A new quasioscillatory translational motion has been observed for big Janus catalytic micromotors with a fast CCD camera. Such motional behavior is found to coincide with both the bubble growth and burst processes resulting from the catalytic reaction, and the competition of the two processes generates a net forward motion. Detailed physical models have been proposed to describe the above processes. It is suggested that the bubble growth process imposes a growth force moving the micromotor forward, while the burst process induces an instantaneous local pressure depression pulling the micromotor backward. The theoretic predictions are consistent with the experimental data.

Using basic principles of diffusion and reaction, a one-dimensional mass transport model inside a catalytic microjet has been proposed. The effect of microjet geometry on mass transport has been investigated, and its effect on bubble growth and microjet motion has been predicted. Oxygen generation and its flux to one end of the microjet induce nucleation and growth of bubbles. The bubble growth and ejection/burst cause the microjet to move forward. Numerical investigations of the motion-related parameters, such as O2 flux, bubble generation rate and frequency, and average speed of the microjet motors during bubble growth, are found to depend closely on the length and opening radius of the microjet and concentration of H2O2 in the surrounding environment. The predicted results are compared to experimental data obtained from graphene oxide-based microjets, and they show good qualitative agreement. These results demonstrate that this simple model could be used to optimize catalytic microjet design.

Combining conventional physical vapor deposition and wet chemical etching, nanoshell catalytic motors with catalyst coated inside the shell have been fabricated. Those motors are propelled by bubble ejection or burst mechanism due to small bubble nucleation energy, and they move much faster than the Janus catalytic motors of the same size. The speeds of the motors (∼100 μm s–1) are closely related to the bubble size and generation frequency. The experimental data show that the bubbles do not totally block the opening of the shell and, thus, achieve a fast mass transport and sustain continuous motion of the motors.

Developing a fundamental understanding of ultrafast non-thermal processes in metallic nanosystems will lead to applications in photodetection, photochemistry and photonic circuitry. Typically, non-thermal and thermal carrier populations in plasmonic systems are inferred either by making assumptions about the functional form of the initial energy distribution or using indirect sensors like localized plasmon frequency shifts. Here we directly determine non-thermal and thermal distributions and dynamics in thin films by applying a double inversion procedure to optical pump-probe data that relates the reflectivity changes around Fermi energy to the changes in the dielectric function and in the single-electron energy band occupancies. When applied to normal incidence measurements our method uncovers the ultrafast excitation of a non-Fermi-Dirac distribution and its subsequent thermalization dynamics. Furthermore, when applied to the Kretschmann configuration, we show that the excitation of propagating plasmons leads to a broader energy distribution of electrons due to the enhanced Landau damping.

Layered heterostructures containing graphene oxide (GO) nanosheets and 20-35 nm bimetal coatings can detach easily from a Si substrate upon sonication-spontaneously forming freestanding, micrometer-sized scrolls with GO on the outside-due to a combination of material stresses and weak bonding between GO layers. Simple procedures can tune the scroll diameters by varying the thicknesses of the metal films, and these results are confirmed by both experiment and modeling. The selection of materials determines the stresses that control the rolling behavior, as well as the functionality of the structures. In the GO/Ti/Pt system, the Pt is located within the interior of the scrolls, which can become self-propelled microjet engines through O2 bubbling when suspended in aqueous H2O2.