Electron Beam Lithography Method Research Articles

Bowtie Nanoantenna LSPR Biosensor for Early Prediction of Preeclampsia.

The concentration of the placental circulating factor in early pregnancy is often extremely low, and the traditional prediction method cannot meet the clinical demand for early detection preeclampsia in high-risk gravida. It is of prime importance to seek an ultra-sensitive early prediction method. In this study, finite-different time-domain (FDTD) and Discrete Dipole Approximation (DDA) simulation, and electron beam lithography (EBL) methods were used to develop a bowtie nanoantenna (BNA) with the best field enhancement and maximum coupling efficiency. Bio-modification of the placental circulating factor (sFlt-1, PLGF) to the noble nanoparticles based on the amino coupling method were explored. A BNA LSPR biosensor which can specifically identify the placental circulating factor in preeclampsia was constructed. The BNA LSPR biosensor can detect serum placental circulating factors without toxic labeling. Serum sFlt-1 extinction signal (Δλmax) in the preeclampsia group was higher than that in the normal pregnancy group (14.37 ± 2.56 nm vs. 4.21 ± 1.36 nm), p = 0.008, while the serum PLGF extinction signal in the preeclampsia group was lower than that in the normal pregnancy group (5.36 ± 3.15 nm vs. 11.47 ± 4.92 nm), p = 0.013. The LSPR biosensor detection results were linearly consistent with the ELISA kit. LSPR biosensor based on BNA can identify the serum placental circulating factor of preeclampsia with high sensitivity, without toxic labeling and with simple operation, and it is expected to be an early detection method for preeclampsia.

Plasmonic Titanium Nitride Nanohole Arrays for Refractometric Sensing.

Group IVB metal nitrides have attracted great interest as alternative plasmonic materials. Among them, titanium nitride (TiN) stands out due to the ease of deposition and relative abundance of Ti compared to those of Zr and Hf metals. Even though they do not have Au or Ag-like plasmonic characteristics, they offer many advantages, from high mechanical stability to refractory behavior and complementary metal oxide semiconductor-compatible fabrication to tunable electrical/optical properties. In this study, we utilized reactive RF magnetron sputtering to deposit plasmonic TiN thin films. The flow rate and ratio of Ar/N2 and oxygen scavenging methods were optimized to improve the plasmonic performance of TiN thin films. The stoichiometry and structure of the TiN thin films were thoroughly investigated to assess the viability of the optimized operation procedures. To assess the plasmonic performance of TiN thin films, periodic nanohole arrays were perforated on TiN thin films by using electron beam lithography and reactive ion etching methods. The resulting TiN periodic nanohole array with varying periods was investigated by using a custom microspectroscopy setup for both reflection and transmission characteristics in various media to underline the efficacy of TiN for refractometric sensing.

Preparation method and application of silicon nanowires

In recent years, silicon nanowires have become a hot spot in the new material industry. As a kind of nanomaterial, silicon nanowires have excellent physical and chemical properties. However, the preparation method of silicon nanowires is not mature enough, which limits its further application. This paper mainly analyses the mechanism, advantages and disadvantages of several mainstream silicon nanowires preparation methods, and discusses the application of silicon nanowires and the future development direction. The results show that the chemical vapor deposition method can be used for large-scale preparation of silicon nanowires, while the laser ablation method can produce silicon nanowires with higher purity, and the electron beam lithography method has the advantages of high flexibility. However, the efficiency of these three methods is not high, and the cost is high, which is also the problem that the silicon nanowire preparation industry is looking forward to solve. Relying on the excellent conductivity, thermal conductivity and other characteristics of silicon nanowires, silicon nanowires can be applied to a variety of new energy industries. Based on the properties of silicon nanowires, this paper analyses the application of silicon nanowires in lithium batteries, solar cells, biosensors and thermoelectric materials in recent years, and forecasts its development trend, so as to provide a certain reference for researchers to further explore the research of silicon nanowires.

