Nanoscale Gratings Research Articles

Modelling and experimental study of surface morphology evolution during layer growth on nanograting structures

Coating nano/micro-structured elements with a single or multi-layered film can greatly enhance their functionality. The experimental enhancement, however, is significantly limited by the smoothing and distortion of the structural profile after coating. This requires a comprehensive understanding of the layer growth behavior on nanoscale non-isotropic surface with a proper model to analyze and predict the structure evolution. Here, a simplified linear growth model with single free parameter was successfully used for analysis of the smoothening of grating grooves. The model enables a quantitative description of the evolution of surface morphology from substrate to the top surface with sub-nanometer accuracy. Based on this, the smoothing behavior of single-Si layer and W/Si multilayer growth on nanoscale gratings (period ∼ 40 nm) and flat substrates were studied experimentally, for applications in X-ray optics. The smoothing effect of the W/Si multilayer coating is more pronounced than that of the single Si layer for both substrate types. The corrugated nanogratings suppressed the smoothing effect as compared to the flat isotropic surface. These works provide new guidance to predict and control the growth of layers on nanostructures.

Hierarchical Surface Structures and Large-Area Nanoscale Gratings in As2S3 and As2Se3 Films Irradiated with Femtosecond Laser Pulses.

Chalcogenide vitreous semiconductors (ChVSs) find application in rewritable optical memory storage and optically switchable infrared photonic devices due to the possibility of fast and reversible phase transitions, as well as high refractive index and transmission in the near- and mid-infrared spectral range. Formed on such materials, laser-induced periodic surface structures (LIPSSs), open wide prospects for increasing information storage capacity and create polarization-sensitive optical elements of infrared photonics. In the present work, a possibility to produce LIPSSs under femtosecond laser irradiation (pulse duration 300 fs, wavelength 515 nm, repetition rate up to 2 kHz, pulse energy ranged 0.03 to 0.5 μJ) is demonstrated on a large (up to 5 × 5 mm2) area of arsenic sulfide (As2S3) and arsenic selenide (As2Se3) ChVS films. Scanning electron and atomic force microscopy revealed that LIPSSs with various periods (170-490 nm) and orientations can coexist within the same irradiated region as a hierarchical structure, resulting from the interference of various plasmon polariton modes generated under intense photoexcitation of nonequilibrium carriers within the film. The depth of the structures varied from 30 to 100 nm. The periods and orientations of the formed LIPSSs were numerically simulated using the Sipe-Drude approach. A good agreement of the calculations with the experimental data was achieved.

Application and realization of Norland optical adhesive 73 novel photosensitive macromolecular material for the rapid preparation of periodically tunable nanoscale gratings.

Periodically tunable nano-gratings have an irreplaceable role in spectral scanning and optical communication, but the performance of gratings manufactured from different materials varies considerably, and the development of superior materials has energized the preparation of high-precision devices. This paper presents a nanoscale preparation process based on Norland Optical Adhesive 73 (NOA73), which enables the rapid preparation of periodically tunable nano-gratings with up to 100% light transmission. The powerful fluidity and shear rate of NOA73 make it uniquely suited to the preparation of precision devices, allowing the production of up to dense grating structures and offering the possibility of making nanoscale gratings. This paper uses multi-angle hierarchical lithography, die stretching, and replication to achieve further improvements in accuracy and successfully prepare gratings with a period of 500nm. The successful preparation of NOA73 nano-gratings demonstrates the practicality of NOA73 as a material for precision device fabrication.

Resonant Subwavelength and Nano-Scale Grating Structures for Biosensing Application: A Comparative Study.

