Dr. Halldór Guðfinnur Svavarsson


Position: Associate Professor
Website: http://www.ru.is/haskolinn/starfsfolk/halldorsv


Research projects

  • Photoconductive oxide films
  • Arrays of Silicon nanowires for photo- and thermovoltaics

My research areas of expertise include nanolithography, nanophotonics, nanoplasmonics, optical bio- and chemical sensors, nanofabrication, integrated nanoscale devices and thin-films. In particular I have been focusing on fabrication and characterization of periodic nanostructures of metals, dielectrics and semiconductors for thermoelectric, photovoltaic and photonic applications and with a special emphasize on silicon nanowires (SiNWs). These researches have been done in close collaboration with the Nanophotonics Device group at the Electrical Engineering department of the University of Texas at Arlington (http://leakymoderesonance.com/).


Publication

Google Scholar profile

  1. R Magnusson, J W Yoon, M Niraula, K J Lee and H G Svavarsson.
    Resonance-based nanophotonic device technology: Filters, reflectors, and absorbers.
    In 2016 IEEE Aerospace Conference. (March 2016), 1-13.
    Abstract We review nanophotonic device technology that is based on fundamental photonic resonance effects. We present the physics behind resonance device operation, illustrate their design with rigorous methods, discuss fabrication processes, and present results of physical and spectral characterization. We indicate the application potential of this field, discuss some past device examples, and provide new and emerging aspects. In particular, we present new wideband resonant reflectors designed with gratings in which the grating ridges are matched to an identical material thereby eliminating local reflections and phase changes. This critical interface therefore possesses zero refractive-index contrast; hence we call them “zero-contrast gratings.” For simple gratings with two-part periods, we show that zero-contrast grating reflectors outperform comparable high-contrast grating reflectors with nearly 700-nm bandwidth achieved at 99% reflectance. Resonance elements functioning as simultaneous spatial and spectral filters are introduced and substantiated with computed and experimental results that are in excellent agreement. Single-layer bandpass filters are presented and compared to their classic multilayer counterparts. An example bandpass filter with narrow transmission band fashioned with a single periodic layer compares in functionality with a classic Bragg stack with ~30 layers. We discuss deep Si grating structures that efficiently absorb fully-hemispherical unpolarized light in the entire visible spectral domain. This absorber provides a broad spectral continuum of densely populated resonant photonic states as well as a cooperating wide-angular antireflection effect, resulting in broadband, omnidirectional, and polarization-insensitive light absorption. We experimentally verify the absorber performance with precise fabrication and conical input beam spectral analysis. The promise and limitations of this class of devices is discussed.
    DOI BibTeX

    @inproceedings{7500645,
    	author = "R. Magnusson and J. W. Yoon and M. Niraula and K. J. Lee and H. G. Svavarsson",
    	booktitle = "2016 IEEE Aerospace Conference",
    	title = "Resonance-based nanophotonic device technology: Filters, reflectors, and absorbers",
    	year = 2016,
    	pages = "1-13",
    	abstract = "We review nanophotonic device technology that is based on fundamental photonic resonance effects. We present the physics behind resonance device operation, illustrate their design with rigorous methods, discuss fabrication processes, and present results of physical and spectral characterization. We indicate the application potential of this field, discuss some past device examples, and provide new and emerging aspects. In particular, we present new wideband resonant reflectors designed with gratings in which the grating ridges are matched to an identical material thereby eliminating local reflections and phase changes. This critical interface therefore possesses zero refractive-index contrast; hence we call them “zero-contrast gratings.” For simple gratings with two-part periods, we show that zero-contrast grating reflectors outperform comparable high-contrast grating reflectors with nearly 700-nm bandwidth achieved at 99% reflectance. Resonance elements functioning as simultaneous spatial and spectral filters are introduced and substantiated with computed and experimental results that are in excellent agreement. Single-layer bandpass filters are presented and compared to their classic multilayer counterparts. An example bandpass filter with narrow transmission band fashioned with a single periodic layer compares in functionality with a classic Bragg stack with ~30 layers. We discuss deep Si grating structures that efficiently absorb fully-hemispherical unpolarized light in the entire visible spectral domain. This absorber provides a broad spectral continuum of densely populated resonant photonic states as well as a cooperating wide-angular antireflection effect, resulting in broadband, omnidirectional, and polarization-insensitive light absorption. We experimentally verify the absorber performance with precise fabrication and conical input beam spectral analysis. The promise and limitations of this class of devices is discussed.",
    	keywords = "antireflection coatings;band-pass filters;diffraction gratings;elemental semiconductors;light absorption;light polarisation;nanophotonics;optical fabrication;optical filters;periodic structures;silicon;spatial filters;Si;broad spectral continuum;broadband light absorption;conical input beam spectral analysis;critical interface;deep Si grating structures;densely populated resonant photonic states;fully-hemispherical unpolarized light;grating ridges;identical material;narrow transmission band;omnidirectional light absorption;photonic resonance effects;physical characterization;polarization-insensitive light absorption;resonance device operation;resonance elements;resonance-based nanophotonic device technology;single periodic layer;single-layer bandpass filters;spatial filters;spectral characterization;spectral filters;visible spectral domain;wide-angular antireflection effect;wideband resonant reflectors;zero refractive index contrast;zero-contrast grating reflectors;Band-pass filters;Gratings;Nanoscale devices;Reflectivity;Silicon;Wideband",
    	doi = "10.1109/AERO.2016.7500645",
    	month = "March"
    }
    
