Nanowire Arrays Research Articles

Improved electrical and thermoelectric properties of electrodeposited Bi1-xSbx nanowire networks by thermal annealing

Arrays of thermoelectric nanowires embedded in organic films are attracting increasing interest to fabricate flexible thermoelectric devices with adjustable dimensions and complex shapes, useful for sustainable power sources of portable...

Surface energy and stress driven growth of extremely long and high-density ZnO nanowires using a thermal step-oxidation process.

Formation of highly crystalline zinc oxide (ZnO) nanowires with an extremely high aspect ratio (length = 60 μm, diameter = 50 nm) is routinely achieved by introducing an intermediate step-oxidation method during the thermal oxidation process of thin zinc (Zn) films. High-purity Zn was deposited onto clean glass substrates at room temperature using a vacuum-assisted thermal evaporation technique. Afterwards, the as-deposited Zn layers were thermally oxidized under a closed air ambient condition at different temperatures and durations. Structural, morphological, chemical, optical and electrical properties of these oxide layers were investigated using various surface characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoemission spectroscopy (XPS). It was noticed that the initial thermal oxidation of Zn films usually starts above 400 °C. Homogeneous and lateral growth of the ZnO layer is usually preferred for oxidation at a lower temperature below 500 °C. One-dimensional (1D) asymmetric growth of ZnO started to dominate thermal oxidation above 600 °C. Highly dense 1D ZnO nanowires were specifically observed after prolonged oxidation at 600 °C for 5 hours, followed by short-step oxidation at 700 °C for 30 minutes. However, direct oxidation of Zn films at 700 °C resulted in ZnO nanorod formation. The formation of ZnO nanowires using step-oxidation is explained in terms of surface free energy and compressive stress-driven Zn adatom kinetics through the grain boundaries of laterally grown ZnO seed layers. This simple thermal oxidation process using intermittent step-oxidation was found to be quite unique and very much useful to routinely grow an array of high-density ZnO nanowires. Moreover, these ZnO nanowires showed very high sensitivity and selectivity towards formaldehyde vapour sensing against few other VOCs.

High sensitive SERS film of Ag-coated aggregated nanowire structure and benzene gas detection

A highly sensitive surface-enhanced Raman spectroscopy (SERS) film was fabricated based on anodic aluminum oxide template and Ag coating techniques. The array of alumina nanowires of ∼5 μm length and 26 nm thickness was fabricated and then made collapse to build a micro-scale funnel array, where each cell consists of hundreds of nanowires. Ag film was deposited on the nanowire structure by thermal evaporation. Due to numerous tapered nanogaps and efficient illumination of incident light in the micro-funnel structures, Raman signal enhancement factor (E.F.) as high as ∼1.8 × 107 could be obtained at 785 nm. The SERS film functionalized by 1-propanethiol was used for benzene gas detection, where the sensitivity of <0.3 ppm (3-σ) was realized within 120 s. This nanostructure is expected to be widely used for highly sensitive chemical and bio-sensors and have higher E.F. when the morphology is optimized further.

The dopant (n- and p-type)-, band gap-, size- and stress-dependent field electron emission of silicon nanowires.

This study investigates the electron field emission (EFE) of vertical silicon nanowires (Si NWs) fabricated on n-type Si (100) and p-type Si (100) substrates using catalyst-induced etching (CIE). The impact of dopant types (n- and p-types), optical energy gap, crystallite size and stress on EFE parameters has been explored in detail. The surface morphology of grown SiNWs has been characterized by field emission scanning electron microscopy (FESEM), showing vertical, well aligned SiNWs. Optical absorption and Raman spectroscopy confirmed the presence of the quantum confinement (QC) effect. The EFE performance of the grown nanowire arrays has been examined through recorded J-E measurements under the Fowler-Nordheim framework. The Si NWs grown on p-type Si showed a minimum turn-on field and also a higher field enhancement factor. The band-bending diagram also suggests a lower barrier height of p-type Si NWs compared to n-type Si NWs, which plays a key role in enhancing the EFE performance. These investigations suggest that dopant types (n- and p-types), band gap, crystallite size and stress influence the EFE parameters and Si NWs grown on p-type Si (100) substrates are much more favorable for the investigation of EFE properties.

Magnetism of metastable γ-Fe85Pd15 nanowire arrays across an unusually broad temperature range (5 K to 800 K).

