Eng. Proc. 2021, 4, 13. https://doi.org/10.3390/Micromachines2021-09544 www.mdpi.com/journal/engproc Abstract Hollow AFM Cantilever with Holes † Wujoon Cha *, Matthew F. Campbell, Akshat Jain and Igor Bargatin * Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104, USA; cammat@seas.upenn.edu (M.F.C.); akshatj@seas.upenn.edu (A.J.) * Correspondence: wujoon@seas.upenn.edu (W.C.); bargatin@seas.upenn.edu (I.B.) † Presented at the 1st International Conference on Micromachines and Applications, 15–30 April 2021; Available online: https://micromachines2021.sciforum.net/. Keywords: atomic force microscopy (AFM); flexural mode; torsional mode; hollow cantilever Since its invention, atomic force microscopy (AFM) has enhanced our understanding of physical and biological systems at sub-micrometer scales. As the performance of AFM depends greatly on the properties of the cantilevers, many works have been carried out to improve cantilevers by means of modifying their geometries via lithography [1] and ion beam milling [2,3] that primarily involve opening areas on the cantilever’s face, result- ing in high resonant frequency, low spring constant, and low hydrodynamic damping. Similar improvements were achieved using a hollow beam cantilever with nanoscale wall thickness [4]. In fact, the combination of these two approaches (in-plane opening and hol- low beam) can result in unique metamaterial structures with tunable properties [5], but it has not been explored for AFM application. In this work, we explore hollow AFM canti- levers with in-plane modifications. We accomplish this by (1) taking a commercial solid silicon cantilever, (2) making a different number of holes on the face using pulsed laser micromachining, and (3) coating it with alumina using atomic layer deposition and etch- ing the internal silicon which results in a hollow probe with holes. We present the effects of these modifications on the cantilever’s resonant frequency, quality factor, and spring constant in air. This work provides an insight into strategies for tuning a cantilever’s prop- erties for both flexural and torsional modes. Supplementary Materials: The following are available online at https://www.mdpi.com/arti- cle/10.3390/Micromachines2021-09544/s1. References 1. Nilsen, M.; Port, F.; Roos, M.; Gottschalk, K.-E.; Strehle, S. Facile Modification of Freestanding Silicon Nitride Microcantilever Beams by Dry Film Photoresist Lithography. J. Micromech. Mi- croeng. 2019, 29, 025014. 2. Bull, M.S.; Sullan, R.M.A.; Li, H.; Perkins, T.T. Improved Single Molecule Force Spectroscopy Using Micromachined Cantilevers. ACS Nano 2014, 8, 4984–4995. 3. Hodges, A.R.; Bussmann, K.M.; Hoh, J.H. Improved Atomic Force Microscope Cantilever Per- formance by Ion Beam Modification. Rev. Sci. Instrum. 2001, 72, 3880–3883. 4. Cha, W.; Nicaise, S.; Lilley, D.; Lin, C.; Bargatin, I. Hollow Flexural Resonators with Nanoscale Thickness. In Solid-State Sensors, Actuators and Microsystems Workshop, Hilton Head Island, South Carolina, 2018; Transducer Research Foundation: Hilton Head Island, SC, USA, 2018; pp. 232– 233. 5. Lin, C.; Nicaise, S.M.; Lilley, D.E.; Cortes, J.; Jiao, P.; Singh, J.; Azadi, M.; Lopez, G.G.; Metzler, M.; Purohit, P.K.; et al. Nanocardboard as a Nanoscale Analog of Hollow Sandwich Plates. Nat. Commun. 2018, 9, 4442. Citation: Cha, W.; Campbell, M.F.; Jain, A.; Bargatin, I. Hollow AFM Cantilever with Holes. Eng. Proc. 2021, 4, 13. https://doi.org/10.3390/ Micromachines2021-09544 Academic Editor: Ion Stiharu Published: 14 April 2021 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institu- tional affiliations. Copyright: © 2021 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (http://crea- tivecommons.org/licenses/by/4.0/).