Nanometer Height Research Articles

Comprehensive surface and crystallographic structure investigation of MnGaGe nanoislands grown on GaAs

The growth of islands with nanometer height and diameter sizes of the ternary compound MnGaGe with tetragonal structure on the GaAs (001) substrate surface was investigated. Topographic analyses performed by atomic and magnetic force microscopy are consistent with the formation of ferromagnetic MnGaGe nanoislands, constituted by the preferential stacking of (001) and (110) planes whose are the most favorable to the epitaxial relationship on the (001) surface of GaAs wafer, not tested yet. As the spontaneous magnetization tends to align preferentially perpendicular to the Mn basal planes of the tetragonal crystallographic structure, one part of the nanoislands has magnetic dipole or even single- domains whose magnetization is in-plane and another part out-of-plane directions, in the remanent state. Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy analysis obtained the work function, not measured in the literature, and indicates the intermetallic character of the MnGaGe nanoislands, whose near-stoichiometry and good crystalline structure are confirmed by energy dispersive X-ray spectroscopy, X-ray diffraction together with nanodiffraction probe and X-ray fluorescence mapping carried out at a synchrotron installation. The high chemical stability of the MnGaGe nanoislands exhibiting ferromagnetism at room temperature with magnetization perpendicular to the substrate is very promising for spintronic applications at nanoscale.

Correcting retrace and system imaging errors to achieve nanometer accuracy in full aperture, single-shot Fizeau interferometry.

X-ray mirrors with single-digit nanometer height errors are required to preserve the quality of ultra-intense photon beams produced at synchrotron or free electron laser sources. To fabricate suitable X-ray mirrors, accurate metrology data is needed for deterministic polishing machines. Fizeau phase-shifting interferometers are optimized to achieve accurate results under nulled conditions. However, for curved or aspheric mirrors, a limited choice of reference optic often necessitates measurement under non-nulled conditions, which can introduce retrace error. Using experimental measurements of a multi-tilted calibration mirror, we have developed an empirical model of Fizeau retrace error, based on Zernike polynomial fitting. We demonstrate that the model is in good agreement with measurements of ultra-high quality, weakly-curved X-ray mirrors with sags of only a few tens of microns. Removing the predicted retrace error improves the measurement accuracy for full aperture, single shot, Fizeau interferometry to < 2 nm RMS.

Fast shaping control of x ray beams using a closed-loop adaptive bimorph deformable mirror

High-speed adaptive correction of optics, based on real-time metrology feedback, has benefitted numerous scientific communities for several decades. However, it remains a major technological challenge to extend this concept into the hard x ray regime due to the necessity for active mirrors with single-digit nanometer height errors relative to a range of aspheric forms. We have developed a high-resolution, real-time, closed-loop “adaptive” optical system for synchrotron and x ray free electron laser (XFEL) applications. After calibration of the wavefront using x ray speckle scanning, the wavefront diagnostic was removed from the x ray beam path. Non-invasive control of the size and shape of the reflected x ray beam was then demonstrated by driving a piezoelectric deformable bimorph mirror at ∼ 1 H z . Continuous feedback was provided by a 20 kHz direct measurement of the optical surface with picometer sensitivity using an array of interferometric sensors. This enabled a non-specialist operator to reproduce a series of pre-defined x ray wavefronts, including focused or non-Gaussian profiles, such as flattop intensity or multiple split peaks with controllable separation and relative amplitude. Such changes can be applied in any order and in rapid succession without the need for invasive wavefront diagnostic sensors that block the x ray beam for scientific usage. These innovations have the potential to profoundly change how x ray focusing elements are utilized at synchrotron radiation and XFEL sources and provide unprecedented dynamic control of photon beams to aid scientific discoveries in a wide range of disciplines.

