Tunable Resonance Research Articles

Scalable On‐Chip Microdisk Resonator Spectrometer

AbstractOn‐chip micro‐spectrometers are sought after with great effort owing to extensive potential applications in mobile optical sensing and imaging. By multiplexing more physical channels, the reconstructive spectrometers based on the spectral‐to‐spatial mapping technique can improve the spectral range. However, this method is challenging to implement and sustain due to the increase in system complexity and the decrease of dynamic range or spectral resolution. Here, a micro‐spectrometer utilizing a single tunable microdisk resonator (MDR) is demonstrated. Such a single MDR spectrometer has only one physical channel to receive all spectral components with a compact size, overcoming the trade‐off among spectral resolution, spectral range, and dynamic range. Leveraging the wavelength and temperature‐dependent response matrix, unknown spectra are reconstructed from their corresponding output light intensity vector. The fabricated device illustrates a high resolution of 0.01 nm for a dual peak and a medium resolution of 0.2 nm in the 20 nm spectral range. A wide variety of complex input spectra, including narrowband and broadband spectral signals, can be well recovered, exhibiting the robustness of the spectral reconstruction approach. Moreover, this proposed spectrometer exhibits ease of scalability and flexible configuration to a spectrometer array covering a set of desired and even discrete spectral ranges.

Plasmonic visible-near infrared photothermal activation of olefin metathesis enabling photoresponsive materials.

Light-induced catalysis and thermoplasmonics are promising fields creating many opportunities for innovative research. Recent advances in light-induced olefin metathesis have led to new applications in polymer and material science, but further improvements to reaction scope and efficiency are desired. Herein, we present the activation of latent ruthenium-based olefin metathesis catalysts via the photothermal response of plasmonic gold nanobipyramids. Simple synthetic control over gold nanobipyramid size results in tunable localized surface plasmon resonance bands enabling catalyst initiation with low-energy visible and infrared light. This approach was applied to the ROMP of dicyclopentadiene, affording plasmonic polymer composites with exceptional photoresponsive and mechanical properties. Moreover, this method of catalyst activation was proven to be remarkably more efficient than activation through conventional heating in all the metathesis processes tested. This study paves the way for providing a wide range of photoinduced olefin metathesis processes in particular and photoinduced latent organic reactions in general by direct photothermal activation of thermally latent catalysts.

Diffusion-controlled bridging of the Au Island and Au core in Au@Rh(OH)3 core-shell structure.

Hybrid nanostructures have garnered considerable interest because of their fascinating properties owing to the hybridization of materials and their structural varieties. In this study, we report the synthesis of [Au@Rh(OH)3]-Au island heterostructures using a seed-mediated sequential growth method. Through the thiol ligand-mediated interfacial energy, Au@Rh(OH)3 core-shell structures with varying shell thicknesses were successfully obtained. On these Au@Rh(OH)3 core-shell seeds, by modulating the diffusion of HAuCl4 in the porous Rh(OH)3 shell, site-specific growth of Au islands on the inner Au core or on the surface of the outer Rh(OH)3 shell was successfully achieved. Consequently, two types of distinct structures, the Au island-on-[Au@Rh(OH)3] dimer and Au island-Au bridge-[Au@Rh(OH)3] dumbbell structures with thin necks were obtained. Further modulations of the growth kinetics led to the formation of Au plate-Au bridge-[Au@Rh(OH)3] heterostructures with larger structural anisotropy. The flexible structural variations were demonstrated to be an effective means of modulating the plasmonic properties; the Au-Au heterostructures exhibited tunable localized surface plasmon resonance in the visible-near-infrared spectral region and can be used as surface-enhanced Raman scattering (SERS) substrates capable of emitting strong SERS signals. This diffusion-controlled growth of Au bridges in the Rh(OH)3 shells (penetrating growth) is an interesting new approach for structural control, which enriches the tool box for colloidal nanosynthesis. This advancement in structural control is expected to create new approaches for colloidal synthesis of sophisticated nanomaterials, and eventually enable their extensive applications in various fields.

