Two new ARC funded research positions are available for a period of up to 3 years to study different aspects of quantum dot luminescence.
The first positon is for an instrument based person to work on further development of our confocal microscopy systems for single quantum dot spectroscopy. The ideal candidate will have: Demonstrated experience in confocal microscopy, Demonstrated experience in building experiments on optical tables, Demonstrated experience in spectroscopic measurement and analysis, Demonstrated experience in single photon counting methods and data collection. The starting salary is $75,404- $80,939 p.a. including employer benefits. The goal is to study unique processes associated with single QDs such as FRET, blinking, and electron transfer to acceptors. Applicants would be expected to have a PhD in physics, chemistry, engineering or related discipline. A publication record in nanoscale spectroscopy is desirable. The appointee will need good personal skills and be able to liaise with other academics and researchers in physics and applied mathematics.
The second position is for a theory based person working with Prof. John Sader in the Applied Mathematics Department. This project involves theoretical modelling of quantum dots and the effect of their surrounding fluid environment on their spectroscopic properties. Additionally, competent guidance of graduate, honours and early postgraduate students working within the group is required. The position will involve interactions with the Chemistry and Physics departments and the Bio21 Institute. The theoretical program will focus on simulation techniques such as molecular dynamics, Monte Carlo, lattice Boltzmann, finite difference, finite element and other computational methods. Excellent skills in computational methods and analytical ability are required. Applicants would be expected to have a PhD in mathematics, physics, chemistry, engineering or related discipline. A publication record in numerical simulation is desirable. The appointee will need good personal skills and be able to liaise with other academics and researchers in surface science, nanomaterials, engineering and applied mathematics.
Apply online at http://jobs.unimelb.edu.au using the position number 0030815 or email mulvaney@unimelb.edu.au for more details. Applications close February 28, 2013.
Mark J. Fernee, Chiara Sinito, Yann Louyer, Christian Potzner, Tich-Lam Nguyen, Paul Mulvaney, Philippe Tamarat & Brahim Lounis
Published 18 December 2012, Nature Communications. doi:10.1038/ncomms2300
Abstract:
Charged quantum dots provide an important platform for a range of emerging quantum technologies. Colloidal quantum dots in particular offer unique advantages for such applications (facile synthesis, manipulation and compatibility with a wide range of environ- ments), especially if stable charged states can be harnessed in these materials. Here we engineer the CdSe nanocrystal core and shell structure to efficiently ionize at cryogenic temperatures, resulting in trion emission with a single sharp zero-phonon line and a mono exponential decay. Magneto-optical spectroscopy enables direct determination of electron and hole g-factors. Spin relaxation is observed in high fields, enabling unambiguous identi- fication of the trion charge. Importantly, we show that spin flips are completely inhibited for Zeeman splittings below the low-energy bound for confined acoustic phonons. This reveals a characteristic unique to colloidal quantum dots that will promote the use of these versatile materials in challenging quantum technological applications.
The surface plasmon modes of self-assembled gold nanocrystals
Steven J. Barrow, Xingzhan Wei, Julia S. Baldauf, Alison M. Funston & Paul Mulvaney
Nature Communications, 11 December 2012, doi: 10.1038/ncomms2289
Abstract:
The three-dimensional (3D) self-assembly of nanocrystals constitutes one of the most important challenges in materials science. A key milestone is the synthesis of simple, regular structures, such as platonic solids, composed of nanocrystal building blocks. Such objects are predicted to have unique optical and electronic properties such as polarization-independent light-scattering and intense local fields. Here we present a two-stage process for fabricating well-defined and highly symmetric, 3D gold nanocrystal structures, including tetrahedra, 3D pentamers and 3D hexamers. Polarized scattering spectra are used to elucidate the plasmon modes present in each structure, and these are compared with computational models. We conclude that self-assembly of highly symmetric, polarization-independent structures with interparticle spacings of order 0.5nm can now be fabricated. Drastically, enhanced local fields, 1000 times higher than the incident field strength, are produced within the interstices. Fano resonances are generated if the symmetry is broken.
