Si Nanomaterials Research Articles

Bright silicon quantum dot synthesis and LED design: insights into size–ligand–property relationships from slow- and fast-band engineering

Abstract Multicolor, bright silicon quantum dots (SiQDs)—SiQDs with photoluminescence in a range of colors and quantum yields (PLQYs) of >90%—are promising heavy-metal-free light sources for full-color displays, lighting, and biomedical imaging. Colloidal SiQDs can be used to manufacture devices via printing and roll-to-roll processing. Furthermore, the in vivo use of biodegradable SiQDs and Si nanomaterials, for imaging cancer cells and as drug delivery systems, has been demonstrated. However, a large body of research demonstrates that the photoluminescence (PL) wavelength and PLQY of colloidal SiQDs are dependent not only on the SiQD particle size but also on the methods and/or procedures and chemical reagents used to synthesize them. This is because SiQDs are quite sensitive to both the intrinsic properties of Si and external factors. These intrinsic and external factors can be respectively linked to different PL mechanisms: the quantum confinement effect, which produces a slow-decaying “S”-band PL signal, and surface ligand effects, corresponding to fast-decaying “F”-band PL. This review focuses on mechanistic insights into the relationships linking the structures, ligands, and optical properties of SiQDs. Synthesis methods and the application performance of bright multicolor colloidal SiQDs, based on excellent state-of-the-art experimental and theoretical studies, are also reviewed.

Key developments in magnesiothermic reduction of silica: insights into reactivity and future prospects.

Porous Si (p-Si) nanomaterials are an exciting class of inexpensive and abundant materials within the field of energy storage. Specifically, p-Si has been explored in battery anodes to improve charge storage capacity, to generate clean fuels through photocatalysis and photoelectrochemical processes, for the stoichiometric conversion of CO2 to value added chemicals, and as a chemical H2 storage material. p-Si can be made from synthetic, natural, and waste SiO2 sources through a facile and inexpensive method called magnesiothermic reduction (MgTR). This yields a material with tunable properties and excellent energy storage capabilities. In order to tune the physical properties that affect performance metrics of p-Si, a deeper understanding of the mechanism of the MgTR and factors affecting it is required. In this perspective, we review the key developments in MgTR and discuss the thermal management strategies used to control the properties of p-Si. Additionally, we explore future research directions and approaches to bridge the gap between laboratory-scale experiments and industrial applications.

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Si nanomaterials in lithium-ion battery anode

Due to its high specific capacity, silicon anode has gained interest on a global scale as the anode of next-generation lithium-ion batteries (LIBs). However, it is challenging for silicon anodes to replace graphite anodes for widespread use due to the inevitable volume expansion and SEI film development generated by silicon during the lithiation/delithiation process. Among these, the advancement of nanotechnology has sped up the development of silicon anodes. This paper reviews nanotechnology applied in the Si anode to improve the battery performance. The volume expansion of Si is effectively decreased by reducing the volume of the silicon anode in order to increase its specific surface area. Additionally, the smaller negative electrode reduces the distance traveled by lithium ions, greatly increasing the silicon negative electrode's efficiency. At present, the main silicon nano-anode materials include nanoparticles, nanowires, nanosheets, nanotubes, nanoporous materials and so on. It is hoped that this review will provide a deep prospect introduction to the nano-silicon anode. Pure silicon nanoparticles and silicon nanowires, and new nanomaterials composed of them with graphite, graphene, metals, etc.

Influence of Gate Oxide and Subthreshold Leakage in Domino Using Si Nano-Materials

Influence of Gate Oxide and Subthreshold Leakage in Domino Using Si Nano-Materials

The Investigation of Gate Oxide and Temperature Changes on Electrostatic and Analog/RF and Behaviour of Nanotube Junctionless Double-Gate-All Around (NJL-DGAA) MOSFETs using Si Nano-materials

The Investigation of Gate Oxide and Temperature Changes on Electrostatic and Analog/RF and Behaviour of Nanotube Junctionless Double-Gate-All Around (NJL-DGAA) MOSFETs using Si Nano-materials

Restricted-magnesium-vapor-reduction of amorphous SiO/C precursors to polycrystalline Si/SiOx/C hybrid anodes.

Considering the electrochemical activity/stability and preparation feasibility of silicon (Si) nanomaterials, we designed a restricted-magnesium-vapor-reduction to fabricate sustainable Si/SiOx/C porous anodes with nanopores and polycrystalline structures.

