Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Straße 9, D-07745 Jena, Germany.
Chem Soc Rev. 2017 Jul 3;46(13):3922-3944. doi: 10.1039/c7cs00203c.
Recent years have seen tremendous improvement of our understanding of high resolution reachable in TERS experiments, forcing us to re-evaluate our understanding of the intrinsic limits of this field, but also exposing several inconsistencies. On the one hand, more and more recent experimental results have provided us with clear indications of spatial resolutions down to a few nanometres or even on the subnanometre scale. Moreover, lessons learned from recent theoretical investigations clearly support such high resolutions, and vice versa the obvious theoretical impossibility to evade high resolution from a purely plasmonic point of view. On the other hand, most of the published TERS results still, to date, claim a resolution on the order of tens of nanometres that would be somehow limited by the tip apex, a statement well accepted for the past 2 decades. Overall, this now leads the field to a fundamental question: how can this divergence be justified? The answer to this question brings up an equally critical one: how can this gap be bridged? This review aims at raising a fundamental discussion related to the resolution limits of tip-enhanced Raman spectroscopy, at revisiting our comprehension of the factors limiting it both from a theoretical and an experimental point of view and at providing indications on how to move the field ahead. It is our belief that a much deeper understanding of the real accessible lateral resolution in TERS and the practical factors that limit them will simultaneously help us to fully explore the potential of this technique for studying nanoscale features in organic, inorganic and biological systems, and also to improve both the reproducibility and the accuracy of routine TERS studies. A significant improvement of our comprehension of the accessible resolution in TERS is thus critical for a broad audience, even in certain contexts where high resolution TERS is not the desired outcome.
近年来，我们对 TERS 实验中可达的高分辨率的理解有了巨大的提高，这迫使我们重新评估我们对该领域固有限制的理解，但也暴露了一些不一致之处。一方面，越来越多的最新实验结果为我们提供了明确的迹象，表明分辨率可低至几纳米甚至亚纳米尺度。此外，最近的理论研究的经验教训清楚地支持了如此高的分辨率，反之亦然，从纯等离子体的角度来看，规避高分辨率在理论上是不可能的。另一方面，到目前为止，大多数发表的 TERS 结果仍然声称分辨率在几十纳米左右，这在某种程度上受到尖端顶点的限制，这一说法在过去 20 年中得到了很好的认可。总的来说，这使得该领域提出了一个基本问题：这种分歧如何得到证明？这个问题引出了一个同样关键的问题：如何弥合这一差距？本文旨在提出与针尖增强拉曼光谱分辨率限制相关的基本讨论，重新审视我们从理论和实验角度理解限制它的因素，并提供如何推动该领域前进的指示。我们相信，对 TERS 中实际可达到的横向分辨率以及限制这些分辨率的实际因素有更深入的了解，将有助于我们充分挖掘该技术在研究有机、无机和生物系统中纳米级特征的潜力，同时提高常规 TERS 研究的重现性和准确性。因此，对于广大读者来说，提高我们对 TERS 中可达到分辨率的理解具有重要意义，即使在某些不希望得到高分辨率 TERS 的情况下也是如此。
