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目录 contents

    摘要

    亚波长人工超构材料可以实现特定波长的近完美吸收,在红外光电器件应用中能够克服传统红外材料吸收效率低、厚度较大、工作波长受限于带隙等缺陷.本文利用金属/介质/金属结构构造了一种可大面积制备的亚波长结构,可以实现1-10 μm波段内的双波段红外超吸收.通过时域有限差分法模拟和实验分析,我们认为该吸收器高频的吸收峰,主要来源F-P共振干涉增强吸收;而低频红外波段的吸收峰,主要得益于电偶极共振和磁共振模式的激发.利用退火工艺调节上层金颗粒的大小,可以有效地调节两个吸收峰的位置.

    Abstract

    The sub-wavelength artificial metamaterials which demonbstrate nearly-perfect absorption of a specific wavelength can overcome the defects of low absorption efficiency, large thickness, and working wavelength limitation of band gap in the infrared photoelectric device application. In this paper, a metal/medium/metal structure is used to construct a sub-wavelength structure that can be prepared over a large area, which can achieve dual-band infrared perfect absorption in the 1-10 μm band. Through analyzing the results of Finite-Difference Time-Domain simulation and experiment, we believe that the high-frequency absorption peak of the absorber is mainly derived from FP resonance interference enhanced absorption; while the absorption peak in the low-frequency infrared band is mainly due to the excitation of the electric dipole resonance and the magnetic resonance mode. By adjusting the size of the upper layer of gold particles in the way of annealing, the positions of the two absorption peaks can be effectively regulated.

    F-P resonance

  • 引言

    1~10 μm红外波段,覆盖三个红外窗口,该波段探测器在卫星遥感、信息传输、地质勘探等领域都有着广泛的应[1].目前利用碲镉汞、铟镓砷、硒化铅等材料制备的红外探测器,响应截止波长取决于材料的禁带宽[2,3,4].器件对材料的光学参数和厚度有严格的要求,但是仍然存在吸收率较低,吸收峰位难以调节的问[5,6].增强光吸收是提高红外探测器效率的重要途径,近年来随着等离激元和超材料等概念的引入,超吸收体(super absorber)获得了越来越多的关[7].2008年W.J.Padill小组在实验上首次利用三层膜结构即金属/介质/金属(Metal/Insulator/Metal,简称MIM)成功制备了超吸收[8,9],在微波波段实现近完美吸收,通过改变结构参数还可以调节共振吸收峰的峰位.利用超材料提高红外探测器的吸收,不仅可以大幅度减少材料厚度,降低材料生长成本,并且可以调节超吸收波段和克服角度敏感问题.

    利用超材料还可以制备双波段超吸收器,满足多波段探测器发展的需[10,11] ,吸引了众多研究者的兴趣.报道较多的多波段超吸收器大多是基于MIM结构,其顶层为有序的金属开口或闭口环阵列,利用非对称结构产生不同的电磁场耦合,及其与底层金属形成的等效回路,形成多波段的超吸收 [12,13].李兴玮等采用渔网结构通过腔共振和电场共振的方法实现了近红外双频段吸收[14];另外,也有利用非对称图形结构如金字塔、半球形等,实现多波段甚至超宽波段的红外吸[15,16,17].

    MIM结构是一种常用的超吸收体,一般利用掩膜版光刻、电子束曝光、纳米压印技术制备上层的金属有序或者周期性结构.但是微结构制备还是有工艺复杂和价格较高问题,给大面积、低成本应用带来挑战.基于局域表面等离子体共振增强的超吸收体对周期性的要求不高,利用无序结构也可以实现完美吸收,因此可以弥补应用方面的劣势.我们在MIM结构中基于无序结构实现了可见光波段的吸收[18].