Early tension regulation coupled to surface myomerger is necessary for the primary fusion of C2C12 myoblasts

Here, we study the time-dependent regulation of fluctuation–tension during myogenesis and the role of the fusogen, myomerger. We measure nanometric height fluctuations of the basal membrane of C2C12 cells after triggering differentiation. Fusion of cells increases fluctuation–tension but prefers a transient lowering of tension (at ~2–24 h). Cells fail to fuse if early tension is continuously enhanced by methyl-β-cyclodextrin (MβCD). Perturbing tension regulation also reduces fusion. During this pre-fusion window, cells that finally differentiate usually display lower tension than other non-fusing cells, validating early tension states to be linked to fate decision. Early tension reduction is accompanied by low but gradually increasing level of the surface myomerger. Locally too, regions with higher myomerger intensity display lower tension. However, this negative correlation is lost in the early phase by MβCD-based cholesterol depletion or later as differentiation progresses. We find that with tension and surface-myomerger’s enrichment under these conditions, myomerger clusters become pronouncedly diffused. We, therefore, propose that low tension aided by clustered surface-myomerger at the early phase is crucial for fusion and can be disrupted by cholesterol-reducing molecules, implying the potential to affect muscle health.

A review of the dual-wavelength technique for phase imaging and 3D topography

Optically transmissive and reflective objects may have varying surface profiles, which translate to arbitrary phase profiles for light either transmitted through or reflected from the object. For high-throughput applications, resolving arbitrary phases and absolute heights is a key problem. To extend the ability of measuring absolute phase jumps in existing 3D imaging techniques, the dual-wavelength concept, proposed in late 1800s, has been developed in the last few decades. By adopting an extra wavelength in measurements, a synthetic wavelength, usually larger than each of the single wavelengths, can be simulated to extract large phases or height variations from micron-level to tens of centimeters scale. We review a brief history of the developments in the dual-wavelength technique and present the methodology of this technique for using the phase difference and/or the phase sum. Various applications of the dual-wavelength technique are discussed, including height feature extraction from micron scale to centimeter scale in holography and interferometry, single-shot dual-wavelength digital holography for high-speed imaging, nanometer height resolution with fringe subdivision method, and applications in other novel phase imaging techniques and optical modalities. The noise sources for dual-wavelength techniques for phase imaging and 3D topography are discussed, and potential ways to reduce or remove the noise are mentioned.

Wide-field parallel mapping of local spectral and topographic information with white light interference microscopy.

Fourier analysis of interferograms captured in white light interference microscopy is proposed for performing simultaneous local spectral and topographic measurements at high spatial resolution over a large field of view. The technique provides a wealth of key information on local sample properties. We describe the processing and calibration steps involved to produce reflectivity maps of spatially extended samples. This enables precise and fast identification between different materials at a local scale of 1 µm. We also show that the recovered spectral information can be further used for improving topography measurements, particularly in the case of samples combining dielectric and conducting materials in which the complex refractive index can result in nanometric height errors.

Molecular height measurement by cell surface optical profilometry (CSOP)

The physical dimensions of proteins and glycans on cell surfaces can critically affect cell function, for example, by preventing close contact between cells and limiting receptor accessibility. However, high-resolution measurements of molecular heights on native cell membranes have been difficult to obtain. Here we present a simple and rapid method that achieves nanometer height resolution by localizing fluorophores at the tip and base of cell surface molecules and determining their separation by radially averaging across many molecules. We use this method, which we call cell surface optical profilometry (CSOP), to quantify the height of key multidomain proteins on a model cell, as well as to capture average protein and glycan heights on native cell membranes. We show that average height of a protein is significantly smaller than its contour length, due to thermally driven bending and rotation on the membrane, and that height strongly depends on local surface and solution conditions. We find that average height increases with cell surface molecular crowding but decreases with solution crowding by solutes, both of which we confirm with molecular dynamics simulations. We also use experiments and simulations to determine the height of an epitope, based on the location of an antibody, which allows CSOP to profile various proteins and glycans on a native cell surface using antibodies and lectins. This versatile method for profiling cell surfaces has the potential to advance understanding of the molecular landscape of cells and the role of the molecular landscape in cell function.

