Sub-100nm Resolution Research Articles

Imaging of microcrack propagation in 3D nanostructures applying laboratory nano-XCT

Abstract Laboratory X-ray microscopy and nano X-ray computed tomography (nano-XCT) have the unique capability to combine sub-100nm resolution and high object penetration. Therefore, these are appropriate non-destructive inspection techniques for the detection of flaws with a size of 100 nm and below in opaque objects and bulk materials. Another advantage of X-ray microscopy – as opposed to destructive failure analysis methods – is that kinetic processes such as microcrack evolution can be imaged. The unique combination of micromechanics and high-resolution 3D imaging allows to study degradation and failure mechanisms in opaque 3D nanopatterned structures, and it allows to provide essential information for fracture mechanics in small dimensions. The high-resolution in-situ/operando imaging of microcrack propagation in microelectronic products and in battery electrodes is demonstrated.

Ultralow-Frequency Tip-Enhanced Raman Scattering Discovers Nanoscale Radial Breathing Mode on Strained 2D Semiconductors.

Collective excitations including plasmons, magnons, and layer-breathing vibration modes emerge at an ultralow frequency (<1 THz) and are crucial for understanding van der Waals materials. Strain at the nanoscale can drastically change the property of van der Waals materials and create localized states like quantum emitters. However, it remains unclear how nanoscale strain changes collective excitations. Herein, ultralow-frequency tip-enhanced Raman spectroscopy (TERS) with sub-10nm resolution under ambient conditions is developed to explore the localized collective excitation on monolayer semiconductors with nanoscale strains. A new vibrational mode is discovered at around 12 cm-1 (0.36 THz) on monolayer MoSe2 nanobubbles and it is identified as the radial breathing mode (RBM) of the curved monolayer. The correlation is determined between the RBM frequency and the strain by simultaneously performing deterministic nanoindentation and TERS measurement on monolayer MoSe2. The generality of the RBM in nanoscale curved monolayer WSe2 and bilayer MoSe2 is demonstrated. Using the RBM frequency, the strain of the monolayer MoSe2 on the nanoscale can be mapped. Such an ultralow-frequency vibration from curved van der Waals materials provides a new approach to study nanoscale strains and points to more localized collective excitations to be discovered at the nanoscale.

Deep learning-based spectroscopic single-molecule localization microscopy.

Spectroscopic single-molecule localization microscopy (sSMLM) takes advantage of nanoscopy and spectroscopy, enabling sub-10nm resolution as well as simultaneous multicolor imaging of multi-labeled samples. Reconstruction of raw sSMLM data using deep learning is a promising approach for visualizing the subcellular structures at the nanoscale. Develop a novel computational approach leveraging deep learning to reconstruct both label-free and fluorescence-labeled sSMLM imaging data. We developed a two-network-model based deep learning algorithm, termed DsSMLM, to reconstruct sSMLM data. The effectiveness of DsSMLM was assessed by conducting imaging experiments on diverse samples, including label-free single-stranded DNA (ssDNA) fiber, fluorescence-labeled histone markers on COS-7 and U2OS cells, and simultaneous multicolor imaging of synthetic DNA origami nanoruler. For label-free imaging, a spatial resolution of 6.22nm was achieved on ssDNA fiber; for fluorescence-labeled imaging, DsSMLM revealed the distribution of chromatin-rich and chromatin-poor regions defined by histone markers on the cell nucleus and also offered simultaneous multicolor imaging of nanoruler samples, distinguishing two dyes labeled in three emitting points with a separation distance of 40nm. With DsSMLM, we observed enhanced spectral profiles with 8.8% higher localization detection for single-color imaging and up to 5.05% higher localization detection for simultaneous two-color imaging. We demonstrate the feasibility of deep learning-based reconstruction for sSMLM imaging applicable to label-free and fluorescence-labeled sSMLM imaging data. We anticipate our technique will be a valuable tool for high-quality super-resolution imaging for a deeper understanding of DNA molecules' photophysics and will facilitate the investigation of multiple nanoscopic cellular structures and their interactions.