Silicon nanostructures and nanocomposites for antibacterial and theranostic applications

Silicon (Si) nanomaterials are extensively explored to address the multidrug resistance bacteria/diseases and to enable developments of novel and innovative approaches for next-generation highly efficient, cost-effective, and reliable multifunctional biomedical tools. This article reviews the contemporary developments in the utilization of Si nanostructures (Si-NSs) and nanocomposites for antibacterial surfaces and theranostic agents as powerful instruments to tackle pathogenic bacteria and diseases related to them. Realization of nature-inspired antibacterial surfaces, photoresponsive smart antibacterial surfaces, and selective functionality of Si-NSs has been discussed by biomedical imaging and drug delivery applications of Si-NSs. Photoresponsive Si nanocomposite systems enable in-situ non-invasive process monitoring utilizing surface-enhanced Raman spectroscopy (SERS) or photothermal imaging phenomenon is also addressed. Finally, crucial challenges and several research trends of implementing Si-NSs and their hybrid systems as multifunctional platforms for advanced biomedical tools and their clinical translation are highlighted.

Electrochemical Synthesis of Multidimensional Nanostructured Silicon as a Negative Electrode Material for Lithium-Ion Battery.

Silicon (Si) is a promising negative electrode material for lithium-ion batteries (LIBs), but the poor cycling stability hinders their practical application. Developing favorable Si nanomaterials is expected to improve their cyclability. Herein, a controllable and facile electrolysis route to prepare Si nanotubes (SNTs), Si nanowires (SNWs), and Si nanoparticles (SNPs) from halloysite clay (Al2(OH)4Si2O5·nH2O) is developed. It is found that HCl-etching temperature and electrolysis potential play key roles in controlling the morphologies of Si. After being HCl-etched at 80 or 90 °C, halloysite clay can be reduced into Si nanotubes at a suitable potential of -1.45 V or Si nanowires at a wide potential from -1.40 to -1.60 V, respectively, while Si nanoparticles can be only obtained at a more negative potential of -1.60 V without HCl-etching. The different morphologies of Si are associated with the change of reduction kinetics after HCl-etching. Besides, when serving as negative electrode materials for LIBs, Si nanotubes exhibit better Li storage performance than Si nanoparticles and Si nanowires, showing a capacity of 3044 mAh g-1 at 0.20 A g-1 and 1033 mAh g-1 after 1000 cycles at 1 A g-1. This work provides a controllable approach for the synthesis of Si nanomaterials for LIBs.

A Strategic Approach to Use Upcycled Si Nanomaterials for Stable Operation of Lithium-Ion Batteries.

Silicon, as a promising next-generation anode material, has drawn special attention from industries due to its high theoretical capacity (around 3600 mAh g−1) in comparison with conventional electrodes, e.g., graphite. However, the fast capacity fading resulted by a large volume change hinders the pragmatic use of Si anodes for lithium ion batteries. In this work, we propose an efficient strategy to improve the cyclability of upcycled Si nanomaterials through a simple battery operation protocol. When the utilization degree of Si electrodes was decreased, the electrode deformation was significantly alleviated. This directly led to an excellent electrochemical performance over 100 cycles. In addition, the average charge (delithation) voltage was shifted to a lower voltage, when the utilization degree of electrodes was controlled. These results demonstrated that our strategic approach would be an effective way to enhance the electrochemical performance of Si anodes and improve the cost-effectiveness of scaling-up the decent nanostructured Si material.

Silicon nanorod formation from powder feedstock through co-condensation in plasma flash evaporation and its feasibility for lithium-ion batteries

Si nanowires/nanorods are known to enhance the cycle performance of the lithium-ion batteries. However, viable high throughput production of Si nanomaterials has not yet attained as it requires in general expensive gas source and low-rate and multiple-step approach. As one of the potential approaches, in this work, we report the fast-rate Si nanorod synthesis from low-cost powder source by the modified plasma flash evaporation and the fundamental principle of structural formation during gas co-condensation. In this process, while Si vapors are formed in high temperature plasma jet, molten copper droplets are produced separately at the low temperature region as catalysts for growth of silicon nanorods. Si rods with several micrometers long and a few hundred of nanometers in diameter were produced in a single process at rates up to 40 µm s−1. The growth of the Si nanorods from powder source is primarily characterized by the vapor–liquid–solid growth which is accelerated by the heat extraction at the growth point. The battery cells with the Si nanorods as the anode have shown that a higher capacity and better cyclability is achieved for the nanorods with higher aspect ratios.

