Queensland researchers have shown that single crystals, typically thought of as brittle and inelastic, are flexible enough to be bent repeatedly and even tied in a knot.

Researchers from Queensland University of Technology and The University of Queensland (UQ) determined and measured the structural mechanism behind the elasticity of the crystals down to the atomic level using the Australian Synchrotron.

Video: Copyright QUT

Their work, published in Nature Chemistry, opens the door for the use of flexible crystals in applications in industry and technology. 

The research was led by ARC Future Fellows Associate Professor Jack Clegg in UQ’s School of Chemistry and Molecular Biosciences and Associate Professor John McMurtrie in QUT’s Science and Engineering Faculty. 

Associate Professor McMurtrie said the results challenged conventional thinking about crystalline structures.

“Crystals are something we work with a lot – they’re typically grown in small blocks, are hard and brittle, and when struck or bent they crack or shatter,” he said.

“While it has previously been observed that some crystals could bend, this is the first study to examine the process in detail.

“We found that the crystals exhibit traditional characteristics of not only hard matter, but soft matter like nylon.”

The researchers grew bendable crystals about the width of a fishing line and up to five centimetres long from a common metal compound – copper (II) acetylacetonate.

They mapped changes in the atomic scale structure when the crystals were bent using X-ray measurements performed at the Australian Synchrotron.

A view of the structural deformation on the elongated (left) and compressed (right) areas of the crystal.

Dr Jason Price, a beamline scientist at the Australian Synchrotron, who helped design the experiments, explained that preliminary studies were undertaken on the MX1 beamline and followed by extensive measurements on the MX2 beamline.

“This experiment really shows the opportunity to look at variation within a single crystal. The microfocus capacity of the beam at MX2 is such that it can gather data from different parts of the crystal, so, when it is under strain from expansion or compression.”

 Crystals from six other structurally related compounds, some containing copper and some other metals, were also tested and found to be flexible.  

Associate Professor Clegg said the experiments showed that the crystals can be repeatedly bent and return quickly to their original shape with no signs of breaking or cracking when the force bending them is removed.

“Under strain the crystal molecules reversibly rotate and reorganise to allow the compression and expansion required for elasticity and still maintain the integrity of the crystal structure,” he said.

“The ability of crystals to bend flexibly had wide-ranging implications in industry and technology.

“Crystallinity is a property that underpins a variety of existing technologies, including semi-conductors and lasers which are used in almost every electronic device from DVD players to mobile phones and computers.

“But the hardness that makes them suitable for high-strength industrial components limits their use in other technologies. Flexible crystals like these could lead to new hybrid materials for numerous applications from components of planes and spacecraft to parts of motion or pressure sensors and electronic devices.”

Associate Professor McMurtrie said the method the researchers have developed to measure the changes during bending could also be used to explore flexibility in any other crystals.

“This is an exciting prospect given that there are millions of different types of crystals already known and many more yet to be discovered,” he said.

“Bending the crystal changes its optical and magnetic properties, and our next step is to explore these optical and magnetic responses with a view to identifying applications in new technologies.”

The research was funded by an ARC Discovery Grant and supported by the Australian Synchrotron. Research collaborators and co-authors of the study are: Anna Worthy, Professor Chen Yan, and Yanan Xu (QUT) and Dr Arnaud Grosjean, Dr Michael Pfrunder and Dr Grant Edwards (UQ).

http://dx.doi.org/10.1038/nchem.2848  

For interview:

QUT Associate Professor John McMurtrie, j.mcmurtrie@qut.edu.au   07 3138 1220

UQ Associate Professor Jack Clegg, j.clegg@uq.edu.au  0408 642082

International researchers led by Assoc Prof Chris McNeill’s group at Monash University have used an X-ray scattering at the Australian Synchrotron to understand how microstructure contributes to the performance of an organic solar cell made with a semiconducting polymer and fullerene thin film.

The investigators evaluated the performance, microstructure and photophysics of dual stack bulk heterojunction (BH) solar cells made with a low bandgap polymer and fullerene thin film in a study published in Advanced Energy Materials.

The research relied on a range of techniques including X-ray scattering, photoluminescence spectroscopy, ultrafast transient absorption spectroscopy and transient photovoltage measurements, to gain a better understanding of how the choice of fullerene acceptor influences microstructure,  photophysics and contribute to device performance.

