Tunable Enhanced Second-Harmonic Generation in InP-InAsP Quantum Well Nanomembranes.

Second-harmonic generation (SHG) offers a convenient approach for infrared-to-visible light conversion in tunable nanoscale light sources and optical communication. Semiconductor nanostructures offer rich possibilities to tailor their nonlinear optical properties. In this study, strong second-harmonic generation in InP nanomembranes with InAsP quantum well (QW) is demonstrated. Compared with bulk InP, up to 100 times enhancement of SHG is achieved in the short-wave infrared range. This enhancement is shown to be predominantly induced by the resonance-enhanced absorption and quantum confinement of fundamental wavelengths in the InAsP QW. The thin nanomembrane structure will also provide nanocavity enhancement for second-harmonic wavelengths. The enhanced SHG peak wavelengths can also be tuned by changing the QW composition. These findings provide an effective strategy for enhancing and manipulating the second-harmonic generation in semiconductor quantum-confined nanostructures for on-chip all-optical applications.

Epitaxially Grown InP Micro-Ring Lasers.

In the near future, technological advances driven by the Fourth Industrial Revolution will boost the demand for integrated, power-efficient miniature lasers, which are important for optical data communications and advanced sensing applications. Although top-down fabricated III-V semiconductor micro-disk and micro-ring lasers have been shown to be efficient light sources, challenges such as etching-induced sidewall roughness and poor fabrication scalability have been limiting the potential for high-density on-chip integration. Here, we demonstrate InP micro-ring lasers fabricated with a highly scalable epitaxial growth technique. With an optimized cavity design, the optically pumped micro-ring lasers show efficient room-temperature lasing with a lasing threshold of around 50 µJ cm-2 per pulse. Remarkably, through comprehensive modeling of the micro-ring laser, we demonstrate lasing mode engineering experimentally by tuning the vertical ring height. Our work is a major step toward realizing the high-density monolithic integration of III-V miniature lasers on submicrometer-scale optoelectronic devices.

Understanding Shape Evolution and Phase Transition in InP Nanostructures Grown by Selective Area Epitaxy.

There is a strong demand for III-V nanostructures of different geometries and in the form of interconnected networks for quantum science applications. This can be achieved by selective area epitaxy (SAE) but the understanding of crystal growth in these complicated geometries is still insufficient to engineer the desired shape. Here, the shape evolution and crystal structure of InP nanostructures grown by SAE on InP substrates of different orientations are investigated and a unified understanding to explain these observations is established. A strong correlation between growth direction and crystal phase is revealed. Wurtzite (WZ) and zinc-blende (ZB) phases form along <111>A and <111>B directions, respectively, while crystal phase remains the same along other low-index directions. The polarity induced crystal structure difference is explained by thermodynamic difference between the WZ and ZB phase nuclei on different planes. Growth from the openings is essentially determined by pattern confinement and minimization of the total surface energy, regardless of substrate orientations. A novel type-II WZ/ZB nanomembrane homojunction array is obtained by tailoring growth directions through alignment of the openings along certain crystallographic orientations. The understanding in this work lays the foundation for the design and fabrication of advanced III-V semiconductor devices based on complex geometrical nanostructures.

Two-photon luminescence and second harmonic generation from gold micro-plates.

Micron-sized gold plates were prepared by reducing chloroauric acid with lemongrass extract. Their two-photon luminescence (TPL) and second harmonic generation (SHG) were investigated. The results show that the TPL and SHG intensity of gold plates is dependent on the wavelength and polarization of excitation laser. The TPL intensity of gold plates decreases with the increase of the excitation wavelength except for a small peak around 820-840 nm, while SHG intensity increases with the excitation wavelength redshift. In addition, it is found that the TPL intensity of the gold plate's edge is related with the angle between the edge orientation and the polarization direction of the excitation light. The TPL intensity increases with the angle increase from 0° to 90°.

Scalable Bright and Pure Single Photon Sources by Droplet Epitaxy on InP Nanowire Arrays.

High-quality quantum light sources are crucial components for the implementation of practical and reliable quantum technologies. The persistent challenge, however, is the lack of scalable and deterministic single photon sources that can be synthesized reproducibly. Here, we present a combination of droplet epitaxy with selective area epitaxy to realize the deterministic growth of single quantum dots in nanowire arrays. By optimization of the single quantum dot growth and the nanowire cavity design, single emissions are effectively coupled with the dominant mode of the nanowires to realize Purcell enhancement. The resonance-enhanced quantum emitter system boasts a brightness of millions of counts per second with nanowatt excitation power, a short radiation lifetime of 350 ± 5 ps, and a high single-photon purity with g(2)(0) value of 0.05 with continuous wave above-band excitation. Finite-difference time-domain (FDTD) simulation results show that the emissions of single quantum dots are coupled into the TM01 mode of the nanowires, giving a Purcell factor ≈ 3. Our technology can be used for creating on-chip scalable single photon sources for future quantum technology applications including quantum networks, quantum computation, and quantum imaging.

