SURFACE-ENHANCEMENT OF FIBER PROBES FOR BIOSENSOR As this is a broad project where different approaches are suggested, it will be possible for several master students to apply. Background Spectroscopy for qualitative and quantitative sensing is a rapidly expanding area of sensing that employs optical methods. Spectroscopy has traditionally been used for gas sensing and other industrial uses, and is now extending into other fields such as sensing applications in medicine. Raman spectroscopy is a method that employs Raman scattering in order to detect specific compounds. Raman scattering occurs due to vibrational and rotational modes in a molecule, and provides a fingerprint which can be used to identify specific molecules and quantitatively measure them. The major limitation of Raman spectroscopy is the small scattering cross-section, which gives a very small signal strength. Many variants of Raman spectroscopy have been developed in order to enhance the response and increase the usefulness of the method. For example, the Raman scattering signal can be increased by surface-enhanced Raman scattering (SERS), due to excitation of localized surface plasmon resonances (LSPRs) of nanostructured metal surfaces. LSPRs are a resonant oscillation of conduction electrons in the nanostructures or nanoparticles, which occur when the frequency of the photons from the laser matches the oscillation frequency of the surface electrons. This leads to a magnification of the incident light, which gives a direct increase in the amount of Raman scattering. The Raman-scattered light is then further amplified by the LSPRs. Research in Raman spectroscopy for biological measurements is a quite new activity at the Department of Electronic Systems. Both theoretical and experimental work are being explored. Several Phds and a Postdoc are developing a set-up for Raman spectroscopy. The project will be integrated with the Digital Life Norway, Double Intraperitoneal Artificial Pancreas project funded by the Research Council of Norway (2016-2020). See http://ww.ntnu.ed/web/dln/research-projects. Goals The aim of this project is to design and optimise the surface-enhancement of a fiber probe used for Raman spectroscopy of biological fluids. Surface enhancement can be achieved by coating the fiber probe with gold or silver nanoparticles. The coating process can be performed at the NTNU Nanolab, and testing of the fiber probe will be done at the Electronic Systems Department. If there is interest, it will also be possible to numerically simulate the structures, for example with COMSOL Multiphysics. Part of the project will be to perform a literature study on the state-of-the-art SERS systems. Techniques for surface-enhancement will be studied in particular. In order to attach the nanoparticles to the fiber probe, the surface will have to be prepared with a chosen method. Both the surface preparation method and the type of nanoparticles used can be investigated during this project. Two main experimental methods are suggested for optimising the surface-enhancement. Method 1: The surface of the probe can be prepared through silanization, which covers the surface in a type of functional molecule. Nanoparticles can then be deposited in a semi-monolayer by dipping the fiber in a solution containing the nanoparticles. The quality of the surface-enhancement will depend on the size and geometry of the nanoparticles.
