Complex Three-dimensional Nanostructures Research Articles

Study on the roughen process of branches of AuAg nanostars for the improved surface-enhanced Raman scattering (SERS) to detect crystal violet in fish

The techniques used to precisely tune the morphologies of noble metal nanoparticles are of vital importance as complex three-dimensional nanostructures can generate many “hot spots” for Surface-enhanced Raman Scattering (SERS). Especially, the SERS properties of star-shaped nanoparticles are closely related to the position, number and morphology of branches, making the control over the final morphology of them more important. By adding different reducing agents during the growth process of AuAg nanostars, we accurately controlled the morphology of branches, and synthesized three kinds of hyperbranched star-shaped nanostructures: Lamellar nanostars, Sea urchin-shaped nanostars and Serrated nanostars. The SERS performance of the hyperbranched nanostars were all stronger than that of common AuAg nanostars. Among them, Lamellar nanostars gained the best SERS enhanced factor about 1 × 107 due to the built-in nanogaps and sharp edges. The SERS detection probes prepared with purified Lamellar nanostars had high uniformity and stability, and showed excellent sensitivity in detecting crystal violet in fish, with detection range of 0.01–10 nM and detection limit of 0.015 nM. The results of this work not only provide guidance for the construction of complex Au and Ag bimetallic nanostructures, but also supply a superior material to develop highly sensitive optical chemical sensors and biosensors.

Review of the key milestones in the development of critical dimension small angle x-ray scattering at National Institute of Standards and Technology

An x-ray scattering based metrology was conceived over 20 years ago as part of a collaboration between National Institute of Standards and Technology (NIST) and International Business Machines Corporation (IBM) to evaluate the performance of lithographic patterning materials for the semiconductor industry. This methodology treated a periodic array of lithographic structures as a diffraction grating and focused on extracting the physical dimensions of the structures in the grating by analyzing the diffraction patterns. In the early stages of the work the focus was on developing the transmission small-angle x-ray scattering (tSAXS) as a metrology tool to measure the critical dimensions (CD) of the lithographic features vital to the integrated circuit chip fabrication. Later, the focus shifted to include grazing incident small-angle x-ray scattering and x-ray reflectivity as parts of the CD metrology tool due to their unique capabilities. Frequently the term critical dimension small-angle x-ray scattering (CDSAXS) has been used as a synonym for the metrology of using tSAXS for CD measurements without mentioning transmission. Various milestones in the CDSAXS development are reviewed in this article together with some prospects regarding the future growth of x-ray-based metrology for complex three-dimensional nanostructures important to semiconductor industries.

Generating nano-incised graphene kirigami membrane via selective tearing

By virtue of its single-layer thickness, nanoscale incisions and flexible structure, graphene kirigami (GK) owns a great prospect to be an ultra-permeable membrane for separation engineering. However, the difficulty in creating nanoscale incisions has prevented GK from being considered as a membrane candidate in the past. This situation has been improved recently by some emerging kirigami-inspired synthetic strategies and techniques for constructing complex three-dimensional nanostructures. Here, we reveal the potential fabrication of nano-incised GK membranes via an innovative selective tearing method using molecular dynamics simulation. The results exhibit that through the selective tearing method, the periodic wrinkles could be generated on the defective graphene, contributing to the stress concentration around the defects and causing the CC bonds to break, finally forming nano-incisions. The initial defective graphene, including its size, defects density, parallelogram angle and aspect ratio, as well as the shear angle, are crucial to the incision distribution on the formed GK-like membrane after selecting tearing treatment. The desalination simulation demonstrates that the selective tearing formed graphene kirigami (STGK) membrane has ultra-high water permeability, achieving 1197 L/m2/h/bar with 100 % salt rejection, 5.2–6.3 times higher than the previously reported nanoporous graphene and more than two orders of magnitude higher than current reverse osmosis membranes. We expect this work will inspire the next-generation membranes for separation and purification technology.

