SiO2 Dielectric Layer Research Articles

Uniform propagation of cathode-directed surface ionization waves at atmospheric pressure

The uniform propagation of positive-polarity surface plasmas in air at atmospheric pressure has been achieved using a multi-layer structure, consisting of a silicon wafer covered by a 1 μm thick dielectric SiO2 layer as a propagation surface. Instead of the branched streamers observed in the same conditions when using conventional bulk dielectric surfaces, the plasma exhibits a homogenous ring-shaped structure with a high degree of reproducibility and stability. The plasma is generated by applying nanosecond positive voltage pulses to a tungsten wire touching the dielectric surface. The plasma has been imaged in single shot operation at high spatial resolution with an ultraviolet reflective microscope coupled with a fast intensified charge-coupled device camera. Time- and space-resolved optical emission spectroscopy shows that the homogenous ring corresponds to the propagation of an ionization front with a region of high N2+* emission. We discuss the origin of the ring-shaped ionization wave, considering the role of the Si–SiO2 interface and the effect of illumination by an external light source. The ring ionization wave may result from branching inhibition, due to a photoelectric effect at the interface created by the photons emitted by the plasma. The generation of stable uniform surface ionization waves, in ambient air at atmospheric pressure, could be of interest for further advanced plasma–surface interaction studies or flow control applications.

Characterizing the Interactions of DNA Oligomers with Graphene Field-Effect Transistors

Introduction: Graphene field-effect transistors (G-FETs) constitute an emerging platform for biosensing applications. Indeed, graphene is an ideal material for the detection of biomolecules: every atom of its monolayer structure is in contact with its environment, resulting in an electrical conductivity that is highly responsive to local electrostatic fluctuations from adjacent molecules. For genomic applications, most detection methods use DNA probe sequences bound to the graphene surface, in order to capture a specific target DNA sequence and detect the corresponding change in the electrical response of the sensor1 - 2. However, the effect of interactions between DNA and graphene on the electrical conductance is still not fully understood. Here, we investigate specifically the adsorption of short DNA oligomers on graphene field-effect transistors, in order to model and control the effect of such interactions in biosensing applications with G-FETs. Methods and Results: First, we fabricated G-FET sensors as follow3: Using photolithography techniques, an array of source and drain electrodes were patterned in gold on a Si wafer with a SiO2 insulator layer, as well as a common on-chip gate electrode in platinum. High-quality monolayer CVD-grown graphene was transferred onto the substrate and then etched to create 6 x 4 µm ribbons between each source-drain pair. Transfer curves (Isd vs. Vg) performed in saline buffer solution revealed a conductance minimum at the charge neutrality point of the graphene. Devices were then exposed to solutions of DNA, consisting in 22-single-stranded nucleotides (ssDNA) or double-stranded nucleotides (dsDNA) DNA oligomers diluted in 0,01X PBS buffer. Selected G-FET devices were exposed to different ssDNA concentrations during 15 min, followed by washing steps with 0,01X PBS. Electrical curves were recorded before, during and after each DNA exposure. In this presentation, we will present results showing that ssDNA exposure causes a left-shift of the charge neutrality point above a concentration threshold, and that this shift is proportional to ssDNA concentration. In addition, non-covalent adsorption of ssDNA on graphene appears to be reversible upon washing. Finally, we will discuss differences between the adsorption of dsDNA and ssDNA. Conclusion and Relevance: Our results suggest that unspecific DNA adsorption on graphene can lead to a G-FET response, which needs to be modeled, compensated and /or passivated in biosensing experiments, especially in order to achieve low detection limits for target sequences in complex biological media.