Prosjekt-/masteroppgaver om elektromagnetiske metamaterialer Metamaterialer er kunstige, periodiske strukturer der gitterkonstanten er mye mindre enn en bølgelengde. Dermed vil materialet ideelt se ut som et homogent medium, med en effektiv permeabilitet og permittivitet. Man kan oppnå permeabiliteter og permittiviteter som ikke finnes i naturlige materialer. F.eks. har det blitt demonstrert negative parametre, som igjen gir negativ brytningsindeks. Slike materialer kan brukes til å lage perfekte linser (som kan oppløse detaljer mindre enn en bølgelengde). Man kan også lage mer kompliserte, anisotrope materialer som kan implementere en vilkårlig transformasjon av det elektromagnetiske feltet, slik som den som trengs for å få til en usynlighetskappe. Fordi gitterkonstanten må være mye mindre enn en bølgelengde, er det lettest å lage metamaterialer for bruk innen radio- og mikrobølgeteknologi. Det er en rekke interessante anvendelser her, f.eks. effektive, miniatyriserte antenner. Etter hvert som man kan strukturere materialene på nanonivå, kan metamaterialene å få stor betydning innen fotonikk/optikk. Oppgave: Numerisk homogenisering av metamaterialer Når man skal designe metamaterialer og/eller forstå egenskapene deres, trengs det algoritmer for å beregne den effektive permittiviteten og permeabiliteten. Denne oppgaven går ut på å bruke og videreutvikle en numerisk algoritme på datamaskin for å beregne disse, til et vilkårlig metamateriale som funksjon av frekvens og bølgetall. Metoden er en såkalt Plane Wave Expansion Method sammen med gitte metoder for homogenisering. Oppgaven vil bestå i først et lite litteraturstudium, deretter analytiske argumenter og programmering av den numeriske algoritmen. Den kan utføres på Kjeller eller i Trondheim. Oppgave: Multipoler i metamaterialer I praksis vil ikke bare elektriske og magnetiske dipoler, men også kvadrupoler ha betydning i metamaterialer. Faktisk så viser det seg at elektriske kvadrupoler ofte har like stor betydning som magnetiske dipoler. Vi ønsker derfor å vurdere hvordan dette kan utnyttes til nye typer kunstige materialer, hvilket kan vise seg å være nyttig for anvendelser fra radio-frekvenser til fotonikk. I denne oppgaven skal det derfor undersøkes hvilken betydning kvadrupolleddet har når man løser Maxwells ligninger i noen aktuelle situasjoner, slik som f.eks. refleksjon og transmisjon på en grenseflate (Fresnels ligninger). Oppgaven vil bestå i først et litteraturstudium, deretter analytiske argumenter og muligheter for numeriske beregninger. Den kan utføres på Kjeller eller i Trondheim. Veileder: Hans Olaf Hågenvik, hans.hagenvik@iet.ntnu.no. Faglærer: Johannes Skaar, tlf. 48497352, johannes.skaar@ntnu.no.
Forslag til prosjektoppgaver H2017 Nanoteknologi/elektronikk Jostein Grepstad Ved Institutt for elektroniske systemer drives forskning basert på epitaksiell vekst og nanoskala strukturering av funksjonelle oksid tynnfilmer. Forskningen omfatter nye dielektrika, ferroelektrika (i.e., piezoelektriske og elektrooptisk aktive materialer), magnetiske og elektrisk ledende oksider og deres grensesjikt i flerlags strukturer (herunder funksjonelle oksid multilag, substrat, metallkontakter og maskelag for strukturering). Oppgaven nedenfor er tilknyttet denne forskningen, og vil kunne videreføres i en påfølgende hovedoppgave. 1. Røntgen fotoemisjonsstudier (XPS) av grenseflatekjemi i metallmasker for fremstilling nanomagnetiske strukturer i (La,Sr)MnO3 tynnfilmer 1 student Magnetoelektroniske (spinntronikk) komponenter, så som lesehodet i moderne platelager (hard drives) og magnetiske hurtigminne (MRAM), hviler i stor grad på multilag av magnetiske tynnfilmer, der et antiferro-magnetisk lag tjener til å låse magnetiseringen i et tilstøtende ferromagnetisk referansesjikt vha. en effekt kjent som exchange bias (EB). Ved hjelp av en to-trinns struktureringsteknikk 1 har vi påvist 2 hvordan doménestruktur og magnetisk svitsjing av nanomagneter, definert vha. elektronstrålelitografi i epitaksielle tynnfilmer av LaFeO 3 og LaFeO 3/La 0.7Sr 0.3MnO 3 (LSMO) bilag, påvirkes av magnetenes geometri, størrelse og orientering relativt filmens krystallakser. Denne prosjektoppgaven er knyttet til mønstringen av filmene, som skjer ved elektronstrålelitografi i kombinasjon Ar + ioneimplantasjon gjennom ei metallmaske. Vi har så langt benyttet Cr som maskemetall. Nye undersøkelser viser imidlertid