BSc & MSc Projects

Magneto-optics of perovskite nanocrystals

Master and BEP students are wanted for a project in an exciting and popular field of semiconductor physics: Spectroscopy of Perovskites. These are materials which have seen a sudden increase in popularity, due to numerous interesting properties, such as superconductivity, ferroelectricity, and their excellent performance as light harvesting materials for solar cells and light emitting materials for LEDs and even lasers.   

We will be using experimental data to characterize CsPbBr3 nanocrystals on a fundamental level, in order to explain their remarkable properties.

If you want your Masters or Bachelor project to be in a modern, competitive and exciting field of physics, then this is surely the project for you.  

For more information, contact Andrei Silov (Flux 2.098, a.y.silov@tue.nl) or Claudiu Iaru (Flux 2.097, c.m.iaru@tue.nl)

BSc/MSc/internship projects: Studying Exciton Dynamics of Two-Dimensional Transition Metal Dichalcogenides

Two dimensional (2D) materials such as graphene, black phosphorous, and transition metal dichalcogenides (TMDs) exhibit fascinating physical properties due to their specific band structure and reduced dimensionality. In recent years, TMDs (MX2, where M = Mo, W and X = S, Se) particularly are of much interest from a fundamental point of view but they also provide an excellent platform for ultrathin optoelectronic and photonic devices.

Similar to graphene, monolayer TMDs are composed of a 2D honeycomb lattice. As the material thickness is reduced to a single monolayer, TMDs transition from an indirect to a direct bandgap semiconductor, resulting in a thousand-fold increase in emission quantum efficiency at visible to near infrared wavelengths. Electron-hole pairs form tightly bound excitons with a ~ 1 nm Bohr radius and a > 300 meV binding energy, which are extremely stable at room temperature compared to traditional semiconductors.

The properties and characteristics of  monolayer TMDs provide us an elegant tool to study light-matter interaction at nanoscale. Combing 2D TMDs with nanophotonic structures (for example, plasmonic hole arrays as in Figure 1 or nanoparticle arrays), we investigate the fundamental properties of light emitters. In this project, we will concentrate on studying the exciton dynamics of 2D TMDs strongly coupled to nanophotonic structures, including the emission quantum yield, the photoluminescence lifetime and the photoconductivity of  both non-passivated and passivated TMDs.

If you are interested, please contact Dr. Shaojun Wang (s.wang@differ.nl), or Prof. Jaime Gomez Rivas (J.Gomez.Rivas@tue.nl).

Estimating the lifetime and quality factor of resonances with asymmetric lineshape (BSc. project)

Jaime Gomez Rivas/Mohammad Ramezani

Single metallic nanoparticles support localized surface plasmon resonances, i.e., the coherent oscillation of electrons driven by an electromagnetic field at a certain frequency, which can be described  as Lorentz oscillator. The lifetime and the quality factor of Lorentz oscillators can be simply estimated from the full width at half maximum (FWHM) of the resonance . Hence, this width determines  the lifetime of the plasmonic resonances in single particles in a straightforward manner.

However, placing metallic nanoantennas in a lattice leads to a very asymmetric resonance lineshape known as Fano resonance. The origin of this peculiar lineshape has been discussed extensively in the literature. In nutshell, the asymmetric lineshape is attributed to the spectral interference between broad plasmonic resonance and narrow diffraction orders that can be supported simultaneously in the lattice. One consequence of this phenomenon is that the lifetime of the Fano resonance can not be estimated by measuring the FWHM of the resonance anymore and this issue has remained widely unexplored.

In this project we would like to estimate the lifetime of Fano resonances in a generic array of metallic nanoparticle using two different method. The primary approach is implementing full 3D numerical simulations using existing Finite-Difference Time-Domain software to estimate the lifetime of the resonance. In addition, we would like to calculate the lifetime of this system using the model known as coupled oscillators. In this model we analytically solve two coupled differential equations that analogously describe the behaviour of our system. Solutions of these equations enables us to extract the information related to the dynamics and the lifetime of the system. Moreover, we would like to see how the parameters involved in the differential equations can modify the lifetime of the system.