Spring constant calibration of atomic force microscope cantilevers of arbitrary shape
John E. Sader , Julian A. Sanelli , Brian D. Adamson , Jason P. Monty , Xingzhan Wei, Simon A. Crawford, James R. Friend, Ivan Marusic, Paul Mulvaney, and Evan J. Bieske
REVIEW OF SCIENTIFIC INSTRUMENTS 83, 103705 (2012)
Abstract:
The spring constant of an atomic force microscope cantilever is often needed for quantitative measurements. The calibration method of Sader et al. [Rev. Sci. Instrum. 70 , 3967 (1999)] for a rectangular cantilever requires measurement of the resonant frequency and quality factor in fluid (typically air), and knowledge of its plan view dimensions. This intrinsically uses the hydrodynamic function for cantilever of rectangular plan view geometry. Here, we present hydrodynamic functions for a series of irregular and non-rectangular atomic force microscope cantilevers that are commonly used in practice.
The Nanoscience Laboratory is offering a wide range of summer, "399" and MSc projects. Listed below are a few. The Laboratory has 5 postdoctoral research fellows and 15 PhD students at present.
I. Phase Transfer of Gold Nanoparticles (supervisor: Dr Marco Lista)
This project explores how nanoscale catalysts can be moved from solvent to solvent. Gold particles are ruby red. They do not aggregate due to the presence of ligands chemically bound to the surface. By changing the ligand polarity, the particles move spontaneously into different solvents. In this project we aim to start assembling these particles by using ligands that can also cross link the particles to form dimers etc.
2. Designer Peptides for Quantum Dot FRET Spacers (Supervisor: Gary Beane)
This project uses the peptide synthesizer at Bio21 to build peptide sequences. These peptides are used to cap quantum dots (fluorescent semiconductor nanocrystals). A dye bound to the QD will quench the QD luminescence, but its efficiency is controlled by the separation, which will be controled by the peptide length. This project suits an organic chemistry student.
3. Compatibility study of quantum dots in biochemical buffers (Supervisor: Dr. Tich Lam Nguyen)
Quantum dots (QDs) have been utilised in biological and medical research for assay detection, as well as for in-vitro and in-vivo imaging. Their unique optical properties overcome many of the drawbacks encountered using organic dyes including superior quantum yields and high resistance to photo-bleaching. For these applications to be possible, QDs are bio-functionalised by making them water dispersible and then conjugating them to the bio-molecule of interest.
One of the key challenges is to keep QDs colloidally and optically stable. It is, therefore, important to explore the compatibility of QDs with immonobuffers. This project aims to:
1. Synthesize biocompatible QDs using established protocols and characterise them using absorption spectroscopy, fluorescent spectroscopy and Transmission Electron Microscopy;
2. Investigate their colloidal and optical stabilities in a range of buffers using spectroscopy.
4. Synthesis of fluorescent upconverting nanocrystals (Supervisor: Dr. Tich Lam Nguyen)
Near infrared (NIR) – to – visible upconverting fluorescent nanoparticles are materials that convert NIR excitation into visible emission. They are usually composed of rare earth metal fluorides or oxide doped with rare earth ions. These nanocrystals are perfect as fluorescent probes for biological detection and imaging because they can be excited at the non-damaging 980nm wavelength to cells and where auto fluroescence in biological specimen is not a problem. Furthermore, their sharp emission peaks in the visible region make them an ideal candidate for the development of future lasers.
This project will be undertaken in collaboration with the Institute for Photonic and Advanced Sensing at The University of Adelaide to explore the feasibility of using them in chip lasers and other waveguide materials. This project aims to:
1. SynthesizeNIR upconverting nanocrystals using established protocols and characterise them using fluorescent spectroscopy, X-Ray Diffraction and Transmission Electron Microscopy;
2. Explore the feasibility of embedding them into a range of metal oxide and fluoride matrices
5. Investigations of the role of water in the synthesis of CdSe nanoparticles for quantum rod growth (Supervisor Dr Klaus Boldt)
CdSe quantum dots exhibit a wide range of fluorescence colours, depending on size. Trace amounts of water seems to play an important role in the growth of monodisperse CdSe nanoparticles. The aim of the project is to investigate the effect of water by systematically adding it to the reaction mixture. The products shall be investigated by optical spectroscopy, transmission electron microscopy and possibly x-ray diffraction. If successful, the results will be applied to the seeded growth of CdSe/CdS "quantum rods".
