Split Hole Research Articles

Split ring hole metamaterial-enhanced pyroelectric detector for efficient multi-narrowband terahertz detection

Derived from infrared pyroelectric detection, typical terahertz (THz) pyroelectric detectors have low sensitivity at low-frequency THz bands. Based on the high-efficiency absorption of the metamaterial perfect absorber (MPA), a novel split ring hole metamaterial-enhanced pyroelectric detector is proposed to achieve efficient multi-narrowband THz detection. Using high frequency simulation software (HFSS), the dimensional parameters including ring radius, ring width, connection beam width, array period, and thickness, are optimized to enhance efficient multi-narrowband absorption. The as-optimized metamaterial-enhanced detectors are fabricated via micro-nano manufacturing technology. The voltage responsiveness and noise equivalent power of the metamaterial-enhanced detector are tested by THz focused optical path and compared with those of the typical pyroelectric detector and the simulated MPA absorptivity. The results indicate that the metamaterial-enhanced detector has a multi-narrowband detection capability at 0.245 THz, 0.295 THz, and 0.38 THz, which is close to the simulated MPA absorptivity. Compared to the typical pyroelectric detector, the split ring hole metamaterial-enhanced detector can simultaneously achieve thermal absorption, thermal conduction, and pyroelectricity in the same MPA structure, providing faster response speed above 100 Hz chopper frequency and two times higher detection sensitivity at multi-narrowband THz frequencies. This research can be used for THz sensing, absorption filtering, biological macromolecule detection, and other applications.

Anomalous Laser-Fluence Dependence of Electron Spin Excitation in CdS Colloidal Quantum Dots: Surface Effects.

Electron spin dynamics in CdS quantum dots (QDs) with hole acceptor 1-octanethiol organic molecules are investigated by time-resolved ellipticity spectroscopy. An anomalous dependence of laser fluences on electron spin excitation for the first time is reported. Increasing the laser fluence, the electron spin is switched from one direction to an antiparallel direction (spin direction switching, SDS) when adding enough 1-octanethiol hole acceptors in an air atmosphere. The analysis shows that the electron spin direction changes from heavy hole excitation defined to spin-orbit split hole excitation defined. In as-grown CdS QDs with native ligands, laser-fluence-dependent SDS phenomena are absent. Electron wave function spread into 1-octanethiol molecules is demonstrated to be important for the presence of SDS phenomena. The finding here thus reveals the importance of surface conditions on electron spin excitation processes in semiconductor QDs and that the surface can be used as an important factor to manipulate the spin.

Emergence of Fermi arcs due to magnetic splitting in an antiferromagnet.

The Fermi surface plays an important role in controlling the electronic, transport and thermodynamic properties of materials. As the Fermi surface consists of closed contours in the momentum space for well-defined energy bands, disconnected sections known as Fermi arcs can be signatures of unusual electronic states, such as a pseudogap1. Another way to obtain Fermi arcs is to break either the time-reversal symmetry2 or the inversion symmetry3 of a three-dimensional Dirac semimetal, which results in formation of pairs of Weyl nodes that have opposite chirality4, and their projections are connected by Fermi arcs at the bulk boundary3,5-12. Here, we present experimental evidence that pairs of hole- and electron-like Fermi arcs emerge below the Neel temperature (TN) in the antiferromagnetic state of cubic NdBi due to a new magnetic splitting effect. The observed magnetic splitting is unusual, as it creates bands of opposing curvature, which change with temperature and follow the antiferromagnetic order parameter. This is different from previous theoretically considered13,14 and experimentally reported cases15,16 of magnetic splitting, such as traditional Zeeman and Rashba, in which the curvature of the bands is preserved. Therefore, our findings demonstrate a type of magnetic band splitting in the presence of a long-range antiferromagnetic order that is not readily explained by existing theoretical ideas.

Flexible Manipulation of the Reflected Wavefront Using Acoustic Metasurface with Split Hollow Cuboid.

