Skip to ContentSkip to Navigation
OnderzoekZernike (ZIAM)OnderwijsTop Master Program in Nanoscience

NS194. Small research project -- projects for 2014 [now obsolete]

The available small research projects for 2014 are listed here. Please contact the supervisor mentioned in case you are interested in a project. First come, first served...

For contact information on all mentioned professors and groups see
http://www.rug.nl/research/zernike/research/people
http://www.rug.nl/research/zernike/research/labs

_________________________________________________________

1 Group: Molecular Dynamics

Project 1.1

Supervisor(s): Prof. Siewert-Jan Marrink and Dr. Alex de Vries

Computer simulation of gating of mechanosensitive membrane channels

Mechanosensitive channels are small membrane proteins that sense the tension in the cell membrane. Once the tension gets above a certain threshold, the channels open. By this mechanism, bacterial cells protect themselves against hypoosmotic shocks. The exact opening mechanism, however, is largely unknown as it can not be easily probed experimentally.

In this project you will use a state-of-the-art computer simulation technique, multi-scale molecular dynamics, to unravel the molecular details of the gating process [1]. Everything in-silico, no need to clean up afterwards! You will even have the chance to play God, and design artificially modified channels with specific gating properties. Engineered protein channels hold promise in many technological applications, for instance, in drug delivery and sensing.

[1] M. Louhivuori, H.J. Risselada, E. van der Giessen, S.J. Marrink. Release of content through mechano-sensitive gates in pressurized liposomes. PNAS, 107:19856-19860, 2010.

Project 1.2

Supervisor(s): Prof. Siewert-Jan Marrink and Dr. Alex de Vries

Adaptive resolution simulations of lipid bilayers

Traditionally, molecular dynamics simulations of (bio)materials are performed at the all-atom level. More recently, coarse-grain models in which some of the atomic details have been replaced by effective, coarse-grained, interaction sites have gained a lot of popularity [2]. The current challenge is to combine the accuracy of all-atom models with the computational speed obtained with coarse-grained models.

In this project you will pioneer the use of an adaptive resolution approach [3] to perform simulations of lipid bilayers. The idea is that lipids in the central part of the membrane (i.e., the part of primary interest) are represented in full atomic detail, but when they diffuse away are gradually changing their resolution on-the-fly. Further away from the central zone, the lipids are treated completely coarse-grained. This project is about method development, and requires someone not afraid of computational algorithms; some coding might actually be part of the project.

[2] S.J. Marrink, D.P. Tieleman. Perspective on the Martini model. Chem. Soc. Rev., 42:6801-6822, 2013.
[3] M. Praprotnik, L. Delle Site, K. Kremer. Multiscale simulation of soft matter: From scale bridging to adaptive resolution. Ann. Rev. Phys. Chem., 59:545-571, 2008.

2 Group: Theory of Condensed Matter

Project 2.1

Supervisor(s): MSc Jasper Compaijen, Prof. Jasper Knoester and Dr. Victor Malyshev

Disorder in sub-diffraction optical waveguides made from metal nanoparticles

It has been shown that chains of plasmonic metal nanoparticles are able to guide optical signals, even if the lateral dimensions of the particles are far below the diffraction limit. Using this idea, one could think of designing optical splitters, bends or localizers. These systems can be easily simulated using dipole-dipole interactions. From a theoretical perspective it is tempting to do calculations on an idealized system, consisting for example of identical and perfectly spherical nanoparticles. As we all know such a system is not very realistic, because there will always be small deviations due to the fabrication process. In this project we will study the influence of this disorder on the device operation and explore if it could be used to add functionality to the device, for example considering localization of optical excitations. Furthermore, it will allow us to decide if the device fabrication needs to be very precise, but therefore slow and expensive, or methods with less precision can be used.

Project 2.2

Supervisor(s): MSc Jasper Compaijen, Prof. Jasper Knoester and Dr. Victor Malyshev

Dipole radiation in metal-dielectic-metal systems

On the interface between a metal and a dielectric, so-called surface plasmon polaritons (SPPs) can be excited. These modes are bound to the interface and can propagate along this interface and are of key importance for the development of nano-optical devices. In a metal-dielectric-metal (MDM) structure two of these SPPs modes are brought together and form coupled modes, of which the dispersive properties can be altered tremendously by changing the thickness of the dielectric layer. It is well known that SPPs can be excited using the near field of an emitter, for example an oscillating dipole. In this project we like to study the emission profile of an oscillating dipole embedded in a MDM system as a function of the thickness of the dielectric layer and investigate the influence of the excitation of the SPP modes, in particular when the thickness becomes smaller than the emission wavelength of the dipole. It has been shown that in this limit a mode with a refractive index near zero can arise, which implies that there will be no phase advance of the emitted radiation.

Project 2.3

Supervisor(s): Assistant prof. Thomas L.C. Jansen

Water Interfaces: Overcoming phobias

Water and hydrophobic solvents as octane are well-known to avoid each other - an effect that is for example crucial in the folding of proteins. This makes the study of the interaction between these molecules notoriously difficult. Recent studies have overcome this problem utilising the surface specific sum-frequency generation technique. The experimental result is highly surprising as the sign of the signal generated is opposite that observed for water-air interfaces. This points to a very different organisation at the two different interfaces. In this theoretical study the water octane surface will be simulated, the sum-frequency generation signal will be calculated and the reason for the sign change will be analysed on the molecular level providing a better understanding of how water and hydrophobes, when they are forced to interact.


