Sub-μm Resolution Research Articles

X-Ray Fluorescence Analysis of Historic Art Paint Pigments

Utilizing synchrotron radiation, X-ray fluorescence (XRF) microscopy enables researchers to deduce the elemental composition of paint pigments with a higher sensitivity and resolution than that of lab-based XRF instruments. With this information, art historians can date paintings by examining the elemental makeup of paint pigments and the time periods in which they were used. One painting, Christ and the Woman Taken in Adultery, has been duplicated by Pieter Brueghel the Younger and other artists, leading to confusion over which artworks are Brueghel masterpieces or copies by other artists. Art historian Maurizio Seracini, retaining a painting that could be assigned to Brueghel, confirmed the artwork was a reproduction not created by Brueghel. With radiocarbon dating, Dr. Seracini discovered that the painting was created between 1679 and 1939, after Brueghel’s death in 1638. Dr. Seracini also employed X- ray imaging to differentiate between the painting’s visible and lower layers. This technique uncovered a seated woman within the artwork’s lower layers, indicating that the artist has painted over the original artwork. Substantiating Dr. Seracini’s findings, the sub-µm spatial resolution of Brookhaven National Laboratory’s (BNL’s) Submicron Resolution X-ray Spectroscopy (SRX) beamline was used to conduct an XRF microscopy analysis on a paint fragment from the artwork. The software PyXRF was used to identify elements based on emission spectra, contributing to the discovery of titanium within the painting. The presence of titanium, an element incorporated into paint pigments starting in 1921, indicates that the artwork may be more modern than previously thought. These results illustrate the applicability of synchrotron radiation in characterizing the physical and chemical properties of cultural heritage artifacts, supporting historians in their quests to discover the stories behind these objects.

(Invited) Direct Laser Induced Gold Wiring of 2D Materials with Sub-Μm Resolution

One of the most influential technologies of our modern world are integrated electronics. Almost all parts of our daily life include some bearing with any kind of electrical technologies. The fabrication methods itself, for integrated miniatured electrical devices have had not much innovation in terms of production. Several processing steps still mainly consist of different kinds of lithography. This situation may change with new challenges on the production of smaller quantities with specialized functions, or the use of temperature critical or atomically thin surfaces, where the thermal evaporation of metals damages the sample.For some decades now, printing of all types of electronics have gained great attraction. While lithography is a time-consuming multi-step process (including resist preparation, illuminating, developing, evaporation and lift-off) with expensive and harmful photoresists and harsh environmental conditions (high-vacuum and thermal treatments), ink printing allows for direct and simple application of the desired structures [1]. Two main types of inks are typically applied: colloidal solutions of metal nanoparticles [2, 3] or metal-organic precursor solutions [4]. In both cases, thermal curing after deposition is required to achieve metallic conduction. To this end, laser writing is often advantageous over thermal sintering due to the overall lower thermal stress applied to the material, particularly on flexible, thermally sensitive substrates [5] whereas metal nanoparticles suffer from a relatively high photothermal stability and the need for a large laser power to achieve sufficient sintering [3]. In contrast, metal-organic precursor solutions feature a relatively low metal content (≤34 wt-%)10, and undergo large volume contractions during laser writing. These challenges have so far prevented the definition of metallic gold contacts with diffraction-limited feature sizes by ink printing and laser writing.Here, we introduce atomically-precise, metalloid Au32(nBuP12Cl8) nanoclusters (Au32NCs) [6] as an ink for resistless, direct laser writing of metallic gold micro- and nanostructures. The unique advantages of this ink over Au nanoparticles or typical metal-organic Au precursors are their high photosensitivity in combination with a large gold content of 70 wt-%. This allows for writing gold structures with feature sizes of 250 nm and line spacings < 200 nm using 1.86 mW laser power at 488 nm with a scan speed of 0.1 mm/s. We apply this method on a wide range of substrates, including flexible polymer membranes, find metallic conductance with conductivities ~ 1 × 106 S/m and demonstrate that defining such Au contacts on two-dimensional semiconductors results in fully functional optical switches and field effect transistors made out from 2D materials.[1] Raut NC. et al., Jour. Mat. Chem. C 2018, 6(7): 1618-1641.[2] Ko E. et al., Nanotechnology 2007, 18(34): 345202.[3] Hong S. et al., ACS Nano 2013, 7(6): 5024-5031.[4] Schoner C et al., Thin Solid Films 2013, 531: 147-151.[5] Skylar-Scott MA et al., PNAS 2016, 113(22): 6137-6142.[6] Kenzler S et al., Angew. Chem. Int. Ed. 2019, 58(18): 5902-5905. Figure 1

