We demonstrate the bulk self-alignment of dispersed gold nanorods imposed by the intrinsic cylindrical micelle selfassembly in nematic and hexagonal liquid crystalline phases of anisotropic fluids. External magnetic field and shearing allow for alignment and realignment of the liquid crystal matrix with the ensuing long-range orientational order of well-dispersed plasmonic nanorods. This results in a switchable polarization-sensitive plasmon resonance exhibiting stark differences from that of the same nanorods in isotropic fluids. The device-scale bulk nanoparticle alignment may enable optical metamaterial mass production and control of properties arising from combining the switchable nanoscale structure of anisotropic fluids with the surface plasmon resonance properties of the plasmonic nanorods.KEYWORDS Nanorods, liquid crystals, optical metamaterials, self-assembly, plasmonic nanoparticles H aving predesigned structural units different from those in a conventional matter, metamaterials exhibit many unusual properties of interest from both fundamental science and applications standpoints. However, manufacturing such bulk optical metamaterials with three-dimensional (3D) structure 1-4 using lithography techniques presents a significant challenge, especially for the large-scale production. Mass production of bulk optical metamaterials from self-aligning and self-assembling nanoparticles is poised to revolutionize scientific instruments, technologies,andconsumerdevices.5-7 Althoughthemetamaterial self-assembly from nanoparticles remains a significant challenge, recent advances in colloidal science show that it may be realized and the emerging nanoscale alignment and assembly approaches utilize surface monolayers, 8,9 stretched polymer films, 10,11 and functionalized nanoparticles 12,13 but are usually restricted to only short-range ordering, twodimensional rather than three-dimensional assembly, and limited switching.7 Tunable metamaterials may potentially be obtained by nanoparticle self-assembly in liquid crystals (LCs) 14 through the LC-mediated realignment and rearrangement of incorporated nanoparticles in response to applied fields. However, experimental realization of such self-assembling switchable metamaterial composites is lacking. In this work, we demonstrate spontaneous long-range orientational ordering of gold nanorods (GNRs) dispersed in surfactant-based lyotropic LCs and use polarizing optical microscopy, darkfield microscopy, spectroscopy, and freezefracture transmission electron microscopy (FFTEM) to study these composites on the scales ranging from nanometers to millimeters. We find that the anisotropic fluids in both columnar hexagonal and nematic LC phases impose nematic-like long-range orientational ordering of GNRs with no correlation of their centers of mass but with the GNRs aligning along the LC director n (a unit vector describing the average local orientation of cylindrical micelles forming the LC), Figure 1. The unidirectional alignment of nanorods with high order parameter is...
We demonstrate the first (to our knowledge) general purpose full-field reflection-mode extreme ultraviolet (EUV) microscope based on coherent diffractive imaging. This microscope is capable of nanoscale amplitude and phase imaging of extended surfaces at an arbitrary angle of incidence in a noncontact, nondestructive manner. We use coherent light at 29.5 nm from high-harmonic upconversion to illuminate a surface, directly recording the scatter as the surface is scanned. Ptychographic reconstruction is then combined with tilted plane correction to obtain an image with amplitude and phase information. The image quality and detail from this diffraction-limited tabletop EUV microscope compares favorably with both scanning electron microscope and atomic force microscope images. The result is a general and completely extensible imaging technique that can provide a comprehensive and definitive characterization of how light at any wavelength scatters from a surface, with imminent feasibility of elemental imaging with few-nanometer resolution. OCIS codes: (120.5050) Phase measurement; (180.0180) Microscopy; (180.7460) X-ray microscopy; (190.2620) Harmonic generation and mixing. http://dx.
Scanning electron microscopy and atomic force microscopy are well-established techniques for imaging surfaces with nanometer resolution. Here we demonstrate a complementary and powerful approach based on tabletop extreme-ultraviolet ptychography that enables quantitative full field imaging with higher contrast than other techniques, and with compositional and topographical information. Using a high numerical aperture reflection-mode microscope illuminated by a tabletop 30 nm high harmonic source, we retrieve high quality, high contrast, full field images with 40 nm by 80 nm lateral resolution (≈1.3 λ), with a total exposure time of less than 1 min. Finally, quantitative phase information enables surface profilometry with ultra-high, 6 Å axial resolution. In the future, this work will enable dynamic imaging of functioning nanosystems with unprecedented combined spatial (<10 nm) and temporal (<10 fs) resolution, in thick opaque samples, with elemental, chemical and magnetic sensitivity.
We extend coherent diffraction imaging (CDI) to a high numerical aperture reflection mode geometry for the first time. We derive a coordinate transform that allows us to rewrite the recorded far-field scatter pattern from a tilted object as a uniformly spaced Fourier transform. Using this approach, FFTs in standard iterative phase retrieval algorithms can be used to significantly speed up the image reconstruction times. Moreover, we avoid the isolated sample requirement by imaging a pinhole onto the specimen, in a technique termed apertured illumination CDI. By combining the new coordinate transformation with apertured illumination CDI, we demonstrate rapid high numerical aperture imaging of samples illuminated by visible laser light. Finally, we demonstrate future promise for this technique by using high harmonic beams for high numerical aperture reflection mode imaging.
We report 3D coherent diffractive imaging (CDI) of Au/Pd core-shell nanoparticles with 6.1 nm spatial resolution with elemental specificity. We measured single-shot diffraction patterns of the nanoparticles using intense x-ray free electron laser pulses. By exploiting the curvature of the Ewald sphere and the symmetry of the nanoparticle, we reconstructed the 3D electron density of 34 core-shell structures from these diffraction patterns. To extract 3D structural information beyond the diffraction signal, we implemented a super-resolution technique by taking advantage of CDI’s quantitative reconstruction capabilities. We used high-resolution model fitting to determine the Au core size and the Pd shell thickness to be 65.0 ± 1.0 nm and 4.0 ± 0.5 nm, respectively. We also identified the 3D elemental distribution inside the nanoparticles with an accuracy of 3%. To further examine the model fitting procedure, we simulated noisy diffraction patterns from a Au/Pd core-shell model and a solid Au model and confirmed the validity of the method. We anticipate this super-resolution CDI method can be generally used for quantitative 3D imaging of symmetrical nanostructures with elemental specificity.
Characterizing buried layers and interfaces is critical for a host of applications in nanoscience and nano-manufacturing. Here we demonstrate non-invasive, non-destructive imaging of buried interfaces using a tabletop, extreme ultraviolet (EUV), coherent diffractive imaging (CDI) nanoscope. Copper nanostructures inlaid in SiO2 are coated with 100 nm of aluminum, which is opaque to visible light and thick enough that neither optical microscopy nor atomic force microscopy can image the buried interfaces. Short wavelength (29 nm) high harmonic light can penetrate the aluminum layer, yielding high-contrast images of the buried structures. Moreover, differences in the absolute reflectivity of the interfaces before and after coating reveal the formation of interstitial diffusion and oxidation layers at the Al-Cu and Al-SiO2 boundaries. Finally, we show that EUV CDI provides a unique capability for quantitative, chemically-specific imaging of buried structures, and the material evolution that occurs at these buried interfaces, compared with all other approaches.
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