions on the sample are inverted numerically to retrieve its image. The technique recovers the phase lost by detecting th...

Quantitative probing of correlation of structure, chemistry, and properties of energy storage materials

Characterization of microscopic structural order and in particular medium range order (MRO) in amorphous materials is challenging. A new technique is demonstrated that allows analysis of MRO using X-rays. Diffraction data were collected from a sample consisting of densely packed polystyrene-latex micro-spheres. Ptychography is used to reconstruct t...

Coherent diffraction imaging (CDI) typically requires that the light source should be highly coherent both laterally and longitudinally. Beamlines at synchrotrons usually install a monochromator and slits to achieve a highly coherent source, leading to a large reduction of beam flux. We demonstrate that lateral and longitudinal partial coherence ca...

Phase-diverse X-ray coherent diffractive imaging (CDI) provides a route to high sensitivity and spatial resolution with moderate radiation dose. It also provides a robust solution to the well-known phase-problem, making on-line image reconstruction feasible. Here we apply phase-diverse CDI to a cellular sample, obtaining images of an erythrocyte in...

Nanoporous gold has many potential applications in various fields, including energy storage, catalysis, sensing and actuating. Dealloying of Ag-Au alloys under free corrosion conditions is a simple method to fabricate nanoporous gold. Here, we systematically investigate the dealloying rate of Ag-xAu alloy for a range of alloy compositions (x = 20-4...

The Hard X-ray Nanoprobe at the Argonne Center for Nanoscale Materials and Advanced Photon Source is a precision platform for scanning probe and full-field microscopy with 8-12 keV x-rays at 30 nm spatial resolution [1]. This multimodel microscope is capable of scanning fluorescence, diffraction, and nanotomographic imaging experiments. The Nanopro...

We have perfected a micromachining technology based on microlithography and electroforming for producing uniformly redundant arrays (URA) and Young's slits for coherence measurements in synchrotron radiation beamlines. The structures may act as absorbent objects or as phase objects. Two microfabrication techniques were used. Optical lithography in...

X-ray tomography can provide structural information of whole cells in close to their native state. Radiation-induced damage, however, imposes a practical limit to image resolution, and as such, a choice between damage, image contrast, and image resolution must be made. New coherent diffractive imaging techniques, such Fresnel Coherent Diffractive I...

Supplementary Info - Figure S1

Supplementary Video

Zeolites are crystalline aluminosilicate minerals featuring a network of 0.3-1.5-nm-wide pores, used in industry as catalysts for hydrocarbon interconversion, ion exchangers, molecular sieves and adsorbents. For improved applications, it is highly useful to study the distribution of internal local strains because they sensitively affect the rates o...

Magnetic ferroelectric (“multiferroic”) materials with a strong magnetoelectric coupling are of high interest for potential information technology applications, e.g. non-volatile memories. HoMnO3 is a hexagonal manganite possessing both ferroelectric and frustrated antiferromagnetic order, and is hence termed a multiferroic material. Topological de...

We employ x-ray coherent diffraction imaging to map the lattice strain distribution, elastic properties and device responses to external stimuli such as magnetic and electric field in a host of device nanostructures. For the case isolated Ni (001) nanowire grown vertically on an amorphous SiO2 /Si substrate we utilize the retrieved projection of la...

The dealloying process is directly imaged, for the first time, by using transmission X-ray microscopy for the case of an Ag–30 at.% Au wire dealloyed under free corrosion in nitric acid. The propagation of a sharp dealloying front separating the alloy from nanoporous Au was observed by two-dimensional real-time in situ imaging at 30 nm resolution a...

Coherent diffraction imaging (CDI) typically requires that the source should be highly coherent both laterally and longitudinally. In this paper, we demonstrate that lateral and longitudinal partial coherence can be successfully included in a CDI reconstruction algorithm simultaneously using experimental x-ray data. We study the interplay between l...

We have applied Fresnel Coherent Diffractive Imaging (FCDI) to image an intact pollen grain from Convallaria majalis. This approach allows us to resolve internal structures without the requirement to chemically treat or slice the sample into thin sections. Coherent X-ray diffraction data from this pollen grain–composed of a hologram and higher reso...

We demonstrate Fresnel Coherent Diffractive Imaging (FCDI) tomography in the X-ray regime. The method uses an incident X-ray illumination with known curvature in combination with ptychography to overcome existing problems in diffraction imaging. The resulting tomographic reconstruction represents a 3D map of the specimen’s complex refractive index...

