English:
[0001] Surface Enhanced Raman Spectroscopy (SERS) is a surface- sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces or nanostructures.
[0002] Figs. 1 -3 illustrate an example of a SERS structure, in which ten metal nanoparticles are clustered in two layers in a single cone shaped hole.
[0003] Figs. 4-6 illustrate an example of a SERS structure, in which five metal nanoparticles are clustered in two layers in multiple square-base pyramid shaped holes.
[0004] Figs. 7-9 illustrate an example of a SERS structure, in which four metal nanoparticles are clustered in two layers in a single triangle-base pyramid shaped hole.
[0005] Figs. 10-12 illustrate an example of a SERS structure, in which ten metal nanoparticles are clustered in three layers in a single triangle-base pyramid shaped hole.
[0006] Figs. 13-15 illustrate an example of a SERS structure, in which fourteen metal nanoparticles are clustered in three layers in a single square- base pyramid shaped hole.
[0007] Figs. 16-23 present a sequence of views illustrating one example of a process for fabricating a SERS structure, such as a SERS structure shown in Figs. 1 -3, 4-6, 7-9, 10-12 and 13-15.
[0008] Fig. 24 is a flow diagram illustrating an example fabrication process implemented, for example, in the sequence shown in Figs. 16-23.
[0009] The same part numbers designate the same or similar parts throughout the figures. The figures are not necessarily to scale.
[0010] Metal nanoparticle structures can provide substantial surface enhancement for SERS. However, reliably fabricating metal nanoparticle structures that provide repeatable strong surface enhancement may present difficult challenges. The new metal nanoparticle structures provided herein have been developed for SERS to help provide repeatable strong surface enhancement with less difficult fabrication. In one example, the new structure includes a cluster of metal nanoparticles in a hole in the surface of a silicon or other suitable SERS substrate. A "cluster" of nanoparticles as used in this document means a three dimensional group of nanoparticles that are close together. (A single layer of nanoparticles is not a "cluster".) A SERS structure may include a single hole with clustered nanoparticles or an array of holes each with clustered nanoparticles. In one specific implementation, the hole is tapered and filled with a nanoparticle cluster having fewer nanoparticles across the bottom, narrower part of the hole and more nanoparticles across the top, broader part of the hole.
[0011] Three dimensional nanoparticle assemblies formed by clustering nanoparticles in holes in the surface of a SERS substrate may be desirable in many SERS applications to provide multiple orientations of coupled nanoparticles. SERS enhancement is strengthened when light interacts with neighboring nanoparticles in such a way that the polarization of the light is aligned to a dipole axis of the nanoparticles. Multiple dipole orientations increase the potential for incoming light to favorably interact with the nanoparticle clusters for a strong SERS signal.
[0013] These and other examples shown and described herein illustrate but do not limit the scope of the patent, which is defined in the Claims following this Description.
[0014] Figs. 1 -3 illustrate one example of a structure 10 for SERS. The plan view of Fig. 1 illustrates a structure 10 with a single hole 12 in a silicon or other suitable SERS substrate 14. Referring to Figs. 1 -3, structure 10 includes a cluster 16 of metal nanoparticles 18 in hole 12. In the example shown, hole 12 is tapered in the shape of a truncated cone. A correspondingly tapered cluster 16 includes fewer nanoparticles 18 in a narrower part of hole 12 and more nanoparticles 18 in a broader part of hole 12. Also, in this example, hole 12 and nanoparticles 18 are configured with respect to one another such that a total of ten nanoparticles 18 fill hole 12 in two layers 20, 22 - three nanoparticles 18 in bottom layer 20 and seven nanoparticles 18 in top layer 22.
[0015] Strong SERS enhancement results when light interacts with neighboring nanoparticles in such a way that the polarization of the light is aligned to a dipole axis of the nanoparticles. In one example, because it is difficult to control the polarization of incoming light without filtration, the larger range of dipole orientations provided by a three dimensional nanoparticle assembly such as cluster 16 may increase the potential for incoming light to favorably interact with the nanoparticles to generate a strong SERS signal. Consequently, a nanoparticle cluster 16 may help reduce the dependence of surface enhancement on the polarization/incidence angle of the incoming light, allowing a more flexible SERS structure design with fewer criteria to be satisfied by the excitation source. In addition, the sidewalls of a tapered hole 12 reflect incident light at an angle to the collections optics, rather than directly back into the collection optics. Collection optics usually share some components with the excitation path and, therefore, filters are used to remove a stronger laser signal to better detect a weaker Raman signal. By reflecting the laser signal away from the collection optics, the use of filters may be reduced, allowing more simple and thus less expensive collection optics.