    本文构造了一种简单的MIM超吸收结构,最下层为金属银,中间层为薄膜硅,最上层为无序的金纳米颗粒.金属银和硅薄膜在一定条件下可以形成常用的F-P腔结构,在特定波长会有干涉增强吸收效应.而上层无序的金纳米颗粒和下层金属银之间会产生电磁场共振效应,形成超吸收体系.利用以上两种超吸收效应在红外区域(1-10 μm)实现双波段吸收器.另外通过时域有限差分法模拟电磁场分布,对两个超吸收峰物理机制进行了分析,通过和实验对比验证了两个吸收峰的来源.

  • 1 实验设计

  • 1.1 数值仿真模型

    本文利用MIM结构来设计双波段超吸收器,其结构示意图如图1所示.底层金属层选择载流子浓度最大的银,厚度大于100 nm,中间介质层为硅薄膜,最上层为无序的金纳米颗粒.首先采用时域有限差分法(FDTD solution, Lumerical, Inc.)进行数值模拟,为简化计算量,在FDTD模拟过程中,用纳米方块来模拟金颗粒,其中t为金纳米方块的厚度,w为宽(长宽设置为相等),周期为p,硅介质厚度为d,结构整体周期为p.银衬底的光学参数取自Palik的固体光学参数手[19,20].金纳米颗粒的介电常数由椭偏测试后根据Lorenz-Drude模型反解得到,其表达式如下:

    ε=ε1+Aj2(Ecenter)j2-E2+iEνj-ωp2E(E+iν)
    (1)
    图1
                            设计的红外超吸收器结构示意图.自下而上分别为银衬底(厚度超过100nm)、硅薄膜(厚度为d)、金纳米方块.

    图1 设计的红外超吸收器结构示意图.自下而上分别为银衬底(厚度超过100nm)、硅薄膜(厚度为d)、金纳米方块.

    Fig.1 Structure schematic diagram of the infrared super absorber. From the bottom to the top layer are Ag substrate (thickness is more than 100 nm), silicon film (thickness is d.) and Au nanoparticles.

    只取了一阶洛伦兹振子,具体参数如下,ε=5.42, ωp=3.17 eV, ν=-0.048 eV, Ecenter=-0.52 eV, A1=1.95 eV, ν1=0.78 eV.硅薄膜光学参数由椭偏测试后根据Herzberger型色散公式拟合得到,其表达式如下:

    n=3.42+0.16λ2-0.028-0.12×(1λ2-0.028)2+1.27×10-6λ2-1.95×10-3λ4
    (2)

    在0.8~10 μm波段范围内,硅薄膜的消光系数k接近0,这与文献中报道的参数是相符[21,22].当入射光辐照到样品表面时,满足A+R+T+S=1的表达式,其中A为吸收率,R为镜面反射率,T为透射率,S为散射率.对于深亚波长结构,尺寸远小于入射光波长可忽略高阶衍射,散射率接近0.因此吸收率表达式可简化为,A=1-R.

  • 1.2 结构制备流程及测试设备

    按照设计,通过以下流程制备双波段超吸收器:(1)在蓝宝石片上沉积一层大于100 nm的银薄膜;(2)在银薄膜表面制备硅薄膜介质层;(3)表面溅射一层超薄金薄膜;(4)一定温度下快速退火,上层金薄膜形成金纳米颗粒.上层金纳米颗粒的尺寸通过金纳米薄膜的厚度和退火工艺调控.采用扫描电子显微镜(SEM, FEI Sirion 200)表征样品形貌;采用分光光谱仪(PerkinElmer, Lamda 950) 测试样品在0.2~2.5 μm波段的反射光谱;采用显微傅里叶光谱仪(FTIR, Thermo Scientific, Nicolet iN10)测试样品在1.2~10 μm波段的反射光谱.

