Nanoneedle Structure Research Articles

Graphene/MnO2-based composites reduced via different chemical agents for supercapacitors

Graphene/MnO2 composites are synthesized by the chemical reduction of GO/MnO2 using both hydrazine hydrate (H-RGO/MnO2) and sodium borohydride (S-RGO/MnO2) as reducing agents. The morphology and microstructure of the as-prepared composites are characterized by X-ray diffractometry, field-emission scanning electron microscopy, Raman microscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy. Characterizations indicate that MnO2 is successfully formed on the GO surface and GO is reduced successfully by using both hydrazine hydrate and sodium borohydride as reducing agents. H-RGO/MnO2 shows higher electrical conductivity than that of S-RGO/MnO2 since it has a lower concentration of oxygen-containing functional groups. The capacitive properties of the H-RGO/MnO2 and S-RGO/MnO2 electrodes are measured using cyclic voltammetry and galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in a three-electrode experimental setup using a 1 M Na2SO4 aqueous solution as the electrolyte. The H-RGO/MnO2 electrode displays a specific capacitance as high as 327.5 F g−1 at 10 mV s−1, which is higher than that of the S-RGO/MnO2 electrode (278.6 F g−1). It is anticipate that the formation of nanoneedle structures of MnO2 on graphene oxide surfaces after the hydrazine reduction procedure is a promising fabrication method for supercapacitor electrodes.

Concentration dependence of graphene oxide–nanoneedle manganese oxide composites reduced by hydrazine hydrate for an electrochemical supercapacitor

Graphene-MnO2 composites are reduced from GO-MnO2 using various concentrations of hydrazine hydrate with a fixed reduction time to optimize the hydrazine concentration to obtain excellent electrochemical performance. Changes in the oxygen-containing functional groups are observed as the concentration of hydrazine is varied. These changes affect the electrical conductivity and density of MnO2 nanoneedles, which impact the surface area and can significantly affect the supercapacitive performance. The characterization of morphology and microstructure of the as-prepared composites demonstrates that MnO2 is successfully formed on the GO surface and GO is successfully reduced by using hydrazine hydrate as a reducing agent. The capacitive properties of the graphene-MnO2 electrodes which reduced 50 mM of hydrazine (RGO-MnO2(50)) show a low sheet resistance value as well as a high surface area, resulting in excellent electrochemical performance (383.82 F g(-1) at a scan rate of 10 mV s(-1)). It is anticipated that the formation of nanoneedle structures of MnO2 on graphene oxide surfaces utilizing the 50 mM hydrazine reduction procedure is a promising fabrication method for supercapacitor electrodes.

Highly sensitive tactile sensors integrated with organic transistors

This paper presents a highly sensitive capacitive pressure sensor composed of a polymer dielectric film with a nano-needle structure. The nano-needle polymer films were prepared by facile fabrication methods including breath figures formation followed by stamping. The pressure sensitivity of the sensor reached 1.76 kPa−1 in the low pressure range (<1 kPa), which is comparable to the sensitivity of human skin. Analysis of the geometries and densities effect was shown, and the nano-needle film showed better sensitivity in comparison to films with hemispherical or conical structures. The pressure sensors were integrated with printed organic thin film transistors to enable flexible, large-area tactile sensing applications.

Enhanced light output of InGaN/GaN blue light emitting diodes with Ag nano-particles embedded in nano-needle layer

2.7 times increase in room temperature photoluminescence (PL) intensity and 3.2 times increase in electroluminescence (EL) intensity were observed in blue multi-quantum-well (MQW) GaN/InGaN light emitting diodes (LEDs) as a result of introduction of nano-needle structure embedded with Ag nanoparticles (NPs) into n-GaN film underlying the active MQW region and thick p-GaN contact layer of LEDs. The nano-needle structure was produced by photoelectrochemical etching. Simultaneously a measurable decrease in room temperature decay time from 2.2 ns in control samples to 1.6 ns in PL was observed. The results are explained by strong coupling of recombination in GaN/InGaN MQWs with Ag NPs related localized surface plasmons.

Photocatalytic Properties of α-Bi&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Nanoneedle Array Synthesized by Hydrothermal Method

Pureα-Bi2O3with nanoneedle array structure was synthesized directly by hydrothermal method. The optic absorption of theα-Bi2O3paricles was cut off at ~483 nm and the band gap of theα-Bi2O3was estimated to be 2.57 eV. The photocatalytic activity of theα-Bi2O3samples was higher than TiO2under a visible light irradiation. As a conclusion, relative narrow band gap ofα-Bi2O3nanoneedle array compared to anatase and the special morphology of nanoneedle array structures may improve the photocatalytic activity in visible light irradiation.

