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

NS194 Small research project -- available projects 2011 [now obsolete]

The available small research projects for 2011 are listed here. Please contact the supervisor mentioned in case you are interested in a project.

1  Group: Physics of nanodevices

Project 1.1 No longer available

Supervisor: Prof. C.H. van der Wal

Optical pump-probe studies of suppressed spin dephasing for electron ensembles in semiconductor devices

Optical time-resolved Kerr rotation measurements allow for preparing and detecting the spin states of electron ensembles in GaAs with very high (subpicosecond) time resolution. We use this to study how electron spin states evolve and dephase while they are localized or transported in  small semiconductor channels. The spin signals in GaAs typically decay fast due to spin-orbit interactions. The central question in this project is whether one can engineer devices which automatically suppress or counter-act this relaxation mechanism for spins, by guiding the electron orbitals with respect to the spin-orbit fields. Even more exciting is that such a mechanism can in principle be switched on at off with an electrostatic gate, such that spin signals in devices can be switched between 0 and 1. You will participate in, and report on taking Kerr data on a new generation of devices with such an electrostatic gate.

Project 1.2 No longer available

Supervisor: Prof. C.H. van der Wal

The influence of electron many-body interactions on quantum transport

Quantum point contacts (QPCs) are the most simple and cleanest model systems for investigating electronic currents at the nanoscale. They consist of a single short channel, in which the electron transport is carried by ballistic wave packets. The signature of control over electron transport in this regime is the observation of quantized conductance: As a function of channel width the conductance increases in quantum steps. However, even the cleanest systems show deviations from perfect quantization due to the influence of many-body effects on transport. These have been observed for over 20 years, but are not yet understood. Understanding these effects is of course crucial for insight in the possibilities and limits of electronic currents at the ultimate nanoscale. In the Spring of 2011 we will carry out a new set of experiments on devices that allow for unprecedented control over these many-body effects. Your task is to participate in this research effort.

Project 1.3

Supervisor: Dr. Tamalika Banerjee

Spin transport in novel devices based on correlated oxide materials

Oxide spintronics is an emerging research direction where the fundamental thrust in on understanding the physics of electron charge/spin/orbital interactions in perovskite oxide interfaces at the nanoscale. Spectacular phenomena [1-2], arising due to strong electron correlation, and ranging from metallic to magnetic have been observed, quite recently, at well-defined interfaces of two insulating oxide layers. The technological relevance of these materials is reinforced by its recent inclusion in the roadmap for semiconductors, popularly known as ITRS.

A current research theme in our group is on fabricating and studying spin transport in novel devices based on correlated oxide materials. After our first successful demonstration and investigation of hot-electron charge transport in perovskite oxide based devices (LaSrMnO3 on Nb doped SrTiO3) using the technique of Ballistic Electron Emission Microscopy (BEEM), our current research efforts are on tailoring the interface of these devices. We do this by carefully identifying the transport properties in differently doped oxide semiconducting substrates and simultaneously tailoring (viz. strain/growth parameters) its interface transport with various epitaxial oxide films. Further, establishing the relevant time and length scales for electron spin transport, across such epitaxial interfaces, hitherto unexplored is a major ongoing thrust in this project, where a prospective student is expected to participate. The ultimate aim is to build an all-oxide spintronic device which will offer a new platform to study the intriguing and rich physical properties at the interface between such perovskite oxides.

The student will have hands-on experience in the growth and transport facilities available at NanoLab-Groningen (e-beam evaporation, sputtering, UV and e-beam lithography etc.) and within the Physics of Nanodevices (nanoscale transport using BEEM/standard device characterization) and Solid State Materials for Electronics (PLD, PPMS, MPMS XRD) groups.