C3a and C5a promote renal ischemia-reperfusion injury.

Renal ischemia reperfusion injury triggers complement activation, but whether and how the small proinflammatory fragments C3a and C5a contribute to the pathogenesis of this injury remains to be elucidated. Using C3aR-, C5aR-, or C3aR/C5aR-deficient mice and models of renal ischemia-reperfusion injury, we found that deficiency of either or both of these receptors protected mice from injury, but the C3aR/C5aR- and C5aR-deficient mice were most protected. Protection from injury was associated with less cellular infiltration and lower mRNA levels of kidney injury molecule-1, proinflammatory mediators, and adhesion molecules in postischemic kidneys. Furthermore, chimera studies showed that the absence of C3aR and C5aR on renal tubular epithelial cells or circulating leukocytes attenuated renal ischemia-reperfusion injury. In vitro, C3a and C5a stimulation induced inflammatory mediators from both renal tubular epithelial cells and macrophages after hypoxia/reoxygenation. In conclusion, although both C3a and C5a contribute to renal ischemia-reperfusion injury, the pathogenic role of C5a in this injury predominates. These data also suggest that expression of C3aR and C5aR on both renal and circulating leukocytes contributes to the pathogenesis of renal ischemia-reperfusion injury.

Bottom-up, Chip-Scale Engineering of Low Threshold, Multi-Quantum-Well Microring Lasers.

Integrated, on-chip lasers are vital building blocks in future optoelectronic and nanophotonic circuitry. Specifically, III-V materials that are of technological relevance have attracted considerable attention. However, traditional microcavity laser fabrication techniques, including top-down etching and bottom-up catalytic growth, often result in undesirable cavity geometries with poor scalability and reproducibility. Here, we utilize the selective area epitaxy method to deterministically engineer thousands of microring lasers on a single chip. Specifically, we realize a catalyst-free, epitaxial growth of a technologically critical material, InAsP/InP, in a ring-like cavity with embedded multi-quantum-well heterostructures. We elucidate a detailed growth mechanism and leverage the capability to deterministically control the adatom diffusion lengths on selected crystal facets to reproducibly achieve ultrasmooth cavity sidewalls. The engineered devices exhibit a tunable emission wavelength in the telecommunication O-band and show low-threshold lasing with over 80% device efficacy across the chip. Our work marks a significant milestone toward the implementation of a fully integrated III-V materials platform for next-generation high-density integrated photonic and optoelectronic circuits.

Vertical Emitting Nanowire Vector Beam Lasers.

Due to the peculiar structured light field with spatially variant polarizations on the same wavefront, vector beams (VBs) have sparked research enthusiasm in developing advanced super-resolution imaging and optical communications techniques. A compact VB nanolaser is intriguing for VB applications in miniaturized photonic integrated circuits. However, determined by the diffraction limit of light, it is a challenge to realize a VB nanolaser in the subwavelength scale because the VB lasing modes should have laterally structured distributions. Here, we demonstrate a VB nanolaser made from a 300 nm thick InGaAs/GaAs nanowire (NW). To select the high-order VB lasing mode, a standing NW as-grown from the selective-area-epitaxial (SAE) growth process is utilized, which has a bottom donut-shaped interface with the silicon oxide growth substrate. With this donut-shaped interface as one of the reflective mirrors of the nanolaser cavity, the VB lasing mode has the lowest threshold. Experimentally, a single-mode VB lasing mode with a donut-shaped amplitude and azimuthally cylindrical polarization distribution is obtained. Together with the high yield and uniformity of the SAE-grown NWs, our work provides a straightforward and scalable path toward cost-effective co-integration of VB nanolasers on potential photonic integrated circuits.

Self-frequency-conversion nanowire lasers.