Nanostructured Transition Metal Dichalcogenide Multilayers for Advanced Nanophotonics

AbstractTransition metal dichalcogenides (TMDs) attract significant attention due to their exceptional optical, excitonic, mechanical, and electronic properties. Nanostructured multilayer TMDs were recently shown to be highly promising for nanophotonic applications, as motivated by their exceptionally high refractive indices and optical anisotropy. Here, this vision is extended to more sophisticated structures, such as periodic arrays of nanodisks and nanoholes with ultra sharp walls, as well as proof‐of‐concept all‐TMD waveguides and resonators. Specific focus is given to various advanced nanofabrication strategies, including careful selection of resists for electron beam lithography and etching methods, especially for non‐conductiven but relevant for nanophotonic applications substrates, such as SiO2. The specific materials studied here include semiconducting WS2, in‐plane anisotropic ReS2, and metallic TaSe2, TaS2, and NbSe2. The resulting nanostructures can potentially impact several nanophotonic and optoelectronic areas, including high‐index nanophotonics, plasmonics and on‐chip optical circuits. The knowledge of TMD material‐dependent nanofabrication parameters developed here will help broaden the scope of future applications of all‐TMD nanophotonics.

Exploration of a Flexible Metasurface for Strain Sensors: A Perspective from 2D Grating Fabrication to Spectral Characterization

The flexible plasmonic metasurface is a novel optical device consisting of a large number of subwavelength-sized noble metal (gold, silver, etc.) structures arranged in a specific pattern on a flexible substrate. The usual method for a fabricating flexible metasurface is to build nanostructures on rigid substrates and then transfer them to flexible substrates. However, problems such as structural distortion and structural loss can occur during fabrication. To address these issues, this work improved the process to fabricate and characterize a flexible plasma 2D grating–a type of metasurface composed of gold cubelets with a thickness of 50 nm and a side length of 250 nm. First, an electron beam lithography method modified by proximity effect correction was used to fabricate nanostructures on a rigid substrate. Then, the structures were transferred by a chemical functionalization and a sacrificial layer etching method. In addition, the feasibility of using flexible plasmonic 2D gratings as strain sensors was investigated in this work through a stretching test. Experimental results show that electron beam lithography improved by correcting the proximity effect enabled the fabrication of more precisely shaped nanostructures; the chemical functionalization method significantly improved the transfer yield; and the spectroscopic analysis in the stretching test demonstrated the potential of the flexible plasmonic 2D gratings for sensing applications.

Thermally-curable nanocomposite printing for the scalable manufacturing of dielectric metasurfaces

Metasurfaces consisting of artificially designed meta-atoms have been popularized recently due to their advantages of amplitude and phase of light control. However, the electron beam lithography method for metasurface fabrication has high cost and low throughput, which results in a limitation for the fabrication of metasurfaces. In this study, nanocomposite printing technology is used to fabricate high-efficiency metasurfaces with low cost. To demonstrate the efficiency of the proposed fabrication method, a metahologram is designed and fabricated using a nanocomposite. The metahologram exhibits conversion efficiencies of 48% and 35% at wavelengths of 532 and 635 nm, respectively. The nanocomposite is composed of polymers with nanoparticles, so durability tests are also performed to evaluate the effects of temperature and humidity on the metasurfaces. The test verifies that at temperatures below the glass transition temperature of the base resin, the nanostructures do not collapse, so the efficiency of the metasurfaces remains almost the same. The surrounding humidity does not affect the nanostructures at all. Hence, the durability of the nanocomposite metasurfaces can be further enhanced by replacing the base resin, and this nanocomposite printing method will facilitate practical metasurface use at low cost.

Fast, Economical, and Reproducible Sensing from a 2D Si Wire Array: Accurate Characterization by Single Wire Spectroscopy.

Silicon (Si) is promising as a field enhancement material because of its high abundance, low toxicity, and high refractive index. The field enhancement effect intensifies light-matter interactions, which improves photocatalysis, solar cell performance, and sensor sensitivity. To manufacture field enhancement materials on a production scale, the fabrication technique must be simple, cost-effective, fast, and highly reproducible and must produce a high enhancement factor (EF). Herein, we report on an economical and efficient fabrication method for a field enhancement substrate consisting of a two-dimensional Si wire array (2D-SiWA). This substrate was demonstrated as a fluorescence sensor with high sensitivity (EF > 200) and composed of a large area (6.0 mm2). In addition, single wire spectroscopy was used to identify very high reproducibility of the sensor sensitivity in regular regions (97%) and a mixture of regular and irregular regions (87%) of the 2D-SiWA. The large-area Si fluorescence sensor fabrication was cost-effective and rapid and was 50× less expensive, 20×faster, and 60,000×larger than the typical electron beam lithography method.

Side edge emission from a waveguide substrate.