Three-dimensional coherent diffraction snapshot imaging using extreme-ultraviolet radiation from a free electron laser

The possibility of obtaining a three-dimensional (3D) representation of a single object with sub-µm resolution is crucial in many fields, from material science to clinical diagnostics. This is typically achieved through tomography, which combines multiple 2D images of the same object captured with different orientations. However, this serial imaging method prevents single-shot acquisition in imaging experiments, a mandatory feature for the development of time-resolved 3D imaging. In the present experiment, we report on an approach for extracting information on the 3D structure of an object by using extreme-ultraviolet (EUV) radiation. In this method, two EUV pulses hit an isolated 3D object simultaneously from different directions, generating independent coherent diffraction patterns, resulting in two distinct bidimensional projections after phase retrieval. These views are then used, in combination with a ray tracing algorithm, to retrieve information on the 3D structure. This EUV stereoscopic imaging approach, similar to the natural process of binocular vision, provides sub-µm spatial resolution and single-shot capability. Moreover, ultrafast time resolution and spectroscopy can be readily implemented, and a further extension to x-ray wavelengths can be envisioned as well.

Nanometer Sized Direct Laser-Induced Gold Printing for Precise 2D-Electronic Device Fabrication.

Flexible electronics manufacturing technologies are essential and highly favored for future integrated photonic and electronic devices. Direct laser induced writing (DIW) of metals has shown potential as a fast and highly variable method in adaptable electronics. However, most of the DIW procedures use silver structures, which tend to oxidize and are limited to the micrometer regime. Here, a DIW technique is introduced that not only enables electrical gold wiring of 2D van-der-Waals materials with sub-µm structures and 100nm interspacing resolution but is also capable of fabricating photo switches and field effect transistors on various rigid and elastic materials. Light sensitive metalloid Au32 -nanoclusters serve as the ink that allows for low-power cw-laser exposure without further post-treatment. With a simple lift-off procedure, the unexposed ink can be removed. The technique realizes ultrafast, high resolution, and high precision production of integrated electronics and may pave the way for personalized circuits even printed on curved surfaces.

An advanced Bragg diffraction imaging technique to characterize defects: The examples of GaN and AlN

An advanced X-ray Bragg diffraction imaging technique known as Rocking Curve Imaging (RCI) was implemented and developed at the European Synchrotron Radiation Facility (ESRF), where it complements the simpler and faster, but less accurate, “white beam topography” technique. These techniques allow the observation and characterization of defects in bulk crystals, as well as in crystalline layers with a thickness in the μm range. We recall the basics of X-ray Bragg diffraction imaging (historically called X-ray topography) and describe the technical aspects of RCI, including the approximations we often use to analyse the images, and the information we can extract from the various produced maps (Integrated Intensity, Full Width Half Maximum and Peak Position). We show, as examples, results of its application to aluminium nitride (AlN) and gallium nitride (GaN) crystals that are used as substrates for microelectronic devices. More in particular we describe the images of individual dislocations in crystals of both materials, and the particular arrangement of threading dislocations in ammonothermally grown GaN that lead to subgrain boundaries and hexagonal shaped (“honeycomb”) defects. These examples show that the RCI Bragg diffraction imaging technique allows obtaining unique results, in the sub-μm spatial resolution and the μradian range angular resolution ranges, when the characterization of high-quality crystals is required.

Liquid Phase Epitaxy growth and luminescence of Terbium-doped Gd3Ga5O12 crystalline layers

Tb3+-doped single-crystalline Gd3Ga5O12 layers are grown by Liquid Phase Epitaxy on (111)-oriented undoped substrates, and their structure, composition, morphology and photo- and radioluminescence are studied. Layers doped with 6 at.% Tb3+ with a thickness up to 20 μm appear promising for single crystal film scintillators with a sub-μm spatial resolution and waveguide lasers as they exhibit good quality, uniform distribution of Tb3+ ions, optimized light output (~50% of that for Ce:YAG), weak concentration quenching of luminescence and low afterglow for a 15 bit dynamic range.

Surface wetting to enhance thermoreflectance characterization of integrated circuits.

