Quantifying the Short-Range Order in Amorphous Silicon by Raman Scattering Priyanka Yogi, † Manushree Tanwar, † Shailendra K. Saxena,* ,‡ Suryakant Mishra, § Devesh K. Pathak, Anjali Chaudhary, Pankaj R. Sagdeo, and Rajesh Kumar* Material Research Laboratory, Discipline of Physics & MEMS, Indian Institute of Technology Indore, Simrol-453552, India * S Supporting Information ABSTRACT: Quantification of the short-range order in amorphous silicon has been formulized using Raman scattering by taking into account established frameworks for studying the spectral line-shape and size dependent Raman peak shift. A theoretical line-shape function has been proposed for representing the observed Raman scattering spectrum from amorphous-Si-based on modified phonon confinement model framework. While analyzing modified phonon confinement model, the term “confinement size” used in the context of nanocrystalline Si was found analogous to the short-range order distance in a-Si thus enabling one to quantify the same using Raman scattering. Additionally, an empirical formula has been proposed using bond polarizability model for estimating the short-range order making one capable to quantify the distance of short-range order by looking at the Raman peak position alone. Both the proposals have been validated using three different data sets reported by three different research groups from a-Si samples prepared by three different methods making the analysis universal. N anoscience and nanotechnology has been established as an important area, which makes it equally important to characterize these materials which were considered amorphous for long. 1,2 At the junction of the (poly-)crystalline and amorphous, in a particular crystallite size window, 3,4 a size- dependent property variation was observed, which marks the domain of the nanoscience. 5,6 The length of ordered material 7 (in the crystallinity) remained the distinguishing parameter between the three phases of solid, 8 crystalline, 9,10 nanocrystal- line, 11 and amorphous, 12 with crystalline material having the longest range of order of crystallinity, whereas amorphous material 13 has the least. The distance up to which a (poly- )crystalline solid maintains the crystallinity defines the degree of order, 14 which is quantified by the crystallite size. Though the crystallite size quantifies the degree of order in crystalline materials, ambiguity remains inherently, while quantifying the term in amorphous material as the range of the order is rather “short” and usually not defined even empirically. Whereas, in nanocrystalline materials the crystallite size comparable to the Bohr’s radius 15,16 declares the onset of the “nano” regime and can be defined as the distance of the range of order. Such kind of quantification of the degree of order may prove to be of scientific and technological importance and thus needs attention. As an example, it is often observed that efficiency of amorphous silicon (a-Si) solar cells 17,18 depends on the method of material preparation though the actual player responsible for this variation is unknown. It is possible to see a correlation between the quantified short-range order and solar cell efficiency thus will be helpful in designing an appropriate a- Si device. Additionally, quantification of the short-range order in amorphous materials may help in identifying any possible scientific information in this gray area, which may lead to great discoveries as in the case of nanoscience. Presence of order, whether short-range or long-range, can be examined by X-ray diffraction (XRD) qualitatively but can not be quantified by this method. Raman scattering, 19-21 which has been established as a widely used versatile spectroscopic tool, may prove to be just appropriate for the purpose because of its various scientific merits. The only disadvantage, being a weak phenomenon, has been taken care of in the instrumentation because of the availability of very good source and detectors making it an unmatchable characterization tool used by scientists across all the disciplines. Raman scattering is not only a probe to study the phase identification, 22,23 chemical compositions, 24,25 and level of doping 26,27 but it also has shown a promising potential for acting as a sensitive probe to monitor various physical phenomena taking place at microscopic levels, such as confinement, 21,28-31 defect structures, and crystalline nature of materials. 32 Because of its immense advantages and broader acceptability, Raman spectroscopy has not lagged behind even in understanding di fferent phenomena in comparatively newer but exceptionally important field of nanosciences and nanotechnology. 33,34 At times, Raman spectroscopy has been proved to be superior to other methods Received: March 26, 2018 Accepted: June 1, 2018 Article pubs.acs.org/ac Cite This: Anal. Chem. XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.analchem.8b01352 Anal. Chem. XXXX, XXX, XXX-XXX