Direct Writing Micro/Nano Structures on PZT Wafer by Laser Micromaching

The PZT is used for piezoelectric actuators that have high area efficiency but no good machinability. A direct writing micro structures on PZT wafer by excimer laser micromaching method has been proposed and confirmed. PZT nano-needle structures have also been fabricated by the direct writing method only by changing the laser micromachiong process parameters. The fabricated nano-needle structures can be very useful because of the need for studies on ferroelectric size effects as well as for potential applications such as ultra-high density memory devices.The relationship of process depth with the excimer laser parameters has been tested.

Comparison of GaN Nanoneedle Structures Formed by Using the HVPE Method

Comparison of GaN Nanoneedle Structures Formed by Using the HVPE Method

Fabrication and surface characterization of biomimic superhydrophobic copper surface by solution-immersion and self-assembly

Biomimic superhydrophobic surfaces with contact angle greater than 150° and low sliding angle on copper substrate were fabricated by means of a facile solution immersion and surface self-assembly method. The scanning electron microscopy showed a nanoneedle structure copper surface with sporadic flower-like aggregates after treatment with sodium hydroxide and potassium persulfate solution. X-ray photoelectron spectroscopy and X-ray diffraction results confirmed that the formed nanoneedles were crystallized Cu(OH) 2. And the hydrophilic Cu(OH) 2 surface can be further modified into superhydrophobic through surface self-assembly with dodecanoic acid.

Morphological Transformations and Electrochemical Properties of Hydrothermally Synthesized MnO2 Nanostructures

MnO2 nanostructures with various morphologies were synthesized by the hydrothermal method with control over the reaction temperature and dwell time. One dimensional (1D) nanoneedle structure can self-assemble to form three dimensional (3D) microspheres of MnO2 nanoneedles at 95oC by extending the dwell time from 3 hours to 15 hours. Alternatively, the 3D microspheres of nanoneedles can transform into 1D nanobelts and nanorods by increasing the reaction temperature to 120oC and 165oC, respectively, while maintaining constant dwell time of 15 hours. The supercapacitance of these nanostructures shows strong morphology dependence, and nanobelts have the highest specific capacitance of 323.7 F g-1.

Field emission property of printed CNTs-mixed ZnO nanoneedles

ZnO nanoneedles were synthesized via thermal evaporation method without any catalyst. Scanning electron microscopy and transmission electron microscopy investigations showed that these products presented a nanoneedle structure. To enhance the field emission (FE) properties of screen printed ZnO nanoneedles, a given amount (0.05 g) carbon nanotubes (CNTs) mixed with (0.5 g) ZnO nanoneedles paste via screen printed method and heat-treatment at (600 °C, 500 °C and 450 °C) was presented. The CNTs-mixed ZnO nanoneedles heat-treated at 450 °C had the lowest turn-on field of 3.75 V/μm, highest field emission current of 0.16 mA at 7.5 V/μm and highest β of 830. An efficiency FE enhancement of 450 °C sample was attributed to melioration of conductance between ZnO nanoneedles and ITO surface by CNTs.

SiRNA delivery with functionalized carbon nanotubes

Carbon nanotubes (CNTs) have been studied for drug, antigen and nucleic acid delivery both in vitro and in vivo. Due to their nano-needle structure, they are supposed to cross the plasma membrane and enter directly into the cytoplasm likely upon an endocytosis-independent mechanism without inducing cell death. In this study, two cationically functionalized CNTs (CNT-PEI and CNT-pyridinium) were investigated for siRNA delivery. Both functionalized CNTs complexed siRNA and showed 10–30% silencing activity and a cytotoxicity of 10–60%. However, in terms of reduced toxicity or increased silencing activity, CNT-PEI and CNT-pyridinium did not show an added value over PEI and other standard transfection systems. Probably, the type of functionalization of carbon nanotubes might be a key parameter to obtain an efficient and non-cytotoxic CNT-based delivery system. Nevertheless, in view of the present results and importantly also of the non-degradability of CNTs, preference should currently be given to designing biodegradable carriers which mimic the needle structure of CNTs.