Arrays of 50 nm diameter Fe85Pd15 cylindrical nanowires were electrochemically grown, crystallizing in a metastable γ-Fe(Pd) fcc A1 disordered solid solution. After performing a heating-cooling thermal cycle between 300 K and 1000 K, the γ-Fe(Pd) fcc metastable phase still predominates (97%), coexisting with a not-fully-identified minority phase. The thermal cycling induces a moderate increase in the crystallite size and a reduction of the lattice parameter although leading to a significant heating-cooling magnetic hysteresis. No further changes in temperature-dependent magnetization, M(T), are observed during subsequent cycling. The full-range (5 K to 800 K) saturation magnetization Ms(T) curve is quite accurately described by a phenomenological expression, which provides a Bloch-type contribution as T → 0 and undergoes the critical behavior near the Curie temperature TC. An upturn in Ms(T) is observed below 100 K which is described by a spin-glass-like second contribution, with freezing temperature Tf = (80 ± 2) K, and kBTf comparable to the exchange interactions in Fe-Pd systems. A Curie temperature of TC = 830 K, and a critical exponent value β = 0.42 ± 0.05 are estimated. These regimes (below and above 100 K) are also observed in the magnetization process. The temperature dependence of coercivity between 100 K and 800 K is consistent with a nucleation/propagation remagnetization mechanism, with activation energy of (320 ± 20) kJ mol-1 and critical field for magnetization reversal of (65 ± 1) mT, at 0 K. The analysis of the effective magnetic anisotropy as a function of temperature allows us to conclude that it essentially arises from the balance between different magnetostatic contributions.

Switchable selectivity to electrocatalytic reduction of furfural over Cu2O-derived nanowire arrays.

Electrocatalytic reduction of biomass-derived furan compounds provides a green and sustainable approach to produce value-added fuels and chemicals. Despite the achievements in unimolecular transformation, C-C coupling which holds great promise to yield precursors for high-density fuels has not received extensive attention. Herein, we report a Cu2O-derived nanowire array material with switchable selectivity to electrocatalytic reduction of furfural depending on the electrolyte pH. Besides a high selectivity of 98.4% to furfuryl alcohol via hydrogenation at pH 9.5, the Cu2O-derived array structure also exhibits a high selectivity of 83.5% to hydrofuroin via C-C coupling at pH 14. Upon control experiments and detailed characterization of the electrodes, the array architecture is proposed to decrease the diffusion of ketyl radicals which are the key intermediates for C-C coupling. The confined diffusion results in a high local concentration of the radicals in the array and facilitates their collision for enhancing the formation of hydrofuroin.

Controlling by Defects of Switching of ZnO Nanowire Array Surfaces from Hydrophobic to Hydrophilic: First-Principles Calculations

Controlling by Defects of Switching of ZnO Nanowire Array Surfaces from Hydrophobic to Hydrophilic: First-Principles Calculations

Construction of NiCo2S4−xPx nanowire arrays for efficient hydrogen evolution reactions in both acidic and alkaline media

Construction of NiCo2S4−xPx nanowire arrays for improved HER performances in both acidic and alkaline media.

Templated Synthesis of CsPbBr3 Nanowire Arrays Toward Low Current Drift and Stable X-ray Detector

All-inorganic halide perovskite CsPbBr3 with superior environmental stability, remarkable radiation hardness and great defect tolerance has emerged as a competitive material in radiation detection. However, the operation stability of CsPbBr3...

Fabrication and Electrochemical Analysis of NiCo2O4@Ni-MOF Nanoarchitectonics Composites on Ni-Foam Substrate for Supercapacitor Electrodes

To produce the free-standing electrodes, a binder-free direct growth method was employed for electrode fabrication. A NiCo2O4@Ni-MOF (metal–organic framework) composite was synthesized using a one-pot hydrothermal method. Initially, a NiCo2O4 nanowire array was cultivated on Ni foam, serving as a connecting bridge to ensure robust adherence of the Ni-MOF to the substrate. The structures of NiCo2O4 nanowire arrays exhibit the capacity for numerous redox reactions. Hybridizing MOF with transition metal oxide (TMO) nanoarchitectures can significantly alleviate the small specific surface area and aggregation tendency of TMOs. The highest energy storage capacity was obtained when the ratio of nickel to terephthalic acid (TPA) was 4:1. NiCo2O4@Ni-MOF (Ni:[Formula: see text]:1) exhibited a high storage capacitance of 1700[Formula: see text]F/g. The integration of MOF with TMO nanoarchitectonics as materials for supercapacitor electrodes can enhance porous structure and facilitate diffusion during both charging and discharging processes.