Thermoreflectance (TR) imaging enables non-contact thermal imaging of devices and integrated circuits (ICs) with sub-µm spatial resolution. TR coefficient of most metals and semiconductors in visible wavelengths is in the 10-5 to 10-3K-1 range, which gives a temperature resolution of 0.1-0.5 °C with a few minutes of averaging. Here, we show that surface wetting with various solvents, such as water, methanol, as well as Fluorinert, which is a commonly used coolant for high-power ICs, can enhance the TR coefficient by up to 19 times. Systematic characterizations as a function of the heating power, illumination-wavelength, liquid layer thickness, sample's tilt, and objective lens's numerical aperture are presented. TR images are distorted due to interference in the liquid layer, but this technique could be used for fast detection of small temperature variations and hot spots in ICs.

Direct observation of antiferromagnetic parity violation in the electronic structure of Mn2Au

Using momentum microscopy with sub-µm spatial resolution, allowing momentum resolved photoemission on individual antiferromagnetic domains, we observe an asymmetry in the electronic band structure, , in Mn2Au. This broken band structure parity originates from the combined time and parity symmetry, , of the antiferromagnetic order of the Mn moments, in connection with spin–orbit coupling. The spin–orbit interaction couples the broken parity to the Néel order parameter direction. We demonstrate a novel tool to image the Néel vector direction, N, by combining spatially resolved momentum microscopy with ab-initio calculations that correlate the broken parity with the vector N.

Fatigue and fracture-induced defect structures of metals investigated by positron microscopy

Abstract Defect distributions close to cracks from monotonic and fatigue fractures have been investigated for the first time by positron lifetime studies. The positron beams probe either the depth profile of defects at sub-μm resolution or the lateral distribution of defects at a few μm spatial resolution. Both in pure Cu and in the precipitation-hardened alloy Al 6013, in addition to dislocations, large clusters of up to 30 vacancies were detected close to a fatigue crack exclusively, whereas at monotonic fractures only the annihilation characteristics of dislocations were observed. If this characteristic difference holds as a general rule, then positron lifetime microscopy will provide a simple, quantitative method to distinguish a posteriori monotonic fractures from fatigue fractures without any further fractographic studies.

Three-dimensional imaging on a chip using optofluidics light-sheet fluorescence microscopy.

Volumetric, sub-micron to micron level resolution imaging is necessary to assay phenotypes or characteristics at the sub-cellular/organelle scale. However, three-dimensional fluorescence imaging of cells is typically low throughput or compromises on the achievable resolution in space and time. Here, we capitalise on the flow control capabilities of microfluidics and combine it with microoptics to integrate light-sheet based imaging directly into a microfluidic chip. Our optofluidic system flows suspended cells through a sub-micrometer thick light-sheet formed using micro-optical components that are cast directly in polydimethylsiloxane (PDMS). This design ensures accurate alignment, drift-free operation, and easy integration with conventional microfluidics, while providing sufficient spatial resolution, optical sectioning and volumetric data acquisition. We demonstrate imaging rates of 120 ms per cell at sub-μm resolution, that allow extraction of complex cellular phenotypes, exemplified by imaging of cell clusters, receptor distribution, and the analysis of endosomal size changes.

Area-Selective Atomic Layer Deposition Patterned by Electrohydrodynamic Jet Printing for Additive Manufacturing of Functional Materials and Devices.

There is an increasing interest in additive nanomanufacturing processes, which enable customizable patterning of functional materials and devices on a wide range of substrates. However, there are relatively few techniques with the ability to directly 3D print patterns of functional materials with sub-micron resolution. In this study, we demonstrate the use of additive electrohydrodynamic jet (e-jet) printing with an average line width of 312 nm, which acts as an inhibitor for area-selective atomic layer deposition (AS-ALD) of a range of metal oxides. We also demonstrate subtractive e-jet printing with solvent inks that dissolve polymer inhibitor layers in specific regions, which enables localized AS-ALD within those regions. The chemical selectivity and morphology of e-jet patterned polymers towards binary and ternary oxides of ZnO, Al2O3, and SnO2 were quantified using X-ray photoelectron spectroscopy, atomic force microscopy, and Auger electron spectroscopy. This approach enables patterning of functional oxide semiconductors, insulators, and transparent conducting oxides with tunable composition, Å-scale control of thickness, and sub-μm resolution in the x-y plane. Using a combination of additive and subtractive e-jet printing with AS-ALD, a thin-film transistor was fabricated using zinc-tin-oxide for the semiconductor channel and aluminum-doped zinc oxide as the source and drain electrical contacts. In the future, this technique can be used to print integrated electronics with sub-micron resolution on a variety of substrates.