av metalliseringen i kombinasjon med påfølgende ets for stripping av Cr-masken skader filmene og deres magnetiske egenskaper. Dette trenger vi å finne ut av, og ønsker derfor å gjennomføre en XPS (x-ray photoemission spectroscopy) studie av LSMO-filmer metallisert med Cr og alternative maskematall (Cu, Au) og deretter strippet. Vi ønsker også å studere LSMO filmoverflaten før og etter oksygen ashing, som vi har funnet skader de magnetiske egenskaper til filmen. Filmene vil bli fremstilt i PLD-laboratoriet ved Institutt for elektroniske systemer (IES), metallisering vil finne sted i NTNU NanoLab. XPS-målingene vil bli utført i laboratoriet ved IES (administrativt underlagt NanoLab f.o.m. 2017). Prøvematerialet vil også bli karakterisert med scanning elektronmikroskopi (SEM), atomær-kraftmikroskopi (AFM) og magnetiske målinger (VSM) i NanoLab og laboratoriene ved IES. 1 Y.Takamura et al., Nano Lett. 6, 1287 (2006); E. Folven et al., J. Electron Spectroscopy and Related Phenomena 185, 381 (2012) 2 E. Folven et al., Nano Lett. 10, 4578 (2010); E. Folven et al., Phys. Rev. B 84, 220410(R) (2011); E. Folven et al., Nano Lett. 12, 2386 (2012), Y. Takamura et al., Phys. Rev. Lett. 111, 107201 (2013); E. Folven et al., Phys. Rev. B 92, 094421 (2015); M.S. Lee et al., ACS Nano, DOI:10.1021/acsnano.6b03770 (2016) Faglærer: Prof. Jostein Grepstad, rom A471, e-post: grepstad@ntnu.no (p.t. ved Paul-Drude-Institut für Festkörperelekttronik, Berlin) Veileder: Ambjørn Dahle Bang, rom A4xx, e-post:
2. Modellering av spinnkopling og magnetisk doménestruktur i tynnfilm nanomagneter 1 student Mikro-/nanomagnetisme omhandler magnetiske materialer og komponenter på mesoskopisk skala, dvs. større enn atomær skala, men med dimensjoner som innebærer at materialets volumegenskaper ikke gir en representativ beskrivelse av observerte magnetiske fenomen og egenskaper. Mikro-/nanomagnetisk modellering benyttes for å beskrive både harde og myke magnetiske materialer, flerlags magnetiske tynnfilmstrukturer, materialer for magnetisk minne og komponenter som lesehoder og magnetiske sensorer. Denne prosjektoppgaven går ut på simulering av doménestruktur og magnetisk svitsjing for nanomagneter av forskjellig størrelse og geometri, til støtte for eksperimentelle studier av magnetiske tynnfilm nano-strukturer i vår Oxide Electronics Group ved Institutt for elektronikk og telekommunikasjon. 2-6 Arbeidet vil være basert på bruk av åpen programvare kjent under akronymet OOMMF (The Object Oriented Micro-Magnetic Framework). 1 Oppgaven vil egne seg for en student med interesse for modellering. 1 http://www.ctcms.nist.gov/~rdm/mumag.org.html, http://math.nist.gov/~mdonahue/micromag.html 2 E. Folven et al., Nano Lett. 10, 4578 (2010) 3 E. Folven et al., Phys. Rev. B 84, 220410(R) (2011) 4 E. Folven et al., Nano Lett. 12, 2386 (2012) 5 E. Folven et al., J. Electron Spectroscopy and Related Phenomena 185, 381 (2012) 6 Y. Takamura et al., Phys. Rev. Lett. 111, 107201 (2013) Faglærer: Prof. Jostein Grepstad, rom A471, e-post: jostein.grepstad@iet.ntnu.no Veileder: Dr. Erik Folven, rom A481, e-post: folven@iet.ntnu.no
Master thesis suggestion Relevant for: Physics/Chemistry/Materials science/nanotechnology Synthesis and/or device modeling of organic silicon hybrid solar cells Organic-Si hybrid solar cells are one of the emerging photovoltaic (PV) technologies. Efficiencies in excess of 20% have already been reported recently, and this high efficiency has been achieved only within the past few years. The cells are composed of an n-type Si wafer and an organic polymer called poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) used as the emitter, with p-type electrical conductivity. This type of solar cell provides a unique possibility to combine the high energy conversion efficiency of crystalline Si solar cells with the potentially low fabrication cost of organic solar cells. The goal of