  2. Halldor Gudfinnur Svavarsson, Birgir Hrafn Hallgrimsson, Manoj Niraula, Kyu Jin Lee and Robert Magnusson.
    Large arrays of ultra-high aspect ratio periodic silicon nanowires obtained via top–down route.
    Applied Physics A 122, 1–6 (2016).
    Abstract Metal-catalysed etching (MCE) is a simple and versatile method for fabrication of silicon nanowires, of high structural quality. When combined with laser interference lithography (LIL), large areas of periodic structures can be generated in only few steps. The aspect ratio of such periodic structure is however commonly not higher than several decades or very few hundred. Here, a combined MCE and LIL techniques were applied to fabricate dense (4 \texttimes 108 cm−3), periodic arrays of vertically aligned silicon nanowires with aspect ratio of up to 103. This is a considerable higher number than previously reported on for periodic silicon wire arrays prepared with top–down approaches. The wires were slightly tapered, with top and bottom diameters ranging from 370 to 195 nm and length of up to 200 $\mu$m. A potential use of the nanowires as light absorber is demonstrated by measuring reflection in integrating sphere. An average total absorption of \textasciitilde97 % was observed for 200-$\mu$m-long wires in the spectral range of 450–1000 nm. A comparison to simulated absorption spectra is given.
    URL, DOI BibTeX

    @article{Svavarsson2016,
    	author = "Svavarsson, Halldor Gudfinnur and Hallgrimsson, Birgir Hrafn and Niraula, Manoj and Lee, Kyu Jin and Magnusson, Robert",
    	title = "Large arrays of ultra-high aspect ratio periodic silicon nanowires obtained via top--down route",
    	journal = "Applied Physics A",
    	year = 2016,
    	volume = 122,
    	number = 2,
    	pages = "1--6",
    	abstract = "Metal-catalysed etching (MCE) is a simple and versatile method for fabrication of silicon nanowires, of high structural quality. When combined with laser interference lithography (LIL), large areas of periodic structures can be generated in only few steps. The aspect ratio of such periodic structure is however commonly not higher than several decades or very few hundred. Here, a combined MCE and LIL techniques were applied to fabricate dense (4 {\texttimes} 108 cm−3), periodic arrays of vertically aligned silicon nanowires with aspect ratio of up to 103. This is a considerable higher number than previously reported on for periodic silicon wire arrays prepared with top--down approaches. The wires were slightly tapered, with top and bottom diameters ranging from 370 to 195 nm and length of up to 200 $\mu$m. A potential use of the nanowires as light absorber is demonstrated by measuring reflection in integrating sphere. An average total absorption of {\textasciitilde}97 \% was observed for 200-$\mu$m-long wires in the spectral range of 450--1000 nm. A comparison to simulated absorption spectra is given.",
    	issn = "1432-0630",
    	doi = "10.1007/s00339-015-9589-y",
    	url = "http://dx.doi.org/10.1007/s00339-015-9589-y"
    }
    