Amyloid-beta peptide detection via aptamer-functionalized nanowire sensors exploiting single-trap phenomena

New highly sensitive direct methods for the early detection of peptides involved in Alzheimer's disease (AD) are required in order to prolong effective and healthy memory and thinking capabilities and also to stop the factors resulting in AD. In this contribution, we report the successful demonstration of a label-free approach for the detection of amyloid-beta (Aβ) peptides by highly selective aptamers immobilized onto the SiO2 surface of the fabricated sensors. A modified single-stranded deoxyribonucleic acid (ssDNA) aptamer was specially designed and synthesized to detect the target amyloid beta-40 sequence (Aβ-40). Electrolyte–insulator–semiconductor (EIS) structures as well as silicon (Si) nanowire (NW) field-effect transistors (FETs) covered with a thin SiO2 dielectric layer have been successfully functionalized with Aβ-40-specific aptamers and used to detect ultra-low concentrations of the target peptide. The binding of amyloid-beta peptides of different concentrations to the surface of the sensors varied in the range from 0.1 pg/ml to 10 μg/ml resulting in a change of the surface potential was registered by the fabricated devices. Moreover, we show that the single-trap phenomena observed in the novel Si two-layer (TL) NW FET structures with advanced characteristic parameters can be effectively used to increase the sensitivity of nanoscale sensors. The obtained experimental data demonstrate a highly sensitive and reliable detection of ultra-low concentrations of the Aβ-40 peptides. This opens up prospects for the development of real-time electrical biosensors for studying and understanding different stages of AD by utilizing Si TL NW FET structures fabricated on the basis of cost-efficient CMOS-compatible technology.

Plasmonic Metasurface for Spatially Resolved Optical Sensing in Three Dimensions.

The highly localized sensitivity of metallic nanoparticles sustaining localized surface plasmon resonance (LSPR) enables detection of minute events occurring close to the particle surface and forms the basis for nanoplasmonic sensing. To date, nanoplasmonic sensors typically consist of two-dimensional (2D) nanoparticle arrays and can therefore only probe processes that occur within the array plane, leaving unaddressed the potential of sensing in three dimensions (3D). Here, we present a plasmonic metasurface comprising arrays of stacked Ag nanodisks separated by a thick SiO2 dielectric layer, which, through rational design, exhibit two distinct and spectrally separated LSPR sensing peaks and corresponding spatially separated sensing locations in the axial direction. This arrangement thus enables real-time plasmonic sensing in 3D. As a proof-of-principle, we successfully determine in a single experiment the layer-specific glass transition temperatures of a bilayer polymer thin film of poly(methyl methacrylate), PMMA, and poly(methyl methacrylate)/poly(methacrylic acid), P(MMA-MAA). Our work thus demonstrates a strategy for nanoplasmonic sensor design and utilization to simultaneously probe local chemical or physical processes at spatially different locations. In a wider perspective, it stimulates further development of sensors that employ multiple detection elements to generate distinct and spectrally individually addressable LSPR modes.

ALD Al2O3 gate dielectric on the reduction of interface trap density and the enhanced photo-electric performance of IGO TFT.

The amorphous indium gallium oxide thin film transistor was fabricated using a cosputtering method. Two samples with different gate dielectric layers were used as follows: sample A with a SiO2 dielectric layer; and sample B with an Al2O3 dielectric layer. The influence of the gate dielectrics on the electric and photo performance has been investigated. Atomic layer deposition deposited the dense film with low interface trapping density and effectively increased drain current. Therefore, sample B exhibited optimal parameters, with an Ion/Ioff ratio of 7.39 × 107, the subthreshold swing of 0.096 V dec−1, and μFE of 5.36 cm2 V−1 s−1. For ultraviolet (UV) detection, the UV-to-visible rejection ratio of the device was 3 × 105, and the photoresponsivity was 0.38 A W−1 at the VGS of −5 V.

