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The patterning of x-ray grating surfaces by electron-beam lithography offers large flexibility to realize complex optical functionalities. Here, we report on a proof-of-principle experiment to demonstrate the correction of slope errors of the substrates by modulating the local density of the grating lines. A surface error map of a test substrate was determined by optical metrology and served as the basis for an aligned exposure of a corrected grating pattern made by electron-beam lithography. The correction is done by a variation of the local line density in order to compensate for the local surface error. Measurements with synchrotron radiation and simulations in the soft X-ray range confirm that the effects of slope errors were strongly reduced over an extended wavelength range.
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Detection of heavy elements, such as metals, in macromolecular crystallography (MX) samples by X-ray fluorescence is a function traditionally covered at synchrotron MX beamlines by silicon drift detectors, which cannot be used at X-ray free-electron lasers because of the very short duration of the X-ray pulses. Here it is shown that the hybrid pixel charge-integrating detector JUNGFRAU can fulfill this function when operating in a low-flux regime. The feasibility of precise position determination of micrometre-sized metal marks is also demonstrated, to be used as fiducials for offline prelocation in serial crystallography experiments, based on the specific fluorescence signal measured with JUNGFRAU, both at the synchrotron and at SwissFEL. Finally, the measurement of elemental absorption edges at a synchrotron beamline using JUNGFRAU is also demonstrated.
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X-ray absorption spectroscopy (XAS) is a powerful element-specific technique that allows the study of structural and chemical properties of matter. Often an indirect method is used to access the X-ray absorption (XA). This work demonstrates a new XAS implementation that is based on off-axis transmission Fresnel zone plates to obtain the XA spectrum of La0.6Sr0.4MnO3 by analysis of three emission lines simultaneously at the detector, namely the O 2p-1s, Mn 3s-2p and Mn 3d-2p transitions. This scheme allows the simultaneous measurement of an integrated total fluorescence yield and the partial fluorescence yields (PFY) of the Mn 3s-2p and Mn 3d-2p transitions when scanning the Mn L-edge. In addition to this, the reduction in O fluorescence provides another measure for absorption often referred to as the inverse partial fluorescence yield (IPFY). Among these different methods to measure XA, the Mn 3s PFY and IPFY deviate the least from the true XA spectra due to the negligible influence of selection rules on the decay channel. Other advantages of this new scheme are the potential to strongly increase the efficiency and throughput compared with similar measurements using conventional gratings and to increase the signal-to-noise of the XA spectra as compared with a photodiode. The ability to record undistorted bulk XA spectra at high flux is crucial for future in situ spectroscopy experiments on complex materials.
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Macromolecular crystallography often requires focused high-intensity x-ray beams for solving challenging protein structures from micrometer-sized crystals using current synchrotron radiation sources. The design of optical focusing schemes for hard x-rays showing high efficiency and flexibility in beam size is therefore continuously pursued. Here, we present an innovative solution based on a two-stage demagnification of the undulator source for photon energies from 6 keV to 19 keV, commissioned at the X10SA beamline of the Swiss Light Source, where a secondary source is imaged by two crossed silicon kinoform x-ray diffractive lenses with 75 nm outermost zone width. A source-size limited spot with a size of 4.8 µm×1.7 µm(h×v,FWHM) and flux of 7.5×1010 photons/s at 12.4 keV is demonstrated at the sample position.
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We have implemented and successfully tested an off-axis transmission Fresnel zone plate as a novel type of analyzer optics for resonant inelastic x-ray scattering (RIXS). We achieved a spectral resolution of 64 meV at the nitrogen K-edge (E/dE = 6200), closely matching theoretical predictions. The fundamental advantage of transmission optics is the fact that it can provide stigmatic imaging properties. This opens up a variety of advanced RIXS configurations, such as efficient scanning RIXS, parallel detection for varying incident energy and time-resolved measurements.
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High-efficiency microfocusing of multi-keV X-rays at synchrotron sources is highly profitable for spatially resolved structural analysis of many kinds. Because radiation from synchrotron sources is typically elongated along the horizontal dimension, generating a microbeam that is isotropic in size requires a carefully designed optics system. Here we report on using a combination of a horizontally tunable slit downstream of the undulator source with elliptical diffractive Fresnel zone plates. We demonstrate the arrangement in context of small-angle X-ray scattering experiments, obtaining a microbeam of 2.2 µm × 1.8 µm (X × Y) with a flux of 1.2 × 1010 photons/s at an energy of 11.2 keV at the sample position.
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The focusing efficiency of conventional diffractive x-ray lenses is fundamentally limited due to their symmetric binary structures and the corresponding symmetry of their focusing and defocusing diffraction orders. Fresnel zone plates with asymmetric structure profiles can break this limitation; yet existing implementations compromise either on resolution, ease of use, or stability. We present a new way for the fabrication of such blazed lenses by patterning two complementary binary Fresnel zone plates on the front and back sides of the same membrane chip to provide a compact, inherently stable, single-chip device. The presented blazed double-sided zone plates with 200 nm smallest half-pitch provide up to 54.7% focusing efficiency at 6.2 keV, which is clearly beyond the value obtainable by their binary counterparts.