We imaged nanoscale lattice strain in a multilayer semiconductor device prototype with a new X-ray technique, nanofocused Bragg projection ptychography. Applying this technique to the epitaxial stressor layer of a SiGe-on-SOI structure, we measured the internal lattice behavior in a targeted region of a single device and demonstrated that its inter...

The Hard X-ray Nanoprobe Beamline (or Nanoprobe Beamline) is an X-ray microscopy facility incorporating diffraction, fluorescence and full-field imaging capabilities designed and operated by the Center for Nanoscale Materials and the Advanced Photon Source at Sector 26 of the Advanced Photon Source at Argonne National Laboratory. This facility was...

Scanning X-ray fluorescence microscopy (XFM) is a particularly useful method for studying the spatial distribution of trace metals in biological samples. Here we demonstrate the utility of combining coherent diffractive imaging (CDI) with XFM for imaging biological samples to simultaneously produce high-resolution and high-contrast transmission ima...

The three-dimensional evolution of nanoligaments of nanoporous gold created by Ag–Au dealloying was studied during isothermal coarsening by X-ray nanotomography and microbeam Laue diffraction. The surface normal orientation, curvature and size of the gold nanoligaments were measured as a function of coarsening time (from 2 to 320 min). The followin...

A dedicated in-vacuum coherent x-ray diffraction microscope was installed at the 2-ID-B beamline of the Advanced Photon Source for use with 0.7-2.9 keV x-rays. The instrument can accommodate three common implementations of diffractive imaging; plane wave illumination; defocused-probe (Fresnel diffractive imaging) and scanning (ptychography) using e...

Crucial to understanding fundamental physics puzzles such as colossal magnetoresistance and developing future technologies for magnetic data storage is an understanding of the nanoscale behavior of magnetism. We study Gd/Fe multilayers exhibiting ordered stripes due to perpendicular magnetic anisotropy (PMA) that are pinned by artificial Au pattern...

We report the application of iterative phase retrieval from magnetic x-ray diffraction for imaging magnetic domain structures of magnetic thin films. Using coherent x-ray scattering at the x-ray photon energy corresponding to the L3,2 absorption edges of the 3d material Co, we demonstrate that linearly polarized soft x rays can be used to obtain th...

In recent years, the relevance of physico-chemical heterogeneity patterns in soils at the micron and submicron scale for the regulation of biogeochemical processes has become increasingly evident. For an organic surface soil horizon from a forested Histosol in Germany, microspatial patterns of element distribution (sulfur, phosphorus, aluminium, si...

Research into phase singularities and orbital angular momentum states of light now extends across a tremendous spectral reach, from terahertz frequencies to the hard x-ray regime. X-ray experiments on OAM have yielded intriguing results unique to this part of the spectrum. We have generated x-ray vortices with coherent beams using both refractive a...

We present in this paper a novel methodology that combines scanning x-ray fluorescencee microscopy and atomic force microscopy. The combination of these two techniques allows the determination of a concentration map of Mg in whole (not sectioned) cells.

Several non-destructive imaging techniques offer the possibility to observe rapid phenomena in real time, yet most of these techniques fail when it comes to bulky samples and micrometer precision in three dimensions. Therefore there is clearly a need to develop approaches that address such conditions. We identified the large potential that lies in...

We demonstrate the use of physically justified object constraints in x‐ray Fresnel coherent diffractive imaging on a sample of nanoporous gold prepared by dealloying. Use of these constraints in the reconstruction algorithm enabled highly reliable imaging of the sample’s shape and quantification of the 23‐ to 52‐nm pore structure within it without...

To access the risks and chances of deposition of submicron particles in the gas-exchange area of the lung, a precise three-dimensional (3D)-localization of the sites of deposition is essential--especially because local peaks of deposition are expected in the acinar tree and in individual alveoli. In this study we developed the workflow for such an...

A prominent feature of soil colloids is their huge specific surface. It determines colloidal properties such as adsorption capacity or diffusion. The colloidal interactions differ significantly from the behavior of the same materials in a bulk system. Interactions in the colloidal regime are crucial, for example, for the transport and release of n...

Coherent x-ray diffractive imaging (CXDI) is a microscopy technique that numerically inverts measured diffraction intensities to arrive at the complex index of refraction of the specimen under investigation. We explore here the performance of scanning CXDI using the Difference Map algorithm when using diffraction with degraded signal-to-noise ratio...

A combination of x-ray microscopy, elemental mapping, and XANES spectroscopy at the K-absorption edge of sulfur was used to analyze the elemental and particulate composition of an urban soil loaded with building rubble from WWII, exemplarily from Berlin, Germany. This combination of element specific high-resolution microscopy with high spectral res...

