Publications by authors named "Linwei Yu"

54 Publications

Robust neuronal differentiation of human iPSC-derived neural progenitor cells cultured on densely-spaced spiky silicon nanowire arrays.

Sci Rep 2021 Sep 22;11(1):18819. Epub 2021 Sep 22.

Center for Hybrid Nanostructures, Universität Hamburg, Luruper Chaussee 149, 22761, Hamburg, Germany.

Nanostructured cell culture substrates featuring nanowire (NW) arrays have been applied to a variety of basic cell lines and rodent neurons to investigate cellular behavior or to stimulate cell responses. However, patient-derived human neurons-a prerequisite for studying e.g. neurodegenerative diseases efficiently-are rarely employed due to sensitive cell culture protocols and usually long culturing periods. Here, we present human patient induced pluripotent stem cell-derived neurons cultured on densely-spaced spiky silicon NW arrays (600 NWs/ 100 µm[Formula: see text] with NW lengths of 1 µm) which show mature electrophysiological characteristics after only 20 days of culturing. Exemplary neuronal growth and network formation on the NW arrays are demonstrated using scanning electron microscopy and immunofluorescence microscopy. The cells and neurites rest in a fakir-like settling state on the NWs only in contact with the very NW tips shown by cross-sectional imaging of the cell/NW interface using focused ion beam milling and confocal laser scanning microscopy. Furthermore, the NW arrays promote the cell culture by slightly increasing the share of differentiated neurons determined by the quantification of immunofluorescence microscopy images. The electrophysiological functionality of the neurons is confirmed with patch-clamp recordings showing the excellent capability to fire action potentials. We believe that the short culturing time to obtain functional human neurons generated from patient-derived neural progenitor cells and the robustness of this differentiation protocol to produce these neurons on densely-spaced spiky nanowire arrays open up new pathways for stem cell characterization and neurodegenerative disease studies.
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http://dx.doi.org/10.1038/s41598-021-97820-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8458299PMC
September 2021

Unexpected phosphorus doping routine of planar silicon nanowires for integrating CMOS logics.

Nanoscale 2021 Sep 17;13(35):15031-15037. Epub 2021 Sep 17.

School of Electronics Science and Engineering/National Laboratory of Solid-State Microstructures, Nanjing University, 210093 Nanjing, P. R. China.

Complementary doping control in silicon nanowire (SiNW) channels is crucial for the construction of high-performance CMOS logics. Though planar in-plane solid-liquid-solid (IPSLS) growth, with an amorphous Si (a-Si) thin film as a precursor, has demonstrated a precise and scalable integration of orderly SiNWs, a complementary and tunable n-type doping has not been accomplished. This has been hindered by the fact that the phosphorus (P) gas dopants will react with the indium (In) catalyst droplet to form insoluble InP precipitates. Nevertheless, we herein report on an unexpected discovery that the P dopants first incorporated into the a-Si matrix can easily diffuse over the In catalyst droplets, without forming an InP compound, and thus reverse continuously the initial p-type SiNWs into an n-type channel. Uniform and efficient doping effects have been confirmed by both atomic probe tomography mapping and the transfer properties of SiNW FETs, which demonstrate a steep subthreshold swing of 105 mV dec, an on/off ratio of >10 and an electron mobility of 142 cm V s. Finally, true CMOS inverters are successfully demonstrated based on the closely-packed SiNW channels of distinct doping polarities, indicating a new convenient and highly efficient doping routine to construct more advanced SiNW logics and sensors.
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http://dx.doi.org/10.1039/d1nr03014kDOI Listing
September 2021

Coupled Investigation of Contact Potential and Microstructure Evolution of Ultra-Thin AlO for Crystalline Si Passivation.

Nanomaterials (Basel) 2021 Jul 12;11(7). Epub 2021 Jul 12.

School of Physical Science and Technology, Ningbo University, Ningbo 315211, China.

In this work, we report the same trends for the contact potential difference measured by Kelvin probe force microscopy and the effective carrier lifetime on crystalline silicon (c-Si) wafers passivated by AlO layers of different thicknesses and submitted to annealing under various conditions. The changes in contact potential difference values and in the effective carrier lifetimes of the wafers are discussed in view of structural changes of the c-Si/SiO/AlO interface thanks to high resolution transmission electron microscopy. Indeed, we observed the presence of a crystalline silicon oxide interfacial layer in as-deposited (200 °C) AlO, and a phase transformation from crystalline to amorphous silicon oxide when they were annealed in vacuum at 300 °C.
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http://dx.doi.org/10.3390/nano11071803DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8308321PMC
July 2021

Terrace-confined guided growth of high-density ultrathin silicon nanowire array for large area electronics.