1. Ohtomo et al., Nature 419, 378, (2002).

2. Yajima et al., Nature Materials, 23rd Jan2011, doi:10.1038/nmat2946

Project 1.4

Supervisor: Dr. Tamalika Banerjee

Graphite/Graphene Spintronics

We have recently demonstrated [1] perfect spin transmission across graphite which comprises of weakly interacting graphene planes. The work also indicated large spin relaxation length in graphite, quite comparable to that found in graphene. Our device geometry allows us to study current-perpendicular-to-plane transport in graphene/graphite, thus allowing us to probe spin transport across all the interfaces and bulk layers. We have now extended this work to a unique epitaxial-metal device geometry that enables us to study spin transport in graphene. Hot electron attenuation lengths in thin ferromagnetic Ni films, deposited on lattice matched silicides on Si substrates, have been determined and reveal the crucial role of momentum conservation across such epitaxial interfaces. An ongoing research thrust, where a prospective student will be involved, is in the studying of spin transport in graphene in vertical device structures using the versatile technique of Ballistic Electron Magnetic Microscopy.

The student will have hands-on experience in the growth and fabrication of such nanodevices using the facilities available at NanoLab Groningen (evaporation, sputtering, UV and e-beam lithography), at the Physics of Nanodevices (BEEM and strandard magnetotransport measurements) and at Surfaces and Thin film (Molecular Beam Epitaxy) groups .

1. Banerjee et al., Phys. Rev B, 81, 214409 (2010).



Group: Surfaces and thin films

Project 2.1

Supervisor: Dr. M. Stöhr

On-surface polymerization

The implementation of one- and two-dimensional organic polymers as active materials in nanoelectronic devices is a promising alternative to conventional silicon-based materials. Advantages are much lower fabrication costs and tunable properties. With the extremely high charge carrier mobility of graphene in mind, the prospect to achieve similar values for conjugated two-dimensional polymers is very stimulating for performing research towards their controlled fabrication.

The aim of the project is to create one-dimensional polymers on a substrate surface and to perform a detailed characterization regarding structural properties. In a first step, the starting molecular building blocks (monomers), from which the polymeric material will be fabricated, need to be characterized with respect towards intermolecular and molecule substrate interactions. This will be done with scanning tunneling microscopy under ultrahigh vacuum conditions at either room or low temperature. In retrospect, this information will help to understand the underlying principles for polymer formation on surfaces like diffusion and / or pre-organization of the monomers. In a second step, the chemical reaction leading to the polymer formation will be initiated. This will be done by heating up the sample. The obtained polymeric material will be characterized in a similar way as the monomers were already characterized. A careful analysis of all the data will result in a better understanding of the various parameters controlling on-surface reactions.

Project 2.2

Supervisor: Dr. M. Stöhr

Surface-supported supramolecular networks

One of the most commonly employed strategies for the generation of supramolecular architectures is molecular self-assembly. The molecular components organize spontaneously and reversibly into ordered patterns or structures without human intervention. Since the individual components interact with each other only via non-covalent interactions, relatively defect-free structures are obtained and furthermore, the systems are often self-healing if damaged. The fact that self-assembly is one of the few practical strategies for making ensembles of nano- and microstructures makes it attractive for both scientific research and technological applications. For many of the envisaged applications of self-assembled supramolecular structures, a detailed understanding of the interactions involved in the formation of the first few molecular layers is indispensable. In particular, the molecule - substrate and intermolecular interactions responsible for the resulting structures are of great research interest.

Within the project, porous molecular networks shall be formed through triple H-bonding between two specially synthesized molecules featuring complementary functional end groups. The molecules will be deposited under ultrahigh vacuum conditions on silver and gold surfaces. The investigations of the samples will be carried out with low temperature scanning tunneling microscopy while the influence of both molecular coverage and mixing ratio of the two molecules on the resulting arrangement are in the focus.

3  Group: Physics of organic semiconductors

Project 3.1

Supervisor: Prof. Maria Antonietta Loi

Towards high performance thin film transistor with semiconducting single walled carbon nanotube (SWNTs)

Carbon nanomaterials have been accepted as the most important candidates for the new generation semiconductor technology [1]. Among all the carbon allotropes, single walled carbon nanotubes (SWNTs) show superb electronic properties which can be utilized for high performance electronic device application. The key issue for this purpose is to find a scalable route for the separation of metallic and semiconducting carbon nanotubes [2].