  • 2 结果与讨论

  • 2.1 超吸收结构优化

    为了实现1~10 μm波段内可调节的红外超吸收器,我们利用FDTD数值模拟进行了结构的参数优化.由于结构没有偏振选择性,因此入射光选垂直入射的横电模式(TE mode),电场偏振方向垂直于入射面.首先,固定模型结构参数:d=72 nm,t=16 nm,w=p-10 nm,金纳米方块尺寸随周期改变,p在20~500 nm之间变化.图2.(a)为该模型在波长0.8~10 μm范围内反射光谱数值模拟图,可以看到在波长0.98 μm及中波红外波段内分别有一个较强的吸收峰,标记为Peak I和Peak II.图2.(b)是对应的反射谱mapping图,可以看出随着金块的长宽从10 nm增加到490 nm,Peak I峰位几乎不发生变化,且反射率接近0;而Peak II的吸收峰位却从1 μm左右逐渐红移至10 μm.同时从图2.(a-b)中可以看到,当金方块大于一定值时两峰之间出现了第三个峰,标记为Peak III.我们认为这是由于纳米方块尺寸较大时,局域电磁场共振峰Peak II在高频波段出现了高阶模式造成的.当固定参数:t=16 nm,w=72 nm,p=82 nm,d从0 nm逐渐增大到500 nm,仿真结果如图2.(c).可以看到随着d的增加,Peak I与Peak II同时发生红移且Peak I出现多支吸收峰.当固定参数:d=72 nm,t=16 nm,p=500 nm,金纳米方块的长/宽w从0~500 nm逐渐增加,如图2.(d)所示.可以看到在Peak I与Peak II之间出现了很多杂峰,其中一个比较明显的峰Peak III便是Peak II的高阶模,随着w值增加,其发生红移的特征与Peak II类似,这与之前的报道也是相符[23].由于金纳米方块的尺寸限制,图2.(d)只出现了一个比较明显的共振吸收峰的高阶模.

    图2
                            基于FDTD模拟得到不同结构参数的反射光谱图.(a)结构参数:d=72 nm, t=16 nm, w=(p-10) nm,改变结构周期p从100~500 nm.为方便讨论,反射谱中出现的三个峰分别记为Peak I, Peak II, 和Peak III,(b) 结构参数:d=72 nm, t=16 nm, w=(p-10) nm,改变p从20~500 nm逐渐增加.这是与(a)相对应的反射谱mapping图,(c) 结构参数:t=16 nm, w=174 nm, p=184 nm,改变d,从0~500 nm逐渐增加的反射谱mapping图,(d) d=72 nm, t=16 nm, p=500,改变w,从0~500 nm逐渐增加的反射谱mapping图

    图2 基于FDTD模拟得到不同结构参数的反射光谱图.(a)结构参数:d=72 nm, t=16 nm, w=(p-10) nm,改变结构周期p从100~500 nm.为方便讨论,反射谱中出现的三个峰分别记为Peak I, Peak II, 和Peak III,(b) 结构参数:d=72 nm, t=16 nm, w=(p-10) nm,改变p从20~500 nm逐渐增加.这是与(a)相对应的反射谱mapping图,(c) 结构参数:t=16 nm, w=174 nm, p=184 nm,改变d,从0~500 nm逐渐增加的反射谱mapping图,(d) d=72 nm, t=16 nm, p=500,改变w,从0~500 nm逐渐增加的反射谱mapping图

    Fig.2 Simulated reflectance spectra based on FDTD solutions.(a)Reflectance spectra of the structure with thickness of silicon membrane d=72 nm, thickness of Au nanocubes t=16 nm, side length w=(p-10) nm, and variable period p changing from 100 to 500 nm. There are three absorption peaks appeared at the spectra, recorded as Peak I, Peak II, and Peak III, respectively;(b)Reflectance spectra mapping of the structure in (a) with p changing from 0 to 500 nm. (c) Reflectance spectra mapping of the sample with t=16 nm, w=174 nm, p=184 nm, and variable d changing from 0 to 500 nm. (d) Reflectance spectra mapping of the sample with d=72 nm, t=16 nm, p=500, and variable w changing from 0 to 500 nm.

    根据以上的模拟结果发现Peak I对参数wp不敏感.当wp逐渐增大时,Peak I固定不动,而Peak II在1~10 μm的范围发生红移.此外,Peak I和Peak II两个吸收峰对介质层的厚度d比较敏感,随着d的增加都出现明显红移.因此,调整介质层厚度d可以同时移动两个吸收峰的峰位,而改变金纳米方块的尺寸w及结构周期p可以调整两个吸收峰的相对位置.峰位确定后,还要考虑结构参数对吸收峰强度的影响,如调节金纳米方块的厚度t,对结构参数进行优化,从而实现1~10 μm的范围内可调制的双波段近完美吸收器.