2013 PhD Projects at the NSL
Current PhD Research Projects – Prof. Paul Mulvaney
The Nanoscience Laboratory works on the chemistry & physics of nanoscale systems. The Laboratory currently has 15 PhD students and 5 post-doctoral research fellows. We are looking for suitably qualified, high-achieving* graduate students to tackle projects listed below:
* Australian students with H1 degree or overseas students who can secure IPRS (MIFRS) scholarships.
Single Quantum Dot Spectroscopy
The luminescent properties of semiconductor nanocrystals can be probed by single photon counting methods. In this project we will study CdSe/CdS nanorods and the differences in crystal structure between wurtzite and zincblende particles. We also study energy transfer to dye molecules at the single particle level. The project suits students with strong interest in spectroscopy.
Plasmonic Logic Gates and Metamaterials
Surface plasmon resonances could be utilized to try and engineer logic gates for optical circuitry. At present we are trying to understand how the plasmon modes couple in gold particle dimers and other superstructures. The answer may lie in mixing dark modes to form Fano resonances. The project will involve measurement of spectra and modelling their optical properties using plasmon hybridization, COMSOL and other techniques. This project suits students with a strong interest in optics and modelling.
Molecular Simulations of Order and Disorder in Nanocrystal Systems
Working with Dr Gray-Weale we have found that nanocrystals undergo interesting phase transitions that depend critically on the ligands used to offset van der Waals forces. In this project we aim to understand how solvation forces, entropy and ligands can be used to direct nanocrystal assembly. Suits a student with strong computation interests. A second experimental project on the collection of data via SANS and SAXS of nanocrystal superlattices to test the simulations is also available.
Atomic Force Microscopy (AFM) Studies of Surface Forces, Quantum Friction and Nanoscale Slip
Lubrication is an important problem but at the nanoscale is poorly understood. Using model self-assembled monolayers on atomically smooth surfaces we will study slip and nanoscale friction. This project will suit people with an interest in advanced instrumentation such as AFM.
Quantum Dot Transistors
By embedding quantum dots into bulk semiconductor films of ZnS or ZrO2 we aim to make optoelectronic devices whereby the photoluminescence is switched on and off electrically. This would enable simple tunable LED style light emitters to be developed. It also enables us to probe doping and mobility in QDs. This project suits students with strong background in solid state physics and electronics.
The Quantum Decoherence Microscope
Together with Prof Lloyd Hollenberg in Physics we are studying how the luminescence from single defects in nanodiamonds can be used to as a sensor probe the biological environments. The PL is sensitive to the presence of spin states, local ion currents and fluctuating magnetic fields. Our goal is to put these nanodiamonds onto AFM tips and sue them to create a microscope that can map surface spins and ion currents in biological systems. This project suits students with a strong interest in AFM and instrumentation.
Conjugation of Transferrin to Azide-Modified CdSe/ZnS Core–Shell Quantum Dots using Cyclooctyne Click Chemistry
Christine Schieber,* Alessandra Bestetti, Jet Phey Lim, Anneke D. Ryan, Tich-Lam Nguyen, Robert Eldridge, Anthony R. White, Paul A. Gleeson, Paul S. Donnelly,* Spencer J. Williams,* and Paul Mulvaney*
Angew. Chem. Int. Ed. 2012, 51, 10523 –10527
Researchers at the Bio21 Institute have developed a new generic pathway for linking semiconductor nanocrystals or quantum dots to biological targets such as oligonucleotides, proteins, antibodies and peptides. The new method allows the surface chemistry of the nanocrystal to be tailored to the target and to minimise non-specific binding to substrates. The new work builds on the use of designer click chemicals to enable room-temperature, covalent bonds between the biological molecule and the nanocrystal. The work has just been published in Angew Chemie and is the subject of 2 University of Melbourne patents.