3 Group: Optical Condensed Matter Physics

Project 3.1

Supervisor(s): Assistant prof. Ron Tobey and Jasper Compaijen, MSc

Surface Plasmon Polaritons in Coupled Plasmonic Systems

Surface Plasmon Polaritons (SPP) are propagating electromagnetic excitations that are localized to the interface of a dielectric and a conductor. These modes are coupled electromagnetic waves and plasma oscillations of free electrons in the metal. In conventional noble metals such as silver and gold, excitation can be readily achieved in the visible spectral regime.

In this short project, students will measure the SPP dispersion relation for a silver film when in close proximity to plasmonic silver nanoparticles. Coupling of the SPP to the plasmonic nanoparticles is expected to alter the dispersion relation of the bare SPP when near the plasmonic resonance of the nanoparticles. Extension of this technique includes tethered plasmonic nanoparticles and their coupling to the SPP mode.

1. Experimental – Measure SPP dispersion curves of thin silver film in close proximity to plasmonic nanoparticles.

2. Modeling – Calculate/model using Matlab the dispersion relation for SPPs in silver and compare to that observed in the experiment above. Theory and Modeling in close collaboration with the condensed matter theory group.

4 Group: FOM Focus Group, Next-Generation Organic Photovoltaics
(for this project the Zernike groups Photophysics and opto-electronics, and (Bio)Organic Materials and Devices)

Project 4.1

Supervisor(s): Assistant prof. Ryan Chiechi and assistant prof. Jan Anton Koster

Constructing 3-D Images of the Nano-morphology of Polymer Solar Cells by Electron Microscopy

The morphology of the mixture of the donor and acceptor components of organic solar cells is a bulk-heterojunction; an intimate mixture of nano-scale domains that forms spontaneously. The precise structure of the heterojunction hugely impacts the properties of organic solar cells, but its size and complexity make direct imaging impossible. Indirect techniques such as X-Ray diffraction give information about the overall order, but direct imaging with electron microscopy is hindered by the lack of contrast between the materials in thin films. In this short masters project you will construct bulk-heterojunction polymer solar cells on epoxy substrates and then cut them into 50 nm-thick sections using a form of edge lithography called nanoskiving. You will then image them by transmission electron microscopy (TEM) at a resolution of ~1 nm and re-assemble these images into a complete, 3D rendering of the bulk-heterojunction.

This project has four components:
1) Forming bulk-heterojunction structures from conjugated polymers and fullerene derivatives.
2) Making ultra-thin sections of these heterojunctions by nanoskiving.
3) Imaging these sections by TEM.
4) Reconstructing the 3D structure of the bulk-heterojunction from these images.

You can expect to learn about:
• Organic photovoltaic devices
• The morphology of bulk-heterojunctions
• Working in the clean room, fabricating solar cell devices
• Nanoskiving
• Electron microscopy
• 3D image reconstruction

5 Group: Nanostructured Materials and Interfaces

Project 5.1

Supervisor(s): Prof. Bart J. Kooi

SeSbTe phase-change alloys studied by ultrafast differential scanning calorimetry (DSC)

Phase-change materials (PCMs) are currently investigated intensely, mainly to replace in the near future the popular Flash-type memory, which is used in e.g. mobile phones, tablet computers, USB memory sticks etc.. PCMs already have been applied successfully in optical recording, well-known from the rewritable CD, DVD and Blu-Ray Disk formats. Phase-change memories can be switched reversibly more than a million times between amorphous and crystalline states and exploit the large differences in optical reflectivity or electrical resistance of the two states.

Recently we were the first in the world to study the reversible amorphous-crystalline phase change in a chalcogenide model PCM material using ultrafast DSC, which allows heating rates up to 40000 K/s and cooling rates down to -4000 K/s. The chalcogenide model PCM was SeTe where we studied a large composition range between 15 and 60 at.% Te. For this small research project we want to extend this work by analyzing the ternary SeSbTe alloy. Measurements in the ultrafast DSC involve rapidly cooling (with various rates) a melt into an amorphous state and then measuring the glass transition and crystallization peak during heating with various heating rates allowing determination of the activation energies of the transitions. Important outcome will be the effect of the addition of Sb on the properties of SeTe.

Project 5.2

Supervisor(s): Associate prof. George Palasantzas

Surface roughness influence on capillary forces

The capillary force has measured by atomic force microscopy between a gold coated sphere mounted on a cantilever and gold surfaces with different roughness. A substantial decrease in the capillary force was observed by increasing the roughness ampltitude a few nanometers between 1-10 nm. From these measurements two limits can be defined: a smooth limit where a closely macroscopic size contact surface interacts through the capillary force, and the rough limit where only a few asperities give a capillary contribution. This project will perform statistical analysis of high surface peaks contributing to capillary forces and sum the contribution of these micro-capillary contributions via proper implementation of height probability distributions from measurements via AFM of surface topologies. Finally the theoretical predictions will be compared to those observed in experiments extrapolating between smooth-rough limits. These results are of high importance for industrial applications. For any info contact G. Palasantzas: G.palasantzas@rug.nl