Analysis of Line-Edge Roughness Using EUV Scatterometry

Smaller and more complex three-dimensional periodic nanostructures are part of the next generation of integrated electronic circuits. Additionally, decreasing the dimensions of nanostructures increases the effect of line-edge roughness on the performance of the nanostructures. Efficient methods for characterizing three-dimensional nanostructures are required for process control. Here, extreme-ultraviolet (EUV) scatterometry is exploited for the analysis of line-edge roughness from periodic nanostructures. In line with previous observations, differences are observed between line edge and line width roughness. The angular distribution of the diffuse scattering is an interplay of the line shape, the height of the structure, the roughness along the line, and the correlation between the lines. Unfortunately, existing theoretical methods for characterizing nanostructures using scatterometry do not cover all these aspects. Examples are shown here and the demands for future development of theoretical approaches for computing the angular distribution of the scattered X-rays are discussed.

Catalytic synthesis of graphite oxide and graphite nanostructures in transient glow-to-arc plasma discharge

Carbon and carbon-based materials like graphene and graphene oxide exhibit a constantly expanding field of applications in science, medicine, and industry. However, their implementation is still hindered by the absence of a reliable, flexible, and highly productive method of synthesis. Most of the existing methods rely on the use of chemical reagents potentially dangerous for the environment. In this paper, a physical method based on the use of a transient glow-to-arc discharge is developed, and the carbon nanostructures are obtained during a single-step production in a plasma reactor. Argon and oxygen are used to grow either carbon or carbon oxide nanostructures on the surfaces of expanded graphite samples. To enhance the growth of the carbon nanostructures, an anode made of copper is employed in the setup, to serve as a source of the copper catalyst. As a result, complex three-dimensional carbon nanostructures with a density of about 0.01 μm-2 were detected using scanning electron microscopy (SEM) on the entire surface of the sample after the oxygen plasma treatment. An enlarged view of nanostructures shows that they are a composition of 2D and 1D nanostructures connected by jumpers, as well as the presence of tree-like and petal nanostructures with dimensions of approximately 3 μm in length and 30 nm in diameter. The replacement of oxygen with argon led to a significant change in the appearance of nanostructures. Layered 2D graphene-like and tree-like carbon nanostructures capped with copper particles of diameters up to 10 μm were found. The obtained nanostructures suggest that expanded graphite is an excellent source for the production of two-dimensional nanostructures, like graphene and graphene oxide, which can be used as components for field-effect transistors, nanofluidic applications, supercapacitors, and electromagnetic absorbers.

Single-Step Dual-Layer Photolithography for Tunable and Scalable Nanopatterning.

Conventional photolithography, due to its scalability, robustness, and straightforward processes, has been widely applied to micro- and nanostructure manufacturing in electronics, optics, and biology. However, optical diffraction limits the ultimate resolution of conventional photolithography, which hinders its potential in nanoscale patterning for broader applications. Here, we introduce a derivative of conventional photolithography for nanoscale patterning called dual-layer photolithography (DLPL), which is based on the controlled exposure and development of overlapping positive and negative photoresists. In a typical experiment, substrates are sequentially coated by two layers of photoresists (both positive and negative). Then, we purposefully control the exposure time to generate slightly larger features in the positive photoresist than those in the negative photoresist. After development, their overlapping areas become the final features, which outline the original features. We demonstrate line widths down to 300 nm here, which can be readily improved with more precise control. By adjusting the lithography parameters and material deposition, the feature sizes, shapes (e.g., rings, numbers, letters), line widths (300-900 nm), and materials (e.g., SiO2, Cr, and Ag) of these features can be independently controlled. Combined with anisotropic etching, more complex three-dimensional nanostructures can be fabricated as well, as we demonstrate here with Si. We further fabricate photodetectors as an example application to show that these nanostructures fabricated by DLPL can be used to promote light-trapping MAPbI3 perovskite films to achieve good photoelectric properties. This strategy is not limited to ultraviolet photolithography and may also be incorporated into other energetic beam-based lithographic approaches, including deep and extreme ultraviolet photolithographies and electron beam lithography, to enhance their resolution.

Mastering of NIL Stamps with Undercut T-Shaped Features from Single Layer to Multilayer Stamps.

Biomimetic structures such as structural colors demand a fabrication technology of complex three-dimensional nanostructures on large areas. Nanoimprint lithography (NIL) is capable of large area replication of three-dimensional structures, but the master stamp fabrication is often a bottleneck. We have demonstrated different approaches allowing for the generation of sophisticated undercut T-shaped masters for NIL replication. With a layer-stack of phase transition material (PTM) on poly-Si, we have demonstrated the successful fabrication of a single layer undercut T-shaped structure. With a multilayer-stack of silicon oxide on silicon, we have shown the successful fabrication of a multilayer undercut T-shaped structures. For patterning optical lithography, electron beam lithography and nanoimprint lithography have been compared and have yielded structures from 10 µm down to 300 nm. The multilayer undercut T-shaped structures closely resemble the geometry of the surface of a Morpho butterfly, and may be used in future to replicate structural colors on artificial surfaces.