Enhancements of preparation efficiency and magnetic properties for Fe-based amorphous magnetic flake powder cores upon the adoption of a novel double-paralleled slits nozzle

The thick and brittle amorphous ribbons with the maximum thickness up to 58 μm were successfully fabricated using melt-spinning method upon the adoption of a novel double-paralleled slits nozzle (DPSN). The magnetic properties of the two magnetic flake powder cores (MFPCs) prepared from the conventional thin ribbon pulverization and the thick ribbon pulverization were analyzed and compared. Hereinto, a coupling model of fluid flow with free surface and surface tension, and heat transfer with phase transform was developed to design the slit spacing for the DPSN, and sol-gel method was employed to create SiO2 insulation layer on the surfaces of the magnetic flake powders to improve electrical resistivity. Results show that a quasi-steady-state can be reached for the puddle with the upstream and downstream menisci in crescent and slope shapes, respectively, by adopting the DPSN with slit spaces of 2.0 mm and 2.5 mm. The embrittlement process for the conventional thin ribbon can be omitted to enhance the efficiency of the powder preparation when using the thick ribbon before the ribbon pulverization. The MFPCs fabricated using the thick amorphous ribbon pulverization exhibit a higher permeability of 65.27, lower total core loss with the frequency being less than 234 kHz for Bm = 0.08 T, and a better DC-bias property of 70.97% as compared to the MFPCs made from the conventional thin amorphous ribbon pulverization. This work provides a promising approach to further development of Fe-based amorphous MFPCs with high preparation efficiency and excellent magnetic properties at the frequency below 234 kHz.

Gate Failure Physics of SiC MOSFETs Under Short-Circuit Stress

The unique gate failure mode of SiC MOSFETs is often identified but has not been fully understood yet. In this letter, post-failure cell inspections demonstrate that its main cause is the crack at the SiO2 dielectric layer with melted source aluminum inside. An electro-thermal-mechanical simulation is performed to reproduce the failure transition, and it reveals that the crack forms at an early stage. This new failure mechanism further enlightens on the vulnerability of the vertical power MOSFET structure in extremely high-temperature operation.

Withdrawn: Tunable plasmonic absorber in THz-band range based on graphene “arrow” shaped metamaterial

Abstract A tunable selective absorber consisting of a periodic “arrow” shaped graphene array that operates in the far infrared and terahertz range is proposed. It is achieved by depositing a set of graphene “arrow” shaped ribbon on a SiO2 dielectric spacer layer. The absorption characteristics of the structure are investigated by the Finite Difference Time Domain (FDTD) method. The results show that the maximum pure absorption rate at the resonant wavelength increases from 1.09% corresponding to Fermi energy level 0.2 eV to 12.76% corresponding to 0.8 eV, which is improved by nearly 12 times. Moreover, the relaxation time is increased from 0.1 ps to 1.0 ps with the other parameters are unchanged, and the maximum value of the pure graphene absorption peak increases from 1.62% to 11.55%. Moreover, the resonance wavelengths of the absorber possess angle insensitivity, nevertheless the absorption peak intensity is sensitive to the angle of incidence. In addition, this paper also compares the double-symmetric “arrow” shaped structure on the basis of this structure. The absorption spectrum of the structure shows a double peak phenomenon, which can achieve the purpose of selective absorption. The research results have certain guiding significance and important reference value for the design of next–generation graphene-based perfect terahertz absorbers, and the design can be applied to the fields of label-free biomedical sensing, photodetectors and photonic devices.

A Novel Three-Axial Magnetic-Piezoelectric MEMS AC Magnetic Field Sensor.

We report a novel three-axial magnetic-piezoelectric microelectromechanical systems (MEMS) magnetic field sensor. The sensor mainly consists of two sensing elements. Each of the sensing elements consists of a magnetic Ni thick film, a Pt/Ti top electrode, a piezoelectric lead zirconate titanate (PZT) thin film, a Pt/Ti bottom electrode, a SiO2 insulation layer, and a moveable Si MEMS diaphragm. When the sensor is subjected to an AC magnetic field oscillating at 7.5 kHz, a magnetic force interaction between the magnetic field and Ni thick film is produced. Subsequently, the force deforms and deflects the diaphragms as well as the PZT thin film deposited on the diaphragms. The deformation and deflection produce corresponding voltage outputs due to the piezoelectric effect. By analyzing the voltage outputs through our criterion, we can obtain details of the unknown magnetic fields to which the sensor is subjected. This achieves sensing of three-axial magnetic fields. The experimental results show that the sensor is able to sense three-axial magnetic fields ranging from 1 to 20 Oe, with X-axial, Y-axial, and Z-axial sensitivities of 0.156 mVrms/Oe, 0.156 mVrms/Oe, and 0.035 mVrms/Oe, respectively, for sensing element A and 0.033 mVrms/Oe, 0.044 mVrms/Oe, and 0.130 mVrms/Oe, respectively, for sensing element B.

