Sub-10 nm fabrication:methods and applications

Reliable fabrication of micro/nanostructures with sub-10 nm features is of great significance for advancing nanoscience and nanotechnology.While the capability of current complementary metal-oxide semiconductor(CMOS)chip manufacturing can produce structures on the sub-10 nm scale,many emerging applications,such as nano-optics,biosensing,and quantum devices,also require ultrasmall features down to single digital nanometers.In these emerging applications,CMOS-based manufacturing methods are currently not feasible or appropriate due to the considerations of usage cost,material compatibility,and exotic features.Therefore,several specific methods have been developed in the past decades for different applications.In this review,we attempt to give a systematic summary on sub-10 nm fabrication methods and their related applications.In the first and second parts,we give a brief introduction of the background of this research topic and explain why sub-10 nm fabrication is interesting from both scientific and technological perspectives.In the third part,we comprehensively summarize the fabrication methods and classify them into three main approaches,including lithographic,mechanics-enabled,and post-trimming processes.The fourth part discusses the applications of these processes in quantum devices,nano-optics,and high-performance sensing.Finally,a perspective is given to discuss the challenges and opportunities associated with this research topic.

3D printed ultra-fast photothermal responsive shape memory hydrogel for microrobots

Hydrogels with stimuli-responsive capabilities are gaining more and more attention nowadays with prospective applications in biomedical engineering,bioelectronics,microrobot,etc.We develop a photothermal responsive hydrogel based on N-isopropylacrylamide that achieved a fast and reversible deformation manipulated only by near-infrared(NIR)light.The hydrogel was fabricated by the projection micro stereolithography based 3D printing technique,which can rapidly prototype complex 3D structures.Furthermore,with the variation of the grayscale while manufacturing the hydrogel,the deformation of the hydrogel structure can be freely tuned within a few seconds by losing and absorbing water through adjusting the intensity and the irradiation direction of the NIR light,showing a potential application in ultra-fast object grabbing and transportation.The present study provides a new method for designing ultrafast photothermal responsive hydrogel based microrobot working in water.

Nanobridged rhombic antennas supporting both dipolar and high-order plasmonic modes with spatially superimposed hotspots in the mid-infrared

Mid-infrared antennas(MIRAs)support highly-efficient optical resonance in the infrared,enabling multiple applications,such as surface-enhanced infrared absorption(SEIRA)spectroscopy and ultrasensitive mid-infrared detection.However,most MIRAs such as dipolar-antenna structures support only narrow-band dipolar-mode resonances while high-order modes are usually too weak to be observed,severely limiting other useful applications that broadband resonances make possible.In this study,we report a multiscale nanobridged rhombic antenna(NBRA)that supports two dominant reson-ances in the MIR,including a charge-transfer plasmon(CTP)band and a bridged dipolar plasmon(BDP)band which looks like a quadruple resonance.These assignments are evidenced by scattering-type scanning near-field optical micro-scopy(s-SNOM)imaging and electromagnetic simulations.The high-order mode only occurs with nanometer-sized bridge(nanobridge)linked to the one end of the rhombic arm which mainly acts as the inductance and the resistance by the circuit analysis.Moreover,the main hotspots associated with the two resonant bands are spatially superimposed,en-abling boosting up the local field for both bands by multiscale coupling.With large field enhancements,multiband detec-tion with high sensitivity to a monolayer of molecules is achieved when using SEIRA.Our work provides a new strategy possible to activate high-order modes for designing multiband MIRAs with both nanobridges and nanogaps for such MIR applications as multiband SEIRAs,IR detectors,and beam-shaping of quantum cascade lasers in the future.

