Deep-subwavelength single grooves prepared by femtosecond laser direct writing on Si

It is well known that femtosecond laser pulses can easily spontaneously induce deep-subwavelength periodic surface structures on transparent dielectrics but not on non-transparent semiconductors.Nevertheless,in this study,we demonstrate that using high-numerical-aperture 800 nm femtosecond laser direct writing with controlled pulse energy and scanning speed in the near-damage-threshold regime,polarization-dependent deep-subwavelength single grooves with linewidths of~180 nm can be controllably prepared on Si.Generally,the single-groove linewidth increases slightly with increase in the pulse energy and decrease in the scanning speed,whereas the single-groove depth significantly increases from~300 nm to~600 nm with decrease in the scanning speed,or even to over 1μm with multi-processing,indicating the characteristics of transverse clamping and longitudinal growth of such deep-subwavelength single grooves.Energy dispersive spectroscopy composition analysis of the near-groove region confirms that single-groove formation tends to be an ultrafast,non-thermal ablation process,and the oxidized deposits near the grooves are easy to clean up.Furthermore,the results,showing both the strong dependence of groove orientation on laser polarization and the occurrence of double-groove structures due to the interference of pre-formed orthogonal grooves,indicate that the extraordinary field enhancement of strong polarization sensitivity in the deep-subwavelength groove plays an important role in single-groove growth with high stability and collimation.

Development of massively parallel electron beam direct write lithography using active-matrix nanocrystalline-silicon electron emitter arrays

Nanoscale lithographic technologies have been intensively studied for the development of the next generation of semiconductor manufacturing practices.While mask-less/direct-write electron beam(EB)lithography methods serve as a candidate for the upcoming 10-nm node approaches and beyond,it remains difficult to achieve an appropriate level of throughput.Several innovative features of the multiple EB system that involve the use of a thermionic source have been proposed.However,a blanking array mechanism is required for the individual control of multiple beamlets whereby each beamlet is deflected onto a blanking object or passed through an array.This paper reviews the recent developments of our application studies on the development of a high-speed massively parallel electron beam direct write(MPEBDW)lithography.The emitter array used in our study includes nanocrystalline-Si(nc-Si)ballistic electron emitters.Electrons are drifted via multiple tunnelling cascade transport and are emitted as hot electrons.The transport mechanism allows one to quickly turn electron beamlets on or off.The emitter array is a micro-electro-mechanical system(MEMS)that is hetero-integrated with a separately fabricated active-matrix-driving complementary metal-oxide semiconductor(CMOS)large-scale integration(LSI)system that controls each emitter individually.The basic function of the LSI was confirmed to receive external writing bitmap data and generate driving signals for turning beamlets on or off.Each emitted beamlet(10×10μm^(2))is converged to 10×10 nm^(2) on a target via the reduction electron optic system under development.This paper presents an overview of the system and characteristic evaluations of the nc-Si emitter array.We examine beamlets and their electron emission characteristics via a 1:1 exposure test.

Laser direct writing of Ga_(2)O_(3)/liquid metal-based flexible humidity sensors

Flexible and wearable humidity sensors play a vital role in daily point-of-care diagnosis and noncontact human-machine interactions.However,achieving a facile and high-speed fabrication approach to realizing flexible humidity sensors remains a challenge.In this work,a wearable capacitive-type Ga_(2)O_(3)/liquid metal-based humidity sensor is demonstrated by a one-step laser direct writing technique.Owing to the photothermal effect of laser,the Ga_(2)O_(3)-wrapped liquid metal particles can be selectively sintered and converted from insulative to conductive traces with a resistivity of 0.19Ω·cm,while the untreated regions serve as active sensing layers in response to moisture changes.Under 95%relative humidity,the humidity sensor displays a highly stable performance along with rapid response and recover time.Utilizing these superior properties,the Ga_(2)O_(3)/liquid metal-based humidity sensor is able to monitor human respiration rate,as well as skin moisture of the palm under different physiological states for healthcare monitoring.