Polyaniline–graphene oxide nanocomposite microelectromechanical sensor for stink bugs pheromone detection

A novel polyaniline–graphene oxide nanocomposite microelectromechanical (PANI/GO/MEM) sensor was developed and applied in the detection of the synthetic pheromone of E. heros. The sensitive layer was characterized and demonstrates uniform structure with nanometric height and smooth surface. The PANI/GO/MEM sensor exhibits a linear response at concentration range 0.005 to 0.03 μg/mL, with sensitivity of 6.24 Hz/fg, detection limit of 0.91 fg/mL, quantification limit of 1.54 fg/mL, and hysteresis of 0.02 %. The PANI/GO/MEM sensor shows excellent performance and reproducibility in the exposition to volatile molecules of pheromone, with 1.1 % relative standard deviation (RSD). In this way, the results demonstrate the promising candidature of the designed PANI/GO/MEM sensor for detecting these semiochemicals, released in small quantities by the brown stink bug in the agriculture, can be a strategy for pest management.

Plasmon reflection reveals local electronic properties of natural graphene wrinkles**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0203500), the National Natural Science Foundation of China (Grant No. 11874407), and Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB 30000000).

We systematically studied surface plasmons reflection by graphene wrinkles with different heights on SiC substrate. Combined with numerical simulation, we found that the geometry corrugation of a few nanometer height wrinkle alone does not causes a reflection of graphene plasmons. Instead, the separated wrinkle from substrate exhibits a nonlinear spatial Fermi energy distribution along the wrinkle, which acts as a heterojunction. Therefor a higher graphene wrinkle induces a stronger damped region when propagating graphene surface plasmons encounter the wrinkle and get reflected.

3D profile measurement for stepped microstructures using region-based transport of intensity equation

One of the major challenges in the semiconductor industry is to measure the three-dimensional (3D) profile of objects with large step height (>100 µm), as well as nanometer-level surface profiles. In this work, a novel technique called region-based transport of intensity equation (R-TIE) is explored to measure both large step heights as well as local surface profiles with nanometer resolution. The key factors of the R-TIE are the use of composite image segmentation, transport of intensity equation (TIE), and a smart imaging system. The imaging system incorporates an electrically tunable lens to record objects at different focus positions with large field of view, high speed, and no mechanical moving parts. The TIE part of the system allows for nanometer height measurement at areas of interest. We demonstrate the basic principle and feasibility of the proposed method by experimentally measuring different stepped specimens.

Surface Layer Formation in the Earliest Stages of Corrosion of Steel in CO2-Saturated Brine at 80°C: Studied by In Situ Synchrotron X-ray Methods

Grazing-incidence small-angle X-ray scattering (GISAXS) from polycrystalline steel shows features associated with the underlying microstructure, and, in the initial stages of corrosion, with the development of very small-scale surface roughness, on the nanometer height scale. A 1Cr0.25Mo pipeline steel in hot, CO2-saturated brine develops the very small-scale surface roughness significantly faster than a simple carbon steel, although the overall dissolution current density for the two steels is almost the same. We speculate that it is due to the presence of a layer comprising ‘blobs’ of amorphous FeCO3, which grow to spread over the surface and eventually cover it, because it is significantly larger in height scale than the roughness developed during the initial stages of anodic dissolution in acidified NaCl solution, where no surface film is expected. The greater roughness on the 1Cr0.25Mo steel can be interpreted as due to small pre-crystalline nuclei, that form at much lower supersaturation, and grow faster, than on mild steel. Grazing-incidence X-ray diffraction studies show at later stages the apparent preferential dissolution of smaller crystallites of iron, with spatial size scale 0.1–1 μm. This develops significantly more slowly on the 1Cr0.25Mo than on the simple carbon steel.