Tunable Metasurfaces Based on Mechanically Deformable Polymeric Substrates

The emergence of metamaterials has presented an unprecedented platform to control the fundamental properties of light at the nanoscale. Conventional metamaterials, however, possess passive properties that cannot be modulated post-fabrication, limiting their application spectrum. Recent metasurface research has explored a plethora of active control mechanisms to modulate the optical properties of metasurfaces post-fabrication. A key active control mechanism of optical properties involves the use of mechanical deformation, aided by deformable polymeric substrates. The use of deformable polymeric substrates enables dynamic tuning of the optical properties of metasurfaces including metalenses, metaholograms, resonance, and structural colors, which are collectively relevant for biosensing and bioimaging. Deformable–stretchable metasurfaces further enable conformable and flexible optics for wearable applications. To extend deformable–stretchable metasurfaces to biocompatible metasurfaces, a fundamental and comprehensive primer is required. This review covers the underlying principles that govern the highlighted representative metasurface applications, encompassing stretchable metalenses, stretchable metaholograms, tunable structural colors, and tunable plasmonic resonances, while highlighting potential advancements for sensing, imaging, and wearable biomedical applications.

Plasmonic Zn0.5Cd0.5S/NaxMoO3 composites with excellent full-spectrum driven photocatalytic hydrogen activity

Developing the full-spectrum driven photocatalysts is considered as a potential strategy to realize the high-efficient photocatalytic hydrogen. Herein, plasmonic NaxMoO3 with oxygen vacancies was coupled with Zn0.5Cd0.5S to construct Z-scheme heterostructure. The Zn0.5Cd0.5S /NaxMoO3 photocatalysts perform UV–vis-NIR-driven extraordinary photocatalytic hydrogen activity: the H2 rates of Zn0.5Cd0.5S/NaxMoO3-5 under the irradiation of full-spectrum, > 420 nm, > 520 nm and > 780 nm are 6033, 2846, 92, 54 μmolg-1h−1, respectively, showing an energy distribution that eligible the distribution of solar energy. Benefiting from the synergistic impact of the interfacial Z-type heterojunction and the tunable plasmonic resonance of NaxMoO3, the composites shows excellent full-spectrum absorption and the high charge separation efficiency. This work endows Zn0.5Cd0.5S the NIR-driven photocatalytic H2 ability by utilizing the LSPR effect of NaxMoO3, which provides a new horizon to realize the high-efficient photocatalytic performance and the sufficient usage of solar light.

Lightweight bandgap tunable low-frequency local resonance structure

Local resonance (LR) structure can effectively suppress the low-frequency noise and vibration, but it is still a great challenge to design a kind of lightweight small-size structure with the low-frequency bandgap. This paper proposes a lightweight small-size LR structure with adjustable stiffness ratio, and there are two equivalent negative stiffness regions formed in the LR structure, which are not only greatly enlarged, but also coupled at last only by adjusting the stiffness ratio of the system (changing radius), and finally the negative stiffness region is successfully enlarged more than 2 times in this way. Based on the theory of regulating negative stiffness region, the mechanism of regulating the low-frequency bandgap within the lightweight small-size LR structure is further revealed. It is found that there are two low-frequency bandgaps in the LR structure, and its lower bound of the first bandgap is decreased from 54 Hz to 34 Hz only through adjusting the stiffness ratio (changing radius), and a low-frequency bandgap with 34–248 Hz is obtained by FEM at last. Most importantly, the mechanism of regulating the low-frequency bandgap only by adjusting the stiffness ratio can provide an important idea for designing the lightweight small-size LR structure since it can break out the limitation of the heavy mass and big structures in traditional methods, so it has great practical value for vibration isolation and noise reduction in engineering.

Tunable terahertz hybrid metamaterials supported by 3D Dirac semimetals

By utilizing the three-dimensional Dirac semimetal (DSM)-strontium titanate (SrTiO3, STO) elliptical hybrid metamaterials, the tunable Fano resonances were systematically analyzed in the THz regime, for example, the effects of asymmetric degrees, DSM Fermi levels, and operation frequencies. Interestingly, an obvious Fano peak is observed by introducing a displacement (asymmetric degree) between STO and DSM resonators. In particular, the amplitude modulation depth (MD) of the Fano transmission peak (reflection dip) is 49.5% (86.65%) when the asymmetric degree ranges from 0 to 20 µm. Furthermore, on the condition that the asymmetric degree is larger than 10 µm, the LC resonance is also excited with an extraordinary Q–factor of more than 25. Additionally, by modifying the Fermi level of DSM layer, the amplitude MD of Fano transmission peak (reflection dip) is 32.86% (67.26%). The results facilitate our understanding of the tunable mechanisms of DSM metamaterials and potentially promote the development of novel plasmonic devices, including filters, modulators and sensors.

