Aksamija, Zlatan

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Assistant Professor, Department of Electrical and Computer Engineering
Last Name
Aksamija
First Name
Zlatan
Discipline
Electrical and Computer Engineering
Expertise
Computational nanoscience
Dissipation in nanoscale devices
Electro-thermal simulation
Nanoscale heat transfer
Semiconductor nanostructures for energy applications
Thermal devices
Thermoelectric energy conversion
Introduction
About: My research is in the area of Computational Materials Engineering--my group is using computer simulation to study the properties of semiconductor nanostructures, such as nanoscale FET transistors, graphene nanoribbons, superlattices, and nanowires, from first principles. We merge theory and computational science to explore physics at the nanoscale using computational tools ranging from Density Functional Theory bandstructure and dispersion calculations, to solving the coupled electron and phonon Boltzmann transport equations with the Monte Carlo method. We are particularly interested in the impact of dimension and boundaries on heat and charge transfer, with applications in thermoelectric energy conversion.

Bio: Zlatan Aksamija received his B.S. in Computer Engineering (Summa Cum Laude, James Honors Scholar, Mathematics Minor) in 2003, and his M.S. and Ph.D. in Electrical Engineering (with Computational Science and Engineering option) in 2005 and 2009, respectively, all from the University of Illinois at Urbana/Champaign. His dissertation on “Thermal effects in semiconductor materials and devices” was supported by a DOE Computational Science Graduate Fellowship (2005-2009). Zlatan was awarded an Outstanding Paper award at the EIT’07 conference and a Greg Stillman Memorial semiconductor graduate research award in 2008. From 2009 to 2013, Zlatan was a Computing Innovation Postdoctoral Fellow and an NSF CI TraCS Fellow in the ECE department at the University of Wisconsin-Madison. His research focused on semiconductor nanostructures for thermoelectric energy conversion applications, as well as numerical methods for the simulation of electronic and thermal transport in nanostructures. In 2013, Zlatan became an Assistant Professor in the Electrical and Computer Engineering Department at the University of Massachusetts-Amherst and founded NET (NanoEnergy & Thermophysics) lab, where he studies nanoscale dissipation and heat transfer in 2-dimensional materials, alloys, and nanocomposites. He received the Best Paper award from IEEE Nano (2014) and a Lilly Teaching Fellowship from the UMass Institute for Teaching and Faculty Development.
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Now showing 1 - 4 of 4
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    Electronic transport across extended grain boundaries in graphene
    (2021-01-01) Majee, Arnab K.; Aksamija, Zlatan
    Owing to its superlative carrier mobility and atomic thinness, graphene exhibits great promise for interconnects in future nanoelectronic integrated circuits. Chemical vapor deposition (CVD), the most popular method for wafer-scale growth of graphene, produces monolayers that are polycrystalline, where misoriented grains are separated by extended grain boundaries (GBs). Theoretical models of GB resistivity focused on small sections of an extended GB, assuming it to be a straight line, and predicted a strong dependence of resistivity on misorientation angle. In contrast, measurements produced values in a much narrower range and without a pronounced angle dependence. Here we study electron transport across rough GBs, which are composed of short straight segments connected together into an extended GB. We found that, due to the zig-zag nature of rough GBs, there always exist a few segments that divide the crystallographic angle between two grains symmetrically and provide a highly conductive path for the current to flow across the GBs. The presence of highly conductive segments produces resistivity between 102 to 104 Ω μm regardless of misorientation angle. An extended GB with large roughness and small correlation length has small resistivity on the order of 103 Ω μm, even for highly mismatched asymmetric GBs. The effective slope of the GB, given by the ratio of roughness and lateral correlation length, is an effective universal quantifier for GB resistivity. Our results demonstrate that the probability of finding conductive segments diminishes in short GBs, which could cause a large variation in the resistivity of narrow ribbons etched from polycrystalline graphene. We also uncover spreading resistance due to the current bending in the grains to flow through the conductive segments of the GB and show that it scales linearly with the grain resistance. Our results will be crucial for designing graphene-based interconnects for future integrated circuits.
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    Tuning charge transport dynamics via clustering of doping in organic semiconductor thin films
    (2019-01-01) Boyle, Connor J.; Upadhyaya, Meenakshi; Wang, Peijan; Renna, Lawrence A.; Lu-Díaz, Michael; Jeong, Seung Pyo; Hight-Huf, Nicholas; Korugic-Karasz, Ljiljana; Barnes, Michael D.; Aksamija, Zlatan; Venkataraman, Dhandapani
    A significant challenge in the rational design of organic thermoelectric materials is to realize simultaneously high electrical conductivity and high induced-voltage in response to a thermal gradient, which is represented by the Seebeck coefficient. Conventional wisdom posits that the polymer alone dictates thermoelectric efficiency. Herein, we show that doping — in particular, clustering of dopants within conjugated polymer films — has a profound and predictable influence on their thermoelectric properties. We correlate Seebeck coefficient and electrical conductivity of iodine-doped poly(3-hexylthiophene) and poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl)-alt-(2,2′;5′,2′′;5′′,2′′′-quaterthiophen-5,5′′′-diyl)] films with Kelvin probe force microscopy to highlight the role of the spatial distribution of dopants in determining overall charge transport. We fit the experimental data to a phonon-assisted hopping model and found that the distribution of dopants alters the distribution of the density of states and the Kang–Snyder transport parameter. These results highlight the importance of controlling dopant distribution within conjugated polymer films for thermoelectric and other electronic applications.
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    Source Data for "Tuning charge transport dynamics via clustering of doping in organic semiconductor thin films"
    (2019-01-01) Boyle, Connor J.; Upadhyaya, Meenakshi; Lu-Díaz, Michael; Venkataraman, Dhandapani; Aksamija, Zlatan
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    Experimental Study of Operating Conditions and Integration of Thermoelectric Materials in Facade Systems
    (2019-01-01) Aksamija, Ajla; Aksamija, Zlatan; Counihan, Chris; Brown, Dylan; Upadhyaya, Meenakshi
    This article discusses the application of thermoelectric (TE) materials in building facade systems, which can be used to create active exterior enclosures. TEs are semiconductors that have the ability to produce a temperature gradient when electricity is applied, exploiting the Peltier effect, or to generate a voltage when exposed to a temperature gradient, utilizing the Seebeck effect. TEs can be used for heating, cooling, or electricity generation. In this research, heating and cooling applications of these novel systems were explored. We designed and constructed two prototypes, where one prototype was used to study integration of TE modules (TEMs) as stand-alone elements in the facade, and one prototype was used to explore integration of TEMs and heat sinks in facade assemblies. Both prototypes were tested for heating and cooling potential, using a thermal chamber to represent four different exterior environmental conditions (−18°,−1°,16°, and 32°C). The interior ambient conditions were kept constant at room temperature. The supplied voltage to facade-integrated TEMs varied from 1 to 8 V. We measured temperature outputs of TEMs for all investigated thermal conditions using thermal imaging, which are discussed in this article. The results indicate that while stand-alone facade-integrated TEMs are not stable, addition of heat sinks improves their performance drastically. Facade-integrated TEMs with heatsinks showed that they would operate well in heating and cooling modes under varying exterior environmental conditions.