Nanofabrication of a gold fiducial array on specimen support for electron tomography.
ABSTRACT: Here we describe the production, using lithography and micro-engineering technologies, of patterned arrays of nanofabricated gold dots on a thin Si3N4 electron transparent layer, supported by silicon. We illustrate that the support with a patterned structure of nanosized gold can be exploited for (cryo) electron tomography application as a specimen support with predefined alignment markers. This nanogold patterned support has several advantages. The Si3N4 window provides a 50 nm thin, strong and flat support with a ~0.7 mm(2) large electron-beam transparent window. The nanogold pattern has a user-defined size and density, is highly regular and stable. This facilitates accurate tracking during tilt series acquisition, provides sufficient contrast for accurate alignment during the image reconstruction step and avoids an uneven lateral distribution and movement of individual fiducials. We showed that the support is suitable for electron tomography on plastic sections.
Project description:A major challenge in nanofabrication is to pattern unconventional substrates that cannot be processed for a variety of reasons, such as incompatibility with spin coating, electron beam lithography, optical lithography, or wet chemical steps. Here, we present a versatile nanofabrication method based on re-usable silicon membrane hard masks, patterned using standard lithography and mature silicon processing technology. These masks, transferred precisely onto targeted regions, can be in the millimetre scale. They allow for fabrication on a wide range of substrates, including rough, soft, and non-conductive materials, enabling feature linewidths down to 10 nm. Plasma etching, lift-off, and ion implantation are realized without the need for scanning electron/ion beam processing, UV exposure, or wet etching on target substrates.
Project description:The preparation of ultra-thin semi-transparent solar cells with potential applications in windows or transparent roofs entails several challenges due to the very small thickness of the layers involved. In particular, problems related to undesired inter-diffusion or inhomogeneities originated by incomplete coverage of the growing surfaces must be prevented. In this paper, undoped SnO?, CdS, and CdTe thin films with thickness suitable for use in ultra-thin solar cells were deposited with a radiofrequency (RF) magnetron sputtering technique onto conductive glass. Preparation conditions were found for depositing the individual layers with good surface coverage, absence of pin holes and with a relatively small growth rate adapted for the control of very small thickness. After a careful growth calibration procedure, heterostructured solar cells devices were fabricated. The influence of an additional undoped SnO? buffer layer deposited between the conductive glass and the CdS window was studied. The incorporation of this layer led to an enhancement of both short circuit current and open circuit voltage (by 19 and 32%, respectively) without appreciable changes of other parameters. After the analysis of the cell parameters extracted from the current-voltage (I-V) curves, possible origins of these effects were found to be: Passivation effects of the SnO?/CdS interface, blocking of impurities diffusion or improvement of the band alignment.
Project description:We report a novel low-noise nanopore device employing a polymer substrate. The Si substrate of a fabricated Si-substrate-based silicon nitride (Si3N4) membrane was replaced with a polymer substrate. As such, laser machining was used to make a micro-size hole through the polyimide (PI) substrate, and a thin Si3N4 membrane was then transferred onto the PI substrate. Finally, a nanopore was formed in the membrane using a transmission electron microscope for detection of biomolecules. Compared to the Si-substrate-based device, the dielectric noise was greatly reduced and the root-mean-square noise level was decreased from 146.7 to 5.4 pA. Using this device, the translocation of double-strand deoxyribonucleic acid (DNA) was detected with a high signal/noise (S/N) ratio. This type of device is anticipated to be available for future versatile sequencing technologies.
Project description:Superconducting nanowire single-photon detectors are an ideal match for integrated quantum photonic circuits due to their high detection efficiency for telecom wavelength photons. Quantum optical technology also requires single-photon detection with low dark count rate and high timing accuracy. Here we present very low noise superconducting nanowire single-photon detectors based on NbTiN thin films patterned directly on top of Si3N4 waveguides. We systematically investigate a large variety of detector designs and characterize their detection noise performance. Milli-Hz dark count rates are demonstrated over the entire operating range of the nanowire detectors which also feature low timing jitter. The ultra-low dark count rate, in combination with the high detection efficiency inherent to our travelling wave detector geometry, gives rise to a measured noise equivalent power at the 10(-20) W/Hz(1/2) level.
Project description:Immunocytochemistry visualizes the exact spatial location of target molecules. The most common strategy for ultrastructural immunocytochemistry is the conjugation of nanogold particles to antibodies as probes. However, conventional nanogold labelling requires time-consuming nanogold probe preparation and ultrathin sectioning of cell/tissue samples. Here, we introduce an in situ strategy involving nanogold nucleation in immunoenzymatic products on universal paraffin/cryostat sections and provide unique insight into nanogold development under hot-humid air conditions. Nanogold particles were specifically localized on kidney podocytes to target synaptopodin. Transmission electron microscopy revealed secondary growth and self-assembly that could be experimentally controlled by bovine serum albumin stabilization and phosphate-buffered saline acceleration. Valuable retrospective nanogold labelling for gastric H<sup>+</sup>/K<sup>+</sup>-ATPase was achieved on vintage immunoenzymatic deposits after a long lapse of 15 years (i.e., 15-year-old deposits). The present in situ nanogold labelling is anticipated to fill the gap between light and electron microscopy to correlate cell/tissue structure and function.
