Carbon nanodot arrays grown as replicas of specially widened anodic aluminum oxide pore arrays

Via a specially widened anodic aluminum oxide (AAO) pore arrays, carbon nanodot arrays with uniform size and high density were obtained through filtered cathodic arc plasma (FCAP) technique. The AAO template was prepared in oxalic acid by multi-steps to get a specially enlarged opening which plays an important role in the deposition of nanodots. The morphology of the nanodots was studied by a field emission scanning electron microscopy (FESEM). The diameter of the as-prepared nanodot demonstrated here is about 100 nm at the bottom and less than 40 nm at the top, and the density was estimated to 10¹⁰ cm⁻². Field emission properties of the nanodot arrays were investigated and a low threshold field of 5.1 V/μm at 10 mA/cm² was obtained. In this paper, the carbon nanodot arrays grown as replicas of the specially widened AAO template may support a strategy to realize the fabrication of nanodot arrays with various materials.     

Preparation and modification of well-aligned CNTs grown on AAO template

Anodic aluminum oxide (AAO) template was prepared by a two-step anodization method and cobalt particles were carefully deposited at the bottom of pores of the template. CVD method was used to grow carbon nanotubes (CNTs) on the template with this cobalt as catalyst and C₂H₂ as carbon source. Well-aligned carbon nanotubes were obtained perpendicular to the substrate. To modify the CNTs, ultrasonic treatment of the samples in alcoholic (or water) was applied and the results showed that the length of CNTs became equalized and their tips were opened without catalyst particles due to ultrasonically cutting off CNTs for the upper parts out of AAO pores. The mechanism is also discussed.     

Facile Synthesis of Carbon Dots from Biomass Material and Multi-Purpose Applications

Selective and sensitive water content measurement in organic solvents is extremely significant for both industrial use and laboratory preparation. Carbon nanodots are promising carbon nanomaterials with unique and novel properties and thus have drawn growing attention. However, the hydrothermal approach for the preparation of carbon dots always uses water as solvent, and consequently, the development of carbon dots from biomass materials for fluorescence detection of water content remains unexplored. Here, carbon dots were prepared from gallic acid via a cheap and facile one-step method. The as-prepared carbon dots present excellent sensitivity and selectivity toward water content and exhibits good linear relationships with water content in range of 0–10%. The carbon dots demonstrated a strong antioxidation capacity and colour-reaction of Fe³⁺ like gallic acid. The carbon dots also showed solid-state lighting.

     

Fabrication and magnetic behaviour of 2D ordered Fe/SiO2 nanodots array

We have demonstrated a simple and universal morphology-controlled growth of 2D ordered Fe/SiO₂ magnetic nanodots array, which was based on 2D colloidal monolayer template composed of polystyrene (PS) spheres and one-step sol-gel spin-coating technique. The Fe/SiO₂ nanodots have a well-ordered structure arranged in a hexagonal pattern. The dots have the shape of quasi-pyramidal tetrahedron, which reside in the interstitial region between three PS spheres and the substrate. Magnetic measurements reveal that the nanodots array exhibits the in-plane easy magnetization direction. Compared with the unpatterned Fe/SiO₂ thin film, the dots array has lower saturated field, higher remanence and coercivity. The present method is applicable to 2D ordered nanodots array of other magnetic materials.     

Fluorescence Turn-On Analysis of Trace Protein Based on Carbon Nanodots and Hybridization Chain Reaction

In this work, an ultrasensitive method for trace protein detection based on fluorescent carbon nanodots and hybridization chain reaction (HCR) is designed. Generally, the synthesized bright carbon nanodots are conjugated with two hairpin-structured DNA probes, respectively, which act as subsequent HCR fuel strands. Since single-stranded parts of DNA probes could be easily absorbed on graphene oxide (GO) nanosheets, fluorescence emission of carbon nanodots is effectively quenched via fluorescence resonance energy transfer. However, in the presence of target protein, the aptamer sequence in another hairpin-structured DNA probe specially interacts with target and the hairpin is opened. A single-stranded region is thus exposed, which initiates HCR by coupling with the DNA fuel strands on carbon nanodots. The formed HCR product displays a rigid, long double-stranded structure, which facilitates the release of carbon nanodots from GO surface. As a result, fluorescence of carbon nanodots is recovered and initial concentration of target protein can be estimated. This protein detection method shows a favorable linear response with a low limit of detection (2.3 fg mL⁻¹). Furthermore, it is highly selective and capable of detecting target in biological fluids like serum samples, which demonstrates the promising applications of this method.     