Nanotechnology 2021 Mar 22. Epub 2021 Mar 22.

School of Electronic Science and Engineering, Nanjing University, Nanjing, CHINA.

Ultrathin silicon nanowires (SiNWs) are ideal 1D channels to construct high performance nanoelectronics and sensors. We here report on a high-density catalytic growth of orderly ultrathin SiNWs, with diameter down to D_nw=27±2 nm and narrow NW-to-NW spacing of only S_nw~80 nm, without the use of high-resolution lithography. This has been accomplished via a terrace-squeezing strategy, where tiny indium (In) droplets move on sidewall terraces to absorb precoated amorphous Si layer as precursor and produce self-aligned SiNW array. It is found that, under proper parameter control, a tighter terrace-step confinement can help to scale the dimensions of the SiNW array down to the extremes that have not been testified before, while maintaining still a stable guiding growth over complex contours. Prototype SiNW field effect transistors demonstrate a high Ion/Ioff current ratio ~10^7, low leakage current of ~0.3 pA and steep subthreshold swing of 220 mV/dec. These results highlight the unexplored potential of catalytic growth in advanced nanostructure fabrication that is highly relevant for scalable SiNW logic and sensor applications.
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http://dx.doi.org/10.1088/1361-6528/abf0c9DOI Listing
March 2021

Highly Sensitive Ammonia Gas Detection at Room Temperature by Integratable Silicon Nanowire Field-Effect Sensors.

ACS Appl Mater Interfaces 2021 Mar 22;13(12):14377-14384. Epub 2021 Mar 22.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, P. R. China.

Toxic gas monitoring at room temperature (RT) is of great concern to public health and safety, where ultrathin silicon nanowires (SiNWs), with diameter <80 nm, are ideal one-dimensional candidates to achieve high-performance field-effect sensing. However, a precise integration of the tiny SiNWs as active gas sensor channels has not been possible except for the use of expensive and inefficient electron beam lithography and etching. In this work, we demonstrate an integratable fabrication of field-effect sensors based on orderly SiNW arrays, produced via step-guided in-plane solid-liquid-solid growth. The back-gated SiNW sensors can be tuned into suitable subthreshold detection regime to achieve an outstanding field-effect sensitivity (75.8% @ 100 ppm NH), low detection limit (100 ppb), and excellent selectivity to NH gas at RT, with fast response/recovery time scales (/) of 20 s (at 100 ppb NH) and excellent repeatability and high stability over 180 days. These outstanding sensing performances can be attributed to the fast charge transfer between adsorbed NH molecules and the exposed SiNW channels, indicating a convenient strategy to fabricate and deploy high-performance gas detectors that are widely needed in the booming marketplace of wearable or portable electronics.
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http://dx.doi.org/10.1021/acsami.1c00585DOI Listing
March 2021

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

Nano Lett 2021 04 17;21(7):2773-2779. Epub 2021 Mar 17.

National Laboratory of Solid State Microstructures, School of Electronics Science and Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P.R. China.

Free-standing silicon nanoprobes (SiNPs) are critical tools for intracellular bioelectrical signal recording, while a scalable fabrication of these tiny SiNPs with 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.
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http://dx.doi.org/10.1021/acs.nanolett.0c04804DOI Listing
April 2021

Superfast Growth Dynamics of High-Quality Silicon Nanowires on Polymer Films via Self-Selected Laser-Droplet-Heating.

Nano Lett 2021 Jan 22;21(1):569-576. Epub 2020 Dec 22.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering, Nanjing University, 210093 Nanjing, China.

Growing high quality silicon nanowires (SiNWs) at elevated temperature on cooler polymer films seems to be contradictive but highly desirable for building high performance flexible and wearable electronics. In this work, we demonstrate a superfast ( > 3.5 μm·s) growth of high quality SiNWs on polymer/glass substrates, powered by self-selected laser at 808 nm heating of indium catalyst droplets that absorb amorphous Si layer to produce SiNWs. Because of the tiny heat capacity of the nanodroplets, the SiNW growth can be quickly heated up and frozen via rapid laser ON/OFF switching, enabling a deterministic diameter modulation in the ultralong SiNWs. Finally, prototype field effect transistors are also fabricated upon the laser-droplet-heating grown SiNWs with a high / ratio of >10 and reasonable subthreshold swing of 386 mV·dec, opening a generic new route to integrate high-quality NW channels directly upon large area and lightweight polymer substrates for developing high-performance flexible electronics.
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http://dx.doi.org/10.1021/acs.nanolett.0c04058DOI Listing
January 2021

Unprecedented Uniform 3D Growth Integration of 10-Layer Stacked Si Nanowires on Tightly Confined Sidewall Grooves.