This work proposes a method for actively constructing acoustic metasurface (AMS) based on the split hollow cuboid (SHC) structure of local resonance, with the designed AMS flexibly manipulating the direction of reflected acoustic waves at a given frequency range. The AMS was obtained by precisely adjusting any one or two types of structural parameters of the SHC unit, which included the diameter of the split hole, the length, width, height, and shell thickness of the SHC. The simulation results showed that the AMS can flexibly manipulate the direction of the reflected acoustic waves, and the anomalous reflection angle obeys the generalized Snell’s law. Furthermore, among the five structural parameters, the AMS’s response frequency band is widest with the hole diameter and height, followed by the length and width, and narrowest with the shell thickness. It is worth noting that comprehensive manipulation of two parameters not only broadens the response frequency band, but also strengthens the effect of the anomalous reflection at the same response frequency. The subwavelength size of the AMS constructed with such a comprehensive method has the advantages of a small size, wide response band, simple preparation, and flexible modulation, and can be widely used in various fields, such as medical imaging and underwater stealth.

Tripod-Loop Metasurfaces for Terahertz-Sensing Applications: A Comparison

The high electric field intensity achieved on the surface of sensors based on metasurfaces (metasensors) makes them an excellent alternative for sensing applications where the volume of the sample to be identified is tiny (for instance, thin-film sensing devices). Various shapes and geometries have been proposed recently for the design of these metasensors unit-cells (meta-atoms) such as split ring resonators or hole arrays, among others. In this paper, we propose, design, and evaluate two types of tripod metasurfaces with different complexity in their geometry. An in-depth comparison of their performance is presented when using them as thin-film sensor devices. The meta-atoms of the proposed metasensors consist of a simple tripod and a hollow tripod structure. From numerical calculations, it is shown that the best geometry to perform thin-film sensing is the compact hollow tripod (due to the highest electric field on its surface) with a mean sensitivity of 3.72 × 10−5 nm−1. Different modifications are made to this structure to improve this value, such as introducing arms in the design and rotating the metallic pattern 30 degrees. The best sensitivity achieved for extremely thin film analytes (5–25 nm thick) has an average value of 1.42 × 10−4 nm, which translates into an extremely high improvement of 381% with respect to the initial hollow tripod structure. Finally, a comparison with other designs found in the literature shows that our design is at the top of the ranking, improving the overall performance by more than one order of magnitude. These results highlight the importance of using metastructures with more complex geometries so that a higher electric field intensity distribution and, therefore, designs with better performance can be obtained.

Orbital crossing in spin-split Fermi surfaces and anisotropic effective mass of the noncentrosymmetric heavy-fermion paramagnet UPt5

We report the single-crystal growth of the noncentrosymmetric cubic heavy-fermion paramagnet ${\mathrm{UPt}}_{5}$ and comparative Fermi surface studies of de Haas-van Alphen (dHvA) experiments and theoretical band calculations. We also present the results of single-crystal x-ray diffraction, electrical resistivity, heat capacity, and magnetization measurements using single crystals of ${\mathrm{UPt}}_{5}$. The dHvA experiments reveal nearly spherical split hole Fermi surfaces and largely split electron Fermi surfaces, which are in agreement with the results of a band-structure calculation. The largely split electron Fermi surfaces may be understood through the antisymmetric spin-orbit interaction derived from U-$5f$ and Pt-$5d$ electrons. We explain the observed unexpected dHvA frequencies quasiquantitatively based on orbital crossing using the coupled network analysis in the split hole Fermi surface pair. Furthermore, the temperature dependence of the dHvA amplitude reveals enhanced cyclotron effective masses of up to $29{m}_{0}$ and a peculiar anisotropic effective mass in the paramagnetic cubic heavy-fermion ${\mathrm{UPt}}_{5}$.