Dynamic Gold Nanostructures Based on DNA Self Assembly.

The combination of DNA nanotechnology and Nano Gold (NG) plasmon has opened exciting possibilities for a new generation of functional plasmonic systems that exhibit tailored optical properties and find utility in various applications. In this review, the booming development of dynamic gold nanostructures are summarized, which are formed by DNA self-assembly using DNA-modified NG, DNA frameworks, and various driving forces. The utilization of bottom-up strategies enables precise control over the assembly of reversible and dynamic aggregations, nano-switcher structures, and robotic nanomachines capable of undergoing on-demand, reversible structural changes that profoundly impact their properties. Benefiting from the vast design possibilities, complete addressability, and sub-10nm resolution, DNA duplexes, tiles, single-stranded tiles and origami structures serve as excellent platforms for constructing diverse 3D reconfigurable plasmonic nanostructures with tailored optical properties. Leveraging the responsive nature of DNA interactions, the fabrication of dynamic assemblies of NG becomes readily achievable, and environmental stimulation can be harnessed as a driving force for the nanomotors. It is envisioned that intelligent DNA-assembled NG nanodevices will assume increasingly important roles in the realms of biological, biomedical, and nanomechanical studies, opening a new avenue toward exploration and innovation.

Fabrication of microneedles using two photon-polymerization with low numerical aperture

Three-dimensional (3D) micro-nano fabrication through two-photon polymerization (TPP) is a prominent approach for fabricating complex 3D structures. However, the existing techniques face limitations, such as small fabrication area, dependence on high numerical aperture (e.g., oil immersion) objective lenses, which are more expensive. We developed a 780 nm fs laser system integrated with a 2D galvanometer system and Z axis to create a 3D micro-nano printing system. A method to print arbitrarily complex 3D structures while maintaining an extremely high lateral spatial resolution of sub-100nm is proposed by using a cheap low numerical aperture objective lens with the laser power and exposure time precisely controlled. The impact of the laser power and exposure time on the resolution of 3D micro-nano processing is investigated, and we identify the optimal processing environment for achieving the best resolution. The printed linewidth of 62 nm was achieved without the use of an oil immersed objective lens, and only one laser beam was used instead of stimulated emission depletion. Microneedle arrays for animal injection were fabricated using this strategy, which can improve the performance of animal organoid repair. Our results suggest that TPP micro-nano fabrication is an effective method for processing microneedle arrays for biomedical engineering, with the ability to improve the processing resolution with a cheap low numerical aperture objectives lens (e.g., NA = 0.4) through meticulous control of laser power and exposure time. This approach opens up possibilities for affordable and scalable fabrication in sub-100nm structures.

Assessing crosstalk in simultaneous multicolor single-molecule localization microscopy

Single-molecule localization microscopy (SMLM) can reach sub-50nm resolution using techniques such as stochastic optical reconstruction microscopy (STORM) or DNA-point accumulation for imaging in nanoscale topography (PAINT). Here we implement two approaches for faster multicolor SMLM by splitting the emitted fluorescence toward two cameras: simultaneous two-color DNA-PAINT (S2C-DNA-PAINT) that images spectrally separated red and far-red imager strands on each camera, and spectral demixing dSTORM (SD-dSTORM) where spectrally close far-red fluorophores appear on both cameras before being identified by demixing. Using S2C-DNA-PAINT as a reference for low crosstalk, we evaluate SD-dSTORM crosstalk using three types of samples: DNA origami nanorulers of different sizes, single-target labeled cells, or cells labeled for multiple targets. We then assess if crosstalk can affect the detection of biologically relevant subdiffraction patterns. Extending these approaches to three-dimensional acquisition and SD-dSTORM to three-color imaging, we show that spectral demixing is an attractive option for robust and versatile multicolor SMLM investigations.

Nanoscale thermometry under ambient conditions via scanning thermal microscopy with 3D scanning differential method.