  3. Halldor G Svavarsson, Sigurbjorn Einarsson and Asa Brynjolfsdottir.
    Adsorption applications of unmodified geothermal silica.
    Geothermics 50, 30 - 34 (2014).
    Abstract Abstract Silica, precipitated out of geothermal fluid discharged from a geothermal powerplant in Svartsengi on the Reykjanes peninsula in Iceland, was used as a chromatographic adsorbent to extract blue colored protein, C-phycocyanin, from coccoid blue-green algae. The only supplement used was salt obtained by evaporating the geothermal fluid. Analysis of the silica, using scanning electron microscopy, X-ray diffractometry and Brunauer–Emmett–Teller (BET) adsorption confirmed it has a high specific surface area and is amorphous. Upon adsorption and subsequent elution the purity of the extracted protein, measured as the ratio of the light absorbance of 620 and 280 nm, increased from 0.5 to above 2.0. Our results could facilitate utilization of a mostly unused byproduct of geothermal powerplants as chromatographic material.
    URL, DOI BibTeX

    @article{Svavarsson201430,
    	title = "Adsorption applications of unmodified geothermal silica",
    	journal = "Geothermics",
    	volume = 50,
    	number = 0,
    	pages = "30 - 34",
    	year = 2014,
    	note = "",
    	issn = "0375-6505",
    	doi = "10.1016/j.geothermics.2013.08.001",
    	url = "http://www.sciencedirect.com/science/article/pii/S0375650513000576",
    	author = "Halldor G. Svavarsson and Sigurbjorn Einarsson and Asa Brynjolfsdottir",
    	keywords = "Phycocyanin",
    	abstract = "Abstract Silica, precipitated out of geothermal fluid discharged from a geothermal powerplant in Svartsengi on the Reykjanes peninsula in Iceland, was used as a chromatographic adsorbent to extract blue colored protein, C-phycocyanin, from coccoid blue-green algae. The only supplement used was salt obtained by evaporating the geothermal fluid. Analysis of the silica, using scanning electron microscopy, X-ray diffractometry and Brunauer–Emmett–Teller (BET) adsorption confirmed it has a high specific surface area and is amorphous. Upon adsorption and subsequent elution the purity of the extracted protein, measured as the ratio of the light absorbance of 620 and 280 nm, increased from 0.5 to above 2.0. Our results could facilitate utilization of a mostly unused byproduct of geothermal powerplants as chromatographic material."
    }
    
  4. T Khaleque, H G Svavarsson and R Magnusson.
    Fabrication of nano-imprinted resonant structures for thin-film solar cell applications.
    In Photonics Conference (IPC), 2013 IEEE. (2013), 580-581.
    Abstract A simple fabrication approach of replicating nanoscale patterns with 300-nm periods on thermoplastic polymethyl methacrylate substrates using thermal nano-imprint lithography is reported. The resonant structures hold potential application in light trapping for thin-film solar cells.
    DOI BibTeX

    @inproceedings{6656696,
    	author = "Khaleque, T. and Svavarsson, H.G. and Magnusson, R.",
    	booktitle = "Photonics Conference (IPC), 2013 IEEE",
    	title = "Fabrication of nano-imprinted resonant structures for thin-film solar cell applications",
    	year = 2013,
    	month = "Sept",
    	pages = "580-581",
    	keywords = "nanofabrication;nanolithography;optical fabrication;radiation pressure;replica techniques;soft lithography;solar cells;light trapping;nanoimprinted resonant structure fabrication;thermal nanoimprint lithography;thermoplastic polymethyl methacrylate substrates;thin-film solar cells;Gratings;Heating;Optical device fabrication;Photovoltaic cells;Substrates;Temperature measurement",
    	doi = "10.1109/IPCon.2013.6656696",
    	abstract = "A simple fabrication approach of replicating nanoscale patterns with 300-nm periods on thermoplastic polymethyl methacrylate substrates using thermal nano-imprint lithography is reported. The resonant structures hold potential application in light trapping for thin-film solar cells."
    }
    