Nanostructuring Si surface and Si/SiO2 interface using porous-alumina-on-Si template technology. Electrical characterization of Si/SiO2 interface

In this work, anodic porous alumina thin films with pores in the nanometer range are grown on silicon by electrochemistry and are used as masking material for the nanopatterning of the silicon substrate. The pore diameter and density are controlled by the electrochemical process. Through the pores of the alumina film chemical oxidation of the silicon substrate is performed, leading to the formation of regular arrays of well-separated stoichiometric silicon dioxide nanodots on silicon, with a density following the alumina pores density and a diameter adjustable by adjusting the chemical oxidation time. The alumina film is dissolved chemically after the SiO₂ nanodots growth, revealing the arrays of silicon dioxide dots on silicon. In a next step, the nanodots are also removed, leaving a nanopatterned bare silicon surface with regular arrays of nanopits at the footprint of each nanodot. This silicon surface structuring finds interesting applications in nanoelectronics. One such application is in silicon nanocrystals memories, where the structuring of the oxidized silicon surface leads to the growth of discrete silicon nanocrystals of uniform size. In this work, we examine the electrical quality of the Si/SiO₂ interface of a nanostructured oxidized silicon surface fabricated as above and we find that it is appropriate for electronic applications (an interface trap density below 1–3×10¹⁰ eV⁻¹ cm⁻² is obtained, indicative of the high quality of the thermal silicon oxide).     

Red/Near‐Infrared Emissive Metalloporphyrin‐Based Nanodots for Magnetic Resonance Imaging‐Guided Photodynamic Therapy In Vivo

Near‐infrared emissive (NIR) porphyrin‐implanted carbon nanodots (PCNDs or MPCNDs) are prepared by selectively carbonization of free base or metal complexes [M = Zn(II) or Mn(III)] of tetra‐(meso‐aminophenyl)porphyrin in the presence of citric acid. The as‐prepared nanodots exhibit spontaneously NIR emission, small size, good aqueous dispersibility, and favorable biocompatibility characteristic of both porphyrins and pristine carbon nanodots. The subcellular localization experiment of nanodots indicates a lysosome‐targeting feature. And the in vitro photodynamic therapy (PDT) results on HeLa cells indicate the nanodots alone have no adverse effect on tumor cells, but display remarkable photodynamic efficacy upon irradiation. Moreover, MnPCNDs containing paramagnetic Mn(III) ions, which possesses good biocompatibility, NIR luminescence, and magnetic resonance imaging and efficient singlet oxygen production, are further studied in magnetic resonance imaging‐guided photodynamic therapy in vivo.     

应用于生物医疗领域的碳纳米点及其复合物

碳纳米点作为新兴的碳纳米材料,具备制备成本低、尺寸小、低毒、生物相容性高、水溶性好、易修饰、光物理性质独特等诸多优点,在生物医疗领域展现了独有的优势和应用前景。由于具有丰富的表面官能团,碳纳米点可以与靶向配体、医学影像造影剂、核酸、化学药物、光敏剂、光热转换试剂等功能性诊断治疗试剂相互作用形成复合物。目前,碳纳米点及其复合物在医学影像、基因治疗、化学药物治疗、光热、光动力治疗等生物医学诊断治疗领域的应用正在被广泛的开发和报道。这些工作对开发基于碳纳米点的医学诊断治疗试剂及其临床推进具有重要意义,为推进人类重大疾病的个体化、可视化、非入侵式、小损伤的诊断治疗提供一种新的药物体系。本文将关注应用于诊断治疗领域的碳纳米点及其复合物的设计、构建及性能研究,对已报道的基于碳纳米点的诊断治疗试剂在生物医疗领域的研究进展进行总结和讨论。     

Growth mechanisms of spatially separated copper dendrites in pores of a SiO2 template

Abstract

n-Si/SiO₂(Cu) structures with different morphologies of copper deposits are produced using the template synthesis method. Deposition of Cu nanostructures and their structural features is thoroughly studied, and mechanisms for the formation of compact and dendrite-like deposits in the pores of the SiO₂ template on the n-type single-crystal silicon substrate are established. Spatially separated copper dendrites are obtained and used to investigate the efficiency of Raman scattering enhancement using the aqueous solution of the Rhodamine 6G dye.     