A Designed Broadband Absorber Based on ENZ Mode Incorporating Plasmonic Metasurfaces.

In this paper, we present a numerical study of a metamaterial absorber that provides polarization-insensitive absorption over a broad bandwidth of operation over the mid-infrared region. The absorber consists of a periodically patterned metal-dielectric-metal structure integrated with an epsilon-near-zero (ENZ) nanolayer into the insulating dielectric gap region. Such an anomalous broadband absorber is achieved thanks to a couple of resonant modes including plasmon and ENZ modes that are excited under mid-IR light illumination. By adding a 0.06-μm-thick ENZ layer between the patterned gold rectangular grating and the SiO2 dielectric layer, the absorber captures >95% light over a 1.5 µm bandwidth centered at a near-8-μm wavelength over a wide range of oblique incidence under transverse-magnetic and -electric polarizations. The designed ENZ-based wideband absorber has potential for many practical applications, including sensing, imaging and solar energy harvesting over a wide frequency regime.

Temperature-controlled conversion from Fe–Si particles to integrated Fe–Si/SiO2 core–shell structure particles during fluidised bed chemical vapour deposition

In the synthesis of ferromagnetic/SiO2 core–shell structures, the minimum formation conditions and evolution mechanism are worth investigating. In the present study, to determine the minimum formation temperature of an integrated Fe–Si/SiO2 core–shell structure during chemical vapour deposition in a fluidised bed, the effects of deposition temperature on the structural and magnetic performances of SiO2 insulation coatings on Fe–Si particles were investigated. Thermodynamic calculations and differential scanning calorimetry were used to understand the thermal decomposition of C8H20O4Si. The results of the theoretical and structural studies showed that the minimum deposition temperature of the amorphous SiO2 insulation coating on the Fe–Si particle surface was ~880 K and that the Fe–Si/SiO2 composite structure started to convert into an integrated Fe–Si/SiO2 core–shell structure after the deposition temperature was raised above 920 K. The increase in the thickness of the SiO2 insulation layer due to the increased deposition temperature was studied using X-ray diffraction and scanning electron microscope analyses. The results of X-ray photoelectron spectroscopy showed that four and five types of electronic structures existed in the SiO2 insulation shell for silicon and oxygen, respectively, and that only 32.74 at.% of the oxygen from the Si(OSi)3(OH) group interacted with the Fe–Si alloy surface. The results of the performance test indicated that the integrated Fe–Si/SiO2 core–shell structure led to a substantial enhancement in the electrical resistivity of the particles and reduction in their saturation magnetisation, but hardly affected the coercive force.

Development of bacteria sensing platform through layered (metal-dielectric-metal) nanoparticles

Trilayer possessing metal-dielectric-metal layer of nanometric thickness was prepared through multiple processes such as direct current (DC) and radio frequency (RF) Sputter Coating. This trilayer was used for a biosensing platform. Metal layer of gold having a thickness of 30 nm was deposited through direct DC Sputter Coating while the dielectric layer of SiO2 having a thickness of 177 nm was deposited through RF Sputter Coating. The trilayer coated sample was subjected to thermal annealing at 470 °C for 2 h in a temperature controlled furnace. The top layer of continuous gold film gets converted into randomly distributed gold nanoparticles (AuNPs) while the bottom gold layer undergoes minor morphological change. The reflectance spectrum of the dewetted trilayer is changed by presence of the Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria. The average reflectance of the as-deposited trilayer was found to be 60.06% while presence of E. coli and S. aureus on the trilayer reduces its reflectance to 21.84% and 47.58% respectively. The fabricated platform is more effective for the detection of S. aureus as it produced sharp detectable shift (70 nm to left) in spectra due to the spherical shape of bacterium. The shift in reflectance spectra depends on the incubation period which gives information about the amount of bacteria present on the platform.