Absolute intensity calibration for carbon-edge soft X-ray scattering.

Resonant soft X-ray scattering (RSOXS) has become a premier probe to study complex three-dimensional nanostructures in soft matter through combining the robust structural characterization of small-angle scattering with the chemical sensitivity of spectroscopy. This technique borrows many of its analysis methods from alternative small-angle scattering measurements that utilize contrast variation, but thus far RSOXS has been unable to reliably achieve an absolute scattering intensity required for quantitative analysis of domain compositions, volume fraction, or interfacial structure. Here, a novel technique to calibrate RSOXS to an absolute intensity at the carbon absorption edge is introduced. It is shown that the X-ray fluorescence from a thin polymer film can be utilized as an angle-independent scattering standard. Verification of absolute intensity is then accomplished through measuring the Flory-Huggins interaction parameter in a phase-mixed polymer melt. The necessary steps for users to reproduce this intensity calibration in their own experiments to improve the scientific output from RSOXS measurements are discussed.

Ultrathin Silica Coating of DNA Origami Nanostructures

DNA origami technique has emerged as one of the most versatile bottom-up nanofabrication methods due to its ability to construct well-defined complex three-dimensional nanostructures and guide asse...

Dislocations as channels for the fabrication of sub-surface porous GaN by electrochemical etching

Porosification of nitride semiconductors provides a new paradigm for advanced engineering of the properties of optoelectronic materials. Electrochemical etching creates porosity in doped layers while leaving undoped layers undamaged, allowing the realization of complex three-dimensional porous nanostructures, potentially offering a wide range of functionalities, such as in-distributed Bragg reflectors. Porous/non-porous multilayers can be formed by etching the whole, as-grown wafers uniformly in one simple process, without any additional processing steps. The etch penetrates from the top down through the undoped layers, leaving them almost untouched. Here, atomic-resolution electron microscopy is used to show that the etchant accesses the doped layers via nanometer-scale channels that form at dislocation cores and transport the etchant and etch products to and from the doped layer, respectively. Results on AlGaN and non-polar GaN multilayers indicate that the same mechanism is operating, suggesting that this approach may be applicable in a range of materials.

Complex Three-Dimensional Co₃O₄ Nano-Raspberry: Highly Stable and Active Low-temperature CO Oxidation Catalyst.

Highly stable and active low-temperature CO oxidation catalysts without noble metals are desirable to achieve a sustainable society. While zero-dimensional to three-dimensional Co3O4 nanoparticles show high catalytic activity, simple-structured nanocrystals easily self-aggregate and become sintered during catalytic reaction. Thus, complex three-dimensional nanostructures with high stability are of considerable interest. However, the controlled synthesis of complex nanoscale shapes remains a great challenge as no synthesis theory has been established. In this study, 100 nm raspberry-shaped nanoparticles composed of 7–8 nm Co3O4 nanoparticles were synthesized by hydrothermally treating cobalt glycolate solution with sodium sulfate. Surface single nanometer-scale structures with large surface areas of 89 m2·g−1 and abundant oxygen vacancies were produced. The sulfate ions functioned as bridging ligands to promote self-assembly and suppress particle growth. The Co3O4 nano-raspberry was highly stable under catalytic tests at 350 °C and achieved nearly 100% CO conversion at room temperature. The addition of bridging ligands is an effective method to control the formation of complex but ordered three-dimensional nanostructures that possessed extreme thermal and chemical stability and exhibited high performance.