Project 5.3

Supervisor(s): Associate prof. George Palasantzas

Casimir force measurement between conductive SiC and B-Silicate smooth surfaces

In this project the we will attempt the measurement between smooth (rms ~0.13 nm) planar conductive SiC surfaces and smooth (rms~0.7 nm) B-Silicate spheres attached onto cantilevers. The results will be compared to Casimir force theory predictions derived from Lifshitz theory calculations using as input measured optical data in the frequency range 0.01 to 8.9 eV via ellispsometry. Measurements will be performed both in air and under vacuum conditions, as well as dry nitrogen atmosphere. The aim is towards genuine high adhesion surfaces between stiff materials with smooth surfaces. For any info contact G. Palasantzas: G.palasantzas@rug.nl

6 Group: Theoretical Chemistry group and Materials Science group

Project 6.1

Supervisor(s): Dr. Remco Havenith (Theoretical Chemistry group) and Dr. Willem F. van Dorp (Materials Science)

Between chemistry and physics: electron-induced chemistry

To produce faster computers and smartphones, two techniques are important. Firstly, extreme ultraviolet (EUV) lithography, where patterns are transferred from a mask onto a wafer by exposing a photosensitive layer (resist) to EUV light. Secondly, focused electron beam induced processing (FEBIP) enables the local modification of samples through the etching and deposition of material.

However, these techniques have their limitations. The throughput of EUV lithography is sub-optimal and it is unknown how far we can push the resolution. In FEBIP, most of the gases that are used for the etching and deposition typically yield inferior products.

We face these limitations, because we understand little of the underlying chemistry. In both EUV lithography and FEBIP, low-energy electrons induce reactions in molecules through ionization. These reactions are fundamentally different from those between neutral species. We want to understand what happens when electrons interact with a molecule. What makes one reaction path more favourable than the other? How does a molecule respond to an extra electron? And how important is the energy of the electron?

Using (time-dependent) density functional theory, you will be among the first to study how electrons induce chemistry in organometallic molecules. You will calculate the decomposition of organometallic complexes, the results of which we can compare to experimental data.

7 Group: Device Physics of Complex Materials

Project 7.1

Supervisor (s): Prof. J. Ye

Magnetic ionic liquids for field effect transistors

Ionic liquids are room temperature molten salts in which movable ions are able to mediate a field effect charge doping mimicking the operation of a field effect transistor. The ion-mediated charge injection can create surfaces with dense carriers reaching the order of 1014 cm-2. This highly doped surface has been a prolific playground for controlling various quantum phase transitions such as metal-insulator transition, Mott-transition, superconductivity, ferromagnetism, etc.

In this short project, we will make a bold venture to build transistors using magnetic ionic liquids, a new class of ionic liquids with magnetic moment associated with moving ions. Adding magnetic properties in addition to ionic motion is designed to mediate carrier doping for novel magnetic quantum phase phenomena and device functionalities.

The research comprises two parts.

1.     Synthesize magnetic ionic liquids (one step chemical process has been already developed) using ions of different magnetic elements.

2.     Field effect device operation of ion-mediated transistors using new ionic liquids. Searching for possible effect from magnetic ions on the transport of induced carriers on channel surface.

Project 7.2

Supervisor (s): Prof. J. Ye

Optical study of valley polarization in nanosheets of transition metal dichalcogenide

Isolating atomically thin nanosheets from transition metal dichalcogenides (TMDs) is a recent method to prepare two-dimensional valley-sensitive materials on which a new type of electronics: valleytronics could be developed. Here, the valley degree of freedom is originated from the band structure of TMDs, in which electrons occupy multiple conduction band minimum/valence band maximum with same energies but at different positions of momentum space. Generating, controlling and detecting electrons at inequivalent valleys will act as an emerging way to exploit electrons in a new internal degree of freedom (valley index).

The key motivation here is to realize an optical control of valley polarization in varieties of TMDs with the chemical form of MX2 (where M stands for transition metal such as Mo, W, Ta, Zr, V, etc. and X stands for S, Se, and Te). Studying valley-polarized optical properties in many MX2 nanosheets will serve as a guideline to establish the control of valley-sensitive responses as the basis for developing valleytronics.

Two steps will be included in this project:

1.     Synthesizing bulk semiconducting TMDs (MoS2, WSe2, etc.) using the facility of solid-state chemistry group (an optional step as some TMD crystals have already been synthesized).

2.     Making nanosheets using micro-cleavage (graphene method) on various TMDs, optical control of valley responses from TMD nanosheets using circular polarized light and electric-field control on valley polarization.

8 Group: Systems Chemistry

Project 8.1

Supervisor(s): Prof. Sijbren Otto ( s.otto@rug.nl ); d aily guidance by Elio Mattia ( e.mattia@rug.nl )

Modelling the evolution of self-replicating molecules that form nano-sized assemblies

Replicators play a fundamental role in studies on the origins of life [1] and we recently discovered that supramolecular nanofibrils originating from two different food materials can replicate themselves generating a library of highly diverse replicators. We now want to discover how subjecting such systems to a continuous replication/death regime might act as a selection pressure resulting in the survival of the fittest replicators. The high complexity of this system requires a combined experimental and computational effort. [2-4]

During the research project, the student will first be introduced to the experimental reality of our supramolecular replicators[5] and to the analytical techniques employed to study them. The bulk of the project will focus on the development of deterministic and stochastic (Gillespie-type [3]) kinetic models of the replication/death reaction using Matlab (integrated with the C language where necessary). These models will then be explored and probed under diverse conditions in order to gain a better fundamental understanding of the principles of Darwinian evolution with molecules. The student will have the opportunity to focus on model development with the technique he/she feels more comfortable with, while at the same time becoming acquainted with the mathematical and computational details of the other techniques and improving his/her general programming skills overall. The theoretical and practical importance of the results within the context of origins of life studies will be thoroughly discussed.