Nano Lett 2020 Oct 1;20(10):7489-7497. Epub 2020 Oct 1.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, 210093 Nanjing, P. R. China.

Bottom-up catalytic growth offers a high-yield, versatile, and powerful tool for the construction of versatile 3D nanocomplexes, while the major challenge is to achieve a precise location and uniformity control, as guaranteed by top-down lithography. Here, an unprecedented uniform and reliable growth integration of 10-layer stacked Si nanowires (SiNWs) has been accomplished, for the very first time, via a new groove-confined and tailored catalyst formation and guided growth upon the truncated sidewall of SiO/SiN multilayers. The SiNW array accomplishes a narrow diameter of = 28 ± 2.4 nm, NW-to-NW spacing of = 40 nm, and extremely stable growth over > 50 μm and bending locations, which can compete with or even outperform the top-down lithography and etching approaches, in terms of stacking number, channel uniformity at different levels, fabrication cost, and efficiency. These results provide a solid basis to establish a new 3D integration approach to batch-manufacture various advanced electronic and sensor applications.
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http://dx.doi.org/10.1021/acs.nanolett.0c02950DOI Listing
October 2020

Room-temperature valleytronic transistor.

Nat Nanotechnol 2020 Sep 20;15(9):743-749. Epub 2020 Jul 20.

School of Electronic Science and Engineering, Nanjing University, Nanjing, China.

Valleytronics, based on the valley degree of freedom rather than charge, is a promising candidate for next-generation information devices beyond complementary metal-oxide-semiconductor (CMOS) technology. Although many intriguing valleytronic properties have been explored based on excitonic injection or the non-local response of transverse current schemes at low temperature, demonstrations of valleytronic building blocks similar to transistors in electronics, especially at room temperature, remain elusive. Here, we report a solid-state device that enables a full sequence of generating, propagating, detecting and manipulating valley information at room temperature. Chiral nanocrescent plasmonic antennae are used to selectively generate valley-polarized carriers in MoS through hot-electron injection under linearly polarized infrared excitation. These long-lived valley-polarized free carriers can be detected in a valley Hall configuration even without charge current, and can propagate over 18 μm by means of drift. In addition, electrostatic gating allows us to modulate the magnitude of the valley Hall voltage. The electrical valley Hall output could drive the valley manipulation of a cascaded stage, rendering the device able to serve as a transistor free of charge current with pure valleytronic input/output. Our results demonstrate the possibility of encoding and processing information by valley degree of freedom, and provide a universal strategy to study the Berry curvature dipole in quantum materials.
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http://dx.doi.org/10.1038/s41565-020-0727-0DOI Listing
September 2020

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

Nano Lett 2020 Jul 18;20(7):5072-5080. Epub 2020 Jun 18.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P.R. China.

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.
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http://dx.doi.org/10.1021/acs.nanolett.0c01265DOI Listing
July 2020

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

Nanoscale 2020 Apr;12(16):8949-8957

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China.

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.
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http://dx.doi.org/10.1039/d0nr01283aDOI Listing
April 2020

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

Nanoscale 2020 Jan 21;12(4):2787-2792. Epub 2020 Jan 21.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China.

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 >10 and a hole mobility of 57 cm V s, 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.
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http://dx.doi.org/10.1039/c9nr09000bDOI Listing
January 2020

Coupled boron-doping and geometry control of tin-catalyzed silicon nanowires for high performance radial junction photovoltaics.