Local temperature measurement with high resolution and accuracy is a key challenge in nowadays science and technologies at nanoscale. Quantitative characterization on temperature with sub-100nm resolution is of significance for understanding the physical mechanisms of phonon transport and energy dissipation in nanoelectronics, optoelectronics, and thermoelectric devices. Scanning thermal microscopy (SThM) has been proved to be a versatile method for nanoscale thermometry. In particular, 2D profiling of the temperature field on the order of 10nm and 10 mK has already been achieved by SThM with modulation techniques in ultrahigh vacuum to exclude the parasitic heat flow between air and the cantilever. However, few attempts have been made to truly realize 2D profiling of temperature quantitatively under ambient conditions, which is more relevant to realistic applications. Here, a 3D scanning differential method is developed to map the 2D temperature field of an operating nanodevice under ambient environment. Our method suppresses the thermal drift and the parasitic heat flow between air and the cantilever by consecutively measuring the temperatures in thermal contact and nonthermal contact scenarios rather than in a double-scan manner. The local 2D temperature field of a self-heating metal line with current crowding by a narrowing channel is mapped quantitatively by a sectional calibration with a statistic null-point method and a pixel-by-pixel correction with iterative calculation. Furthermore, we propose a figure of merit to evaluate the performance of thermocouple probes on temperature field profiling. The development of nanoscale thermometry under ambient environment would facilitate thermal manipulation on nanomaterials and nanodevices under practical conditions.

Sub-10 nm electron and helium ion beam lithography using a recently developed alumina resist

Electron Beam Lithography (EBL) at sub-10nm resolution is mainly limited by resist contrast and proximity effects. In this work, we investigate the use of a recently developed alumina-based resist as a negative-tone resist for EBL at 100keV and focused helium ion beam lithography (FHIBL). The resist is synthesized using a sol-gel method and turns into a near completely inorganic alumina system when exposed to the electron/ion beam. We first investigate the effect on the resist contrast curve on i) development temperature; ii) stability of the resist after exposure and before post-baking and development; and iii) aging of the resist solution. We demonstrate the patterning of isolated features as small as 6.5nm using an EBL and 5nm using FHIBL and a resolution down to 10nm for FHIB exposed films. Finally, we demonstrate the pattern transfer of 10nm lines with an aspect ratio of 10 in silicon, using an optimized reactive ion etching process.

CsiLSFM combines light-sheet fluorescence microscopy and coherent structured illumination for a lateral resolution below 100 nm

Light-sheet-based fluorescence microscopy (LSFM) features optical sectioning in the excitation process. It minimizes fluorophore bleaching as well as phototoxic effects and provides a true axial resolution. The detection path resembles properties of conventional fluorescence microscopy. Structured illumination microscopy (SIM) is attractive for superresolution because of its moderate excitation intensity, high acquisition speed, and compatibility with all fluorophores. We introduce SIM to LSFM because the combination pushes the lateral resolution to the physical limit of linear SIM. The instrument requires three objective lenses and relies on methods to control two counterpropagating coherent light sheets that generate excitation patterns in the focal plane of the detection lens. SIM patterns with the finest line spacing in the far field become available along multiple orientations. Flexible control of rotation, frequency, and phase shift of the perfectly modulated light sheet are demonstrated. Images of beads prove a near-isotropic lateral resolution of sub-100 nm. Images of yeast endoplasmic reticulum show that coherent structured illumination (csi) LSFM performs with physiologically relevant specimens.

Improved Interference configuration for structured illumination microscopy

We present an improved structured illumination configuration for structured illumination microscopy (SIM) based on spatial light modulator. Precise phase shifts and rotation of illumination fringes can be dynamically controlled using a spatial light modulator. The method is different from the conventional illumination configuration that are based on interference of ±1 diffractive order light. The experimental setup requires less optical elements making it compact, reliable, and suitable for integration. The method has been applied in the standing-wave total internal reflection fluorescent microscopy. High lateral resolution of sub-100nm was achieved in single directional resolution enhancement experiments.