this project is a theoretical and/or experimental study of organic/si hybrid cells. The experimental part of the project will be deposition of commercially available PEDOT:PSS on n-si wafers usingthe spin coating and characterization of optical and electrical properties of this structure. Si surface passivation will be studied by functionalizing PEDOT:PSS with different types of inorganic nanoparticles, such as, e.g., Si, produced in the IFE Department for Solar Energy. Finally, Si/organic heterojunction solar cells will be fabricated and characterized. The theoretical part consists of device modeling of two different solar cell designs, with the polymer emitter layer placed in the front side or back side of the cells. Optimal solar cell parameters and ultimate device performance will be estimated. The software to be used is Silvaco Atlas, for which IFE has the necessary competence and software license. The work will be performed at the IFE Department for Solar Energy and at NTNU. Well-developed infrastructure and experienced supervisors and lab engineers will be available for both the experimental and theoretical work. No prior knowledge of using the Silvaco Atlas or the experimental techniques is necessary. IFE is located at Kjeller, ~20 km east of the center of Oslo. The solar energy group usually trains multiple master students from the universities at any given time, and the laboratory is relatively new with state-of-the-art equipment and offices. Welcome to IFE! Contacts: Erik S. Marstein Director of the FME Centre Solar United Department for Solar Energy, IFE Mobile: (+47) 9011 7762 E-mail: erik.stensrud.marstein@ife.no S. Zh. Karazhanov and Halvard Haug Department for Solar Energy, IFE E-mail: smagulk@ife.no E-mail: Halvard.Haug@ife.no Jostein Grepstad Professor, Department of Electronic Systems Tel: +47 73592721 Tel: +47 47418251 E-mail: jostein.grepstad@ntnu.no
1. Magnetisk mikroskopi på nanostrukturer for bruk i spinn-logikk 1 student Digital elektronikk som baserer seg på vekselvirkende magnetiske spinn fremfor transport av elektrisk ladning vil ha mange av de karakteristika som er ønskelige i neste generasjons applikasjoner for digital logikk. Ved å flippe spinn i stedet for å flytte ladning kan de ohmske tapene som er uunngåelige i konvensjonell elektronikk elimineres og med dette den primære kilden for spillvarme i mikrochips fjernes. Nanomagnetisk logikk (NML) er et paradigme innen elektronisk databehandling som baserer seg på propagasjon og prosessering av digital informasjon i nettverk av vekselvirkende nanomagneter [1]. NML er en sterk kandidat for ultra-lavenergi databehandling og kan kombinert med f.eks. multiferroisk initialisering gi en effektreduksjon på opptil tre størrelsesordener sammenliknet med dagens CMOS teknologi [2]. Vi har gjennom flere år studert hvordan doménestruktur i nanomagneter kan kontrolleres via geometri, størrelse, orientering og magnetisk kopling over grenseflater [3-6]. Denne prosjektoppgaven bygger videre på dette arbeidet og vil primært omfatte bruk av et nytt lavtemperatur MFM (magnetic force microscope) ved Institutt for elektroniske systemer (IES). Dette for å undersøke nanomagneter til mulig bruk i NML. Filmene vil bli fremstilt i PLD-laboratoriet ved IES, mens struktureringen vil bli utført i NTNU NanoLab. De nanostrukturerte prøvene vil bli karakterisert med sveipelektronmikroskopi (SEM) og atomærkraftmikroskopi (AFM) forut for de magnetiske målingene. 1 A. Imre et al., Science 311, 205 (2006) 2 M. S. Fashami et al., Nanotechnology 23, 105201 (2012) 3 E. Folven et al., Nano Lett. 10, 4578 (2010) 4 E. Folven et al., Nano Lett. 12, 2386 (2012) 5 Y. Takamura et al., Phys. Rev. Lett. 111, 107201 (2013) 6 E. Folven, et al. Phys. Rev. B 92, 094421 (2015) Faglærere: Førsteamanuensis Erik Folven, rom A-467, e-post: erik.folven@ntnu.no Prof. Jostein Grepstad, rom A471, e-post: jostein.grepstad@ntnu.no Veileder: Ambjørn Dahle Bang, rom A-461, e-post: ambjorn.bang@ntnu.no