The desmid green alga Closterium moniliferum belongs to a small number of organisms that form barite (BaSO(4)) or celestite (SrSO(4)) biominerals. The ability to sequester Sr in the presence of an excess of Ca is of considerable interest for the remediation of (90)Sr from the environment and nuclear waste. While most cells dynamically regulate the...

Understanding electronic structure at the nanoscale is crucial to untangling fundamental physics puzzles such as phase separation and emergent behavior in complex magnetic oxides. Probes with the ability to see beyond surfaces on nanometer length and subpicosecond time scales can greatly enhance our understanding of these systems and will undoubted...

We report the first proof-of-principle experiment of iterative phase retrieval from magnetic x-ray diffraction. By using the resonant x-ray excitation process and coherent x-ray scattering, we show that linearly polarized soft x rays can be used to image both the amplitude and the phase of magnetic domain structures. We recovered the magnetic struc...

This paper demonstrates the application of the high sensitivity, low radiation dose imaging method recently presented as phase diverse coherent diffraction imaging, to the study of biological and other weakly scattering samples. The method is applied, using X-ray illumination, to quantitative imaging of the granular precursors of underwater adhesiv...

High-resolution X-ray imaging techniques using optical elements such as zone plates are widely used for viewing the internal structure of samples in exquisite detail. The resolution attainable is ultimately limited by the manufacturing tolerances for the optics. Combining ideas from crystallography and holography, this limit may be surpassed by the...

As the resolution in coherent diffractive imaging improves, interexposure and intraexposure sample dynamics, such as motion, degrade the quality of the reconstructed image. Selecting data sets that include only exposures where tolerably little motion has occurred is an inefficient use of time and flux, especially when detector readout time is signi...

Magnetism at the nanoscale is central to understanding emergent complexity in transition metal oxides and engineered rare earth-transition metal multilayers, and in designing new magnetic data storage and spintronic technology. We study magnetism at the nanoscale here using coherent x-ray diffractive imaging (CXDI), which is a technique with potent...

We report a novel experimental approach to derive quantitative concentration map of light elements in whole cells by combining two complementary nano-probe methods: X-ray fluorescence microscopy (XRFM) and atomic force microscopy (AFM). The concentration is derived by normalizing point-by-point the elemental (here Mg) spatial distribution obtained...

This Letter demonstrates that coherent diffractive imaging (CDI), in combination with phase-diversity methods, provides reliable and artefact free high-resolution images. Here, using x rays, experimental results show a threefold improvement in the available image contrast. Furthermore, in conditions requiring low imaging dose, it is demonstrated th...

Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy was performed on phosphate mineral specimens including (a) twelve specimens from the apatite group covering a range of compositional variation and crystallinity; (b) six non-apatite calcium-rich phosphate minerals; (c) 15 aluminium-rich phosphate minerals; (d) ten phosphate...

X-ray fluorescence tomography promises to map elemental distributions in unstained and unfixed biological specimens in three dimensions at high resolution and sensitivity, offering unparalleled insight in medical, biological, and environmental sciences. X-ray fluorescence tomography of biological specimens has been viewed as impractical-and perhaps...

Statistical information about measurement errors is incorporated in an algorithm that reconstructs the image of an object from x-ray diffraction data. The distribution function of measurement errors is included directly into reconstruction processes using a statistically based amplitude constraint. The algorithm is tested using simulated and experi...

Magnesium is the most abundant intracellular divalent cation. We present an innovative experimental approach to localizing intracellular magnesium that combines elemental and morphological information from individual cells with high-resolution spatial information. Integration of information from scanning fluorescence X-ray microscopy with informati...

An in-line X-ray beam energy and intensity monitor has been developed for use in focussed X-ray absorption near-edge spectroscopy (XANES) measurements. The monitor uses only the X-ray intensity that would otherwise bypass our zone-plate focussing optic and relies on a measurement of photoemission current. The monitor is inexpensive, easy to align,...

Tomographic coherent imaging requires the reconstruction of a series of two-dimensional projections of the object. We show that using the solution for the image of one projection as the starting point for the reconstruction of the next projection offers a reliable and rapid approach to the image reconstruction. The method is demonstrated on simulat...

Nanoporous metallic foams have potential applications as chemical sensors, actuators, catalytic conversion systems, and voltage-tunable components. Due to the complex internal structure, the kinetics behind nanofoam formation by dealloying is not well understood, especially for nanoporous metals with pore radii less than 50 nm. We studied the morph...