Near-zero-adhesion-enabled intact wafer-scale resist-transfer printing for high-fidelity nanofabrication on arbitrary substrates

There is an urgent need for novel processes that can integrate different functional nanostructures onto specific substrates,so as to meet the fast-growing need for broad applications in nanoelectronics,nanophotonics,and fexible optoelectronics.Existing direct-lithography methods are difficult to use on fexible,nonplanar,and biocompatible surfaces.Therefore,this fabrication is usually accomplished by nanotransfer printing.However,large-scale integration of multiscale nanostructures with unconventional substrates remains challenging because fabrication yields and quality are often limited by the resolution,uniformity,adhesivity,and integrity of the nanostructures formed by direct transfer.Here,we proposed a resist-based transfer strategy enabled by near-zero adhesion,which was achieved by molecular modification to attain a critical surface energy interval.This approach enabled the intact transfer of wafer-scale,ultrathin-resist nanofilms onto arbitrary substrates with mitigated cracking and wrinkling,thereby facilitating the in situ fabrication of nanostructures for functional devices.Applying this approach,fabrication of three-dimensional-stacked multilayer structures with enhanced functionalities,nanoplasmonic structures with~10 nm resolution,and MoS2-based devices with excellent performance was demonstrated on specific substrates.These results collectively demonstrated the high stability,reliability,and throughput of our strategy for optical and electronic device applications.

3D-Integrated metasurfaces for full-colour holography

Metasurfaces enable the design of optical elements by engineering the wavefront of light at the subwavelength scale.Due to their ultrathin and compact characteristics,metasurfaces possess great potential to integrate multiple functions in optoelectronic systems for optical device miniaturisation.However,current research based on multiplexing in the 2D plane has not fully utilised the capabilities of metasurfaces for multi-tasking applications.Here,we demonstrate a 3D-integrated metasurface device by stacking a hologram metasurface on a monolithic Fabry–Pérot cavity-based colour filter microarray to simultaneously achieve low-crosstalk,polarisation-independent,high-efficiency,full-colour holography,and microprint.The dual functions of the device outline a novel scheme for data recording,security encryption,colour displays,and information processing.Our 3D integration concept can be extended to achieve multi-tasking flat optical systems by including a variety of functional metasurface layers,such as polarizers,metalenses,and others.

Stepwise-Nanocavity-Assisted Transmissive Color Filter Array Microprints

Visible-light color flters using patterned nanostructures have attracted much interest due to their various advantages such as compactness,enhanced stability,and environmental friendliness compared with traditional pigment or dye-based optical flters.While most existing studies are based on planar nanostructures with lateral variation in size,shape,and arrangement,the vertical dimension of structures is a long-ignored degree of freedom for the structural colors.Herein,we demonstrate a synthetic platform for transmissive color flter array by coordinated manipulations between height-varying nanocavities and their lateral flling fractions.Te thickness variation of those nanocavities has been fully deployed as an alternative degree of freedom,yielding vivid colors with wide gamut and excellent saturation.Experimental results show that the color-rendering capability of the pixelated nanocavities can be still retained as pixels are miniaturized to 500 nm.Crosstalk between closely spaced pixels of a Bayer color flter arrangement was calculated,showing minimal crosstalk for 1μm2 square subpixels.Our work provides an approach to designing and fabricating ultracompact color flter arrays for various potential applications including stained-glass microprints,microspectrometers,and high-resolution image sensing systems.

原位化学氧化构建高性能MoS2-MoO3面内同质异质结光敏晶体管

由组成相同的材料构建具有清晰边界的平面内p-n异质结是二维晶体管研究面临的主要挑战之一,在下一代集成电路和光电器件领域具有重要的潜在应用.因此有必要开发一种可实现p-n界面的简便、可控的操作方法.硫化钼(MoS2)作为一种具有原子层厚度的n型半导体材料已经在电子学和光电子学领域展现出巨大的应用前景.在本研究中,我们通过KI/I2溶液化学氧化诱导方法实现了从n型MoS2到p型MoO3的原位转化,进而形成了横向面内p-n异质结.MoS2/MoO3 p-n异质结显示出高效的光响应和整流特征,0 V、~3.6 mA W-1条件下最大外部量子产率达到~650%,同时光开关比达到~102.构筑的p-n异质结的高性能也被光电流面扫描所证实.由于器件在低源漏电压(VDS)和栅压(VG)条件下具有高的光响应性能,MoS2/MoO3 p-n二极管在光电器件及集成电路中的应用具有低功耗的特点.本研究为局部进行载流子种类转变提供了可能的途径,并将MoS2进一步应用于电子学、光电子学及CMOS逻辑电路领域.