Temporal superoscillations of subterahertz coherent acoustic phonons

We observe coherent acoustic phonon superoscillations at sub-terahertz frequencies. The superoscillations result from the interference of optically excited coherent longitudinal acoustic phonon modes in a GaAs/AlGaAs superlattice. The superoscillations are seen in local temporal regions and their frequency is up to 60% larger than the highest frequency excited/detected phonon mode. Such superoscillatory phonon pulses may potentially be used for high-resolution acoustic measurement in strong scattering media. Coherent acoustic phonons with frequencies in the 100s of GHz range, which are also known as acoustic nanowaves, are a powerful tool for investigating nano-scale objects with high temporal and spatial resolution. The established technique, known as picosecond acoustics, uses ultrafast (femtosecond) pulsed lasers to optically generate and detect coherent acoustic phonons with frequencies up to ~1 THz [1]. Such acoustic nanowaves can be used to probe the structural and mechanical properties of matter with sub-nm axial resolution and sub-µm transverse resolution [2]. Examples of the applications include studies of various nano-objects [3, 4], interfaces [5], defects in solids [6], soft condensed matter [7], liquids [8] and biological matter (single cells) [9] (for a review see also [10]). Acoustic nanowaves have also been used for ultrafast control of photonic [11], electronic [12], and spintronic [13] devices. Despite the successes of the picosecond acoustics technique, it suffers from a significant practical drawback: the strong attenuation and/or scattering, i.e. short mean free path, of high frequency (>~100s of GHz) phonons in many of the objects of interest. Causes of phonon attenuation and scattering include: propagation through non-ideal interfaces [14], e.g. between a stick-on optoacoustic transducer and the object under investigation; propagation in polycrystalline materials and crystals with a high defect density [15]; viscous damping [16]; natural isotope (point mass defect) scattering [17], which occurs even in perfect crystals. At ambient, room, temperature, the mean free path of THz acoustic phonons in high-quality (semiconductor grade) crystals is only a few µm [18]. The result of these is that the mean free path decreases strongly with increasing phonon frequency with the net effect of imposing a bandwidth limit, restricting the highest frequency of the phonons that can be propagated in the system. This determines the highest phonon frequency that can be used in a picosecond acoustic measurement and hence the best resolution that could normally be obtained. Bandwidth limitations also occur in measurements using electromagnetic waves and the search for ways to overcome these has led to renewed interest in the phenomenon of superoscillation. Superoscillations occur in a band-limited function due the interference of a series of harmonic waves, Fourier series, with the appropriate amplitudes and phases. They are oscillations found in local temporal regions having rates arbitrarily higher than the highest frequency Fourier component [19]. Superoscillations have relevance in all areas of physics where waves are superposed, e.g. in quantum mechanics [20]. It has also been proposed and demonstrated that superoscillations could be exploited

Antagonists Pharmacologically Chaperone Opioid Receptors

More than 100 people die daily in the United States from opioid-related drug overdoses. µ-Opioid receptor (MOR) antagonists, such as naltrexone (Ntx) and naloxone, partially suppress overdose effects, but also induce supersensitivity to MOR activation. Opioid receptors are folded in the endoplasmic reticulum (ER), undergo transport to the Golgi, eventually reach the plasma membrane, and may also later undergo endocytosis. We examined the effects of opioid ligands on MOR trafficking during the earlier processes. Properly folded protein cargo recruits ER exit sites (ERES) and then enters coated vesicles for delivery to the Golgi. We transfected SH-SY5Y cells with fluorescently tagged Sec24 variants to visualize and quantify ERES, and with the strongly ER-retained MOR mutant, MOR[N190K]. We attained sub-µm resolution, for information on ligand effects on ERES levels in live cells. Forster resonance energy transfer (FRET) showed that MOR closely interacts with both Sec24C and Sec24D. Using Sec24D-eGFP to fluorescently mark ERES, we observed that the antagonists increase the fraction of the cytoplasm occupied by ERES. We also found that SH-SY5Y cells overexpressing wild-type δ-opioid receptors have increased ERES levels after exposure to naloxone. These effects most likely occur when an antagonist acts as a pharmacological chaperone of opioid receptors. We rule out the alternative hypothesis that antagonists affect ERES levels via changes in [cAMP] because Ntx did not detectably change [cAMP]. In contrast to these effects of antagonists, several opioid agonists (morphine, fentanyl, buprenorphine, and methadone) lacked detectable effects on ERES levels. Full or partial agonists, but not antagonists, phosphorylate MOR at S375, but SH-SY5Y cells overexpressing MOR[N190K][S375A] showed no change in ERES density in response to agonists. The possibility that antagonists induce supersensitivity by pharmacologically chaperoning opioid receptors could suggest innovative approaches for opioid abuse disorder.