On the Crystallization of Compacted and Chunky Graphite from Liquid Multicomponent Iron-Carbon-Silicon-Based Melts

Extensive SEM work was carried out on deep-etched specimens to reveal the evolution of compacted and chunky graphite in magnesium-modified multicomponent Fe-C-Si alloys during early solidification and at room temperature. The findings of this research were then integrated in the current body of knowledge to produce an understanding of the crystallization of compacted and chunky graphite. It was confirmed that growth from the liquid for both compacted and chunky graphite occurs radially from a nucleus, as foliated crystals and dendrites. The basic building blocks of the graphite aggregates are hexagonal faceted graphite platelets with nanometer height and micrometer width. Thickening of the platelets occurs through growth of additional graphene layers nucleated at the ledges of the graphite prism. Additional thickening resulting in complete joining of the platelets may occur from the recrystallization of the amorphous carbon that has diffused from the liquid through the austenite, once the graphite aggregate is enveloped in austenite. With increasing magnesium levels, the foliated graphite platelets progressively aggregate along the c-axis forming clusters. The clusters that have random orientation, eventually produce blocky graphite, as the spaces between the parallel platelets disappear. This is typical for compacted graphite irons and tadpole graphite. The chunky graphite aggregates investigated are conical sectors of graphite platelets stacked along the c-axis. The foliated dendrites that originally develop radially from a common nucleus may aggregate along the c-axis forming blocky graphite that sometimes exhibits helical growth. The large number of defects (cavities) observed in all graphite aggregates supports the mechanism of graphite growth as foliated crystals and dendrites.

On the crystallization of graphite from liquid iron–carbon–silicon melts

Extensive SEM work was carried out on deep etched specimens to reveal the evolution of graphite shape in Fe–C–Si alloys of industrial composition during early solidification and at room temperature. The samples had various magnesium and titanium levels designed to produce graphite morphologies ranging from coarse lamellar to interdendritic lamellar to mixed compacted – spheroidal. The present findings were then integrated in previous knowledge to produce an understanding of the crystallization of lamellar, compacted and spheroidal graphite.It was demonstrated that most forms of graphite grow radially from a common center, most of the time as foliated dendrites (see Figure). The basic building blocks of the graphite aggregates are hexagonal faceted graphite platelets with nanometer height and micrometer width. During solidification, thickening of the platelets occurs through growth of additional graphene layers nucleated at the ledges of the graphite prism. In the magnesium-free irons that graphite platelets assemble into foliated crystals and dendrites, forming graphite plates that grow along the a-axis. In the magnesium-modified melts the graphite platelets stack along the c-axis, producing clusters with random orientation. The clusters are then assembled into quasi-cylindrical shapes connected to more or less curved walls to form tadpole graphite, compacted graphite, or chunky graphite. If enough magnesium is added, conical sectors made of platelets stacked in the c-direction grow from the same nucleus. The conical sectors may occupy the whole volume of the sphere forming a graphite spheroid, or only part of it like in chunky graphite. The large number of cavities observed between the platelets is consistent with growth of foliated dendrites.

Topographic optical profilometry of steep slope micro-optical transparent surfaces.

Optical profilometers based on light reflection may fail at surfaces presenting steep slopes and highly curved features. Missed light, interference and diffraction at steps, peaks and valleys are some of the reasons. Consequently, blind areas or profile artifacts may be observed when using common reflection micro-optical profilometers (confocal, scanning interferometers, etc…). The Topographic Optical Profilometry by Absorption in Fluids (TOPAF) essentially avoids these limitations. In this technique an absorbing fluid fills the gap between a reference surface and the surface to profile. By comparing transmission images at two different spectral bands we obtain a reliable topographic map of the surface. In this contribution we develop a model to obtain the profile under micro-optical observation, where high numerical aperture (NA) objectives are mandatory. We present several analytical and experimental results, validating the technique's capabilities for profiling steep slopes and highly curved micro-optical surfaces with nanometric height resolution.