Rapid spread, slow evaporation: a long-lasting water film on hydrogel nanowire arrays for continuous wearables.

A successful flexible wearable not only has to fulfill its function, but also has to ensure long-term wettability and comfort during wearing. In biological systems, tears spread rapidly across the cornea to ensure clear imaging while slowly evaporating to maintain moisture in the eyes. This dynamic behavior of 'rapid spread, slow evaporation' ensures durative humidity and comfort, which can provide design guidelines for continuous wearable devices. However, realizing this dynamic process in vitro remains a challenge. Herein, inspired by a healthy ocular surface, we biomimetically construct a hybrid surface featuring mucin-like hydrophilic layer@hydrogel nanowire arrays (HL@HNWs). A droplet (2 μL) rapidly spreads into a thin film, stabilizing for ∼10 minutes, whereas the contrast sample rapidly ruptures and dewets within 1 minute. We demonstrate that enhancing the proportion of hydrated water (HW), which includes intermediate water (IW) and bound water (BW), and introducing the capillary resistance of the nanowire arrays could synergistically stabilize the water film and improve the wettability. Hydrogel-based nanowire array contact lenses can ensure wettability during continuous wear, and a stable water film can substantially improve comfort and provide superior visual quality.

Rationalization of the light-induced electron injection mechanism in a model 1D ZnO nanowire-dye complex: insights from real-time TD-DFTB simulations.

Zinc oxide nanowires (ZnO NWs) possess a unique one-dimensional (1D) morphology that offers a direct pathway for charge transport. In this article, we present the first application of the real-time time-dependent density functional tight-binding (real-time TD-DFTB) method for a model hybrid system consisting of a catechol molecule adsorbed on a ZnO nanowire. The rationalization of the photoinduced electron injection to the 1D nanostructure is attained through quantum dynamics simulations, stressing the role of charge transfer in the new optical transitions upon dye adsorption. We provide a momentum-resolved picture of the photoexcitation dynamics, highlighting the charge accumulation in certain k-points, which could improve our understanding of these ultrafast processes. Finally, in the context of dye-sensitized solar cells (DSSCs) based on ZnO NW arrays, we provide a method to calculate the photoresponse obtaining similar results to experiments. This work paves the way towards the fast and accurate theoretical design of 1D optoelectronic nanodevices.

Vertical MOF film supported on an organic–inorganic mixed substrate for complex wastewater purification

Flexible metal–organic framework (MOF) films are greatly desired for the separation of hazardous molecules and ions from wastewater. The current MOF films are usually horizontally deposited on the substrates, and thus restricted by brittleness, low exposure of surface area, as well as poor separation functions. Here, an organic–inorganic mixed substrate is firstly fabricated by growing hydroxyapatite (HA) nanowire arrays on the cellulose fiber (CF). Subsequently, MIL-100(Fe) nanocrystals are assembled on the surfaces of HA nanowire arrays through a layer-by-layer manner, leading to a unique vertical MOF film. The resulting vertical MOF films show competitive advantages over the horizontal counterparts: (i) they show excellent flexibility and they are tolerant to serious physical damage; (ii) they have multiple separation functions including ion exchange of HA, excellent adsorption of MOFs, and strong electrostatic interaction of CF; and (iii) the agglomeration of MIL-100(Fe) nanocrystals is effectively suppressed. Therefore, the average roughness, specific surface area, and average pore size of films are optimized. As a result, the vertical MOF films show universal separation of positively/negatively-charged dyes and Pb2+ ion, with high removal rates of > 94 %. More appealing, the mixed pollutants in the complex wastewater can be one-step separated through the vertical MOF films, with high removal rates of > 96 %.