Rapid CO2 exfoliation of Zintl phase CaSi2-derived ultrathin free-standing Si/SiOx/C nanosheets for high-performance lithium storage

Semiconducting silicon (Si) nanomaterials have great potential for the applications in electronics, physics, and energy storage fields. However, to date, it is still a challenge to realize the batch production of Si nanomaterials via efficient and low-cost approaches, owing to some long-standing shortcomings, e.g., complex procedures and time and/or energy consumption. Herein, we report a green and inexpensive method to rapidly obtain two-dimensional (2D) free-standing Si/SiOx nanosheets via the rapid thermal exfoliation of layered Zintl compound CaSi2. With the help of the rapid exfoliation reaction of CaSi2 in the atmosphere of greenhouse gas CO2, and the following mild sonication, 2D free-standing Si/SiOx nanosheets can be produced with very high yield. After applying the coating of a thin carbon outer layer, the electrodes of Si/SiOx/C nanosheets serving as the anodes for lithium-ion batteries exhibit ultrahigh reversible capacity and outstanding electrochemical stability. We expect this study will provide new insights and inspirations for the convenient and batch production of nanostructural Si-based anode materials towards high-performance lithium-ion batteries.

(Invited) Silicon Nanosheets as Candidates for Silicon-Based Optoelectronics

Colloidal Group IV nanomaterials (Si, Ge, Sn and their alloys) are of great interest due to their potential to offer broadly tunable optical properties. By manipulating composition, size, or surface chemistry Group IV nanomaterials have potential to serve as nontoxic, earth abundant phosphors or semiconductors that can be used for optoelectronic applications that span the ultraviolet to the mid-infrared spectral ranges. The synthesis of colloidal Group IV nanostructures is challenging due to the highly covalent character of Si and Ge, and typically require temperatures in excess of 400°C to form crystalline particles. We have recently reported new synthetic methods for Si and Ge nanomaterials derived from precursors synthesized in the solid-state, including suboxides and Zintl phases. In each of these cases, colloidal nanostructures can be accessed by selectively removing unwanted components from the solid-state precursor, liberating nanostructures that are terminated with atomic or molecular species such as hydrogen atoms or methyl groups. We also characterize the structural properties of the Group IV nanostructures that we synthesized using a combination of infrared spectroscopy, solid-state NMR, and pair distribution function analysis to confirm the structure and order. In the case of Si and Ge, single-atom thick nanosheets were synthesized, their stability and decomposition at elevated temperatures were characterized. The optical properties of Group IV nanomaterials have sparked debate over the past few decades. We found that Si nanosheets exhibit fast (nanosecond) photoluminescence lifetime, which is several orders of magnitude greater than Si nanocrystals, and offer potential explanations for the observed difference. Finally we show that Si and Ge nanocrystals and nanosheets can be used for sensing applications, including infrared photodetectors and ionophore-based sensing schemes.

Enhanced capacity retention based silicon nanosheets electrode by CMC coating for lithium-ion batteries

Si nanosheets (SiNS) as two dimensional Si nanomaterials are promising candidates for anodes of lithium ion batteries (LIBs) by their large surface area and excellent mechanical durability. In this study, we fabricated polymeric binder (carboxymethyl cellulose, CMC) coated SiNS electrodes using a spin-coating process and characterized the electrochemical properties. The CMS coated SiNS electrodes were homogeneously covered with a CMC polymer layer and showed the improved capacity retention with maintaining over 90% of initial capacity after several cycles. The result of electrochemical impedance spectroscopy indicates that the CMC layer provide the chemical stability of Si surface and suppress the continuous growth of the SEI layer. Furthermore, CMC coated layer on SiNS provide improved mechanical stability that maintains the adhesion of SiNS to the current collector during the discharge–charge cycles.

Solvent‐Induced Growth of Free‐Standing 2D Si Nanosheets

2D Si nanomaterials draw great interest owing to their fascinating properties and potential applications in electronic devices, catalysts, and energy storage and conversion devices. However, high-quality and large-scale synthesis of Si nanosheets remains a big challenge, despite the limited reports on their preparations via chemical exfoliation of layered Zintl silicide, magnesiothermic reduction of layered silicon oxide, and chemical vapor deposition. In this work, a facile, solution method to produce free-standing Si nanosheets in high yields and low cost, based on the reaction of commercial magnesium powder with trichlorosilane and tripropylamine in dichloromethane under mild conditions, is reported. The prepared Si nanosheets have an average thickness of ≈2nm and show photoluminescence. Experiments demonstrate that the key to the formation of Si nanosheets is the use of dichloromethane as a solvent. This method can be used to prepare Si nanosheets in large scale for various potential applications and possibly Si crystals with specific crystal morphology.

