Converting nanoparticles or monomeric compounds into larger supramolecular structures by endogenous or external stimuli is increasingly popular because these materials are useful for imaging and treating diseases. However, conversion of microstructures to nanostructures is less common. Here, we show the conversion of microbubbles to nanoparticles using low-frequency ultrasound. The microbubble consists of a bacteriochlorophyll-lipid shell around a perfluoropropane gas. The encapsulated gas provides ultrasound imaging contrast and the porphyrins in the shell confer photoacoustic and fluorescent properties. On exposure to ultrasound, the microbubbles burst and form smaller nanoparticles that possess the same optical properties as the original microbubble. We show that this conversion is possible in tumour-bearing mice and could be validated using photoacoustic imaging. With this conversion, our microbubble can potentially be used to bypass the enhanced permeability and retention effect when delivering drugs to tumours.

Light-emitting sources and devices permeate every aspect of our lives and are used in lighting, communications, transportation, computing, and medicine. Advances in multifunctional and “smart lighting” would require revolutionary concepts in the control of emission spectra and directionality. Such control might be possible with new schemes and regimes of light–matter interaction paired with developments in light-emitting materials. Here we show that all-dielectric metasurfaces made from III–V semiconductors with embedded emitters have the potential to provide revolutionary lighting concepts and devices, with new functionality that goes far beyond what is available in existing technologies. Specifically, we use Mie-resonant metasurfaces made from semiconductor heterostructures containing epitaxial quantum dots. By controlling the symmetry of the resonant modes, their overlap with the emission spectra, and other structural parameters, we can enhance the brightness by 2 orders of magnitude, as well as reduce its far-field divergence significantly.

This letter reports a two-step growth process for improving microstructural quality of semipolar (112̱2) GaN on nitridized m-plane sapphire. The two-step growth of (112̱2) GaN, islanding growth under high pressure followed by islands coalescence under low pressure, went through a roughening-recovery process, which was found very effective in reducing the density of stacking faults and dislocations in (112̱2) GaN. The x-ray rocking curves of both on-axis and off-axis planes were narrowed down by more than 50%. The improvement of GaN quality was confirmed by a boost in blue and green optical output of semipolar (112̱2) InGaN/GaN quantum wells.

This work represents a comprehensive attempt to correlate the heteroepitaxial dynamics in experiments with fundamental principles in crystal growth using the kinetic Wulff plot (or v-plot). Selective area growth is employed to monitor the advances of convex and concave facets toward the construction of a comprehensive v-plot as a guidepost for GaN heteroepitaxy. A procedure is developed to apply the experimentally determined kinetic Wulff plots to the interpretation and the design of evolution dynamics in nucleation and island coalescence. This procedure offers a cohesive and rational model for GaN heteroepitaxy on polar, nonpolar, and semipolar orientations and is broadly extensible to other heteroepitaxial material systems. We demonstrate furthermore that the control of morphological evolution, based on invoking a detailed knowledge of the v-plots, holds a key to the reduction of microstructural defects through effective bending of dislocations and geometrical blocking of stacking faults, paving a way to device-quality heteroepitaxial nonpolar and semipolar GaN materials.

We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV-visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.

For nonpolar and semipolar orientations of GaN heteroepitaxially grown on sapphire substrates, the development of growth procedures to improve surface morphology and microstructure has been driven in a largely empirical way. This work attempts to comprehensively link the intrinsic properties of GaN faceted growth, across orientations, in order to understand, design and control growth methods for nonpolar (1 1 2 0) GaN and semipolar (1 1 2 2) GaN on foreign substrates. This is done by constructing a comprehensive series of kinetic Wulff plots (or v-plots) by monitoring the advances of convex and concave facets in selective area growth. A methodology is developed to apply the experimentally determined v-plots to the interpretation and design of evolution dynamics in nucleation and island coalescence. This methodology offers a cohesive and rational model for GaN heteroepitaxy along polar, nonpolar and semipolar orientations, and is broadly extensible to the heteroepitaxy of other materials. We demonstrate furthermore that the control of morphological evolution, based on invoking a detailed knowledge of the v-plots, holds a key to the reduction of microstructural defects through effective bending of dislocations and blocking of stacking faults. The status and outlook of semipolar and nonpolar GaN growth on sapphire substrates will be presented.

Ultrasound and photoacoustic imaging are highly complementary modalities since both use ultrasonic detection for operation. Increasingly, photoacoustic and ultrasound have been integrated in terms of hardware instrumentation. To generate a broadly accessible dual-modality contrast agent, we generated microbubbles (a standard ultrasound contrast agent) in a solution of methylene blue (a standard photoacoustic dye). This MB2 solution was formed effectively and was optimized as a dual-modality contrast solution. As microbubble concentration increased (with methylene blue concentration constant), photoacoustic signal was attenuated in the MB2 solution. When methylene blue concentration increased (with microbubble concentration held constant), no ultrasonic interference was observed. Using an MB2 solution that strongly attenuated all photoacoustic signal, high powered ultrasound could be used to burst the microbubbles and dramatically enhance photoacoustic contrast (>800-fold increase), providing a new method for spatiotemporal control of photoacoustic signal generation.

Single crystalline nanomembranes (NMs) represent a new embodiment of semiconductors having a two-dimensional flexural character with comparable crystalline perfection and optoelectronic efficacy. In this Letter, we demonstrate the preparation of GaN NMs with a freestanding thickness between 90 to 300 nm. Large-area (>5 × 5 mm(2)) GaN NMs can be routinely obtained using a procedure of conductivity-selective electrochemical etching. GaN NM is atomically flat and possesses an optical quality similar to that from bulk GaN. A light-emitting optical heterostructure NM consisting of p-GaN/InGaN quantum wells/GaN is prepared by epitaxy, undercutting etching, and layer transfer. Bright blue light emission from this heterostructure validates the concept of NM-based optoelectronics and points to potentials in flexible applications and heterogeneous integration.