changes

\documentclass[aip, nobibnotes, nofootinbib, citeautoscript, reprint, superscriptaddress]{revtex4-2}

\documentclass[aip, nobibnotes, nofootinbib, citeautoscript, showkeys, reprint, nolongbibliography, superscriptaddress]{revtex4-2}

\usepackage{amsmath, amssymb}

\usepackage[paperheight=10.98in,paperwidth=8.27in,top=0.5in,bottom=0.5in,right=0.5in,left=0.5in]{geometry}

\usepackage{graphicx}% Include figure files

\usepackage{dcolumn}% Align table columns on decimal point

\usepackage[paperheight=10.87in,paperwidth=8.27in,margin=0.75in]{geometry}

\usepackage[version=3]{mhchem}

\usepackage{multirow}

\usepackage{sourcecodepro, sourcesanspro, sourceserifpro}

%\usepackage{kpfonts}

\usepackage[T1]{fontenc}

\usepackage{sfmath, sansmath, sansmathaccent}

\usepackage[protrusion=true,expansion=true,final]{microtype}

		We thus demonstrate how 4D-STEM can bridge the gap between traditional imaging and diffractometry techniques, providing crystallographic information at a spatial resolution that was previously unattainable.

	\end{abstract}

	\keywords{4D-STEM, Strain Mapping, Nanoparticle Catalysts, Alloy Catalysts}

    \maketitle

	\section{\label{sec:intro}Introduction}

		However, the oxygen reduction reaction (ORR) component of this redox reaction needs to be catalyzed \cite{strain_np_surface,HP_Pt_ORR,PEMFC_review}. 

		Among the commonly used catalysis systems, platinum group metals (PGMs) such as platinum, palladium are some of the most widely used systems\cite{pgm_review}. 

		\subsection{\label{ssec:why_strain}The importance of measuring strain in catalyst nanoparticles}

		%\subsection{\label{ssec:why_strain}The importance of measuring strain in catalyst nanoparticles}

		However, the issue with PGM catalysts is that such elements have low crustal abundance and are finite resources\cite{pt_abundance}. 

		Thus, there has a significant research effort to decrease the PGM content of catalyst materials. Among such systems, platinum-cobalt alloys offer performance close to pure PGM metal catalysts while reducing the PGM loading \cite{core_shell_ordered_np,ultralow_ptco}. 

		Such systems have been observed to demonstrate high mass activity that is maintained for over 25,000 cycles\cite{the_joule_paper}. 

		However, the biggest question in nanoparticle catalysts has been the role of surface strain in catalytic activity. 

		It's well known that increasing bond length increases catalytic activity, due to a weakening of the bond strength\cite{atomic_distance_review}, but statistical quantification of surface strain in nanoparticles still remains challenging.

		\subsection{\label{ssec:how_strain}Measuring strain with electron microscopy}

		%\subsection{\label{ssec:how_strain}Measuring strain with electron microscopy}

		Transmission Electron microscopy (TEM), especially in the scanning (STEM) mode, is a potent tool for studying nanoparticles' chemical composition and lattice structure, due to the high spatial resolution available. 

		Multiple STEM studies have been performed on nanoparticles, including catalyst systems similar to the platinum-cobalt alloy systems studied in this work\cite{strain_tem_vs_stem, original_gpa, gpa_strain, hrem_strain, ef_cbed_strain, PtCo_strain_haadf}. 

		When combined with multiple tilts, STEM can be used to generate three-dimensional atom positions maps to generate strain tensors across all the major crystallographic axes\cite{tomo_strain}. 

		The first is that strain measurements, even with aberration-corrected STEM, are highly susceptible to drift distortions, which arise from mechanical vibrations, thermal instabilities, and so on \cite{original_gpa, gpa_strain}. 

		While advancements in stage design and post-acquisition drift correction algorithms have mitigated this problem to some extent, it's still non-negligible \cite{revstem, colin_drift,lewys_drift,kevin_drift}. 

		\subsection{\label{ssec:why_4dstem}Why 4D-STEM?}

		%\subsection{\label{ssec:why_4dstem}Why 4D-STEM?}

		One proposed solution for this issue has been 4D-STEM, where the entire convergent beam electron diffraction (CBED) pattern is collected at every single scan position, with results demonstrating that the errors in 4D-STEM measurement are significantly lower than the errors from even drift-corrected annular dark field (ADF) STEM imaging, even when looking at the same particle\cite{4dstem_nanoparticles}.

		This results in a four-dimensional dataset, where two of the data dimensions correspond to a grid of scan positions, and two of the dimensions correspond to the CBED pattern collected at that particular position\cite{colin_review}. 

		With advancements in computational hardware and high-speed electron detectors, 4D-STEM experiments are becoming increasingly common, with applications in strain metrology, phase reconstruction, and symmetry quantification \cite{nbed_strain1, neg_capacitance, ptycho_deep,ncem_camera}.