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Well-defined submicrometer structures of poly(dimethylaminoethyl methacrylate) (PDMAEMA) were grafted from 100 µm thick films of poly(ethene-alt-tetrafluoroethene) after electron-beam lithographic exposure. To explore the possibilities and limits of the method under different exposure conditions, two different acceleration voltages (2.5 and 100 keV) were employed. First, the influence of electron energy and dose on the extent of grafting and on the structure's morphology was determined via atomic force microscopy. The surface grafting with PDMAEMA was confirmed by advanced surface analytical techniques such as time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. Additionally, the possibility of effective postpolymerization modification of grafted structures was demonstrated by quaternization of the grafted PDMAEMA to the polycationic QPDMAEMA form and by exploiting electrostatic interactions to bind charged organic dyes and functional proteins.
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The fabrication of high aspect ratio metallic nanostructures is crucial for the production of efficient diffractive X-ray optics in the hard X-ray range. We present a novel method to increase their structure height via the double-sided patterning of the support membrane. In transmission, the two Fresnel zone plates on the two sides of the substrate will act as a single zone plate with added structure height. The presented double-sided zone plates with 30 nm smallest zone width offer up to 9.9% focusing efficiency at 9 keV, that results in a factor of two improvement over their previously demonstrated single-sided counterparts. The increase in efficiency paves the way to speed up X-ray microscopy measurements and allows the more efficient utilization of the flux in full-field X-ray microscopy.
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High-efficiency nanofocusing of hard X-rays using stacked multilevel Fresnel zone plates with a smallest zone width of 200 nm is demonstrated. The approach is to approximate the ideal parabolic lens profile with two-, three-, four- and six-level zone plates. By stacking binary and three-level zone plates with an additional binary zone plate, the number of levels in the optical transmission function was doubled, resulting in four- and six-level profiles, respectively. Efficiencies up to 53.7% focusing were experimentally obtained with 6.5 keV photons using a compact alignment apparatus based on piezoelectric actuators. The measurements have also been compared with numerical simulations to study the misalignment of the two zone plates.
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Multiple scattering represents a challenge for numerous modern tomographic imaging techniques. In this Letter, we derive an appropriate line integral that allows for the tomographic reconstruction of angular resolved scattering distributions, even in the presence of multiple scattering. The line integral is applicable to a wide range of imaging techniques utilizing various kinds of probes. Here, we use x-ray grating interferometry to experimentally validate the framework and to demonstrate additional structural sensitivity, which exemplifies the impact of multiple scattering tomography.
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Interferometria/métodos , Tomografia Computadorizada por Raios X/métodos , Modelos Teóricos , Espalhamento de RadiaçãoRESUMO
We report the fabrication and field emission properties of high-density nano-emitter arrays with on-chip electron extraction gate electrodes and up to 10(6) metallic nanotips that have an apex curvature radius of a few nanometers and a the tip density exceeding 10(8) cm(-2). The gate electrode was fabricated on top of the nano-emitter arrays using a self-aligned polymer mask method. By applying a hot-press step for the polymer planarization, gate-nanotip alignment precision below 10 nm was achieved. Fabricated devices exhibited stable field electron emission with a current density of 0.1 A cm(-2), indicating that these are promising for applications that require a miniature high-brightness electron source.
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Phase contrast x-ray imaging (PCXI) is a promising imaging modality, capable of sensitively differentiating soft tissue structures at high spatial resolution. However, high sensitivity often comes at the cost of a long exposure time or multiple exposures per image, limiting the imaging speed and possibly increasing the radiation dose. Here, we demonstrate a PCXI method that uses a single short exposure to sensitively capture sample phase information, permitting high speed x-ray movies and live animal imaging. The method illuminates a checkerboard phase grid to produce a fine grid-like intensity reference pattern at the detector, then spatially maps sample-induced distortions of this pattern to recover differential phase images of the sample. The use of a phase grid is an improvement on our previous absorption grid work in two ways. There is minimal loss in x-ray flux, permitting faster imaging, and, a very fine pattern is produced for homogenous high spatial resolution. We describe how this pattern permits retrieval of five images from a single exposure; the sample phase gradient images in the horizontal and vertical directions, a projected phase depth image, an edge-enhanced image, and a type of scattering image. Finally, we describe how the reconstruction technique can achieve subpixel distortion retrieval and study the behavior of the technique in regard to analysis technique, Talbot distance, and exposure time.