Requirement: basic programming skills and basic knowledge of differential equations. Specific basic knowledge of Matlab (and/or C) and familiarity with statistics are a plus but not strictly required.

Further reading:

1.       A. Pross. Toward a general theory of evolution: Extending Darwinian theory to inanimate matter. J. Syst. Chem. 2011, 2, 1.
2.       J. A. Bachman, P. Sorger. New approaches to modeling complex biochemistry. Nature Methods 2011, 8, 2, 130-131.
3.       D. Gillespie. A general method for numerically simulating the stochastic time evolution of coupled chemical reactions. J. Comp. Phys. 1976, 22, 403-434.
4.       M. W. Sneddon, J. R. Faeder, T. Emonet. Efficient modeling, simulation and coarse-graining of biological complexity with NFsim. Nature Methods 2011, 8, 2, 177-183.
5.       J. M. A. Carnall, C. A. Waudby, A. M. Belenguer, M. C. A. Stuart, J. J.-P. Peyralans, S. Otto. Mechanosensitive self-replication driven by self-organization. Science 2010, 327, 1502-1506.

Project 8.2

Supervisor(s): Prof. Sijbren Otto ( s.otto@rug.nl ); d aily guidance by Giulia Leonetti ( g.leonetti@rug.nl )

Self-assembly driven emergence of self-replicators: environment matters!

Self-replication and self-organization are often considered as the hallmarks of living systems. Self-replicating molecules are likely to have played an important role in the origin of life. To create de-novo life, one key step is the emergence of self-replicators from complex mixtures, a process that is still not understood. Dynamic Combinatorial Chemistry (DCC) provides us an opportunity to shed some light on this intriguing process. In a Dynamic Combinatorial Library (DCL), a mixture of continuously interconverting molecules is formed in a combinatorial way by linking building blocks together through reversible chemical bonds. All these library species will compete with each other for building blocks required for their own formation. The concentration of the various library members is governed by a thermodynamic equilibrium. Those species that have a lower energy level will be present in a larger concentration. If one of the library species can bind to copies of itself, this species will self-assemble and the equilibrium will be shifted, amplifying its concentration. In this way, the self-assembling library members are essentially self-replicating. From our previous studies we know that self-replication can be affected by environment changes. For example, controlling the strength of mechanic agitation may lead to the emergence of different self-replicators. [1]

In this project, we will study how the environmental changes by cosolvents could dictate the emergence of different replicators. First results have beenobtainedby using trifluoroethanoland led us to the conclusion that indeed the solvent composition influences the nature of the emerging replicators. A logical development would be to explore the behavior of related cosolvents such as ethanol and hexafluoroisopropanol, for a deeper understanding of the role of fluorine atoms (as part of the solvent molecule) in the emergence of the self-replicators. A number of libraries of various solvent composition will be set up and followed by UPLC. UPLC-MS analysis may also be carried out, as well as flow experiments. Possible training on further experimental skills will depend on the results.

1.      J. M. A. Carnall, C. A. Waudby, A. M. Belenguer, M. C. A. Stuart, J.J.-P. Peyralans, S. Otto Science, 2010, 327, 1502-1506.

9 Group: Physics of Nanodevices (Quantum Devices subgroup)

Project 9.1

Supervisor(s): Prof. Caspar van der Wal and Olger Zwier

Optical Control of Electron Spins in a Semiconductor

Background: The possibility to store optical information in electron spins is important for classical and quantum communication . Quantum communication holds promise for an internet in which eavesdropping is fundamentally impossible. However information in present-day communication networks obeys the laws of classical physics. Towards this goal, a very recent research development in the group of Prof. Caspar van der Wal has shown that ensembles in a semiconductor can be very homogeneous and show a quantum optical phenomenon. This phenomenon is Electromagnetically Induced Transparency (EIT) and relies on three-level quantum systems with two low-energy spin states that both have an optical transition to a common excited state.

Project: We plan to explore the physics of Coherent Population Trapping (CPT, which is similar to EIT) in a collection of electronic spins in Silicon Carbide (SiC) in the context of using it as a quantum memory . In parallel, this project will investigate the role of unavoidable inhomogeneities leading to dephasing, which has been an obstacle for state-of-the-art semiconductor systems to date. The project will employ laser beams to appropriately couple the ground and excited states of atom-like divacancies in SiC. This includes techniques such as photoluminescence spectroscopy and single photon counting. The project shall take place in an entirely new experimental setup, and for this reason it will be conducted in close cooperation with new and existing research efforts of the van der Wal team.

Further information: http://www.quantumdevices.nl/

Project 9.2

Supervisor(s): Prof. Caspar van der Wal and Jakko de Jong

Optical Manipulation of Gallium Arsenide Spins

Background: This project is in an experimental research effort that explores the fundamental physics of how quantum information in an optical pulse can be stored in a quantum memory. This memory is formed by an electron-spin ensemble in a semiconductor. This work is relevant for developing quantum-computation and quantum-communication systems with solid-state devices, and for research on the foundations of quantum theory.

