Nitride Nanocrystals Research Articles

Enhanced microwave absorption properties of graphite nanoflakes by coating hexagonal boron nitride nanocrystals

We report herein the synthesis of a novel hexagonal boron nitride nanocrystal/graphite nanoflake (h-BNNC/GNF) composite through a wet-chemistry coating of graphite nanoflakes and subsequent in-situ thermal treatment process. The characterization results of X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive X-ray spectrum, and X-ray photoelectron spectroscopy demonstrate that h-BNNCs with diameter of tens of nanometers are highly crystallized and anchored on the surfaces of graphite nanoflakes without obvious aggregation. The minimum reflection loss (RL) value of the h-BNNC/GNF based absorbers could reach −32.38dB (>99.99% attenuation) with the absorber thickness of 2.0mm. This result is superior to the other graphite based and some dielectric loss microwave absorption materials recently reported. Moreover, the frequency range where the RL is less than −10dB is 3.49–17.28GHz with the corresponding thickness of 5.0–1.5mm. This reveals a better electromagnetic microwave absorption performance of h-BNNC/GNFs from the X-band to the Ku-band. The remarkable enhancement of the electromagnetic microwave absorption properties of h-BNNC/GNFs can be assigned to the increase of multiple scattering, interface polarization as well as the improvement of the electromagnetic impedance matching of graphite nanoflakes after being coated with h-BNNCs.

(Invited) Non-Thermal Plasmas for the Production of Sustainable Functional Materials

This talk will highlight the potential of non-thermal plasmas as a viable synthetic approach for materials that are difficult to produce using other techniques. Materials such as titanium and zirconium nitride are impossible to produce in nanoparticle form using liquid phase chemistry techniques, and are not compatible with approaches such as flame and spray pyrolysis because they are not oxide-based ceramics. At the same time, they are quickly attracting interest because they are predicted to show plasmonic response in the visible, making them great candidates for the replacement of silver and gold-based plasmonics. Our recent investigation in this material system confirms that low-temperature, non-thermal plasma processes are compatible with the synthesis of titanium and zirconium nitride nanocrystals. Particles are produced using metal chlorides and ammonia as precursors. The plasma reactor is designed in a continuous flow configuration, where precursors are continuously fed into the plasma volume and nanoparticles are continuously collected downstream of the plasma by filtering. This technique allows producing TiN and ZrN nanocrystals with average size below 10 nm, with narrow size distribution (all particles are within 5 nm and 15 nm) and with perfect stoichiometry. In partial agreement with the theoretical predictions, such particles show plasmon resonance in the visible and in the near-infrared part of the spectrum. Yet the plasmon energy is lower than theoretically predicted, a behavior that has not been observed before and that we attribute to the presence of a native oxide shell. This observation is justified by simple experiments in which the particles are annealed in air at moderate temperature (<300°C), leading to the progressive growth of an oxide shell, as confirmed by elemental analysis and by XPS. The plasmon peak energy continuously red shifts during the annealing process, suggesting that a strategy for limiting oxide growth needs to be developed to enable the use of these nanomaterials for refractory plasmonic applications. In addition to discussing the properties of these novel plasma-produce nanomaterials, this talk will summarize our most recent findings with respect of their nucleation and growth. A combination of in-situ FTIR and optical emission spectroscopy measurements suggests that the nucleation process is initiated via atomic hydrogen-induced dissociation of the chlorine-based metal precursor, in this case titanium tetrachloride. This talk will also cover our most recent studies on the interaction between nanoparticles and plasmas. Despite operating near room temperature, and despite the short residence time (tens to hundreds of milliseconds) these systems are capable of producing nanocrystals of high melting point materials. Moreover, there is mounting evidence that such systems are compatible with the production of a broad range of high melting point materials. Therefore it is necessary to achieve a detailed understanding of the phenomena occurring in such reactors to fully take advantage of their capabilities as a nanomaterial synthetic approach. Using the silane-based chemistry as a testbed, we have performed careful in-situ FTIR characterization of the surface of silicon nanoparticles immersed in a non-thermal plasma. The hydrogen surface coverage decreases as the input power density increases. We attribute this to plasma-induced heating of nanoparticles to temperatures sufficiently high to lead to hydrogen desorption. This observation confirms the prediction of several theoretical studies that there is a non-equilibrium between nanoparticle temperature in a dusty plasma and the background gas temperature.