SILICON NANOPHOTONIC BIOSENSOR Introduction Photonics is currently one of the most rapidly developing branches of science that explores the properties of light for solving various problems. The list of applications is extensive and the impact it has on our lives is often compared to that of what electronics has achieved since the invention of a transistor. Information processing, ultrafast telecommunication, medical diagnosis, optical displays of various kinds, ultrahigh-precision sensors are only few examples where photonics has become prominent. With continuously expanding ranges of new applications and materials, this branch of research is believed to transform our societies in the next few decades. Silicon as platform for photonic devices is interesting due to its high light confinement, and because standard lithography and CMOS processes can be used to fabricate micro- and nanoscale components. Because silicon is CMOS compatible, integrated systems on a single semiconductor chip can be realized. Examples of micro- and nanophotonic components are dielectric waveguides, microresonators of various types, light modulators, couplers, periodic structures and more. Especially, a certain type of periodic structures, known as photonic crystals, due to their extraordinary ability of light confinement, possess a truly remarkable potential for applications in both fundamental research and industry. Research in silicon photonics is an ongoing activity at the Department of Electronic Systems. Both theoretical and experimental work is explored. A number of master students and PhD students have been/are designing and processing silicon-based photonic crystal and waveguide structures. Processes and recipes have been developed at the NTNU Nanolab to fabricate these silicon-based structures. Optimization is an ongoing task. The project will be integrated with the Digital Life Norway, Lab-on-a-chip biophotonic sensor platform for diagnostics project funded by the Research Council of Norway (2016-2020). See http://www.ntnu.edu/web/dln/researchprojects. Goals The aim of this project is to design and simulate a silicon nanophotonic biosensor. To achieve high sensitivity it is likely that the sensor will be ring resonator based or interferometric (e.g. based on a Mach - Zehnder configuration). Both waveguide and photonic crystal structures can be pursued. The component can be processed at the
NTNU Nanolab as part of the master s project, or the student can continue to optimize simulations. Part of the project will be to perform a literature study on the stateof-the-art silicon photonic sensors. In particular surface functionalized biosensors will be studied. To make the sensor specific to a target biomolecule, the surface is coated with antibodies via chemically activated functional groups. These surface coated antibodies act as specific capture agents and protein binding to these surface receptors induces a sensor response. The antigen - antibody binding causes a surface refractive index change of the functionalized sensor and the concentration of the binding antigens can be measured. In parallel with the literature study the student will learn the basics of the simulation software. The main goal of the project will be to design the photonic sensor by the aid of numerical simulations using COMSOL Multiphysics, which is based on Finite Element Method (FEM). Other simulation tools may also be utilized such as, MIT Photonic Bandgaps (MPB) to calculate eigenmodes and MIT Electromagnetic Equation Propagation (MEEP), which is finite-difference time-domain (FDTD) based. If time allows during the Fall semester, cleanroom courses will be taken at the Nanolab to qualify the student to fabricate the device in the NTNU Nanolab. It is also possible to take these courses at the beginning of the master s project.
