Heyou's Reserach News and Notes
16.Jun.2024
Encrypt information purely optically! Our resreach publication is online!
Our research article has been publised on Advanced Optical Materials. Love Letters at the Nanoscale!
Purely Optical, Reversible, Read‐Write‐Erase Cycling Using Photoswitchable Beads in Micropatterned Arrays Heyou Zhang, Pankaj Dharpure, Michael Philipp, Mukundan Thelakkat, Paul Mulvaney, and Jürgen Köhler*,
Advanced Optical Materials, 2024, 2401029.
DOI: 10.1002/adom.202401029
Abstract
Using surface-templated electrophoretic deposition, arrays of polymer beads (photonic units) incorporating photo-switchable DAE molecules are created, which can be reversibly and individually switched between high and low emission states by direct photo-excitation, without any energy or electron transfer processes within the molecular system. The micropatterned array of these photonic units is spectroscopically characterized in detail and optimized with respect to both signal contrast and cross-talk. The optimum optical parameters including laser intensity, wavelength and duration of irradiation are elucidated and ideal conditions for creating reversible on/off cycles in a micropatterned array are determined. 500 such cycles are demonstrated with no obvious on/off contrast attenuation. The ability to process binary information is demonstrated by selectively writing information to the given photonic unit, reading the resultant emissive signal pattern and finally erasing the information again, which in turn demonstrates the possibility of continuous recording. This basic study paves the way for building complex circuits using spatially well-arranged photonic units.
Cite from: DOI: 10.1002/adom.202401029
01.Feb.2024
Review and Perspective on Electrophoretic Deposition of Single Nanoparticles! Our resreach publication is online!
Our minireview has been publised on Langmuir. We are summarizing current results in Electrophoretic Deposition of Nanoparticles and giving our perspective on its future development.
Electrophoretic Deposition of Single Nanoparticles Heyou Zhang, Yawei Liu, Yue Dong, Arun Ashokan, Asaph Widmer-Cooper, Jürgen Köhler, and Paul Mulvaney*, Langmuir, 2024, 40, 6, 2783–2791. DOI: 10.1021/acs.langmuir.3c02951
Abstract
The controlled assembly of colloid particles on a solid substrate has always been a major challenge in colloid and surface science. Here we provide an overview of electrophoretic deposition (EPD) of single charge-stabilized nanoparticles. We demonstrate that surface templated EPD (STEPD) assembly, which combines EPD with top-down nanofabrication, allows a wide range of nanoparticles to be built up into arbitrary structures with high speed, scalability, and excellent fidelity. We will also discuss some of the current colloid chemical limitations and challenges in STEPD assembly for sub-10 nm nanoparticles and for the fabrication of densely packed single particle arrays.
Cite from: DOI: 10.1021/acs.langmuir.3c02951
25.Dec.2023
2023 - A year of Awards!
It is my great horour to be awarded three prestigious Awards/Prizes in recognition of my PhD life in the University of Melbourne.Masson Award for Best PhD Thesis in Chemistry, Faculty of Science. 2023 Dean's Honours Award, Faculty of Science. The Chancellor's Prize for Excellence, University of Melbourne. 
04.Jun.2022
A Universal Direct Assembly Method for Nanocrystal Arrays! Our resreach publication is online!
Our research article has been publised on Advanced Optical Materials. We are expanding our direct EPD assembly method towards most kinds of nanomaterials.
A General Method for Direct Assembly of Single Nanocrystals Heyou Zhang, Yawei Liu, Arun Ashokan, Can Gao, Yue Dong, Calum Kinnear, Nicholas Kirkwood, Samantha Zaman, Fatemeh Maasoumi, Timothy D. James, Asaph Widmer-Cooper, Ann Roberts, and Paul Mulvaney*, Advanced Optical Materials, 2022, 202200179 DOI: 10.1002/adom.202200179
Abstract
Controlled nanocrystal assembly is a pre-requisite for incorporation of these materials into solid state devices. Many assembly methods have been investigated which target precise nanocrystal positioning, high process controllability, scalability, and universality. However, most methods are unable to achieve all of these goals. Here, surface templated electrophoretic deposition (STED) is presented as a potential assembly method for a wide variety of nanocrystals. Controlled positioning and deposition of a wide range of nanocrystals into arbitrary spatial arrangements including gold nanocrystals of different shapes and sizes, magnetic nanocrystals, fluorescent organic nanoparticles, and semiconductor quantum dots is demonstrated. Nanoparticles with diameters below 10 nm are unable to be deposited due to their low surface charge and strong Brownian motion (low Péclet number). It is shown that this limit can be circumvented by forming clusters of nanocrystals or by silica coating nanocrystals to increase their effective size.