Femtosecond laser direct writing of functional stimulus-responsive structures and applications

Diverse natural organisms possess stimulus-responsive structures to adapt to the surrounding environment.Inspired by nature,researchers have developed various smart stimulus-responsive structures with adjustable properties and functions to address the demands of ever-changing application environments that are becoming more intricate.Among many fabrication methods for stimulus-responsive structures,femtosecond laser direct writing(FsLDW)has received increasing attention because of its high precision,simplicity,true three-dimensional machining ability,and wide applicability to almost all materials.This paper systematically outlines state-of-the-art research on stimulus-responsive structures prepared by FsLDW.Based on the introduction of femtosecond laser-matter interaction and mainstream FsLDW-based manufacturing strategies,different stimulating factors that can trigger structural responses of prepared intelligent structures,such as magnetic field,light,temperature,pH,and humidity,are emphatically summarized.Various applications of functional structures with stimuli-responsive dynamic behaviors fabricated by FsLDW,as well as the present obstacles and forthcoming development opportunities,are discussed.

A direct laser-synthesized magnetic metamaterial for low-frequency wideband passive microwave absorption

Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications.

Direct ink writing to fabricate porous acetabular cups from titanium alloy

Acetabular cups,which are among themost important implants in total hip arthroplasty,are usually made from titanium alloys with high porosity and adequate mechanical properties.The current three-dimensional(3D)printing approaches to fabricate customized acetabular cups have some inherent disadvantages such as high cost and energy consumption,residual thermal stress,and relatively low efficiency.Thus,in this work,a direct ink writing method was developed to print a cup structure at room temperature,followed by multi-step heat treatment to form microscale porous structure within the acetabular cup.Our method is facilitated by the development of a self-supporting titanium-6 aluminum-4 vanadium(Ti64)ink that is composed of Ti64 particles,bentonite yield-stress additive,ultraviolet curable polymer,and photo-initiator.The effects of Ti64 and bentonite concentrations on the rheological properties and printability of inks were systematically investigated.Moreover,the printing conditions,geometrical limitations,and maximum curing depth were explored.Finally,some complex 3D structures,including lattices with different gap distances,honeycomb with a well-defined shape,and an acetabular cup with uniformly distributed micropores,were successfully printed/fabricated to validate the effectiveness of the proposed method.

Periodic transparent nanowires in ITO film fabricated via femtosecond laser direct writing

This paper reports the fabrication of regular large-area laser-induced periodic surface structures(LIPSSs)in indium tin oxide(ITO)films via femtosecond laser direct writing focused by a cylindrical lens.The regular LIPSSs exhibited good properties as nanowires,with a resistivity almost equal to that of the initial ITO film.By changing the laser fluence,the nanowire resistances could be tuned from 15 to 73 kΩ/mm with a consistency of±10%.Furthermore,the average transmittance of the ITO films with regular LIPSSs in the range of 1200-2000 nm was improved from 21%to 60%.The regular LIPSS is promising for transparent electrodes of nano-optoelectronic devices-particularly in the near-infrared band.

A systematic printability study of direct ink writing towards high-resolution rapid manufacturing

Direct ink writing(DIW)holds enormous potential in fabricating multiscale and multi-functional architectures by virtue of its wide range of printable materials,simple operation,and ease of rapid prototyping.Although it is well known that ink rheology and processing parameters have a direct impact on the resolution and shape of the printed objects,the underlying mechanisms of these key factors on the printability and quality of DIW technique remain poorly understood.To tackle this issue,we systematically analyzed the printability and quality through extrusion mechanism modeling and experimental validating.Hybrid non-Newtonian fluid inks were first prepared,and their rheological properties were measured.Then,finite element analysis of the whole DIW process was conducted to reveal the flow dynamics of these inks.The obtained optimal process parameters(ink rheology,applied pressure,printing speed,etc)were also validated by experiments where high-resolution(<100μm)patterns were fabricated rapidly(>70 mm s^(-1)).Finally,as a process research demonstration,we printed a series of microstructures and circuit systems with hybrid inks and silver inks,showing the suitability of the printable process parameters.This study provides a strong quantitative illustration of the use of DIW for the high-speed preparation of high-resolution,high-precision samples.

