This paper reports a simple and economical method for the fabrication of nanopatterned optical fiber nanotips. The proposed patterning approach relies on the use of the nanosphere lithography of the optical fiber end facet. Polystyrene (PS) nanospheres are initially self-assembled in a hexagonal array on the surface of water. The created pattern is then transferred onto an optical fiber tip (OFT). The PS monolayer colloidal crystal on the OFT is the basic building block that is used to obtain different periodic structures by applying further treatment to the fiber, such as metal coating, nanosphere size reduction and sphere removal. Ordered dielectric and metallo-dielectric sphere arrays, metallic nanoisland arrays and hole-patterned metallic films with feature sizes down to the submicron scale are achievable using this approach. Furthermore, the sizes and shapes of these periodic structures can be tailored by altering the fabrication conditions. The results indicate that the proposed self-assembly approach is a valuable route for the development of highly repeatable metallo-dielectric periodic patterns on OFTs with a high degree of order and low fabrication cost. The method can be easily extended to simultaneously produce multiple fibers, opening a new route to the development of fiber-optic nanoprobes. Finally, we demonstrate the effective application of the patterned OFTs as surface-enhanced Raman spectroscopy nanoprobes.

We report microwave cavity perturbation measurements of the temperature dependence of the penetration depth, $\lambda \left(T\right)$, and conductivity, $\sigma \left(T\right)$ of ${\mathrm{Pr}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4-\delta }$ (PCCO) crystals, as well as parallel-plate resonator measurements of $\lambda \left(T\right)$ in PCCO thin films. Penetration depth measurements are also presented for a ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4-\delta }$ (NCCO) crystal. We find that $\Delta \lambda \left(T\right)$ has a power-law behavior for $T<\mathrm{}{T}_c/3$, and conclude that the electron-doped cuprate superconductors have nodes in the superconducting gap. Furthermore, using the surface impedance, we have derived the real part of the conductivity, ${\sigma }_1\left(T\right)$, below $T_c$ and found a behavior similar to that observed in hole-doped cuprates.

Controlling the crystallization of perovskite in a thin film is essential in making solar cells. Processing tin-based perovskite films from solution is challenging because of the uncontrollable faster crystallization of tin than the most used lead perovskite. The best performing devices are prepared by depositing perovskite from dimethyl sulfoxide because it slows down the assembly of the tin-iodine network that forms perovskite. However, while dimethyl sulfoxide seems the best solution to control the crystallization, it oxidizes tin during processing. This work demonstrates that 4-(tert-butyl) pyridine can replace dimethyl sulfoxide to control the crystallization without oxidizing tin. We show that tin perovskite films deposited from pyridine have a 1 order of magnitude lower defect density, which promotes charge mobility and photovoltaic performance.

We propose the use of n-doped silicon oxide as alternative n-layer in thin film Si p-i-n solar cells. By varying input gas ratios, films with a wide range of optical and electrical properties are obtained. Applying these layers in solar cells, good electrical and optical properties are demonstrated. A relative efficiency increase up to 13.6% has been observed on the cells adopting a simple Ag back contact. A similar spectral response as with the cell with standard n-layer plus ZnO/Ag back contact is obtained. The deposition of a buffer layer at the back contact can therefore be avoided.

We have observed a nonmonotonic behavior of the superconducting critical temperature $T_c$ versus the CuMn layer thickness in multilayers of Nb/CuMn with fixed Nb layer thickness (∼250 Å). The results have been interpreted assuming the presence of the $\pi$ phase in the case of layered superconducting systems with weak magnetic coupling, where the phase $\phi$ of the superconducting order parameter can vary in the range $0<\mathrm{}\phi <\pi$ between adjacent superconducting layers.