Resonant-based sensors are attractive optical structures due to the easy detection of shifts in the resonance location in response to variations in the analyte refractive index (RI) in comparison to non-resonant-based sensors. In particular, due to the rapid progress of nanostructures fabrication methods, the manufacturing of subwavelength and nano-scale gratings in a large area and at a low cost has become possible. A comparative study is presented involving analysis and experimental work on several subwavelength and nanograting structures, highlighting their nano-scale features’ high potential in biosensing applications, namely: (i) Thin dielectric grating on top of thin metal film (TDGTMF), which can support the excitation of extended surface plasmons (ESPs), guided mode resonance, or leaky mode; (ii) reflecting grating for conventional ESP resonance (ESPR) and cavity modes (CMs) excitation; (iii) thick dielectric resonant subwavelength grating exhibiting guided mode resonance (GMR) without a waveguide layer. Among the unique features, we highlight the following: (a) Self-referenced operation obtained using the TDGTMF geometry; (b) multimodal operation, including ESPR, CMs, and surface-enhanced spectroscopy using reflecting nanograting; (c) phase detection as a more sensitive approach in all cases, except the case of reflecting grating where phase detection is less sensitive than intensity or wavelength detection. Additionally, intensity and phase detection modes were experimentally demonstrated using off-the-shelf grating-based optical compact discs as a low-cost sensors available for use in a large area. Several flexible designs are proposed for sensing in the visible and infrared spectral ranges based on the mentioned geometries. In addition, enhanced penetration depth is also proposed for sensing large entities such as cells and bacteria using the TDGTMF geometry.

Strong geometry dependence of the Casimir force between interpenetrated rectangular gratings

Quantum fluctuations give rise to Casimir forces between two parallel conducting plates, the magnitude of which increases monotonically as the separation decreases. By introducing nanoscale gratings to the surfaces, recent advances have opened opportunities for controlling the Casimir force in complex geometries. Here, we measure the Casimir force between two rectangular silicon gratings. Using an on-chip detection platform, we achieve accurate alignment between the two gratings so that they interpenetrate as the separation is reduced. Just before interpenetration occurs, the measured Casimir force is found to have a geometry dependence that is much stronger than previous experiments, with deviations from the proximity force approximation reaching a factor of ~500. After the gratings interpenetrate each other, the Casimir force becomes non-zero and independent of displacement. This work shows that the presence of gratings can strongly modify the Casimir force to control the interaction between nanomechanical components.

Characterization of nanoscale gratings by spectroscopic reflectometry in the extreme ultraviolet with a stand-alone setup.

The authors present a study on the dimensional characterization of nanoscale line gratings by spectroscopic reflectometry in the extreme ultraviolet spectral range (5 nm to 20 nm wavelength). The investigated grating parameters include the line height, the line width, the sidewall angle and corner radii. The study demonstrates that the utilization of shorter wavelengths in state-of-the-art optical scatterometry provides a high sensitivity with respect to the geometrical dimensions of nanoscale gratings. Measurable contrasts are demonstrated for dimensional variations in the sub-percent regime, down to one tenth of a nanometer and one tenth of a degree in absolute terms. In an experimental validation of the method, it is shown that reflectance curves can be obtained in a stand-alone setup using the broadband emission of a discharge produced plasma as the source of EUV radiation, demonstrating the potential scalability of the method for industrial uses. Simulated reflectance curves are fit to the experimental curves by variation of the grating parameters using rigorous electromagnetic modeling. The obtained grating parameters are cross-checked by a scanning electron microscopy analysis.

Characterizing profile tilt of nanoscale deep-etched gratings via x-ray diffraction

The authors report the development of fast, nondestructive, and high accuracy metrology for the characterization of profile tilt relative to the surface normal in nanoscale gratings using x-ray diffraction. Gratings were illuminated with a collimated x-ray beam (Cu Kα), similar to variable-angle small-angle x-ray scattering, to record changes of diffraction efficiency (DE) as a function of incidence angle. Simulations using scalar diffraction theory and rigorous coupled wave analysis predict extrema (0th order DE minimized, ±1st order DE maximized) when local grating bars are parallel to the incident x-ray beam. The surface normal was measured independently by reflecting a laser beam from the grating surface. The independent measurements using x rays and laser beams were referenced to each other via a slit reference plane to characterize the bar tilt angle relative to the surface normal. The fast x-ray measurement can be repeated at arbitrary points to study the spatial variation of the bar tilt angle across large gratings. Two test gratings etched with different deep reactive-ion etch chambers were prepared to investigate the performance of the proposed method. The authors report a repeatability of <0.01° and an accuracy of ∼0.08° with a fast scan speed (total integration time of 108 s to scan a line across ∼55 mm large grating samples at an interval of ∼2 mm). High spatial resolution (<50 μm) can be easily achieved at the expense of speed by limiting the incident x-ray spot size. This process is applicable to any periodic nanostructure as long as x-ray diffraction is well modeled.