3D直写制备ZIF-8/PVDF杂化体系及性能分析

采用溶剂法合成沸石咪唑骨架-8(ZIF-8),然后利用静电直写技术,采用物理混合法制备得到具有较好光催化性能、立体有序的ZIF-8/PVDF杂化膜。研究表明,采用物理混合的方法加入ZIF-8,对纤维膜的形貌及性能的影响较显著。随着ZIF-8含量的增加,ZIF-8/PVDF杂化膜的表面粗糙度逐渐增大,并且,出现微孔结构,水接触角呈先降低后增大的趋势变化。当ZIF-8的含量为2%时,杂化膜微孔分布较均匀,亲水性较好,杂化膜对盐酸四环素(TCH)溶液的降解效果最佳,降解率为77.9%;另外,其对诺氟沙星、环丙沙星和磺胺甲恶唑的降解率均能达到77%,并且,与第一次循环相比,经过5次循环使用后,杂化膜对TCH的降解率仅有小幅下降。

直写成型用碳化硅浆料及其流变性能研究

碳化硅(SiC)凭借高强度、轻质性以及耐高温性能等优势已成为时下应用最广泛的陶瓷材料之一。传统的制备方法生产周期长、成本高且难以制造相对复杂结构的陶瓷。本文利用直写成型方法制备三维复杂结构的SiC陶瓷,研究分散剂含量、pH值、固相体积分数和增稠剂等因素对SiC浆料流变性能的影响,制备可打印的SiC浆料并直写成型,获得SiC的三维点阵结构。结果表明:调节分散剂含量能使浆料黏度获得最低值;pH值影响分散剂的解离度进而改变浆料的黏度;固相体积分数越高,打印结构完整性越好;添加甲基纤维素(MC)可增加浆料的黏度和剪切弹性模量,使其可打印。优化的SiC浆料配方为:分散剂聚丙烯酸(PAA)质量分数为0.01%,固相体积分数为63%和MC质量分数为0.04%,pH>10。

喷头流道结构参数对高黏度含能材料直写成型3D打印挤出过程稳定性影响

为了研究直写成型技术(DIW)中挤出系统的喷头流道结构参数(锥角角度、出口直径、成型段长度)对含能材料挤出过程的流体流动影响,研究建立了基于Polyfow Extrusion模块的高黏度含能材料挤出模型,并采用直写成型3D打印工况的挤出实验对其进行了验证。研究通过所建立的模型分析了锥角角度范围90°~130°,出口直径0.75~2 mm以及成型段长度5~20 mm对高黏度含能材料挤出过程的影响。结果表明:采用Polyflow Extrusion模块可以较准确地模拟复合含能材料的流动行为,同时发现锥角为100°、喷头出口直径为1.5~1.75 mm时挤出成型过程相对稳定、挤出膨胀较小,且成型段的增长会在增大所需入口压强的同时减小出口膨胀效应。

《秋雨叹三首》写作笔法平议

杜甫的《秋雨叹三首》以直笔书写天宝十三载长安六十日霖雨事。诗有曲笔,前人亦曾指出,惜只针对前两首,且语焉不详。其实这组诗三首都是看似直笔,实为曲笔。第一首“决明”是香草美人笔法,比喻正直之士遭遇打击;第二首暗传心曲,“农夫田妇无消息”隐指无人关注农民生活;第三首立象讽世,以写实之“秋来未曾见白日”象征时代政治之昏暗,以“泥污后土何时干”象征对海晏河清之向往。曲笔直用与直笔曲用是组诗之笔法,故解诗需直笔曲解与曲笔直解,以还原诗意之真。