  • 2.2 电磁场分布

    为了确认两个吸收峰形成的物理机制,对Peak I和 Peak II的电磁场分布进行了详细研究.对设计的Ag/Si/Au结构选择两个参数模型进行电磁场分布模拟.模型I结构参数为d=72 nm, t=16 nm, w=p=407 nm,最上层为16 nm的连续金薄膜,模拟的反射谱如图3.(a)所示.该从反射谱看到该结构只在0.98 μm附近出现一个吸收峰,标记为Peak 0 (0.98 μm);模型II的结构参数为d=72 nm,t=16 nm,w=397 nm,p=407 nm,顶层的金薄膜层替换为金纳米方块(nanocubes),模拟的反射谱如图3.(b)所示.可以看到此结构产生了三个吸收峰,Peak I 处于0.98 μm;Peak II 处于6.1 μm;Peak III 处于1.8 μm.

    图3
                            (a)样品模型Ag/Si/Au film 的反射谱,其结构参数为d=72 nm, t=16 nm, w=p=407 nm,其吸收峰标记为Peak 0;(b)样品Ag/Si/Au nanocubes的反射谱,结构参数为d=72 nm, t=16 nm, w=397 nm, p=407 nm,三个吸收峰分别标记为Peak I, Peak II和Peak III;(c)和(d)是Peak 0计算的电场与磁场分布图;(e)和(f)是Peak I计算的电场与磁场分布图;(g)和(h)是Peak III计算的电场与磁场分布图;(i)和(j)是Peak II计算的电场与磁场分布图.

    图3 (a)样品模型Ag/Si/Au film 的反射谱,其结构参数为d=72 nm, t=16 nm, w=p=407 nm,其吸收峰标记为Peak 0(b)样品Ag/Si/Au nanocubes的反射谱,结构参数为d=72 nm, t=16 nm, w=397 nm, p=407 nm,三个吸收峰分别标记为Peak I, Peak II和Peak III(c)和(d)是Peak 0计算的电场与磁场分布图;(e)和(f)是Peak I计算的电场与磁场分布图;(g)和(h)是Peak III计算的电场与磁场分布图;(i)和(j)是Peak II计算的电场与磁场分布图.

    Fig.3 (a) The calculated reflectance spectrum of the sample Ag/Si/Au film, with d=72 nm, t=16, w=p=407 nm. One absorption peak is denoted as Peak 0. (b) The calculated reflectance spectrum of Ag/Si/Au nanocubes, with d=72 nm, t=16 nm, w=397 nm, p=407 nm. Three absorption peaks, Peak I, Peak II, and Peak III are recognized in the spectrum. Calculated electric field |E| (c), and magnetic field |H| (d) mapping of Peak 0. Calculated electric field |E| (e), and magnetic field |H| (f) mapping of Peak I.Calculated electric field |E| (g), and magnetic field |H| (h) mapping of Peak III. Calculated electric field |E| (i), and magnetic field |H| (j) mapping of Peak II.

    图3(c)和图3(d)分别是Peak 0在0.98 μm峰位处的电场及磁场分布图.从图3(c)中可以看到电场主要局域在金薄膜和银衬底中间部分;图3(d)显示磁场主要分布在银衬底上表面及金薄膜下表面两个位置.这是典型的平面波驻波模式F-P腔效应,即入射光在金属衬底-介质层-金属薄膜结构中产生了干涉增强吸收.当将上层金薄膜换成金纳米方块,由于金纳米方块具有很高的占空比(w=397 nm, p=407 nm),F-P腔效应依然存在.我们看到在图3(b)中,同样在λ=0.98 μm位置出现吸收峰Peak I.对Peak I进行模拟电场和磁场分布图3(e-f),发现同样具备图3(c-d)中驻波叠加的特征.只是由于受到其他共振模式的影响,该F-P共振的电磁场分布略有变形.F-P腔引起的吸收峰峰位由介质层的材料厚度及折射率决定,上层金属的大小或周期对该吸收峰峰位影响不大,这就解释了图2.(b)和图2.(d)中Peak I固定不动的物理原因.当增加介质层的厚度时,其吸收峰会发生红移,且当厚度超过一定值时,会出现F-P共振吸收的高阶模,这个结果和图2.(c)的结果相一致.综上所述,我们认为在0.98 μm处的超吸收峰是由于光在三层结构中干涉形成的吸收增强.