Use of photoresist templates in the synthesis of highly-ordered arrays of titania nanorods

Template synthesis of nanostructures entails the deposition of the desired materials within the pores of a nanoporous membrane or solid. Nanofibrils or tubules of the desired material are obtained within the pores depending on the deposition time and parameters. Methods such as electrochemical and electroless deposition, in situ polymerization, and sol–gel process have been used to deposit nanomaterials within the nanopores of templates such as track-etch polymeric membranes and anodic alumina. This paper reports on the first use of photoresist spin-coated on a conductive glass substrate as a template for nanofabrications. TiO₂ nanofibrils in diameters were synthesized by sol–gel process within the pores of the template. Removal of the template resulted in highly-ordered arrays of nanofibrils vertically standing on the conducting glass substrate. The aspect rations of the obtained nanofibrils were similar to those of the template nanopores, 35 nm in diameter and ∼1.3 microns in length. The photoresist template is shown to be functionally similar to anodic alumina template.     

2019年5期 电子期刊

碳纳米点（碳点）是一种新型的纳米发光材料,具有优异的发光性能、良好的生物相容性、低毒性、水溶性好和表面易功能化等特性,在光电器件、生物成像、光热治疗等领域展现了潜在应用价值。然而,合成碳点的前驱体材料多种多样,合成方法各有不同,导致其发光机理复杂多样。本文主要针对使用柠檬酸作为碳源、尿素或氨水作为氮源,采用微波和溶剂热的合成方法制备的氮掺杂碳点,探索碳点的发光机理和抑制碳点聚集诱导荧光猝灭的方法,并进一步研究碳点在固态照明、可见光光通讯、生物成像和光热治疗等领域的应用前景。     

Preparation of well-aligned carbon nanotubes by pyrolysis of phenolic resin in anodic alumina pores

Well-aligned carbon nanotubes (CNTs) of high quality were synthesized by pyrolysis of phenolic resin at 800 °C in anodic alumina oxide (AAO) pores under argon protection. The innocuous source materials and safe operational conditions permit this method to synthesize well-aligned CNTs in large-scale and low cost. The formation mechanism of the synthesized CNTs is also proposed in this work by a series of visual sketches and is proved with obvious evidence. Firstly, phenolic resin nanotubes form in the template pores through the evaporation of solvent. Heat treatment then transfers these tubes into CNTs.     

Influence of induced anisotropy on the processes of magnetization reversal of cobalt circular nanodots

The magnetic structure and the processes of magnetization reversal of individual cobalt nanodots and arrays of cobalt nanodots have been studied using the magneto-optical Kerr effect and magnetic force microscopy. Arrays of nanodots have been prepared by ion etching from a continuous cobalt film. Magnetic anisotropy is induced during deposition of the cobalt films. The nanodots have the diameter d = 600 nm and the period varying from 1.5d to 3.0d. Magnetic force microscopy images have shown that the induced magnetic anisotropy affects the orientation of magnetization of noninteracting nanodots and the direction of displacement of the magnetic vortex center in the nanodots coupled by the dipole-dipole interaction.     

Self-organized InGaN nanodots grown by metal-organic chemical vapor deposition system

It has been demonstrated that self-organized InGaN nanodots can be vertically grown by utilizing metal-organic chemical vapor deposition epitaxy (MOCVD). We report the investigation of the characteristics of InGaN with various indium contents and the fabrication of self-organized InGaN nanodots will also be discussed. Using a temperature ramping growth method, self-organized InGaN nanodots were formed vertically protruding above the sample. It was found that typical height of these nanodots is around 45 nm with an average width of 5 nm. It was also found that the local density of the vertically grown self-organized InGaN nanodots could reach 8.2 × 10¹² cm⁻². These self-organized InGaN nanodots will result in a red shift in PL spectrum indicating that In droplets act as an indium source to form an InGaN intermediate layer near the heterointerface.     

Selective growth of ZnO nanodots prepared by metalorganic chemical vapor deposition on focused-ion beam-nanopatterned substrates

Selective formation of ZnO nanodots grown by metalorganic chemical vapor deposition (MOCVD) was achieved on focused-ion beam (FIB)-nanopatterned SiO₂ and Si substrates. The selective formation characteristics, dimension, and density of ZnO nanodots on FIB-nanopatterned substrates strongly depended on the FIB-patterning and MOCVD-growth conditions. The mechanism of the selective formation of ZnO nanodots on FIB-nanopatterned SiO₂ substrates is attributed to a surfactant effect of the implanted Ga which leads to the formation of the preferred nucleation sites for the growth of ZnO nanodots, while that of ZnO nanodots on nanopatterned Si substrates is mainly considered in terms of the generation of surface atomic steps and kinks, which are created by Ga⁺ ion sputtering, on the patterned Si areas.     