Opt Express 2019 Dec;27(26):37248-37256

Geometry and doping control in silicon nanowires (SiNWs) are both crucial aspects in fabricating three-dimensional (3D) radial junction thin film solar cells, while the coupling between them remains a peculiar aspect to be better understood. In this work, we focus on the geometry evolution and the doping effects realized in tin-catalyzed SiNWs grown via a plasma-enhanced vapor-liquid-solid procedure by using different diborane (BH) dopant flows. It is shown that with the increase of BH flow rate from 0.3 to 2.1 SCCM, the radial growth of SiNWs is greatly accelerated by more than 30%, while the length is shortened to 50%. This can be related to the enhanced chemisorption probability of SiH radicals, with the addition of BH, on the SiNW sidewall during silane (SiH) plasma deposition in PECVD system, which leads to easier nucleation directly on the sidewalls and faster radial expansion of the SiNWs. A trade-off has to be sought between seeking a strong light trapping and ensuring a sufficient doping for high-quality PIN junction with the increase of BH doping flow. These new understandings lay a critical basis for understanding and searching for an optimal growth control for constructing high-performance 3D radial junction thin-film solar cells.
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http://dx.doi.org/10.1364/OE.27.037248DOI Listing
December 2019

Three-dimensional a-Si/a-Ge radial heterojunction near-infrared photovoltaic detector.

Sci Rep 2019 Dec 24;9(1):19752. Epub 2019 Dec 24.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China.

In this work, three-dimensional (3D) radial heterojunction photodetectors (PD) were constructed over vertical crystalline Si nanowires (SiNWs), with stacked hydrogenated amorphous germanium (a-Ge:H)/a-Si:H thin film layer as absorbers. The hetero absorber layer is designed to benefit from the type-II band alignment at the a-Ge/a-Si hetero-interface, which could help to enable an automated photo-carrier separation without exterior power supply. By inserting a carefully controlled a-Si passivation layer between the a-Ge:H layer and the p-type SiNWs, we demonstrate first a convenient fabrication of a new hetero a-Ge/a-Si structure operating as self-powered photodetectors (PD) in the near-infrared (NIR) range up to 900 nm, indicating a potential to serve as low cost, flexible and high performance radial junction sensing units for NIR imaging and PD applications.
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http://dx.doi.org/10.1038/s41598-019-56374-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6930292PMC
December 2019

Germanium quantum dot infrared photodetectors addressed by self-aligned silicon nanowire electrodes.

Nanotechnology 2020 Apr 20;31(14):145602. Epub 2019 Dec 20.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Center of Advanced Microstructures, Nanjing University, 210093 Nanjing, People's Republic of China.

Germanium quantum dots (GeQDs), addressed by self-aligned and epitaxial silicon nanowires (SiNWs) as electrodes, represent the most fundamental and the smallest units that can be integrated into Si optoelectronics for 1550 nm wavelength detection. In this work, individual GeQD photodetectors have been fabricated based on a low temperature self-condensation of uniform amorphous Si (a-Si)/a-Ge bilayers at 300 °C, led by rolling indium (In) droplets. Remarkably, the diameter of the GeQD nodes can be independently controlled to achieve wider GeQDs for maximizing infrared absorption with narrower SiNW electrodes to ensure a high quality Ge/Si hetero-epitaxial connection. Importantly, these hetero GeQD/SiNW photodetectors can be deployed into predesigned locations for scalable device fabrication. The photodetectors demonstrate a responsivity of 1.5 mA W and a photoconductive gain exceeding 10 to the communication wavelength signals, which are related to the beneficial type-II Ge/Si alignment, gradient Ge/Si epitaxial transition and a larger QD/NW diameter ratio. These results indicate a new approach to batch-fabricate and integrate GeQDs for ultra-compact Si-compatible photodetection and imaging applications.
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http://dx.doi.org/10.1088/1361-6528/ab647eDOI Listing
April 2020

Photoelectric Cardiac Pacing by Flexible and Degradable Amorphous Si Radial Junction Stimulators.

Adv Healthc Mater 2020 01 3;9(1):e1901342. Epub 2019 Dec 3.

National Laboratory of Solid State Microstructures, School of Electronics Science and Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China.

