{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/73006"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/73006","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Experimental determination of the thermoelectric properties of porous silicon nanowires","abstract":"\"The thermoelectric properties of nanostructured silicon have attracted significant attention in recent work. The objective is to reduce thermal conductivity through the introduction of phonon scattering mechanisms while preserving charge transport. Initial reports on electrolessly etched silicon nanowires and periodic \\holey\"\" silicon membranes contained several puzzling aspects that remain unresolved. Here, we present measurements on mesoporous silicon nanowires fabricated through electroless etching of degenerately doped silicon. While thermal conductivity in this material at room temperature is attractive for thermoelectric applications at ~2 W/(m K), charge transport is severely degraded due to the disordered yet nanocrystalline structure. We investigate post doping conditions to improve the electrical conductivity by ~3 orders of magnitude. TEM characterization confirmed that porosity and crystalline structure are retained after doping. We characterized the boron concentration before and after doping by secondary ion mass spectroscopy (SIMS). Raman spectroscopy was also employed to extract the free carrier concentrations as well as nanocrystalline size. We measured the Seebeck coefficient and thermal conductivity from 30 K to 400 K by a frequency domain technique. Analysis of Seebeck coefficient reveals the electron scattering mechanism in porous silicon nanowire before and after post-doping. The carrier concentrations extracted from Seebeck coefficient are in good agreement with the Raman spectrum analysis. In order to interpret the thermal conductivity data, we propose a frequency dependent multiple scattering of phonons across the porous wire. This work provides detailed insight into charge and heat transport in disordered yet nanocrystalline materials and advances their engineering for thermoelectric waste heat harvesting amongst other applications.\"","abstract_html":""The thermoelectric properties of nanostructured silicon have attracted significant attention in recent work. The objective is to reduce thermal conductivity through the introduction of phonon scattering mechanisms while preserving charge transport. Initial reports on electrolessly etched silicon nanowires and periodic \\holey"" silicon membranes contained several puzzling aspects that remain unresolved. Here, we present measurements on mesoporous silicon nanowires fabricated through electroless etching of degenerately doped silicon. While thermal conductivity in this material at room temperature is attractive for thermoelectric applications at ~2 W/(m K), charge transport is severely degraded due to the disordered yet nanocrystalline structure. We investigate post doping conditions to improve the electrical conductivity by ~3 orders of magnitude. TEM characterization confirmed that porosity and crystalline structure are retained after doping. We characterized the boron concentration before and after doping by secondary ion mass spectroscopy (SIMS). Raman spectroscopy was also employed to extract the free carrier concentrations as well as nanocrystalline size. We measured the Seebeck coefficient and thermal conductivity from 30 K to 400 K by a frequency domain technique. Analysis of Seebeck coefficient reveals the electron scattering mechanism in porous silicon nanowire before and after post-doping. The carrier concentrations extracted from Seebeck coefficient are in good agreement with the Raman spectrum analysis. In order to interpret the thermal conductivity data, we propose a frequency dependent multiple scattering of phonons across the porous wire. This work provides detailed insight into charge and heat transport in disordered yet nanocrystalline materials and advances their engineering for thermoelectric waste heat harvesting amongst other applications."","abstract_has_math":false,"creators":["Tian, Hongxiang"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Mechanical Engineering","degree_department":null,"school":null,"contributors":["Sinha, Sanjiv","Li, Xiuling","Ertekin, Elif","Toussaint, Kimani"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015-01-21T19:55:58Z","date_published":"2015-01-21T19:55:58Z","updated_at":"2026-07-22T22:26:07Z","subjects":["thermoelectric","porous silicon nanowire","phonon transport in porous silicon nanowire","electron transport"],"languages":["en"],"rights":["Copyright 2014 Hongxiang Tian"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/73006","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Sinha, Sanjiv","Li, Xiuling","Ertekin, Elif","Toussaint, Kimani"]},{"key":"dc:creator","label":"Author","values":["Tian, Hongxiang"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2015-01-21T19:55:58Z","2017-01-22T10:15:20Z","2014-12","2015-01-21"]},{"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":["thermoelectric","porous