Kirigami-inspired multiscale patterning of metallic structures via predefined nanotrench templates

Reliable fabrication of multiscale metallic patterns with precise geometry and size at both the nanoscale and macroscale is of importance for various applications in electronic and optical devices.The existing fabrication processes,which usually involve film deposition in combination with electron-beam patterning,are either timeconsuming or offer limited precision.Inspired by the kirigami,an ancient handicraft art of paper cutting,this work demonstrates an electron-beam patterning process for multiscale metallic structures with significantly enhanced efficiency and precision.Similar to the kirigami,in which the final pattern is defined by cutting its contour in a paper and then removing the unwanted parts,we define the target multiscale structures by first creating nanotrench contours in a metallic film via an electron-beam-based process and then selectively peeling the separated film outside the contours.Compared with the conventional approach,which requires the exposure of the whole pattern,much less exposure area is needed for nanotrench contours,thus enabling reduced exposure time and enhanced geometric precision due to the mitigated proximity effect.A theoretical model based on interface mechanics allows a clear understanding of the nanotrench-assisted selective debonding behaviour in the peeling process.By using this fabrication process,multiscale metallic structures with sub-10-nm up to submillimetre features can be reliably achieved,having potential applications for anti-counterfeiting and gap-plasmon-enhanced spectroscopy.

3D Printed Ultrastretchable,Hyper-Antifreezing Conductive Hydrogel for Sensitive Motion and Electrophysiological Signal Monitoring

Conductive hydrogels with high stretchability can extend their applications as a flexible electrode in electronics,biomedicine,human-machine interfaces,and sensors.However,their time-consuming fabrication and narrow ranges of working temperature and working voltage severely limit their further potential applications.Herein,a conductive nanocomposite network hydrogel fabricated by projection microstereolithography(PμSL)based 3D printing is proposed,enabling fast fabrication ability with high precision.The 3D printed hydrogels exhibit ultra-stretchability(2500%),hyper-antifreezing(-125℃),extremely low working voltage(<100μV),and super cyclic tensile stability(1 million cycles).The hydrogel-based strain sensor can probe both large-scale and tiny human motions,even with ultralow voltage of 100μV at extremely low temperature around-115℃.It is demonstrated that the present hydrogels can be used as a flexible electrode for capturing human electrophysiological signals(EOG and EEG),where the alpha and beta waves from the brain can be recorded precisely.Therefore,the present hydrogels will pave the way for the development of next-generation intelligent electronics,especially for those working under extremely lowtemperature environments.

Evaluating the bioavailability of heavy metals in natural-zeoliteamended aquatic sediments using thin-film diffusive gradients

The effectiveness of natural zeolite amendment of sediments as a restorative material was studied,as was the feasibility of utilizing thin-film gradient diffusion(DGT)as a proxy for the accumulation of heavy metals in Venerupis philippinaram.The results showed that addition of natural zeolite to sediment,significantly decreased the equilibrium partitioning of Cu,Pb,Cd,Cr and As between the sediment pore water and natural zeolite over 24 h by 67%,81%,72%,62%and 71%,respectively.Furthermore,the accumulation of Cu,Pb,Cd,Cr and As in V.philippinaram in the zeolite-amended sediments decreased by 44%,37%,54%,30%and 59%,respectively after 28 days and the absorption rates also declined.The amount of heavy metals enriched into the DGT film and V.philippinaram over 28 days showed a significant correlation(P<0.001)and indicated that DGT has the potential as a proxy to predict the bioaccumulation of heavy metals in benthic organisms in sediments amended by natural zeolite.Further studies focused on the modification of natural zeolite and the predictive ability of DGT in different sediments/organism scenarios are warranted.

Superpixel-based segmentation algorithm for mature citrus

With the decrease of agricultural labors and the increase in production costs,harvesting robots have become a research hotspot in recent years.To guide harvesting robots to pick mature citrus more precisely under variable illumination conditions,an image segmentation algorithm based on superpixel was proposed.Efficient simple linear iterative clustering(SLIC)algorithm which takes similarity of adjacent pixels into account was adopted to segment the images captured under variable illumination conditions into superpixels.The color and texture features of these superpixels were extracted and fused into feature vectors as descriptors to train backpropagation neural networks(BPNN)classifier in the next step.The adjacency information of superpixels was considered by calculating the global-local binary pattern(LBP)in R component images when extracting texture features.To accelerate the classification process,the mean of Cr-Cb image was utilized to find superpixels of interest which were regarded as candidates of citrus superpixels.These candidates were then classified by a pre-trained BPNN model with superpixel-level accuracy of 98.77%and pixel-level accuracy of 94.96%,while the average time to segment one image was 0.4778 s.Therefore,the results indicated that a superpixel-based segmentation algorithm toward citrus images had decent light robustness as well as high accuracy that could guide harvesting robot to pick mature citrus efficiently.