Cite from: DOI: 10.1002/adom.202200179
31.Aug.2021
How the Gold Nanorod Was Tempered! Our resreach publication is online!
Our research article has been publised on the Journal of Physical Chemistry C. We are trying to understand the birth of the gold nanorods.
Growth of Gold Nanorods: A SAXS Study Susanne Seibt, Heyou Zhang, Stephen Mudie, Stephan Förster, and Paul Mulvaney*, The Journal of Physical Chemistry C, 2021,125, 36, 19947-19960 DOI: 10.1021/acs.jpcc.1c06778
Abstract
Using simultaneous, in situ optical spectroscopy and time-resolved, small-angle X-ray scattering (SAXS), we have directly monitored the seeded growth of nearly monodisperse gold nanorods using hydroquinone as the reductant. Growth of the rods is much slower than with the ascorbate ion, allowing the rate of growth along both the longitudinal and transverse directions to be independently determined. The thickness of the stabilizing CTAB layer (3.2 ± 0.3 nm) has also been extracted. We find that increasing the hydrogen tetrachloroaurate(III) concentration produces longer rods, while conversely, increasing the hydroquinone concentration reduces the final aspect ratio. The final number of gold rods is smaller than the initial number of seed particles and decreases in the presence of larger concentrations of HAuCl4. The SAXS data reveal an early transition from a spherical morphology to an ellipsoidal one and then to spherically capped cylinders. The growth curve exhibits at least three distinct regimes: an initial phase comprising spherical seed growth, followed by symmetry breaking and slow elongation. A third phase is marked by rapid rod growth and increases in the aspect ratio. This process is temporally well resolved from the initial symmetry breaking but typically occurs when the rods are around 6 nm in diameter using hydroquinone as the reductant. The results provide qualitative support for the “popcorn model” proposed by Edgar et al. [Formation of Gold Nanorods by a Stochastic “Popcorn” Mechanism. ACS Nano 2012, 6, 1116 1125].
Cite from: DOI: 10.1021/acs.jpcc.1c06778
03.Feb.2021
Our resreach publication is online!
Our research article has been publised on Advanced Functional Materials. This paper is about how to command gold nanorods standing vertically during our EPD assembly method.
Direct Assembly of Vertically Oriented, Gold Nanorod Arrays
Heyou Zhang, Yawei Liu, Muhammad Faris Shahin Shahidan, Calum Kinnear, Fatemeh Maasoumi, Jasper Cadusch, Eser Metin Akinoglu, Timothy D. James, Asaph Widmer-Cooper, Ann Roberts, Paul Mulvaney*,
Advanced Functional Materials, 2021, 31, 2006753. DOI: 10.1002/adfm.202006753
Abstract
Although many nanoscale materials such as quantum dots and metallic nanocrystals exhibit size dependent optical properties, it has been difficult to incorporate them into optical or electronic devices because there are currently no methods for precise, large-scale deposition of single nanocrystals. Of particular interest is the need to control the orientation of single nanocrystals since the optical properties are usually strongly anisotropic. Here a method based on electrophoretic deposition (EPD) is reported to precisely assemble vertically oriented, single gold nanorods. It is demonstrated that the orientation of gold nanorods during deposition is controlled by the electric dipole moment induced along the rod by the electric field. Dissipative particle dynamics simulations indicate that the magnitude of this dipole moment is dominated by the polarizability of the solution phase electric double layer around the nanorod. The resulting vertical gold nanorod arrays exhibit reflected colors due to selective excitation of the transverse surface plasmon mode. The EPD method allows assembly of arrays with a density of over one million, visually resolvable, vertical nanorods per square millimeter.
Cite from: DOI: 10.1002/adfm.202006753
01.Jan.2021
An amazing logo of the University of Melbourne made by gold nanorods array
Catch up with our works in 2018 (Direct Assembly of Large Area Nanoparticle Arrays. ACS Nano, 2018, 12, 8, 7529–7537 DOI: 10.1021/acsnano.8b02932 ), we present a logo of the University of Melbourne constructed by exact 6205 gold nanorods assembled by our diretct EPD assemlby method. Credit to the ability of nanometre level precise control, all gold nanorods are alinged in the same orientation by our diretct EPD assemlby method. Due to the asymmetric optical property of gold nanorod along long and short rod axis, the colour of the logo swith from red to green and back to red dependent on the orientaion of the polariser under dark field microscope.
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