In this study, we fabricated embedded titanium dioxide (TiO2) nanograting structures with slanted cross section on a silicon dioxide (SiO2) substrate using electron beam lithography (EBL) and reactive ion etching (RIE) methods, and we analyzed their optical signals. The surface morphologies of the embedded TiO2 nanograting structures were monitored by a scanning optical microscope (SEM). By focusing the transverse electric (TE) polarized beam with the wavelength λ=633nm at the incident angle θ=22.0∘ from the rear side of TiO2 face, we could observe +1st and -2nd diffraction orders with diffraction efficiencies (I/Itotal): I1=23% and I2=19%, respectively, on a SiO2/TiO2 interface. Diffraction beams were waveguided to both left and right directions in a SiO2 substrate via total internal reflection (TIR); next, two guided beams were emitted from the side edges of the substrate. This work is expected to develop a highly efficient two-way waveguide optical interconnector.

Fabrication and Characterization of Nanonet-Channel LTPS TFTs Using a Nanosphere-Assisted Patterning Technique.

We present the fabrication and electrical characteristics of nanonet-channel (NET) low-temperature polysilicon channel (LTPS) thin-film transistors (TFTs) using a nanosphere-assisted patterning (NAP) technique. The NAP technique is introduced to form a nanonet-channel instead of the electron beam lithography (EBL) or conventional photolithography method. The size and space of the holes in the nanonet structure are well controlled by oxygen plasma treatment and a metal lift-off process. The nanonet-channel TFTs show improved electrical characteristics in terms of the ION/IOFF, threshold voltage, and subthreshold swing compared with conventional planar devices. The nanonet-channel devices also show a high immunity to hot-carrier injection and a lower variation of electrical characteristics. The standard deviation of VTH (σVTH) is reduced by 33% for a nanonet-channel device with a gate length of 3 μm, which is mainly attributed to the reduction of the grain boundary traps and enhanced gate controllability. These results suggest that the cost-effective NAP technique is promising for manufacturing high-performance nanonet-channel LTPS TFTs with lower electrical variations.

A Theoretical and Simulation Analysis of the Sensitivity of SiNWs-FET Sensors.

Theoretical study and software simulation on the sensitivity of silicon nanowires (SiNWs) field effect transistor (FET) sensors in terms of surface-to-volume ratio, depletion ratio, surface state and lattice quality are carried out. Generally, SiNWs-FET sensors with triangular cross-sections are more sensitive than sensors with circular or square cross-sections. Two main reasons are discussed in this article. Firstly, SiNWs-FET sensors with triangular cross-sections have the largest surface-to-volume ratio and depletion ratio which significantly enhance the sensors’ sensitivity. Secondly, the manufacturing processes of the electron beam lithography (EBL) and chemical vapor deposition (CVD) methods seriously affect the surface state and lattice quality, which eventually influence SiNWs-FET sensors’ sensitivity. In contrast, wet etching and thermal oxidation (WETO) create fewer surface defects and higher quality lattices. Furthermore, the software simulation confirms that SiNWs-FET sensors with triangular cross-sections have better sensitivity than the other two types of SiNWs-FET sensors under the same conditions, consistent with the theoretical analysis. The article fully proved that SiNWs-FET sensors fabricated by the WETO method produced the best sensitivity and it will be widely used in the future.

Wide-range displacement sensor based on variable line-spacing grating and Y-type twin-core fibre

In the paper, a wide range displacement sensor based on the variable line-spacing (VLS) grating was proposed and its displacement characteristics at different temperature environments were measured. The VLS grating was inscribed by electron beam lithography method, and the sensor mechanical structure was designed and fabricated. A broadband light was irradiated to the VLS grating though a twin-core Y-type fibre, and an aluminizing reflector mirror was used to adjust light spot positions to change the displacement. In the experiment, the temperature stabilities of sensor were tested when the temperature rose from −20°C to 60°C, and the maximum drift of diffraction peak was less than 1.01 nm. In 30 mm length displacements, the diffraction wavelength was shifted simultaneously, the sensitivity was 15.941 and 15.917 nm/mm at 20°C and 50°C respectively, and the linearity was 0.994 both at 20°C and 50°C.

