Understanding chirality, or handedness, in molecules is important because of the enantioselectivity that is observed in many biochemical reactions , and because of the recent development of chiral metamaterials with exceptional light-manipulating capabilities, such as polarization control, a negative refractive index and chiral sensing . Chiral nanostructures have been produced using nanofabrication techniques such as lithography and molecular self-assembly, but large-scale and simple fabrication methods for three-dimensional chiral structures remain a challenge. In this regard, chirality transfer represents a simpler and more efficient method for controlling chiral morphology. Although a few studies have described the transfer of molecular chirality into micrometre-sized helical ceramic crystals, this technique has yet to be implemented for metal nanoparticles with sizes of hundreds of nanometres. Here we develop a strategy for synthesizing chiral gold nanoparticles that involves using amino acids and peptides to control the optical activity, handedness and chiral plasmonic resonance of the nanoparticles. The key requirement for achieving such chiral structures is the formation of high-Miller-index surfaces ({hkl}, h ≠ k ≠ l ≠ 0) that are intrinsically chiral, owing to the presence of 'kink' sites in the nanoparticles during growth. The presence of chiral components at the inorganic surface of the nanoparticles and in the amino acids and peptides results in enantioselective interactions at the interface between these elements; these interactions lead to asymmetric evolution of the nanoparticles and the formation of helicoid morphologies that consist of highly twisted chiral elements. The gold nanoparticles that we grow display strong chiral plasmonic optical activity (a dis-symmetry factor of 0.2), even when dispersed randomly in solution; this observation is supported by theoretical calculations and direct visualizations of macroscopic colour transformations. We anticipate that our strategy will aid in the rational design and fabrication of three-dimensional chiral nanostructures for use in plasmonic metamaterial applications.

A thermochromic-based interactive sensor that can generate local color switching and pressure mapping is developed using a 2D array of resistive pressure sensor switch. This thermochromic-based interactive sensor will enable the visualization of localized information in arbitrary shapes with dynamic responses in the context of serial/parallel pressure mapping and quantifying capability without optoelectronic arrays.

Photoinduced threshold switching processes that lead to bistability and the formation of metastable phases in photoinduced phase transition of VO2 are elucidated through ultrafast electron diffraction and diffusive scattering techniques with varying excitation wavelengths. We uncover two distinct regimes of the dynamical phase change: a nearly instantaneous crossover into an intermediate state and its decay led by lattice instabilities over 10 ps timescales. The structure of this intermediate state is identified to be monoclinic, but more akin to M2 rather than M1 based on structure refinements. The extinction of all major monoclinic features within just a few picoseconds at the above-threshold-level (~20%) photoexcitations and the distinct dynamics in diffusive scattering that represents medium-range atomic fluctuations at two photon wavelengths strongly suggest a density-driven and nonthermal pathway for the initial process of the photoinduced phase transition. These results highlight the critical roles of electron correlations and lattice instabilities in driving and controlling phase transformations far from equilibrium.

The electron-phonon mechanism that gives rise to various charge-ordered systems is often controversial because of the cooperative nature of the transformation and that the structural aspect of the transformation is generally poorly understood. Using femtosecond electron crystallography, we reveal a two-step (≈400 fs and 3.3 ps) suppression of the structural order parameter of a 2D charge density wave (CDW) that clearly decouples from its electronic counterpart following fs optical quenching. Through atomic fluctuational analysis on Bragg reflections and satellite features, we identify important momentum-dependent electron-phonon couplings appearing on both timescales that can be related to interactions between the unidirectional CDW collective modes, the lattice phonons, and the perturbed electronic subsystem. We show that the characteristic timescales of these couplings and relative fluctuational amplitudes as characterized by fs crystallography jointly determine the cooperativity between the electronic and structural subsystems and from this it is possible to elucidate the underlying mechanism of the charge-ordered system.

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