Implanted pacemakers are usually bulky and rigid electronics that are constraint by limited battery lifetimes, and need to be installed and repaired via surgeries that risk secondary infection and injury. In this work, a flexible self-powered photoelectric cardiac stimulator is demonstrated based on hydrogenated amorphous Si (a-Si:H) radial p-i-n junctions (RJs), constructed upon standing Si nanowires grown directly on aluminum thin foils. The flexible RJ stimulators, with an open-circuit voltage of 0.67 V and short-circuit current density of 12.7 mA cm under standard AM1.5G illumination, can be conformally attached to the uneven tissue surface to pace heart-beating under modulated 650 nm laser illumination. In vivo pacing evaluations on porcine hearts show that the heart rate can be effectively controlled by the external photoelectric stimulations, to increase from the normal rate of 101-128 beating min . Importantly, the a-Si:H RJ units are highly biofriendly and biodegradable, with tunable lifetimes in phosphate-buffered saline environment controlled by surface coating and passivation, catering to the needs of short term or lasting cardiac pacing applications. This implantable a-Si:H RJ photoelectric stimulation strategy has the potential to establish eventually a self-powered, biocompatible, and conformable cardiac pacing technology for clinical therapy.
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http://dx.doi.org/10.1002/adhm.201901342DOI Listing
January 2020

Planar Growth, Integration, and Applications of Semiconducting Nanowires.

Adv Mater 2020 Jul 20;32(27):e1903945. Epub 2019 Nov 20.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China.

Silicon and other inorganic semiconductor nanowires (NWs) have been extensively investigated in the last two decades for constructing high-performance nanoelectronics, sensors, and optoelectronics. For many of these applications, these tiny building blocks have to be integrated into the existing planar electronic platform, where precise location, orientation, and layout controls are indispensable. In the advent of More-than-Moore's era, there are also emerging demands for a programmable growth engineering of the geometry, composition, and line-shape of NWs on planar or out-of-plane 3D sidewall surfaces. Here, the critical technologies established for synthesis, transferring, and assembly of NWs upon planar surface are examined; then, the recent progress of in-plane growth of horizontal NWs directly upon crystalline or patterned substrates, constrained by using nanochannels, an epitaxial interface, or amorphous thin film precursors is discussed. Finally, the unique capabilities of planar growth of NWs in achieving precise guided growth control, programmable geometry, composition, and line-shape engineering are reviewed, followed by their latest device applications in building high-performance field-effect transistors, photodetectors, stretchable electronics, and 3D stacked-channel integration.
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http://dx.doi.org/10.1002/adma.201903945DOI Listing
July 2020

Planar Growth, Integration, and Applications of Semiconducting Nanowires.

Adv Mater 2020 Jul 20;32(27):e1903945. Epub 2019 Nov 20.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China.

Silicon and other inorganic semiconductor nanowires (NWs) have been extensively investigated in the last two decades for constructing high-performance nanoelectronics, sensors, and optoelectronics. For many of these applications, these tiny building blocks have to be integrated into the existing planar electronic platform, where precise location, orientation, and layout controls are indispensable. In the advent of More-than-Moore's era, there are also emerging demands for a programmable growth engineering of the geometry, composition, and line-shape of NWs on planar or out-of-plane 3D sidewall surfaces. Here, the critical technologies established for synthesis, transferring, and assembly of NWs upon planar surface are examined; then, the recent progress of in-plane growth of horizontal NWs directly upon crystalline or patterned substrates, constrained by using nanochannels, an epitaxial interface, or amorphous thin film precursors is discussed. Finally, the unique capabilities of planar growth of NWs in achieving precise guided growth control, programmable geometry, composition, and line-shape engineering are reviewed, followed by their latest device applications in building high-performance field-effect transistors, photodetectors, stretchable electronics, and 3D stacked-channel integration.
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http://dx.doi.org/10.1002/adma.201903945DOI Listing
July 2020

Nanoscale Photovoltaic Responses in 3D Radial Junction Solar Cells Revealed by High Spatial Resolution Laser Excitation Photoelectric Microscopy.

ACS Nano 2019 Sep 5;13(9):10359-10365. Epub 2019 Sep 5.

Research Institute of Superconductor Electronics (RISE)/School of Electronics Science and Engineering , Nanjing University , Nanjing , 210023 , People's Republic of China.

The actual light absorption photovoltaic responses realized in three-dimensional (3D) radial junction (RJ) units can be rather different from their planar counterparts and remain largely unexplored. We here adopt a laser excitation photoelectric microscope (LEPM) technology to probe the local light harvesting and photoelectric signals of 3D hydrogenated amorphous silicon (a-Si:H) RJ thin film solar cells constructed over a Si nanowire (SiNW) matrix, with a high spatial resolution of 600 nm thanks to the use of a high numerical aperture objective. The LEPM scan can help to resolve clearly the impacts of local structural damages, which are invisible to optical and SEM observations. More importantly, the high-resolution photoelectric mapping establishes a straightforward link between the local 3D geometry of RJ units and their light conversion performance. Surprisingly, it is found that the maximal photoelectric signals are usually recorded in the void locations among the standing SiNW RJs, instead of the overhead positions above the RJs. This phenomenon can be well explained and reproduced by finite element simulation analysis, which highlights unambiguously the dominant contribution of inter-RJ-unit scattering against direct mode incoupling in the 3D solar cell architecture. This LEPM mapping technology and the results help to achieve a straightforward and high-resolution evaluation of the local photovoltaic responses among the 3D RJ units, providing a solid basis for further structural optimization and performance improvement.
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http://dx.doi.org/10.1021/acsnano.9b04149DOI Listing
September 2019

