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Structured Metallic Films for Enhanced Light Transmission and Absorption
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.ORCID iD: 0000-0001-5170-265X
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Photonic devices such as light emitters, detectors, solar cells etc. are playing increasingly important roles in modern society. Yet their structures and designs are still under constant improvement, driven mostly by advances in material science and progress in integration techniques. A common challenge in these devices is to precisely manage transmission and absorption of light when it enters or escapes active regions. In certain devices it is even required to have both high optical transmission as well as high electrical conductivity. The current thesis investigates how structured metallic films can be devised to meet these challenges. Our work demonstrates that nanostructured noble metals can be tailored as either transparent or highly absorptive at wavelengths of interest, with or without electrical conductivity.In the first part of this work, metallic photonic crystals in the form of a thin gold film with an array of holes were fabricated with various geometrical parameters (hole size, pitch and metal thickness) on different substrate materials to investigate the impact of each parameter on the transmittance spectra at mid- to long-wave infrared wavelengths. Pitch size is shown to be the dominating factor for the high-transmittance band positions. Fill factor and metal thickness collectively define the selectivity of the pass bands. The selective transmission of infrared light can be used to improve the performance of infrared detectors. In the second part of this work, a thin-film multilayer structure based on two coupled metal-insulator-metal optical resonators was investigated for achieving a transparent conductor at visible wavelength range. The fabricated silver-based sample has a figure of merit (transmissivity-over-resistance) comparable to that of the traditionally used indium tin oxide. Such structures can potentially be used in light-emitting diodes and displays. In the third part of this work, a thin gold nanoparticle layer is obtained from a thermal annealing process. The interplay between this nanoparticle layer and a substrate metal reflector gives rise to broadband extinction of light at the near-infrared wavelength range. Specular and diffuse reflectances were singled out. Samples with high absorption or high diffuse reflection are identified. The structures can potentially be incorporated in solar cells as diffuse back reflectors or as spectrally selective absorbers for solar thermal collectors. In the fourth part of this work, the possibility of using a metal-insulator-metal structure (based on titanium, alumina, and aluminum) for achieving artificial coloration is explored. Through a diffusion-assisted deposition procedure, the dielectric spacer has a laterally varying thickness. Thereby the sample exhibits a continuum of visible colors. The reflectance spectra of the fabricated sample in the visible range were measured, and agreement to theoretical calculation is found to be very good. The artificial colors can be patterned at various geometries. Their potential application, besides functioning as spectrally selective absorbers in optoelectronic devices, can be used for security applications of consumer and artistic products.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , vi, 74 p.
Series
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2015:04
National Category
Nano Technology Atom and Molecular Physics and Optics
Research subject
Physics; Information and Communication Technology
Identifiers
URN: urn:nbn:se:kth:diva-166706ISBN: 978-91-7595-519-3 (print)OAI: oai:DiVA.org:kth-166706DiVA: diva2:811938
Public defence
2015-06-02, Sal C, Electrum, KTH-ICT, ISAFJORDSGATAN 22, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20150519

Available from: 2015-05-19 Created: 2015-05-13 Last updated: 2015-05-19Bibliographically approved
List of papers
1. Transmission of Infrared Radiation Through Metallic Photonic Crystal Structures
Open this publication in new window or tab >>Transmission of Infrared Radiation Through Metallic Photonic Crystal Structures
2013 (English)In: IEEE Photonics Journal, ISSN 1943-0655, Vol. 5, no 5, 4500608- p.Article in journal (Refereed) Published
Abstract [en]

Monolithic integration of a metallic photonic crystal (mPhC) structure onto semiconductor infrared (IR) photodetectors can enhance the detector performances. In order to experimentally investigate the parameters involved in optimizing the transmission spectra of the mPhC structures matching the detector operating wavelength in mid- and long-wave IR (MWIR and LWIR) regimes, square thin gold (Au) hole arrays having periodicities of 4.0, 3.6, 2.4, and 1.8 mu m with various fill factors were fabricated on Si or GaAs substrates in a wafer scale. The thicknesses of the Au films are 50, 100, and 200 nm, respectively. Through this systemic study, suitable mPhC structures were revealed that can be readily integrated onto our type-II InGaSb-based quantum dot MWIR and LWIR photodetectors.

Keyword
Infrared photodetectors, plasmonics, subwavelength structures, metallic photonic crystal
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-133530 (URN)10.1109/JPHOT.2013.2278527 (DOI)000325410400012 ()2-s2.0-84885642400 (Scopus ID)
Funder
VinnovaKnowledge FoundationSwedish Foundation for Strategic Research Swedish Research Council
Note

QC 20131107

Available from: 2013-11-07 Created: 2013-11-06 Last updated: 2015-05-19Bibliographically approved
2. Multi-resonator structure based on continuous silver thin films for transparent conductors
Open this publication in new window or tab >>Multi-resonator structure based on continuous silver thin films for transparent conductors
Show others...
2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 6, 061110- p.Article in journal (Refereed) Published
Abstract [en]

A type of metal-dielectric multilayered structures is investigated theoretically and experimentally for achieving optical transparency with a high electrical conductivity. The structure in our demonstrated case comprises of two coupled metal-dielectric-metal planar optical resonators with metal-layer thicknesses near to its skin depth. Simulations show that the maximum transmittance for visible light can easily reach 90% for silver-based structures. Experimentally, the sample fabricated exhibits a transmission window with a bandwidth of 150 nm and a maximum transmittance of 76% around 643 nm wavelength at normal incidence. Its sheet resistance is measured to be less than 10 Omega/square, much smaller than that of common indium-tin-oxide films. Transparent conductors functioning for blue light and even for the whole visible light are also shown to be theoretically possible. Owing to their simple fabrication procedure as well as design flexibility, such a layered structure can serve as a compelling alternative as transparent conductors for optoelectronic devices, especially for liquid-crystal displays and light-emitting diodes.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-153269 (URN)10.1063/1.4893144 (DOI)000341188700010 ()2-s2.0-84905988227 (Scopus ID)
Note

QC 20141009

Available from: 2014-10-09 Created: 2014-10-03 Last updated: 2017-12-05Bibliographically approved
3. Near-infrared light absorption and scattering based on a mono-layer of gold nanoparticles
Open this publication in new window or tab >>Near-infrared light absorption and scattering based on a mono-layer of gold nanoparticles
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-166808 (URN)
Note

QS 2015

Available from: 2015-05-18 Created: 2015-05-18 Last updated: 2015-05-19Bibliographically approved
4. A continuum of color from layered Ti-Al2O3-Al thin films
Open this publication in new window or tab >>A continuum of color from layered Ti-Al2O3-Al thin films
(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-166809 (URN)
Note

QS 2015

Available from: 2015-05-18 Created: 2015-05-18 Last updated: 2015-05-19Bibliographically approved

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