Semiconductor nanowires (NWs) could simultaneously provide gain medium and optical cavity for performing nanoscale lasers with easy integration, ultracompact footprint, and low energy consumption. Here, we report III-V semiconductor NW lasers can also be used for self-frequency conversion to extend their output wavelengths, as a result of their non-centrosymmetric crystal structure and strongly localized optical field in the NWs. From a GaAs/In0.16Ga0.84As core/shell NW lasing at 1016 nm, an extra visible laser output at 508 nm is obtained via the process of second-harmonic generation, as confirmed by the far-field polarization dependence measurements and numerical modeling. From another NW laser with a larger diameter which supports multiple fundamental lasing wavelengths, multiple self-frequency-conversion lasing modes are observed due to second-harmonic generation and sum-frequency generation. The demonstrated self-frequency conversion of NW lasers opens an avenue for extending the working wavelengths of nanoscale lasers, even to the deep ultraviolet and THz range.

Dendritic cell function in allostimulation is modulated by C5aR signaling.

Regulation of T cell immunity by C5a has been suggested from recent studies. However, the underlying mechanisms, particularly the involved cells and biochemical basis, are not well defined. In this study, the direct modulation of dendritic cell (DC) activation and its function in T cell stimulation by C5a-C5aR interaction and the involved signaling pathways were investigated. We show that DCs from C5aR(-/-) mice and normal DCs treated with C5aR antagonist have less-activated phenotype characterized with increased IL-10 and decreased IL-12p70 production in response to LPS stimulation, lowered surface expression of MHC class II, B7.2, and consequently have reduced capacity to stimulate allospecific T cells. Conversely, C5a stimulation up-regulates DC activation and its function in allostimulation. Furthermore, stimulation of C5aR mediates the inhibition of cAMP production and protein kinase A activity and is involved in activation of PI3K/AKT and NF-kappaB signaling in DCs. These results demonstrate that C5a acts directly on C5aR expressed on DCs resulting in the cell activation and subsequently enhances its capacity for allospecific T cell stimulation. It also suggests that NF-kappaB signaling induced by down-regulation of cAMP/ protein kinase A pathway and up-regulation of PI3K/AKT pathway following C5a stimulation may contribute to up-regulation of DC function.

Deficiency of C5aR prolongs renal allograft survival.

Interaction between C5a, a product of complement activation, and its receptor (C5aR) upregulates antigen-specific T cell responses by modulating the activation of antigen-presenting cells and T cells. Whether this C5a-C5aR interaction contributes to the immune responses that promote renal allograft rejection is unknown. Here, we found that deficiency of C5aR in both graft and recipient reduced allospecific T cell responses and prolonged renal allograft survival. In addition, lack of C5aR impaired the function of donor and recipient antigen-presenting cells and inhibited the response of recipient T cells to allostimulation. Furthermore, deficiency of C5aR in both graft and recipient reduced early inflammation in the grafts, with less cellular infiltration around the vessels and fewer F4/80 positive cells in the peritubular interstitium. These data demonstrate that C5aR is critical for a full adaptive immune response and mediates renal allograft rejection. Engagement of C5aR on dendritic cells and T cells modulates their function, enhancing allospecific T cell responses that lead to allograft rejection. Targeting C5a signaling may have therapeutic potential for T cell-mediated graft rejection.

Ultralow Threshold, Single-Mode InGaAs/GaAs Multiquantum Disk Nanowire Lasers.

We present single-mode nanowire (NW) lasers with an ultralow threshold in the near-infrared spectral range. To ensure the single-mode operation, the NW diameter and length are reduced specifically to minimize the longitudinal and transverse modes of the NW cavity. Increased optical losses and reduced gain volume by the dimension reduction are compensated by an excellent NW morphology and InGaAs/GaAs multiquantum disks. At 5 K, a threshold low as 1.6 µJ/cm2 per pulse is achieved with a resulting quality factor exceeding 6400. By further passivating the NW with an AlGaAs shell to suppress surface nonradiative recombination, single-mode lasing operation is obtained with a threshold of only 48 µJ/cm2 per pulse at room temperature with a high characteristic temperature of 223 K and power output of ∼0.9 µW. These single-mode, ultralow threshold, high power output NW lasers are promising for the development of near-infrared nanoscale coherent light sources for integrated photonic circuits, sensing, and spectroscopy.

Cyclic AMP plays a critical role in C3a-receptor-mediated regulation of dendritic cells in antigen uptake and T-cell stimulation.