    图3(i)和图3(j)分别是吸收峰Peak II (λ=6.1 μm)的电磁场分布图,可以看到电场主要局域在金纳米方块的两端,形成非常强的电偶极共振.在金纳米方块两端聚集大量周期性正负变化的热电子,在银衬底对应位置会产生与之极性相反的感生电荷,与金纳米方块下表面的电极化矢量方向相反,形成等效回路,使得磁场局域在银衬底与金纳米方块之间,方向垂直于纸面,产生磁共[23,24].据此,我们认为该波段的超吸收来源于入射光激发了局域磁场及电偶极共振,从而产生了Peak II (λ=6.1 μm)的近完美吸收.另外,如图3.(g)和图3.(h)所示,从Peak III (λ=1.8 μm) 电场和磁场分布图可以看到,金纳米方块两端仍然局域了很强的电场.而磁场强度除了在银衬底与金纳米方块中间位置,两端也出现了很强的磁共振现象.我们认为Peak III是Peak II电磁场共振模式的高阶模.这也是解释了图2.(d)中随着金纳米方块变大,Peak III逐渐出现,并形成超吸收效应.以上的计算结果表明我们可以利用F-P腔和局域电磁场共振可以实现双波段红外的超吸收,其工作波段在1~10 μm可调.

  • 3 实验验证

    所制备的超吸收器的SEM截面图及退火处理后金纳米颗粒的形貌图如图4所示,从图中可以看到实际的结构与设计图基本相符,底层银衬底的厚度大于100 nm,保证在1~10 μm波段内均是全反射,透射几乎为零.介质层硅的厚度为72 nm,由于硅消光系数k在该波段内接近零,所以可作为透明介质层材料.最上层为不规则的金纳米颗粒,如图4.(b)所示.我们在SEM图中随机取500 nm×500 nm的范围,统计出该范围内所有金颗粒的长轴,取纵数近似认为是金纳米颗粒的粒径,统计大小约为72 nm.

    图4
                            实验上制备的红外超吸收器SEM截面图(a)及表面图(b)

    图4 实验上制备的红外超吸收器SEM截面图(a)及表面图(b)

    Fig.4 (a)Cross-section view, and (b) top view SEM image of the experimentally fabricated infrared super absorber

    图5(a)是该吸收器制备流程图,我们对每一步制备过程都做了光谱测试,如图5(c)所示.其中编号为1的曲线是银衬底的反射率,证实厚度超过100 nm的银薄膜在1~10 μm波段内反射率接近100%;编号为2的曲线是第二步硅薄膜转移到银衬底后的反射率曲线,在1.4 μm附近出现了一个较小的反射谷.由于硅薄膜在该波段内k几乎为零,所以该反射谷对应的吸收峰来源于F-P干涉增强吸收.在该模式下,红外光穿过“透明”硅介质层时,硅上表面反射光及经银层反射后透射出硅上表面的两束光,为相干光且相位差为半波长,干涉相消促进了介质层的吸收.由于硅在该波长下阻抗并不完全匹配,所以只出现一个比较小的反射谷.为了进一步证实该F-P共振模式,在图5(b)中给出了Ag/Si在0.2~10 μm全波段的反射谱,可以清楚的看到F-P共振的高阶模式,分别在0.52、0.39 μm等更短的波长范围内出现了二阶,三阶干涉增强的吸收峰;编号为3的反射谱,是在硅表面镀上一层5 nm的金薄膜后测得的,可以看到该F-P共振模式被极大的增强了,在1.4 μm附近实现了近完美吸收.因为模拟用的是金属体相的光学参数,所以Peak I的实验上测出的峰位和数值计算的峰位有一些偏差.编号4的曲线,是样品退火处理后,金薄膜变成了不规则的金纳米颗粒后测得的反射光谱.可以看到Peak I的反射谷升高,即吸收峰强变弱,但是峰位并没有改变,这与前文理论计算的结果也是相符的.但Peak II在6.5 μm处出现了超吸收,这是由于金纳米颗粒产生了非常强的电偶极共振及磁共振导致的.另外我们在1.9 μm附近也能观察到一个较小的超吸收峰,这是由于在金纳米颗粒尺寸较大的情况下,产生了电磁场共振的高阶模.这些实验测出的峰与我们在电磁场分布中的讨论是相符的,其吸收的物理机制也在前文中做了详细解释.