General Fabrication of Boride, Carbide, and Nitride Nanocrystals via a Metal-Hydrolysis-Assisted Process.

Metal boride, carbide, and nitride materials are useful owing to their wide variety of interesting chemical and physical properties. However, the synthesis of these materials with nano or mesoscale sizes is challenging due to the usually required high temperatures and long reaction durations. To our knowledge, the exploration of a number of simultaneous chemical reactions through rapid synthesis still remains a great challenge. In this study, a general route for the reduction and transformation of metal oxides into related metal boride (TiB2, MoB2, DyB4, ErB4, YB4, LaB6, CeB6, SmB6, EuB6), carbide (SiC, TiC, VC, WC, W2C, ZrC, MoC, NbC), and nitride (TiN, VN, BN, AlN, CrN, MgSiN2) nanocrystals were achieved at 150 °C. Here, the exothermic reaction of metal magnesium hydrolysis is utilized to assist the reaction in sealed stainless steel autoclaves. In situ temperature monitoring showed that the inside temperature increased quickly from 139 to 902 °C at the initial stage. The obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and high-resolution TEM techniques. The low reaction temperature and cheap raw materials make it possible for large-scale synthesis of those nanomaterials.

Title: Periodic Mesoporous Hexagonal Boron Nitride at High Pressure: A Route to Cubic Boron Nitride Nanocrystals and Mesoporous Cubic Boron Nitride

AbstractPeriodic mesoporous hexagonal boron nitride was investigated as a precursor for nanoscale forms of cubic boron nitride. Cubic boron nitride (c‐BN) nanocrystals were obtained at a pressure of 14 GPa and a temperature of 1300 °C. The synthesized nanocrystals have diameters of ∼ 50 nm and are solution‐processible. Mesoporous c‐BN formed at a pressure of 10 GPa and 1000 °C. The mesoporous c‐BN has a pore size distribution centered around 3 nm and a surface area of 122 m2/g as determined by electron tomography. At pressures of 8 and 6 GPa near monodisperse h‐BN nanodiscs with diameters of 0.5‐1 μm and 0.2‐0.5 μm were formed, respectively. The discs formed colloidal solutions in acetone. The hydrodynamic radius of the discs matched the radii determined by dynamic light scattering indicating absence of nanodisc aggregation in solution.

Mild preparation and high fluorescence emission efficiency of europium-doped gallium nitride nanocrystals and first-principles density functional theoretical analysis of optical properties

Eu:GaN nanocrystals have strong fluorescence emission and efficient energy transfer by means of DFT simulations. SiO2 coating improves the fluorescence quantum yield.

Magnetic Properties of Pure and Doped Gallium Nitride Nanocrystals.

In the present paper, Ga(1− x) Co(x) N, Ga(1− x) Ni(x) N and Ga(1− x) Tb(x) N (0 ≤ x ≤ 0.1) nanocrystals have been synthesized by a facile solvothermal method. Crystallographic characterization of synthesized materials has been done using powder X-ray diffraction technique. Recorded diffraction patterns reveal the formation of wurtzite (hexagonal) structured GaN nanocrystals. Electron microscopic studies have been carried for the detailed topographical and morphological analyses of synthesized nanomaterials. Recorded electron micrographs indicate the formation of nearly mono-disperse nanoparticles, having average size ˜4 nm. Magnetic measurements of doped nanocrystals revealed ferromagnetic behavior at room temperature however pure GaN is diamagnetic at room temperature.