Thermal tunable silicon valley photonic crystal ring resonators at the telecommunication wavelength.

Tunable ring resonators are essential devices in integrated circuits. Compared to conventional ring resonators, valley photonic crystal (VPC) ring resonators have a compact design and high quality factor (Q-factor), attracting broad attention. However, tunable VPC ring resonators haven't been demonstrated. Here we theoretically demonstrate the first tunable VPC ring resonator in the telecommunication wavelength region, the resonance peaks of which are tuned by controlling the temperature based on the thermal-optic effect of silicon. The design is ultracompact (12.05 µm by 10.44 µm), with a high Q-factor of 1281.00. By tuning the temperature from 100 K to 750 K, the phase modulation can reach 7.70 π, and the adjustment efficiency is 0.062 nm/K. Since thermal tuning has been broadly applied in silicon photonics, our design can be readily applied in integrated photonic circuits and will find broad applications. Furthermore, our work opens new possibilities and deepens the understanding of designing novel tunable VPC photonic devices.

Unifying stability and plasmonic properties in hybrid nanoislands: Au–Ag synergistic effects and application in SERS

In plasmon-based devices, the choice of metal for the nanostructures often leads to an undesirable tradeoff between either the superb performance of Ag or the stability of Au. There is a great interest in combining Au and Ag in a way that preserves both their favourable properties, while also exploiting synergistic effects to boost surface-enhanced Raman scattering (SERS) performance beyond the capabilities of a single metal. To address this issue, a large-area nanofabrication procedure based on galvanic replacement was used to create hybrid Au–Ag nanoislands with a diverse morphology and highly tunable (through visible to NIR) plasmon resonance. Their stability was comprehensively studied and shown to be complex to achieve. However, in the right conditions, Au–Ag nanoislands with silver-like plasmonic properties were fabricated, and shown to be stable over a period of at least 5 months. Moreover, their SERS efficiency considerably outperformed even that of Ag nanoislands. Computational investigation helped explain the advantageous properties and provided insights for future sensor design. Detection of the model molecules was achieved in the nanomolar range and in mild conditions (low laser power), indicating great potential for biomedicine sensing. Beyond that, nanoislands with simultaneous stability and good plasmonic properties can find application in a wide variety of photonic devices.

A Telomerase-Activated Magnetic Resonance Imaging Probe for Consecutively Monitoring Tumor Growth Kinetics and In Situ Screening Inhibitors.

Telomerase has long been considered as a biomarker for cancer diagnosis and a therapeutic target for drug discovery. Detecting telomerase activity in vivo could provide more direct information of tumor progression and response to drug treatment, which, however, is hampered by the lack of an effective probe that can generate an output signal without a tissue penetration depth limit. In this study, using the principle of distance-dependent magnetic resonance tuning, we constructed a telomerase-activated magnetic resonance imaging probe (TAMP) by connecting superparamagnetic ferroferric oxide nanoparticles (SPFONs) and paramagnetic Gd-DOTA (Gd(III) 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) complexes via telomerase-responsive DNA motifs. Upon telomerase-catalyzed extension of the primer in TAMP, Gd-DOTA-conjugated oligonucleotides can be liberated from the surface of SPFONs through a DNA strand displacement reaction, restoring the T1 signal of the Gd-DOTA for a direct readout of the telomerase activity. Here we show that, by tracking telomerase activity, this probe provides consistent monitoring of tumor growth kinetics during progression and in response to drug treatment and enables in situ screening of telomerase inhibitors in whole-animal models. This study provides an alternative toolkit for cancer diagnosis, treatment response assessment, and anticancer drug screening.

