Sub‐5 nm metal nanogaps have attracted widespread attention in physics, chemistry, material sciences, and biology due to their physical properties, including great plasmon‐enhanced effects in ...light–matter interactions and charge tunneling, Coulomb blockade, and the Kondo effect under an electrical stimulus. These properties especially meet the needs of many cutting‐edge devices, such as sensing, optical, molecular, and electronic devices. However, fabricating sub‐5 nm nanogaps is still challenging at the present, and scaled and reliable fabrication, improved addressability, and multifunction integration are desired for further applications in commercial devices. The aim of this work is to provide a comprehensive overview of sub‐5 nm nanogaps and to present recent advancements in metal nanogaps, including their physical properties, fabrication methods, and device applications, with the ultimate aim to further inspire scientists and engineers in their research.
Sub‐5 nm metal nanogaps have attracted widespread attention in physics, chemistry, material sciences, and biology due to their physical properties. However, fabricating sub‐5 nm nanogaps is still challenging, impeding their further applications in commercial devices. This work aims to provide a comprehensive overview and recent advancements in sub‐5 nm metal nanogaps, including their physical properties, fabrication methods, and device applications.
Controlling the spin angular momentum of light (or circular polarization state) plays a crucial role in the modern photonic applications such as optical communication, circular dichroism ...spectroscopy, and quantum information processing. However, the conventional approaches to manipulate the spin of light require naturally occurring chiral or birefringent materials of bulky sizes due to the weak light–matter interactions. Here we experimentally demonstrate an approach to implement spin-selective transmission in the infrared region based on chiral folded metasurfaces that are capable of transmitting one spin state of light while largely prohibiting the other. Due to the intrinsic chirality of the folded metasurface, a remarkable circular dichroism as large as 0.7 with the maximum transmittance exceeding 92% is experimentally demonstrated. The giant circular dichroism is interpreted within the framework of charge-current multipole expansion. Moreover, the intrinsic chirality can be readily controlled by manipulating the folding angle of the metasurface with respect to the cardinal plane. Benefiting from its strong chirality and spin-dependent transmission characteristics, the proposed folded metasurface may be applied to a range of novel photon-spin selective devices for optical communication technologies and biophotonics.
Resistive switching processes in HfO2
are studied by electron holography and in situ energy‐filtered imaging. The results show that oxygen vacancies are gradually generated in the oxide layer under ...ramped electrical bias, and finally form several conductive channels connecting the two electrodes. It also shows that the switching process occurs at the top interface of the hafnia layer.
► Electronic transport and mechanical properties of individual conducting polymer nanotubes/fibers are reviewed. ► Various preparation methods of one-dimensional conducting polymer nanostructures are ...summarized. ► Several potential applications and corresponding challenges of conducting polymer nanotubes/fibers are discussed.
This article summarizes and reviews the various preparation methods, physical properties, and potential applications of one-dimensional nanostructures of conjugated polyaniline (PANI), polypyrrole (PPY) and poly(3,4-ethylenedioxythiophene) (PEDOT). The synthesis approaches include hard physical template method, soft chemical template method, electrospinning, and lithography techniques. Particularly, the electronic transport (e.g., electrical conductivity, current–voltage (
I–
V) characteristics, magnetoresistance, and nanocontact resistance) and mechanical properties of individual nanowires/tubes, and specific heat capacity, magnetic susceptibility, and optical properties of the polymer nanostructures are presented with emphasis on size-dependent behaviors. Several potential applications and corresponding challenges of these nanofibers and nanotubes in chemical, optical and bio-sensors, nano-diodes, field effect transistors, field emission and electrochromic displays, super-capacitors and energy storage, actuators, drug delivery, neural interfaces, and protein purification are also discussed.
Kirigami, with facile and automated fashion of three-dimensional (3D) transformations, offers an unconventional approach for realizing cutting-edge optical nano-electromechanical systems. Here, we ...demonstrate an on-chip and electromechanically reconfigurable nano-kirigami with optical functionalities. The nano-electromechanical system is built on an Au/SiO
/Si substrate and operated via attractive electrostatic forces between the top gold nanostructure and bottom silicon substrate. Large-range nano-kirigami like 3D deformations are clearly observed and reversibly engineered, with scalable pitch size down to 0.975 μm. Broadband nonresonant and narrowband resonant optical reconfigurations are achieved at visible and near-infrared wavelengths, respectively, with a high modulation contrast up to 494%. On-chip modulation of optical helicity is further demonstrated in submicron nano-kirigami at near-infrared wavelengths. Such small-size and high-contrast reconfigurable optical nano-kirigami provides advanced methodologies and platforms for versatile on-chip manipulation of light at nanoscale.