Monolithic Integration of Silicon Nanowire Networks as a Soft Wafer for Highly Stretchable and Transparent Electronics.

Nano Lett 2019 Sep 26;19(9):6235-6243. Epub 2019 Aug 26.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Center of Advanced Microstructures , Nanjing University , 210093 Nanjing , China.

Assembling nanoscale building blocks into an orderly network with a programmable layout and channel designs represents a critical capability to enable a wide range of stretchable electronics. Here, we demonstrate the growth-in-place integration of silicon nanowire (SiNW) springs into highly stretchable, transparent, and quasicontinuous functional networks with a close to unity interconnection among the discrete electrode joints because of a unique double-lane/double-step guiding edge design. The SiNW networks can be reliably transferred to a soft elastomer substrate, conformally attached to highly curved surfaces, or deployed as self-supporting/movable membranes suspended over voids. A high stretchability of >40% is achieved for the SiNW network on an elastomer, which can be employed as a transparent and semiconducting thin-film material endowed with a high carrier mobility of >50 cm/(V s), / ratio >10, and a tunable transmission of >80% over a wide spectrum range. Reversibly stretchable and bendable sensors based on the SiNW network have been successfully demonstrated, where the local strain distribution within the spring network can be directly observed and analyzed by finite element simulations. This SiNW network has a unique potential to eventually establish a new generically purposed waferlike platform for constructing electronics with Si-based performances.
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http://dx.doi.org/10.1021/acs.nanolett.9b02291DOI Listing
September 2019

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

Nanoscale 2019 Aug;11(31):14777-14784

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering/Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China.

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.
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http://dx.doi.org/10.1039/c9nr05019aDOI Listing
August 2019

The Effect of Decomposed PbI on Microscopic Mechanisms of Scattering in CHNHPbI Films.

Nanoscale Res Lett 2019 Jun 18;14(1):208. Epub 2019 Jun 18.

National Laboratory of Solid State Microstructures and School of Electronic Science and Engineering and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China.

Hybrid organic-inorganic perovskites (HOIPs) exhibit long electronic carrier diffusion length, high optical absorption coefficient, and impressive photovoltaic device performance. At the core of any optoelectronic device lie the charge transport properties, especially the microscopic mechanism of scattering, which must efficiently affect the device function. In this work, CHNHPbI (MAPbI) films were fabricated by a vapor solution reaction method. Temperature-dependent Hall measurements were introduced to investigate the scattering mechanism in MAPbI films. Two kinds of temperature-mobility behaviors were identified in different thermal treatment MAPbI films, indicating different scattering mechanisms during the charge transport process in films. We found that the scattering mechanisms in MAPbI films were mainly influenced by the decomposed PbI components, which could be easily generated at the perovskite grain boundaries (GBs) by releasing the organic species after annealing at a proper temperature. The passivation effects of PbI in MAPbI films were investigated and further discussed with emphasis on the scattering mechanism in the charge transport process.
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http://dx.doi.org/10.1186/s11671-019-3022-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6582041PMC
June 2019

Plasmon Excited Ultrahot Carriers and Negative Differential Photoresponse in a Vertical Graphene van der Waals Heterostructure.

Nano Lett 2019 05 26;19(5):3295-3304. Epub 2019 Apr 26.

Department of Information Science & Electronic Engineering , Zhejiang University , Hangzhou 310058 , China.