Structure and photoluminescence properties of Ag-coated ZnO nano-needles

A large number of zinc oxide (ZnO) nano-needles were synthesized by thermal oxidation of pure zinc. The surfaces of ZnO nano-needles were coated with a layer of Ag by pulse electro-deposition technique. The uncoated and coated ZnO nano-needles were characterized by using the X-ray diffraction and the scanning electron microscope (SEM). The results showed that the uncoated samples were close-packed hexagonal structure, which showed needle-like morphology. Their average diameter is about 40 nm, lengths up to 5 μm. At the same time we observed that the prepared ZnO nano-needles have been coated with Ag successfully. The photoluminescence spectrums of ZnO nano-needles with Ag-coated and uncoated were analyzed, finding that the uncoated ZnO nano-needles have two fluorescence peaks at 388 nm and 470.8 nm, respectively, the relative intensity of 143.4 and 93.61; and the Ag-coated ZnO nano-needles showed a pair of strong peaks at 387.4 nm and 405.2 nm, the relative intensity of 1366 and 1305, respectively, indicating that the Ag-coated ZnO nano-needles can increase the absorption of UV light.

Closed-Space Flux Sublimation Growth and Properties of (Cu-Mn)-Doped ZnO Films in Nanoneedle-Like Morphologies

The Cu and Mn co-doped ZnO dilute magnetic semiconductor Zn1-x(Cu-Mn)xO films with unique nanoneedle like structure were deposited at ≤300°C by a two step closed space flux sublimation and periodic oxidation method. Morphology studies establish complex growth process involving a eutectic metal condensate on the substrate and spontaneous emergence of nanoneedle structure by oxidative process controlled by the vapor-liquid-solid mechanism. X-ray diffraction studies show that Zn1-x(Cu-Mn)xO films retain the typical wurtzite hcp structure of the un-doped ZnO. The absence of extraneous reflections indicates that neither the Mn and Cu dopant metal clusters nor their oxide phases are included in the nanostructure Zn1-x(Cu-Mn)xO films. The Raman peaks of Zn1-x(Cu-Mn)xO nanocrystalline films are consistent with the Raman active phonon modes for ZnO. The red shifted E2 (Low) and E2 (high) peaks confirm that Mn and Cu substitute at Zn site in the nanostructure Zn1-x(Cu-Mn)xO films. Optical transition at direct band gap energy occurs at 3.11 eV and an upward energy shift in the direct band to 3.58 eV is assigned to the quantum size effects of the nanoneedle structure of Zn1-x(Cu-Mn)xO films.

The structure and growth mechanism of Si nanoneedles prepared by plasma-enhancedchemical vapor deposition

Silicon nanowires and nanoneedles show promise for many device applications innanoelectronics and nanophotonics, but the remaining challenge is to grow them at lowtemperatures on low-cost materials. Here we present plasma-enhanced chemical vapordeposition of crystalline/amorphous Si nanoneedles on glass at temperatures as low as250 °C. High resolution electron microscopy and micro-Raman spectroscopy have been used tostudy the crystal structure and the growth mechanism of individual Si nanoneedles. TheH2 dilutionof the SiH4 plasma working gas has caused the formation of extremely sharp nanoneedle tips that insome cases do not contain a catalytic particle at the end.

Controlling the Morphology of Nano-Hybrid Materials

Problem statement: It is known that layer double hydroxide is one of the nano ordered layered compounds and possesses plate-like morphology if carefully crystallized. Approach: In this study, Co-Sn LDH consisting of divalent and tetravalent cations was prepared with new morphology. XRD patterns of the prepared Co-Sn LDH showed that the interlayer spacing of the LDH was 0.78 nm and SEM image showed nano-needles structure. Results: By intercalation reaction with monocarboxylic acids at room temperature, XRD patterns indicated that the interlayered spacing increased to 3-4.8 nm and formed organic-inorganic nano-hybrid materials. Also, SEM images showed that the nano-needles structure of Co-Sn LDH changes to plate like-structure. Conclusion: Thermal analyses (TG, DTG and DTA) and Infrared spectrum confirmed the intercalation processes of n-capric acid and n-stearic acid inside Co-Sn LDH and the formation of nano-hybrid materials.