Graphitic carbon nitride nanocrystals decorated AgVO3 nanowires with enhanced visible-light photocatalytic activity

In the present study, a novel graphitic carbon nitride (g-C3N4) nanocrystals/AgVO3 photocatalyst was successfully synthesized by a simple two-step method. The as-prepared g-C3N4/AgVO3 heterostructures included g-C3N4 nanocrystals assembling uniformly on the surface of AgVO3 nanowires. The successful modification of AgVO3 nanowires by g-C3N4 nanocrystals was found to improve the photocatalyst activity significantly because of enhanced light absorption and improved separation of photo-generated electron–hole pairs.

Ca-assisted nitrogen-rich molecular approach for the synthesis of monodisperse tantalum oxide and (oxy)nitride nanocrystals for visible light&amp;ndash;induced water oxidation

The visible-light-induced photocatalytic water oxidation activity without cocatalyst has been demonstrated for the first time on tantalum (oxy)nitride nanocrystals synthesized by a Ca-assisted nitrogen-rich molecular approach. Monodisperse TaON and Ta3N5 nanocrystals were synthesized by using suitable urea /Ta ratios in the presence of Ca2+ions. The as-synthesized (oxy)nitrides are in the form of spherically-shaped and well-defined nanocrystals with an average diameter of ca. 7 nm. Both nanocrystals showed absorption edges in the visible region. The band gap energies of TaON and Ta3N5 nanocrystals were determined from the Tauc’s plots of the UV ­ Vis diffuse reflectance spectra to be 2.27 and 2.08 eV for indirect allowed transitions,respectively. The O2 evolution rate was increased and reached the maximum in the following order: 2.01, 3.32, and 4.66 mol·h¹1 for the samples synthesized with Ca2+/urea molar ratio of 0.10, 0.50, and 0.25, respectively, due to the decrease in the optical band gap. ©2016 The Ceramic Society of Japan. All rights reserved.

Synthesis and characterization of terbium doped gallium nitride nanocrystals

Intrinsic and extrinsic gallium nitride (GaN) nanostructures due to their size tunable photo-physical and photo-chemical behavior have attracted great interest for the fabrication of various smart optoelectronic devices. In the present paper, Ga1−xTbxN (0 ≤ x ≤ 0.1) nanocrystals have been synthesized by facile solvothermal method. Crystallographic characterization of synthesized materials has been done using powder X-ray diffraction technique. Recorded diffraction patterns reveal the formation of wurtzite (hexagonal) structured GaN nanocrystals. Electron microscopic studies have been carried for the detailed topographical and morphological analyses of synthesized nanomaterials. Recorded electron micrographs indicate the formation of nearly mono-disperse nanoparticles having average size ~4 nm. Spectroscopic studies like energy dispersive X-ray spectroscopy, UV–visible absorption, Fourier Transform infra-red spectroscopy, X-ray photoelectron spectroscopy and steady state energy resolved and time resolved photoluminescence (PL) spectroscopy studies have been used for the investigation of quantitative, qualitative and optical behavior of synthesized nanomaterials. Room temperature PL studies show that the synthesized gallium nitride nanostructures have excitation wavelength tunable emission spectra, which explore the new possibility for applications of these nanomaterials in the fabrication of colour tunable light emitting diodes and flat panel displays. Time resolved florescence spectroscopy depicts the fast decay time in ns range of synthesized nanomaterials and decay time shortens with the augmentation of dopant concentration.

Synthesis and optical characterization of pure and nickel doped gallium nitride nanocrystals

In the present Letter, Ga1−xNixN (0≤x≤0.1) nanocrystals have been synthesized by facile solvothermal method. Crystallographic characterization of synthesized materials has been done, using powder X-ray diffraction technique, reveal the formation of wurtzite (hexagonal) structured GaN nanocrystals. Electron microscopic studies have been carried for the detailed topographical and morphological analysis of synthesized nanomaterials. Spectroscopic studies like energy dispersive X-ray spectroscopy (EDS), UV–visible absorption, X-ray photo electron spectroscopy (XPS), steady state energy resolved and time resolved photoluminescence (PL) spectroscopy have been opted for the investigation of quantitative, qualitative and optical behavior of synthesized nanomaterials.