Indium Aluminum Zinc Oxide Thin Film Transistor With Al2O3 Dielectric for UV Sensing

Two bottom-gate indium aluminum zinc oxide thin-film transistors (TFTs) were fabricated with different dielectric layers. The TFT with Al2O3 deposited through atomic layer deposition (ALD) had higher field mobility of 0.48 cm $^{\mathbf {2}}/\text{V}\cdot \text{s}$ , Ion/Ioff of $9.7{}\boldsymbol {\times }{} 10^{\mathbf {7}}$ , and lower subthreshold swing of 0.3 V/dec. The hysteresis of the two devices showed that the device with Al2O3 dielectric layer had a lower threshold voltage shift (−0.065 V) compared with that of the device with the SiO2 dielectric layer (−0.352 V). These results revealed that the device with Al2O3 dielectric layer had fewer interface traps between the active layer and dielectric layer than the device with the SiO2 dielectric layer deposited through plasma-enhanced chemical vapor deposition. Because of the improvement of interface traps, the device with Al2O3 dielectric layer had high responsivity (6.18 A/W) and rejection ratio ( $1.74{}\boldsymbol {\times }{} 10^{\mathbf {3}}$ ); this device has high potential for use in ultraviolet sensing applications.

Performance Analysis of DC, UV and RF Characteristics of ZnO Based Thin Film Transistors with HfO2, Si3N4 and SiO2 Dielectric Layers for Optoelectronic Applications

Performance Analysis of DC, UV and RF Characteristics of ZnO Based Thin Film Transistors with HfO₂, Si₃N₄ and SiO₂ Dielectric Layers for Optoelectronic Applications

Efficacy of annealing and fabrication parameters on photo-response of SiGe in TiO2 matrix

SiGe nanoparticles dispersed in a dielectric matrix exhibit properties different from those of bulk and have shown great potential in devices for application in advanced optoelectronics. Annealing is a common fabrication step used to increase crystallinity and to form nanoparticles in such a system. A frequent downside of such annealing treatment is the formation of insulating SiO2 layer at the matrix/SiGe interface, degrading the optical properties of the structure. An annealing process that could bypass this downside would therefore be of great interest. In this work, a short-time furnace annealing of a SiGe/TiO2 system is applied to obtain SiGe nanoparticles without formation of the undesired SiO2 layer between the dielectric matrix (TiO2) and SiGe. The structures were prepared by depositing alternate layers of TiO2 and SiGe films, using direct-current magnetron sputtering technique. A wide range spectral response with a response-threshold up to ∼1300 nm was obtained, accompanied with an increase in photo-response of more than two-orders of magnitude. Scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy and grazing incidence x-ray diffraction were used to analyze the morphological changes in respective structures. Photoconductive properties were studied by measuring photocurrent spectra using applied dc-voltages at various temperatures.

Planar optical waveguide for refractive index determining with high sensitivity and dual-band characteristic for Nano-sensor application

In this paper, we develop an optical waveguide based on metal–insulator-metal as a refractive index sensor with dual-band feature and a high figure of merit (FOM) and sensitivity. In this model, we utilize a Z-shape slot based on two stubs model in both metal layers and this structure is placed over a dielectric layer of SiO2 as a substrate for planar application in the optical systems. In addition, the parametric studies are used to clarifying the elements influence on controlling the transmission and working frequency to achieve a dual-band characteristic at 1550 and 3100 nm which is suitable for optical fiber application. In fact, the compound stubs technique is suggested to modify the resonances of the waveguide for dual-band attributes based on the transmission line model. We simulate this waveguide using the Finite Integrated Technique (FIT) method. It is supposed that the waveguide is filled by various materials with the different refractive indexes in the range of 1 to 1.5. We obtain the FOM for these materials while the Fano response provides high FOM about the 3800 RIU−1 and the sensitivity is 1790 nm/RIU. Therefore, the compound stubs strategy help to improve the FOM factor in the optical waveguide.

