Nan Zhang

Gold nanoparticles (Au NPs) provide useful but difficult-to-measure heating in optical tweezers used for colloidal transport, assembly, optofluidics, and bubble-mediated manipulation. Here, we combine 60 nm Au NPs with 5 μm polystyrene (PS) microspheres in a dual-laser Raman optical-tweezers platform. Au NPs serve as heat sources and PS microspheres report the microscale temperature through their Raman spectra. The PS band near 1,000 cm-1 has a calibrated temperature coefficient of -0.0054 cm-1·K-1. For Au stock-dispersion fractions of 0, 0.3, and 1 vol.%, the temperature-power coefficients are 53.5 ± 10.9, 110.4 ± 23.8, and 170.3 ± 18.2 K·W-1, respectively. At 1 vol.% Au suspension, extrapolation of the pre-bubble temperature-power relation to 0.341 W gives a PS-reported temperature of approximately 351 K, below the normal boiling point of water. Electromagnetic simulations show that normalized per-particle absorption increases from 1.00 for an isolated Au nanoparticle to 15.35 for a seven-particle cluster, supporting aggregation-induced nanoscale heating as a mechanism for bubble formation. The PS reporter thus gives the microscale thermal response, and the nanoscale hotspots associated with bubble formation are inferred, not measured directly.

The β-phase of gallium oxide (β-Ga2O3) is an ultrawide bandgap semiconductor with excellent electrical properties and strong radiation tolerance, making it a promising candidate for electronic devices operating in harsh radiation environments. However, the monoclinic symmetry of β-Ga2O3 dictates highly anisotropic lattice dynamics, yet how electron irradiation-induced defects perturb these phonons along different crystallographic orientations remains experimentally unexplored. Herein, temperature-dependent Raman spectroscopy was employed to investigate the phonon responses of the (100) and (2¯01) planes of β-Ga2O3 single crystals under electron irradiation with an energy of 10 MeV and total fluence of 1 × 1017 cm−2. The results show that irradiation significantly reduces Raman peak intensities and induces distinct orientation-dependent frequency shifts. The (100) plane exhibits blue shifts in low- and mid-frequency modes but red shifts in high-frequency modes, whereas the (2¯01) plane shows nearly unchanged peak positions, indicating that the (2¯01) plane possesses higher radiation resistance. Furthermore, the irradiation-induced variation in first-order temperature coefficients is considerably larger for the (100) plane, revealing stronger phonon anharmonicity and phonon-defect interactions. This work provides insights into the orientation-dependent phonon dynamics of β-Ga2O3 under irradiation and guidance for the design of radiation-hardened β-Ga2O3-based electronic and thermal management devices.

As fourth-generation refrigerants with great development prospects, hydrofluoroolefins (HFOs) can be mixed with other refrigerants, such as carbon dioxide (CO2), to form refrigerant mixtures with low global warming potential (GWP) and zero ozone depleting potential (ODP) while retaining the advantages of each component. Refrigerants can work together to achieve complementary benefits. Combinations of CO2 and HFOs can strengthen the thermodynamic properties of CO2 while inhibiting the flammability of HFOs. At present, relatively few studies have been conducted on the CO2 + 3,3,3-trifluoropropene (R1243zf) mixture. Besides experimental approaches, molecular simulation has grown in importance as a way to determine thermodynamic and transport properties in recent years. In this study, the Gibbs Ensemble Monte Carlo (GEMC) method was used to simulate the vapor-liquid equilibrium (VLE) properties of the CO2 + R1243zf binary mixture in the temperature range of 273.15 to 313.15 K, in which the three-site rigid TraPPE force field and a fully flexible transferable all-atom force field were selected to describe CO2 and R1243zf, respectively. By comparing the GEMC simulation results with the experimental data, it was found that the average deviation of pressure is 2.33%, the average deviation of liquid phase molar fraction Delta x is 0.0099, and the mean deviation of gaseous phase molar fraction Delta y is 0.0204. The simulation results accord well with the experimental data and the fitting data of the correlation model in the literature, indicating that the molecular models used for CO2 and R1243zf can reliably predict the VLE properties. Finally, the critical parameters of the mixture at a temperature of 313.15 K were predicted, and the radial distribution functions (RDFs) of pure R1243zf and the mixture at 273.15 K and 3.5 MPa were calculated and analyzed by molecular dynamics (MD) simulation.