This project mainly involves analytical calculations of differential equations and numerical calculations of Maxwell equations. Consequently, the candidate is expected to be familiar with ordinary differential equations and electrodynamics theory.

For more information please contact M. Ramezani ( m.ramezani@differ.nl) or J. Gomez Rivas (j.gomezrivas@differ.nl).

Reference:

Nano Lett., 2011, 11 (7), pp 2835–2840

Physical Review X 1 (2), 021019

Dynamics of Exciton-plasmon-polaritons in plasmonic nanoparticle arrays (Master and BSc projects)

Jaime Gomez Rivas/Alexei Halpin

Strong-light matter coupling has emerged as a major cross-disciplinary field of study over recent years. This regime was originally constrained to the realm of low-temperature studies, however, extensions to room temperature through advances in the fabrication of nanophotonic structures have opened the door for numerous new research lines. In this manner, strong-coupling has been proposed as a means for modifying the internal physics of condensed matter systems, with great potential for light-harvesting, energy-transport and catalysis.

In the Photonics for Energy (PFE) group at DIFFER, we explore strong coupling of organic materials to plasmonic lattice resonances in periodic arrays of metallic nanoparticles, resulting in plasmon-exciton polaritons (PEPs). Due to the short-lived nature of PEPs, linear spectroscopy can be restrictive, however, in determining how the energy landscape in molecular systems is affected by strong-coupling.

The project described here, suitable for a 10 month internship, would involve the construction of a time-resolved photoluminescence spectroscopy instrument, in order to dynamically track the evolution of excited-state species in PEP systems on ~100 fs timescales. This project would be well-suited for students having interest in optics, energy transfer, and spectrosocpy. The project would have the following two main goals:

1) The investigation of relaxation mechanisms which result in non-equilibrium condensation or PEP lasing in these systems [see M. Ramezani et al., Optica 4 (1), 31-37 (2017)]

2) Studying exciton transport in donor-acceptor PEP systems for light-harvesting applications.If you are interested in this project, please contact Dr. Alexei Halpin (a.halpin@differ.nl) or Prof. Jaime Gomez-Rivas (j.gomezrivas@differ.nl).

Please note: this internship is only available to EU citizens and permanent residents, or to students registered at a Dutch university.

Nonlinear polaritonics in plasmonic nanoparticle arrays (Master and BSc. project)

Jaime Gomez Rivas/Alexei Halpin

Strong-light matter coupling has emerged as a major cross-disciplinary field of study over recent years. This regime was originally constrained to the realm of low-temperature studies, however, extensions to room temperature through advances in the fabrication of nanophotonic structures have opened the door for numerous new research lines.

In the Photonics for Energy (PFE) group at DIFFER, we explore strong coupling of organic materials to plasmonic lattice resonances in periodic arrays of metallic nanoparticles, resulting in plasmon-exciton polaritons (PEPs). PEP lasing has previously been demonstrated by our group (see M. Ramezani et al., Optica 4 (1), 31-37 (2017)), where optical pumping leads to the formation of a non-equilibrium Bose-Einstein condensate of PEPs. This phenomenon, a subset of the broader polariton lasing field, presents an intriguing platform for the low-threshold generation of coherent light.

In this project, the internship student would explore different organic emitters for achieving polariton lasing at the lowest possible threshold. Somewhat counterintuitively, emitters with the highest intrinsic quantum yields are not necessarily those best suited for polariton lasing. The student will be required to explore emitters with strong or weak electronic-vibrational coupling, and also dyes and molecular aggregates which possessing intrinsic optical nonlinearities.

While no synthesis will be involved in the project, we expect that the candidate will possess some experience in chemistry environment, or the desire to learn, as the project will require the preparation of thin luminescent layers. This project should appeal to students interested in optics, lasing, molecular physics and nanophotonics.