In this small research project, we propose the separation of semiconducting and metallic nanotubes by matrix-free electrophoresis for mass-production. Your task covers the sample preparation, material characterization and device fabrications. General working experience in chemistry, spectroscopy and clean room is predictable. This project will provide you a broad knowledge on material science and electronic devices.

References:

[1] Carbon Nanotube Science, by P.J.F. Harris, Cambridge University Press, 2009

[2] M. Kwak, J. Gao, D. K. Prusty, A. J. Musser, V. A. Markov, N. Tombros, M. C. A. Stuart, W. R. Browne, E. J. Boekema, G. ten Brinke, H. T. Jonkman, B. J. van Wees, M. A. Loi, A. Herrmann, Angewandte Chemie (in press) 2011

Project 3.2

Supervisors: Prof. Dago de Leeuw (dago.de.leeuw@philips.com) and Ilias Katsouras MSc

Study of polymer charge transport in Large Area Molecular Junctions

We recently demonstrated a technology to measure the charge transport through single molecules self-assembled in a monolayer (Nature, 441, 2006 / Nature NanoTechnology, 3, 2008). This highly reproducible experimental testbed can also be used to study the charge transport properties of various polymers (such as poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene: MEH-PPV) at a wide range of voltages and temperatures. This project is a joint collaboration between Philips Research Laboratories in Eindhoven and RUG, and includes cleanroom work for device fabrication, data collection using a specialized cryogenic probestation, as well as data analysis. The duration of this assignment can be adapted to fit both a short or a master thesis project.

Project 3.3

Supervsiors: Prof. Dago de Leeuw (dago.de.leeuw@philips.com) and Ilias Katsouras MSc

A plastic ferroelectric tunnel junction

In this project we aim at using the highly reproducible experimental testbed of Large Area Molecular Junctions (Nature, 441, 2006 / Nature NanoTechnology, 3, 2008) to fabricate a polymeric ferroelectric tunnel junction. Such a device has never been made before, owing to the inability to spincoat the required extremely thin layers of the ferroelectric polymer PVDF-TrFE (copolymer of vinylidene fluoride & trifluoroethylene). We have invented a method to bypass this problem. This project is a joint collaboration between Philips Research Laboratories in Eindhoven and RUG, and includes cleanroom work for device fabrication, as well as data collection/analysis. The duration of this assignment can be adapted to fit both a short or a master thesis project.

Project 3.4

Supervisor: Prof. Maria Antonietta Loi

Colloidal nanocrystal Field Effect Transistors (FET): Optimization of the surface ligand exchange and selection of the best ligands.

Colloidal nanocrystals (NCs) are tiny crystal of metals or semiconductor with size ranges from 2-3 to about 20 nm. Due to this size regime the electronic structure, optical and magnetic properties of the materials can be tuned by varying the physical size of the crystal leading to new phenomena and placing them among the hottest research topic of the last decades.

The electronic properties of NC solids depend equally strongly on the NCs themselves and on the surface ligands. The surface ligands that cover the surface are introduced during the synthesis in order to control the nucleation and to ensure the chemical and colloidal stability. Most of the native ligands are bulky insulating barrier between NCs, which hinder the charge transport. To improve conductivity the strategy is the removal of the original surface ligand and the replacement by small molecules able to preserve the stability but at the same time allowing better charge transport.

The objective of this project is the realization of NC based FET for the selection of the best ligands.The student will test a library of different ligands by optimizing exchange procedures already developed in our group [1,2] and by measuring the performance of the devices. The final goal is the evaluation of the ligand characteristics that are necessary for improving the mobility.

[1] Szendrei, K.; Jarzab, D.; Yarema, M.; Sytnyk, M.; Pichler, S.; Hummelen, J. C.; Heiss, W.; Loi, M. A. Journal of Materials Chemistry, 20(39), 8470-8473, 2010.