[0016] Suitable metals for SERS nanoparticles 18 include gold (Au), silver (Ag), copper (Cu) and other such plasmon supporting metals. "Metal" as used in this document includes elemental metals, metal alloys and metal compounds suitable for use in SERS. Although spherical nanoparticles 18 are shown, other particle shapes may be used, including randomly shaped particles. A
[0017] As discussed below with reference to Figs. 16-23, nanoparticles 18 may be processed to self-assemble in a cluster 16 conforming to the shape of hole 12 and not on surface 24 surrounding hole 12. Hole 12 may be sized and shaped to cluster nanoparticles 18 in the desired configuration, for example a two layer cluster 16 of ten nanoparticles 18 shown in Figs. 1 -3.
[0019] In another example, shown in Figs. 7-9, structure 10 includes a triangle-base pyramid shaped hole 12 sized to contain a two-layer cluster 16 of four nanoparticles.
[0020] In another example, shown in Figs. 10-12, structure 10 includes a triangle-base pyramid shaped hole 12 sized to contain a three-layer cluster 16 of ten nanoparticles.
[0021] In another example, shown in Figs. 13-15, structure 10 includes a square-base pyramid shaped hole 12 sized to contain a three-layer cluster 16 of fourteen nanoparticles.
[0022] Although the number of nanoparticles 18 in a cluster 16 may vary, it is expected that a cluster 16 with fewer than three nanoparticles 18 or a cluster 16 with more than ten nanoparticles 18 across the top (broadest part) of a hole 12 will not be effective to help improve surface enhancement. Other suitable shapes for a hole 12 are possible and, while it is expected that a SERS structure 10 with clustered nanoparticles 18 usually will be implemented with tapered holes 12 to achieve the desired surface enhancement, it may be possible to use holes with parallel walls (not tapered) effectively in some implementations.
[0023] Figs. 16-23 present a sequence of views illustrating one example of a process for making a SERS nanostructure 10 with three dimensional nanoparticle clusters 16. Fig. 24 is a flow diagram illustrating a fabrication process 100 implemented, for example, in the sequence shown in Figs. 16-23. Tapered holes 12 are formed in a silicon or other suitable SERS substrate 14 (block 102 in Fig. 24), for example by photolithographic masking and etching techniques that may also be used in semiconductor fabrication. In Fig. 16, substrate 14 is masked (mask 30) in the desired pattern for holes 12. In Fig. 17, substrate 14 is etched to form tapered holes 12. Etch mask 30 is removed in Fig. 18.
[0024] A reflective layer 26 may be formed on substrate 14, as shown in Fig. 19, if desired to improve light scattering (as described above). Reflective layer 26 usually will be gold or another metal and, thus, a dielectric layer 28 may be formed on layer 26 as shown in Fig. 20 to prevent an electrical connection between layer 26 and metal nanoparticles 18.
[0025] In Fig. 21 , nanoparticles 18 are deposited into holes 12 by drawing a solution 32 containing nanoparticles 18 across substrate 14 (block 104 in Fig. 24). Fig. 22 is a detail view from Fig. 21 showing the deposition of nanoparticles 18 into one of the holes 12 in substrate 14. Solution 32 is dispensed on to substrate 14 and a plate 34 placed on substrate 14 to create a thin film of solution 32. By drawing plate 34 slowly across substrate 14, the rate of evaporation of liquid from solution 32 can be controlled so that nanoparticles 18 assemble preferentially in holes 12 and not on surface 24 surrounding the holes. Fig. 23 shows a cluster 16 of nanoparticles 18 in a hole 12 after deposition in Figs. 21 and 22.
[0026] Suitable solvents for depositing metal nanoparticles 18 include, for example, water and ethanol. While the draw rate for plate 34 will vary depending on the type of solvent and other process parameters, for gold nanoparticles 18 dispersed in water it is expected that a draw rate of 1 mm/minute or slower will be adequate to allow nanoparticles 18 to self- assemble into clusters 16 preferentially in holes 12 for the configurations shown in Figs. 1 -15.