Synthesis of crystalline metal nanomonoliths by e-beam reduction of negatively electrified jets

Direct writing of nanoscale structures with focused electron beam–induced deposition (FEBID) is a promising route to atom-by-atom growth of complex three-dimensional nanostructures, but application has been constrained by slow growth rates (largely due to low precursor density), a limited selection of non-carbonaceous precursors, and a highly carbonaceous material composition resulting from the dissociative decomposition growth mechanism and organometallic precursors used in gas-phase FEBID. In this article, we report on the discovery of a new mode for liquid phase FEBID that enables growth of large metallic crystalline monoliths at exceptionally high growth rates (>1 μm3/s) from water-dissolved metal salts using nanoelectrospray-induced non-equilibrium electrochemistry. Deposit morphology is controlled using the bias of the electrospray, with negative electrospray promoting crystallinity (as opposed to positive electrospray which results in granular deposits). Crystallinity is further promoted by elevating the pH of the electrospray solution. This approach opens a pathway for rapid direct writing of larger-scale monolithic metal structures using an electron beam.

The Kinematic Principle for Designing Deoxyribose Nucleic Acid Origami Mechanisms: Challenges and Opportunities1

Deoxyribose nucleic acid (DNA) origami nanotechnology is a recently developed self-assembly process for design and fabrication of complex three-dimensional (3D) nanostructures using DNA as a functional material. This paper reviews our recent progress in applying DNA origami to design kinematic mechanisms at the nanometer scale. These nanomechanisms, which we call DNA origami mechanisms (DOM), are made of relatively stiff bundles of double-stranded DNA (dsDNA), which function as rigid links, connected by highly compliant single-stranded DNA (ssDNA) strands, which function as kinematic joints. The design of kinematic joints including revolute, prismatic, cylindrical, universal, and spherical is presented. The steps as well as necessary software or experimental tools for designing DOM with DNA origami links and joints are detailed. To demonstrate the designs, we presented the designs of Bennett four-bar and crank–slider linkages. Finally, a list of technical challenges such as design automation and computational modeling are presented. These challenges could also be opportunities for mechanism and robotics community to apply well-developed kinematic theories and computational tools to the design of nanorobots and nanomachines.

Machining Complex Three-Dimensional Nanostructures With an Atomic Force Microscope Through the Frequency Control of the Tip Reciprocating Motions

A novel method relying on atomic force microscope (AFM) tip based nanomachining is presented to enable the fabrication of microchannels that exhibit complex three-dimensional (3D) nanoscale floor surface geometries. To achieve this, reciprocating lateral displacements of the tip of an AFM probe are generated, while a high-precision stage is also actuated to move in a direction perpendicular to such tip motions. The width and length of microchannels machined in this way are determined by the amplitude of the tip motion and the stage displacement, respectively. Thus, the processing feed can be changed during the process as it is defined by the combined control of the frequency of the tip reciprocating motions and the stage speed. By employing the built-in force feedback loop of conventional AFM systems during such operations, the variation of the feed leads to different machined depths. Thus, this results in the capability to generate complex 3D nanostructures, even for a given normal load, which is set by the AFM user prior to the start of the process. In this paper, the fabrication of different microchannels with floor surfaces following half triangular, triangular, sinusoidal, and top-hat waveforms is demonstrated. It is anticipated that this method could be employed to fabricate complex nanostructures more readily compared to traditional vacuum-based lithography processes.

Realizing omnidirectional light harvesting by employing hierarchical architecture for dye sensitized solar cells.

To improve the omnidirectional light-harvesting in dye-sensitized solar cells (DSSCs), here we present a dandelion-like structure composed of ZnO hemispherical shells and nanorods. Uniformly distributed hemispherical shells effectively suppress the reflection over the broadband region at incident angles up to 60°, greatly improving the optical absorption of the DSSCs. In addition, modulating the length of the ZnO nanorods controls the omnidirectional characteristics of DSSCs. This phenomenon is attributed to the degree of periodicity of the ZnO dandelion-like structures. Cells with shorter rods exhibit a high degree of periodicity, thus the conversion efficiencies of the cells show specific angle-independent features. On the other hand, the cells with longer lengths reveal angle-dependent photovoltaic performance. Along with the simulation, the cells with dandelion-like ZnO structures can couple incident photons efficiently to achieve excellent broadband and omnidirectional light-harvesting performances experimentally, and the DSSCs enhanced the conversion efficiency by 48% at large incident angles. All these findings not only provide further insight into the light-trapping mechanism in these complex three-dimensional nanostructures but also offer efficient omnidirectional and broadband nanostructured photovoltaics for advanced applications.