AFM-based 3D nanofabrication using ultrasonic vibration assisted nanomachining

This paper presents a novel AFM-based 3D nanofabrication process using ultrasonic vibration assisted nanomachining. A set of three dimensional nanostructures on polymethyl methacrylate (PMMA) samples are fabricated with the assistance of high frequency in-plane circular xy-vibration and ultrasonic tip-sample z-vibration. Two methods for fabricating 3D nanostructures were investigated in this study, which are layer-by-layer nanomachining and one pass nanomachining with the depth controlled by setpoint force. Critical parameters in the process are identified, including setpoint force, overlap percentage, amplitude of z vibration and machining speed. By regulating these process parameters, multi-level 3D nanostructures were fabricated by multi-layer machining in vector mode and raster scan mode. Using different setpoint forces for regulating feature depths, other nanostructures, such as convex and concave circles, were fabricated in raster scan mode from gray-scale bitmap pattern images. Under each mode, 3D nanostructure over microscale area can be fabricated in just a few minutes with sub-10nm resolution in z direction.

Carbohydrate-based block copolymer self-assemblies: Sub_10nm highly nanostructured thin films

Event Abstract Back to Event Carbohydrate-based block copolymer self-assemblies: Sub_10nm highly nanostructured thin films Tiffany Gomez1*, Issei Otsuka1, Cécile Bouilhac2*, Eric Reynaud1*, Sami Halila1* and Redouane Borsali1* 1 CERMAV-CNRS, Grenoble Alpes University, Physico-chemistry and self-assembly of glycopolymers, France 2 Université de Montpellier, Equipe Ingénierie et Architectures Macromoléculaires, France Introduction: The design of smaller, faster, more efficient devices is a major scientific and technological challenge, driven in part by a constant need for smaller features and higher resolution patterns. To this end, self-assembling soft materials[1],[2] continue to play an important role in societal and economical goals for smaller and hierarchically nanostructured devices. Block copolymer thin films belong to this class of materials where self-assembly takes place on nanometer length scales. This makes them ideal for emerging nanotechnologies, including applications, for instance, in nano-templating, nano-porous membranes, organic optoelectronics and anti-reflection coatings. Nano-organized thin films are made today from synthetic di-block copolymers (petroleum) and their self-assembly is constrained to 20 nm resolution (domain and size spacing). This is a consequence of the small incompatibility between both blocks (typical model system: PS-PMMA)[3]. To make those systems more attractive for bit-patterned media applications, attempts were made to achieve smaller domains and sizes. These attempts have, however, had only limited success. Materials and Methods: Indeed, to date, numerous studies have been focused on the self-assembly of petroleum-based BCPs for potential applications in multidisciplinary fields, such as nanoparticles for drug delivery, or nano-organized films for biosensors, or nanolithography, etc. Such materials are derived from fossil resources that are being rapidly depleted and have negative environmental impacts. In contrast, carbohydrates are abundant, renewable and constitute a sustainable source of materials. Such materials (bio-sourced block copolymer systems) have been obtained using "click" chemistry consisting of linking oligo/polysaccharide to another block (synthetic or natural). Those bio-based systems are currently attracting much interest in various sectors and their industrial applications at the nanoscale level will have to expand quickly in response to the transition to a bio-based economy. Results and Discussion: To overcome these two bottlenecks -substitution of petroleum molecules and resolution limit - R. Borsali et al[3]-[6] have recently made an important breakthrough by using carbohydrate-based block copolymer and have achieved the highest resolution ever reached to date (5 nm features)-(see illustrations on Figures 1 and 2). We will in this paper present new and recent results on the self-assemblies of oligosaccharide-based block copolymer (synthetic block-Maltoheptaose, where synthetic block stands for Polystyrene or Polyisoprene) leading to highly nanostructured thin films (sub-10nm resolution). Conclusion: This new class of carbohydrate based-block copolymer systems lead to nano-organized thin films (resolution sub_10nm) that could open the horizon to numerous applications in flexible opto-electronics, biosensors, photovoltaic cells and new generation of nanolithography. The authors acknowledge the CNRS, Greenanofilms project (Seventh Framework Program under grant agreement n° 603519), Institut Carnot Polynat and Labex ARCANE for financial supports.