[0027] As noted at the beginning of this Description, the examples shown in the figures and described above illustrate but do not limit the scope of the patent. Other examples are possible. Therefore, the foregoing description should not be construed to limit the scope of the patent, which is defined in the following Claims.

中文:
[0001]表面增强拉曼光谱(SERS)是一种表面敏感技术,其通过吸附在粗糙金属表面或纳米结构上的分子来增强拉曼散射。
[0002]图1-图3图示了SERS结构的示例,其中,十个金属纳米颗粒在单个圆锥形孔中聚集成两层。
[0003]图4-图6图示了SERS结构的示例,其中,五个金属纳米颗粒在多个方形基座的金字塔形孔中聚集成两层。
[0004]图7-图9图示了SERS结构的示例,其中,四个金属纳米颗粒在单个三角形基座的金字塔形孔中聚集成两层。
[0005]图10-图12图示了SERS结构的示例,其中,十个金属纳米颗粒在单个三角形基座的金字塔形孔中聚集成三层。
[0006]图13-图15图示了SERS结构的示例,其中,十四个金属纳米颗粒在单个方形基座的金字塔形孔中聚集成三层。
[0007]图16-图23呈现了视图序列,其图示了用于制造SERS结构的工艺的一个示例,比如图1-图3、图4-图6、图7-图9、图10-图12和图13-图15中所示的SERS结构。
[0008]图24是图示了例如在图16-图23中所示的序列中实现的示例制造工艺的流程图。
[0009]在整个附图中,相同的部件标号表示相同或相似的部件。附图不一定是按比例的。
[0010]金属纳米颗粒结构可以为SERS提供实质的表面增强。然而,可靠地制造提供可重复的强表面增强的金属纳米颗粒结构可能会带来困难的挑战。本文所提供的新型金属纳米颗粒结构已经开发用于SERS,以帮助在不太难于制造的情况下提供可重复的强表面增强。在一个示例中,新的结构包括在硅或其它合适的SERS基底的表面中的孔中的金属纳米颗粒簇。本文档中使用的纳米颗粒“簇”是指紧密在一起的纳米颗粒的三维组。(单层纳米颗粒不是“簇”)。SERS结构可以包括具有聚集的纳米颗粒的单个孔或者每个具有聚集的纳米颗粒的孔阵列。在一个具体的实现中,孔是锥形的并且填充有纳米颗粒簇,有较少的纳米颗粒穿过孔的较窄部分——底部,而有较多的纳米颗粒穿过孔的较宽部分——顶部。
[0011]通过将纳米颗粒聚集在SERS基底的表面中的孔中形成的三维纳米颗粒组装在许多SERS应用中可以是可期望的,以提供耦合的纳米颗粒的多个取向。当以光的偏振与纳米颗粒的偶极轴对准的这样方式光与相邻的纳米颗粒相互作用时,SERS增强得到了加强。多个偶极取向增加了入射光与纳米颗粒簇有利地相互作用以获得强SERS信号的潜力。
[0013]这里示出和描述的这些和其他示例说明而非限制在本说明书之后的权利要求中定义的专利的范围。
[0014]图1-图3图示出了用于SERS的结构10的一个示例。图1的平面视图图示了在硅或其它合适的SERS基底14中有单个孔12的结构10。参见图1-图3,结构10包括孔12中的金属纳米颗粒18的簇16。在所示的示例中,孔12是以截圆锥型的锥形。相应的锥形簇16在孔12的较窄部分中包括较少的纳米颗粒18,并且在孔12的较宽部分中具有更多的纳米颗粒18。此外,在该示例中,孔12和纳米颗粒18相对于彼此配置,使得总共十个纳米颗粒18在两层20、22中填充孔12——底层20中三个纳米颗粒18以及顶层22中七个纳米颗粒18。