Electron beam lithography inscribed varied-line-spacing and uniform integrated reflective plane grating fabricated through line-by-line method

A varied-line-spacing (VLS) and uniform integrated reflective plane grating was inscribed by electron beam lithography (EBL) and reactive ion etching method, and its displacement sensing characteristics was tested. For the VLS grating, the groove density was varied from 868 to 442 L/mm over the device, according to the designed linear density function, and the device was coated with an aluminized surface to reflect light. For the uniform grating, the groove density was 655 L/mm. A Y-type twin-core fiber with a collimator head was used to input light from a broadband source and collect reflected light from the integrated grating for analysis by an optical spectrum analyzer. The inscribed integrated grating length and width were 50 × 10 mm, and the input light angle was fixed at 23°.The integrated grating displacement characteristics was varied, when the light spot was irradiated at VLS and uniform grating simultaneously, with the result that as the light spot moved to different grating positions, two peaks of diffracted light were collected. For 0–35 mm displacement changes in 5 mm increments, for the VLS grating, the diffracted light wavelength changed from 945.3 to 1612.2 nm with sensitivity of 18.68 nm/mm, and linearity of 0.975; for the uniform grating, the wavelength shift was less than 3.2 nm.

Increasing the circular dichroism of the planar chiral nanostructure by inducing coupling between the coverage layer and the planar nanostructure.

Circular dichroism (CD) has been widely studied in recent decades because of its wide application in biomedical detection. Nanostructures with different heights (NDH) usually increase the transmission CD effect. To achieve such nanostructures, one needs to repeatedly perform the electron-beam lithography (EBL) method twice or more, layer-by-layer, which is a very complicated process. Here, we propose a method to prepare NDH by combining the EBL and oblique angle deposition (OAD) techniques. L-shaped planar silver nanostructures are prepared using EBL and normal electron beam deposition, and the OAD method is then used to partially cover one arm of the L-shaped nanostructure. Numerical simulations reveal that the height difference in the two arms of the L-shaped NDH (LSNDH) causes a difference in the polarization directions of the left- (LCP) and right-circularly polarized (RCP) incident light, thereby, generating CD effects. A 2D material is used to cover the LSNDH to further increase the charge polarization direction differences, which considerably increases the CD effect. These results are useful in simplifying and increasing the convenience of the preparation method of 3D chiral nanostructures. Furthermore, the proposed nanostructure may have potential application in biosensor, such as chiral enantiomer sensors.

Single step electron-beam lithography archiving lift-off for T-gate in high electron mobility transistor fabrication

In this paper, a new method of electron-beam lithography was proposed to directly obtain a floating T-shaped gate. In the method, only one step of exposure and one step of development were operated on a three-layer photoresist of PMMA/P(MMA-MAA)/ P(MMA-MAA) to form an obvious undercut structure which is very benefit for subsequent lift-off process of gate metal. A high electron mobility transistor (HEMT) with an 80 nm floating T-shaped gate was fabricated on a SiC substrate which has a 10 nm InAlN barrier. Finally, the obtained device by above process has a fT/fmax of 90/200 GHz.

Fabrication process of InGaAs-based nanodiode array using electron-beam lithography technique

Self-switching diode (SSD) is a unipolar two-terminal planar device which has a typical channel in nanoscale dimension. It has shown outstanding properties as a microwave and submillimeter wave rectifier by exploiting its nonlinear current-voltage (I-V) characteristic and intrisically low parasitic capacitance. In detection systems, SSDs are often used with an antenna to form a rectifying antenna (rectenna). The large impedance mismatch between SSD and antenna, due to high resistance of a single SSD, has always hampered the rectenna to achieve good extrinsic rectification performance (e.g., voltage responsivity > 400 V/W). As such, a large array of SSDs connected in parallel is very much desired to reduce the device resistance, and hence minimizing the impedance mismatching issue. In this work, an interdigital structure which can accommodate approximately 2,000 SSDs in parallel has been utilized. The material used was InGaAs/InAlAs heterostructure grown onto an InP substrate. The fabrication of the SSD array has implemented an electron-beam lithography (EBL) technique and the use of polymethyl methacrylate (PMMA) as a masking layer. The fabricated SSD array has shown a typical diode-like I-V characteristic, indicating that EBL method is not only convenient to realize nanoscale electronic devices, but also very practical for large area operations.

Development of an in-situ nanofabrication instrument for ice lithography

Ice lithography (IL) enables in-situ nanofabrication by electron-beam patterning and subsequent pattern transfer of water ice deposited on cryogenic samples. Here we report the design and operation of an IL instrument consisting of a scanning electron microscope, a gas injection system, cryogenic components, a metal deposition chamber, and a sample transfer assembly. The steps required and the amount of equipments involved are significantly reduced compared with ordinary electron beam lithography methods. Different from the previous apparatus, thermal evaporation and internal cooling were implemented and evaluated in this instrument. The in-situ nanofabrication is demonstrated by decorating nanoparticles on or close to a single nanowire and constructing three-dimensional layered structures. Finally, we present an outlook on the further improvement of our instrument.