Focal adhesion clustering drives endothelial cell morphology on patterned surfaces.

In many cell types, shape and function are intertwined. In vivo, vascular endothelial cells (ECs) are typically elongated and aligned in the direction of blood flow; however, near branches and bifurcations where atherosclerosis develops, ECs are often cuboidal and have no preferred orientation. Thus, understanding the factors that regulate EC shape and alignment is important. In vitro, EC morphology and orientation are exquisitely sensitive to the composition and topography of the substrate on which the cells are cultured; however, the underlying mechanisms remain poorly understood. Different strategies of substrate patterning for regulating EC shape and orientation have been reported including adhesive motifs on planar surfaces and micro- or nano-scale gratings that provide substrate topography. Here, we explore how ECs perceive planar bio-adhesive versus microgrooved topographic surfaces having identical feature dimensions. We show that while the two types of patterned surfaces are equally effective in guiding and directing EC orientation, the cells are considerably more elongated on the planar patterned surfaces than on the microgrooved surfaces. We also demonstrate that the key factor that regulates cellular morphology is focal adhesion clustering which subsequently drives cytoskeletal organization. The present results promise to inform design strategies of novel surfaces for the improved performance of implantable cardiovascular devices.

Room temperature III–V nanolasers with distributed Bragg reflectors epitaxially grown on (001) silicon-on-insulators

Efficient, scalable, bufferless, and compact III–V lasers directly grown on (001)-oriented silicon-on-insulators (SOIs) are preferred light sources in Si-photonics. In this article, we present the design and operation of III–V telecom nanolaser arrays with integrated distributed Bragg reflectors (DBRs) epitaxially grown on industry-standard (001) SOI wafers. We simulated the mirror reflectance of different guided modes under various mirror architectures, and accordingly devised nanoscale DBR gratings to support high reflectivity around 1500 nm for the doughnut-shaped TE01 mode. Building from InP/InGaAs nanoridges grown on SOI, we fabricated subwavelength DBR mirrors at both ends of the nanoridge laser cavities and thus demonstrated room-temperature low-threshold InP/InGaAs nanolasers with a 0.28 μm2 cross-section and a 20 μm effective cavity length. The direct growth of these bufferless nanoscale III–V light emitters on Si-photonics standard (001) SOI wafers opens future options of fully integrated Si-based nanophotonic integrated circuits in the telecom wavelength regime.

Nanoscale transient gratings excited and probed by extreme ultraviolet femtosecond pulses.

Advances in developing ultrafast coherent sources operating at extreme ultraviolet (EUV) and x-ray wavelengths allow the extension of nonlinear optical techniques to shorter wavelengths. Here, we describe EUV transient grating spectroscopy, in which two crossed femtosecond EUV pulses produce spatially periodic nanoscale excitations in the sample and their dynamics is probed via diffraction of a third time-delayed EUV pulse. The use of radiation with wavelengths down to 13.3 nm allowed us to produce transient gratings with periods as short as 28 nm and observe thermal and coherent phonon dynamics in crystalline silicon and amorphous silicon nitride. This approach allows measurements of thermal transport on the ~10-nm scale, where the two samples show different heat transport regimes, and can be applied to study other phenomena showing nontrivial behaviors at the nanoscale, such as structural relaxations in complex liquids and ultrafast magnetic dynamics.

Angle-dependent structural colors in a nanoscale-grating photonic crystal fabricated by reverse nanoimprint technology.