If you are interested in this project, please contact Dr. Alexei Halpin (a.halpin@differ.nl) or Prof. Jaime Gomez-Rivas (j.gomezrivas@differ.nl).  

Please note: this internship is only available to EU citizens and permanent residents, or to students registered at a Dutch university. 

 

 

Single-photon emission in plasmonic structures with single quantum dots (Master project)

Paul Koenraad/Andrei Silov

The Year 2015 is the International Year of Light and Light-based Technologies.  Play marbles with photons in our group and celebrate the Year of Ligh by doing your Master Project in PSN!

Goal of the study

Realization of single-photon emission in hybrid structures combining gold plasmonic nano-antennas and InAs/AlGaAs quantum dot (QD) heterostructures. Under optical pumping the designed gold nano-structures (smart apertures) should provide efficient excitation of just a few QDs located within “hot spots” of a local electromagnetic field, as well as efficient outcoupling of the QD emission as far-field radiation.

Existing background 1. Full electromagnetic calculation in a specific metal-semiconductor structure representing an aperture opened in a gold mask deposited above a QD heterostructure, with a cylindrical gold nano antenna in the middle (in collaboration with ITMO University, St. Petersburg).  Below on the left is a design of the smart aperture, the central disk of about 300 nm in diameter, acting as nano antenna. On the right the electric field distribution in the smart aperture, top view, the electric field hot spots are shown in red.

In practically all research projects there are ample opportunities for Bachelor and Master projects. Often, the student is in charge of a project that is part of a larger PhD research plan, and works in close collaboration with a PhD student. Examples of projects are listed below.

Students, interested in a Bachelor or Master project within the PSN Group are invited to contact prof.dr. Paul Koenraad.

For informal contacts or information all other members of the scientific staff are available for consultation as well, after appointment (contact details: see people page).

Mass peak identification and assignment (Master project)

Paul Koenraad/Sebastian Kölling

Atom Probe Tomography is based on the field evaporation of atomic layers from a tip-shaped sample. By applying a standing voltage of a few kilovolt to a cryogenically cooled tip with a diameter of less than 200 nm an electric field is induced on the curved apex that enables a field induced removal of ions from the surface. The successive removal of millions of ions results in an analysis of a volume of several 100.000 cubic nanometer of material.
In addition, a laser or voltage pulse can be superposed to the standing field which confines the removal of ions in time and hence enables time-of-flight mass spectrometry. In this way it is possible to record a time-of-flight mass spectrum of the ions removed from the specimen. As shown in the figure below, the resulting mass spectra can become very complex, containing up to several hundred separable mass-peaks, as different ionic complexes are formed on the surface of the specimen.
In this project we want to develop an algorithm that automatically identifies the peaks in the mass spectrum and relates each of the identified peaks to complex ions that can potentially be generated from the elements present in the sample. Hence, the algorithm takes a number of elements and a mass-spectrum as input and then identifies all peaks and finds the complex molecular ions whose mass to charge ratio fit each of the peaks. Preferably, the algorithm should be implemented in MATLAB, R or Python. Candidates should be able to program and have an interest in analyzing complex and large data sets.

Hierarchical mass spectrum decomposition (Master project)