Graphene has drawn considerable attention due to its intriguing properties in photonics and optoelectronics. However, its interaction with light is normally rather weak. Meta-surfaces, artificial ...structures with single planar function-layers, have demonstrated exotic performances in boosting light-matter interactions, e.g., for absorption enhancement. Graphene based high efficiency absorber is desirable for its potential applications in optical detections and signal modulations. Here we exploit graphene nanoribbons based meta-surface to realize coherent perfect absorption (CPA) in the mid-infrared regime. It was shown that quasi-CPA frequencies, at which CPA can be demonstrated with proper phase modulations, exist for the grapheme meta-surface with strong resonant behaviors. The CPA can be tuned substantially by merging the geometric design of the meta-surface and the electrical tunability of graphene. Furthermore, we found that the graphene nanoribbon meta-surface based CPA is realizable with experimentally achievable graphene sample.
With strong spin–orbit coupling (SOC), ultrathin two-dimensional (2D) transitional metal chalcogenides (TMDs) are predicted to exhibit weak antilocalization (WAL) effect at low temperatures. The ...observation of WAL effect in VSe2 is challenging due to the relative weak SOC and three-dimensional (3D) transport nature in thick VSe2. Here, we report on the observation of quasi-2D transport and WAL effect in sublimed-salt-assisted low-temperature chemical vapor deposition (CVD) grown few-layered high-quality VSe2 nanosheets. The WAL magnitudes in magnetoconductance can be perfectly fitted by the 2D Hikami–Larkin–Nagaoka (HLN) equation in the presence of strong SOC, by which the spin–orbit scattering length l SO and phase coherence length l ϕ have been extracted. The phase coherence length l ϕ shows a power law dependence with temperature, l ϕ∼ T –1/2, revealing an electron–electron interaction-dominated dephasing mechanism. Such sublimed-salt-assisted growth of high-quality few-layered VSe2 and the observation of WAL pave the way for future spintronic and valleytronic applications.
Abstract
Metalenses as miniature flat lenses exhibit a substantial potential in replacing traditional optical component. Although the metalenses have been intensively explored, their functions are ...limited by poor active ability, narrow operating band and small depth of field (DOF). Here, we show a dielectric metalens consisting of TiO
2
nanofins array with ultrahigh aspect ratio to realize active multiband varifocal function. Regulating the orbital angular momentum (OAM) by the phase assignment covering the 2π range, its focal lengths can be switched from 5 mm to 35 mm. This active optical multiplexing uses the physical properties of OAM channels to selectively address and decode the vortex beams. The multiband capability and large DOFs with conversion efficiency of 49% for this metalens are validated for both 532 nm and 633 nm, and the incidence wavelength can further change the focal lengths. This non-mechanical tunable metalens demonstrates the possibility of active varifocal metalenses.
Strain engineering provides an important strategy to modulate the optical and electrical properties of semiconductors for improving devices performance with mechanical force or thermal expansion ...difference. Here, we present the investigation of the local strain distribution over few-layer MoS
2
bubbles, by using scanning photoluminescence and Raman spectroscopies. We observe the obvious direct bandgap emissions with strain in the few-layer MoS
2
bubble and the strain-induced continuous energy shifts of both resonant excitons and vibrational modes from the edge of the MoS
2
bubble to the center (10 µm scale), associated with the oscillations resulted from the optical interference-induced temperature distribution. To understand these results, we perform
ab initio
simulations to calculate the electronic and vibrational properties of few-layer MoS
2
with biaxial tensile strain, based on density functional theory, finding good agreement with the experimental results. Our study suggests that local strain offers a convenient way to continuously tune the physical properties of a few-layer transition metal dichalcogenides (TMDs) semiconductor, and opens up new possibilities for band engineering within the 2D plane.
Specific biorecognition is essential for many biological processes, for which highly sensitive and label-free biosensors are strongly demanded. The recently developed metamaterials are a potential ...choice for biosensing due to their exotic properties. In the current work, a label-free and specific sensor for streptavidin-agarose (SA) was fabricated based on terahertz metamaterial functionlized by octadecanthiols and biotins. Both low and high frequency resonant modes from the metamaterials are found applicable for the detection of SA, and a redshift up to 6.76 GHz for the high frequency mode was measured in the undiluted commercial solution. The low frequency mode is attributed to inductor-capacitor (LC) oscillation, while the high frequency mode originates from the plasmonic dipole oscillator, both of which are highly sensitive to the micro-environment change. Adsorption of SA of different concentrations causes different redshifts, and the replacement of high refractive-index substrate with low refractive-index substrate can efficiently promote the sensitivity, well agreeing with the numerical simulation. Moreover, for a particular biomolecule, the sensitivity can be further improved by optimizing the metamaterial design. This method might be very helpful for desirable biorecognition in biology, medicine, and drug industry.
PDF