空间整形飞秒激光高效制备纳米光栅

针对常规物镜聚焦飞秒激光光斑较小,难以单次直写加工成型大面积纳米光栅结构的问题,提出了利用空间狭缝整形的飞秒激光脉冲直写方法。通过开展单晶硅表面纳米光栅结构对加工系统的参数依赖关系研究,获得入射整形飞秒激光能量密度8.00μJ/cm^(2)、扫描速度9 mm/s、狭缝宽度0.40 mm的优化条件。采用SEM、AFM等手段对光栅进行微观表征,结果表明,单次扫描所制备的纳米光栅结构具有极高的宽度(41.20μm),说明提出的方法可以显著提升一次成型大面积纳米光栅结构的制备效率。

锌铝合金熔融三维直写成形尺寸建模与组织分析

为了实现金属熔融三维直写工艺过程的控形控性,开展锌铝合金熔融三维直写成形尺寸建模与组织分析研究。首先,以锌铝合金熔融直写的最小控制单元单道成形为研究对象,采用多元非线性回归方法拟合成形道宽,将成形特征参数w作为响应变量,D和H作为预测变量,进行回归分析;其次,建立不同工艺参数下单道成形尺寸参数模型,并对模型进行拟合度校验;最后,对单道成形流固耦合过程进行数值模拟,分析典型凝固组织,通过引入熔融直写成形重熔预备时间tr,预测计算成形中层间结合效果好的工艺参数。研究结果表明:在单道成形道宽预测模型中,喷嘴直径D是影响成形道宽的第一要素,其次是喷嘴距成形底板高度H;当成形轨迹宽度近似等于凝固层宽度时,这是成形下一层的最佳时间。

基于FSR嵌入的智能泡沫在气动夹爪的应用

如何控制工业夹爪对易损物体的夹持力是一件具有挑战的任务,通常是利用有着力传感器的电动夹爪进行反馈控制,但这种方法昂贵且额外增加了夹爪的复杂程度。基于直书写3D打印,设计了一种内嵌力敏电阻器(FSR)的智能硅橡胶泡沫,安装在气动夹爪的指尖,不仅能监测夹持状态,还能在气压超过阈值后一定范围内,保持夹持力的恒定,以保护物体。实验结果表明:智能泡沫在4~12 N的工作范围内,误差不超过1.5N。当气压在450~560kPa范围内,能维持夹持力约14.6N。

梯形内嵌多方孔模块发射药的打印制备及定容燃烧性能

为了设计和制备弧厚小、燃烧时间短、渐增性好的新型发射药,以12.7 mm枪弹装药为对象,设计了梯形内嵌多方孔结构,采用直写成型工艺制备了外层弧厚不同、内嵌多方孔结构的梯形模块发射药。发射药长41 mm,内嵌方孔单边长为0.4 mm,内孔个数为3105。通过密闭爆发器试验,研究了模块发射药和制式药/模块发射药混合装药的定容燃烧性能。结果表明:打印发射药燃烧正常,在相对压力B>0.2后,外层弧厚为1.0 mm的模块发射药的动态燃烧活度相对外层弧厚为0.5 mm的下降较缓;当混合装药质量比为55时,分裂点后移,燃烧渐增性较好;打印发射药在爆发器内燃烧时间小于8 ms,与制式药燃烧时间相当,能满足小口径武器快速燃烧的要求。

微细直写掩膜电解加工非晶合金平面微线圈工艺研究

针对掩膜电解加工工艺固化、流程复杂等问题,提出一种基于微细直写聚合物材料的图案化掩膜电解加工方法。对直写掩膜工艺应用于微细电解加工平面线圈工艺进行研究。采用单因素法获得了直写加工参数对掩膜的影响规律。采用正交实验获得了加工电压、阴极振动频率和占空比等工艺参数对成形精度的规律。建立了加工微结构尺寸的预测模型,利用优化的工艺参数在厚度30μm合金薄片上加工出宽度为300μm平面微线圈结构,通过网络分析仪对电流传感效应进行检测,获得了阻抗变化率为3.46%的响应。证明了直写掩膜应用于微细掩膜电解加工的可行性。

