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Wavelength-dependent photoconductivity of single-walled carbon nanotube layers
KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Micro and Nanosystems.ORCID iD: 0000-0003-0368-1668
(Department of Photonics and Optical Information Technologies, ITMO University)ORCID iD: 0000-0002-6260-2694
(Department of Electronics and Nanoengineering, Aalto University)ORCID iD: 0000-0002-9546-9391
KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Micro and Nanosystems.ORCID iD: 0000-0003-1443-403x
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2019 (English)In: RSC Advances, E-ISSN 2046-2069, Vol. 9, no 26, p. 14677-14682Article in journal (Refereed) Published
Abstract [en]

A number of electronic devices such as phase shifters, polarizers, modulators, and power splitters are based on tunable materials. These materials often do not meet all the requirements namely low losses, fast response time, and technological compatibility. Novel nanomaterials, such as single-walled carbon nanotubes, are therefore widely studied to fill this technological gap. Here we show how the dielectric constant of single-walled carbon nanotube layers can be substantially modified by illuminating them due to unique light–matter interactions. We relate the optical excitation of the nanotube layers to the illumination wavelength and intensity, by resistance and capacitance measurements. The dielectric constant is modified under laser illumination due to the change of material polarization and free carrier generation, and is shown to not be temperature-related. The findings indicate that SWCNT layers are a prospective tunable optoelectronic material for both high and low frequency applications.

Place, publisher, year, edition, pages
RSC Publishing, 2019. Vol. 9, no 26, p. 14677-14682
National Category
Nano Technology
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-251605DOI: 10.1039/C9RA01467EISI: 000468641300013PubMedID: 35516325Scopus ID: 2-s2.0-85065863568OAI: oai:DiVA.org:kth-251605DiVA, id: diva2:1316010
Funder
EU, Horizon 2020, 675683EU, Horizon 2020, 616846
Note

QC 20190515

Available from: 2019-05-15 Created: 2019-05-15 Last updated: 2024-03-18Bibliographically approved
In thesis
1. Tunable Nanomaterials and their Applications for Terahertz Devices: Carbon Nanotubes and Silver Nanowires
Open this publication in new window or tab >>Tunable Nanomaterials and their Applications for Terahertz Devices: Carbon Nanotubes and Silver Nanowires
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interest in terahertz (THz) technologies is growing in academia and industry. The design of electronic components at THz frequencies is relevant to application areas such as telecommunication, radar, material spectroscopy, and medical imaging and diagnosis. Even though high-performance THz instrumentation becomes more available, the systems are not commonly found outside of the laboratory environment. Researchers have recently demonstrated a platform based on dielectric rod waveguides (DRWs) that is suitable for integrating THz electronics. The electromagnetic waves propagate inside a low-loss dielectric structure, a concept similar to optical fibres. DRWs have seen many advances for THz electronics in recent years. However, the platform still lacks essential active and passive components for building complete systems. 

This thesis investigates ways to integrate tunable nanomaterials to dielectric waveguides in order to design novel terahertz devices. First, silicon rectangular DRWs are investigated at 75 GHz to 500 GHz frequencies. In particular, the interface with the measurement instrumentation and the tapered transitions to hollow metallic waveguides are considered by electromagnetic simulations. Additionally, ways to implement phase shifters and attenuators are explored using thin layers of nanomaterials that are modelled by an impedance surface in the simulations. 

Second, several nanomaterials are studied by optical spectrophotometry, Raman spectroscopy, and terahertz time-domain and frequency- domain spectroscopy. Thin layers of silver nanowires are fabricated with increasing densities, ranging from individual nanowires to nanowire networks at the percolation threshold, to thick semi-continuous layers. This technique allows the manufacturing of optically transparent samples with a tunable THz conductivity. Additionally, thin layers of single-walled carbon nanotubes are investigated. Their dielectric properties are shown to be tunable by light illumination, supported by measurements at low frequencies and in the terahertz range. 

Finally, tunable THz devices based on dielectric waveguides are designed, manufactured, and characterized. Thin layers of carbon nanotubes are integrated with DRWs and used as a surface impedance to modify the wave propagation in the waveguide. The presented phase shifters are tunable by light with wideband operation at sub-THz and potentially higher frequencies, and further device improvements are proposed. 

Abstract [sv]

Intresset för terahertz (THz) -teknologi ökar både i den akademiska världen och inom industrin. Design av elektroniska komponenter i THz-frekvenser är relevanta för applikationsområden som telekommunikation, radar, materialspektroskopi och medicinsk bildbehandling och diagnostik. Även om högpresterande THz-instrumentering blir mer tillgängligt finns systemen ofta inte utanför laboratoriemiljöer. Forskare har nyligen demonstrerat en plattform baserad på dielektriska vågledare (DRWs) som är lämplig för att integrera THz-elektronik. De elektromagnetiska vågorna sprids inuti en lågförlustdielektrisk struktur, ett koncept som liknar den optiska fibern. DRW har sett många framsteg för THz-elektronik på senare år. Plattformen saknar dock fortfarande väsentliga aktiva och passiva komponenter för att bygga kompletta system. 

Denna avhandling undersöker olika sätt att integrera avstämbara nanomaterial till dielektriska vågledare för att designa nya terahertzenheter. Först undersöks rektangulära kisel-DRWs vid frekvenserna 75 GHz till 500 GHz. I synnerhet används elektromagnetiska simuleringar för att efterlikna gränssnittet mellan mätinstrumentet och de avsmalnande övergångarna till de ihåliga metalliska vågledarna. Dessutom utforskas sätt för att implementera  fasväxlare och dämpare med hjäp av tunna lager av nanometrial som modelleras av en impedansyta i simuleringarna. 

Sedan studeras även flera nanomaterial genom optisk spektrofotometri, Ramanspektroskopi och terahertztidsdomän- och frekvensdomänspektroskopi. Tunna lager av silvernanotrådar tillverkas med ökande densiteter, allt från enskilda nanotrådar till nanotrådsnät vid perkolationströskeln, till tjockare halvkontinuerliga lager. Denna teknik möjliggör tillverkning av optiskt transparenta prover med en avstämbar THz-konduktivitet. Dessutom undersöks tunna lager av enkelväggiga kolnanorör. Deras dielektriska egenskaper påvisas vara avstämbara med belysning, vilket även stöds av mätningar vid låga frekvenser och i terahertz-omfånget. 

Slutligen designas, tillverkas och karakteriseras inställbara THz-enheter baserade på dielektriska vågledare. Tunna lager av kolnanorör integreras med DRW och används som ytimpedans för att ändra vågutbredningen i vågledaren. De presenterade fasskiftarna kan ställas in med hjälp av ljus med bredbandsoperationer vid sub-THz och potentiellt högre frekvenser, även ytterligare enhetsoptimeringar föreslås.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2021. p. 61
Series
TRITA-EECS-AVL ; 2021:33
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-293982 (URN)978-91-7873-878-6 (ISBN)
Public defence
2021-06-07, MST Conference Room, Malvinas väg 10, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20210518

Available from: 2021-05-18 Created: 2021-05-11 Last updated: 2022-06-25Bibliographically approved

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Smirnov, SergueiAnoshkin, Ilya V.Lioubtchenko, DmitriOberhammer, Joachim

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