Solid State NMR Spectroscopy a Valuable Technique for Structural Insights of Advanced Thin Film Materials: A Review

Abstract

Solid-state NMR has proven to be a versatile technique for studying the chemical structure, 3D structure and dynamics of all sorts of chemical compounds. In nanotechnology and particularly in thin films, the study of chemical modification, molecular packing, end chain motion, distance determination and solvent-matrix interactions is essential for controlling the final product properties and applications. Despite its atomic-level research capabilities and recent technical advancements, solid-state NMR is still lacking behind other spectroscopic techniques in the field of thin films due to the underestimation of NMR capabilities, availability, great variety of nuclei and pulse sequences, lack of sensitivity for quadrupole nuclei and time-consuming experiments. This article will comprehensively and critically review the work done by solid-state NMR on different types of thin films and the most advanced NMR strategies, which are beyond conventional, and the hardware design used to overcome the technical issues in thin-film research.

Keywords: magic angle spinning (MAS); polarization enhancement; sensitivity boosting; solid-state NMR spectroscopy; solvent-matrix interactions; thin films.

Figure 1

¹¹B NMR spectrum for the (111) film, the fitted red curve shows 2 boron sites, which are identified as B(1) blue and B(2) green, respectively. Reproduced with permission [73]. Copyright 2006, Taylor & Francis. www.tandfonline.com. (accessed on April 2021).

Figure 2

(a) ¹⁷O NMR spectrum for CeO₂-SrTiO₃ nanopillar lift-off isotopically enriched films. (b,c) DFT-calculated isotopic chemical shifts as a function of distance from the interface of different interfacial structures. Three structure interfaces of the simple model and a low-energy structure were found from random structure searching in 0° interface (b) and 45° interface (c). Reproduced with permission. [76] Copyright 2020, American Chemical Society.

Figure 3

³¹P CSA NMR spectra for POPy₂ film with (black) and without (gray) DNP enhancement: (a) vacuum-deposited on SiO₂ (12 sheets), (b) drop-cast on SiO₂ (15 sheets) and (c) vacuum-deposited on SiO₂ (1 sheets). Reproduced with permission. [111] Copyright 2017, Angewandte Chemie, Wiley-VCH.

Figure 4

(a) ¹³C DNP-CPMAS NMR spectra for DPP-DTT bulk polymer with (upper spectrum) and without (lower spectrum) DNP enhancement. (b) ¹H-¹³C DNP-HETCOR NMR spectra for DPP-DTT bulk polymer. (c) ¹H-¹³C DNP-HETCOR NMR spectra for the drop-cast film. (d) ¹³C DNP-CPMAS NMR spectra for DPP-DTT drop-cast (red) and spin-coated (blue) films. Reproduced with permission. [112] Copyright 2017, The Royal Society of Chemistry.

Figure 5

(a) A schematic description for the disk MAS design, including its fit in the NMR probe (b) a side and front view of a 4 mm pencil type rotor (Agilent technology, Inc.) with an attached 12 mm quartz disk, and (c) a photograph of the square quartz substrate. Reproduced with permission. [124] Copyright 2011, Elsevier.

Figure 6

Parameters that are varied for optimization of the resolution. Reproduced with permission. [134] Copyright 2009, Elsevier.

Figure 7

(a) A schematic description of the MRFM setup and (b) showing the original cantilever tip where the sample is deposited (appearing dark). Reproduced with permission. [77] Copyright 2013, Nature.

Figure 8

A schematic description of the β-NMR setup where the experiment starts with a 4 s long ⁸Li⁺ pulse, followed by the β particles emitted anisotropically during the decay of spin-polarized nuclei. The β trajectory (orange line) is shown hitting the detector. Reproduced with permission. [149] Copyright 2017, The Royal Society of Chemistry.