{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/78308"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/78308","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Mechanisms of focused ion beam (FIB) material removal and rearrangement at high beam flux","abstract":"Focused ion beam (FIB) is widely used as a material removal tool for applications ranging from electron microscope sample preparation to nanopore processing for DNA sequencing. Despite the wide spread use of FIB, the basic material removal mechanisms are not well understood and may depend upon FIB operations. We present the first complete atomistic simulation of high-flux FIB using large-scale parallel molecular dynamics (MD) simulations of nanopore fabrication in freestanding thin films. We focus on the root mechanisms as described by large-scale MD simulations of FIB and describe the role of explosive boiling and Marangoni effect as a material removal and rearrangement mechanism and the mixing and transport that occur at the atomic scale. Nanopore fabrication using FIB is typically understood to occur via sputter erosion. While this theory may describe low-flux systems, where individual ion impacts are sufficiently separated in time to consider them as independent events, it cannot explain the thermal events observed during high flux simulations. A dimensionless number is introduced, which is constructed from the key variables including material properties and FIB parameters. This number suggests strong thermal effects when it is greater than unity. Similarly, our detailed MD simulations suggest that for ion beam fluxes above a threshold level, the dominant mechanism of material removal changes to a significantly accelerated, thermally dominated process, consistent with our dimensional analysis. During this time, the target is heated faster than it cools, leading to melting, with local temperatures approaching the critical temperature. This leads to an explosive boiling of the target material with spontaneous bubble formation. Atomic mass is rapidly rearranged via bubble growth and coalescence and material removal is orders of magnitude faster than would occur by simple sputtering. For a range of ion intensities in a realistic configuration, a recirculating melt region develops, which is seen to flow at high speed though symmetrically rather than driven by the ion momentum flux. Relevant length and time scales and estimated physical properties of silicon under these extreme conditions suggest that thermocapillary effects are important. A flow model with a Marangoni forcing term, based upon the temperature gradient from the atomistic simulation, confirms the presence of thermocapillary effect by reproducing the flow.","abstract_html":"Focused ion beam (FIB) is widely used as a material removal tool for applications ranging from electron microscope sample preparation to nanopore processing for DNA sequencing. Despite the wide spread use of FIB, the basic material removal mechanisms are not well understood and may depend upon FIB operations. We present the first complete atomistic simulation of high-flux FIB using large-scale parallel molecular dynamics (MD) simulations of nanopore fabrication in freestanding thin films. We focus on the root mechanisms as described by large-scale MD simulations of FIB and describe the role of explosive boiling and Marangoni effect as a material removal and rearrangement mechanism and the mixing and transport that occur at the atomic scale. Nanopore fabrication using FIB is typically understood to occur via sputter erosion. While this theory may describe low-flux systems, where individual ion impacts are sufficiently separated in time to consider them as independent events, it cannot explain the thermal events observed during high flux simulations. A dimensionless number is introduced, which is constructed from the key variables including material properties and FIB parameters. This number suggests strong thermal effects when it is greater than unity. Similarly, our detailed MD simulations suggest that for ion beam fluxes above a threshold level, the dominant mechanism of material removal changes to a significantly accelerated, thermally dominated process, consistent with our dimensional analysis. During this time, the target is heated faster than it cools, leading to melting, with local temperatures approaching the critical temperature. This leads to an explosive boiling of the target material with spontaneous bubble formation. Atomic mass is rapidly rearranged via bubble growth and coalescence and material removal is orders of magnitude faster than would occur by simple sputtering. For a range of ion intensities in a realistic configuration, a recirculating melt region develops, which is seen to flow at high speed though symmetrically rather than driven by the ion momentum flux. Relevant length and time scales and estimated physical properties of silicon under these extreme conditions suggest that thermocapillary effects are important. A flow model with a Marangoni forcing term, based upon the temperature gradient from the atomistic simulation, confirms the presence of thermocapillary effect by reproducing the flow.","abstract_has_math":false,"creators":["Das, Kallol"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Mechanical Engineering","degree_department":null,"school":null,"contributors":["Johnson, Harley T.","Freund, Jonathan B.","Bellon, Pascal","Ertekin, Elif"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015-07-22T22:15:48Z","date_published":"2015-07-22T22:15:48Z","updated_at":"2026-07-22T22:26:11Z","subjects":["surface energy nanopore","DNA sequencing nanopore","high flux focused ion beam (FIB)","Marangoni effect","rapid vaporization","explosive boiling","focused ion beam"],"languages":[],"rights":["Copyright 2015 Kallol Das"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/78308","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Johnson, Harley T.","Freund, Jonathan B.","Bellon, Pascal","Ertekin, Elif"]},{"key":"dc:creator","label":"Author","values":["Das, Kallol"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2015-07-22T22:15:48Z","2015-05","2015-02-03","2015-5"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Mechanical Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["surface