TaSBr: A Cluster Mott Insulator with a Corrugated, Van der Waals Layered Structure.

The compound TaSBr was prepared by a comproportionation reaction of tantalum bromide with tantalum and elemental sulfur. The crystal structure, as refined by single-crystal X-ray diffraction, is composed of clusters with TaS cores, arranged in corrugated van der Waals layers. Individual layers appear to be displaced relative to each other along one direction.

A simple 230 MHz photodetector based on exfoliated WSe multilayers.

We demonstrate 230 MHz photodetection and a switching energy of merely 27 fJ using WSe multilayers and a very simple device architecture. This improvement over previous, slower WSe devices is enabled by systematically reducing the RC constant of devices through decreasing the photoresistance and capacitance. In contrast to MoS, reducing the WSe thickness toward a monolayer only weakly decreases the response time, highlighting that ultrafast photodetection is also possible with atomically thin WSe.

Dual polarization-enabled ultrafast bulk photovoltaic response in van der Waals heterostructures.

The bulk photovoltaic effect (BPVE) originating from spontaneous charge polarizations can reach high conversion efficiency exceeding the Shockley-Queisser limit. Emerging van der Waals (vdW) heterostructures provide the ideal platform for BPVE due to interfacial interactions naturally breaking the crystal symmetries of the individual constituents and thus inducing charge polarizations. Here, we show an approach to obtain ultrafast BPVE by taking advantage of dual interfacial polarizations in vdW heterostructures.

Toward Gigahertz Photodetection with Transition Metal Dichalcogenides.

ConspectusTransition metal dichalcogenides (TMDCs) exhibit favorable properties for optical communication in the gigahertz (GHz) regime, such as large mobilities, high extinction coefficients, cheap fabrication, and silicon compatibility. While impressive improvements in their sensitivity have been realized over the past decade, the bandwidths of these devices have been mostly limited to a few megahertz. We argue that this shortcoming originates in the relatively large RC constants of TMDC-based photodetectors, which suffer from high surface defect densities, inefficient charge carrier injection at the electrode/TMDC interface, and long charging times.

Electronic structure and transport in the potential Luttinger liquids CsNbBrS and RbNbBrS.

The crystal structures of ANbBrS (A = Rb and Cs) have been refined by single crystal X-ray diffraction, and are found to form highly anisotropic materials based on chains of the triangular Nb cluster core. The Nb cluster core contains seven valence electrons, six of them being assigned to Nb-Nb bonds within the Nb triangle and one unpaired d electron. The presence of this surplus electron gives rise to the formation of correlated electronic states.

Edge contacts accelerate the response of MoS photodetectors.

We use a facile plasma etching process to define contacts with an embedded edge geometry for multilayer MoS photodetectors. Compared to the conventional top contact geometry, the detector response time is accelerated by more than an order of magnitude by this action. We attribute this improvement to the higher in-plane mobility and direct contacting of the individual MoS layers in the edge geometry.

Substrate effects on the speed limiting factor of WSe photodetectors.

We investigate the time-resolved photoelectric response of WSe crystals on glass and flexible polyimide substrates to determine the effect of a changed dielectric environment on the speed of the photodetectors. We show that varying the substrate material can alter the speed-limiting mechanism: while the detectors on polyimide are limited, those on glass are limited by slower excitonic diffusion processes. We attribute this to a shortening of the depletion layer at the metal electrode/WSe interface caused by the higher dielectric screening of glass compared to polyimide.

Sub-nanosecond Intrinsic Response Time of PbS Nanocrystal IR-Photodetectors.

Colloidal nanocrystals (NCs), especially lead sulfide NCs, are promising candidates for solution-processed next-generation photodetectors with high-speed operation frequencies. However, the intrinsic response time of PbS-NC photodetectors, which is the material-specific physical limit, is still elusive, as the reported response times are typically limited by the device geometry. Here, we use the two-pulse coincidence photoresponse technique to identify the intrinsic response time of 1,2-ethanedithiol-functionalized PbS-NC photodetectors after femtosecond-pulsed 1560 nm excitation.

Substrate Effects on the Bandwidth of CdSe Quantum Dot Photodetectors.

We investigate the time-resolved photocurrent response of CdSe quantum dot (QD) thin films sensitized with zinc β-tetraaminophthalocyanine (Zn4APc) (Kumar , , 2019, 11, 48271-48280) on three different substrates, namely, silicon with 230 nm SiO dielectric, glass, and polyimide. While Si/SiO (230 nm) is not suitable for any transient photocurrent characterization due to an interfering photocurrent response of the buried silicon, we find that polyimide substrates invoke the larger optical bandwidth with 85 kHz vs 67 kHz for the same quantum dot thin film on glass. Upon evaluation of the transient photocurrent, we find that the photoresponse of the CdSe quantum dot films can be described as a combination of carrier recombination and fast trapping within 2.

Polycationic gold nanorods as multipurpose microtubule markers.

Gold nanoparticles are intriguing because of their unique size- and shape-dependent chemical, electronic and optical properties. Gold nanorods (AuNRs) are particularly promising for various sensor applications due to their tip-enhanced plasmonic fields. For biomolecule attachment, AuNRs are often functionalized with proteins.