We demonstrate terahertz single-pixel imaging is improved by using a photomodulator based on silicon passivated with SiO ${}_2$ . By exploring various SiO ${}_2$ thicknesses, we show that the modulation factor of the as-fabricated terahertz photomodulator can reach 0.9, three times that based on bare silicon. This improvement originates from chemical passivation, as well as anti-reflection. Single-pixel imaging experiments based on the compressed sensing method show that reconstructed images adopting the new photomodulator have better quality than the conventional terahertz modulator based on bare silicon. Since the passivation process is routine and low cost, we expect this work will reduce the cost of terahertz photomodulator and single-pixel THz imaging, and advance their applications.

We numerically investigate the thermal effects in a cornea illuminated by terahertz radiation. By modifying the bioheat and Arrhenius equations, we studied the heat-transfer and temperature distributions in the corneal tissue, and evaluated the potential thermal damage. The influence of the beam radius and power density are discussed. We also estimated the effective cornea-collagen shrinkage region, and evaluated the degree of thermal damage in the cornea. We expect this work to open up a novel effective and safe thermal-treatment approach based on THz radiation for cornea reshaping in the field of ophthalmology.

Cu doping of ZnTe, which is an important semiconductor for various optoelectronic applications, has been successfully achieved previously by several techniques. However, besides its electrical transport characteristics, other physical and chemical properties of heavily Cu-doped ZnTe have not been reported. We found an interesting self-assembled formation of crystalline well-aligned Cu-Te nano-rods near the surface of heavily Cu-doped ZnTe thin films grown via the molecular beam epitaxy technique. A phenomenological growth model is presented based on the observed crystallographic morphology and measured chemical composition of the nano-rods using various imaging and chemical analysis techniques. When substitutional doping reaches its limit, the extra Cu atoms favor an up-migration toward the surface, leading to a one-dimensional surface modulation and formation of Cu-Te nano-rods, which explain unusual observations on the reflection high energy electron diffraction patterns and apparent resistivity of these thin films. This study provides an insight into some unexpected chemical reactions involved in the heavily Cu-doped ZnTe thin films, which may be applied to other material systems that contain a dopant having strong reactivity with the host matrix.