PDGFB-targeted functional MRI nanoswitch for activatable T1–T2 dual-modal ultra-sensitive diagnosis of cancer

As one of the most significant imaging modalities currently available, magnetic resonance imaging (MRI) has been extensively utilized for clinically accurate cancer diagnosis. However, low signal-to-noise ratio (SNR) and low specificity for tumors continue to pose significant challenges. Inspired by the distance-dependent magnetic resonance tuning (MRET) phenomenon, the tumor microenvironment (TME)-activated off–on T1–T2 dual-mode MRI nanoswitch is presented in the current study to realize the sensitive early diagnosis of tumors. The tumor-specific nanoswitch is designed and manufactured on the basis of PDGFB-conjugating ferroferric oxide coated by Mn-doped silica (PDGFB-FMS), which can be degraded under the high-concentration GSH and low pH in TME to activate the T1–T2 dual-mode MRI signals. The tumor-specific off–on dual-mode MRI nanoswitch can significantly improve the SNR and is used successfully for the accurate diagnosis of early-stage tumors, particularly for orthotopic prostate cancer. In addition, the systemic delivery of the nanoswitch did not cause blood or tissue damage, and it can be excreted out of the body in a timely manner, demonstrating excellent biosafety. Overall, the strategy is a significant step in the direction of designing off–on dual-mode MRI nanoprobes to improve imaging accuracy, which opens up new avenues for the development of new MRI probes.

Tunable high-Q resonance and abnormal phase-shift in P T-symmetric meta-molecules

We analyze the optical response of a parity-time ( P T ) symmetric diatomic meta-molecular array. We show that the P T symmetry can transform an initial dark antisymmetric mode of the diatomic meta-molecule into bright, featured by a high-Q peak in the scattering spectrum. The Q factor is tunable by managing the magnitudes of the gain and loss. Furthermore, around this high-Q resonance an abnormal phase-shift is obtained, which persists even at exceptional point. We also show that the effective dielectric constant of the P T -symmetric meta-molecular array can be modeled by an anomalous doubly-resonant Lorentz oscillator, which is different from that in electromagnetically induced transparency and Autler-Townes splitting. This study contributes to the advances of non-Hermitian optics and slow light.

Slow-light effects based on the tunable Fano resonance in a Tamm state coupled graphene surface plasmon system.

We theoretically realize the tunable Fano resonance in a hybrid structure that allows the coupling between Tamm plasmon-polaritons (TPPs) and graphene surface plasmon-polaritons (SPPs). In this coupling system, a distributed Bragg reflector (DBR)/Ag structure is designed to generate the TPP with a narrow resonance, and the graphene SPP is excited by grating coupling with a broad resonance. The overlap of these two kinds of resonances results in the Fano resonance with a high-quality factor close to 1500. The behaviors of the Fano resonance are discussed carefully, and the results show that both the graphene Fermi level and the incidence angle can actively tune the profile of the Fano resonance. Owing to the ultrasharp spectrum of the tunable Fano resonance, our design may offer an alternative strategy for developing various optoelectronic devices such as filters, sensors, and nonlinear and slow-light devices. Finally, as an example of the potential applications, we apply the tunable Fano resonance to the slow-light effect, a high performance slow-light effect can be achieved, and the group delay can reach up to 52 ps.

Communication-Less Receiver-Side Resonant Frequency Tuning for Magnetically Coupled Wireless Power Transfer Systems

Compensating for deviations in the resonant frequency is crucial in magnetic resonance coupling wireless power transfer (WPT) systems. Thus, this study proposes a communication-less receiver-side resonant frequency-tuning scheme that compensates for the reactance in the receiver without communicating with the transmitter. The proposed scheme comprises an inductor-capacitor-capacitor compensation topology at the transmitter and a half-bridge circuit at the receiver, whose operating phase is set to be orthogonal to the receiver current. Resonant frequency tuning can be achieved by adjusting the DC voltage applied to the half-bridge circuit to maximize the power received at the load. The reactance compensation ability of the proposed scheme is analyzed through experiments on a 200 kHz WPT system. When the secondary capacitance deviated from –20% to +20%, the efficiency degradation was maintained within 6.7% with the proposed scheme, whereas the efficiency degraded by up to 33.3% without compensation.