silicon nanowire","phonon transport in porous silicon nanowire","electron transport"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2014 Hongxiang Tian"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/73006"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["\"The thermoelectric properties of nanostructured silicon have attracted significant attention in recent work. The objective is to reduce thermal conductivity through the introduction of phonon scattering mechanisms while preserving charge transport. Initial reports on electrolessly etched silicon nanowires and periodic \\holey\"\" silicon membranes contained several puzzling aspects that remain unresolved. Here, we present measurements on mesoporous silicon nanowires fabricated through electroless etching of degenerately doped silicon. While thermal conductivity in this material at room temperature is attractive for thermoelectric applications at ~2 W/(m K), charge transport is severely degraded due to the disordered yet nanocrystalline structure. We investigate post doping conditions to improve the electrical conductivity by ~3 orders of magnitude. TEM characterization confirmed that porosity and crystalline structure are retained after doping. We characterized the boron concentration before and after doping by secondary ion mass spectroscopy (SIMS). Raman spectroscopy was also employed to extract the free carrier concentrations as well as nanocrystalline size. We measured the Seebeck coefficient and thermal conductivity from 30 K to 400 K by a frequency domain technique. Analysis of Seebeck coefficient reveals the electron scattering mechanism in porous silicon nanowire before and after post-doping. The carrier concentrations extracted from Seebeck coefficient are in good agreement with the Raman spectrum analysis. In order to interpret the thermal conductivity data, we propose a frequency dependent multiple scattering of phonons across the porous wire. This work provides detailed insight into charge and heat transport in disordered yet nanocrystalline materials and advances their engineering for thermoelectric waste heat harvesting amongst other applications.\"","Item withdrawn by Laura Spradlin (lspradl2@illinois.edu) on 2014-12-02T19:35:28Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 4 Tian_PhD_thesis.pdf: 10267159 bytes, checksum: 9e9b09c37a2253c8985e931a3ef067d2 (MD5) Tian_PhD_thesis.pdf: 10288172 bytes, checksum: 215e3bee518a1c0ee18202c5ad7c7e7d (MD5) Tian_PhD_thesis.pdf: 10288081 bytes, checksum: dfb41be1ff99ad9a2834a9304248a3aa (MD5) Tian_PhD_thesis.pdf: 10266700 bytes, checksum: aff96718b7595517989bded5c1648b19 (MD5)","Made available in DSpace on 2015-01-21T19:55:58Z (GMT). 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Initial reports on electrolessly etched silicon nanowires and periodic \\holey\"\" silicon membranes contained several puzzling aspects that remain unresolved. Here, we present measurements on mesoporous silicon nanowires fabricated through electroless etching of degenerately doped silicon. While thermal conductivity in this material at room temperature is attractive for thermoelectric applications at ~2 W/(m K), charge transport is severely degraded due to the disordered yet nanocrystalline structure. We investigate post doping conditions to improve the electrical conductivity by ~3 orders of magnitude. TEM characterization confirmed that porosity and crystalline structure are retained after doping. We characterized the boron concentration before and after doping by secondary ion mass spectroscopy (SIMS). Raman spectroscopy was also employed to extract the free carrier concentrations as well as nanocrystalline size. We measured the Seebeck coefficient and thermal conductivity from 30 K to 400 K by a frequency domain technique. Analysis of Seebeck coefficient reveals the electron scattering mechanism in porous silicon nanowire before and after post-doping. The carrier concentrations extracted from Seebeck coefficient are in good agreement with the Raman spectrum analysis. In order to interpret the thermal conductivity data, we propose a frequency dependent multiple scattering of phonons across the porous wire. This work provides detailed insight into charge and heat transport in disordered yet nanocrystalline materials and advances their engineering for thermoelectric waste heat harvesting amongst other applications.\"","Item withdrawn by Laura Spradlin (lspradl2@illinois.edu) on 2014-12-02T19:35:28Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 4 Tian_PhD_thesis.pdf: 10267159 bytes, checksum: 9e9b09c37a2253c8985e931a3ef067d2 (MD5) Tian_PhD_thesis.pdf: 10288172 bytes, checksum: 215e3bee518a1c0ee18202c5ad7c7e7d (MD5) Tian_PhD_thesis.pdf: 10288081 bytes, checksum: dfb41be1ff99ad9a2834a9304248a3aa (MD5) Tian_PhD_thesis.pdf: 10266700 bytes, checksum: aff96718b7595517989bded5c1648b19 (MD5)","Made available in DSpace on 2015-01-21T19:55:58Z (GMT). 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