Droplet manipulation and horizontal growth of high-quality self-catalysed GaAsP nanowires

Self-catalyzed horizontal nanowires (NWs) can greatly simplify the CMOS integration processing compared with the regular vertical counterparts. However, self-catalyzed growth mode poses challenges in manipulating the droplets to produce single-crystalline horizontal NWs with a uniform diameter. Here, we demonstrated a novel method to manipulate the droplet through altering the droplet surface energy. Ga-droplet was successfully moved from top to sidewalls in GaAsP NWs by introducing Be and lowering the surface energy, and pinned at the tip despite the absence of planar defects. This can switch the growth direction, with a successful rate of 100 %, from vertical to horizontal through the assistance of few sparse twins. The produced NWs tend to be bounded by low energy facets, which leads to the self-catalysed growth of horizontal NWs with a greatly improved diameter uniformity along the axis. Besides, the lowered surface energy can effectively suppress the wurtzite nucleation, producing pure zinc blende single-crystalline horizontal NWs. This study establishes an essential step toward the efficient integration of NWs into CMOS compatible devices

Growth of Pure Zinc-Blende GaAs(P) Core-Shell Nanowires with Highly Regular Morphology

The growth of self-catalyzed core–shell nanowires (NWs) is investigated systematically using GaAs(P) NWs. The defects in the core NW are found to be detrimental for the shell growth. These defects are effectively eliminated by introducing beryllium (Be) doping during the NW core growth and hence forming Be–Ga alloy droplets that can effectively suppress the WZ nucleation and facilitate the droplet consumption. Shells with pure zinc-blende crystal quality and highly regular morphology are successfully grown on the defect-free NW cores and demonstrated an enhancement of one order of magnitude for room-temperature emission compared to that of the defective shells. These results provide useful information on guiding the growth of high-quality shell, which can greatly enhance the NW device performance

Kemnitz’ conjecture revisited

AbstractA conjecture of Kemnitz remained open for some 20 years: each sequence of 4n-3 lattice points in the plane has a subsequence of length n whose centroid is a lattice point. It was solved independently by Reiher and di Fiore in the autumn of 2003. A refined and more general version of Kemnitz’ conjecture is proved in this note. The main result is about sequences of lengths between 3p-2 and 4p-3 in the additive group of integer pairs modulo p, for the essential case of an odd prime p. We derive structural information related to their zero sums, implying a variant of the original conjecture for each of the lengths mentioned. The approach is combinatorial

Effects of phosphorous and antimony doping on thin Ge layers grown on Si

Suppression of threading dislocations (TDs) in thin germanium (Ge) layers grown on silicon (Si) substrates has been critical for realizing high-performance Si-based optoelectronic and electronic devices. An advanced growth strategy is desired to minimize the TD density within a thin Ge buffer layer in Ge-on-Si systems. In this work, we investigate the impact of P dopants in 500-nm thin Ge layers, with doping concentrations from 1 to 50 × 1018 cm−3. The introduction of P dopants has efficiently promoted TD reduction, whose potential mechanism has been explored by comparing it to the well-established Sb-doped Ge-on-Si system. P and Sb dopants reveal different defect-suppression mechanisms in Ge-on-Si samples, inspiring a novel co-doping technique by exploiting the advantages of both dopants. The surface TDD of the Ge buffer has been further reduced by the co-doping technique to the order of 107 cm−2 with a thin Ge layer (of only 500 nm), which could provide a high-quality platform for high-performance Si-based semiconductor devices

Human airway-like multilayered tissue on 3D-TIPS printed thermoresponsive elastomer/collagen hybrid scaffolds

Developing a biologically representative complex tissue of the respiratory airway is challenging, however, beneficial for treatment of respiratory diseases, a common medical condition representing a leading cause of death in the world. This study reports a successful development of synthetic human tracheobronchial epithelium based on interpenetrated hierarchical networks composed of a reversely 3D printed porous structure of a thermoresponsive stiffness-softening elastomer nanohybrid impregnated with collagen nanofibrous hydrogel in vitro. Human bronchial epithelial cells (hBEpiCs) were able to attach and grow into an epithelial monolayer on the hybrid scaffolds co-cultured with either human bronchial fibroblasts (hBFs) or human bone-marrow derived mesenchymal stem cells (hBM-MSCs), with substantial enhancement of mucin expression, ciliation, well-constructed intercellular tight junctions and adherens junctions. The multi-layered co-culture 3D scaffolds consisting of a top monolayer of differentiated epithelium, with either hBFs or hBM-MSCs proliferating within the hyperelastic nanohybrid scaffold underneath, created a tissue analogue of the upper respiratory tract, validating these 3D printed guided scaffolds as a platform to support co-culture and cellular organization. In particular, hBM-MSCs in the co-culture system promoted an overall matured physiological tissue analogue of the respiratory system, a promising synthetic tissue for drug discovery, tracheal repair and reconstruction. Statement of significance Respiratory diseases are a common medical condition and represent a leading cause of death in the world. However, the epithelium is one of the most challenging tissues to culture in vitro, and suitable tracheobronchial models, physiologically representative of the innate airway, remain largely elusive. This study presents, for the first time, a systematic approach for the development of functional multilayered epithelial synthetic tissue in vitro via co-culture on a 3D-printed thermoresponsive elastomer interpenetrated with a collagen hydrogel network. The viscoelastic nature of the scaffold with stiffness softening at body temperature provide a promising matrix for soft tissue engineering. The results presented here provide new insights about the epithelium at different surfaces and interfaces of co-culture, and pave the way to offer a customizable reproducible technology to generate physiologically relevant 3D biomimetic systems to advance our understanding of airway tissue regeneration

Thermally-driven formation method for growing (quantum) dots on sidewalls of self-catalysed thin nanowires

Embedding quantum dots (QDs) on nanowire (NW) sidewalls allows the integration of multi-layers of QDs into the active region of radial p-i-n junctions to greatly enhance light emission/absorption. However, the surface curvature makes the growth much more challenging compared with growths on thin-films, particularly on NWs with small diameters (Ø < 100 nm). Moreover, the {110} sidewall facets of self-catalyzed NWs favor two-dimensional growth, with the realization of three-dimensional Stranski-Krastanow growth becoming extremely challenging. Here, we have developed a novel thermally-driven QD growth method. The QD formation is driven by the system energy minimization when the pseudomorphic shell layer (made of QD material) is annealed under high-temperature, and thus without any restriction on the NW diameter or the participation of elastic strain. It has demonstrated that the lattice-matched Ge dots can be grown defect-freely in a controllable way on the sidewall facets of the thin (∼50 nm) self-catalyzed GaAs NWs without using any surfactant or surface treatment. This method opens a new avenue to integrate QDs on NWs, and can allow the formation of QDs in a wider range of materials systems where the growth by traditional mechanisms is not possible, with benefits for novel NWQD-based optoelectronic devices

Influence of droplet size on the growth of self-catalyzed ternary GaAsP nanowires

The influences of droplet size on the growth of self-catalyzed ternary nanowires (NWs) were studied using GaAsP NWs. The size-induced Gibbs–Thomson (GT) effect makes the smaller catalytic droplets have lower effective supersaturations and hence slower nucleation rates than the larger ones. Large variation in droplet size thus led to the growth of NWs with low uniformity, while a good size uniformity of droplets resulted in the production of highly uniform NWs. Moreover, thinner NWs were observed to be richer in P, indicating that P is more resistant to the GT effect than As because of a higher chemical potential inside Ga droplets. These results provide useful information for understanding the mechanisms of self-catalyzed III–V NW nucleation and growth with the important ternary III–V material systems