The structural color of angle-sensitive photonic crystals has attracted great interest because of a possible application in visual sensors. The appearance of a photonic crystal is mainly influenced by the optical properties, structural parameters and the observation angle. In this work, an angle-sensitive photonic crystal with nanoscale gratings was fabricated through reverse nanoimprint lithography. The periodicity and the structural color were investigated through measuring reflection spectra. The structural color of the photonic crystal has a period of 90°. Distinctive colors spanning the entire visible spectrum can be seen when the crystal is rotated. In addition, there is a blue-shift of the peak wavelength when the observation angle is increased. An equation for the observed wavelength as a function of the observation angle is proposed.

Narrow-Strip 670 nm Gain-Coupled Distributed Feedback Laser Based on Periodic Anodes Fabricated by I-Line Lithography

A narrow-strip single-longitudinal-mode gain-coupled distributed feedback semiconductor laser with a central wavelength of approximately 670 nm is demonstrated. We fabricate a novel micro-scale regrowth-free gain-coupled grating with an island-like shape without nanoscale gratings by i-line lithography only. The maximum output power from the fiber of the device with butterfly package is 48.1 mW at 100 mA and its slope efficiency is 0.79 W/A. The laser can be continuously tuned from 670.750 to 670.784 nm with a side-mode suppression ratio of over 40 dB, covering the absorptive peak of lithium atoms. Our easily fabricated devices have great potential as light sources in many applications such as lithium atom detectors.

Smith–Purcell Radiation from Low-Energy Electrons

Recent advances in the fabrication of nanostructures and nanoscale features in metasurfaces offer new prospects for generating visible light emission from low-energy electrons. Here we present the experimental observation of visible light emission from low-energy free electrons interacting with nanoscale periodic surfaces through the Smith–Purcell (SP) effect. We demonstrate SP light emission from nanoscale gratings with periodicity as small as 50 nm, enabling the observation of tunable visible radiation from low-energy electrons (1.5 to 6 keV), an order of magnitude lower in energy than previously reported. We study the emission wavelength and intensity dependence on the grating pitch and electron energy, showing agreement between experiment and theory. Our results open the way to the production of SP-based nanophotonics integrated devices. Built inside electron microscopes, SP sources could enable the development of novel electron–optical correlated spectroscopic techniques and facilitate the observatio...

Narrow-Strip Single-Longitudinal-Mode Laser Based on Periodic Anodes Defined by i-Line Lithography

A low-cost regrowth-free narrow-strip single-longitudinal-mode diode laser, based on periodic anodes defined only by i-line lithography is proposed. With the periodic anodes separated by surface insulated grooves acting as a 44th-order gain grating, a high gain contrast is achieved without introducing effective index coupling. The CW output power of the device without facet coatings is up to 100.9 mW/facet at 980.63 nm in single-longitudinal-mode operation with a single facet having a power conversion efficiency of up to 18.6% and a slope efficiency of 0.53 W/A. The highest side-mode suppression ratio is 45 dB with a linewidth below 889 MHz, at 350 mA. The beam parameter product, M ${\,}^{2}$ , in the slow axis is 1.85, achieving a near diffraction-limited beam quality. A novel method for easy surface gratings fabrication is first presented, wherein, 4-μm-width periodic surface grooves, acting as waveguide ridges, are defined once by i-line lithography only without regrowth, nanoscale gratings fabrication, or facet coating. Owing to the low-cost fabrication methods and good performances, our single-longitudinal-mode devices can be used for widespread practical applications.

P‐118: Nanoscale Gratings Induced Enhancement of Self‐assembly Quantum Rods Polarization

Nanoscale gratings was employed in this work to align the quantum rods (QRs) by self‐assembly and the preliminary results showed a polarization degree up to 35%. The gratings on silicon had 100nm for both spacing and line width which was comparable to the length of the synthesized QRs (average length=82nm). The QRs aspect ratio has reached up to 1:12 which was ideal for QRs alignment along the channel. The alignment was assisted by solvent evaporation during the self‐assembly process.