  5. Kristian Spilling, Ása Brynjólfsdóttir, Dagmar Enss, Heiko Rischer and Halldór Guðfinnur Svavarsson.
    The effect of high pH on structural lipids in diatoms.
    Journal of Applied Phycology 25, 1435-1439 (2013).
    Abstract We tested the hypothesis that increased pH reduces the amount of structural lipids. To do this, we used three different diatoms (Phaeodactylum tricornutum CCAP strain, P. tricornutum TV strain and Amphiprora sp). We tested the effect of rapid increase from pH?7.5 to 10 by adding NaOH. The total lipid content was reduced by 13, 36 and 47 % in the P. tricornutum CCAP strain, TV strain and Amphiprora sp., respectively, 1 h after increasing the pH. The P. tricornutum CCAP strain was used for further testing the effect of pH on the lipid content during active growth. This strain was cultivated at pH?7.5 and 10, and the pH was regulated by the CO2 inflow. The growth rate was similar (0.3 day?1) in both pH treatments, but the lipid content in the pH?10 treatment was on average 28 % lower than in the pH?7.5 treatment. Our data support the hypothesis that structural lipids are reduced when pH increases to high levels. The results suggest that regulating the pH during algae cultivation could be used to refine the lipid composition in the harvested algal biomass.
    URL PDF, DOI BibTeX

    @article{spilling2013effect,
    	year = 2013,
    	issn = "0921-8971",
    	journal = "Journal of Applied Phycology",
    	volume = 25,
    	number = 5,
    	doi = "10.1007/s10811-012-9971-5",
    	title = "The effect of high pH on structural lipids in diatoms",
    	url = "http://dx.doi.org/10.1007/s10811-012-9971-5",
    	publisher = "Springer Netherlands",
    	keywords = "Membrane lipids; Glycolipids; Phospholipids; Polyunsaturated fatty acids",
    	author = "Spilling, Kristian and Brynjólfsdóttir, Ása and Enss, Dagmar and Rischer, Heiko and Svavarsson, Halldór Guðfinnur",
    	pages = "1435-1439",
    	language = "English",
    	pdf = "http://www.researchgate.net/profile/Kristian_Spilling/publication/235332242_The_effect_of_high_pH_on_structural_lipids_in_diatoms/links/0fcfd510ec13ecf3c2000000.pdf",
    	abstract = "We tested the hypothesis that increased pH reduces the amount of structural lipids. To do this, we used three different diatoms (Phaeodactylum tricornutum CCAP strain, P. tricornutum TV strain and Amphiprora sp). We tested the effect of rapid increase from pH?7.5 to 10 by adding NaOH. The total lipid content was reduced by 13, 36 and 47 % in the P. tricornutum CCAP strain, TV strain and Amphiprora sp., respectively, 1 h after increasing the pH. The P. tricornutum CCAP strain was used for further testing the effect of pH on the lipid content during active growth. This strain was cultivated at pH?7.5 and 10, and the pH was regulated by the CO2 inflow. The growth rate was similar (0.3 day?1) in both pH treatments, but the lipid content in the pH?10 treatment was on average 28 % lower than in the pH?7.5 treatment. Our data support the hypothesis that structural lipids are reduced when pH increases to high levels. The results suggest that regulating the pH during algae cultivation could be used to refine the lipid composition in the harvested algal biomass."
    }
    
  6. Tanzina Khaleque, Halldor Gudfinnur Svavarsson and Robert Magnusson.
    Fabrication of resonant patterns using thermal nano-imprint lithography for thin-film photovoltaic applications.
    Opt. Express 21, A631–A641 (July 2013).
    Abstract A single-step, low-cost fabrication method to generate resonant nano-grating patterns on poly-methyl-methacrylate (PMMA; plexiglas) substrates using thermal nano-imprint lithography is reported. A guided-mode resonant structure is obtained by subsequent deposition of thin films of transparent conductive oxide and amorphous silicon on the imprinted area. Referenced to equivalent planar structures, around 25% and 45% integrated optical absorbance enhancement is observed over the 450-nm to 900-nm wavelength range in one- and two-dimensional patterned samples, respectively. The fabricated elements provided have 300-nm periods. Thermally imprinted thermoplastic substrates hold potential for low-cost fabrication of nano-patterned thin-film solar cells for efficient light management.
    URL, DOI BibTeX