Synthesis and optical characterization of pure and cobalt doped gallium nitride nanocrystals

Intrinsic and extrinsic gallium nitride (GaN) nanostructures, due to their size tunable photo-physical and photo-chemical behavior, have attracted great interest for the fabrication of various smart optoelectronic devices. In the present paper, Ga1−xCoxN (0 ≤ x ≤ 0.1) nanocrystals have been synthesized by facile solvothermal method. Crystallographic characterization of synthesized materials has been done using powder X-ray diffraction technique. Recorded diffraction patterns reveal the formation of wurtzite (hexagonal) structured GaN nanocrystals. Electron microscopic studies have been carried for the detailed topographical and morphological analyses of synthesized nanomaterials. Recorded electron micrographs indicate the formation of nearly mono-disperse nanoparticles having average size ~4 nm. Spectroscopic studies like energy dispersive X-ray spectroscopy, UV–visible absorption, Fourier transform infra-red spectroscopy, X-ray photoelectron spectroscopy and steady state energy resolved and time resolved photoluminescence spectroscopy studies have been opted for the investigation of quantitative, qualitative and optical behavior of synthesized nanomaterials.

Tungsten nitride nanocrystals on nitrogen-doped carbon black as efficient electrocatalysts for oxygen reduction reactions.

The direct synthesis of tungsten nitride (WN) nanoparticles on nitrogen-doped carbon black (N-carbon black) was achieved through facile nucleation and growth of WN nanoparticles on simultaneously generated N-carbon black under ammonia annealing. As a noble-metal-free catalyst, the WN/N-carbon black hybrid exhibited excellent performance in ORR, coupled with superior methanol tolerance and long-term stability in comparison to commercial Pt/C catalysts, through an efficient four-electron-dominant ORR process.

A Near-Infrared Range Photodetector Based on Indium Nitride Nanocrystals Obtained Through Laser Ablation

We present a proof-of-concept photodetector that is sensitive in the near-infrared (NIR) range based on InN nanocrystals. Indium nitride nanocrystals (InN-NCs) are obtained through laser ablation of a high pressure chemical vapor deposition grown indium nitride thin film and are used as optically active absorption region. InN-NCs are sandwiched between thin insulating films to reduce the electrical leakage current. Under -1 V applied bias, the recorded photoresponsivity values within 600-1100-nm wavelength range are as high as 3.05 × 10 -2 mA/W. An ultrathin layer of nanocrystalline InN thin film is, therefore, a promising candidate for NIR detection in large area schemes.

Low-temperature collapsing boron nitride nanospheres into nanoflakes and their photoluminescence properties

Flake-like boron nitride (BN) nanocrystals with a uniform diameter of ∼200 nm and thickness of ∼20 nm were fabricated by directly transforming from BN nanospheres with the assistance of NaCl salt at 1300 °C. The transformation from nanospheres to nano-pies and further to nanoflakes was achieved in a simple procedure of Na or Cl ions intercalation/deintercalation procedure at such low temperature. The morphologies of the spherical precursor and resulting nanoflakes were almost identical. X-ray powder diffractions revealed that the BN nanoflakes (BNfs) were well crystallized in the hexagonal structure via graphitizing index calculation. Elemental content analysis, FTIR spectra and TEM images were also used to characterize the products. Strong ultraviolet (UV) emissions were detected by photoluminescence (PL) spectroscopic analysis, in which the emission regions could be facilely tuned by controlling the reaction temperature. Detailed studies indicated that the collapsing temperature of unstable BN nanospheres into nanoflakes was strongly dependent on the introduction of NaCl molten salts or not. We believe the use of the NaCl molten salt medium may enhance the kinetics of the crystallization and also purification. The green fabrication characteristics, such as using NaCl salt as the additive, energy saving (300 °C lower than the commercial process), non-toxicity of byproduct and easy scale-up, make the present novel synthetic route likely to be of interest to commercial-scale production of BN nanoflakes.