Designing CuO@MnCo2O4 nanowire arrays electrode on copper foam and foil substrates via chemical synthesis methods for asymmetric supercapacitor

In this study, CuO nanowires were grown on copper foam (Cufoam) and copper foil (Cufoil) substrate with a cost-effective anodization method as core, and then MnCo2O4 nanowires were grown by hydrothermal synthesis method and three-dimensional (3D) core-shell nanowire arrays (NWAs) were obtained. The synthesized CuO NWAs, which provide a high surface area, contribute to the capacitance with the faradaic redox reaction and act as a current collector for the MnCo2O4 NWAs. Therefore, the 3D electrode design can increase the redox reaction, shorten the ions diffusion pathway, and exhibit low intrinsic resistance. The areal capacitance values of Cufoil/CuO, Cufoam/CuO, and Cufoam/CuO@MnCo2O4 electrodes were obtained at a current density of 0.5 mA cm−2 as 0.21, 1.02, and 2.82 F cm−2, respectively. The Cufoam/CuO@MnCo2O4 NWAs electrode exhibits excellent cycling stability of 97.3 % retention after 5000 cycles. In addition, an asymmetric supercapacitor (ASC) device was assembled by using the Cufoam/CuO@MnCo2O4 electrode and active carbon (AC) as the positive and negative electrodes, respectively. The ASC device operates in a potential range of 0–1.5 V and an energy density of up to 7.1 × 10−2 mWh cm−2 at a power density of 1.56 mW cm−2. This work may contribute to developing low-cost materials for energy storage devices.

(Invited) Local pH in the (Photo/Electro) Catalytic Environment

(Photo)electrodes designed for improved efficiency and selectivity for CO2 reduction are often nanostructured, for example highly roughened metal films, nanowire arrays, and catalyst particles within a gas diffusion electrode. In all cases, local pockets of water with dissolved CO2 and ions are necessary for the reduction reaction. Although these regions are thought of as having a pH, they are often too small to have a well-defined pH or be at thermodynamic equilibrium until a minimum electrolyte pool size is reached. Computational studies using stochastic chemical kinetics provide a window into this environment, bridging the nanometer scale to the bulk-like scale. The calculations show that the compositions of these regions are characterized by large concentration fluctuations including periods of time when some ions are not present at all. The calculations enable useful trends in electrolyte composition to be identified as a function of electrolyte pool size, providing insights to the complex environments surrounding the catalytic center.

(Invited) Gravitational Level Effects on Electrochemical Interfacial Phenomena

Electrochemical copper refining technology invented in Niagara area made a great progress over more than 100 years through better understanding of natural convection phenomena. Ionic mass-transfer rate enhanced by natural convection developing along 1m high vertical electrode surfaces has been unconsciously utilized by trial-and-error method. As the local electrolyte composition is partly stratified in an electrolytic cell (roughly 5m long x 1.3m wide x 1.3m depth). The industrial electrolytic tank house is composed of about 1000 cells through which the electrolyte is continuously supplied. Thus, the electrolyte circulation is a key technology in industrial copper refining processes as well as appropriate selection of effective additive and stable sedimentation of anode slime containing precious metals on the electrolytic tank bottom.On the other hand, Cu nanowire arrays were electrodeposited potentiostatically with PC filter template in two kinds of electrolytic cell configurations: cathode over anode (C/A) and anode over cathode (A/C). The effect of gravitational level on the coupling phenomena between the morphological variation and the ionic mass transfer rate in nanosized pores(a mesoscopic scale of a fewμm high and 30nm in diameter) was also found. Hitherto, the coupling phenomena accompanied with the electrochemical interfacial reactions confined in such a mesoscopic space has not been studies in spite of the great technological interest for the production of micro- or meso-scale fabrication techniques encountered in microelectronics and energy conversion & storage technology field. The initial stage including nucleation and growth process during electrochemical phase transformation reactions must be at first focused to profoundly comprehend the present subject in order to reasonably design such an advanced device technology.Fundamental aspects in electrochemical processes in microgravity environments have not been frequently reported. However, Artemis projects may provide the large opportunities on the energy storage and power generation, as well as materials processing. The effects of gravitational level and magnetic field gradient on the electrochemical interfacial phenomena should be understood. The drop tower facility surely offers the appropriate & “unique” experimental opportunities to propose such research program in the future space engineering fields. Electrocrystallization of metals is selected as a good subject for starting direction of research. Its reaction mechanism is relatively simple, the deposition rate can be easily varied by changing the current density or potential, and a smooth copper film is deposited so long as it is not too thick.By the way, the damascene process has been introduced to copper wiring process in ULSI field by IBM almost 25 years ago. It is important to control the nucleation and crystal growth in the initial stages of electrodeposition process. For this purpose, many effects of additive have been intensively examined. However, few quantitative examinations have been reported on the coupling phenomena of ionic mass transfer and nucleation and crystal growth. In the present work, we introduce various gravitational levels as new parameters into the nonequilibrium electrochemical processing in order to create or tailor the unique physical properties in nano space field. It is fruitful in terms of physicochemical hydrodynamics that the experiments are done under various gravitational levels. In fact, it has been confirmed that the gravitational levels as well as the magnetic field introduce the intensified effects from that under 1 G normal environment. Here is a report to analyze the effect of gravitational level on the initial stages of Cu electrodeposition on TaN or TiN substrate.