    @article{Khaleque:13,
    	author = "Tanzina Khaleque and Halldor Gudfinnur Svavarsson and Robert Magnusson",
    	journal = "Opt. Express",
    	keywords = "Waveguides; Deposition and fabrication; Guided waves; Solar energy; Nanolithography; Subwavelength structures",
    	number = "S4",
    	pages = "A631--A641",
    	publisher = "OSA",
    	title = "Fabrication of resonant patterns using thermal nano-imprint lithography for thin-film photovoltaic applications",
    	volume = 21,
    	month = "Jul",
    	year = 2013,
    	url = "http://www.opticsexpress.org/abstract.cfm?URI=oe-21-104-A631",
    	doi = "10.1364/OE.21.00A631",
    	abstract = "A single-step, low-cost fabrication method to generate resonant nano-grating patterns on poly-methyl-methacrylate (PMMA; plexiglas) substrates using thermal nano-imprint lithography is reported. A guided-mode resonant structure is obtained by subsequent deposition of thin films of transparent conductive oxide and amorphous silicon on the imprinted area. Referenced to equivalent planar structures, around 25\% and 45\% integrated optical absorbance enhancement is observed over the 450-nm to 900-nm wavelength range in one- and two-dimensional patterned samples, respectively. The fabricated elements provided have 300-nm periods. Thermally imprinted thermoplastic substrates hold potential for low-cost fabrication of nano-patterned thin-film solar cells for efficient light management."
    }
    
  7. H G Svavarsson, J W Yoon, M Shokooh-Saremi, S H Song and R Magnusson.
    Fabrication and Characterization of Large, Perfectly Periodic Arrays of Metallic Nanocups.
    Plasmonics 7, 653-657 (2012).
    Abstract Fabrication of plasmonic resonance devices composed of large arrays of highly ordered gold nanocups is presented. The nanostructures are generated from periodic photoresist templates created by interference lithography and subsequent reflow, deposition, and dislodging. The nanocups are hemispherical in shape and arranged in both rectangular and hexagonal arrays with periods of ~500 nm. Their ability to support surface plasmonic resonances is manifested experimentally by reflectance spectroscopy. Theoretical modeling to ascertain the plasmonic spectra of these nanostructures is performed. The computed spectra of the rectangular structure are in qualitative agreement with the measurements. A weaker correlation observed for the hexagonal structure is explained by its more intricate symmetry which complicates the spectral response.
    URL PDF, DOI BibTeX

    @article{Svavar2012,
    	year = 2012,
    	issn = "1557-1955",
    	journal = "Plasmonics",
    	volume = 7,
    	number = 4,
    	doi = "10.1007/s11468-012-9355-3",
    	title = "Fabrication and Characterization of Large, Perfectly Periodic Arrays of Metallic Nanocups",
    	url = "http://scitation.aip.org/content/aip/journal/apl/100/9/10.1063/1.3690951",
    	publisher = "Springer US",
    	keywords = "Nanocups; Periodic arrays; Nano-indented films; Plasmonics; Hexagonal arrays; Rectangular arrays",
    	author = "Svavarsson, H.G. and Yoon, J.W. and Shokooh-Saremi, M. and Song, S.H. and Magnusson, R.",
    	pages = "653-657",
    	abstract = "Fabrication of plasmonic resonance devices composed of large arrays of highly ordered gold nanocups is presented. The nanostructures are generated from periodic photoresist templates created by interference lithography and subsequent reflow, deposition, and dislodging. The nanocups are hemispherical in shape and arranged in both rectangular and hexagonal arrays with periods of ~500 nm. Their ability to support surface plasmonic resonances is manifested experimentally by reflectance spectroscopy. Theoretical modeling to ascertain the plasmonic spectra of these nanostructures is performed. The computed spectra of the rectangular structure are in qualitative agreement with the measurements. A weaker correlation observed for the hexagonal structure is explained by its more intricate symmetry which complicates the spectral response.",
    	language = "English",
    	pdf = "http://optics.hanyang.ac.kr/~shsong/Plasmonics%202012-03-Fabrication%20and%20Characterization%20of%20Large,%20Perfectly%20Periodic%20Arrays%20of%20Metallic%20Nanocups.pdf"
    }
    