A versatile and robust surface-poison-resisting Scanning Amperometric Proton Microscopy

Abstract A sensitive and accurate measurement of localized pH with improving spatial resolution is highly desirable to the scientific understanding of many processes ranging from clean energy production to biological cellular mechanisms. In this study, we report the observation that the diffusion-limited current (DLC) of hydrogen evolution reaction (HER) on Pt surface is largely surface poison-resisting to carbon monoxide and thiol, two well-known Pt surface poisons. Building upon this observation, we proposed and tested a technique for amperometrically measuring localized proton concentration with a sub-μm spatial resolution through the utilization of a linear pH dependence of HER DLC on a Pt ultramicroelectrode, hereby referred to as Scanning Amperometric Proton Microscopy (SAPM). By bringing the Pt ultramicroelectrode close to a proton generating/consuming substrate through resonance feedback on an atomic force microscopy (AFM) tuning fork, SAPM can be used to measure and image localized proton concentrations and changes in pH caused by an active catalytic surface during reactions, largely free of concerns about the presence of surface-poisoning species. This was demonstrated through three proof-of-concept cases: methanol oxidation reaction (MOR) on a Pt thin film substrate, active proton-coupled electron transfer by a membrane-tethered protein (cytochrome c oxidase) in biological compatible electrolyte, and SAPM imaging of PtRu islands electrodeposited onto a Pt film substrate during MOR. The development of this surface-poison-resisting scanning probe technique through this study shows the potential of a broadly applicable way to study proton-generating or -consuming reactions for catalytically-active substrates with a sub-μm spatial resolution, including biological processes involving localized pH changes in a variety of salts, buffers or broth-type reaction media at near-neutral pH values.

Visualization of internal structure and internal stress in visibly opaque objects using full-field phase-shifting terahertz digital holography.

We construct a full-field phase-shifting terahertz digital holography (PS-THz-DH) system by use of a THz quantum cascade laser and an uncooled, 2D micro-bolometer array. The PS-THz-DH enables us to separate the necessary diffraction-order image from unnecessary diffraction-order images without the need for spatial Fourier filtering, leading to suppress the decrease of spatial resolution. 3D shape of a visibly opaque object is visualized with a sub-millimeter lateral resolution and a sub-µm axial resolution. Also, the digital focusing of amplitude image enables the visualization of internal structure with the millimeter-order axial selectivity. Furthermore, the internal stress distribution of an externally compressed object is visualized from the phase image. The demonstrated results imply a possibility for non-destructive inspection of visibly opaque non-metal materials.

Super-Resolution Scanning Transmission X-Ray Imaging Using Single Biconcave Parabolic Refractive Lens Array

A new super resolution imaging technique which potentially enables sub-µm spatial resolution, using a detector of pixels much larger than the spatial resolution, is proposed. The method utilizes sample scanning through a large number of identical X-ray microprobes periodically spaced (the period corresponds to a multiple of the pixel size), which reduces drastically the scanning time. The information about the sample illuminated by the microprobes is stored by large detector pixels. Using these data and sample position information, a super-resolution image reconstruction is performed. With a one-dimensional (1D) high aspect ratio nickel single lens array designed for theoretically expected sub-µm microprobes at 17 keV and fabricated by deep X-ray lithography and electroforming technique, 2 µm X-ray microprobes with a period of 10 µm were achieved. We performed a first experiment at KARA synchrotron facility, and it was demonstrated that the smallest structure of a test pattern with a size of 1.5 µm could be easily resolved by using images generated from a detector having a pixel size of 10.4 µm. This new approach has a great potential for providing a new microscopic imaging modality with a large field of view and short scan time.

