Search for: All records

The hierarchical structure and dynamics of polymer solutions control the transport of nanoparticles (NPs) through them. Here, we perform multi-particle collision dynamics simulations of solutions of semiflexible polymer chains with tunable persistence length l p to investigate the effect of chain stiffness on NP transport. The NPs exhibit two distinct dynamical regimes – subdiffusion on short time scales and diffusion on long time scales. The long-time NP diffusivities are compared with predictions from the Stokes–Einstein relation (SER), mode-coupling theory (MCT), and a recent polymer coupling theory (PCT). Increasing deviations from the SER as the polymer chains become more rigid ( i.e. as l p increases) indicate that the NP motions become decoupled from the bulk viscosity of the polymer solution. Likewise, polymer stiffness leads to deviations from PCT, which was developed for fully flexible chains. Independent of l p , however, the long-time diffusion behavior is well-described by MCT, particularly at high polymer concentration. We also observed that the short-time subdiffusive dynamics are strongly dependent on polymer flexibility. As l p is increased, the NP dynamics become more subdiffusive and decouple from the dynamics of the polymer chain center-of-mass. We posit that these effects are due to differences in the segmental mobility of the semiflexible chains. 

Surface recombination is a major bottleneck for realizing highly efficient micro/nanostructure solar cells. Here, parametric studies of the influence of Si microwire (SiMW) surface‐facet orientation (rectangular with flat‐facets, {110}, {100} and circular), with a fixed height of 10 µm, diameter (D= 1.5–9.5 µm), and sidewall spacing (S= 2.5–8.5 µm), and mesh‐grid density (1–16 mm⁻²) on recombination and carrier collection in SiMW solar cells with radial p‐n junctions are reported. An effective surface passivation layer composed of thin thermally grown silicon dioxide (SiO₂) and silicon nitride (SiN_x) layers is employed. For a fixedDof 1.5 µm, tight SiMW spacing results in improved short‐circuit current density (J_sc= 30.1 mA cm⁻²) and sparse arrays result in open‐circuit voltages (V_oc= 0.552 V) that are similar to those of control Si planar cells. For a fixedS, smallerDresults in better light trapping at shorter wavelengths and higherJ_scwhile largerDexhibits better light trapping at larger wavelengths and a higherV_oc. With a mesh‐grid electrode the power conversion efficiency increases to 15.3%. These results provide insights on the recombination mechanisms in SiMW solar cells and provide general design principles for optimizing their performance.

 

A zinc oxide thin film transistor is developed and optimized that simultaneously functions as a transistor and a force sensor, thus allowing for scalable integration of sensors into arrays without the need for additional addressing elements. Through systematic material deposition, microscopy, and piezoelectric characterization, it is determined that an O₂rich deposition condition improves the transistor performance and pressure sensing characteristics. With these optimizations, a sensitivity of 4 nA kPa⁻¹and a latency of below 1 ms are achieved, exceeding the criteria for successful commercialization of arrayed pressure sensors. The functionality of 16 × 16 pressure sensor arrays on thin bendable glass substrates for integrated low weight and flexible touchscreen displays is fabricated and demonstrated and read‐out electronics to interface with the arrays and to record their response in real‐time are developed. Finally, the application of these sensors for mobile displays via their operation with an existing commercial touch integrated circuit controller is demonstrated.