Correlation and convolution filtering and image processing for pitch evaluation of 2D micro- and nano-scale gratings and lattices.

We have mathematically explicated and experimentally demonstrated how a correlation and convolution filter can dramatically suppress the noise that coexists with the scanned topographic signals of two-dimensional (2D) gratings and lattices with 2D perspectives. To realize pitch evaluation, the true peaks' coordinates have been precisely acquired after detecting the local maxima from the filtered signal, followed by image processing. The combination of 2D filtering, local-maxima detecting, and image processing make up the pitch detection (PD) method. It is elucidated that the pitch average, uniformity, rotation angle, and orthogonal angle can be calculated using the PD method. This has been applied to the pitch evaluation of several 2D gratings and lattices, and the results are compared with the results of using the center-of-gravity (CG) and Fourier-transform-based (FT) method. The differences of pitch averages which are produced using the PD, CG, and FT methods are within 1.5 pixels. Moreover, the PD method has also been applied to detect the dense peaks of Si (111) 7×7 surface and the highly oriented pyrolytic graphite (HOPG) basal plane.

Animal Signaling and Function: An Integrative Approach. Edited by Duncan J. Irschick, Mark Briffa, and Jeffrey Podos. Hoboken (New Jersey): Wiley Blackwell. $120.95. x + 260 p. + 12 pl.; ill.; index. ISBN: 978-0-470-54600-0. 2015.

Previous articleNext article FreeBehaviorAnimal Signaling and Function: An Integrative Approach. Edited by Duncan J. Irschick, Mark Briffa, and Jeffrey Podos. Hoboken (New Jersey): Wiley Blackwell. $120.95. x + 260 p. + 12 pl.; ill.; index. ISBN: 978-0-470-54600-0. 2015.R. Haven WileyR. Haven WileyBiology, University of North Carolina, Chapel Hill, North Carolina Search for more articles by this author Biology, University of North Carolina, Chapel Hill, North CarolinaPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreThe study of animal communication for the past few decades has focused on a single question, “How does honest communication evolve?” Research on this question has been dominated by a single paradigm, the “Handicap Principle.” According to this principle, a signal can provide honest information about a signaler’s quality only if it is sufficiently costly, so that only high-quality individuals can afford the cost. As this volume reveals, three decades of such research have provided only equivocal support for this paradigm. Several chapters provide up-to-date assessments of previous attempts to measure the costs of signals. In identifying weaknesses in these studies, the authors rightly argue that costs can accrue in several distinct ways: during development and ongoing maintenance, as well as during immediate performance of signals. Furthermore, there are pervasive tradeoffs between costs (expenditure of resources) for signals and costs for development and maintenance. Also any compensation for a signaler’s low intrinsic quality can risk indirect costs of diverting resources from other aspects of development and maintenance. To overcome these weaknesses, the contributors to this volume advocate a “functional” approach, by seeking a broad understanding of the costs of signaling for an individual’s overall performance. All chapters take this inclusive view, but they differ in approach. Some focus on tradeoffs with costs of growth, resistance to disease, or avoidance of predators (chapters by Royle et al. and Husak et al.). Some document unanticipated complexities of the mechanisms for producing signals and the tradeoffs in the consequent costs (chapters by Borgia and Keagy, Kemp and Grether, and Podos and Patek). Some concentrate on honesty in aggressive signals (Briffa) or on evidence for dishonesty (Wilson and Angilletta Jr.).The diverse approaches exemplified here lead to many fascinating new insights about signaling. There are especially noteworthy summaries of recent work on the complex displays of bowerbirds, the combinations of pigments and nanoscale gratings in color patches of fish, butterflies, and birds, the extraordinary instruments for sound production by katydids, the interacting functions of the beaks of Darwin’s finches, and the detailed organization of aggressive interactions in arthropods. This book should thus be in every research library. Even so, it remains unclear that a focus on the costs of signaling, even if broadly interpreted and closely detailed, can alone explain much about the evolution of communication. Previous articleNext article DetailsFiguresReferencesCited by The Quarterly Review of Biology Volume 92, Number 1March 2017 Published in association with Stony Brook University Article DOIhttps://doi.org/10.1086/690871 For permission to reuse, please contact [email protected]PDF download Crossref reports no articles citing this article.