Project: The interaction of nuclear spins with electron spins has recently become an important focus for the ever-growing field of quantum optics with solid-state physics. We use a material system that exploits the spin states of an electron that is bound to a donor atom in a very pure semiconductor (Silicon-doped GaAs). The preservation of long-lived spin states (e.g., spin up and spin down states) is a challenging goal due to the uncontrolled effects of noisy nuclear-electron spin coupling. This coupling limits the generation of coherent quantum superpositions of these two spin states, and thus makes the operation of quantum memories a challenge for research. In the context of your project, you will participate in our experiments to measure the spin relaxation time of donor-bound electrons in gallium arsenide. Additionally, the experimental scheme will employ three state-of-the-art laser systems to measure and control both electron and nuclear spins.

Further information: http://www.quantumdevices.nl/

10 Group: Functional Molecular Materials and Catalytic Systems, and Computational Physics

Project 10.1

Supervisor(s): Prof. W.R. Browne (Functional Molecular Materials and Catalytic Systems) and Prof D.G. Stavenga (Computational Physics)

In situ Raman spectroscopy of pterins and microspectrophotometry of butterfly wing scale pigments

For a project description with Figures please contact Prof. W.R. Browne
Thee wings of pierid butterflies (e.g., the common cabbage butterfly) are studded with scales that contain granular beads with high concentrations of pterin pigments. The pigments’ absorption spectra, measured by in situ microspectro-photometry, deviate from those spectra measured in solution. A priori, this could be ascribed to the quite different chemical environments the compounds experience between the scales and basic aqueous solution. This can either be due to differences in protonation state or to the assembly of the pterin pigments in ordered (e.g., H- or J-) aggregates. The granules contain highly concentrated pterins and thus have a high refractive index. From the point of view of applications, understanding how nature uses these dyes will open up new possibilities in the creation of novel optical properties.

The origin of these differences can be determined using in situ as well as in vitro Raman spectroscopy. Raman spectroscopy is a uniquely informative spectroscopic tool in that it provides detailed vibrational information that can be related directly to specific structures using DFT methods. In this way the two possible reasons for the differences can be discriminated. A key challenge in measuring Raman spectra in such systems, however, is that the concentrations of these compounds is exceedingly low and fluorescence from both the pterins and other components can swamp the very weak Raman scattering.

In this project advantage will be taken of two resonant enhancement phenomena to overcome these challenges – the first is the so-called resonance Raman technique in which the laser employed to generate Raman scattering is chosen to match that of an optical transition and the second is to use surface plasmon resonance from metal surfaces to enhance the Raman scattering of the pterins ex situ.

The project will involve both in situ measurements as well as extraction isolation and ex-situ characterisation of the pigments involved to understand how different species use pterins to create distinct optical patterns and colourations. This project will not only allow you to develop skills in Raman spectroscopy and microscopy but will also challenge and expand molecular knowledge and contribute to new insight in the complexities of biophysical and organic solid state.

11 Group: Computational Physics

Project 11.1

Supervisor(s): Prof. H.A. DeRaedt and Prof D.G. Stavenga

Nanophotonics of Morpho butterfly wing scales and (humming)bird feathers

For a project description with Figures please contact Prof. D.G. Stavenga
This project is devoted to analyzing the optical mechanisms underlying animal coloration. Butterflies and/or birds will be studied. Morpho butterflies have striking blue reflecting wings due to complex structures consisting of combinations of thin films and multilayers. Depending on the specific species, the wings reflect directionally or rather diffusely. The project aims to explain the nanophotonics of the wing reflections from the structuring of the wing scales. The experimental methods involve microspectrophotometry, hemispherical scatterometry, and angledependent reflection measurements, which will be interpreted with computational methods, specifically matrix-transfer methods.

Many birds have feathers with small branches (barbs and barbules) structured as optical multilayers or as quasi-random photonic crystals. The multilayers consist of melanin rodlets, with a high (complex) refractive index (RI) value embedded in chitin, with lower RI. The RI values can be measured with Jamin-Lebedeff interference microscopy, and the measured values enable the modelling of measured transmittance and reflectance spectra. The experiments will for the first time allow a quantitative understanding of the colors of hummingbirds and other animals with complex, nanostructured systems.

12 Group: Solid State Materials for Electronics

Project 12.1

Supervisor(s): Prof. Thomas Palstra

Spin transport in magnetic insulators

For a project description with Figures please contact Prof. Thomas Palstra
Interplay of heat and spin The spin Seebeck effect has unique property to convert heat into electrical voltage by moving spins without moving electrons in a ferromagnetic insulator. In the spin Seebeck effect, a metal contact (Pt) is deposited on top of the ferromagnet to detect spin currents. When the ferromagnet is heated on one side, the magnetization rotates and spins absorb in the Pt contact. The absorbed spins convert into an electrical voltage in Pt (as shown in figure 1b) [2,3]. The goal of research in this area is to realize suitable materials in which heat can efficiently couple to the spin and the thermopower can be improved. However, there are still rather few materials known in which the spin Seebeck effect has been realized. It is therefore necessary to search for new families of materials that exhibit the spin seebeck effect. In this project, the spin Seebeck effect will be studied in a magnetic insulator with a helical spin configuration. The deposition of metal contacts and other device fabrication steps will be carried out in the clean-room and a physical properties measurement system (PPMS) will be used to measure room temperature and low-temperature properties in applied magnetic fields. Both in-plane and out-of-plane response of the sample as a function of thermal gradient will be checked. This project will provide hands-on experience with many of the experimental aspects of device fabrication and condensed matter physics.