Pushing the Limits of Plasmonic Nanoantenna Design Using New Materials and Nanofabrication Tools

Plasmonic nanoantennas are of interest for their capacity of controlling light on the nanoscale [1]. In particular, precise control of plasmonic near-field interactions on sub-nanometer scales is of interest for achieving strongly enhanced local fields as well as for exploring the fundamental limits of nonlocal and quantum plasmonic effect [2]. Such applications require pushing the limits of nanofabrication to new levels of precision and control.Helium ion microscopy (HIM) is a surface imaging technique which involves scanning a helium ion beam across a sample surface and forming an image from secondary electron emission which is similar to an SEM. The larger mass and therefore smaller de Broglie wavelength of a helium ion compared to that of an electron enables the HIM to focus the charged beam to a smaller spot on a sample. The latest commercially available version of the HIM are rated at an edge resolution of 0.35nm[3]. The helium ion microscope is also a patterning tool which can be used to pattern resist like electron beam lithography or can be used for direct writing on a substrate like a focused ion beam.In our recent work, we have demonstrated the ultrafine control of milling partial antenna gaps and narrow conducting bridges with nanometer precision using a helium ion beam microscope (HIM) [4]. A conducting bridge of nanometer height is found sufficient to shift the antenna from the capacitive to conductive coupling regime, in agree with the circuit theory.In addition to new fabrication tools, we are developing new materials systems to combine plasmonics in electrically and optically controlled environments. I will present recent results showing how we can use new hybrid nonlinearities to achieve tunable and reconfigurable plasmonic devices. [1] Novotny, L.; van Hulst, N. Nat. Photonics 2011, (5) 83-90 [2] Savage, K. J.; Hawkeye, M. M.; Esteban, R.; Borisov, A. G.; Aizpurua, J.; Baumberg, J. J. Nature 2012, (491) 574-577. [3] Bell, D. C.; Lemme, M. C.; Stern, L. A.; Williams, J. R. and Marcus, C. M. 2009 Nanotechnology (20) 455301 [4] Wang, Y.; Abb, M.; Boden, S. A.; Aizpurua, J.; de Groot, C. H.; Muskens, O. L. Nano Lett. 2013, 13(11), 5647-5653 Figure 1 (left panel) Illustration showing analogy between radiowave antenna and plasmonic nanoantenna. Bottom: SEM image of antenna fabricated using e-beam lithography. (right panel) SEM image showing nano-gap obtained by helium ion beam milling.

At-wavelength metrology of hard X-ray mirror using near field speckle

We present a method to measure the surface profile of hard X-ray reflective optics with nanometer height accuracy and sub-millimetre lateral resolution. The technique uses X-ray near-field speckle, generated by a scattering membrane translated using a piezo motor, to infer the deflection of X-rays from the surface. The method provides a nano-radian order accuracy on the mirror slopes in both the tangential and sagittal directions. As a demonstration, a pair of focusing mirrors mounted in a Kirkpatrick-Baez (KB) configuration were characterized and the results were in good agreement with offline metrology data. It is hoped that the new technique will provide feedback to optic manufacturers to improve mirror fabrication and be useful for the online optimization of active, nano-focusing mirrors on modern synchrotron beamlines.

Ultrafast Nonlinear Control of Progressively Loaded, Single Plasmonic Nanoantennas Fabricated Using Helium Ion Milling

We demonstrate milling of partial antenna gaps and narrow conducting bridges with nanometer precision using a helium ion beam microscope. Single particle spectroscopy shows large shifts in the plasmonic mode spectrum of the milled antennas, associated with the transition from capacitive to conductive gap loading. A conducting bridge of nanometer height is found sufficient to shift the antenna from the capacitive to the conductive coupling regime, in agreement with circuit theory. Picosecond pump-probe spectroscopy reveals an enhanced nonlinear response for partially milled antennas, reaching an optimum value for an intermediate bridge height. Our results show that manipulation of the antenna load can be used to increase the nonlinear response of plasmonic antennas.