[0015]当以光的偏振与纳米颗粒的偶极轴对准的这样方式光与相邻的纳米颗粒相互作用时,产生强的SERS增强。在一个示例中,由于难以在不过滤的情况下控制入射光的偏振,由诸如簇16之类的三维纳米颗粒组装提供的较大范围的偶极取向可以增加入射光有利地与纳米颗粒相互作用以产生强SERS信号的潜力。因此,纳米颗粒簇16可以帮助减少表面增强对入射光的偏振/入射角的依赖性,从而允许更灵活的SERS结构设计,在该设计中激励源要满足的标准较少。此外,锥形孔12的侧壁将入射光反射以一定角度反射到收集光学器件,而不是直接反射回收集光学器件中。采集光学器件通常与激励路径共享一些组件,并且因此,将滤波器用于去除较强的激光信号以更好地检测较弱的拉曼信号。通过将激光信号反射离开收集光学器件可以减少滤光器的使用,从而允许更简单且因而更便宜的收集光学器件。
[0016]用于SERS纳米颗粒18的合适的金属包括金(Au)、银(Ag)、铜(Cu)和其它这种等离子体支撑金属。本文档中使用的“金属”包括适用于SERS中的元素金属、金属合金和金属化合物。虽然示出了球形纳米颗粒18,但是也可以使用其它颗粒形状,包括随机形状的颗粒。本文档中使用的“纳米颗粒”是指具有范围在10nm至200nm的至少一个维度的颗粒。
[0017]如下面参考图16-图23所讨论的,纳米颗粒18可以被处理以自组装在符合孔12的形状的簇16中,而不是自组装在围绕孔12的表面24上。可以将孔12的尺寸和形状以希望配置设计成纳米颗粒簇18,例如图1-图3中所示的十个纳米颗粒18的两层簇16。
[0019]在另一示例中,如图7-图9中所示,结构10包括被设计尺寸以包含四个纳米颗粒的双层簇16的三角形基座的金字塔形孔12。
[0020]在另一示例中,如图10-图12中所示,结构10包括被设计尺寸以包含十个纳米颗粒的三层簇16的三角形基座的金字塔形孔12。
[0021]在另一示例中,如图13-图15中所示,结构10包括被设计尺寸以包含十四个纳米颗粒的三层簇16的方形基座的金字塔形孔12。
[0022]虽然簇16中的纳米颗粒18的数量可以变化,但是可以预期,具有少于三个纳米颗粒18的簇16或具有多于十个纳米颗粒18的簇16穿过孔12的顶部(最宽部分)将对帮助改善表面增强无效。针对孔12的其它合适的形状是可能的,并且虽然可以预期通常用锥形孔12来实现具有聚集的纳米颗粒18的SERS结构10以实现期望的表面增强,但是在一些实现中可以有效地使用具有平行壁(非锥形)的孔。
[0023]图16-图23呈现了视图序列,其图示了用于制造具有三维纳米颗粒簇16的SERS纳米结构10的工艺的一个示例。图24是图示了例如在图16-图23中所示的序列中实施的制造工艺100的流程图。例如通过也可用于半导体制造的光刻掩模和蚀刻技术,锥形孔12形成在硅或其它合适的SERS基底14(图24中的框102)中。在图16中,以针对孔12所需的图案对基底14进行掩模处理(掩模30)。在图17中,对基底14进行蚀刻以形成锥形孔12。在图18中去除蚀刻掩模30。
[0024]如图19中所示,如果希望改进光散射(如上所述),则可以在基底14上形成反射层26。反射层26通常将是金或另一种金属,并且因此,如图20中所示,可以在层26上形成电介质层28,以防止层26和金属纳米颗粒18之间的电连接。
[0025]在图21中,通过将包含有纳米颗粒18的溶液32拉动穿过基底14,将纳米颗粒18沉积到孔12中(图24中的框104)。图22是来自图21的细节视图,示出了纳米颗粒18向基底14中若干孔12之一的沉积。将溶液32分配到基底14上并且将板34放置在基底14上,以创建出溶液32的薄膜。通过将板34缓慢地拉动穿过基板14,可以控制来自溶液32的液体的蒸发速率,以使得纳米颗粒18优先组装在孔12中而不是组装在围绕孔的表面24上。图23示出了在图21和图22中的沉积之后的孔12中的纳米颗粒18的簇16。
[0026]例如,用于沉积金属纳米颗粒18的合适的溶剂包括水和乙醇。虽然板34的拉动速率将取决于溶剂的类型和其它工艺参数而变化,但是对于分散在水中的金纳米颗粒18来说,可以预期1mm/分钟或更慢的拉伸速率将足以允许纳米颗粒18优选地在孔12中自组装成簇16以用于如图1-图15中所示的配置。
[0027]如在本说明书开头所指出的,附图中和上面所描述的示例说明但不限制本专利的范围。其他示例也是可能的。因此,前面的描述不应被解释为限制在所附权利要求中限定的本专利的范围。