[2] Szendrei, K.; Gomulya, W.; Yarema, M.; Heiss, W.; Loi, M.A. Applied Physics Letters, 97(20), 2010.

4  Group:  Nanostructured materials and interfaces

Project 4.1

Supervisor: Dr. George Palasantzas

Surface patch potentials contribution on contact potential: A headache for Casimir force measurements

The Casimir force exists between a pair of neutral objects due to a quantum mechanical energy fluctuation in vacuum. One of the outstanding problems in Casimir research today is the interplay between the force due to pure quantum fluctuations and the contribution originating from thermal fluctuations at a finite temperature. Although the surface electric forces can be minimized during a Casimir force measurement, they cannot be completely nullified and the presence of the so called contact potential is manifested in Casimir force measurement. The presence of such a long-ranged force can be heavily pronounced in materials preventing the experiment to distinguish among different theoretical models describing the thermal Casimir force. Moreover, it represents an obstacle in search of new forces beyond the standard model since the Casimir effect is a possible probe in this strange world. The situation is rather complex since the contact potential varies with separation distance due to surface patch potentials (areas with different work functions). Therefore, studies with AFM based surface potential imaging (Kelvin probe microscopy) is a tool to augment our understanding of these effects.

Project 4.2

Supervisor: Dr. George Palasantzas

Lateral Casimir force towards contactless motion: rack pinion systems and beyond

The study of Casimir force in complex geometries and novel topologies, such as patterned or corrugated surfaces, nanospheres or small spheroïdal shaped bodies has become a highly active research area. A specific nontrivial geometry that is of particular interest for applications is that of surfaces with periodic corrugations. As lateral translation symmetry is broken, the Casimir force contains a lateral component, which is smaller than the normal one but has been suggested as a method to achieve contactless force transmission in micromachines such as rack pinion systems. These designs exhibit a plethora of novel and often nonintuitive behaviors, which could help inspire the development of alternative routes to mechanical engineering at the nano-scale alongside with recent significant improvements in theoretical calculation of the magnitude of the lateral Casimir force.

5 Group: Micromechanics

Project 5.1

Supervisor: Prof. Patrick Onck

Nanoporous actuators

Nanoporous actuators can provide voltage-induced deformations of 0.1% strain at much lower voltages (1V) than conventional piezoelectric actuators (> 100V).
Because of the low voltage operating capability and small weight, nanoporous actuators can find application in precision manufacturing and medical devices.
The high surface to volume ratio of nanoporous metals is exploited to electrochemically inject charge on the metal surface. The injected charge changes the electronic distribution on the surface atoms, which results in an increase in atomic bond length, eventually giving rise to macroscopic deformation of the metal. The objective of this small research project is to predict the charge-induced strain in ordered nanoporous structures using molecular dynamics simulations, and to study morphological and topological effects on the overall voltage-induced deformation.

Project 5.2

Supervisor: Prof. Patrick Onck

Molecular modeling of transport through the Nuclear Pore Complex

The nuclear pore complex (NPC) is a large protein complex that is embedded in the membrane envelope surrounding the nucleus and transports hundreds of
proteins and nucleic acids in a selective manner. Despite its important biological role, the mechanism of selective transport of the NPC is not yet understood. A wide variety of different theories exists based on experimental observations regarding the interactions between central FG-Nup domain and transport factors. In the current work, we use coarse-grained molecular dynamics simulations to study the deformation of individual FG-nups as a function of their amino-acid sequence. The goal of this small research project is to study the collective behavior of the FG-nups when they are anchored to a substrate, forming thin polymer brushes.


6 Group Single-molecule biophysics

The Single-Molecule Biophysics group is a new group at Groningen University and focuses on the development and use of single-molecule tools to understand how proteins work. One of our goals is to study the interactions between proteins and DNA and how these interactions underlie a variety of important biological processes, such as DNA replication and repair. Furthermore, we have a longstanding interest in understanding the physical mechanisms with which viruses penetrate living cells.