Surface polarity induced three-dimensional wurtzite ZnS/ZnSxSe1−x nano-heterostructures with integrating emission property

By controlling the reaction conditions and molar ratio of precursors carefully, three-dimensional ZnS/ZnS0.3Se0.7 nano-heterostructures were synthesized via a simple two-step magnetic force assistant growth technique. Scanning electron microscopy, X-ray powder diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy were used to characterize and analyze the morphology, phase structure, crystallinity and composition of the as-prepared nano-heterostructures. Remarkably, the epitaxial ZnS nanoribbon is single crystalline and preserves the structure and orientation of the matrix ZnSxSe1−x nanobelt with an epitaxial relationship of (0001)ZnS//(0001)ZnS0.3Se0.7 and (100)ZnS//(100)ZnS0.3Se0.7. A polar-surface induced growth process for the three-dimensional nano-heterostructures is proposed according to the experimental results and crystallography relationship. This approach can offer a prevailing way to fabricate more complex three-dimensional nanostructures with built-in heterojunctions. Room temperature PL spectra were used to investigate the emission property of the as-prepared samples. The PL spectra of ZnSe and ZnSxSe1−x nanobelts show strong near bandgap emission, demonstrating a high crystal quality of these as-synthesized nanobelts. The PL spectrum of three-dimensional ZnS/ZnS0.3Se0.7 nano-heterostructures shows the near bandgap emission of ZnS and ZnS0.3Se0.7 simultaneously, demonstrating the incorporating function. These three-dimensional nano-heterostructures with unique structure and morphology can be used to investigate the incorporating function and find extensive applications in nanophotonics.

Simultaneous additive and subtractive three-dimensional nanofabrication using integrated two-photon polymerization and multiphoton ablation

An international team of researchers has combined two well-known fabrication techniques to produce intricate three-dimensional nanostructures. Yong Fen Lu and co-workers say that their novel approach could be used to make nanosized devices that are difficult to produce through either technique alone. Both techniques employ a femtosecond laser. The first — two-photon polymerization—is used to ‘draw’ 3D structures in a photocurable polymer. The second—femtosecond laser multiphoton ablation—is used to cut voids, such as channels, in the polymer. Combining these two techniques enables the efficient fabrication of complex three-dimensional nanostructures, such as integrated optical circuits and lab-on-a-chip devices.

Polymer nanostructured components machined directly by the atomic force microscopy scratching method

This study aims to machine complex three dimensional nano-structures on polymer surfaces directly using the Atomic Force Microscopy (AFM)-based nano-mechanical processing method. Processing parameters including the normal load, the feed rate, the machining speed and the scanning direction are optimized by the Taguchi method. Their effects on the machined depth and the surface roughness of the machined structures are analyzed. Meanwhile, the AFM PZT tube is controlled to achieve the tip’s three-dimensional motions in space. Using the optimized processing parameters, three-dimensional nanostructures on the surface of PMMA are directly fabricated. It is a novel low-cost manufacturing method for machining complex three-dimensional nano-structures or nano parts on polymer surfaces directly.

Photoemission electron microscopy of three-dimensional magnetization configurations in core-shell nanostructures

We present a photoemission electron microscopy method that combines magnetic imaging of the surface and of the inner magnetization in three-dimensional core-shell nanostructures. The structure investigated consists of a cylindrical nickel core that is completely surrounded by a shell of iron oxide and silicon oxide layers. The method enables one to image the magnetization configuration of the nickel core even though the shell is thicker than the mean-free path of the photoelectrons. Characteristic ${L}_{3}$ and ${L}_{2}$ edges can be observed not only in the yield of the photoelectrons emitted from the surface of the nanostructure but also in its shadow. X-ray magnetic circular dichroism in the electron yield of the x rays absorbed and transmitted by the multilayered nanowire allows for the individual imaging of the magnetization configurations of the iron oxide tube and the nickel core. The method suggests novel approaches for the characterization of the magnetic and material properties of complex three-dimensional nanostructures.

Plastic Deformation Drives Wrinkling, Saddling, and Wedging of Annular Bilayer Nanostructures

We describe the spontaneous wrinkling, saddling, and wedging of metallic, annular bilayer nanostructures driven by grain coalescence in one of the layers. Experiments revealed these different outcomes based on the dimensions of the annuli, and we find that the essential features are captured using finite element simulations of the plastic deformation in the metal bilayers. Our results show that the dimensions and nanomechanics associated with the plastic deformation of planar nanostructures can be important in forming complex three-dimensional nanostructures.