Force detection of IR response at sub-10nm resolution

Force detection of IR response at sub-10nm resolution

Sub-100nm resolution PSIM by utilizing modified optical vortices with fractional topological charges for precise phase shifting.

We demonstrate an all-optical plasmonic structured illumination microscopy (PSIM) technique. A set of plasmonic standing-wave patterns is excited by amplitude-modified optical vortices (OVs), which have fractional topological charges for precise phase shift of {-2π/3, 0, 2π/3}. A specially designed optical aperture is introduced to modify the OVs in order to improve the uniformity of interference patterns. The imaging results of fluorescent beads reveal a sub-100nm resolving capability in aqueous environment. This PSIM technique as a structure-free, wide-field and super-resolved imaging technique is of great potential for low-cost biological dynamic imaging applications.

Polymerization of room-temperature ionic liquid monomers by electron beam irradiation with the aim of fabricating three-dimensional micropolymer/nanopolymer structures.

A novel method for fabricating microsized and nanosized polymer structures from a room-temperature ionic liquid (RTIL) on a Si substrate was developed by the patterned irradiation of an electron beam (EB). An extremely low vapor pressure of the RTIL, 1-allyl-3-ethylimidazolium bis((trifluoromethane)sulfonyl)amide, allows it to be introduced into the high-vacuum chamber of an electron beam apparatus to conduct a radiation-induced polymerization in the nanoregion. We prepared various three-dimensional (3D) micro/nanopolymer structures having high aspect ratios of up to 5 with a resolution of sub-100 nm. In addition, the effects of the irradiation dose and beam current on the physicochemical properties of the deposited polymers were investigated by recording the FT-IR spectra and Young's modulus. Interestingly, the overall shapes of the obtained structures were different from those prepared in our recent study using a focused ion beam (FIB) even if the samples were irradiated in a similar manner. This may be due to the different transmission between the two types of beams as discussed on the basis of the theoretical calculations of the quantum beam trajectories. Perceptions obtained in this study provide facile preparation procedures for the micro/nanostructures.

Illuminated up close: near-field optical microscopy of cell surfaces

Invented in the 1990s, near-field optical microscopy (NSOM) was the first optical microscopy method to hold the promise of finally breaking the diffraction barrier in studies of biological samples. This promise, though, failed to materialize at that time, largely owing to the inability to image soft samples, such as cell surfaces, without damage. However, steady technical improvements have now produced NSOM devices that can routinely achieve images of cell surfaces with sub-100nm resolution in aqueous solution. Further, beyond just optical information, these instruments can also provide simultaneous topographic, mechanical, and/or chemical details of the sample, an ability not yet matched by any other optics-based methodology. With the long recognized important roles of many biological processes at cell surfaces in human health and disease, near-field probing of cell surfaces is indeed now well poised to directly illume in biomedicine what has, until recently, been unknowable with classic light microscopy. From the Clinical EditorThis paper presents a novel and important near-field microscopy-based method directly enabling the imaging of cell surfaces with sub-100nm resolution. Unlike other optics-based methods, the presented technique can also provide topographic, mechanical and chemical details of the samples.

Molecular Layer Deposition of Nanoscale Organic Films for Nanoelectronics Applications

The development of new processes for depositing thin organic films has seen a renewed interest due to an increased demand for nanoelectronic devices. Tools for producing these devices, such as advanced lithographic patterning, often require ultrathin films with a high degree of compositional homogeneity. Molecular layer deposition (MLD) is a promising method for creating films with these qualities. By using an alternating sequence of self-saturating reactions, MLD can produce conformal films with a high degree of control over the composition and thickness. In a series of studies by our group, photoresist films were grown using MLD by incorporated acid-labile groups into a MLD-grown polyurea chain. The inclusion of photo acid generators was demonstrated both as a soaked-in additive as well as a polymer-bound reactive group. These films show potential as good photoresist materials, with some designs exhibiting sensitivities of 30 µC/cm2 with 100 kV electron beam exposure, and a line resolution of sub-100 nm.