热解温度对直写3D打印石墨烯/SiC_(p)/SiC复合材料性能的影响

通过在碳化硅前驱体聚碳硅烷(PCS)溶液中加入石墨烯/SiC_(p)复合粉末,获得石墨烯/SiC_(p)/PCS浆料,采用直写3D打印(DIW)和高温烧结相结合制备了石墨烯/SiC_(p)/SiC复合材料。PCS在不同热解温度下具有不同的产物与性能,本文研究了热解温度对石墨烯/SiC_(p)/SiC复合材料性能的影响。800℃时PCS转化为非晶SiCxOy,随着温度升高至1500℃,非晶SiCxOy逐渐生成导电性更好的β-SiC与游离碳,石墨烯/SiC_(p)/SiC复合材料的电导率从0.93 S·m^(-1)升高至670 S·m^(-1)。1200℃时,复合材料抗压强度和容积密度分别达到最大的12.3 MPa和1.49 g·cm^(-3)。该研究提供了一种基于PCS浆料的直写3D打印工艺制备高导电轻质多孔石墨烯/SiC_(p)/SiC复合陶瓷的方法。

废旧棉用于直接油墨书写3D打印面料及服装

为实现废旧棉织物的绿色和高值化利用,将废旧棉织物经漂白、活化后再溶解在LiCl/DMAc溶剂中,加入羟乙基纤维素以调节油墨的可打印性。对处理前后的废旧棉织物的外观形貌及内部结构分析,发现处理后废旧棉织物有助于进一步的溶解。对油墨的流变性能研究,发现油墨表现出剪切变薄的行为。通过直接油墨书写3D打印技术成功制备出纤维素面料,改善打印面料的舒适性。讨论3D打印纤维素面料的形貌结构、机械强度和舒适性等。结果表明:与3D打印PLA面料相比,3D打印纤维素面料在柔韧性和润湿性方面都有所改善,其机械强度能满足服用要求,各项性能更接近于棉织物。最后,使用纤维素油墨打印不同花型的面料和服装,扩大纺织材料在3D打印领域的应用。这种新颖方法将废旧棉织物得到再利用,也为3D打印柔性面料和服装带来了广阔的前景。

具有内表面拓扑结构的仿生血管设计与制备

针对临床人工血管不具备诱导内皮化的内表面微结构,无法为内皮细胞生长提供合适的力学环境的问题,设计并制备了一种具有内表面拓扑结构的仿生血管(BVST),实现了壁面剪切力的优化分布。基于内皮细胞的形态分布,设计了具有正交、菱形、圆弧三种内表面拓扑结构的仿生血管。通过仿真分析,发现正交与菱形结构的BVST对血液流速影响较小,周期波动相近,且BVST的内表面拓扑结构能减缓细胞流速、增加细胞滞留时间,有利于内皮细胞在进行体外培养时沉积、黏附在BVST内表面。通过对比BVST与无拓扑结构仿生血管的剪切力分布,发现BVST整体剪切力分布更加均匀。分析单个拓扑单元内的剪切力分布,发现菱形拓扑单元内部剪切力分布均匀且连续,剪切力变化较小,有利于内皮细胞的生长。将聚己内酯(PCL)溶于二氯甲烷(DCM)配制质量分数35%的PCL-DCM溶液,采用内径为0.2 mm的针头,在移动速度40 mm/s、电压5.8 kV、针头高度1 mm、挤出气压0.05 MPa的条件下,基于电纺直写技术制备具有拓扑结构的仿生血管内膜;将拓扑结构浸水黏附在纺丝收集柱,基于静电纺丝技术制备仿生血管外膜,获得具有内表面拓扑结构的双层仿生血管。提出的仿生血管设计与制备工艺可为血管内皮化研究提供参考。