Photogenerated nonequilibrium hot carriers play a key role in graphene's intriguing optoelectronic properties. Compared to conventional photoexcitation, plasmon excitation can be engineered to enhance and control the generation and dynamics of hot carriers. Here, we report an unusual negative differential photoresponse of plasmon-induced "ultrahot" electrons in a graphene-boron nitride-graphene tunneling junction. We demonstrate nanocrescent gold plasmonic nanostructures that substantially enhance the absorption of long-wavelength photons whose energy is greatly below the tunneling barrier and significantly boost the electron thermalization in graphene. We further analyze the generation and transfer of ultrahot electrons under different bias and power conditions. We find that the competition among thermionic emission, the carrier-cooling effect, and the field effect results in a hitherto unusual negative differential photoresponse in the photocurrent-bias plot. Our results not only exemplify a promising platform for detecting low-energy photons, enhancing the photoresponse, and reducing the dark current but also reveal the critically coupled pathways for harvesting ultrahot carriers.
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http://dx.doi.org/10.1021/acs.nanolett.9b00908DOI Listing
May 2019

Advanced radial junction thin film photovoltaics and detectors built on standing silicon nanowires.

Nanotechnology 2019 Jul 8;30(30):302001. Epub 2019 Mar 8.

National Laboratory of Solid State Microstructures/School of Electronics Science and Engineering, Nanjing University, 210093 Nanjing, People's Republic of China.

Three-dimensional (3D) construction of radial junction hydrogenated amorphous silicon (a-Si:H) thin film solar cells on standing silicon nanowires (SiNWs) is a promising strategy to maximize the light harvesting performance and improve the photocarrier collection in an optimized junction configuration. The unique light in-coupling and absorption behaviour in the antenna-like 3D photonic structures also necessitates a set of new theoretical models and simulation tools to design, predict and optimize the photovoltaic performance of radial junction solar cells, which can be rather different from planar junction solar cells. Recently, the performance of radial junction a-Si:H thin film solar cells has progressed steadily to a level comparable or even superior to that of their planar counterparts, with plenty of room for further improvement. This review will first address the growth strategy and critical parameter control of SiNWs produced via a plasma-assisted low-temperature vapour-liquid-solid procedure using low-melting-point metals as the catalyst. Then, the construction of high-performance radial junction thin film solar cells over the standing SiNW matrix, as well as their optimal structural designs, will be introduced. At the end, the new applications of 3D radial junction units will be summarized, which include, for example, the construction of very flexible, low-cost and efficient a-Si:H solar cells with the highest power-to-weight ratio, the demonstration of highly sensitive solar-blind photodetectors operating at the ultraviolet wavelength spectrum and the development of novel biomimetic radial tandem junction photodetectors with an intrinsic red-green-blue (RGB) colour distinguishing capability.
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http://dx.doi.org/10.1088/1361-6528/ab0e57DOI Listing
July 2019

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

Nanomaterials (Basel) 2018 Nov 26;8(12). Epub 2018 Nov 26.

National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.

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.
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http://dx.doi.org/10.3390/nano8120974DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6316845PMC
November 2018

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

Nano Lett 2018 11 24;18(11):6931-6940. Epub 2018 Oct 24.

LPICM, CNRS, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau , France.

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.
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http://dx.doi.org/10.1021/acs.nanolett.8b02847DOI Listing
November 2018

Enhancing Hybrid Perovskite Detectability in the Deep Ultraviolet Region with Down-Conversion Dual-Phase (CsPbBr-CsPbBr) Films.

J Phys Chem Lett 2018 Apr 15;9(7):1592-1599. Epub 2018 Mar 15.

School of Materials Science and Engineering , Hefei University of Technology , Hefei 230009 , People's Republic of China.

Hybrid perovskite photodetectors (PDs) exhibit outstanding performance in the ultraviolet-visible (UV-vis) spectrum but have poor detectability in the deep ultraviolet (DUV) region (200-350 nm). In this work, a novel inorganic-hybrid architecture that incorporates a dual-phase (CsPbBr-CsPbBr) inorganic perovskite material as a down-conversion window layer and a hybrid perovskite as a light capture layer was prepared to achieve faster, highly sensitive photodetection in the DUV spectrum. A dual-phase inorganic perovskite film coated on the back surface of the photodetector enables strong light absorption and tunes the incident energy into emission bands that are optimized for the perovskite photodetector. The presence of CsPbBr enhances the capture and down-conversion of the incident DUV light. Due to the down-conversion and transport of the DUV photons, a self-driven perovskite photodetector with this composite structure exhibits a fast response time of 7.8/33.6 μs and a high responsivity of 49.4 mA W at 254 nm without extra power supply.
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http://dx.doi.org/10.1021/acs.jpclett.8b00429DOI Listing
April 2018

Dual-Phase CsPbBr -CsPb Br Perovskite Thin Films via Vapor Deposition for High-Performance Rigid and Flexible Photodetectors.