An Enhanced-Sensitivity Tangential Electric Field Probe With Tunable Resonant Frequency

A novel enhanced-sensitivity tangential <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field probe with tunable resonant frequency is proposed in this paper. This <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field probe consists of a front-end electric dipole induction part, tunable coupling resonators, a balun transmission section, and a coplanar waveguide transmission part. By introducing an improved electric dipole-induced element and resonant transmission, the detection sensitivity of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field probe can be significantly improved. Varactor diodes are loaded into the coupling resonators to achieve an adjustable resonant center frequency, thereby minimizing the contradiction between the high sensitivity and test bandwidth of the resonant <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field probe. A prototype of this tunable resonant frequency probe was fabricated and measured. When the reverse bias voltage applied to the varactors was tuned from 0 V to 20 V, the probe could obtain enhanced-sensitivity tangential <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field detection within the frequency band of 1.61-2.30 GHz. Moreover, this probe was also adopted to measure the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field components in some areas of the microstrip line and antenna based on FR4. This probe can improve detection efficiency and reduce test costs on the premise of enhanced sensitivity detection. It has broad application prospects for near-field measurement in the future.

Tunable Coaxial Bandpass Filters Based on Inset Resonators

A new class of compact, high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> , tunable coaxial filter is presented in this article based on a novel inset resonator concept. The tuning concept is based on the displacement of movable resonators inside a properly modified metallic housing which features wide tuning capabilities and stable high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor performance with minimum variation throughout the tuning window. Various prototypes are designed and implemented to demonstrate and validate the proposed concept. A single tunable inset resonator is first designed and measured showing distinctive results of a 43% tuning range, stable high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 4100% ± 4%, spurious-free band up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.8\times f_{0}$ </tex-math></inline-formula> , and volume-saving up to 50% when compared with the conventional combline and half-wavelength structures. The design procedure for constant absolute bandwidth (CABW) tunable filters is then presented, and two different tunable inset filters are designed and implemented. First, a manually tunable four-pole filter is demonstrated with the merits of a wide 39.3% tuning range, while maintaining a constant bandwidth of 116 MHz ± 6% and a stable high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 1820% ± 6%. Next, an automatically tunable third-order inset filter is designed and measured using high-accuracy piezomotors. Similarly, the measured results exhibit a wide 1.3-GHz tuning range from 2.65 to 3.95 GHz with a stable insertion loss that is less than 0.35 dB, a return loss that is better than 15 dB, and a good spurious performance up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.8\times f_{0}$ </tex-math></inline-formula> . To our own knowledge, the proposed tuning technique and tunable components represent state-of-the-art tuning range and stable high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> with minimal variation when compared with similar loaded-waveguide designs.

Spectrum and size controllable synthesis of high-quality gold nanorods using 1,7-dihydroxynaphthalene as a reducing agent.

The spectrum and size controllable synthesis of gold nanorods is of great value for their widely applicable aspect ratio dependence of anisotropic surface plasmon resonance. Herein, 1,7-dihydroxynaphthalene with a relatively strong reducibility is proposed as a reducing agent for the controllable synthesis of gold nanorods. The result indicated that gold nanorods with high monodispersity, high shape yield, relatively small diameters, and maximum plasmon resonance wavelength of above 1000 nm can be acquired. More importantly, by virtue of the reducing agent used, fine and precise controls over the plasmon wavelength and diameter of the rod can be achieved via changes in experimental conditions. In particular, increases in the concentration of both silver ions and cetyltrimethylammonium bromide (CTAB) can increase the plasmon wavelength from around 600 nm to 1000 nm but respectively show a decreased diameter with the smallest value of around 14.3 nm and a mildly increased diameter from around 9.0 nm to 14.3 nm; moreover, increasing the concentration of reducing agents and gold seeds can simultaneously cause decreases in the plasmon wavelength from around 1000 nm to 800 nm and the diameters from around 14.3 nm to 9.0 and 7.3 nm, respectively. This powerful and efficient method of controllable synthesis of AuNRs could be valuable and attractive for the application of the as-obtained particles.