Carbon Nanotubes Induced Fibrogenesis on Nanostructured Substrates.

While the rapidly evolving nanotechnology has shown promise in electronics, energy, healthcare and many other fields, there is an increasing concern about the adverse health consequences of engineered nanomaterials. To accurately evaluate the toxicity of nanomaterials, in vitro models incorporated with in vivo microenvironment characteristics are desirable. This study aims to delineate the influence of nanotopography on fibrogenic response of normal human lung fibroblasts to multi-walled carbon nanotubes (MWCNTs). Nanoscale gratings and pillars of various heights were fabricated on polydimethylsiloxane substrates. Cell spreading and biomechanics were measured, and fibrogenic responses including proliferation, collagen production and reactive oxygen species generation of the fibroblasts grown on the nanostructured substrates in response to MWCNTs were assessed. It was observed that the cells could be largely stretched on shallow nanogratings, leading to stiffer cytoskeleton and nucleus, enhanced cell proliferation and collagen production, and consequently, toxic response sensitivity of the fibroblasts was undermined. In contrast, the cell spreading and stiffness could be reduced using tall, isotropic nanopillars, which significantly improved the cell toxic sensitivity to the MWCNTs. In addition to highlighting the significant influence of cell-nanotopography interactions on cell sensing CNTs, this study contributed to development of physiologically relevant in vitro models for nanotoxicology study.

Investigation on the special Smith-Purcell radiation from a nano-scale rectangular metallic grating

The special Smith-Purcell radiation (S-SPR), which is from the radiating eigen modes of a grating, has remarkable higher intensity than the ordinary Smith-Purcell radiation. Yet in previous studies, the gratings were treated as perfect conductor without considering the surface plasmon polaritons (SPPs) which are of significance for the nano-scale gratings especially in the optical region. In present paper, the rigorous theoretical investigations on the S-SPR from a nano-grating with SPPs taken into consideration are carried out. The dispersion relations and radiation characteristics are obtained, and the results are verified by simulations. According to the analyses, the tunable light radiation can be achieved by the S-SPR from a nano-grating, which offers a new prospect for developing the nano-scale light sources.

Nanotopographical Modulation of Cell Function through Nuclear Deformation.

Although nanotopography has been shown to be a potent modulator of cell behavior, it is unclear how the nanotopographical cue, through focal adhesions, affects the nucleus, eventually influencing cell phenotype and function. Thus, current methods to apply nanotopography to regulate cell behavior are basically empirical. We, herein, engineered nanotopographies of various shapes (gratings and pillars) and dimensions (feature size, spacing and height), and thoroughly investigated cell spreading, focal adhesion organization and nuclear deformation of human primary fibroblasts as the model cell grown on the nanotopographies. We examined the correlation between nuclear deformation and cell functions such as cell proliferation, transfection and extracellular matrix protein type I collagen production. It was found that the nanoscale gratings and pillars could facilitate focal adhesion elongation by providing anchoring sites, and the nanogratings could orient focal adhesions and nuclei along the nanograting direction, depending on not only the feature size but also the spacing of the nanogratings. Compared with continuous nanogratings, discrete nanopillars tended to disrupt the formation and growth of focal adhesions and thus had less profound effects on nuclear deformation. Notably, nuclear volume could be effectively modulated by the height of nanotopography. Further, we demonstrated that cell proliferation, transfection, and type I collagen production were strongly associated with the nuclear volume, indicating that the nucleus serves as a critical mechanosensor for cell regulation. Our study delineated the relationships between focal adhesions, nucleus and cell function and highlighted that the nanotopography could regulate cell phenotype and function by modulating nuclear deformation. This study provides insight into the rational design of nanotopography for new biomaterials and the cell-substrate interfaces of implants and medical devices.