Heterotwin Zn3P2 superlattice nanowires: the role of indium insertion in the superlattice formation mechanism and their optical properties

Zinc phosphide (Zn3P2) nanowires constitute prospective building blocks for next generation solar cells due to the combination of suitable optoelectronic properties and an abundance of the constituting elements in the Earth’s crust. The generation of periodic superstructures along the nanowire axis could provide an additional mechanism to tune their functional properties. Here we present the vapour–liquid–solid growth of zinc phosphide superlattices driven by periodic heterotwins. This uncommon planar defect involves the exchange of Zn by In at the twinning boundary. We find that the zigzag superlattice formation is driven by reduction of the total surface energy of the liquid droplet. The chemical variation across the heterotwin does not affect the homogeneity of the optical properties, as measured by cathodoluminescence. The basic understanding provided here brings new propsects on the use of II–V semiconductors in nanowire technology

Full moonlight-induced circadian clock entrainment in Coffea arabica

Background It is now well documented that moonlight affects the life cycle of invertebrates, birds, reptiles, and mammals. The lunisolar tide is also well-known to alter plant growth and development. However, although plants are known to be very photosensitive, few studies have been undertaken to explore the effect of moonlight on plant physiology. Results Here for the first time we report a massive transcriptional modification in Coffea arabica genes under full moonlight conditions, particularly at full moon zenith and 3 h later. Among the 3387 deregulated genes found in our study, the main core clock genes were affected. Conclusions Moonlight also negatively influenced many genes involved in photosynthesis, chlorophyll biosynthesis and chloroplast machinery at the end of the night, suggesting that the full moon has a negative effect on primary photosynthetic machinery at dawn. Moreover, full moonlight promotes the transcription of major rhythmic redox genes and many heat shock proteins, suggesting that moonlight is perceived as stress. We confirmed this huge impact of weak light (less than 6 lx) on the transcription of circadian clock genes in controlled conditions mimicking full moonlight

Bi-stability of contact angle and its role in tuning the morphology of self-assisted GaAs nanowires

We demonstrate the existence of two stable contact angles for the gallium droplet on top of self-assisted GaAs nanowires grown by MBE on patterned silicon substrates. Contact angle around 130 degrees fosters a continuous increase in the nanowire radius, while 90 degrees allows for the nanowire thinning, followed by the stable growth of ultra-thin tops. We develop a model that explains the observed morphological evolution under the two different scenarios

Rotated domains in selective area epitaxy grown Zn3P2: Formation mechanism and functionality

Zinc phosphide (Zn3P2) is an ideal absorber candidate for solar cells thanks to its direct bandgap, earth-abundance, and optoelectronic characteristics, albeit it has been insufficiently investigated due to limitations in the fabrication of high-quality material. It is possible to overcome these factors by obtaining the material as nanostructures, e.g. via the selective area epitaxy approach, enabling additional strain relaxation mechanisms and minimizing the interface area. We demonstrate that Zn3P2 nanowires grow mostly defect-free when growth is oriented along the [100] and [110] of the crystal, which is obtained in nanoscale openings along the [110] and [010] on InP(100). We detect the presence of two stable rotated crystal domains that coexist in the structure. They are due to a change in the growth facet, which originates either from the island formation and merging in the initial stages of growth or lateral overgrowth. These domains have been visualized through 3D atomic models and confirmed with image simulations of the atomic scale electron micrographs. Density functional theory simulations describe the rotated domains' formation mechanism and demonstrate their lattice-matched epitaxial relation. In addition, the energies of the shallow states predicted closely agree with transition energies observed by experimental studies and offer a potential origin for these defect transitions. Our study represents an important step forward in the understanding of Zn3P2 and thus for the realisation of solar cells to respond to the present call for sustainable photovoltaic technology

Facet-driven formation of axial and radial In(Ga)As clusters in GaAs nanowires

Embedding quantum dots in nanowires (NWs) constitutes one promising building block for quantum photonic technologies. Earlier attempts to grow InAs quantum dots on GaAs nanowires were based on the Stranski-Krastanov growth mechanism. Here, we propose a novel strain-driven mechanism to form 3D In-rich clusters on the NW sidewalls and also on the NW top facets. The focus is on ternary InGaAs nanowire quantum dots which are particularly attractive for producing single photons at telecommunication wavelengths. In(Ga)As clusters were realized on the inclined top facets and also on the {11-2} corner facets of GaAs NW arrays by depositing InAs at a high growth temperature (630 degrees C). High-angle annular dark-field scanning transmission electron microscopy combined with energy-dispersive x-ray spectroscopy confirms that the observed 3D clusters are indeed In-rich. The optical functionality of the as-grown samples was verified using optical technique of cathodoluminescence. Emission maps close to the NW tip shows the presence of optically active emission centers along the NW sidewalls. Our work illustrates how facets can be used to engineer the growth of localized emitters in semiconducting NWs

Temporal transcriptional logic of dynamic regulatory networks underlying nitrogen signaling and use in plants

This study exploits time, the relatively unexplored fourth dimension of gene regulatory networks (GRNs), to learn the temporal transcriptional logic underlying dynamic nitrogen (N) signaling in plants. Our "just-in-time" analysis of time-series transcriptome data uncovered a temporal cascade of cis elements underlying dynamic N signaling. To infer transcription factor (TF)-target edges in a GRN, we applied a time-based machine learning method to 2,174 dynamic N-responsive genes. We experimentally determined a network precision cutoff, using TF-regulated genome-wide targets of three TF hubs (CRF4, SNZ, and CDF1), used to "prune" the network to 155 TFs and 608 targets. This network precision was reconfirmed using genome-wide TF-target regulation data for four additional TFs (TGA1, HHO5/6, and PHL1) not used in network pruning. These higher-confidence edges in the GRN were further filtered by independent TF-target binding data, used to calculate a TF "N-specificity" index. This refined GRN identifies the temporal relationship of known/validated regulators of N signaling (NLP7/8, TGA1/4, NAC4, HRS1, and LBD37/38/39) and 146 additional regulators. Six TFs-CRF4, SNZ, CDF1, HHO5/6, and PHL1-validated herein regulate a significant number of genes in the dynamic N response, targeting 54% of N-uptake/assimilation pathway genes. Phenotypically, inducible overexpression of CRF4 in planta regulates genes resulting in altered biomass, root development, and (15)NO3(-) uptake, specifically under low-N conditions. This dynamic N-signaling GRN now provides the temporal "transcriptional logic" for 155 candidate TFs to improve nitrogen use efficiency with potential agricultural applications. Broadly, these time-based approaches can uncover the temporal transcriptional logic for any biological response system in biology, agriculture, or medicine