Split sleeve cold expansion of AZ31B sheet: Microstructure, texture and residual stress

Despite magnesium limited formability at room temperature, split sleeve hole cold expansion of AZ31B sheet was successfully implemented. Microstructural analysis showed greater hardness in the immediate vicinity of the notch, which was due to high dislocation density and extensive twinning created because of substantial compressive radial strain during the process. Contribution of twinning in accommodating the tensile tangential strain is believed to be the underlying reason why the sheet endured large plastic strains. Residual stress measurements confirmed variations through the thickness, with the highest value being at the exit side of the sheet. The fatigue performance of cold expanded samples revealed that different degrees of cold expansion result in various levels of life enhancement. Optimum degree of expansion was found to be 5%, which leads to 3 times fatigue life improvement compared to the as-received condition, due to the imposed microstructural changes, including developed compressive residual tangential stresses and the greater hardness at the notch root. Abovementioned factors contribute to enhancement of fatigue life through postponing the crack initiation and impeding the crack propagation.

Simulated and Experimental Research of Multi-Band Acoustic Metamaterial with a Single Resonant Structure.

We present a multi-band acoustic metamaterial (AMM) with a single structural unit of a nested split hollow sphere (NSHS). The transmissions of the NSHS-AMM from the simulation and experiment revealed two dips which were attributed to local coupling resonance. Using the retrieval method from the experimental data, we calculated the effective modulus of the NSHS-AMM and found it to be negative near the bands of the two dips. The AMM with a negative modulus can be easily tuned due to the coupling effect in the NSHS. The two dips can be simultaneously tuned by changing the diameter and the direction angle of the split holes of the interior and exterior split hollow sphere (SHS) in the NSHS. We designed a three-nested SHS-AMM with a negative modulus in three bands. Given the obvious local coupling resonance in the NSHS, such NSHS-AMMs may provide a viable path for the design of broadband AMMs or acoustic metasurfaces.

High-temperature electron-hole liquid in diamond films

The ground state of the electron-hole liquid in diamond films is studied by density functional theory. The energy and equilibrium density of the liquid in films with thicknesses of a few nanometers are calculated. It is shown that the electron-hole liquid is multicomponent and consists of electrons and heavy, light, and spin-orbit split holes. The equilibrium density of electron-hole pairs in (111)-oriented diamond films is much higher than that in films with (100) orientation. The critical temperature of the electron-hole liquid in (111)-oriented diamond films is close to room temperature.

Mutual Inductance and Coupling Effects in Acoustic Resonant Unit Cells.

We present an acoustic metamaterial (AMM) consisting of a dumbbell-shaped split hollow sphere (DSSHS). Transmission results of experiments and simulations both presented a transmitted dip at the resonant frequency of AMM, which demonstrated its negative modulus property. As the two split holes in the DSSHS had strong coupling effects for the acoustic medium in the local region, the dip could be simply manipulated by tuning the distance between the split holes. When the distance was large enough, the mutual inductance tended to disappear, and a weak interaction existed in the structure. According to the property of weak interaction, a multiband AMM and a broadband AMM with a negative modulus could be achieved by arraying DSSHS clusters with different distances. Furthermore, mutual inductance and coupling in DSSHS reinforced the local resonance, and this kind of cell could be used to design the acoustic metasurface to abnormally control the refractive waves.

Single plasmonic split hole resonator nanostructure as an efficient nanoscale light source

We report a brief review of the results of experimental studies on the nonlinear optical interaction of laser radiation with a hybrid plasmonic nanostructure, i.e. a split hole resonator (SHR). We demonstrate second- and third-harmonic generation and mixed-frequency generation from a single SHR nanostructure. The practical application potential of an SHR nanostructure as a nanoprobe for measuring the femtosecond laser pulse duration and designing an all-optical nanodisplay is shown.