We study the evolution of magnetic domains and effect of pinning centers in thin film magnetic systems as a function of magnetic field and dopants to identify the role the disorder in formation and stability of the domains in these systems. We have studied Fe/Gd multilayer exhibiting ordered stripes due to perpendicular magnetic anisotropy (PMA). P...

Crucial to understanding fundamental physics puzzles such as colossal magnetoresistance and developing future technologies for magnetic data storage is an understanding of the nanoscale behavior of magnetism. Probes with the ability to see beyond surfaces on this length scale, ultimately on ultrafast time scales, would greatly enhance this understa...

We used x-ray nanotomography to characterize the three-dimensional (3D) morphology and topology of dealloyed nanoporous gold after coarsening. The interface shape distribution obtained from the nanotomography measurement shows that the coarsening does not proceed by bulk diffusion. The surface normal distribution shows that the morphology of the na...

We demonstrate use of a complex constraint based on the interaction of x-rays with matter for reconstructing images from coherent X-ray diffraction. We show the complementary information provided by the phase and magnitude of the reconstructed wavefield greatly improves the quality of the resulting estimate of the transmission function of an object...

This paper reports improved reconstruction of complex wave fields from extended objects. The combination of ptychography with Fresnel diffractive imaging results in better reconstructions with fewer iterations required to convergence than either method considered separately. The method is applied to retrieve the projected thickness of a gold micros...

The measured spatial coherence characteristics of the illumination used in a diffractive imaging experiment are incorporated in an algorithm that reconstructs the complex transmission function of an object from experimental x-ray diffraction data using 1.4 keV x rays. Conventional coherent diffractive imaging, which assumes full spatial coherence,...

For a toposequence with increasing groundwater influence (Cambisol, Stagnosol, Histosol) and with different groundwater regimes (Histosols 1 and 2) in a forested watershed in the Fichtelgebirge (Germany), the speciation of sulfur (S) and iron (Fe) in the soils was assessed by X-ray absorption near-edge spectroscopy (XANES) after anoxic and conventi...

Differential phase contrast can be realised in the scanning transmission x-ray microscope by use of a detector with an appropriate configuration of detector elements. Use of such a configured detector significantly improves the ability to image specimens with low absorption contrast. A natural application is found in scanning fluorescence x-ray mic...

In forested catchments, retention and remobilization of S in soils and wetlands regulate soil and water acidification. The prediction of long-term S budgets of forest ecosystems under changing environmental conditions requires a precise quantification of all relevant soil S pools, comprising S species with different remobilization potential. In thi...

We study the evolution of magnetic domains and effect of pinning centers in thin film magnetic systems as a function of magnetic field, temperature, and dopants to identify the role the disorder in formation and stability of the domains in these systems. We have studied Fe/Gd multilayer exhibiting ordered stripes due to perpendicular magnetic aniso...

The complex transmission function of an integrated circuit is reconstructed at 20 nm spatial resolution using coherent diffractive imaging. A quantitative map is made of the exit surface wave emerging from void defects within the circuit interconnect. Assuming a known index of refraction for the substrate allows the volume of these voids to be esti...

We describe some of the recent advances in the fluctuation microscopy technique for probing medium-range structural correlations in disordered materials. In particular we show that fluctuation microscopy is a surprisingly sensitive method for detecting trace quantities of C60 in a disordered graphite matrix. This surprising sensitivity arises becau...

The in situ or authigenic formation of calcium phosphate minerals in marine sediments is a major sink for the vital nutrient phosphorus. However, because typical sediment chemistry is not kinetically conducive to the precipitation of these minerals, the mechanism behind their formation has remained a fundamental mystery. Here, we present evidence f...

We obtain quantitative phase reconstructions from differential phase contrast images obtained with a scanning transmission x-ray microscope and 2.5 keV x rays. The theoretical basis of the technique is presented along with measurements and their interpretation.

We consider use of a variable polarizing undulator for generating brilliant x-ray beams carrying orbital angular momentum. We find that higher harmonics of the radiation correspond to Laguerre-Gaussian modes with azimuthal mode indices l equal to one less than the harmonic number when the undulator is operated to produce circularly polarized light....

The availability of third-generation synchrotrons and ultimately X-ray free-electron lasers is driving the development of many new methods of microscopy. Among these techniques, coherent diffractive imaging (CDI) is one of the most promising, offering nanometre-scale imaging of non-crystallographic samples. Image reconstruction from a single diffra...