  8. R Magnusson, H G Svavarsson, J Yoon, M Shokooh-Saremi and S H Song.
    Experimental observation of leaky modes and plasmons in a hybrid resonance element.
    Applied Physics Letters 100, 091106-091106-3 (2012).
    Abstract We provide experimental evidence of a hybrid photonic device supporting simultaneously surface-plasmon polaritons and resonant leaky modes. A fabricated metallo-dielectric structure exhibits a pronounced plasmonic resonance at 799 nm wavelength and a modal resonance at 669 nm in transverse magnetic polarization. In transverse electric polarization, a weak modal resonance appears at 725 nm wavelength. We identify the corresponding modes by computing the attendant internal field distributions. Numerically computed spectra are in good agreement with our measurements. Since traditional modal and plasmonic devices find many uses, their hybrid versions may enable the extension of their applicability.
    PDF, DOI BibTeX

    @article{6163058,
    	author = "Magnusson, R. and Svavarsson, H. G. and Yoon, J. and Shokooh-Saremi, M. and Song, S. H.",
    	journal = "Applied Physics Letters",
    	title = "Experimental observation of leaky modes and plasmons in a hybrid resonance element",
    	year = 2012,
    	volume = 100,
    	number = 9,
    	pages = "091106-091106-3",
    	keywords = "light polarisation;polaritons;surface plasmon resonance;7320Mf",
    	doi = "10.1063/1.3690951",
    	issn = "0003-6951",
    	abstract = "We provide experimental evidence of a hybrid photonic device supporting simultaneously surface-plasmon polaritons and resonant leaky modes. A fabricated metallo-dielectric structure exhibits a pronounced plasmonic resonance at 799 nm wavelength and a modal resonance at 669 nm in transverse magnetic polarization. In transverse electric polarization, a weak modal resonance appears at 725 nm wavelength. We identify the corresponding modes by computing the attendant internal field distributions. Numerically computed spectra are in good agreement with our measurements. Since traditional modal and plasmonic devices find many uses, their hybrid versions may enable the extension of their applicability.",
    	pdf = "http://optics.hanyang.ac.kr/~shsong/APL%202012-02-Experimental%20observation%20of%20leaky%20modes%20and%20plasmons%20in%20a%20hybrid%20resonance%20element.pdf"
    }
    
  9. D M Danielsson, J T Gudmundsson and H G Svavarsson.
    Effect of hydrogenation on minority carrier lifetime in low-grade silicon.
    Physica Scripta 2010, 014005 (2010).
    Abstract Silicon p-n junctions for solar cell applications were prepared by growing thin n-type films on p-type metallurgical-grade silicon (MG-Si) substrate in a liquid solution of arsenic-doped gallium/indium solution. MG-Si has much higher impurity concentrations than traditional solar-grade silicon, but is here being used as a low-cost alternative. The as-grown film showed negligible photovoltaic response. A post-growth exposure of the as-grown p–n junctions to a H 2 /Ar plasma resulted in an active photovoltaic device with V OC of up to several hundred mV. Furthermore, a significant increase in the minority carrier lifetime was observed. The short-circuit current density indicated low efficiency in accordance with the high defect concentration of the impure substrate. An x-ray diffraction study of MG-Si prior to and after film growth revealed textured crystal structure that diminished during film growth, indicating that the film is more homogeneous than the substrate.
    URL BibTeX

    @article{1402-4896-2010-T141-014005,
    	author = "D M Danielsson and J T Gudmundsson and H G Svavarsson",
    	title = "Effect of hydrogenation on minority carrier lifetime in low-grade silicon",
    	journal = "Physica Scripta",
    	volume = 2010,
    	number = "T141",
    	pages = 014005,
    	url = "http://stacks.iop.org/1402-4896/2010/i=T141/a=014005",
    	year = 2010,
    	abstract = "Silicon p-n junctions for solar cell applications were prepared by growing thin n-type films on p-type metallurgical-grade silicon (MG-Si) substrate in a liquid solution of arsenic-doped gallium/indium solution. MG-Si has much higher impurity concentrations than traditional solar-grade silicon, but is here being used as a low-cost alternative. The as-grown film showed negligible photovoltaic response. A post-growth exposure of the as-grown p–n junctions to a H 2 /Ar plasma resulted in an active photovoltaic device with V OC of up to several hundred mV. Furthermore, a significant increase in the minority carrier lifetime was observed. The short-circuit current density indicated low efficiency in accordance with the high defect concentration of the impure substrate. An x-ray diffraction study of MG-Si prior to and after film growth revealed textured crystal structure that diminished during film growth, indicating that the film is more homogeneous than the substrate."
    }