The effect of size on the resistive switching characteristics of NiO nanodots

NiO nanodots were fabricated via a shattering process using an AFM tip, where an NiO nanodot with a diameter of approximately 90 nm was broken into very small pieces. The pieces showed diverse diameters, including three diameters of approximately 10, 20, and 30 nm. The NiO nanodots exhibited unipolar switching characteristics including bistable resistivity during 200 repeated switching cycles. Significantly, the magnitude of the “ON currents” was observed to depend on the formation of conducting filaments in the NiO nanodots. We suggest that the critical diameter of the RRAM NiO nanodots is approximately 30 nm.     

Synthesis of ordered ZnO nanowire arrays from aqueous solution using AAO template

In this paper we report a simple method that enables the easy fabrication of ordered ZnO nanowire arrays using Anodic Aluminium Oxide (AAO) template. We have used a vacuum injection technique to fill solution into the pores of an AAO template. The AAO template has been fabricated by a two-step anodization process using 0.3 M oxalic acid (H₂C₂O₄) solution under a constant voltage of 40 V. The AAO template formed through this process has been detached from Al substrate via an anodic voltage pulse using perchloric acid (HClO₄) solution (70%). The nanowires of ZnO have been synthesized by injecting the saturated Zn(NO₃)₂ solution into the pores of the detached AAO template using a vacuum pump. The ZnO nanowires synthesized by this technique have been found dense & continuous with uniform diameter throughout the length of the wire. The structural characteristics of AAO template and ZnO nanowires have been studied by Field Emission Scanning Electron Microscope (FESEM), Atomic force microscope (AFM) and Transmission Electron Microscope (TEM).     

Enhancement of photoluminescence intensity from Si nanodots using Al2O3 surface passivation layer grown by atomic layer deposition

Temperature-dependent photoluminescence (PL) from Si nanodots with Al₂O₃ surface passivation layers was studied. The Si nanodots were grown by low pressure chemical vapor deposition and the Al₂O₃ thin films were prepared by atomic layer deposition (ALD), respectively. The BOE (Buffer-Oxide-Etch) treatment resulted in the damaged surface of Si nanodots and thus caused dramatic reduction in the PL intensity. Significant enhancement of the PL intensity from Si nanodots after the deposition of Al₂O₃ thin films was observed over a wide temperature range, indicating the remarkable surface passivation effect to suppress the non-radiative recombination at the surface of Si nanodots. The results demonstrated that the Al₂O₃ surface passivation layers grown by ALD are effectually applicable to nanostructured silicon devices.     

Thermally Induced Depolarization of the Photoluminescence of Carbon Nanodots in a Colloidal Matrix

The effect of temperature on fluorescence polarization in a colloidal system of carbon nanodots in glycerol under linearly polarized excitation is investigated for the first time. It is found that the experimentally obtained temperature dependence of the degree of linear polarization of fluorescence can be described by the Levshin–Perrin equation, taking into account the rotational diffusion of luminescent particles (fluorophores) in the liquid matrix. The fluorophore size determined in the context of the Levshin–Perrin model is significantly smaller than the size of carbon nanodots. This discrepancy gives evidence that small atomic groups responsible for nanodot luminescence are characterized by high segmental mobility with a large amplitude of motion with respect to the nanodot core.     

Controllable preparation of tungsten/tungsten carbide nanowires or nanodots in nanostructured carbon with hollow macroporous core/mesoporous shell

Large scale tungsten nanowires and tungsten nanodots are prepared in a controllable way. The preparation is based on mechanisms of chemical vapor transportation and phase transformation during the reduction of ammonium metatungstate (AMT) in H₂. The AMT is first encapsulated into the hollow core of nanostructured carbon with hollow macroporous core/mesoporous shell (NC-HMC/MS) and forms nanorods, which are the precursors of both tungsten nanowires and tungsten nanodots. Just by controlling H₂ flow rate and heating rate in the reduction process, the AMT nanorods could turn into nanowires (under low rate condition) or nanodots (under high rate condition). Besides, via heat treatment at 1200℃, the as-obtained nano-sized tungsten could convert into W₂C nanorods or WC nanodots respectively. Furthermore, the diameter of the as-obtained tungsten or tungsten carbide is confined within 50 nm by the NC-HMC/MS, and no agglomeration appears in the obtained nanomaterials.