Cost-Effective Synthesis of Silicon Quantum Dots

Silicon (Si) nanomaterials with bright luminescence in the visible region are promising materials for use as the next-generation light source in displays, lighting, and biomedical imaging. A scalab...

Revealing the local crystallinity of single silicon core-shell nanowires using tip-enhanced Raman spectroscopy.

Tip-enhanced Raman spectroscopy is combined with polarization angle-resolved spectroscopy to investigate the nanometer-scale structural properties of core–shell silicon nanowires (crystalline Si core and amorphous Si shell), which were synthesized by platinum-catalyzed vapor–liquid–solid growth and silicon overcoating by thermal chemical vapor deposition. Local changes in the fraction of crystallinity in these silicon nanowires are characterized at an optical resolution of about 300 nm. Furthermore, we are able to resolve the variations in the intensity ratios of the Raman peaks of crystalline Si and amorphous Si by applying tip-enhanced Raman spectroscopy, at sample positions being 8 nm apart. The local crystallinity revealed using confocal Raman spectroscopy and tip-enhanced Raman spectroscopy agrees well with the high-resolution transmission electron microscopy images. Additionally, the polarizations of Raman scattering and the photoluminescence signal from the tip–sample nanogap are explored by combining polarization angle-resolved emission spectroscopy with tip-enhanced optical spectroscopy. Our work demonstrates the significant potential of resolving local structural properties of Si nanomaterials at the sub-10 nanometer scale using tip-enhanced Raman techniques.

Lithiation Kinetics in Silicon/Mn3O4 Core–Shell Nanoparticles Anodes for Li-Ion Battery

Silicon is predicted to become a significant component of high energy density Li-ion anodes. Mn-based cathodes for Li-ion batteries have been widely investigated in past years and Mn dissolution into the electrolyte, migration, and deposition on the anode’s solid electrolyte interphase present a major challenge. In this work, we intentionally synthesize manganese oxide with several nanoscale thicknesses on a Si nanomaterial and follow the electrochemical behavior of the core–shell nanoparticles as Li-ion anode. The structure of the nanocomposites is investigated using high-resolution scanning electron microscopy, high-resolution transition electron microscopy, X-ray diffraction, and electron paramagnetic resonance. The synthesis yields uniform nanoshells of Mn3O4 haussmanite phase. We demonstrate that the haussmanite phase is electrochemically active, and its presence improves the lithiation process during cycling. This study reveals that the formation of a thin shell of manganese oxide phase on Si anode can improve the lithiation kinetics of the Si nanomaterials, while a thicker shell slows down the kinetics. In summary, to a certain extent, the contamination of Si anode materials from Mn-based cathodic materials could have a positive impact on their electrochemical behavior.

Structural Analysis of Luminescent Si Nanomaterials Synthesised from Rice Husks

Structural Analysis of Luminescent Si Nanomaterials Synthesised from Rice Husks

Controllable silicon nanostructures featuring stable fluorescence and intrinsic in vitro and in vivo anti-cancer activity.

In this manuscript, we demonstrate that the in situ growth of fluorescent silicon (Si) nanomaterials is stimulated when organosilicane molecules interact with different green teas, producing multifunctional Si nanomaterials with controllable zero- (e.g., nanoparticles), two- (e.g., nanosheets), and three- (e.g., nanospheres) dimensional nanostructures. Such green tea-originated Si nanomaterials (GTSN) exhibit strong fluorescence (quantum yield: ∼19-30%) coupled with ultrahigh photostability, as well as intrinsic anti-cancer activity with high specificity (e.g., the GTSN can accurately kill various cancer cells, rather than normal cells). Taking advantage of these unique merits, we further performed systematic in vitro and in vivo experiments to interrogate the mechanism of the green tea- and GTSN-related cancer prevention. Typically, we found that the GTSN entered the cell nuclei and induced cell apoptosis/death of cancer cells. The prepared GTSN were observed in vivo to accumulate in the tumour tissues after 14-d post-injection, leading to an efficient inhibition of tumour growth. Our results open new avenues for designing novel multifunctional and side-effect-free Si nanomaterials with controllable structures.