Method for detecting 2D grapevine winter pruning location based on thinning algorithm and Lightweight Convolutional Neural Network

In viticulture,there is an increasing demand for automatic winter grapevine pruning devices,for which detection of pruning location in vineyard images is a necessary task,susceptible to being automated through the use of computer vision methods.In this study,a novel 2D grapevine winter pruning location detection method was proposed for automatic winter pruning with a Y-shaped cultivation system.The method can be divided into the following four steps.First,the vineyard image was segmented by the threshold two times Red minus Green minus Blue(2R−G−B)channel and S channel;Second,extract the grapevine skeleton by Improved Enhanced Parallel Thinning Algorithm(IEPTA);Third,find the structure of each grapevine by judging the angle and distance relationship between branches;Fourth,obtain the bounding boxes from these grapevines,then pre-trained MobileNetV3_small×0.75 was utilized to classify each bounding box and finally find the pruning location.According to the detection experiment result,the method of this study achieved a precision of 98.8%and a recall of 92.3%for bud detection,an accuracy of 83.4%for pruning location detection,and a total time of 0.423 s.Therefore,the results indicated that the proposed 2D pruning location detection method had decent robustness as well as high precision that could guide automatic devices to winter prune efficiently.

Stable and unique graphitic Raman internal standard nanocapsules for surface-enhanced Raman spectroscopy quantitative analysis

Graphitic nanomaterials have unique, strong, and stable Raman vibrations that have been widely applied in chemistry and biomedicine. However, utilizing them as internal standards （ISs） to improve the accuracy of surface-enhanced Raman spectroscopy （SERS） analysis has not been attempted. Herein, we report the design of a unique IS nanostructure consisting of a large number of gold nanoparticles （AuNPs） decorated on multilayered graphitic magnetic nanocapsules （AGNs） to quantify the analyte and eliminate the problems associated with traditional ISs. The AGNs demonstrated a unique Raman band from the graphitic component, which was localized in the Raman silent region of the biomolecules, making them an ideal IS for quantitative Raman analysis without any background interference. The IS signal from the AGNs also indicated superior stability, even under harsh conditions. With the enhancement of the decorated AuNPs, the AGN nanostructures greatly improved the quantitative accuracy of SERS, in particular the exclusion of quantitative errors resulting from collection loss and non-uniform distribution of the analytes. The AGNs were further utilized for cell staining and Raman imaging, and they showed great promise for applications in biomedicine.

Stabilization of heavy metals in sediments:A bioavailability-based assessment of carbon adsorbent efficacy using diffusive gradients in thin films

This study investigated the effectiveness of carbon adsorbents as remediation material for sediments contaminated with heavy metals and the feasibility of utilizing diffusive gradients in thin films(DGT)as a biomimetic tool to estimate the accumulation of heavy metals in Venerupis philippinaram(Manila clam).The results showed that carbon materials had significant inhibitory effects(14.0-53.0%)on the enrichment of heavy metals in organisms and the order of increasing overall inhibitory effect was:charcoal,peat,activated carbon,and biochar.There were significant correlations(P<0.0001)between the four heavy metals accumulated in Venerupis philippinaram and those accumulated in DGT devices after 28 days in the laboratory.Observed concentrations of heavy metals enriched in DGT(5.4-42.0%)were less than accumulations in Venerupis philippinaram.The results of in situ DGT applications showed significant correlations between the amount accumulated in DGT and the acid-soluble portion in sediments for both Cu and Pb,with positive linear correlations and R-squares of 0.97 and 0.92,respectively.These results supported the notion that a DGT device can be used as a biomimetic tool that predicts and monitors the accumulation of heavy metals in aquaculture ponds.Future studies should focus on improving the stabilization of heavy metals in sediments using different types of carbon sorbents,as well as minimizing simulation deviations using DGT.