Nanosecond pulse plasma dry reforming of natural gas

CO2 conversion into value-added chemicals and fuels is one of the greatest challenges of human society. Plasma-assisted catalysis is an emerging and rapidly expanding field of research offering promising solutions to this problem. However, conversion rates and energy efficiency of the plasma processes remain insufficient for widespread industrial adoption. The key reasons are highly-complex and ultra-fast reaction kinetics in the gas phase and at the interface with catalytic and supporting materials, which form intricate 3D micro-porous structures, especially in packed bed dielectric barrier discharge (PB-DBD). Our work fills this critical gap in knowledge by developing a novel simulation approach to maximize the conversion rates and energy efficiency of the ns pulse driving PB-DBD based on precise studies of plasma dynamics with sub-ns and sub-μm resolution. The high instantaneous power leads to the expansion of plasma is in the form of surface ionization waves coupled with filamentary microdischarges. The strong electron dissociation reaction in these discharge region results in CO and H2 density of ns pulse PB-DBD are higher than those of other approaches to plasma catalysis. The extremely low duty cycle of ns pulse also decreases the backward recombination reaction. Therefore, the conversion rate and the energy efficiency of plasma catalysis are improved. This approach is generic, is validated by experimental results, and can be applied to other plasma catalysis systems.

Pore space extraction and characterization of sack paper using μ‐CT

This paper is a seemingly abundant material. Its intrinsic porosity enables a vast number of commercial applications. Particularly packing products, e.g. cement bags, often incorporate sack kraft paper due to its high porosity and its additional mechanical strength. A direct quantification of the porosity of sack kraft papers is, hence, particularly desirable. However, experimental quantification of paper porosity or its pore network properties is difficult and often highly indirect. A nondestructive statistical analysis of the 3D microstructure holds the promise to directly assess the pores. In particular, X-ray microcomputed tomography (μ-CT), frequently with sub-μm resolution, has been established as a method to study the fibre and pore structure of paper. The question arises, whether statistical analysis of the microstructure based on μ-CTimaging is sufficient to reliably distinguish between different sack kraft papers. Here, we explore whether the pore structure of paper can be extracted and statistically analysed for larger sample areas despite the fact that a larger sample size directly translates into a lower resolution of the μ-CTscan. We expect that a large sample size increases the region of interest on the basis of which samples can be better distinguished. A lowered resolution poses a severe challenge for the reliable identification of voxel data as pores or as fibres, because the contrast between paper fibres (made of cellulose) and air, which is established due to X-ray absorption, is weak. We show that we can reliably assign each voxel by using an indicator kriging as a two-step method. This method performs an initial voxel identification based on the overall distribution of measured grey values and refines the identification by inspecting the local environment of each voxel. For the pore space extracted in such a way, we can then compute quantities that are related to the geometry and connectivity properties of the pores. Furthermore, we address a paper-born challenge for such an analysis, i.e. we cannot always unambiguously tell whether a pore is located inside the paper sheet or at the surface of the paper. The way the paper surfaces are extracted from the microstructure decisively determines the final specifications of the predicted properties. A significant distinction of the samples is only possible when comparing the properties of the pore network.

Spatial resolution versus contrast trade-off enhancement in high-resolution surface plasmon resonance imaging (SPRI) by metal surface nanostructure design.

Surface plasmon resonance imaging (SPRI) is an optical near-field method used for mapping the spatial distribution of chemical/physical perturbations above a metal surface without exogenous labeling. Currently, the majority of SPRI systems are used in microarray biosensing, requiring only modest spatial resolution. There is increasing interest in applying SPRI for label-free near-field imaging of biological cells to study cell/surface interactions. However, the required resolution (sub-µm) greatly exceeds what current systems can deliver. Indeed, the attenuation length of surface plasmon polaritons (SPP) severely limits resolution along one axis, typically to tens of µm. Strategies to date for improving spatial resolution result in a commensurate deterioration in other imaging parameters. Unlike the smooth metal surfaces used in SPRI that support purely propagating surface modes, nanostructured metal surfaces support "hybrid" SPP modes that share attributes from both propagating and localized modes. We show that these hybrid modes are especially well-suited to high-resolution imaging and demonstrate how the nanostructure geometry can be designed to achieve sub-µm resolution while mitigating the imaging parameter trade-off according to an application-specific optimum.

Synchrotron radiation microbeam X-ray diffraction for nondestructive assessments of local structural properties of faceted InGaN/GaN quantum wells

Synchrotron radiation (SR) X-ray diffraction with a sub-µm spatial resolution is used to nondestructively evaluate the local thickness and alloy composition of three-dimensionally faceted InGaN/GaN quantum wells (QWs). The (0001) facet QW on a trapezoidal structure composed of (0001), , and facets is nonuniform, most likely owing to the migration of adatoms between facets. The thickness and composition markedly vary within a short distance for the facet QW of another pyramidal structure. The QW parameters acquired by SR microbeam X-ray diffraction reproduce the local emission property assessed by cathodoluminescence, thereby indicating the high reliability of this method.