Figure 1: Examples of structures simulated using FEM, COMSOL Multiphysics. Supervisors Astrid Aksnes, Prof., room B413, Astrid.Aksnes@ntnu.no, tel. 73597699 Jens Høvik, PhD student, room B412, Jens.Hovik@ntnu.no
Student/master projects in nano-optoelectronics 2017/18 http://www.iet.ntnu.no/~weman/ The nano-optoelectronics group at the Department of Electronic Systems (IES) focuses on growth, characterization and processing of III-V semiconductors for use in photonics, solar cell technology and sensor applications. A strong focus is being made on III-V semiconductor nanowires (NWs) grown by molecular beam epitaxy (MBE lab). Fabrication of NW devices is being explored by electron beam lithography as well as by nanoimprint and focused ion beam techniques using NTNU NanoLab. Optoelectronic characterization of individual nanosystems using techniques such as low temperature photocurrent and electroluminescence (Nanophotonics lab) is done in order to understand, improve and utilize quantum size effects for future nanophotonic device applications. In collaboration with Prof. Ton van Helvoort at IFY we also perform detailed structural characterization of the nanowires using the TEM Gemini Center. Some of the projects suggested will be performed in collaboration with our spin-off company CrayoNano AS. Normally you will work in close collaboration with a postdoc or a PhD student of the group to achieve your goals in the project. The projects normally have an applied character and can be both theoretical and practical, and some include clean room work in NTNU NanoLab. The projects are most suited for students from the nano-electronics and nanomaterials branch of the Nanotechnology program and the nano-electronics and photonics branch of the Electronics program, but other students with a strong background in these fields are also welcome. Faculty supervisors for the projects are: Prof. Helge Weman, helge.weman@ntnu.no, Room B415 in Electro. Prof. Bjørn-Ove Fimland, bjorn.fimland@ntnu.no, Room A381 in Electro. Some recent publications from our group: 1. A.M. Munshi, D.L. Dheeraj, V.T. Fauske, D.C. Kim, A.T.J. van Helvoort, B.O. Fimland, and H. Weman, Nano Lett. 12, 4570 (2012). 2. L. Ahtapodov, J. Todorovic, P. Olk, T. Mjåland, P. Slåttnes, D.L. Dheeraj, A.T.J. van Helvoort, B.O. Fimland, and H. Weman, Nano Lett. 12, 6090 (2012). 3. D.C. Kim, D.L. Dheeraj, B.O. Fimland, and H. Weman, Appl. Phys. Lett. 102, 142107 (2013). 4. A. M. Munshi, D. L. Dheeraj, V. T. Fauske, D. C. Kim, J. Huh, J. F. Reinertsen, L. Ahtapodov, K. D. Lee, B. Heidari, A. T. J. van Helvoort, B. O. Fimland, and H. Weman, Nano Letters, 14, 960 (2014). 5. G. Signorello, E. Lörtscher, P.A. Khomyakov, S. Karg, D.L. Dheeraj, B. Gotsmann, H. Weman and H. Riel, Nature Communications, 5, 3655 (2014). 6. J. Huh, H. Yun, D.C. Kim, A.M. Munshi, D. L. Dheeraj, H. Kauko, A.T.J. van Helvoort, S.W. Lee, B.O. Fimland, and H. Weman, Nano Letters, 15, 3729 (2015).
1. Fabrication and characterization of vertical III-V semiconductor nanowire/graphene junction devices (involves work in NanoLab) In vertical III-V semiconductor NW/graphene devices where NWs are grown directly on graphene substrates there are many technical and scientific challenges still not fully understood. One of them is how the ohmic contact is formed and works between the NWs and graphene. In this project, the student will focus on the fabrication processes for vertical NW/graphene junction devices. The whole fabrication process from the graphene substrate preparation to the final metallization on top of the NW array will be carried out by using various facilities in NanoLab, in close collaboration with other members in the nanooptoelectronics group in IES and CrayoNano AS. If the process development is successful and time allows, the optoelectronic properties of vertical NW/graphene junction devices will be further investigated. Supervisors: Ph.D. student: Ida-Marie Høiaas, ida.hoiaas@ntnu.no Adjunct associate professor: Dong Chul Kim, dc.kim@ntnu.no
2. Process development and characterization of graphene-si junction devices (involves work in NanoLab) In the field of graphene research, more and more efforts are focused towards integrating graphene with existing technologies and developing actual devices. In our group we have developed a method for depositing large-grained crystalline Si on graphene via a metalinduced crystallization process. The next steps in this work are to investigate the quality of the synthesized materials and the electronic properties of the graphene/si heterostructure by making an actual device. The project will involve clean room work as well as device characterization. Furthermore, process optimization of the Si deposition on graphene and its doping will be performed in parallel with the device development. As such, the project combines in-depth understanding of the structural and functional properties of semiconductor nanomaterials. Supervisors: Ph.D student: Ida-Marie Høiaas, ida.hoiaas@ntnu.no Adjunct associate professor: Dong Chul Kim, dc.kim@ntnu.no