energy nanopore","DNA sequencing nanopore","high flux focused ion beam (FIB)","Marangoni effect","rapid vaporization","explosive boiling","focused ion beam"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2015 Kallol Das"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/78308"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Focused ion beam (FIB) is widely used as a material removal tool for applications ranging from electron microscope sample preparation to nanopore processing for DNA sequencing. Despite the wide spread use of FIB, the basic material removal mechanisms are not well understood and may depend upon FIB operations. We present the first complete atomistic simulation of high-flux FIB using large-scale parallel molecular dynamics (MD) simulations of nanopore fabrication in freestanding thin films. We focus on the root mechanisms as described by large-scale MD simulations of FIB and describe the role of explosive boiling and Marangoni effect as a material removal and rearrangement mechanism and the mixing and transport that occur at the atomic scale. Nanopore fabrication using FIB is typically understood to occur via sputter erosion. While this theory may describe low-flux systems, where individual ion impacts are sufficiently separated in time to consider them as independent events, it cannot explain the thermal events observed during high flux simulations. A dimensionless number is introduced, which is constructed from the key variables including material properties and FIB parameters. This number suggests strong thermal effects when it is greater than unity. Similarly, our detailed MD simulations suggest that for ion beam fluxes above a threshold level, the dominant mechanism of material removal changes to a significantly accelerated, thermally dominated process, consistent with our dimensional analysis. During this time, the target is heated faster than it cools, leading to melting, with local temperatures approaching the critical temperature. This leads to an explosive boiling of the target material with spontaneous bubble formation. Atomic mass is rapidly rearranged via bubble growth and coalescence and material removal is orders of magnitude faster than would occur by simple sputtering. For a range of ion intensities in a realistic configuration, a recirculating melt region develops, which is seen to flow at high speed though symmetrically rather than driven by the ion momentum flux. Relevant length and time scales and estimated physical properties of silicon under these extreme conditions suggest that thermocapillary effects are important. A flow model with a Marangoni forcing term, based upon the temperature gradient from the atomistic simulation, confirms the presence of thermocapillary effect by reproducing the flow.","Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2015-07-22 without embargo terms","The student, Kallol Das, accepted the attached license on 2015-02-03 at 16:30.","The student, Kallol Das, submitted this Dissertation for approval on 2015-02-03 at 16:43.","This Dissertation was approved for publication on 2015-02-03 at 17:12.","DSpace SAF Submission Ingestion Package generated from Vireo submission #7707 on 2015-07-22 at 10:29:44","Made available in DSpace on 2015-07-22T22:15:48Z (GMT). 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Despite the wide spread use of FIB, the basic material removal mechanisms are not well understood and may depend upon FIB operations. We present the first complete atomistic simulation of high-flux FIB using large-scale parallel molecular dynamics (MD) simulations of nanopore fabrication in freestanding thin films. We focus on the root mechanisms as described by large-scale MD simulations of FIB and describe the role of explosive boiling and Marangoni effect as a material removal and rearrangement mechanism and the mixing and transport that occur at the atomic scale. Nanopore fabrication using FIB is typically understood to occur via sputter erosion. While this theory may describe low-flux systems, where individual ion impacts are sufficiently separated in time to consider them as independent events, it cannot explain the thermal events observed during high flux simulations. A dimensionless number is introduced, which is constructed from the key variables including material properties and FIB parameters. This number suggests strong thermal effects when it is greater than unity. Similarly, our detailed MD simulations suggest that for ion beam fluxes above a threshold level, the dominant mechanism of material removal changes to a significantly accelerated, thermally dominated process, consistent with our dimensional analysis. During this time, the target is heated faster than it cools, leading to melting, with local temperatures approaching the critical temperature. This leads to an explosive boiling of the target material with spontaneous bubble formation. Atomic mass is rapidly rearranged via bubble growth and coalescence and material removal is orders of magnitude faster than would occur by simple sputtering. For a range of ion intensities in a realistic configuration, a recirculating melt region develops, which is seen to flow at high speed though symmetrically rather than driven by the ion momentum flux. Relevant length and time scales and estimated physical properties of silicon under these extreme conditions suggest that thermocapillary effects are important. A flow model with a Marangoni forcing term, based upon the temperature gradient from the atomistic simulation, confirms the presence of thermocapillary effect by reproducing the flow.","Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2015-07-22 without embargo terms","The student, Kallol Das, accepted the attached license on 2015-02-03 at 16:30.","The student, Kallol Das, submitted this Dissertation for approval on 2015-02-03 at 16:43.","This Dissertation was approved for publication on 2015-02-03 at 17:12.","DSpace SAF Submission Ingestion Package generated from Vireo submission #7707 on 2015-07-22 at 10:29:44","Made available in DSpace on 2015-07-22T22:15:48Z (GMT). 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