Project 6.1

Supervisor:  Prof. Antoine van Oijen

Watching proteins move on DNA

In this project, you will use state-of-the art fluorescence imaging techniques to visualize how individual, fluorescently tagged proteins move along stretched DNA molecules. In particular, you will study how proteins involved in gene expression are able to very rapidly locate specific sequences on the DNA (so-called promotors) by sliding along the DNA. By chemically modifying DNA molecules, you will be able to couple them at one end specifically to a glass surface. By combining this surface-coupling technology with microfluidics, you will be able to use hydrodynamic flow to stretch the DNA molecules. Fluorescently tagged proteins can now be introduced into the flow cell, excited by laser illumination, and their fluorescence emission visualized by a microscope and CCD camera. Analyzing the protein movement along the DNA will allow you to characterize the diffusional properties of the protein and its ability to search large portions of the DNA for the correct sequence. This project will allow you get hands-on experience with the many different experimental aspects of single-molecule biophysics: laser optics, microfluidics, fluorescence microscopy, image analysis, etc.

Project 6.2

Supervisor:  Prof. Antoine van Oijen

Physical mechanisms of viral infection

Our group also has an interest in trying to understand the physical, molecular mechanisms with which viruses infect cells. Being physicists, we have developed an experimental model system that allows us to directly observe how individual influenza viral particles ‘fuse’ their membrane with a target membrane that mimics the outside of a cell. Using this model system, we can observe the kinetics of this important process and incorporate these data into models describing viral entry. Further, we collaborate with partners in the pharmaceutical industry to characterize how novel vaccine reagents act on the viral entry mechanism. In this project, you will characterize how viral fusion kinetics can be modulated by changing the physical properties of the target membrane (elastic modulus, bending stiffness, etc.).


7 Group Theory of condensed matter

Project 7.1

Supervisor: Thomas la Cour Jansen

Nonlinear spectroscopy of alcohols

The alcohol group is present in many organic and biological systems, with carbohydrates, DNA and proteins as the most prominent examples. The alcohol group can therefore potentially be used as a reporter on structure and dynamics in such systems. In particular the hydrogen bond formation and dynamics should be possible to study. The aim of this project is to develop a map for the OH stretch vibration of alcohols to test it by applying it to calculate the linear and two-dimensional spectrum of alcohol in solution. The map will be constructed using electronic structure calculations of an alcohol unit in different point charge environments mimicking a solvent and a fitting procedure to correlate the vibrational frequency with the local electric field. The solvated alcohol will be simulated using molecular dynamics simulations that will be used to determine how the electric field generated by the solvent behaves. Finally, the spectra will be calculated by combining the electronic structure map and the molecular dynamics simulation according to the spectral simulation protocol developed in the group [1]. The spectra will be compared with experimental spectra [2] and with observations in other hydrogen bonding systems [3,4,5].

[1] Jansen and Knoester, Acc. Chem. Res. 42:1405 (2009)
[2] Farwaneh, Yarwood, Cabaco, and Besnaro, J. Mol. Liquids 56:317 (1993)
[3] Kim and Hochstrasser, J. Phys. Chem. B 110:8531 (2006)
[4] Jansen, Cringus, and Pshenichnikov, J. Phys. Chem. A 113:6260 (2009)
[5] Knop, Jansen, Lindner, and Vohringer, Phys. Chem. Chem. Phys. (2011) DOI: 10.1039/C0CP02143A

8 Group Polymer chemistry and bioengineering

Project 8.1

Supervisor: Prof. Andreas Herrmann

Small molecule detection by protein/DNA interactions
Atomic force microscopy (AFM) has been employed as an extremely sensitive and selective tool for DNA detection [1]. Therefore, single stranded (ss) DNA was immobilized on a flat substrate. After incubation with the complementary target DNA a double helix is formed on the surface. Due to a significant increase in stiffness, when transforming ss to double stranded (ds) DNA, nucleic acid concentrations down to 1 atto Mole could be detected by nanomechanical AFM measurements. During the project it is planned to extend this method to small molecule detection. For that purpose transcriptional regulator proteins are bound to the immobilized ds DNA. These proteins dissociate specifically in the presence of various chemical entities including metal ions, drugs, amino acids and sugars. This dissociation event will be followed by AFM allowing the development of an extremely sensitive platform for small molecule analyte detection with a broad range of applications in environmental testing and as metabolic chips. During the course of this project, the student will become proficient in basic DNA and protein handling, surface characterization with IR and X-ray spectroscopy and cutting-edge AFM measurement techniques.

