Engineering ultrafast carrier dynamics in GeS: nanostructuring and small molecule intercalation
28 Aug 2022-pp 1-2
TL;DR: In this article , the authors used time-resolved THz spectroscopy to investigate ultrafast carrier dynamics in Germanium sulfide (GeS) single crystals as well as in GeS nanoribbons.
Abstract: Germanium sulfide (GeS) is a 2D semiconductor with high carrier mobility and a moderate band gap of about 1.5 eV, which holds promise for high-speed optoelectronics and photovoltaics. We use time-resolved THz spectroscopy to investigate ultrafast carrier dynamics in in GeS single crystals as well as in GeS nanoribbons. In both bulk and nanostructured GeS, we find that near gap excitation at 1.55 eV results in much longer lived photocarriers compared to 3.1 eV excitation. We also explore how intercalation of small molecules influences the photoexcited carrier dynamics in GeS. We find that presence of edge states in nanoribbons results in decreased carrier lifetime. Organic molecules such as octylamine, which do not form chemical bonds with the host GeS layers, increase photoexcited carrier lifetime. These findings demonstrate the possibility of engineering the properties of 2D materials by intercalation.
TL;DR: In this paper, the authors predict anisotropic piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M=Sn or Ge, X=Se or S), including SnSe, SnS, GeSe, and GeS.
Abstract: We predict enormous, anisotropic piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M=Sn or Ge, X=Se or S), including SnSe, SnS, GeSe, and GeS. Using first-principle simulations based on the modern theory of polarization, we find that their piezoelectric coefficients are about one to two orders of magnitude larger than those of other 2D materials, such as MoS2 and GaSe, and bulk quartz and AlN which are widely used in industry. This enhancement is a result of the unique “puckered” C2v symmetry and electronic structure of monolayer group IV monochalcogenides. Given the achieved experimental advances in the fabrication of monolayers, their flexible character, and ability to withstand enormous strain, these 2D structures with giant piezoelectric effects may be promising for a broad range of applications such as nano-sized sensors, piezotronics, and energy harvesting in portable electronic devices.
TL;DR: A general solution-based chemical method for intercalating extraordinarily high densities of zero-valent copper metal into layered Bi(2)Se(3) nanoribbons using a solution disproportionation redox reaction.
Abstract: A major goal of intercalation chemistry is to intercalate high densities of guest species without disrupting the host lattice. Many intercalant concentrations, however, are limited by the charge of the guest species. Here we have developed a general solution-based chemical method for intercalating extraordinarily high densities of zero-valent copper metal into layered Bi2Se3 nanoribbons. Up to 60 atom % copper (Cu7.5Bi2Se3) can be intercalated with no disruption to the host lattice using a solution disproportionation redox reaction.
TL;DR: It is shown that multiple zero-valent atoms can be intercalated through this chemical route into the host lattice of a 2D crystal and can be used to achieve a wide variety of new 2D materials previously inaccessible.
Abstract: We demonstrate the intercalation of multiple zero-valent atomic species into two-dimensional (2D) layered Bi2Se3 nanoribbons. Intercalation is performed chemically through a stepwise combination of disproportionation redox reactions, hydrazine reduction, or carbonyl decomposition. Traditional intercalation is electrochemical thus limiting intercalant guests to a single atomic species. We show that multiple zero-valent atoms can be intercalated through this chemical route into the host lattice of a 2D crystal. Intermetallic species exhibit unique structural ordering demonstrated in a variety of superlattice diffraction patterns. We believe this method is general and can be used to achieve a wide variety of new 2D materials previously inaccessible.
TL;DR: In this article, the terahertz electromagnetic pulses emitted by photoexcited GeS nanosheets without external bias were used to confirm that shift currents are indeed responsible for the observed emission.
Abstract: Ferroelectric semiconductors have been predicted to exhibit strong zero-bias shift current, spurring the search for ferroelectric semiconductors with band gaps in the visible range as candidates for so-called shift current photovoltaics with efficiencies not constrained by the Schockley–Queisser limit Recent theoretical works have predicted that two-dimensional IV–VI monochalcogenides are multiferroic and capable of generating significant shift currents Here we present experimental validation of this prediction, observing ultrafast shift currents by detecting terahertz electromagnetic pulses emitted by the photoexcited GeS nanosheets without external bias We explore excitation fluence, orientation, and excitation polarization dependence of the terahertz emission to confirm that shift currents are indeed responsible for the observed emission Experimental observation of zero-bias photocurrents puts GeS nanosheets forth as a promising candidate material for applications in third-generation photovoltaics