Ab Initio Design, Shaping, and Assembly of Free-Standing Silicon Nanoprobes.

Free-standing silicon nanoprobes (SiNPs) are critical tools for intracellular bioelectrical signal recording, while a scalable fabrication of these tiny SiNPs with ab initio geometry designs has not been possible. In this work, we demonstrate a novel growth shaping of slim Si nanowires (SiNWs) into SiNPs with sharp tips (curvature radii <300 nm), tunable angles of 30°, 60°, to 120° and even programmable triangle/circular shapes. A precise growth integration of orderly single, double, and quadruple SiNPs at prescribed locations enables convenient electrode connection, transferring and mounting these tiny tips onto movable arms to serve as long-protruding (over 4-20 µm) nanoprobes. Mechanical flexibility, resilience, and field-effect sensing functionality of the SiNPs were systematically testified in liquid nanodroplet and cell environments. This highly reliable and economic manufacturing of advanced SiNPs holds a strong potential to boost and open up the market implementations of a wide range of intracellular sensing, monitoring, and editing applications.

Cylindrical Line-Feeding Growth of Free-Standing Silicon Nanohelices as Elastic Springs and Resonators.

Three-dimensional (3D) construction of free-standing silicon (Si) nanohelices has been a formidable challenge for planar lithography and etching technology. We here demonstrate a convenient 3D growth and integration of Si nanohelices (SiNHs) upon bamboolike cylinders with corrugated sidewall grooves, where the indium catalyst droplets grow around the cylinders in a helical fashion, while consuming precoated amorphous Si (a-Si) thin film to produce crystalline Si nanowires on the sidewalls. At the end of each groove cycle, the droplets are enforced to linefeed/switch into the neighbor groove to continue a spiral growth of SiNHs with readily tunable diameter, pitch, aspect-ratio, and chiral/achiral symmetries. In addition, the SiNHs can be reliably released as free-standing units to serve as elastic links, supports and vibrational resonators. These results highlight the unexplored potential of high precision 3D self-assembly growth in constructing a wide range of sophisticated electromechanical, sensor, and optoelectronic functionalities.

Synergetic effect in rolling GaIn alloy droplets enables ultralow temperature growth of silicon nanowires at 70 °C on plastics.

Ultralow temperature growth of silicon nanowires (SiNWs) directly upon cheap plastics is highly desirable for building high performance soft logics and sensors based on mature Si technology. In this work, a low temperature growth of SiNWs at only 70 °C has been demonstrated for the first time, upon polyethylene terephthalate plastics, by using gallium-indium (GaIn) alloy droplets that consume an amorphous Si (a-Si) layer as the precursor. The GaIn alloy droplets enable a beneficial synergetic effect that helps not only to reduce the melting temperature, but also to install a protective Gibbs adsorption layer of In atoms, which are critical to stabilize the rolling catalyst droplet, against otherwise rapid diffusion loss of Ga into the a-Si matrix. Ultra-long SiNWs can be batch-produced with a precise location and preferred elastic geometry, which paves the way for large scale integration. At <70 °C, a transition from rolling to sprawling dynamics is observed by in situ scanning electron microscopy, caused by reduced diffusion transport and rapid formation of discrete nuclei in the alloy droplet, which provides the basis for continuous growth of SiNWs. This unique capability and critical new understanding open the way for integrating high quality c-Si electronics directly over flexible, lightweight and extremely low cost plastics.

Facile 3D integration of Si nanowires on Bosch-etched sidewalls for stacked channel transistors.

Three-dimensional (3D) integration is a promising strategy to integrate more functions into a given footprint. In this work, we report on a convenient new strategy to grow and integrate high density Si nanowire (SiNW) arrays on the parallel sidewall grooves formed by Bosch etching, via a low temperature (<350 °C) in-plane solid-liquid-solid (IPSLS) mechanism. It is observed that both the pitch and the depth of the grooves can be reliably controlled, by tuning the Bosch etching parameters, to adjust the density of SiNWs, and the sidewall growth of SiNWs is rather stable even along the turnings. This approach has demonstrated a facile batch-manufacturing of stacked SiNWs, where the SiNWs exhibit a mean diameter of 40 nm and a spacing of 100 nm, without the use of any high resolution lithography. Prototype stacked channel transistors are also fabricated, with an impressive on/off current of >107 and a hole mobility of 57 cm2 V-1 s-1, in a unique vertical side-gate configuration. These results highlight the unique potential and benefit of combining conventional Bosch processing with high precision 3D guided growth of SiNWs for constructing more complex and functional stacked channel electronics.

High-temperature stable plasmonic and cavity resonances in metal nanoparticle-decorated silicon nanopillars for strong broadband absorption in photothermal applications.

Plasmonic metal nanoparticles in conjunction with the cavity mode resonance in crystalline silicon (c-Si) nanopillars (NPs) can help achieve strongly enhanced broadband light absorption far beyond the limit of bulk c-Si. However, a major concern arises from the stability of metal nanoparticles, particularly at a high temperature, as the diffusion and conglomeration of the nanoparticles will undermine the very basis for the advantageous plasmonic effect. We here carried out a systematic investigation of the thermal stability of different metal nanoparticles coated on 3D Si-based NPs and found that simple Al2O3 encapsulation could help stabilize the gold (Au) particles coated on Si NPs even when subjected to annealing at >1073 K while accomplishing excellent broadband optical absorption (∼95%) from 200 nm to 2500 nm. This could be assigned mainly to the excellent dispersion retention capability of the Al2O3-encapsulated Au nanoparticles and the beneficial plasmon resonance absorption among the Au nanoparticles and Si NPs, as also revealed from the FDTD simulation analysis. Finally, a rapid vapor generation application was demonstrated based on the optimized Au/Si NPs, where salt water drops could be directly injected onto the high-temperature photo-heated Au/Si NPs and could vaporize/bounce off quickly without leaving any salt precipitation on the surface. This new strategy can also pave the way for high-performance Si-based photothermal applications.