A High Performance Silicon Nitride Optical Delay Line With Good Expansibility

In this paper, based on the double strip silicon nitride platform, we designed and fabricated a low loss continuously tunable broadband optical delay line, which contains a 5-bit optical switched delay line and a single tunable optical ring resonator working at “off-resonance”. Optical double sideband modulation link measurement results show it can achieve continuous delay tuning of 395.5 ps and in-band delay fluctuations of about 4 ps and 1 ps were obtained in 8 GHz and 5 GHz working bandwidths, respectively. In addition, the proposed optical delay line has a low on-chip insertion loss of 3 dB and a very low optical loss delay ratio of 0.0022 dB/ps. Moreover, it's delay tuning range can be easily increased by cascading more thermo-optic switches. The delay bandwidth can be expanded by adopting the optical single sideband modulation or increasing the FSR of the optical ring resonator. This integrated tunable optical delay line with good overall performances and expand ability shows great potential for microwave photonic applications.

Research progress of silicon nanowires array photodetectors

As one of the most important semiconductor materials, silicon (Si) is widely used in optoelectronic devices such as solar cells and photodetectors. Owing to the difference in refractive index between silicon and air, a large amount of incident light is reflected back into the air from the silicon surface. In order to suppress the loss caused by this reflection, a variety of silicon nanostructures with strong trapping effect have been developed. Most of the dry-etching schemes encounter the problems of high cost and complex preparation, while the silicon nanowires array prepared by the wet-etching schemes has the problems of low controllability of some parameters such as the spacing between two adjacent nanowires, and the small effective area of heterojunction. The method of using polystyrene microsphere as the mask can integrate the advantages of dry-etching method and wet-etching method, and it is easy to obtain periodic silicon nanowires (pillars) array. In this paper, first, we summarize the properties and preparation methods for silicon nanowires structure, the strategies to effectively improve the performance of silicon nanowires (pillars) array photodetectors, Then we analyze the existing problems. Further, the latest developments of silicon nanowires (pillars) array photodetector are discussed, and the structure, morphology of photosensitive layer and methods to improve the performance parameters of silicon nanowires (pillars) array photodetector are analyzed. Among them, we focus on the ultraviolet light sensitive silicon based photodetector and its method to show tunable and selective resonance absorption through leaky mode resonance, the silicon nanowires array photodetector modified with metal nanoparticles and the method of improving performance through surface plasmon effect, and plasmon hot electrons. Heterojunction photodetectors composed of various low-dimensional materials and silicon nanowires (pillars) array, and methods to improve the collection efficiency of photogenerated charge carriers through the “core/shell” structure, methods to expand the detection band range of silicon-based photodetectors by integrating down-conversion light-emitting materials and silicon nanowires (pillars) array, flexible silicon nanowires array photodetectors and their various preparation methods, are all introduced. Then, the main problems that a large number of defect states will be generated on the silicon nanostructure surface in the MACE process are briefly introduced, and several possible solutions for defect passivation are also presented. Finally, the future development for silicon nanowires (pillars) array photodetectors is prospected.

A super asymmetric cross antenna structure with tunable dual-frequency resonances.

The detection performance of traditional infrared spectroscopy can be very limited in the case of molecular vibrational modes with low absorption cross-sections. On account of its electric field enhancement, plasmonic antenna can be combined with infrared spectroscopy to realize surface enhanced infrared detection and characterization of molecules. In this work, a super asymmetric cross antenna structure with tunable dual-frequency resonance and a high enhancement factor is designed. By systematically studying the transmission spectrum and charge distribution of this super asymmetric cross antenna structure, the physical origin of the dual-frequency resonance and its tunability are characterized in detail. In addition, in order to target desired molecular ensembles, the relationship between the resonance frequency and electric-field intensity of the two resonance modes and the parameters of structure and incident light are examined, yielding an enhancement factor close to 100 in the desired frequency region. Finally, the experimental results show that the proposed super asymmetric cross antenna structure can indeed generate dual-frequency resonances, agreeing reasonably with the theoretical results. It is believed that the super asymmetric cross antenna structure can be widely used to sensitively detect trace molecules, and in monolayered chemistry and bio-molecules, allowing their structures and dynamics to be studied using nonlinear infrared spectroscopy.