[1]. G. E. W. Bauer, E. Saitoh, B. J. van Wees, Nature Mater. 11, 391, (2012).
[2]. K. Uchida, H. Adachi, T. Ota, H. Nakayama, S. Maekawa, E. Saitoh, Appl. Phys. Lett. 97, 172505, (2010).
[3]. K. Uchida, S. Takahashi, K. Harii, J. Ieda, W. Koshibae, K. Ando, S. Maekawa, E. Saitoh, Nature, 455, 778, (2008).

Project 12.2

Supervisor(s): Prof. dr. Beatriz Noheda and Dr. Justin Varghese

Ferroelectric nanopatterns

The International technology road map for semiconductors (ITRS) has identified the need for nanostructured ferroelectric materials with significantly improved properties to meet future technology requirements [1]. Top-down methods such as e-beam lithography have been used for making ferroelectric nanostructures, which posses a number of disadvantages such as low throughput and surface damage of the ferroelectric material [2]. The emerging bottom-up approach of using block copolymer (BCP) templates offers a promising route for generating nanoscale ferroelectric patterns in a simple, fast and inexpensive manner [3]. The ability to precisely control the placement of ferroelectric nanostructures on various substrates greatly enhances the potential of BCP approaches for device integration.

This project will explore the use BCP templating methods in conjunction with chemical solution deposition to fabricate periodic ferroelectric nanopatterns, viz. hexagonally packed dots or lines, on suitable substrates. The nanoscale ferroelectric properties of the structures generated will be probed using piezoresponse force microscopy (PFM). Through this project, the student gets the opportunity to learn the chemistry behind precursor making, as well the physics behind nanoscale ferroelectric properties.

References
[1]
The International Technology Roadmap for Semiconductors: 2011 Edition, Emerging research materials and Emerging research devices .
[2] H. Han, Y. Kim, M. Alexe, D. Hesse and W. Lee, Adv. Mater. 23, 4599 (2011).
[3] H.-C. Kim, S.-M. Park and W. D. Hinsberg, Chem. Rev. 110, 146 (2009).

Project 12.3

Supervisor(s): Prof. dr. Beatriz Noheda and Arnoud Everhardt

SrRuO3 bottom electrodes for oxide thin film applications

Thin films of oxide materials have gained notable interest in fundamental and applied research. Oxide materials show a huge range of interesting properties, including ferroelectricity, superconductivity, colossal magnetoresistance, ferromagnetism and piezoelectricity. In thin film form, when oxides are deposited on a crystalline susbtrate, their physical properties can be tuned due using the epitaxial strain as external parameter. Moreover, in thin films grown with atomic control, nanoscale or interface effects give rise to interesting science and applications.

SrRuO3 is one of the few conducting perovskite oxides, which is often used in thin film applications as a bottom electrode, because of its metallicity, good compatibility with many other oxide thin films and its high chemical stability. SrRuO3 itself is an interesting material, with several structural transitions, ferromagnetism and a bad metallic behavior. Good quality thin films of SrRuO3 have been grown epitaxially (by Pulsed Laser Deposition) on a new substrate (NdScO3) for the first time. Preliminary measurements indicate several interesting properties: a metal-to-insulator transition is observed as a function of film thickness, between d= 3 and d= 6 nm film thickness, together with a structural phase transition (at d= 5 nm). These observations seem to be correlated like in the famous Verwey metal-to-insulator transition in the well-known material magnetite.

It will be the student’s task to find all the details on these transitions. That will be done by performing resistivity measurements in our PPMS (Physical Properties Measurement System) cryostat, thin film XRD (X-Ray Diffraction) to unravel the structure(s) and magnetic measurements in the MPMS (Magnetic Properties Measurement System) to discover its magnetic properties. These measurements will be done at several film thicknesses to investigate the phase transitions.

Project 12.4

Supervisor(s): Assistant prof. Graeme Blake

Novel thermoelectric materials

Thermoelectric materials are of current interest for the conversion of waste heat to electrical power and in solid-state cooling systems. However, the efficiency of current thermoelectric devices is not good enough to be cost effective for widespread commercial applications. Improvements in the thermoelectric properties of basic materials are still necessary.

Some of the best performing thermoelectrics are derived from IV-VI semiconductors such as GeTe, PbTe and PbSe. It has recently been reported in the literature that incorporating small concentrations (1-2%) of magnetic rare-earth elements such as Ce, Yb and Dy in IV-VI semiconductors can result in a remarkable improvement in their thermoelectric properties. Doping with magnetic transition metals such as Mn and Fe also appears to be beneficial. The reasons for this are still unclear; it is not yet understood how and to what extent the substituted elements affect the electrical conductivity, thermopower and crystal structure. No systematic study of the effects of such substitutions has been carried out yet.