[1] S. Husale, H. H. J. Persson, O. Sahin, Nature 2009, 462, 1075.

Project 8.2

Supervisor: Prof. Andreas Herrmann

Cocaine sensing by catalytically active DNA aptamers

Aptamers are folded nanostructures consisting of RNA or DNA, which are evolved in an in vitro selection process and are able to recognize very specifically various molecules including metal ions, aromatic molecules, amino acids and peptides. Based on a well known DNA aptamer that strongly binds to cocaine it is planned to develop a sensor for the detection of this drug. While the aptamer acts as a recognition element the signal amplification is based on a catalytic process. Our group has developed a palladium catalyzed de-iodination reaction that transforms a non-fluorescent substrate into a highly fluorescent product.[1] Two pieces of the aptamer sequence will be functionalized with ligands that upon cocaine binding will form a catalytically active species allowing to produce 1000 fluorophores per single recognition event, which leads to strong signal amplification. During the course of the project the student gets familiar with simple methods to functionalize DNA, handling and fabrication of DNA nanostructures and basic principles of biosensor construction.

[1] Prusty DK, Herrmann A, J. Am. Chem. Soc. 2010, 132, 12197.

Project 8.3

Supervisor: Prof. Andreas Herrmann

Solubilization and Programmed Self-Assembly of Graphene with DNA Amphipiles

Graphene (GR) is a one-atom-thick planar layer of SP2 carbons forming a honeycomb lattice. The Nobel Prize in Physics of 2010 was awarded to Geim and Novoselov,[1] and since then this two-dimensional carbonaceous material has gained explosive interest. The exfoliation technique of GR was instrumental for a lot of fundamental physical studies of GRs providing a simple way to prepare thin mono- or few GR layers.[2] In order to functionalize GRs to enable potential applications in large scale such as electric devices and sensors, (1) a solution process (and functionalization) is preferred and (2) a precise self-assembly method in solution would be the Holy-grail in this field. In this project it is planned to solubilize monolayers of GR with a bispyrene attached to DNA (pyDNA).[3] The amphiphilic DNA hybrid, pyDNA, is expected to fulfill the two requirements of an advanced solution-based self-assembly process as demonstrated by our group for the solubilization of single-walled carbon nanotubes and the DNA-mediated programmable functionalization.[4] PyDNA will be dissolved in water; then through simple sonication, GR will be dispersed with pyDNAs. The key of this proposed method is a strong pi-pi interaction between GR surface and pyrene units while the DNA segments introduce water solubility. The resulting dispersions will be characterized by various techniques: UV/Vis spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Functionalization of the GR sheets is a simple matter through hybridization with complementary DNA (cDNA) conjugated to a target moiety such as gold nanoparticles (AuNP).[5] Watson-Crick base pairing of a DNA segment of pyDNA and cDNA-AuNP will clearly prove our concept and, moreover, will enable quantitative analysis of the functionalization.

[1] Nobel Foundation announcement 2010, http://nobelprize.org/

[2] Geim AK; Novoselov KS, Nature Mater. 2007, 6, 183–191.

[3] An X; Simmons T; Shah R; Wolfe C; Lewis KM, Nano Lett. 2010, 10, 4295–4301.

[4] Kwak M; Gao J; Prusty DK; Musser AJ; Markov VA; Tombros N; Stuart MCA; Browne WR; Boekema EJ; ten Brinke G; Jonkman HT; van Wees BJ; Loi MA; Herrmann A, Angew. Chem. Int. Ed. 2011, in press.

