Photodetector (PD) devices based on carbon nanotube/n-silicon heterojunction (NSH) have been realized, with a linear response in a large optical power range, proving competitive performances with respect to a recent nanostructure-based detector and those currently available on the market. The core of these devices is a thin semi-transparent and conductive single-walled carbon nanotubes film with a multitask role: junction element, light absorber and transmitter, photocarrier transporting layer, and charge collector. The PD exhibits rise times of some nanoseconds, detecting light from ultraviolet (240 nm) to infrared (1600 nm), and external quantum efficiency reaching 300% in the VIS spectra region.

Mismatch between adjacent atomic layers in low-dimensional materials, generating moiré patterns, has recently emerged as a suitable method to tune electronic properties by inducing strong electron correlations and generating novel phenomena. Beyond graphene, van der Waals structures such as three-dimensional (3D) topological insulators (TIs) appear as ideal candidates for the study of these phenomena due to the weak coupling between layers. Here we discover and investigate the origin of 1D moiré stripes on the surface of Bi₂Se₃ TI thin films and nanobelts. Scanning tunneling microscopy and high-resolution transmission electron microscopy reveal a unidirectional strained top layer, in the range 14-25%, with respect to the relaxed bulk structure, which cannot be ascribed to the mismatch with the substrate lattice but rather to strain induced by a specific growth mechanism. The 1D stripes are characterized by a spatial modulation of the local density of states, which is strongly enhanced compared to the bulk system. Density functional theory calculations confirm the experimental findings, showing that the TI surface Dirac cone is preserved in the 1D moiré stripes, as expected from the topology, though with a heavily renormalized Fermi velocity that also changes between the top and valley of the stripes. The strongly enhanced density of surface states in the TI 1D moiré superstructure can be instrumental in promoting strong correlations in the topological surface states, which can be responsible for surface magnetism and topological superconductivity.

A graphene/Si heterojunction device has been realized to overcome many different requests necessary to make it a versatile, widely used and competitive detector. The obtained photodetectors, which operate at room temperature, are sensitive in the spectral region from ultraviolet (240 nm) to infrared (2000 nm) and they can be used in different configurations that allow a high responsivity up to 10 ⁷ A W ⁻¹ , a rise time of a few nanoseconds, an external quantum efficiency greater than 300%, and a linear response for different light sources. This is allowed by the high quality of the graphene deposited on a large area of 8 mm ² , and by the interdigitated design of the contacts, both preserving the excellent properties of graphene when switching from nanoscale to macroscopic dimensions of commonly used devices.

In the last few years, most applications in the field of light sensing have required devices able to detect light intensities as low as pW/cm ² . At the same time, the rise of organic-based sensors is meeting no stops because of the desired properties that organic materials provide, like flexibility, lightweight, low cost, and low temperature processability. Low-intensity light signal detectors are growing in a huge number of fields: in prostate cancer treatment, modern proton therapy is requiring the detection of very low light intensities generated by scintillators that convert the proton flux into a light signal; moreover, in robotics, the most recent products need to detect light both in the sunlight and at the nighttime when the illumination intensity is lower. Here, we report on a flexible organic phototransistor (OPT) with impressive low-light detection, with a limit of detection (LoD) down to 28 pW/cm ² . The OPT works reliably in different environments, acting at low polarization bias down to −1 V. These results show the perspective of a new class of light detectors based on a low-cost manufacturing process for flexible applications.