超高分辨近场光学显微镜近期重点科研成果速览
1. 中国科学院 重庆绿色智能技术研究院 Zhongbo Yang等Near-Field Nanoscopic Terahertz Imaging of Single Proteins. Small. Figure 1. Schematic illustration of the THz s-SNOM setup and its use for single biomolecule imaging. Figure 2. THz near-field signals collected on different substrates. a) Time-domain THz electric field signals, and b) corresponding frequency-domain signals collected on graphene, Au, Si, and mica surfaces, respectively. The signals were demodulated at the second harmonics (2 Ω) of the probe oscillation frequency. c,d) The AFM topography images of graphene and Au substrates with 200 × 200 pixels, respectively. The height scale bars of (c) and (d) are the same. 摘要:太赫兹生物成像因其能以无标记、无创伤和非电离的方式获取样品的物理化学信息而颇受瞩目。但是,低介电常数生物分子的反射率问题,使得单分子精度的太赫兹成像仍是一个挑战。针对于此,作者开发了一种方法,利用石墨烯介导的太赫兹频率散射型扫描近场光学显微镜,对单个蛋白分子直接成像。此项研究发现,拥有较高太赫兹反射率和原子平整度的石墨烯基底可以为蛋白分子提供较高的太赫兹对比度。另外,我们还发现对铂探针的轴长优化能增强太赫兹散射近场信号中的振幅信号强度。基于这两个效应,作者同时获得了尺寸只有数纳米的免疫球蛋白G(IgG)和铁蛋白分子的形貌以及太赫兹散射图像。本文中所用的方法为单生物分子的太赫兹成像提供了新思路。2. 华中科技大学 Chao Chen等Terahertz Nanoimaging and Nanospectroscopy of Chalcogenide Phase-Change Materials. ACS Photonics 2020.Figure 2. THz near-field setup and imaging experiments. (a) Schematics of the THz s-SNOM setup with a bolometer usedas a detector. The inset shows an illustration of the finite dipole model for the layered sample. (b) Approach curve, showing the amplitude signal s2 on c-GST as a function of tip–sample distance. The mark h1/e represents the position at which the signal decays to 1/e of its maximum. The inset displays an optical microscope image of the AFM tip above the sample. The red dotted squares mark the c-GST areas. (c) AFM topography image (top panel) of GST on a silicon oxide substrate, which includes amorphous and crystalline states. Near-field amplitude (s2, middle panel) and phase (φ2, bottom panel) images at 1.89 THz. (d) Topography, (e) near-field amplitude, and (f) phase line profiles (shown as solid symbols) taken from the corresponding images in c. The red solid lines are smoothedcurves based on the experimental data. Horizontal dashed gray lines are a guide for the eye. 摘要:硫属化物相变材料(PCMs)在太赫兹(THz)频率下会发生光学声子共振现象,这个效应可被用于研究相变的基本特性,并产生很强的介电对比度,使其可被用于太赫兹的光子学应用。在本文中,我们证明可以通过频率可调的太赫兹散射型扫描近场光学显微镜(s-SNOM)研究PCM的声子。其具体方法为对包含非晶相和结晶相的PCM样品进行太赫兹纳米光谱成像。我们观察到材料的声子特征使其产生了很强的s-SNOM信号,以及重要的是,非晶态和结晶态PCM的光谱之间存在明显的差异,这使我们可以在纳米尺度上高信度地区分PCM的不同相。我们还发现可以通过增加针的半径来增强以信号强度和频谱对比度为标志的光谱特征。综上所述,我们用太赫兹s-SNOM成功构建了基于局部声子光谱的纳米结构以及化学组成的图谱。3. 