Research Projects

Below is a summary of some of our current research projects. For more information about the research please contact either Dr Stephen Morris (stephen.morris@eng.ox.ac.uk) or Professor Steve Elston (s)

1. Liquid Crystalline Templates and Stretchable Photonic Gels

 A. Chiral Polymer Scaffolds as Templates for Soft Photonic Crystals & Metamaterials

Our research in this area involves the fabrication and characterisation on new photonic and meta-materials based upon chiral nematic and blue phase liquid crystals that have been ‘templated’ using a polymer scaffold that has been created by a cross-linked polymer network. The aim of this work is to harness the self-organising feature of liquid crystalline phases that naturally assemble to form a structure with a periodic modulation of the refractive index that is on the order of the wavelength of visible light. Furthermore, depending upon the liquid crystal phase, this periodicity can exist in either 1-dimension (chiral nematic) or 3-dimensions (blue phase). By forming a template of these structures with a polymer network it is then possible to impart this macroscopic structure onto other materials. An example of the 'templating' process of a blue phase is shown in Figure 1. This work is carried out in collaboration with Dr Flynn Castles in the Department of Materials at the University of Oxford and also previously with the Centre of Molecular Materials for Photonics and Electronics at the University of Cambridge

Blue phase template

Figure 1. A Blue phase template (a self-assembled 3D photonic crystal). 

 B. Stretchable Photonic Crystal-like Gels

In addition, we are also studying the mechanochromic and electro-optic properties of chiral nematic blue phase liquid crystalline gels, which have recently been demonstrated as a result of research carried out at the Departments of Engineering at both Oxford and Cambridge. Examples of free-standing blue phase gels from a recent publication in Nature Materials are shown in Figure 2.

Stretchable liquid crystalline blue phase gels

Figure 2. Stretchable liquid crystalline blue phase gels.

We are also working on stretchable laser gels based upon chiral nematic and blue phase liquid crystals. An example of wavelength tuning of the laser emission from a liquid crystal laser gel is shown in Figure 3. 

 

Figure 3. Stretchable cholesteric liquid crystalline gels

 

Figure 4. Stretchable cholesteric liquid crystalline gels 

Relevant publications:

  • Wavelength-tuneable laser emission from stretchable chiral nematic liquid crystal gels via in situ photopolymerization  RSC Advances, 6, 31919-31924 (2016)
  • Stretchable liquid-crystal blue-phase gels Nature Materials, 13, 817-821(2014)
  • Blue-phase templated fabrication of three-dimensional nanostructures for photonic applications Nature Materials 11, 599 (2012)
  • Simultaneous red-green-blue reflection and wavelength tuning from an achiral liquid crystal and a polymer template Adv. Mater., 22, 53-56, (2010)

 

2. Organic-Inorganic Thin Film Laser Devices

Our research on organic laser devices involves using a combination of liquid crystals and polymer materials to create hybrid lasers that are wavelength tuneable (Figure 4). This work follows on from that carried out by Dr Morris in collaboration with Professor Harry Coles and co-workers at the University of Cambridge. We are interested in developing new laser sources based upon these organic materials in an attempt to create low-threshold lasers that are potentially compatible with low-cost manufacturing techniques. The research includes both fundamental studies of the emission characteristics such as coherence properties as well as the design and fabrication of new device architectures.

liquid crystal laser 

Figure 5. A liquid crystal laser.

Relevant publications:

  • A nano-patterned photonic crystal laser with a dye-doped liquid crystal Appl. Phys. Lett. 103, 051101 (2013)
  • Electrically switchable random to photonic band-edge laser emission in chiral nematic liquid crystals Appl. Phys. Lett, 100, 071110, (2012)
  • High slope efficiency liquid crystal lasers Appl. Phys. Lett. 97 (25), 251109 (2010)
  • Microscopic liquid crystal lasers, Nature Photon, 4, 676-685 (2010)

 

3. Hybrid Organic-Inorganic Incoherent and Coherent Light Sources

 A. Liquid Crystalline Materials and Pure/Mixed-halide Perovskites


We are working in collaboration with the research groups of Professors Henry Snaith FRS and Moritz Reade in the Department of Physics (University of Oxford) to develop new thin-film lasers that combine the absorption and emission properties of perovskite structures with the feedback and reflection properties of chiral liquid crystalline materials. The aim of this work is to develop new, low threshold laser sources that are photostable and can be tuned using external stimuli. We have recently developed an amplified spontaneous emission source based upon a thin layer of perovskite material sandwiched between a chiral nematic (cholesteric) liquid crystal reflector and a gold layer (see publication below). Further work on combining the perovskites with tuneable liquid crystalline polymer reflectors for laser devices is currently in progress. This work was also carried out in collaboration with Professor Albert Schenning's group at the Eindhoven University of Technology and the Optoelectronics Research Group in the Cavendish Laboratory at the University of Cambridge.

 

Figure 6. ASE from a perovskite structure using a chiral nematic (cholesteric) reflector and a gold reflector.

Emission on flexible chiral nematic liquid crystal substrates.

 

LC Perovskite 

Figure 7. ASE from a perovskite structure using a flexible chiral nematic (cholesteric) reflector.

 

Distributed feedback structures for laser emission.

 

 

Figure 8. Illustration of a distributed feedback perovskite laser.

  Relevant publications

  • Enhanced Amplified Spontaneous Emission in Perovskites using a Flexible Cholesteric Liquid Crystal Reflector  Nano Letters 15, 4935-4941 (2015)
  • Structured Organic–Inorganic Perovskite toward a Distributed Feedback Laser Advanced Materials, 28, 923-929 (2016)

 

B. Clustomesogens and Chiral Liquid Crystalline Materials 

 

Clustomesogens

Figure 9. Clustomesogen structures synthesised by the team of Dr. Yann Molard (University of Rennes 1)

 

Clustomesogens 2

Figure 10. Emission characteristics of Molybdenum-based clustomesogens in chiral nematic liquid crystals.

 

Relevant publications

  • Polarized Phosphorescence of Isotropic and Metal-Based Clustomesogens Dispersed into Chiral Nematic Liquid Crystalline Films Advanced Optical Materials, 3, 1368-1372, (2015)

 

4. Direct Laser Writing in Liquid Crystals

 

DLW

Figure 11. Direct laser writing in liquid crystals.

DLW Pillars

Figure 12. Direct laser writing of polymer pillars in liquid crystals.

Relevant publications

 

5. Fast switching liquid crystal devices

 

A. Flexoelectricity in nematic and chiral nematic liquid crystals

 

Our research on flexoelectricity in nematic and chiral nematic liquid crystals involves finding new ways to measure the flexoelectric coefficients and to study, both theoretically and experimentally, related electro-optic effects for the purposes of potential display applications. For example, in chiral nematic liquid crystals we are interested in the flexoelectro-optic effect, which is a fast in-plane rotation of the optic axis.

 

 

 Relevant publications

 

B. Pi Cells and hybrid-aligned nematics