3. Fabrication and characterization of single III-V semiconductor nanowire devices (involves work in NanoLab) Our group has a long history in developing III-V semiconductor nanowire devices ranging from GaAs-based nanowire (NW) array solar cells to GaN-based NW array LEDs. In order to realize such NW array devices it is very important to understand the optoelectrical properties of each single NW. Through this project, the student will have a great opportunity to participate in the fabrication and characterization of single NW devices. She/he will start to learn various fabrication processes including e-beam lithography (EBL) in NanoLab, and finally carry out opto-electrical measurements of the devices at Nanophotonics lab in IES. Supervisors: Ph.D student: Anjan Mukherjee, anjan.mukherjee@ntnu.no Adjunct associate professor: Dong Chul Kim, dc.kim@ntnu.no
4. Fabrication and characterization of embedded nanowire/graphene hybrid devices for gating structure. (involves work in Nanolab) GaAs is one of the most important III-V semiconductor NW structure with a high potential for high-efficiency solar cells and photo detectors. In addition, using graphene as a highly conducting and transparent electrode could lead to enhanced absorption efficiency of single GaAs NW optoelectronic devices as well as enable basic NW contact studies through a Fermi level tuning of the graphene. The key challenge to make a NW/ graphene hybrid devices NW on a flat surfaced structure for successful graphene transfer, has recently been demonstrated by our group. The fabrication of graphene/dielectric/graphene structure (gating structure) on an embedded nanowire configuration is yet to be solved. In this project, the student will study the fabrication process to make a gating structure of graphene on top of an embedded NW and perform optoelectrical measurements. The whole process from substrate preparation to final metallization through several electron beam lithography (EBL) steps will be carried out by using various facilities in Nanolab. Supervisors: Ph.D student: Anjan Mukherjee, anjan.mukherjee@ntnu.no Adjunct associate professor: Dong Chul Kim, dc.kim@ntnu.no
5. Wafer-scale hole array patterning on graphene substrates for the selective area growth of semiconductor nanowires (involves work in NanoLab) The recent demonstration of successful growth of III-V nanowires (NWs) on graphene is an important cornerstone in next generation high functional III-V semiconductor optoelectronic devices where flexible, conducting, and extremely light, single carbon layer graphene is used as a substrate. Together with process engineers in CrayoNano AS, the student will develop a highly reproducible and fast way to make sub-100 nm hole patterning on graphene wafers with an oxide mask for selective area growth of NWs in a well-ordered array form. EBL is primarily used to make the hole patterning with various process parameter optimizations. Other nanolithography techniques such as colloidal lithography will be also investigated and developed as a cheap alternative for EBL. Supervisors: CrayoNano AS engineer: Carl Philip Heimdal, carl.philip.heimdal@crayonano.com Leidulv Vigen, leidulv.vigen@crayonano.com Adjunct associate professor: Dong Chul Kim, dc.kim@ntnu.no
6. InGaN nanowires for water-splitting applications (involves work in NanoLab) Solar-fuel conversion is desirable for high-efficiency green energy production, and the solar water splitting for hydrogen generation can be a potential source of renewable energy for fuel cells used in mobile vehicles etc.. In this project, the student will use the newly installed molecular beam epitaxy (MBE) system equipped with a nitrogen plasma source to grow the GaN/InGaN nanowires, which will be used for the photocatalytic water splitting. The student will aid in growing the GaN/InGaN nanowires, and be involved in analyzing the cell performance with a variety of catalysts, such as Pt, rhodium (Rh)/chromium-oxide (Cr2O3) core shell nanoparticles etc.. In addition, the student will use the high-resolution scanning electron microscopy (SEM) facility with energy dispersive x-ray (EDX) elemental analysis in NTNU Nanolab to characterize the nanowire compositions. Supervisor: Postdoc: Dingding Ren, dingding.ren@ntnu.no