中国地质大学-武汉 Zhigao Dai等人Edge-oriented and steerable hyperbolic polaritons in anisotropic van der Waals nanocavities. Nat. Commun..Figure 1. a Schematic diagram of edge-tailored PhPs in α-MoO3. The edge orientation is defined as angle θ with respect to the [001] direction. Green arrows indicate the incident PhPs waves launched by the laser-illuminated (purple curve arrows) AFM tip and reflected by the edge (red line). b Angle-dependent ke isofrequency contour of PhPs in α-MoO3 at ω = 889.8 cm−1. The solid lines and points stand for experimental results concluded from Fig. 1c. The green and black dotted arrows illustrate the incidence wavevector ki and Poynting vector Si, respectively. Generally, ki and Si are non-collinear. The reflected Poynting vector Se (solid arrows) is not parallel to the reflected wavevector ke (different color solid arrows) but antiparallel to Si. σ is the open angle. c Real-space imaging of edge-tailoring PhPs at angle-dependent α-MoO3 edges (length L: 2.5 µm width W: 200 nm sample thickness d: 210 nm, L andW defined in the Ed1). d s-SNOM line traces along the direction perpendicular to the edges in Ed1-Ed5. e Near-field amplitude s(ω) of PhPs on isosceles triangle α-MoO3 nanocavities with bottom edge perpendicular to the [001] crystal direction (height length: 4.33 μm thickness: d = 175 nm) The angles between adjacent sides of the series of triangles with respect to the [001] direction are approximately 7.5°, 15°, 30°, 45°, and 60°, respectively. 摘要:高度受限和低损耗的化子在石墨烯和六方氮化硼上是沿平面各向同性传播的,这使得对光的控制被限制在了有限的自由度内。而以α-MoO3 and V2O5为代表的新兴双轴范德华材料则展现出了特的化传播特性,它们的辅助光轴是在平面上的。利用这种强平面各向异性,作者通过空间纳米成像观测到了α-MoO3纳米腔的图样内有着受边界导向的双曲化子。并且发现边界的夹角和结晶方向对其光学响应信号有着举足轻重的影响,这对调整化图样的参数是至关重要的。基于此,通过调整α-MoO3纳米腔的几何构型,我们观测到了双曲化子会延边界传播并且会调整自身传播方向的特性以及与之对应的化子绕行禁区。而这种双曲化子的寿命和性能指数则受到纳米腔边界宽高比的限制。4. 国防科学技术大学 Jiangyu Zhang 等人Light-induced irreversible structural phase transition in trilayer graphene. Sci. & App..Figure 4. Raman mapping and s-SNOM imaging of the light-induced structural phase transition in MLG. (a) Optical microscopy image of MLG sample #125. (b) AFM image and height profile of graphene. (c) Raman maps of the integrated G peak intensity (position: 1576 cm−1, width: 5 cm−1) before laser irradiation and (d) after laser irradiation. The laser power is 20 mW, and the exposure time is 34 min. (e) s-SNOM image of graphene after laser irradiation. (f) Magnified s-SNOM image of graphene. Graphene domains with different stacking orders show different contrasts in the s-SNOM image. The marked regions I, II, and III correspond to ABC stacking, ABA stacking and mixed ABC + ABA stacking domains, respectively. The red arrows in (e, f) highlight the additional mixed ABC + ABA stacking domains that were not resolved in the Raman maps. (g) Raman spectra of different graphene regions taken from the marked solid dots before laser irradiation and (h) after laser irradiation摘要:晶体结构对相关材料的物理性质有着深刻的影响。