Manipulation of Magnetic Fano Resonances in Double Split-Hole Disk

The plasmon resonances and magnetic field enhancement in double split-hole disk are investigated by using finite element method. The multipolar modes and the magnetic Fano resonances of the double split-hole disk can be tuned by modifying the structure parameters. The oscillate direction of the closed current in the right and the left split hole can be tuned, achieving the bright and dark magnetic modes of this system. These new emergent phenomena in this nanostructure have potential applications in the propagation of low-loss magnetic plasmons and advanced devices based on magnetic Fano resonances.

Nanoscale and femtosecond optical autocorrelator based on a single plasmonic nanostructure

We demonstrated a nanoscale size, ultrafast and multiorder optical autocorrelator with a single plasmonic nanostructure for measuring the spatio-temporal dynamics of femtosecond laser light. As a nanostructure, we use a split hole resonator (SHR), which was made in an aluminium nanofilm. The Al material yields the fastest response time (100 as). The SHR nanostructure ensures a high nonlinear optical efficiency of the interaction with laser radiation, which leads to (1) the second, (2) the third harmonics generation and (3) the multiphoton luminescence, which, in turn, are used to perform multi-order autocorrelation measurements. The nano-sized SHR makes it possible to conduct autocorrelation measurements (i) with a subwavelength spatial resolution and (ii) with no significant influence on the duration of the laser pulse. The time response realized by the SHR nanostructure is about 10 fs.

Subwavelength light localization based on optical nonlinearity and light polarization

We propose and experimentally realize subwavelength light localization based on the optical nonlinearity of a single nonlinear element in nanoplasmonics-a split hole resonator (SHR). The SHR is composed of two basic elements of nanoplasmonics, a nanohole, and a nanorod. A peak field intensity occurs at the single spot of the SHR nanostructure. We demonstrate the use of the SHR as a highly efficient nonlinear optical element for (i)the construction of a polarization-ultrasensitive nanoelement and, as a practical application, (ii)the building up of an all-optical display.

Design of a Passive Controllable Negative Modulus Metamaterial With a Split Hollow Sphere of Multiple Holes

We present a passive controllable negative modulus metamaterial based on a split hollow sphere (SHS) with multiple holes. The metamaterial is obtained by changing the number of split holes. The experimental results show that the position of one split hole does not affect the transmission dip, whereas the resonance frequency depends on the relative position of two holes. Furthermore, when the number of split holes is increased, the resonance frequency undergoes a blueshift. Simulation results via the finite element method (FEM) are in accord with experimental data. The design of a negative modulus metamaterial at an expected frequency is simple, and the proposed method is expected to provide a basis for the simultaneous control of acoustic metamaterials (AMs) through a variety of methods.

Giant optical nonlinearity of a single plasmonic nanostructure

We realize giant optical nonlinearity of a single plasmonic nanostructure which we call a split hole resonator (SHR). The SHR is the marriage of two basic elements of nanoplasmonics, a nanohole and a nanorod. A peak field intensity in the SHR occurs at the single tip of the nanorod inside the nanohole. The peak field is much stronger than those of the nanorod and nanohole, because the SHR field involves contributions from the following two field-enhancement mechanisms: (1) the excitation of surface plasmon resonances and (2) the lightning-rod effect. Here, we demonstrate the use of the SHR as a highly efficient nonlinear optical element for: (i) the generation of the third harmonic from a single SHR; (ii) the excitation of intense multiphoton luminescence from a single SHR.

Assessment on Screw Fixing Failure Mode for Kitchen Cabinet Particleboard

An observation during screw fixing activities on kitchen cabinet installation was carried out. In collaboration with Signature Kitchen Ptd. Ltd., a kitchen cabinet manufacturer in Malaysia, twenty-eight (28) houses in Kelang Valley, Malaysia were selected for the study. Almost all of the sites selected have shown some damages of the particleboard during the screw fixing activities. Generally, there were cracks, chip-off or swelling occurred in between the panel surface and the screw head edges. The damages observed on the screw joint during installation are in the form of split holes, loose holes and delamination. All damages then were identified for its type of failure mode especially at the screw-driving slot and particleboard surface. Six type of failure mode were identified, documented and discussed.