In this project a series of samples (polycrystalline and single-crystal) of PbSe and GeSe doped with magnetic rare-earth elements will be synthesized. X-ray diffraction will be performed to determine their structures. The thermoelectric properties will be characterized by means of electrical resistivity, thermopower and thermal conductivity measurements. This project will provide hands-on experience of many of the experimental aspects of solid-state chemistry and condensed matter physics.

13 Group: Photophysics and opto-electronics

Project 13.1

Supervisor(s): Assistant prof. Jan Anton Koster and Solmaz Torabi

Organic solar cells: high-k for high efficiency

Organic solar cells bear the potential to develop a long-term technology that is environmentally clean and economically promising for large-scale power generation. Thanks to higher absorption coefficient, organic materials can be incorporated as thin films in organic photovoltaic (OPV) devices leading to a 10-fold reduction in the consumption of the material as compared to their inorganic counterparts. The possibility of using flexible plastic substrates in an easily scalable high-speed printing process results in a faster return on investment. The rapid efficiency improvement of OPV shows the future of OPV is bright.

The dielectric constant (k) is an essential parameter for ef´Čücient solar cells. Current organic materials for organic photovoltaics have low dielectric constants in the range of 2 to 4. This limits their efficiency as light absorption yields excitons rather than free charge carriers. According to recent calculations [1], it is feasible to design more efficient organic solar cells by introducing high-dielectric-constant organic donors and/or acceptors leading to next generation OPV.

This research project involves the characterisation of newly synthesised donor and acceptor materials for OPV. We have recently measured the dielectric constant of these materials at low frequencies (1 kHz -1 MHz) and found a dramatic enhancement of the dielectric constants. To better understand the mechanism by which this happens, we are looking for a student to measure their optical constants with ellipsometry. This will yield the dielectric properties at high frequencies.

14 Group: Polymer Chemistry & Bioengineering

Project 14.1

Supervisor(s): Prof. A. Herrmann (a.herrmann@rug.nl)

Electrochromic devices fabricated from DNA liquid crystals

For a project description with Figures please contact the supervisor
Electrochromic devices (ECDs) with the properties of controllable transmission, absorption and/or reflectance in response to voltage changes have recently gained a great deal of attention in scientific and technological research. ECDs are mainly applied to glare attenuation in automobile rearview mirrors and in smart windows that can regulate the solar gains of buildings. Other application fields of ECDs include solar cells, small- and large-area flat panel displays, frozen-food monitoring and document authentication. However, the functioning of present ECDs is complicated due to multi-layer architectures (five layers or more) composed of many materials and different component combinations including liquid electrolytes that require special sealing of devices. The complex design of ECDs results in high costs and limited durability of current ECDs. Therefore, the development of simple and low-cost ECDs has remained a major challenge. Recently, in the Herrmann group, a novel, electrolyte-free, power saving ECD based on a single-component nucleic acid liquid crystal has been successfully fabricated. Switching between transparent and colored state has been realized in the liquid phase and the red-color impression can be preserved in the mesophase without application of a voltage for several hours. This finding holds great promise for the realization of low-energy consuming electrochromics. In the next steps, rational design of DNA lengths and sequences for realizing multi-color ECDs and optimization of response time will be investigated.

During the project, the student will get familiar with characterization of liquid crystalline materials by SAXS, WAXS, DSC and polarization microscopy. Moreover, he/she will acquire skills in the fabrication and evaluation of EDC devices.

Project 14.2

Supervisor(s): Prof. A. Herrmann (a.herrmann@rug.nl)

Precision macromolecules by DNA-templated polymerization

For a project description with Figures please contact the supervisor
In the living system, nucleic acid-templated polymerization is a fundamental biological process that enables the precise copying of the sequence and length of a DNA or RNA strand into a daughter polymer. In contrast to the biological one, radical polymerization suffers from poor molecular weight control and broad molecular weight distributions. A particularly attractive goal to address these problems would be to mimic the biological templated polymerization in synthetic polymer chemistry. By employing living methods as the template strand, DNA-templated polymerization can possibly result in copying the molecular weight and narrow polydispersity of the parent strand into the synthetic polymer. Also with the DNA-templated polymerization, sequence-controlled polymerization might be achieved via complementary DNA hybridization to build confined block polymers.

To realize the DNA-templated polymerization, oligo-nucleotides containing ATRP initiator needs be synthesized through an automatic DNA synthesizer. Then polymerizable surfactant will be introduced onto DNA electrostatically (Scheme 1a), followed by polymerization under mild ATRP conditions. GPC, MALDI-TOF and electrophoresis will be carried to characterize the polymerization degree and polydispersity. To further explore the templated reaction, different DNA strands containing diverse polymerizable surfactants will specifically hybridize with its complementary single DNA strand, which results in aligning different blocks on the DNA ready for polymerization (Scheme 1b). With the same polymerization condition, we might achieve confined block polymers.