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Iluminação/instrumentação , Microscopia de Contraste de Fase/instrumentação , Refratometria/instrumentação , Transdutores , Difração de Raios X/instrumentação , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de EquipamentoRESUMO
The fabrication and characterization of Fresnel zone plates (FZPs) for hard X-ray microscopy applications are reported. High-quality 500 nm- and 1 µm-thick Au FZPs with outermost zone widths down to 50 nm and 70 nm, respectively, and with diameters up to 600 µm were fabricated. The diffraction efficiencies of the fabricated FZPs were measured for a wide range of X-ray energies (2.8-13.2 keV) showing excellent values up to 65-75% of the theoretical values, reflecting the good quality of the FZPs. Spatially resolved diffraction efficiency measurements indicate the uniformity of the FZPs and a defect-free structure.
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X-ray microscopy based on Fresnel zone plates is a powerful technique for sub-100 nm resolution imaging of biological and inorganic materials. Here, we report on the modeling, fabrication and characterization of zone-doubled Fresnel zone plates for the multi-keV regime (4-12 keV). We demonstrate unprecedented spatial resolution by resolving 15 nm lines and spaces in scanning transmission X-ray microscopy, and focusing diffraction efficiencies of 7.5% at 6.2 keV photon energy. These developments represent a significant step towards 10 nm spatial resolution for hard X-ray energies of up to 12 keV.
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Microscopia Eletrônica de Transmissão e Varredura/instrumentação , Microscopia/instrumentação , Difração de Raios X/instrumentação , Desenho de Equipamento , Lentes , Microscopia/métodos , Microscopia Eletrônica de Transmissão e Varredura/métodos , Dispositivos Ópticos , Fenômenos Ópticos , Espalhamento a Baixo Ângulo , Difração de Raios X/métodosRESUMO
We fabricate computer generated holograms for the generation of phase singularities at extreme ultraviolet (EUV) wavelengths using electron beam lithography and demonstrate their ability to generate optical vortices in the nonzero diffraction orders. To this end, we observe the characteristic intensity distribution of the vortex beam and verify the helical phase structure interferometrically. The presented method forms the basis for further studies on singular light fields in the EUV frequency range, i.e., in EUV interference lithography. Since the method is purely achromatic, it may also find applications in various fields of x ray optics.
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Due to the ability of 100 keV electrons to penetrate deep into resist with little scattering, we were able to directly write various dense and high aspect ratio nanostructures in 540 nm and 1.1 microm thick layers of poly(methyl methacrylate) (PMMA) resist. The PMMA molds produced by electron beam lithography were developed using a high contrast developer. The molds were used to transfer the pattern into metallic nanostructures by filling the developed trenches with Au by electroplating. By exposing lines narrower than the target width, we observed improved process latitude and line width control. The obtained aspect ratios of the dense structures are nearly 20 in 1.1 microm PMMA layers and > 16 for structures electroplated into this PMMA mold. The fabrication method was successfully applied to produce Au diffractive x-ray Fresnel zone plates of exceptionally good quality with 50 and 70 nm outermost zones using 540 nm and 1.1 microm thick PMMA molds. In addition, we also produced regular arrays of high aspect ratio and dense Au nanorods with periods down to 100 nm and high aspect ratio split-ring resonators.
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We investigated the fabrication of dense, high aspect ratio hydrogen silsesquioxane (HSQ) nanostructures by 100 keV electron beam lithography. The samples were developed using a high contrast developer and supercritically dried in carbon dioxide. Dense gratings with line widths down to 25 nm were patterned in 500 nm-thick resist layers and semi-dense gratings with line widths down to 10 nm (40 nm pitch) were patterned in 250 nm-thick resist layers. The dense HSQ nanostructures were used as molds for gold electrodeposition, and the semi-dense HSQ gratings were iridium-coated by atomic layer deposition. We used these methods to produce Fresnel zone plates with extreme aspect ratio for scanning transmission x-ray microscopy that showed excellent performance at 1.0 keV photon energy.
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Novel imaging layer technology for electron-beam and extreme-ultraviolet lithographic processes based upon generation of Pd nanoparticles in the Pd(2+)-loaded TiO(2) films was developed. The electroless metallization of the patterned TiO(2):Pd(2+) films yields both negative and positive nickel images with resolution down to approximately 100 nm.
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High aspect ratio nanostructuring requires high precision pattern transfer with highly directional etching. In this work, we demonstrate the fabrication of structures with ultra-high aspect ratios (up to 10 000 : 1) in the nanoscale regime (down to 10 nm) by platinum assisted chemical etching of silicon in the gas phase. The etching gas is created by a vapour of water diluted hydrofluoric acid and a continuous air flow, which works both as an oxidizer and as a gas carrier for reactive species. The high reactivity of platinum as a catalyst and the formation of platinum silicide to improve the stability of the catalyst pattern allow a controlled etching. The method has been successfully applied to produce straight nanowires with section size in the range of 10-100 nm and length of hundreds of micrometres, and X-ray optical elements with feature sizes down to 10 nm and etching depth in the range of tens of micrometres. This work opens the possibility of a low cost etching method for stiction-sensitive nanostructures and a large range of applications where silicon high aspect ratio nanostructures and high precision of pattern transfer are required.