High Three-Terminal Breakdown Voltage Exfoliated β-Ga2O3 Nanolayer Field-Effect Transistors with Dual Field Modulating Plates

β-Ga2O3 is an intriguing material for high efficiency power devices because of its large direct bandgap (4.85 eV), high breakdown field (~8 MV/cm) and excellent thermal and chemical stability. Baliga’s figure of merit of β-Ga2O3 is 3214.1, superior to those of other materials such as GaN (846.0) or SiC (317.1). Interestingly, although β-Ga2O3 is not a van der Waals material, β-Ga2O3 can be mechanically exfoliated from single crystal substrate into thin layer due to the large anisotropy of the unit cell. The fabrication of high crystal quality β-Ga2O3 nanolayer devices could pave a way for next-generation high-power nanoelectronics devices. In power device operation, the premature electrical induced by the concentrated electric fields limits the device operation under a high bias voltage, and threaten the reliability of devices. Various techniques such as recess gate or field-plate configurations have been proposed to relieve the electric field concentration and prevent premature breakdown. Adopting gate field plate, source field plate, or multiple field plate greatly enhance the performance of power devices, which can be applied to β-Ga2O3 based nanoelectronic power devices that can unlock the full potential of β-Ga2O3. Due to the exceptional mechanical and electronic properties of 2D materials, researches about 2D materials has been at the forefront of this area during the last years. Studies on fabrication of functional devices based on 2D materials, including integration with themselves, are exploding. Among 2D materials, hexagonal boron nitride (h-BN) has been used as a dielectric material of 2D devices due to its excellent thermal conduc tivity (1700 – 2000 W/m∙K) and high dielectric constant (8 – 12 MV/cm), as well as defect-free and atomically flat surface, which can easily be obtained through mechanical exfoliation method. In our work, we used h-BN as a gate field plate dielectric layer by precise and selective transfer on β-Ga2O3 channel by using PDMS film. SiO2 dielectric layer was deposited on devices, followed by metal deposition for source field plate. By applying dual field plate structure β-Ga2O3 based power devices can show excellent performance in high voltage condition than conventional metal-semiconductor field effect transistors (MESFETs). β-Ga2O3 MESFETs with h-BN gate field plate were fabricated by using the β-Ga2O3 and h-BN flakes obtained from respective crystals. Ohmic metal (Ti/Au) was deposited on both end of mechanically exfoliated β-Ga2O3 flakes, followed by precise positioning of exfoliated h-BN flakes on the channel. Top-gate electrode (Ni/Au) was deposited to fabricate β-Ga2O3 MESFETs, with a part of the electrode overlapped with h-BN to achieve a stepped gate field-plate structure. After deposition of SiO2 layer as dielectric layer of source field plate, selective etching of SiO2 layer was performed to construct source field plate structure. Fabricated β-Ga2O3 MESFETs showed excellent n-type DC output and transfer characteristics even after storage for one month in ambient air, which shows excellent long-term air-stability. Three-terminal off-state breakdown voltage of dual field-plated β-Ga2O3 MESFET was measured, which shows improvement in breakdown voltage compared with that of conventional β-Ga2O3 MESFET. The distribution of electric fields was calculated by Silvaco Atlas device simulation framework to study the effect of source field plate and h-BN gate field plate on electric field, which explain the improvement of breakdown voltage in those structure. By adopting dual field plate structure, ease of distribution of concentrated electric field was observed. In this study, we present that the performance of β-Ga2O3 MESFET as a power device can be greatly improved by adopting dual field plate structure, paving a way to the high-power nanoelectronic devices of β-Ga2O3. The details of our work will be discussed in the conference.