    图5
                            (a)红外超吸收器的制备流程图:1.Ag 层; 2.Ag/Si; 3.Ag/Si/Au; 4.Ag/Si/Au颗粒,(b)为了表征硅薄膜的本身的光学性质,利用傅里叶光谱仪(黑色谱线部分,0.2~2.5 μm)和分光光谱仪(红色谱线部分,1.2-10 μm)测出了步骤2对应的0.2~10 μm波段的反射谱,(c)四个步骤每一步对应的反射光谱图(光谱范围1.2~10 μm)

    图5 (a)红外超吸收器的制备流程图:1.Ag 层; 2.Ag/Si; 3.Ag/Si/Au; 4.Ag/Si/Au颗粒,(b)为了表征硅薄膜的本身的光学性质,利用傅里叶光谱仪(黑色谱线部分,0.2~2.5 μm)和分光光谱仪(红色谱线部分,1.2-10 μm)测出了步骤2对应的0.2~10 μm波段的反射谱,(c)四个步骤每一步对应的反射光谱图(光谱范围1.2~10 μm)

    Fig.5 (a) Fabrication procedure of the infrared perfect absorber, 1.Ag film;2.Ag/Si; 3.Ag/Si/Au; 4.Ag/Si/Au nanoparticles,(b) In order to characterize the optical properties of silicon membrane, FTIR (black line, 1.2~10 μm) and UV-VIS spectrophotometers (red line, 0.2~2.5 μm) are used to measure the reflectance spectra of the Ag/Si sample ranging from 0.2~10 μm.(c)The FTIR based reflectance spectra of the 1-4 samples(1.2~10 μm).

    退火后的金纳米颗粒的尺寸由原金膜的厚度和退火的工艺决定.一般选择3~5 nm金膜在350~450°C范围内退火,得到的金纳米颗粒的尺寸在40~72 nm之间.图6给出了不同金纳米颗粒近似尺寸调节下的实际测试光谱和数值计算光谱.图6.(a)是顶层为3 nm金薄膜未退火的样品,其吸收谱只观察到Peak I,说明金薄膜沉积在介质表面后促进了薄膜干涉效应从而增强了光吸收,这是在Peak I处产生近完美吸收的原因.图6.(b-f)是顶层金颗粒的尺寸分别为36 nm、44 nm、55 nm、61 nm、72 nm的模拟计算及实验测试的吸收光谱图,红色为实验结果,黑色为模拟结果.从图中可以看到随着金颗粒尺寸的增加peak II逐渐红移,在颗粒为72 nm时吸收峰已移至λ=6.5 μm,并在λ=1.9 μm形成了磁共振高阶模式的吸收峰.实验测出的吸收谱与数值计算出的结果在峰位上基本吻合,但由于仿真模拟过程中用的是周期性结构,金纳米方块的大小是一个定值,所以模拟谱线的吸收峰较尖锐;而退火过程生成的金颗粒尺寸服从正态分布,在一个较大的范围内变化,所以吸收峰较为平缓,Q因子较低.