7. Growth study of AlGaN nanowires on graphene for UV LED applications (involves work in NanoLab) GaN and its alloys (InGaN and AlGaN) have become one of the most important materials in the semiconductor industry, particularly for light emitting applications. Compared to InGaN, which has been well-exploited for visible LEDs, the development of AlGaN based UV LEDs is much more challenging. Such LEDs are in high demand for UV light based sterilization and disinfection. The utilization of nanowire structures significantly enhance the crystal quality of the active AlGaN material, with no dependence on the crystalline nature of underlying substrate, not achievable using conventional thin film structures. Graphene will be used as an epitaxial substrate for the AlGaN nanowire growth and transparent electrode. Combined such AlGaN nanowire/graphene structure could be a key factor in advancing the progress of future UV LEDs. The student will start the project with a nucleation study of GaN and further AlGaN nanowires grown by molecular beam epitaxy on graphene. Different characterization techniques (SEM, XRD, Raman, PL and electrical characterization) will be employed in order to optimize the structural and electrical properties of the grown AlGaN nanowires. Fully processed UV LED structures can be fabricated and studied a s the part of a master thesis project in the spring 2018. Supervisors: PhD student Andreas Liudi Mulyo, andreas.liudi-mulyo@ntnu.no PhD student Anjan Mukherjee, anjan.mukherjee@ntnu.no
8. Time-resolved spectroscopy and optical pumping of GaAsSb nanowire laser arrays Semiconductor nanowires (NW) have been successfully applied for optoelectronic devices such as lasers and light emitting diodes. GaAs NWs with multiple axial GaAs/GaAsSb heterostructured superlattice inserts have been fabricated at the Nanowire group at NTNU and found to be lasing in the near infrared spectral region. However, all experiments conducted so far have been on single NWs, detached from the growth substrate. The next step towards achieving a NW-based laser device is to study as-grown NW laser arrays with in-plane optical excitation and head-on collection of the luminescence signal. The student will work at the Nanophotonics lab at NTNU on developing an optical setup that will enable conducting this experiment. The project involves working with Class 4 lasers and cryogenic liquids (i.e. liquid He), and has a strong focus on nanophotonics and solid state physics. Supervisor: Postdoc: Lyubomir Ahtapodov, lyubomir.ahtapodov@ntnu.no Postdoc: Dingding Ren, dingding.ren@ntnu.no
9. Correlated micro-photoluminescence and transmission electron microscopy of GaN/InGaN nanowires. GaN/InGaN nanowires (NW) hold great potential for fabricating NW-based light emitting diodes for future micro-display applications (wearables, VR, AR etc.). In this project, the student will conduct micro-photoluminescence spectroscopy (µ- PL) on single GaN/InGaN NWs, deposited on transmission electron microscopy (TEM) substrates in order to allow for post-pl structural characterization of the same single NWs. In the course of the project, an optical setup, which allows for excitation with UV light (i.e. below 300 nm) will be developed. The student will mainly work in the Nanophotonics lab at NTNU, however there will be a close collaboration with the staff at the MBE lab and the TEM facilities at IFY. The project involves using a Class 4 pulsed fs Ti:Saphire laser and a frequency doubler/tripler unit in order to achieve UV excitation of the samples. The project has a strong focus on optics and spectroscopy of advanced nanomaterials. Supervisor: Postdoc: Lyubomir Ahtapodov, lyubomir.ahtapodov@ntnu.no Postdoc: Dingding Ren, dingding.ren@ntnu.no
Method 2: Surface-enhancement by film deposition over nanospheres can also be achieved. In this method one layer of polymer nanospheres is attached to the fiber tip, which is then coated with a thin Ag film (~200 nm) using thermal deposition. Alternatively, by coating microspheres with a gold layer and sonication of the fiber probe, spheres are removed leaving an array of gold triangular islands. Figure 1: Suggested set-up for sensing with the fiber probe (top), enlarged scheme of the sensing mechanism in the probe tip (middle), and an example of a tapered fiber (bottom). Supervisors Astrid Aksnes, Prof., room B413, astrid.aksnes@ntnu.no, tel. 73597699 Karolina Milenko, Postdoc, room B419, karolina.milenko@ntnu.no Ine Jernelv, PhD student, room B419, ine.jernelv@ntnu.no