The biochemical basis for complement acting directly on antigen-presenting cells to enhance their function in T-cell stimulation has been unclear. Here we present evidence that engagement of C3a receptor (C3aR) on the surface of dendritic cells (DCs) leads to alterations in the level of intracellular cyclic adenosine monophosphate (cAMP), a potent negative regulator of inflammatory cytokines. C3aR activation-induced depression of cAMP was associated with enhanced capacity of DCs for antigen uptake and T-cell stimulation. Conversely, C3aR-deficient DCs showed elevation of cAMP and impaired properties for antigen uptake and immune stimulation. Similarities in the phenotype of C3-deficient and C3aR-deficient DCs suggest that local production of C3 with extracellular metabolism to C3a is an important driver of DC alterations in cAMP. The finding of a link between complement and adaptive immune stimulation through cAMP offers new insight into how innate and adaptive immunity combine to generate efficient effector and memory responses.

Facet-dependent growth of InAsP quantum wells in InP nanowire and nanomembrane arrays.

Selective area epitaxy is a powerful growth technique that has been used to produce III-V semiconductor nanowire and nanomembrane arrays for photonic and electronic applications. The incorporation of a heterostructure such as quantum wells (QWs) brings new functionality and further broadens their applications. Using InP nanowires and nanomembranes as templates, we investigate the growth of InAsP QWs on these pure wurtzite nanostructures. InAsP QWs grow both axially and laterally on the nanowires and nanomembranes, forming a zinc blende phase axially and wurtzite phase on the sidewalls. On the non-polar {11[combining macron]00} sidewalls, the radial QW selectively grows on one sidewall which is located at the semi-polar 〈112[combining macron]〉 A side of the axial QW, causing the shape evolution of the nanowires from hexagonal to triangular cross section. For nanomembranes with {11[combining macron]00} sidewalls, the radial QW grows asymmetrically on the {11[combining macron]00} facet, destroying their symmetry. In comparison, nanomembranes with {112[combining macron]0} sidewalls are shown to be an ideal template for the growth of InAsP QWs, thanks to the uniform QW formation. These QWs emit strongly in the near IR region at room temperature and their emission can be tuned by changing their thickness or composition. These findings enrich our understanding of the QW growth, which provides new insights for heterostructure design in other III-V nanostructures.

Induced Ferromagnetic Order of Graphdiyne Semiconductors by Introducing a Heteroatom.

To date, the realization of ferromagnetism in two-dimensional carbon semiconductors containing only sp electrons has remained a challenge for spintronics. Here, we utilize the atomic-level functionalization strategy to obtain three carbon matrix materials by accurately introducing different light elements (H, F, Cl) into graphdiyne's benzene ring. Their magnetic and conductive characteristics are thoroughly clarified via physical property measurements and DFT calculations. All of these carbon matrix materials retain their excellent intrinsic semiconductor properties. In particular, compared with the paramagnetism of HsGDY and ClsGDY, a robust ferromagnetic ordering as well as high mobility of up to 320 cm2 V-1 s-1 was observed in FsGDY, successfully realizing a ferromagnetic semiconductor. Through theory calculations, this unique ferromagnetic coupling can be attributed to the most striking charge transfer between carbon and fluorine atoms, demonstrating the advantages of controllable fabrication. These results not only reveal the important role of atomic-scale doping/substitution in optimizing graphdiyne material but also create new possibilities for manipulating spins and charges in 2D carbon materials.

Unexpected benefits of stacking faults on the electronic structure and optical emission in wurtzite GaAs/GaInP core/shell nanowires.

Wurtzite (WZ) GaAs nanowires (NWs) are of considerable interest for novel optoelectronic applications, yet high quality NWs are still under development. Understanding of their polytypic crystal structure and band structure is the key to improving their emission characteristics. In this work we report that the Ga1-xInxP shell provides ideal passivation on polytypic WZ GaAs NWs, producing high quantum efficiency (up to 80%). From optical measurements, we find that the polytypic nature of the NWs which presents itself as planar defects does not reduce the emission efficiency. A hole transferring approach from the valence band of the zinc blende segments to the light hole (LH) band of the WZ phase is proposed to explain the emission enhancement from the conduction band to LH band. The emission intensity does not correlate to the minority carrier lifetime which is usually used to quantify the optical emission quality. Theoretical calculation predicted type-II band transition in polytypic WZ GaAs NWs is confirmed and presents efficient emission at low temperatures. We further demonstrate the performance of single NW photodetectors with a high photocurrent responsivity up to 65 A W-1 operating over the wavelength range from visible to near infrared.

Shape Engineering of InP Nanostructures by Selective Area Epitaxy.