Low Power Consumption Red Light-Emitting Diodes Based on Inorganic Perovskite Quantum Dots under an Alternating Current Driving Mode.

Inorganic perovskites have emerged as a promising candidate for light-emitting devices due to their high stability and tunable band gap. However, the power consumption and brightness have always been an issue for perovskite light-emitting diodes (PeLEDs). Here, we improved the luminescence intensity and decreased the current density of the PeLEDs based on CsPbI3 quantum dots (QDs) and p-type Si substrate through an alternating current (AC) driving mode. For the different driving voltage modes (under a sine pulsed bias or square pulsed bias), a frequency-dependent electroluminescent (EL) behavior was observed. The devices under a square pulsed bias present a stronger EL intensity under the same voltage due to less thermal degradation at the interface. The red PeLEDs under a square pulsed bias driving demonstrate that the EL intensity drop-off phenomenon was further improved, and the integrated EL intensity shows the almost linear increase with the increasing driving voltage above 8.5 V. Additionally, compared to the direct current (DC) driving mode, the red PeLEDs under the AC condition exhibit higher operating stability, which is mainly due to the reducing accumulated charges in the devices. Our work provides an effective approach for obtaining strong brightness, low power consumption, and high stability light-emitting devices, which will exert a profound influence on coupling LEDs with household power supplies directly.

Nanodroplet Hydrodynamic Transformation of Uniform Amorphous Bilayer into Highly Modulated Ge/Si Island-Chains.

Geometric and compositional modulations are the principal parameters of control to tailor the band profile in germanium/silicon (Ge/Si) heteronanowires (NWs). This has been achieved mainly by alternating the feeding precursors during a uniaxial growth of Ge/Si NWs. In this work, a self-automated growth of Ge/Si hetero island-chain nanowires (hiNWs), consisting of wider c-Ge islands connected by thinner c-Si chains, has been accomplished via an indium (In) droplet-mediated transformation of uniform amorphous a-Si/a-Ge bilayer thin films. The surface-running In droplet enforces a circulative hydrodynamics in the nanoscale droplet, which can modulate the absorption depth into the amorphous bilayer and enable a single-run growth of a superlattice-like hiNWs without the need for any external manipulation. Meanwhile, the separation and accumulation of electrons and holes in the phase-modulated Ge/Si superlattice leads to a modulated surface potential profile that can be directly resolved by Kelvin probe force microscopy. This simple self-assembly growth and modulation dynamics can help to establish a powerful new concept or strategy to tailor and program the geometric and compositional profiles of more complex hetero nanowire structures, as promising building blocks to develop advanced nanoelectronics or optoelectronics.

Androgen receptor expression identifies patient with favorable outcome in operable triple negative breast cancer.

In this study we sought to investigate the prevalence and prognostic value of androgen receptor (AR) status in operable triple-negative breast cancer (TNBC) patients. We collected the clinical data of 360 patients with TNBC, and found a positivity AR expression of 31.4% with a cut-off value of 10%. Tumors expressing the negative CK5/6 (P=0.013) and low Ki-67 (P=0.007) are more likely to have positive AR. In multivariate survival analysis, AR expression is correlated with increased DFS (HR=0.467, 95%CI 0.271-0.805; P=0.006) and OS (HR=0.488, 95%CI 0.267-0.894, P=0.020) independently. In addition, patients with AR+ tumors are more likely to have favorable outcome in patients with young, pre-menopausal, large tumor size, more node involvement (4+), high stage, high grade, vascular invasion+, P53+, CK5/6-, and higher Ki-67. Our study has indicated that the absence of AR might help to identify patients with relatively higher risk of disease relapse and death, and further clinical studies of anti-androgen agents are warranted to enrich the therapeutic strategy options for AR+ TNBCs.

Large-area, size-tunable Si nanopillar arrays with enhanced antireflective and plasmonic properties.

In this paper, a novel method using the modified Langmuir-Blodgett and float-transfer techniques was introduced to construct the perfect PS monolayer nanosphere template with large area up to cm(2). Based on such templates, the diameter, length, packing density, and the shape of Si nanopillar arrays (Si NPAs) could be precisely controlled and tuned through the modified nanosphere lithography combined with a metal-assisted chemical etching (NSL-MACE) method. Manipulation of the etching time can effectively avoid permanent deformation/clumping to generate size-tunable Si NPAs. The optical properties of the Si NPAs can be controlled by the Si NPA morphologies resulting from the different reactive ion etching (RIE) time and chemical etching time. The enhanced antireflective property and electromagnetic field effect of Au/Si NPAs were proved by the results. The new modified NSL-MACE technique with the capability of scale-up fabrication of Si NPAs would be helpful for potential applications in optoelectronic devices.