因此,即使化学组成相同(比如石墨烯和金刚石),我们也可以通过生成具有特定对称性的晶体,来很大范围内调整它们的特性。而当晶体的结构相可以通过外部刺激动态改变时,更多有意思的可能性出现在了我们面前。这样的材料特性虽不常见,但却能引发很多喜人的现象,例如相变记忆效应。具体到三层石墨烯,它有两种常见的堆叠结构(ABA和ABC),二者都具有特的电子能带结构,并展现出了与众不同的特性。而这两种堆叠结构的三层石墨烯里的畴壁,则展现出了新的迷人的物理效应,比如说量子谷霍尔效应。科研工作者在三层石墨烯的相工程上投入了大量的精力。不过,操纵畴壁以实现对材料局部结构和特性的调控仍然是一个难题。本文通过实验表明,通过激光照射可以实现结构相之间的转换,并在三层石墨烯中构建各种形状的畴壁。这种能够控制畴壁位置和方向的能力,使得我们能够更好地调整石墨烯的局部结构相和特性,并为可定制原子结构,电子以及光学特性的人造二维材料的生成提供了一种简洁且有效的路径。 5. 华中科技大学 Peining Li等人Collective near-field coupling and nonlocal phenomena in infrared-phononic metasurfaces for nano-light canalization. Nat.Commun..Figure 2. Near-field imaging of polariton evolution in a hBN metasurface. a Schematic of the near-field nanoimaging experiment. b, c Near-field images measured at two different frequencies, ω = 1415 cm−1 (HPhP region) and ω = 1510 cm−1 (EPhP region). White arrows indicate the polariton fringes observed on the metasurface. 摘要:通过光子耦合激发和偶物质激发所产生的化子可以沿具有双曲线色散或椭圆色散的各向异性超表面传播。而在双曲线色散与椭圆色散之间的转换过程中(对应拓扑结构的转换),有各种有趣的现象被观测到,比如光子态密度的增强、化子的沟道效应和超透镜效应。在本文中,作者从理论角度和实验角度分别研究了这种拓扑结构的转换,单轴红外声子超表面中的化耦合和其强烈的非局域响应信号,以及六方氮化硼 (hBN) 纳米带的光栅。 通过超高分辨红外10纳米成像,研究者观察到了六方氮化硼中余辉带里合成的横向光学声子的共振(即纳米带强烈的集体性近场耦合),这触发了从双曲线色散向椭圆色散的拓扑转换。作者还表征并可视化了跃迁频率附近深亚波长通道模式的空间演化,该模式作为一种准直化子为超透镜和无衍射传播打下了基础。6. 山西大学 PengjuYang 等人Rational electronic control of carbon dioxide reduction over cobalt oxide. J. Cat..Figure 2. (a) XPS Co 2p of Co3O4 and Co3O4/Al-1(1 wt% Co3O4), (b) XPS Al 2p of Co3O4/Al-1 and Al-1, (c-d) the S-SNOM optical image of Co3O4/Al-1(1 wt% Co3O4) and SNOM amplitude S3 of lines A-E.摘要:选择性地将二氧化碳(CO2)还原为燃料和化学品是通过碳中和发展可持续性能源经济的重点所在。而其中CO2的活化则是重中之重。考虑到电子迁移是这一过程的决速步骤,通过调节CO2还原催化剂的电子结构来增强其活性则显得更为关键。不过,人们对催化剂的电子特性与活性的内在关系的理解还不是很深入,这也限制了高效CO2还原催化剂的有理论支撑的设计。本文中,作者设计了一种以铝作为电子供体的催化剂-缘体-金属系统,并以此来调节氧化钴(Co3O4)催化剂的电子结构。这样,铝中的电子便可以高效地通过一种超薄且自主形成的Al2O3缘层穿入Co3O4。实验和理论结果毫无疑问确证了Co3O4的高电子密度有利于CO2的吸收和活化,并同时降低了COOH的生成能垒,尤其是CO*中间体的解吸能垒,这大大加速了CO2到CO的光还原反应的动力学进程。相比Co3O4,Co3O4/Al2O3-Al中的Co的周转频率要高出很多。其表观量子产率在420纳米处能高达3.8%,这一数字超越了大部分文献中对催化剂的记述。另外,Co3O4 中电子密度的提高也有效地抑制了析氢竞相反应。同时对CO的筛选性也从Co3O4的57.9%提高到了Co3O4/Al2O3-Al的82.4%。值得注意的是,通过控制Al的含量和粒径我们还可以合理调节催化剂的催化效率。综上,该项研究建立了催化剂的电子结构与其对 CO2 还原反应的催化活性之间的联系。并且,作者提出的这种Al2O3-Al结构,还有潜力成为其他非均相催化剂电子效应研究的全新平台。7. 中山大学 Yan Shen等人Pyramid-Shaped Single-Crystalline Nanostructure of Molybdenum with Excellent Mechanical, Electrical, and Optical Properties. ACS Appl. Mater. Interfaces. 12. 华中科技大学 Peining Li等人Nanoscale Guiding of Infrared Light with Hyperbolic Volume and Surface Polaritons in van der Waals Material Ribbons. Adv. Mater..Figure 4. Thickn