Small 2018 02 20;14(7). Epub 2017 Dec 20.

School of Materials Science and Engineering, Hefei University of Technology, Hefei, 230009, P. R. China.

Inorganic perovskites with special semiconducting properties and structures have attracted great attention and are regarded as next generation candidates for optoelectronic devices. Herein, using a physical vapor deposition process with a controlled excess of PbBr , dual-phase all-inorganic perovskite composite CsPbBr -CsPb Br thin films are prepared as light-harvesting layers and incorporated in a photodetector (PD). The PD has a high responsivity and detectivity of 0.375 A W and 10 Jones, respectively, and a fast response time (from 10% to 90% of the maximum photocurrent) of ≈280 µs/640 µs. The device also shows an excellent stability in air for more than 65 d without encapsulation. Tetragonal CsPb Br provides satisfactory passivation to reduce the recombination of the charge carriers, and with its lower free energy, it enhances the stability of the inorganic perovskite devices. Remarkably, the same inorganic perovskite photodetector is also highly flexible and exhibits an exceptional bending performance (>1000 cycles). These results highlight the great potential of dual-phase inorganic perovskite films in the development of optoelectronic devices, especially for flexible device applications.
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http://dx.doi.org/10.1002/smll.201702523DOI Listing
February 2018

Deterministic Line-Shape Programming of Silicon Nanowires for Extremely Stretchable Springs and Electronics.

Nano Lett 2017 12 4;17(12):7638-7646. Epub 2017 Dec 4.

LPICM, CNRS, Ecole Polytechnique, Université Paris-Saclay , 91128 Palaiseau, France.

Line-shape engineering is a key strategy to endow extra stretchability to 1D silicon nanowires (SiNWs) grown with self-assembly processes. We here demonstrate a deterministic line-shape programming of in-plane SiNWs into extremely stretchable springs or arbitrary 2D patterns with the aid of indium droplets that absorb amorphous Si precursor thin film to produce ultralong c-Si NWs along programmed step edges. A reliable and faithful single run growth of c-SiNWs over turning tracks with different local curvatures has been established, while high resolution transmission electron microscopy analysis reveals a high quality monolike crystallinity in the line-shaped engineered SiNW springs. Excitingly, in situ scanning electron microscopy stretching and current-voltage characterizations also demonstrate a superelastic and robust electric transport carried by the SiNW springs even under large stretching of more than 200%. We suggest that this highly reliable line-shape programming approach holds a strong promise to extend the mature c-Si technology into the development of a new generation of high performance biofriendly and stretchable electronics.
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http://dx.doi.org/10.1021/acs.nanolett.7b03658DOI Listing
December 2017

On the Mechanism of In Nanoparticle Formation by Exposing ITO Thin Films to Hydrogen Plasmas.

Langmuir 2017 10 11;33(43):12114-12119. Epub 2017 Oct 11.

LPICM, CNRS, Ecole Polytechnique, Université Paris-Saclay , 91128 Palaiseau, France.

We present our systematic work on the in situ generation of In nanoparticles (NPs) from the reduction of ITO thin films by hydrogen (H) plasma exposure. In contrast to NP deposition from the vapor phase (i.e., evaporation), the ITO surface can be considered to be a solid reservoir of In atoms thanks to H plasma reduction. On one hand, below the In melting temperature, solid In NP formation is governed by the island-growth mode, which is a self-limiting process because the H plasma/ITO interaction will be gradually eliminated by the growing In NPs that cover the ITO surface. On the other hand, we show that above the melting temperature In droplets prefer to grow along the grain boundaries on the ITO surface and dramatic coalescence occurs when the growing NPs connect with each other. This growth-connection-coalescence behavior is even strengthened on In/ITO bilayers, where In particles larger than 10 μm can be formed, which are made of evaporated In atoms and in situ released ones. Thanks to this understanding, we manage to disperse dense evaporated In NPs under H plasma exposure when inserting an ITO layer between them and substrate like c-Si wafer or glass by modifying the substrate surface chemistry. Further studies are needed for more precise control of this self-assembling method. We expect that our findings are not limited to ITO thin films but could be applicable to various metal NPs generation from the corresponding metal oxide thin films.
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http://dx.doi.org/10.1021/acs.langmuir.7b01743DOI Listing
October 2017
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