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Fluorine-doped tin oxide (FTO) thin films were deposited on glass substrates using ultrasonic spray pyrolysis (USP) at a fixed substrate temperature of 400 &#176;C and various Fluorine/Tin (F/Sn) atomic ratios of 0, 0.1, 0.5, and 1.0. Effects of F/Sn atomic ratios on structural-morphological, compositional, electrical, optical, and nanomechanical properties of the FTO thin films were systematically studied. The FTO films exhibited a tetragonal structure with preferred orientations of (110), (200), and (211), and polycrystalline morphology with spear-like or coconut shell-like particles on the surfaces. The presence of F-doping was confirmed by XPS results with clear F1s peaks, and F-concentration was determined to be 0.7% for F/Sn = 0.1 and 5.1% for F/Sn = 0.5. Moreover, the resistivity of FTO films reduced remarkably from 4.1 mΩcm at F/Sn = 0 to 0.7 mΩcm at F/Sn = 1, primarily due to the corresponding increase of carrier concentration from 2 &#215; 10²⁰ cm^&#8722;3 to 1.2 &#215; 10²¹ cm^&#8722;3. The average optical transmittance of the films prepared at F/Sn of 0&#8722;0.5 was over 90%, and it decreased to 84.4% for the film prepared at F/Sn = 1. The hardness (<i>H</i>) and Young&#8217;s modulus (<i>E</i>) of the FTO films increased when the F/Sn ratios increased from 0 to 0.5, reaching maximum values of <i>H</i> = 12.3 &#177; 0.4 GPa, <i>E</i> = 131.7 &#177; 8.0 GPa at F/Sn = 0.5. Meanwhile, the <i>H</i> and <i>E</i> reduced considerably when the F/Sn ratio further increased to 1.0, following the inverse Hall-Petch effect approximately, suggesting that the grain boundary effect played a primary role in manipulating the nanomechanical properties of the FTO films. Furthermore, favorable mechanical properties with large <i>H/E_f</i> and <inline-formula> <math display="inline"> <semantics> <mrow> <msup> <mi>H</mi> <mn>3</mn> </msup> <mo>/</mo> <msubsup> <mi>E</mi> <mi>f</mi> <mn>2</mn> </msubsup> </mrow> </semantics> </math> </inline-formula> ratios were found for the FTO film prepared at F/Sn = 0.5, which possessed high crystallinity, large grain size, and compact morphology.