Localized Electrochemical Deposition Using Copper Pyrophosphate-Based Electrolyte

Additive manufacturing (AM) has gained popularity across various industries due to its cost-effectiveness, low material consumption, and minimal environmental impact. Localized electrochemical deposition (LECD), as one of the AM methods, has the capability to produce microcomponents or structures at an microscale in a specific position as designed, without the need for any mask or support material[1]. By reducing copper ions in the local area according to the position of the micro-wire, 3D structures could be produced. This electrochemical deposition process has a significant advantage in that it is a low-temperature process and has lower costs compared to other processes[2].Using the LECD process, the micrometer of copper columns was conventionally deposited in copper sulfate-based electrolyte[3]. However, this electrolyte has the possibility to cause damage to the metal substrate used as the cathode due to its low pH, resulting in metal dissolution. The utilization of copper pyrophosphate-based electrolyte, which is a solution with a pH close to neutral, can solve this problem. Also, copper pyrophosphate-based electrolyte offers an advantage over conventional alkaline-based electrolytes in that it removes cyanide pollution of the environment and hazards to human health.[4]In this study, the microanode was employed using a platinum wire(100 μm in diameter), while a copper substrate was employed as the cathode in the electrochemical deposition process. The micrometer copper columns were deposited using copper pyrophosphate-based electrolyte by varying the main electrochemical deposition factors, such as applied potential and pulse duty cycle. In addition The surface morphology of the deposited micrometer-scale copper columns was observed through scanning electron microscopy.REFERENCES[1] Suryavanshi, Abhijit P., and Min-Feng Yu. "Probe-based electrochemical fabrication of freestanding Cu nanowire array." Applied Physics Letters 88.8 (2006): 083103.[2] Madden, John D., and Ian W. Hunter. "Three-dimensional microfabrication by localized electrochemical deposition." Journal of microelectromechanical systems 5.1 (1996): 24-32.[3] Lin, J. C., et al. "Localized electrochemical deposition of micrometer copper columns by pulse plating." Electrochimica Acta 55.6 (2010): 1888-1894.[4] Chen, C-C. "A New Process for Cyanide-Free Copper Plating."Electroplating and Pollution Control 23.4 (2003): 10-11.