[5] Kwak M; Musser AJ; Lee J; Herrmann A, Chem. Commun. 2010, 46, 4935–4937.

9 Group Theoretical chemistry

Project 9.1

Supervisors: Prof. dr. R. Broer and Dr. R.W.A. Havenith

Water on the rocks

The structure of Opal has been well described [1].Mostly the Opal consists of spheres between 150 – 350 nm in diameter, which are made up of silica.Jones et al state, that “a comprehensive re-examination of natural opals has confirmed that the structure can vary from almost perfect α -Cristobalite to apparently amorphous or near amorphous material”.Further work on the structure of the silicate in Opals has been carried out which suggests that the basic Opal silicate has been built up from α -Cristobalite and Tridymite structures [2].

It has been suggested [3] that cracking of Opals has some relationship to the water in Opal and furthermore it has been suggested that water can diffuse faster in Opal than in bulk water.This has lead to a study of three Opals and indeed it was found that there were significant differences in diffusion and behavior of water confined within three different types of Opal.This leads to some intriguing questions:

1) Can the convolution between water rotation and diffusion be modeled?

2) Is it the interaction of different surfaces within the Opal that leads to the differences?

3) Do cations on the surface play any role in the different water behavior?

Computational studies could throw significant insight to understanding the results.

1) If it were feasible to simulate water motion as a function of water content when water was confined between parallel Opal sheets at several different spacings (say between 5-100 nm) then it may be possible to answer question 1.

2) It may be possible to answer question 2 if simulations were carried out using different walls of confinement

a. from α -Cristobalite

b. from a contrasting material (Halloysite)

3) If it were possible to simulate the presence of a cation (suggestions Na and Ca) by replacing silica with Al in the wall material then this simple model would give an interesting insight into question 3.

[1]J.B. Jones, J.V. Sanders, E.R. Segnit, Nature, 204 (1964), 990-991.

[2]J.M. Elzea, S.B. Rice, Clays and Clay Minerals, 44 (1996), 492-500.

[3]G. Pearson, The Australian Gemmologist, 15 (1985), 435-441.

Project 9.2

Supervisors: Prof. dr. R. Broer and Dr. R.W.A. Havenith

L-methionine

L-methionine can exist in two different crystal structures, viz. a - and b -methionine.It is also experimentally known that the molecules are flexible in the crystal.In this project, calculations on the flexibility of the molecules in the crystal structure will be performed.The calculations will show what kind of disorder in the crystal is expected at which temperatures.Rotations around the different bonds will be considered.

Methionine

Another question concerns the transition from a - to b -methionine.Can we predict the transition temperature and the barrier?And lastly, can we predict the Raman and infrared spectra for methionine?

Project 9.3

Supervisors: Prof. dr. R. Broer and Dr. R.W.A. Havenith

The vanadium-oxygen bond in vanadium catalysts

The activity of vanadium catalysts in the oxidation of methanol to formaldehyde can be related to the ionicity of the V-O bond [1].A way to study these extended systems is by approximating the solid by a molecular cluster, where only the nearest atoms of the central V are taken into account (see picture, with S = Support).

The ionicity of a bond is not an observable property, however, different definitions exist, which allows the calculation of the bond ionicity.One definition relies on the importance of ionic and covalent contributions to the chemical bond (V-O « V+ O - « V - O+).Using valence bond theory, the wavefunction of the system is built as a superposition of Lewis-like structures, and this allows the direct calculation of the different weights for structures.

The simple picture of a single V-O bond is for this structure not completely correct: the lone-pair orbital on oxygen can also donate electrons to the V d-orbitals, thereby forming a partial p bond.In this project, we want to study the effect of this p -backdonation on ionicity of the V-O bond for different supports using valence bond theory.

[1]T. Fievez, B.M. Weckhuysen, P. Geerlings, F. De Proft, J. Phys. Chem. C 113, 19905-19912 (2009).

Last modified:17 November 2017 1.59 p.m.