Project description:The large-scale synthesis of Si3N4 nanobelts from quartz and graphite on a graphite-felt substrate was successfully achieved by catalyst-assisted carbothermal reduction-nitridation. The phase composition, morphology, and microstructure of Si3N4 nanobelts were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The Si3N4 nanobelts were ~4-5 mm long and ~60 nm thick and exhibited smooth surfaces and flexible shapes. The Si3N4 nanobelts were well crystallized and grow along the  direction. The growth is dominated by the combined mechanisms of vapor-liquid-solid base growth and vapor-solid tip growth. The Fe(NO3)3 played a crucial role in promoting the nanobelt formation in the initial stage. The room-temperature photoluminescence spectrum of Si3N4 nanobelts consists of three emission peaks centered at 413, 437, and 462 nm, indicating potential applications in optoelectronic nanodevices.
Project description:We demonstrate a new design of graphene liquid cell consisting of a thin lithographically patterned hexagonal boron nitride crystal encapsulated on both sides with graphene windows. The ultrathin window liquid cells produced have precisely controlled volumes and thicknesses and are robust to repeated vacuum cycling. This technology enables exciting new opportunities for liquid cell studies, providing a reliable platform for high resolution transmission electron microscope imaging and spectral mapping. The presence of water was confirmed using electron energy loss spectroscopy (EELS) via the detection of the oxygen K-edge and measuring the thickness of full and empty cells. We demonstrate the imaging capabilities of these liquid cells by tracking the dynamic motion and interactions of small metal nanoparticles with diameters of 0.5-5 nm. We further present an order of magnitude improvement in the analytical capabilities compared to previous liquid cell data with 1 nm spatial resolution elemental mapping achievable for liquid encapsulated bimetallic nanoparticles using energy dispersive X-ray spectroscopy (EDXS).
Project description:Photoresists are light-sensitive resins used in a variety of technological applications. In most applications, however, photoresists are generally used as sacrificial layers or a structural layer that remains on the fabrication substrate. Thin layers of patterned 1002F photoresist were fabricated and released to form a freestanding film. Films of thickness in the range of 4.5-250 ?m were patterned with through-holes to a resolution of 5 ?m and an aspect ratio of up to 6:1. Photoresist films could be reliably released from the substrate after a 12-hour immersion in water. The Young's modulus of a 50 ?m-thick film was 1.43 ± 0.20 GPa. Use of the films as stencils for patterning sputtered metal onto a surface was demonstrated. These 1002F stencils were used multiple times without deterioration in feature quality. Furthermore, the films provided biocompatible, transparent surfaces of low autofluorescence on which cells could be grown. Culture of cells on a film with an isolated small pore enabled a single cell to be accessed through the underlying channel and loaded with exogenous molecules independently of nearby cells. Thus 1002F photoresist was patterned into thin, flexible, free-standing films that will have numerous applications in the biological and MEMS fields.
Project description:The supported monolayer of Au that accompanies alkanethiolate molecules removed by polymer stamps during chemical lift-off lithography is a scarcely studied hybrid material. We show that these Au-alkanethiolate layers on poly(dimethylsiloxane) (PDMS) are transparent, functional, hybrid interfaces that can be patterned over nanometer, micrometer, and millimeter length scales. Unlike other ultrathin Au films and nanoparticles, lifted-off Au-alkanethiolate thin films lack a measurable optical signature. We therefore devised fabrication, characterization, and simulation strategies by which to interrogate the nanoscale structure, chemical functionality, stoichiometry, and spectral signature of the supported Au-thiolate layers. The patterning of these layers laterally encodes their functionality, as demonstrated by a fluorescence-based approach that relies on dye-labeled complementary DNA hybridization. Supported thin Au films can be patterned via features on PDMS stamps (controlled contact), using patterned Au substrates prior to lift-off (e.g., selective wet etching), or by patterning alkanethiols on Au substrates to be reactive in selected regions but not others (controlled reactivity). In all cases, the regions containing Au-alkanethiolate layers have a sub-nanometer apparent height, which was found to be consistent with molecular dynamics simulations that predicted the removal of no more than 1.5 Au atoms per thiol, thus presenting a monolayer-like structure.
Project description:We present a process for the manufacture of electron cryomicroscopy (cryoEM) specimen supports with an integrated foil-grid structure, using cryogenic vacuum evaporation (cryoEvap) and patterned electroplating on a silicon wafer substrate. The process is designed to produce a pattern of nanometre scale holes in a thin metal foil, which is attached to a pattern of micrometre scale grid bars that support it and allow handling of the millimetre scale device. All steps are carried out on a single 4 inch (100 mm) silicon wafer, without any need to handle individual grids during processing, and yield about 600 supports per wafer. The approach is generally applicable to the problem of creating a thin foil with nanometre scale features and a micrometre scale support structure; here it is used to make an all gold, HexAuFoil type design. It also allows for the addition of custom fiducial markers and patterns which aid in locating and identifying particular regions of a grid at several length scales: by eye, in an optical microscope, and in the electron microscope. Implemented at scale, this manufacturing process can supply ample grids to support the continued growth of cryoEM for determining the structure of biological molecules.