Large energy resolution improvement of LYSO scintillator by electron beam lithography method

A (Lu,Y)2SiO5:Ce (LYSO) crystal, as a heavy inorganic scintillator, is currently in high demand for various applications in the fields of particle detection. However, its high refractive index (n = 1.83) gives restriction on the measurements of rare events or weak particle flow, where high energy resolution is urgently required for detectors based on the crystal. Utilizing the electron beam lithography technique and the ion beam lithography method, we have successfully prepared a 2.0 × 2.0 mm2 large area two-dimensional photonic crystal (PhC) structure on the LYSO crystal surface. Compared with the plain reference sample, the optical measurements show a 53% enhancement of light extraction for the LYSO nanostructured surface, and the resulted improvement of energy resolution (full width at half maximum) is measured to be 43.8% by gaussian fittings to the energy spectra excited by the 241Am α source. With the advantage of high-resolution patterning, high thermal stability, and firm stickiness on the substrate, the present prescription of the PhC fabrication is still favorable for some special fields (e.g., homeland security and space exploration) though the writing process is extremely time consuming and expensive to use.

An ultrasensitive hydrogen fuse based on a single Pd break junction

The development of hydrogen compatibility is crucial for its being a new key energy source. A study of hydrogen fuse based on Pd break junction method is presented to explore the limit of sensitivity. The critical part of this device was fabricated from a Pd nanowire electrode (80 ± 20 nm) made by electron beam lithography (EBL) method. Subsequent electromigration technique is utilized to develop a controllable break junction on the nanowire (1–2 nm). This device shows reversible response cycles of hydrogen in an ultralow pressure range below 0.1±0.002 Pa and fuse-like response above 10 Pa at room temperature. The results show that the relationship between quantum conductance with hydrogen pressure was kept linear because of hydrogen absorption induced expansion of break junction. When the expansion exceeds the threshold value, the break junction gap is closed and becoming conductive. This method opens up a possibility to detect hydrogen under ultralow partial pressure.

An interesting route using electron-beam lithography and photolithography to pattern submicron interdigitated electrodes array for sensing applications

Increasing the interest in the silicon-based devices resulted in developing new methods and techniques to achieve advanced and more reliable designs and devices. In this study, we have developed a combination method of photolithography and electron-beam lithography (EBL) in order to maximize the efficiency and reducing time and costs. Nanometric and micrometric patterns were created using EBL and photolithography methods, respectively. In order to prove the sensing applications, the EBL-based fabricated electrodes were successfully designed and tested as a hydrogen peroxide (H2O2) biosensor using horseradish peroxidase (HRP) enzyme on a graphene oxide substrate. Photoresist provided a passive layer which reduced the passivation steps in the fabrication. The interdigitated electrodes were used to maximize the connections with the graphene oxide substrate. The result was an ohmic biosensor that exhibits a linear relationship with the logarithm of H2O2 concentration in the range between 0.1 µM and 100 mM. The limit of detection (LOD) was about 51 nM.

Study on the Optical Field Distribution of Asymmetric Nanostructures Based on Surface Plasmon

Optical force, which is known as a powerful effect of the light on all objects and is too weak to be perceived directly. While the momentum transfer between light and matter can be greatly improved at the nanometer scale. In this paper, we mainly designed an asymmetric deep subwavelength metal nanostructure to generate a strong optical field gradient force by utilizing the resonant interaction between light and nanostructures as well as coupled excitation of surface plasmon, which can promote the movement of the nanoparticles. After simulating and optimizing, we learned that the intensity of optical field excited by the stepped trapezoidal nanostructure we designed in this paper is 140 times higher than that of incident light. At last, we fabricated and tested the sample of the designed nanostructures with the method of electron-beam lithography (EBL), and get the data of the speckle distribution curve and scattering curve of the sample. We discovered that in the wavelength range from 300 nm to 1100 nm, the sample will be excited to a strong plasma. It can be inferred that the devices cascaded by such structural units can accelerate and emit a large number of nanoparticles to generate considerable thrust, which has a great application prospects for the precise positioning of spacecraft.