Editorial for special issue on structural integrity and failure

This special issue of FFEMS was compiled from 108 papers presented at the International Conference on Structural Integrity and Failure (SIF 2010) held at The University of Auckland, Auckland, New Zealand on 4–7 July 2010, with the exception of the opening paper which was contributed by the first guest editor. Fifteen selected authors were invited to extend their papers for this issue, resulting in a total of ten papers from the following countries: Australia, Canada, China, Hong Kong, New Zealand and South Korea. The selection of papers in this issue highlights fracture mechanics as a discipline describing failure in a diverse range of materials and machine systems. From nanocomposites (Liao & Tjong) to large aircraft components (Jaya, Tiong & Clark), the papers here also represent the significance of multi-scalar approaches, which are increasingly becoming important to solving many of today's intriguing fracture mechanics problems. Brittle or ductile, homogeneous or composite, materials fail almost invariably due to developments at the micro-level, with small defects and discontinuities. The papers by Suh et al. present in fine detail the initiation of such minuscule surface crack formation, its coalescence and growth in stainless steel and Waspaloy. The studies in this issue, such as those on novel methods in micro-indentation to determine KIc of brittle materials (Xie et al.) and computer simulation of the split sleeve hole cold expansion process (Houghton & Campbell), also illustrate the importance of both experimental and modelling techniques to traverse complex realities and concepts in fracture mechanics and material analyses. Validation of current concepts, theories and models is crucial, and in the study by Clegg, Duan & McLeod the authors experimentally investigate the validity of the theory of critical distance (TCD) by analyzing fatigue behaviour of disc-shaped compact tension and notched cylindrical steel specimens. Several of the papers in this issue are concerned with novel aspects of fatigue. For example Merati, Hellier & Zarrabi have obtained, using a unique mixed-mode test rig, Mode II–Mode III fatigue threshold interaction diagrams for two common aluminium aerospace alloys. Representative fatigue fracture surfaces are also presented. Small fatigue cracks can initiate under shear loading at lower applied loads than for Mode I, and then later turn into unexpectedly large Mode I cracks. In addition, the important role of our field of study in the area of forensics is highlighted in the paper by Withy, James & Williams, where careful post-mortem analyses of wear and cracking has led to new insight on the level of safety in present fuel pump design in aircraft. The paper by Jaya, Tiong & Clark further addresses important issues pertaining to current failure of aircraft joints, and offers solutions including one involving the novel application of corrosion-inhibiting compounds. Finally, the paper by Conor et al. provides evidence from a set of investigations that support the need for a systems approach to failure analysis of aircraft structure and propulsion defects, when causal factors are complex. Effective failure avoidance can be achieved in this way. This special issue serves as a testament to the active support for the SIF conference as well as the efforts of the international fracture community to continue a collective and integrated academic approach to achieving excellence in this significant area of engineering and materials science research. We are grateful to all the authors and reviewers for their invaluable contribution and thank you, the reader, for your interest in this issue. We are especially grateful to the journal for the opportunity to put together this special issue.

Acoustic metamaterial with split hollow spheres

We propose an acoustic metamaterial (AM) composed of local resonant split hollow sphere (SHS). The results of numerical simulation and acoustic experiment show that the effective modulus of the AM with SHS is negative. To further investigate the intrinsic resonant mechanism of the SHS, we study the transmission of the AM by adjusting the geometry sizes of the SHS, such as the diameter of split hole and the diameter of hollow sphere. It is found that the geometry sizes of SHS will greatly affect the frequency of transmission dip, say, the resonant frequency. Moreover, we investigate the effects of the arrangement in AM on transmission feature. When the lattice constant and the number of SHSs change, the frequency range of resonance in the single-layer AM keeps unchanged. However, the resonant intensity of AM becomes stronger with the increase of the number of SHSs in single layer and the number of SHS layers.

The 2002 split ozone hole – the wave of the century?

The 2002 split ozone hole – the wave of the century?