(Invited) Confined and Free-Standing Perovskite Nanowires for X-Ray Detection

Metal halide perovskites (MHPs) have shown excellent results in many applications, including X-ray scintillation detection. Nanowires could offer improved sensitivity by exploiting nanophotonic light guiding, and the MHP stability could be improved by growing nanowires physically protected in anodized aluminum oxide (AAO). We use a one-step solution low-temperature method to grow arrays of long single-crystalline CsPbBr3 nanowires in an AAO template. The diameters can be adjusted by the AAO template, ranging from 30 to 360 nm, and the length can be controlled up to 15 μm (Fig 1(a)) [1]. The nanowires show excellent stability, with no obvious lack in photoluminescence after months of storage in air. The X-ray scintillation shows no systematic degradation over 2 weeks of continuous X-ray exposure, but an unexpected positive correlation with room humidity. The excellent stability allows tomographic 3D X-ray imaging at better than 3 μm resolution [2].Surprisingly, we find that free-standing CsPbBr3 nanowires can be obtained by the same method (Fig 1(b)) [3]. The length of the vertically aligned nanowires is controlled from 1 to 20 μm with the precursor amount. The nanowires are single-crystalline and exhibit excellent photoluminescence and clear light guiding (Fig 1(c)). Lithography methods for MHPs have been limited because of their solubility in polar solvents. However, we show that o-xylene can be used in a perovskite-compatible electron beam lithography (EBL) process based on nonpolar solvents [4]. Combining these results, we demonstrate single nanowire devices with excellent photoresponse. Recently, we have developed a gas-phase halide exchange method based on HCl or Cl2 to convert the green-emitting CsPbBr3 to blue-emitting CsPb(BrxCl1-x)3. [5]. Using the aforementioned EBL process, we selectively convert segments of nanowires to CsPb(BrxCl1-x)3 and create axially heterostructured nanowires (Fig 1(d)).1 Z. Zhang, H. Dierks, N. Lamers et al., "Single-Crystalline Perovskite Nanowire Arrays for Stable X-ray Scintillators with Micrometer Spatial Resolution" ACS Applied Nano Materials 5 (1), 881 (2022) http://doi.org/10.1021/acsanm.1c035752 H. Dierks, Z. Zhang, N. Lamers, and J. Wallentin, "3D X-ray microscopy with a CsPbBr3 nanowire scintillator" Nano Res. 16 (1), 1084 (2023) https://doi.org/10.1007/s12274-022-4633-73 Z. Zhang, N. Lamers, C. Sun, C. Hetherington, I. G. Scheblykin, and J. Wallentin, "Free-Standing Metal Halide Perovskite Nanowire Arrays with Blue-Green Heterostructures" Nano Lett. 22 (7), 2941 (2022) http://doi.org/10.1021/acs.nanolett.2c001374 N. Lamers, Z. Zhang, and J. Wallentin, "Perovskite-Compatible Electron-Beam-Lithography Process Based on Nonpolar Solvents for Single-Nanowire Devices" ACS Applied Nano Materials 5 (3), 3177 (2022) http://doi.org/10.1021/acsanm.2c001885 N. Lamers, Z. Zhang, I. G. Scheblykin, and J. Wallentin, "Multisegment Heterostructured CsPb(Br1-xClx)3 Perovskite Nanowires using Gas-Phase Anion Exchange" In review (2023) Figure 1

3D hierarchical NiCo2O4@Co3S4@MnS@PPy core-sheath nanowire arrays as high-performance electrode for all-solid-state asymmetric supercapacitors

To cater to the mushrooming advanced energy storage devices need, designing and preparing novel electrode materials with excellent electrochemical properties (including high capacitance and prominent cycling stability) are urgent but challenging. Here, we successfully synthesized 3D hierarchical NiCo2O4@Co3S4@MnS@PPy (NC@CS@MS@PPy) core-sheath nanowire arrays grown on highly conductive carbon cloth using a multistage process. Owing to a lot of synergy between the multiple components in the as-obtained composite, the prepared electrode material indicates an excellent specific capacitance of 2.67 F cm−2 at 1 mA cm−2 or 2557.58 F g−1 at 1 A g−1 and high cycling stability (83.64 % capacitance retention after 20,000 cycles even at a high current density of 20 mA cm−2). When coupled with the activated carbon (AC, as a negative electrode), the assembled all-solid-state NC@CS@MS@PPy//AC asymmetric supercapacitor (ASC) device showed outstanding electrochemical properties with a high area specific capacitance 684.38 mF cm−2 at 3 mA cm−2 and better long-term cycling stability (96.76 % retention of the initial capacitance after 20,000 cycles). More importantly, by taking advantaging of the multiple compositional merits and structural features of the positive electrode, the device delivered the highest energy density of 81.1 Wh kg−1 at 800 W kg−1 and retained 26.2 Wh kg−1 at the highest power density of 16 KW kg−1. Furthermore, two ASCs connected in series powered 20 red light-emitting diodes (LEDs) for >10 min. This work manifests that the prepared hierarchical NC@CS@MS@PPy core-sheath nanowire arrays have impressive potential as high-performance electrodes for supercapacitor.

Low-threshold single-mode nanowire array flat-band photonic-crystal surface-emitting lasers with high-reflectivity bottom mirrors.

A Si-based nanowire array photonic-crystal surface-emitting laser based on a flat band is designed and simulated. By introducing an air gap between the nanowire and substrate, the bottom reflectivity is significantly enhanced, resulting in much lower threshold and smaller cutoff diameter. Through adjusting the lattice constant (the distance between neighboring nanowires) and nanowire diameter, a photonic crystal structure with a flat band is achieved, in which strong interaction between light and matter occurs in the flat band mode. For the device with a small size, single-mode lasing is obtained with a side-mode suppression ratio of 21 dB, high quality factor of 3940, low threshold gain of 624 cm-1, and small beam divergency angle of ∼7.5°. This work may pave the way for the development of high-performance Si-based surface-emitting nanolasers and high-density photonic integrated circuits.