Greater demand for III-V nanostructures with more sophisticated geometries other than nanowires is expected because of the recent intensive investigation of nanowire networks that show great potential in all-optical logic gates, nanoelectronics, and quantum computing. Here, we demonstrate highly uniform arrays of InP nanostructures with tunable shapes, such as membrane-, prism-, and ring-like shapes, which can be simultaneously grown by selective area epitaxy. Our in-depth investigation of shape evolution confirms that the shape is essentially determined by pattern confinement and the minimization of total surface energy. After growth optimization, all of the different InP nanostructures grown under the same growth conditions show perfect wurtzite structure regardless of the geometry and strong and homogeneous photon emission. This work expands the research field in terms of producing nanostructures with the desired shapes beyond the limits of nanowires to satisfy various requirements for nanoelectronics, optoelectronics, and quantum device applications.

Complement Receptor 3 Has Negative Impact on Tumor Surveillance through Suppression of Natural Killer Cell Function.

Complement receptor 3 (CR3) is expressed abundantly on natural killer (NK) cells; however, whether it plays roles in NK cell-dependent tumor surveillance is largely unknown. Here, we show that CR3 is an important negative regulator of NK cell function, which has negative impact on tumor surveillance. Mice deficient in CR3 (CD11b-/- mice) exhibited a more activated NK phenotype and had enhanced NK-dependent tumor killing. In a B16-luc melanoma-induced lung tumor growth and metastasis model, mice deficient in CR3 had reduced tumor growth and metastases, compared with WT mice. In addition, adaptive transfer of NK cells lacking CR3 (into NK-deficient mice) mediated more efficient suppression of tumor growth and metastases, compared with the transfer of CR3 sufficient NK cells, suggesting that CR3 can impair tumor surveillance through suppression of NK cell function. In vitro analyses showed that engagement of CR3 with iC3b (classical CR3 ligand) on NK cells negatively regulated NK cell activity and effector functions (i.e. direct tumor cell killing, antibody-dependent NK-mediated tumor killing). Cell signaling analyses showed that iC3b stimulation caused activation of Src homology 2 domain-containing inositol-5-phosphatase-1 (SHIP-1) and JNK, and suppression of ERK in NK cells, supporting that iC3b mediates negative regulation of NK cell function through its effects on SHIP-1, JNK, and ERK signal transduction pathways. Thus, our findings demonstrate a previously unknown role for CR3 in dysregulation of NK-dependent tumor surveillance and suggest that the iC3b/CR3 signaling is a critical negative regulator of NK cell function and may represent a new target for preserving NK cell function in cancer patients and improving NK cell-based therapy.

Functional modulation of human monocytes derived DCs by anaphylatoxins C3a and C5a.

Anaphylatoxins C3a and C5a are important modulators for dendritic cell activation and function in mice. In order to verify the significance of these observations in man, we have investigated the functional modulation of human monocytes derived DCs by C3a and C5a. Here we report that engagement of C3aR or C5aR on human monocytes derived DCs (moDCs) enhances the cell activation and their capacity for allostimulation. In addition, we show that intracellular production of cAMP is reduced and PI3K/AKT, ERK and NF-κB signalling is increased following stimulation with C3a or C5a, identifying intracellular signalling pathways that could convert cell surface C3aR and C5aR engagement into changes in moDC functions. Our data provide evidence that human DCs are equipped to react to C3a/C5a and undergo phenotypic change as well as functional modulation. Complement offers a potential route to modulate human DC function and regulate T cell mediated immunity.

Expression of complement components, receptors and regulators by human dendritic cells.

Integration of innate and adaptive arms of the immune response at a cellular and molecular level appears to be fundamental to the development of powerful effector functions in host defence and aberrant immune responses. Here we provide evidence that the functions of human complement activation and antigen presentation converge on dendritic cells (DCs). We show that several subsets of human DCs [i.e., monocyte derived (CD1a(+)CD14(-)), dermal (CD1a(+)DC-SIGN(+)), Langerhans (CD1a(+)Langerin(+)), myeloid (CD1c(+)CD19(-)), plamacytoid (CD45RA(+)CD123(+))] express many of the components of the classical and alternative and terminal pathways of complement. Moreover human DCs have receptors known to detect the biologically active peptides C3a and C5a (C3aR, C5aR) and the covalently bound fragments C3b and metabolites iC3b and C3d which serve in immune adhesion (i.e., CR3, CR4, CRIg). We also show that the human DC surface is characterised by membrane bound regulators of complement activation, which are also known to participate in intracellular signalling (i.e., CD46, CD55, CD59). This work provides an extensive description of complement components relevant to the integrated actions of complement and DC, illuminated by animal studies. It acts as a resource that allows further understanding and exploitation of role of complement in human health and immune mediated diseases.