    图6
                            不同金颗粒尺寸下的模拟计算及实验测试的吸收光谱图.(a)顶层是3 nm金薄膜,(b)顶层金纳米颗粒的平均大小为36 nm,(c)44 nm,(d)55 nm,(e)61 nm,(f)72 nm

    图6 不同金颗粒尺寸下的模拟计算及实验测试的吸收光谱图.(a)顶层是3 nm金薄膜,(b)顶层金纳米颗粒的平均大小为36 nm,(c)44 nm,(d)55 nm,(e)61 nm,(f)72 nm

    Fig.6 The simulated and measured absorptance specatra of (a)The thickness of Au film is 3 nm, and Ag/Si/Au NPs with changing average size of Au NPs, in which the average size of Au NPs are (b)36 nm,(c) 44 nm,(d)55 nm,(e) 61 nm,(f)72 nm.

  • 4 总结

    本文基于经典的MIM结构设计了一种高性能红外超吸收器,通过时域有限差分方法详细分析了结构参数对吸收峰的影响,优化了器件结构参数,并在实验上实现了1~10 μm波段范围内可调的双波段超吸收器,且实验结果和数值模拟相一致.通过对电磁场模拟的分析我们对双波段吸收器的每个吸收峰进行了解析,高频的吸收峰主要来源F-P共振干涉增强吸收;而低频红外波段的吸收峰主要得益于电偶极共振和磁共振模式的激发.MIM结构中最上层为金纳米薄膜退火后形成的无序金纳米颗粒,适合于大面积吸收器的制备.通过改变上层金颗粒的大小,可以调节低频红外波段吸收峰的位置.本文的工作为红外探测器、太阳能电池等领域提供了理论和实践基础.

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俞伟伟

机 构:

1. 中国科学院上海技术物理研究所 红外国家重点实验室,上海 200083

2. 中国科学院大学,北京 100049

Affiliation:

1. State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China

2. University of Chinese Academy of Sciences, Beijing 100049, China

邮 箱:yuw@mail.sitp.ac.cn

作者简介:(Biography):俞伟伟(1989-),男,江苏南京人,博士研究生,超构材料微结构增强吸收. E-mail:yuw@mail.sitp.ac.cn

卢 玥
彭 芳
潘晓航

机 构:中国科学院上海技术物理研究所 红外国家重点实验室,上海 200083

Affiliation:State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China

孙 艳

角 色:通讯作者

Role:Corresponding author

邮 箱:sunny@mail.sitp.ac.cn

作者简介:sunny@mail.sitp.ac.cn

郝加明

机 构:中国科学院上海技术物理研究所 红外国家重点实验室,上海 200083

Affiliation:State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China

陈 鑫
戴 宁

角 色:通讯作者

Role:Corresponding author

邮 箱:ndai@mail.sitp.ac.cn

作者简介:ndai@mail.sitp.ac.cn

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图1 设计的红外超吸收器结构示意图.自下而上分别为银衬底(厚度超过100nm)、硅薄膜(厚度为d)、金纳米方块.

Fig.1 Structure schematic diagram of the infrared super absorber. From the bottom to the top layer are Ag substrate (thickness is more than 100 nm), silicon film (thickness is d.) and Au nanoparticles.

图2 基于FDTD模拟得到不同结构参数的反射光谱图.(a)结构参数:d=72 nm, t=16 nm, w=(p-10) nm,改变结构周期p从100~500 nm.为方便讨论,反射谱中出现的三个峰分别记为Peak I, Peak II, 和Peak III,(b) 结构参数:d=72 nm, t=16 nm, w=(p-10) nm,改变p从20~500 nm逐渐增加.这是与(a)相对应的反射谱mapping图,(c) 结构参数:t=16 nm, w=174 nm, p=184 nm,改变d,从0~500 nm逐渐增加的反射谱mapping图,(d) d=72 nm, t=16 nm, p=500,改变w,从0~500 nm逐渐增加的反射谱mapping图