Surface Study of Vitreous Carbon Obtained from Glassy Carbon Powder

ABSTRACTThis work presents a surface study of monolithic vitreous (or glassy) carbon - MVC - obtained from vitreous carbon powder. Defective MVC pieces are crushed in a ball mill and size classified by sifting. The MVC powder is mixed with furfuryl-alcohol resin and compacted in a mould using a hydraulic press. Samples with different powder granulometries are produced in this way and carbonized in a furnace under nitrogen atmosphere. Complete carbonization of the “powder” is achieved in only one day and losses due to breakage of the pieces is less than 5%. These results compare very favorably with respect to traditional MVC production methods where full carbonization may require up to seven days and losses due to breakage can be as high as 70%. After carbonization, samples are sanded and polished. Surface roughness and microstructure are characterized by light microscopy. Porosity is quantified from micrographs using ImageJ software and nanometric height variations are measured by atomic force microscopy.

Subdiffusive Molecular Motion in Nanochannels Observed by Fluorescence Correlation Spectroscopy

The influence of confinement on biomolecule motion in glass channels of nanometric height has been investigated with fluorescence correlation spectroscopy (FCS). We measured intrachannel molecule diffusion time and concentration based on a single-component diffusion model as a function of molecule size to channel height (r(g)/h). Poly(ethylene glycol) (PEG) of 20 kDa and dextran of 40 kDa showed a reduction of their diffusion coefficients of almost 1 order of magnitude when nanochannel height approached probe diameter, whereas rhodamine 6G (Rh6G) was shown to be almost unaffected from confinement. Subdiffusive motion has been proven for flexible molecules in nanochannels, and deviations toward a square root dependence of mobility with time for confinement up to molecule size r(g)/h approximately 0.5 were registered. Diffusion coefficient time dependence has been evaluated and described with a model that accounts for diffusion time increase due to molecule rearrangements related to molecule flexibility and surface interactions dynamics. The evaluation of the subdiffusive mode and the key parameters extracted at the single-molecule level of partitioning, intrachannel diffusion time, desorption time, and binding probability at surfaces can be exploited for the engineering of bioanalytic nanodevices.

3D Nanometer Tracking of Motile Microtubules on Reflective Surfaces

Biomolecular motor-driven nanodevices are dynamic, soft systems exhibiting rapid energy flow and mechanical motion. To understand the spatial arrangement between nano-objects inthesedevices,afast,non-destructiveimagingtechniquewith nanometer spatial resolution in 3D is required. We employ fluorescence interference contrast microscopy (FLIC) to image the interaction between kinesin-driven microtubules (MTs) and nanoscopic surface structures. We directly image the geometry of crossing MTs with high temporal resolution and investigate how the leading tips of motile MTs explore their environment. We show directly that the length of the free MT tip, which is defined by the average distance between motors on the surface, determines the ability to overcome obstacles. Moreover, we demonstrate that FLIC microscopy in combination with fluorescently-labeled, motile MTs is a versatile tool to scan the geometry of engineered surfaces with nanometer height precision. This method, which is compatible with any kind of reflecting surface, permits dynamic and precise data acquisition in a highly parallel manner using a standard epi-fluorescence microscope. Active movement is a key ability of biological nanomachines, and finds applications in a number of hybrid bionanodevices. [1‐3] Molecular shuttles driven by motors and carrying cargo have been designed by us [4‐6] and others [7‐12] to address the need for nanoscale transport, positioning, and assembly systems. Our approach utilizes MTs—hollow, cylindrical, proteinaceous filaments that can be formed in vitro by self-assembly of tubulin heterodimers—as shuttles (Figure 1). MTs have an outer diameter of 25nm and can be as long as several micrometers. In a typical gliding motility assay, fluorescently-labeled MTs are transported at speeds of about 1 m ms � 1 by kinesin-1 motor proteins immobilized on a substrate surface. Kinesin motors—dimeric proteins capable of generating several piconewtons of mechanical force from the hydrolysis of adenosine 5 0 -triphosphate (ATP)—step towards the so-called ‘‘plus’’ end of the MTs. [13] Typically, several dozen motors contribute to the forward movement of one MT. Due to the high stiffness of MTs, the path that an undisturbed MT follows is normally rather straight (trajectory persistence length � 0.1 mm [14] ) and we expect a constant elevation above the surface. [15] As cargo, a wide range of objects [16‐18] including microspheres, [5] quantum dots, [19]