Structure and Formation Mechanism of Sn-Doped ZnO Nanoneedles

We synthesized Sn-doped ZnO nanoneedles on Si(111) substrates in two steps: sputtering and thermal oxidation.First,a thin layer of the Sn∶Zn films was deposited onto the Si(111) substrates in a JCK-500A radio-frequency magnetron sputtering system.Sn-doped ZnO nanoneedles were then grown by simple thermal oxidation of the as-deposited films at 650 ℃ in Ar atmosphere.The structural,componential,and optical properties of the samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM),energy dispersive X-ray(EDX) spectroscopy,and photoluminescence(PL) spectroscopy.The results reveal that the ZnO nanoneedles doped with 2.5%(x,atomic ratio) Sn are single crystalline with a wurtzite hexagonal structure.The lengths of the grown nanoneedles vary between 1 and 3 μm.The root diameters of the needles range between 200 and 500 nm while the tips have an average diameter of about 40 nm.Moreover,most of the Sn-doped ZnO nanoneedles are of high crystal quality.Room temperature PL spectroscopy shows a blue-shift from the bulk bandgap emission,which can be attributed to a Sn composition in the nanoneedles as detected by EDX.Based on the reaction conditions,the growth mechanism of the Sn-doped ZnO nanoneedles was also discussed.

Growth and Cathodoluminescence of Eu Doped ZnO Nanoneedles and Branched Nanoneedle Structures

Rare-earth (RE) ions are widely investigated luminescent centers because their intraionic-4f transitions generate narrow and intense emission lines. In this work Eu doped ZnO nanoneedles have been grown, by a thermal evaporation-deposition method, and structural and luminescence characterization has been carried out. Mixtures of ZnO and Eu2O3 or of ZnS and Eu2O3 powders were used as precursors. Annealing of the compacted powder mixtures leads to the growth of nanoneedles and nanoneedle networks, as well as rods. EDS and CL measurements enable to detect the incorporation of Eu in these structures. The choice of precursor, ZnO-Eu2O3 or ZnS-Eu2O3 influences the morphology as well as the luminescence properties of the obtained nanostructures. In particular, while in the samples obtained from ZnO, the defect green luminescence band is practically absent, the band is present in the ZnO nanoneedles obtained from ZnS. Besides the broad deep level band, a series of well-separated narrow-peaks characteristic of the intrinsic red luminescence of Eu+3 ions are observed in all cases, whose relative intensities vary from one set of samples to the other. The results suggest that the Eu3+ ions have at least, two possible configurations in the ZnO lattice with different symmetry in the nanoneedles.

Study of temporal current stability and fluctuations of field emitted electrons from ZnO nanostructure films

Stable field emission currents and low fluctuations are important feasibility requirements for the application of materials in field emission devices and displays, more than the low turn on fields that are generally considered. The current stability and current fluctuations of field emitted electrons from ZnO nanostructures were investigated over the period of 2, 12, and 24 h. The films with nanoneedle structure having density around ten/μm2 showed better short and long-term (temporal) stability over a period of 24 h. The short- and long-term stability and the current fluctuations of the nanostructures are reported and the causes for the degradation of the emission current are discussed.

Preparation of oriented SiO 32− doped TiO 2 film and degradation of methylene blue under visible light irradiation

SiO 3 2− doped TiO 2 films with oriented nanoneedle and nanorectangle block structure has been firstly synthesized by hydrothermal synthesis method. The prepared samples are characterized, X-ray diffraction (XRD) results demonstrate that the SiO 3 2− doped TiO 2 films are rutile and brookite phases. The scanning electron microscope (SEM) analysis reveals that the quantity of O 2 affects the morphology of the SiO 3 2− doped TiO 2 films (SiTiA films prepared with unmodified substrate). The SiO 3 2− doped TiO 2 films (SiTiB films prepared with modified substrate) display two layers, one is porous structure, the other is nanoneedle structure. UV–vis, IR, transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) microscopy all prove that SiO 3 2− have been doped in the TiO 2 crystal structure. They have remarkable red shift and higher photocatalytic activity of degradation of methylene blue than P-25 under visible light ( λ > 420 nm) irradiation. Besides, photocatalytic activity of the film is stable during 4 times recycling.

Synthesis and Characterization of Flowerlike ZnO Nanoneedle Arrays on Si (100)

AbstractFlowerlike ZnO nanoneedle arrays have been synthesized on Si (100) substrates by pulsed laser deposition techniques. The tips of the nanoneedles are ˜ 20- 50 nm in diameter and their roots are as thick as ˜ 50- 100 nm. The nanoneedle arrays grow preferentially along the [0001] direction. Raman spectroscopy shows three first order optical normal modes which confirm wurtzite structure of ZnO nanoneedles. In the low frequency zone, additive modes (92, 122, 163, and 275 cm-1) are observed and can be attributed to zone boundary phonons. ZnO nanoneedle arrays exhibit a strong UV luminescence emission, and two strong peaks at 3.258 eV and 3.288 eV are observed.