A bulk heterojunction device is fabricated by coating a blend of two organic semiconductors between two electrodes. Thin films, which are usually less than 100 nanometres thick, offer production advantages for solar cells.

The close blending of materials is required for high performance because photo-generated excitons travel less than 10 nanometres before recombining, with photocurrent generation proceeding through via the dissociation of excitons a material interfaces. Efficient devices therefore require the blend to be optimally structured on the nanoscale.

2-dimensional X-ray scattering patterns of (a) PC61BM, (b) PC71BM and (c) ICBA. (d) line profiles integrated from 2D scattering patterns and (d) fitted parameters.

 

Advanced characterisation techniques are used to understand how microstructure, or morphology, contributes to power conversion efficiency.

Fullerenes act as electron acceptors in a device. Three novel compounds, PC71BM, PC61BM and ICBA were blended with a low band gap polymer, PBDTTT-EFT for the study.

The highest efficiency (9.4%) was found in the blend using the acceptor PC71BM, which also had the highest visible light absorption.

Prof Chris McNeill and collaborators used Synchrotron-based grazing incidence wide angle X-ray scattering (GIWAXS) to determine the molecular orientation of the polymer with respect to the substrate in the bulk of the thin film.  

The GIWAXS measurements provided information about the orientation of polymer crystallites in the bulk, with these crystallites needing to be properly aligned in order for charges to travel through the material more easily.

Resonant soft X-ray scattering was also carried out by co-author Dr Lars Thomsen at the Advanced Light Source at Lawrence Berkley National Laboratory in the US to clarify the structure and purity of domains.

Thomsen, a member the soft x-ray spectroscopy beamline team at the Synchrotron, has undertaken previous collaborations with the McNeill Group on organic electronics.

R-SoXS indicated that one of the blends, PBDTTT-EFT:PC71BM exhibited the largest domain size and highest domain purity, which was thought to facilitate charge separation and transport.

The scattering profiles also provided an indication of the roughness of the interfaces between the domains in the three compounds.

The R-SoXS and other methods suggested that the lower power conversion efficiency of the ICBA compound might be explained by rougher domain interfaces, lower crystallinity and smaller domain size.

Contributors include Dr Wenchao Huang and colleagues at Monash University, Dr Eliot Gann (now at Brookhaven National Lab), researchers from the University of California Los Angeles, the Indian Institute of Technology Bombay and Victoria University of Wellington.

A Monash-led group of geoscientists used the macromolecular crystallography beamline (MX2) Australian Synchrotron to help them determine the atomic structure of a new mineral discovered in a volcanic area of Far Eastern Russia. 

The research, which was published in American Mineralogist by Prof Joel Brugger of Monash and collaborators from Australia and Russia may provide insight into the processes responsible for the geochemical evolution of Earth. 

The authors reported that an analysis of Nataliyamalikite was challenging because of the small size of single crystals, composite nature of larger aggregates and the extreme light sensitivity of the mineral and the surrounding sulfur matrix. 

Nataliyamalikite grains could not be isolated using optical microscopy. 

X-ray powder diffraction measurements on microcrystals of Nataliyamalikite at 100 K indicated that  the structure was orthorhombic. 

The mineral which has only two atoms, thallium and iodide, in the asymmetrical unit cell, is considered to be a distorted version of rock salt.

The beam diameter was reduced to 7.5 nanometres by a collimator at the Australian Synchrotron MX2 micro-focus beamline to match the crystal size of the micro-aggregates of Nataliyamalikite, which were extracted from the amorphous sulfur matrix by focused ion beam scanning electron microscopy.

MX2 beamline scientist Dr Jason Price assisted in processing the beamline data, which was compared with a synthetic equivalent. 

Electron backscatter diffraction at Monash and in Russia confirmed an orthorhombic crystal lattice of the mineral at ambient conditions. 

The thallium-rich Nataliyamalikite forms in high temperature fumaroles, (thermal openings in areas surrounding a volcano) as a component of arsenic and sulfur-rich coating on lava and scoria around the vents.

In the paper, the authors also provided a description of the process that give rise to concentrations of thallium, leading to the formation of Nataliyamalikite.

Read more on the Monash website.