Influence of SiO2 insulation layers thickness distribution on magnetic behaviors of Fe-Si@SiO2 soft magnetic composites

In this study, the influence of the deposit thickness of SiO2 insulation layers on the magnetic behaviors of Fe-Si@SiO2 soft magnetic composites (SMCs) was investigated by adjusting the deposition temperatures (550 °C, 600 °C, 650 °C, 700 °C, and 750 °C) during the fluidized chemical vapor deposition (CVD) process. The microstructures of Fe-Si@SiO2 composite particles and SMCs were also studied systematically. After combining the magnetic behavior results, the regression relationships between the magnetic behaviors of Fe-Si@SiO2 SMCs and the SiO2 insulation layer thickness distribution were obtained. It was found that the thickness, deposition rate, and heterogeneity of the SiO2 insulation layer were severely affected by the deposition temperature, resulting in a remarkable variation of the magnetic properties of Fe-Si@SiO2 SMCs. An increasing SiO2 insulation layer thickness had positive effects on the electrical resistivity and the eddy-current loss, almost no effects on the magnetic moment, and negative effects on the saturation magnetization of Fe-Si@SiO2 SMCs. Hence, these results will provide a new insight to examine the growth mechanism of the SiO2 insulation layer and magnetic performance of SMCs, which will be advantageous for the future design of efficient Fe-Si magnets.

Tunable Dual-Band Perfect Absorber Based on L-Shaped Graphene Resonator

We propose and investigate a tunable dual-band perfect absorber consisting of double asymmetric L-shaped graphene resonators (LSGRs) and a metal ground plane spaced by a thin SiO2 dielectric layer. The numerical results reveal that the presented absorber expresses two resonance peaks in the mid-infrared region, where their absorption coefficients are on average larger than 98.77%. The electromagnetic eigenmode resonances of a single LSGR can induce two absorption peaks with values about 50%. Assembling two LSGRs together, the absorptivity can reach up to almost 100% due to the plasmonic couplings. In addition, the design has the ability to tune the working wavelengths of the absorption peaks within a large wavelength range by changing geometric parameters and the Fermi level of the graphene layer. In addition, wavelength-selective dual-band perfect absorption peaks can be achieved in the wavelength range of interest by merely adjusting the polarization angle. This letter presents a unique route toward the realization of nanophotonic devices and has potential applications in filtering, sensing, and detecting.

Photoinduced Hysteresis of Graphene Field-Effect Transistors Due to Hydrogen-Complexed Defects in Silicon Dioxide.

Photoinduced hysteresis (PIH) of graphene field-effect transistors (G-FETs) has attracted attention because of its potential in developing photoelectronic or nonvolatile memory devices. In this work, we focused on the role of SiO2 dielectric layer on PIH, where G-FETs have only a SiO2 dielectric layer. Adsorbates are effectively removed before the PIH test. The effects of laser wavelength, laser power density, and temperature on the PIH are systematically investigated. The PIH is significantly enhanced by increasing the hydrogen flow in a hydrogen-atmosphere device thermal annealing. This strongly suggests proton-related defects that play a key role. The pure electronic process for PIH is further ruled out by the significant dependence of the doping rate on the temperature. A mechanism of PIH based on proton generation after hole trapping at [O3≡Si-H] is proposed. The proposed mechanism is well-supported by our experimental data: (1) the observed threshold photon energy for PIH is between 2.76 and 2.34 eV, which is close to the energy barrier for [O3≡Si-H], releasing a proton. (2) No obvious carrier mobility degradation after the PIH process suggests that the bulk defects in SiO2 are the major contributors rather than graphene/SiO2 interface defects. (3) The dependence of the doping rate on the temperature and the laser power density matches a theoretical model based on the random hopping of H+. The results in this work are also valuable for the study of degradation of other oxide dielectric materials in various field-effect transistors.