Project 14.3

Supervisor(s): Prof. A. Herrmann (a.herrmann@rug.nl)

Bio-organic photoactive field-effect transistor containing photosystem I

For a project description with Figures please contact the supervisor
Photosynthesis is the most important process on earth to transform sunlight into chemical energy. This process takes place in the thylakoid membranes of photosynthetic bacteria, algae and plants and one of the key players in the light-dependent reactions is the multiprotein complex photosystem I (PSI). PSI contains a large antenna system in which light is harvested by photosynthetic pigments that absorb at various wavelengths and funnel the excitation energy to a special pair of chlorophylls (P700) where extremely efficient charge separation takes place. The internal quantum efficiency of photon-to-charge generation in such a photosystem is near unity. In this project, the aim is to integrate this biological protein complex into a field-effect transistor that comprises an organic semiconductor as charge-transport medium. The photosystem will be incorporated as a self-assembled monolayer on top of the gate dielectric, for which a technique has been developed recently. The organic semiconductor, a transparent conjugated polymer, will then be deposited on top of the PSI monolayer. Upon excitation with light, free charge carriers generated by the photosystem will be used to modulate the channel conductivity, where charges are transported between source and drain through the conjugated polymer. As such, the device could be used as a hybrid bio-organic photodetector. The objective of the project is the fabrication this novel device, as well as characterization of its optoelectronic properties.

15 Group: Physics of Nanodevices ( Spintronics of Functional materials subgroup )

Project 15.1

Supervisor(s): Prof. T. Banerjee and Sander Kamerbeek

Novel magnetic effects in an oxide semiconductor Nb-doped SrTiO3

The key building block in information technology is the semiconductor silicon, where recently, manipulation of both charge and spin of the electron by electric and magnetic fields has been demonstrated. To create new electronics, our team explores the rich physics and strong correlation effects exhibited by complex metal oxides- a direction that will further oxide electronics and oxide spintronics. Recently we have successfully demonstrated spin injection and transport in an oxide semiconductor, Nb:SrTiO3, using suitable spin contacts. Several new transport characteristics, at the interfaces have emerged during this work, which we are currently investigating. In this project, the student will join the team in studying the new magnetic effect observed at the interface of the complex oxide semiconductor with ferromagnets. You will use the NanoLab facilities as thermal evaporation, lithography technique and other fabrication tools to design the devices. You will also perform magnetic field dependent electrical measurements of different metal interfaces with Nb:SrTiO3. Measurements will be performed over a large range of temperatures spanning from close absolute zero to room temperature with the use of a cryogenic system. Different interfaces will be examined which modulate the magnetic behavior. The findings will be compared with known effects in literature to develop a new model to understand the origin of this effect and to assess the possibility for the realization of new functional devices.

Project 15.2

Supervisor(s): Prof. T. Banerjee and Eric de Vries

Optimization of charge and spin transport in Bi2Se­3by top gating

Topological insulators (TIs) like Bi­2Se3 are materials that ideally have an insulating bulk with gapless surface states. These surface states have a Dirac-like dispersion where for TIs the spin orientation of charge carriers is directly related to the momentum known as spin-momentum locking. Currently we are studying the spin properties of these surface states using ingenious, electrical device structures. For a better control on the spin accumulation in our material, we will use top gated structures. Optimization of the top gate allows us to effectively tune the charge carrier density and type in our material. Currently, two different high kdielectrics are under consideration where the gating properties can be tuned by modifying parameters like the oxide layer thickness, oxygen pressure and growth method of the oxide layer.

The student will work on the fabrication of top gate structures in the NanoLab cleanroom and will use facilities as optical lithography, electron beam lithography, reactive ion etching and electron beam deposition. The measurements on oxide top gate performance will also be performed by the student. The homogeneity of the oxide layers will be studied using atomic force microscopy. With functional top gate structures, the (temperature-dependent) magneto-electrical properties of our samples will be investigated.

Project 15.3

Supervisor(s): Prof. T. Banerjee and Roald Ruiter

Lateral charge transport characteristics of graphene on oxides substrates

Extensive research has been performed on charge transport in graphene on SiO2/Si substrates. It has however been found that the substrates play an important role in determining charge transport and electron mobility in graphene. Currently, we are studying electrical charge transport in graphene using functional devices that integrate graphene on complex oxide substrates as SrTiO3. The large dielectric constant in SrTiO3 is expected to screen the charge impurity scattering in graphene and enhance its mobility. Further, the temperature and electric field dependence of the charge transport in graphene on such oxide substrates will also be studied and is expected to be influenced by the enhanced dielectric constant of the oxide substrates at low temperatures. During this project the student will learn how to fabricate the graphene devices on SrTiO3 using the NanoLab clean room facilities. This will involve graphene exfoliation and transfer to the desired substrate, e-beam lithography and evaporation of metal contacts. Thereafter the carrier mobility of graphene on different substrates will be investigated using a cryogenic transport setup at the Physics of Nanodevices group.

Project 15.4

Supervisor(s): Prof. T. Banerjee and Saurabh Roy

Spin transport in complex oxide heterointerfaces

We have recently studied the interplay between the charge and orbital degree of freedom of electrons, at the interface between two dissimilar oxides. For this, we used devices of thin films of ferroelectric oxides and oxide ferromagnets. We would like to study magnetotransport and spin transport properties in a new class of oxide nanopillar devices as LSMO/BFO/SRO. In this short project, the student will fabricate such oxide nanopillars, while working closely with the Ph.D student involved in this project. For this, pulsed laser deposition technique will be used to deposit the oxide thin films. Thereafter, the student is expected to fabricate these thin films into nanopillar structures using the NanoLab facilities. The spin transport properties in such devices that couples the multiferroic property of BFO will be studied. Electrical control of the spin transport and electrical control of the exchange bias in such nanopillars will also be probed.

Last modified:17 November 2017 1.59 p.m.