Paul Koenraad/Sebastian Kölling

Atom Probe Tomography is based on the field evaporation of atomic layers from a tip-shaped sample. By applying a standing voltage of a few kilovolt to a cryogenically cooled tip with a diameter of less than 200 nm an electric field is induced on the curved tip apex that enables a field induced removal of ions from the apex's surface. The successive removal of millions will remove a volume of several 100.000 cubic nanometer of material. The removed ions are projected onto a position-sensitive single ion detector. Based on their impact position, they can be back-projected onto the surface and the atom positions in the removed volume can be reconstructed.
In addition, a laser or voltage pulse can be superposed to the standing field which confines the removal of ions in time and hence enables time-of-flight mass spectrometry based on the mass-to-charge ratio of the removed ions as shown below. Hence the method allows for a three-dimensional analysis of the positions and the chemical identities of the atoms in a nanometer-sized volume. Unfortunately, the time resolution of the time-of-flight mass spectrometry is limited to a few nanoseconds and as a result the mass resolution is not sufficient to distinguish different ions with the same nominal mass to charge ratio (e.g. doubly charged Silicon and singly charged Nitrogen).
In principle, the collected mass spectrum can be decomposed by calculating the best fit between the observed counts of each isotope and the known isotopic distribution of the involved elements. However, this approach relies on a relatively large number of counts in the mass spectrum and is thus usually only viable for estimating the composition of larger volumes containing at least a few thousand atoms (~10x10x10 nm3). In this project, we aim to push the limits of this approach towards estimating the elemental composition of smaller volumes by utilizing a hierarchical way to decompose the mass spectra. Instead of looking at the mass spectrum of a local volume to estimate the local elemental composition we want to start by decomposing the mass spectrum of the entire volume and then repeatedly dissect the volume into halves. The elements found in the mass spectrum decompositions of the two halves naturally have to sum up to the (more accurate) decomposition of the full volume. Repeatedly dissecting the volume into halves and linking the local compositions of the two smaller volumes to the bigger "parent" volume will allow us to get accurate local compositions in much smaller volumes than to date.
Preferably, the decomposition algorithm should be implemented in MATLAB, R or Python. Candidates should have a good understanding of statistics, be able to program and have an interest in analyzing complex and large data sets.

 

Three-dimensional Field Ion Microscopy (Master project)

Paul Koenraad/Sebastian Kölling

The ionization of gas atoms on the cold surface of a needle shaped specimen can be used to make an image of the atomic structure of that very surface. The gas atoms are ionized by an electric field that is induced by applying a voltage to the needle shaped specimen. The atomic scale roughness then causes the electric field to vary over the surface and this field variation can be utilized as a contrast mechanism to image the surface by locally ionizing gas atoms on "top" of each surface atom. In addition, the electric field can also directly ionize atoms of the matrix of the specimen and hence slowly "peel off" the surface atom by atom. By imaging this process with gas atoms it is possible to create a movie that images the three-dimensional arrangement of the atoms in the needle shaped specimen as show on the right.
In this project we aim to analyze movies like the one below in order to extract the positions of all the atoms imaged in the movie with the aim of imaging the crystal lattice and in particular crystal defects in three dimensions with atomic resolution. The main task of the project will be to write a computer code in MATLAB, R or Python that identifies each atom in the movies and then extracts a three-dimensional point cloud of the atom positions. Candidates should hence be well versed in programming and have an interest in image and video content analysis.

Nanowire solar cells (Master project)

Erik Bakkers

Recently we have published our first realization of solar cells based on nanowires. For the transparent top contacting layer, we would like to experimentally investigate the use of a different deposition method; namely atomic layer deposition (ALD). This could increase the performance of the solar cell.Our nanowires are currently employing an axial pn-junction. In principle, the radial junction (core-shell) should be more efficient because of the large surface for light absorption and different direction for charge separation. A comparison of both structures could pave the way for the best possible nanowire solar cells.

Angle-dependent solar cell performance (Master project)

Erik Bakkers

Recently we have developed solar cells based on arrays of absorbing nanowires. We are interested in the angle-dependence behavior of the photocurrent generated by these solar cells. To measure this we use a unique research facility called time-reversed Fourier microscope, which enables us to illuminate the micron-sized solar cells from arbitrary angles. Also, we are able to investigate the directional absorption of various arrays of nanowires. We will also use computational software to simulate the absorption in these nanowire arrays. (This project is in collaboration with Philips Research and carried out at the High Tech Campus Eindhoven.)

Radiative coupling: Plasmonics and quantum dots (QDS)

Jos Haverkort

We study radiative coupling between QDs with/without employing metallic nanoantenna. Radiative coupling includes excitation hopping and modification of the radiative lifetime. Students are welcome to participate in the simulation and fabrication on small nanoantenna and in lifetime measurements using ultrafast lasers