Fig.2 Simulated reflectance spectra based on FDTD solutions.(a)Reflectance spectra of the structure with thickness of silicon membrane d=72 nm, thickness of Au nanocubes t=16 nm, side length w=(p-10) nm, and variable period p changing from 100 to 500 nm. There are three absorption peaks appeared at the spectra, recorded as Peak I, Peak II, and Peak III, respectively;(b)Reflectance spectra mapping of the structure in (a) with p changing from 0 to 500 nm. (c) Reflectance spectra mapping of the sample with t=16 nm, w=174 nm, p=184 nm, and variable d changing from 0 to 500 nm. (d) Reflectance spectra mapping of the sample with d=72 nm, t=16 nm, p=500, and variable w changing from 0 to 500 nm.

图3 (a)样品模型Ag/Si/Au film 的反射谱,其结构参数为d=72 nm, t=16 nm, w=p=407 nm,其吸收峰标记为Peak 0(b)样品Ag/Si/Au nanocubes的反射谱,结构参数为d=72 nm, t=16 nm, w=397 nm, p=407 nm,三个吸收峰分别标记为Peak I, Peak II和Peak III(c)和(d)是Peak 0计算的电场与磁场分布图;(e)和(f)是Peak I计算的电场与磁场分布图;(g)和(h)是Peak III计算的电场与磁场分布图;(i)和(j)是Peak II计算的电场与磁场分布图.

Fig.3 (a) The calculated reflectance spectrum of the sample Ag/Si/Au film, with d=72 nm, t=16, w=p=407 nm. One absorption peak is denoted as Peak 0. (b) The calculated reflectance spectrum of Ag/Si/Au nanocubes, with d=72 nm, t=16 nm, w=397 nm, p=407 nm. Three absorption peaks, Peak I, Peak II, and Peak III are recognized in the spectrum. Calculated electric field |E| (c), and magnetic field |H| (d) mapping of Peak 0. Calculated electric field |E| (e), and magnetic field |H| (f) mapping of Peak I.Calculated electric field |E| (g), and magnetic field |H| (h) mapping of Peak III. Calculated electric field |E| (i), and magnetic field |H| (j) mapping of Peak II.

图4 实验上制备的红外超吸收器SEM截面图(a)及表面图(b)

Fig.4 (a)Cross-section view, and (b) top view SEM image of the experimentally fabricated infrared super absorber

图5 (a)红外超吸收器的制备流程图:1.Ag 层; 2.Ag/Si; 3.Ag/Si/Au; 4.Ag/Si/Au颗粒,(b)为了表征硅薄膜的本身的光学性质,利用傅里叶光谱仪(黑色谱线部分,0.2~2.5 μm)和分光光谱仪(红色谱线部分,1.2-10 μm)测出了步骤2对应的0.2~10 μm波段的反射谱,(c)四个步骤每一步对应的反射光谱图(光谱范围1.2~10 μm)

Fig.5 (a) Fabrication procedure of the infrared perfect absorber, 1.Ag film;2.Ag/Si; 3.Ag/Si/Au; 4.Ag/Si/Au nanoparticles,(b) In order to characterize the optical properties of silicon membrane, FTIR (black line, 1.2~10 μm) and UV-VIS spectrophotometers (red line, 0.2~2.5 μm) are used to measure the reflectance spectra of the Ag/Si sample ranging from 0.2~10 μm.(c)The FTIR based reflectance spectra of the 1-4 samples(1.2~10 μm).

图6 不同金颗粒尺寸下的模拟计算及实验测试的吸收光谱图.(a)顶层是3 nm金薄膜,(b)顶层金纳米颗粒的平均大小为36 nm,(c)44 nm,(d)55 nm,(e)61 nm,(f)72 nm

Fig.6 The simulated and measured absorptance specatra of (a)The thickness of Au film is 3 nm, and Ag/Si/Au NPs with changing average size of Au NPs, in which the average size of Au NPs are (b)36 nm,(c) 44 nm,(d)55 nm,(e) 61 nm,(f)72 nm.

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