Mo tips 50-100 Si tips 50-100 p-type diamond 160 Defective CVD diamond 30-120 Amorphic diamond 20-40 Cesium-coated diamond 20-30 Graphite powders 10-20 Nano-diamond 3-5 (unstable > 30 mA/cm2) Carbon Nanotubes 1-2 (stable >4000mA/cm 2) Table 1. Threshold fields for various cathode materials and some CNT emission characteristics.

We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (E g = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.

SnIP could be the first of a new class of inorganic double-helix materials. [7][8][9] With strong intra-helix covalent bonds and weak inter-helix dispersion forces, SnIP belongs to the group of newly emerging 1D van der Waals (vdW) materials with potential applications in nanoelectronics and photonics. [10][11][12][13] In contrast to the DNA structure, which consists of two equal radius helices, SnIP forms with an outer [SnI] + helix wrapping around an inner [P] − helix, as pictured in Figure 1a. SnIP crystallizes monoclinically with a unit cell containing two opposite-handed double helices so that there is no net chirality. It is composed of abundant and non-toxic elements and can grow uninhibited to cm-length needles with a low-temperature synthesis [6,14] (Sections S1 and S2, Supporting Information) or in nanotubes using vapor deposition. [15,16] Its 1.86 eV band gap, as determined by band structure calculations (Figure 1b,c) and verified experimentally (see ref.[ 6 ] and Section S3, Supporting Information), is well situated for solar absorption and photocatalytic water splitting. [8,10,15] SnIP is also an extremely soft and flexible semiconductor and is therefore a promising material for applications in flexible electronics, [6,10] where these properties are highly desirable. [17] It is predicted to have a high carrier mobility; [8] however, as-grown SnIP is highly resistive so that the current lack of doped samples has made it difficult to explore its electronic properties. [6] Moreover, despite the exciting properties and unique structure of SnIP, there have been no investigations probing its ultrafast photophysical properties.Here, we use time-resolved terahertz (THz) spectroscopy (TRTS) to study picosecond charge carrier dynamics in SnIP nanowire films, as shown in Figure 1d. TRTS, a powerful non-contact ultrafast probe, has been used extensively to probe carrier dynamics in low-dimensional materials, accelerating scientific understanding of transport mechanisms and enabling materials optimization for potential applications. [18,19] From analysis of the photoconductivity spectra, along with insight into the highly anisotropic energy landscape from density functional theory (DFT), we make the first measurement of the carrier mobility in SnIP. We find a maximum electron mobility of 280 cm 2 V −1 s −1 along the double-helix axis, an extraordinarily high mobility for a material as soft and flexible as SnIP. On Tin iodide phosphide (SnIP), an inorganic double-helix material, is a quasi-1D van der Waals semiconductor that shows promise in photocatalysis and flexible electronics. However, the understanding of the fundamental photophysics and charge transport dynamics of this new material is limited. Here, time-resolved terahertz (THz) spectroscopy is used to probe the transient photoconductivity of SnIP nanowire films and measure the carrier mobility. With insight into the highly anisotropic electronic structure from quantum chemical calculations, an electron mobility as high as 280 cm 2 V −1 s −1 along the doub...

No abstract

No abstract