Subscriber access provided by UNIV OF LOUISIANA
Surfaces, Interfaces, and Applications
Reduction and Increase in Thermal Conductivity of Si Irradiated with Ga+ via Focused Ion Beam Seyedhamidreza Alaie, Mohammadhosein Ghasemi Baboly, Ying Bing Jiang, Susan B. Rempe, Dalaver H. Anjum, Sahraoui Chaieb, Brian Francis Donovan, Ashutosh Giri, Chester J Szwejkowski, John Thomas Gaskins, Mirza Elahi, Drew Goettler, Jeffrey L. Braun, Patrick E. Hopkins, and Zayd Chad Leseman ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b11949 • Publication Date (Web): 03 Oct 2018 Downloaded from http://pubs.acs.org on October 4, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
Reduction and Increase in Thermal Conductivity of Si Irradiated with Ga+ via Focused Ion Beam S. Alaie1, M. G. Baboly2, Y.-B. Jiang3, S. Rempe4, D. H. Anjum5, S. Chaieb6,7,8, B. F. Donovan9, A. Giri10, C. J. Szwejkowski10, J. T. Gaskins10, M. M. M. Elahi11, D. F. Goettler12, J. Braun10, P. E. Hopkins10,13,14, Z. C. Leseman15* 1
Department of Radiology, Weill Cornell Medicine, Cornell University New York, NY, 10065, USA. Department of Engineering, University of Jamestown, Jamestown, ND, 58405, USA. 3 Department of Chemical and Biological Engineering, University of New Mexico, Albuquerque, NM, 87131, USA. 4 Sandia National Laboratories, Albuquerque, NM 87123, USA. 5 Advanced Nanofabrication, Imaging, and Characterization Lab, King Abdullah University of Science & Technology, Thuwal, 23955-6900, Kingdom of Saudi Arabia 6 Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology Thuwal, 23955-6900, Kingdom of Saudi Arabia 7 Lawrence Berkeley National Laboratory, Berkeley, CA, 94720 USA 8 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan 9 Department of Physics, United States Naval Academy, Annapolis, 21402, MD, USA. 10 Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, 22904 VA, USA. 11 Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM, 87131, USA. 12 Department of Mechanical Engineering, University of New Mexico, Albuquerque, NM, 87131, USA. 13 Department of Materials Science and Engineering, University of Virginia, Charlottesville, 22904 VA, USA. 14 Department of Physics, University of Virginia, Charlottesville, 22904 VA, USA. 15 Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS, 66506, USA. *Correspondence and requests for materials should be addressed to Zayd C. Leseman (
[email protected]). 2
Abstract Focused Ion Beam (FIB) technology has become a valuable tool for the microelectronics industry and for the fabrication and preparation of samples at the micro/nanoscale. Its effects on the thermal transport properties of Si, however are not well understood, nor do experimental data exist. This paper presents a carefully designed set of experiments for the determination of the thermal conductivity of Si samples irradiated by Ga+ FIB. Generally, the thermal conductivity decreases with increasing ion dose. For doses of >1016 (Ga+/cm2), a reversal of the trend was observed due to recrystallization of Si. This report provides insight on the thermal transport considerations relevant to engineering of Si nanostructures and interfaces fabricated or prepared by FIB. KEYWORDS: Focused Ion Beam (FIB), Thermal Conductivity, Nanostructures, Time Domain Thermo-Reflectance (TDTR)
Gallium,
Irradiated,
Introduction Over the last two decades the thermal conductivity of different nano/micro structured silicon samples has been extensively investigated for a range of purposes. For example, in order to understand the physics of phonon thermal transport at the nanoscale, silicon films with different thicknesses have been experimentally and theoretically investigated1–3. Additionally, the possibility of using silicon as a thermoelectric material has been confirmed4–6. Accordingly, manipulation of the thermal conductivity of silicon, with minimal alteration of the electrical properties, has become an active area of research7–9. To fabricate different Si structures, photolithography7,10 and e-beam lithography4,5 techniques have been employed. Recently, gallium focused ion beam (FIB)8,10 has been used as a
ACS Paragon Plus Environment
ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
promising alternative. However, it is known that FIB can potentially damage, dope or roughen silicon surfaces11–13. Therefore, in this work, a carefully designed set of experiments to determine the effects of FIB, and resulting Ga ion (Ga+) implantation, on the thermal conductivity of Si is undertaken. Though the thermal conductivity of silicon with various (small) dimensions and doping has been previously investigated, the effect of gallium impurities on silicon’s thermal conductivity has not been previously studied. More specifically, the thermal conductivity of thin Si films1–3, Si nanowires6,14, patterned Si films4,10, and other Si structures15 have been the subject of prior work. The literature established that at smaller dimensions the boundary scattering of phonons dominates, which results in a considerable reduction of thermal conductivity (~ 2 W/mK4 ). In addition to the size-effect, effects of different dopants and mass impurities, such as phosphorous16,17 and germanium,18–21 on the thermal conductivity of silicon have been studied. Most remarkably, its shown that SixGe(1-x) can feature a thermal conductivity as low as ~9W/mK in bulk and when combined with the size-effect it can reduce to ~2W/mK18 . However, the effects of gallium as a dopant or mass impurity on the thermal conductivity of silicon are yet unknown, regardless of its common occurrence in FIB-processed silicon. Ga+ FIB has been widely employed in milling13,22,23, imaging9,24, and affixing nanosamples9,25. FIB is a versatile tool for milling thin films with submicron resolution. The FIB’s spot size can be as small as 5-7 nm26 for milling materials and it can also be used to deposit a variety of materials to fabricate sophisticated nanostructures26. For thermal applications, it has been employed to fabricate phononic crystals in silicon thin films13. Additionally, FIB is used for imaging nano/micro samples while they are handled for thermal characterization24,25 and is employed for the deposition of materials for affixing nano/micro samples to microelectromechanical structures for thermal characterization9,23. However, despite its widespread use as a nanoscience tool, the FIB can potentially have a negative impact due to implantation of Ga+ into samples that introduce defects and impurities into the sample. In this work, the thermal conductance and the equivalent thermal conductivity of regions of single crystal Si wafers irradiated by Ga+ FIB is studied. To fully understand the effects of the implanted Ga+, samples with different doses ranging from 1012 to 1018 Ga+/cm2 are studied. After irradiation, samples are coated with a thin layer of aluminum for characterization by Time Domain Thermo-Reflectance (TDTR). The thermal properties gathered by this technique are crucial in understanding the thermal effects of FIB-induced Ga dopants on micro/nanosamples of Si. Results may be extrapolated to other material systems.
Results and Discussion The thermal conductance across the Ga+-irradiated silicon region is reported in Figure 1 for different doses. In practice, due to the small thickness of the Ga+ irradiated region (1016/cm2, an increase is observed in the TBC.
+
Figure 1. Thermal conductance of Ga irradiated region versus the dose of gallium induced by FIB. Due to the + small thickness of the Ga irradiated region (