The State of Nanoparticle-Based Nanoscience and Biotechnology: Progress, Promises, and Challenges
Beatriz Pelaz,†,‡ Sarah Jaber,§ Dorleta Jimenez de Aberasturi,†,^ Verena Wulf,† Takuzo Aida,zJesus M. de la Fuente,‡ Jochen Feldmann,# Hermann E. Gaub,# Lee Josephson,r Cherie R. Kagan,O,[ Nicholas A. Kotov,2 Luis M. Liz-Marza ́n,0,f Hedi Mattoussi,9 Paul Mulvaney,§ Christopher B. Murray,[ Andrey L. Rogach,x Paul S. Weiss,¥ Itamar Willner, and Wolfgang J. Parak†,*
†Fachbereich Physik and WZMW, Philipps Universität Marburg, 35037 Marburg, Germany, ‡Instituto de Nanociencia de Aragon, University of Zaragoza, §Bio 21 Institute & School of Chemistry, University of Melbourne,^Department of Inorganic Chemistry, UPV/EHU, Spain, zDepartment of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, #Physik-Department and Center for NanoScience, Ludwig Maximilians Universität München, rMartinos Center for Biomedical Imaging and the Department of Radiology, Massachusetts General Hospital, ODepartment of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, [Department of Chemistry and Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, 2Department of Chemical Engineering, Department of Material Sciences and Engineering, Department of Biomedical Engineering, Biointerface Institute, University of Michigan, Ann Arbor, 0Centre for Cooperative Research in Biomaterials (CiC biomaGUNE), Spain, fIkerbasque, Basque Foundation for Science,Spain, 9Department of Chemistry and Biochemistry, Florida State University, xDepartment of Physics and Materials Science & Centre for Functional Photonics (CFP), City University of Hong Kong, ¥Department of Chemistry and Biochemistry, Department of Materials Science and Engineering, and California NanoSystems Institute, University of California and Institute of Chemistry,The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem.
Abstract:
Colloidal nanoparticles (NPs) have become versatile building blocks in a wide variety of fields. Here, we discuss the state-of-the-art, current hot topics, and future directions based on the following aspects: narrow size-distribution NPs can exhibit protein-like properties; monodispersity of NPs is not always required; assembled NPs can exhibit collective behavior; NPs can be assembled one by one; there is more to be connected with NPs; NPs can be designed to be smart; surface-modified NPs can directly reach the cytosols of living cells.
www.rsc.org/nanoscale
DOI: 10.1039/c2nr31443f
Enrico Della Gaspera,Marco Bersani, Giovanni Mattei, Tich-Lam Nguyen, Paul Mulvaney and Alessandro Martucci
Abstract:
Metal (Au, Pt, Au@Pt) and metal oxide (TiO2) nanoparticles are synthesized with colloidal techniques and subsequently used as nanocrystal inks for thin films deposition. The optical properties of Au colloids are strongly influenced by both Pt and TiO2 interfaces: while platinum causes a damping and a blue-shift of the Au Surface Plasmon Resonance (SPR) peak as a consequence of the metal–metal interaction, the anatase matrix is responsible for the red shift of the plasmon frequency due to the increased refractive index. By a careful tailoring of the nanoparticles synthesis, high quality, scatteringfree films composed of an anatase matrix embedding Au, Pt and Au@Pt colloids are deposited at room temperature and stabilized at 200 C. Room temperature exposure of these films to hydrogen leads to optical changes. In the case of Au, there is a slow blue shift of the surface plasmon band, resulting in a wavelength dependent optical response. Much faster but smaller optical changes occur for titania films containing Pt. When both metals are present, the optical response of the gold is much faster. This is attributed to spillover of hydrogen atoms from platinum to gold. This synergy enables enhanced optical sensing of hydrogen at room temperature by combining the low temperature dissociation of H2 on Pt with the intensive surface plasmon response of the gold nanocrystals.
dx.doi.org/10.1021/jz300456h | J. Phys. Chem. Lett. 2012, 3, 1716−1720
Mark J. Fernée,Taras Plakhotnik, Yann Louyer, Bradley N. Littleton, Christian Potzner,
Philippe Tamarat, Paul Mulvaney, and Brahim Lounis
Abstract:
Spectral diffusion of the emission line of single colloidal nanocrystals is generally regarded as a random process. Here, we show that each new spectral position has a finite memory of previous spectral positions, as evidenced by persistent anticorrelations in time series of spectral jumps. The anticorrelation indicates that there is an enhanced probability of the charge distribution around the nanocrystal returning to a previous configuration. We show both statistically and directly that this memory manifests as an observable spontaneous “relaxation” in the absence of a pump laser, so that spectral diffusion progresses in a manner of “two steps forward and one step back".