Molecular Layer Deposition of Nanoscale Organic Films for Nanoelectronics Applications

The trend toward nanoelectronics motivates the development of new materials and processes. Novel organic materials are of interest for various applications, and this talk will focus on the development of nanoscale organic films for lithography and patterning. Current photoresist materials are facing many challenges introduced by advanced lithography, particularly the need for excellent compositional homogeneity and ultrathin film thickness. Traditional spin-on polymeric resists have inherent limitations in achieving a high level of control over the chemical composition, leading to interest in alternative methods for making photoresists. In this work, we demonstrate that molecular layer deposition (MLD) is a promising method for synthesizing photoresists because it allows for precise control over organic film thickness and composition. As an analogue to atomic layer deposition (ALD), MLD utilizes sequential, self-limiting reactions of organic precursors to build a thin film directly on a substrate surface. An advantage of MLD is that it grows organic films by depositing only one molecular layer at each precursor dose, which in turn allows for fine tuning of the position and concentration of various functionalities in the deposited film. In our study, we use bifunctional precursors, diamine and diisocyanate, to build polyurea resist films via urea coupling reaction. Acid-labile groups are embedded in the backbone of the diamine precursor and incorporated into the resist film with a highly uniform distribution. Two methods of incorporating photo acid generator (PAG) are employed. The first method is to soak a PAG into the resist film after deposition and the second approach is to form in-situ polymer-bound PAG. By this novel synthetic approach, both aromatic and aliphatic polyurea films were successfully deposited by MLD and characterized for both materials properties and resist response. Electron-beam lithographic tests are carried on the MLD photoresists. Among the various MLD films studied, the aliphatic film performed best as a photoresist material, with a good sensitivity of 30 µC/cm2 with 100kV e-beam exposure, and a patterned line resolution of sub-100 nm. Other uses of MLD for advanced patterning methods, as well as fundamental studies into the mechanism of MLD, will also be described.

Flat super-oscillatory lens for heat-assisted magnetic recording with sub-50nm resolution

Heat-assisted magnetic recording (HAMR) is a future roadmap technology to overcome the superparamagnetic limit in high density magnetic recording. Existing HAMR schemes depend on a simultaneous magnetic stimulation and light-induced local heating of the information carrier. To achieve high-density recorded data, near-field plasmonic transducers have been proposed as light concentrators. Here we suggest and investigate in detail an alternative approach exploiting a far-field focusing device that can focus light into sub-50 nm hot-spots in the magnetic recording layer using a laser source operating at 473 nm. It is based on a recently introduced super-oscillatory flat lens improved with the use of solid immersion, giving an effective numerical aperture as high as 4.17. The proposed solution is robust and easy to integrate with the magnetic recording head thus offering a competitive advantage over plasmonic technology.

Advanced 3D Imaging and Analysis of SOFC Electrodes

Solid Oxide Fuel Cells (SOFC) are electrochemical devices where performance is dependent on reactions inside porous electrode microstructures; their complexity is inadequately described using 2D imaging. Here we use X-ray Nano-CT tomographic techniques to probe 3D electrode structures (anodes and cathodes) at micro-nanometer length scales produced using a focused ion beam. Subsequently, micro/nano structural changes in SOFC electrodes are followed and quantified to facilitate understanding changes that occur in shape, structures and morphology at high sub-100nm resolution. Time-resolved (4D) imaging revealed Ni-YSZ oxidation markedly increased above 500 ºC and LSCF densification at 700 ºC may close pores. Utilising 3D electrode data as geometric inputs for numerical models, revealed that increased strains were located at Ni-YSZ interfaces and at microstructure constrictions for both anodes and cathodes when heated. The results show nano/micro structural changes can affect the performance of SOFC electrodes. This combined experimental and modelling approach can help in establishing structure/performance relationships providing key insights important for transport, electrochemistry and strains in both SOFC anodes and cathodes and understanding sources of performance degradation.