Synthesis of widely tunable and highly luminescent zinc nitride nanocrystals

Highly emissive zinc nitride nanocrystals have been prepared from the reaction of ammonia with diethylzinc. The peak photoluminescence wavelength can be tuned from below 500 nm to above 1100 nm.

Cover Picture: Titanium Nitride Nanocrystals on Nitrogen-Doped Graphene as an Efficient Electrocatalyst for Oxygen Reduction Reaction (Chem. Eur. J. 44/2013)

Cover Picture: Titanium Nitride Nanocrystals on Nitrogen-Doped Graphene as an Efficient Electrocatalyst for Oxygen Reduction Reaction (Chem. Eur. J. 44/2013)

Titanium Nitride Nanocrystals on Nitrogen‐Doped Graphene as an Efficient Electrocatalyst for Oxygen Reduction Reaction

Titanium Nitride Nanocrystals on Nitrogen‐Doped Graphene as an Efficient Electrocatalyst for Oxygen Reduction Reaction

Control of Plasmonic and Interband Transitions in Colloidal Indium Nitride Nanocrystals

We have developed a colloidal synthesis of 4-10 nm diameter indium nitride (InN) nanocrystals that exhibit both a visible absorption onset (∼1.8 eV) and a strong localized surface plasmon resonance absorption in the mid-infrared (∼3000 nm). Chemical oxidation and reduction reversibly modulate both the position and intensity of this plasmon feature as well as the band-to-band absorption onset. Chemical oxidation of InN nanocrystals with NOBF4 is found to red-shift the absorption onset to ∼1.3 eV and reduce the plasmon absorption energy (to 3550 nm) and intensity (by an order of magnitude at 2600 nm). Reduction of these oxidized species with Bu4NBH4 fully recovers the original optical properties. Calculations suggest that the carrier density in these InN nanocrystals decreases upon oxidation from 2.89 × 10(20) cm(-3) to 2.51 × 10(20) cm(-3), consistent with the removal of ∼4 electrons per nanocrystal. This study provides a unique example of the ability to tune the optical properties of colloidal nanomaterials, and in particular the LSPR absorption, with reversible redox reactions that do not affect the semiconductor chemical composition or phase.

Polymer-GaN Bulk Heterojunction Photovoltaic Cells

The hybrid polymer-GaN nanocrystal heterojunction solar cell has been fabricated by blending of GaN and regioregular poly (3-hexylthiophene)(P3HT) through solution process and spin-coating on the glass substrate, in which the Gallium Nitride (GaN) nanocrystal was successfully synthesized by means of sol-gel process The cell shows the Voc and Isc of 0.71V and 3.5mA/cm2

Electrocatalysis on Shape‐Controlled Titanium Nitride Nanocrystals for the Oxygen Reduction Reaction

The high price of platinum (Pt)-based cathode catalysts for the oxygen reduction reaction (ORR) have slowed down the practical application of fuel cells. Thanks to their low cost, and outstanding, stable catalytic properties, titanium nitrides (TiN) are among the most promising non-precious metal electrocatalysts for replacing Pt. However, the shape-activity relationships of TiN electrocatalysts have not been well-studied or understood up to now. In this work, by simply adjusting the shape of TiO2 precursor, we are able to tailor the morphology of the TiN catalysts from nanoparticles to nanotubes. We have synthetized uniform carbon-coated titanium nitride nanotubes (carbon-coated TiN NTs) through a nitridation reaction in NH3 flow using a TiO2 nanotubes/melamine mixture as precursor. The carbon-coated TiN NTs hybrids exhibit excellent electrocatalytic activity for the ORR, coupled with superior methanol tolerance and long-term stability in comparison to commercial Pt/C, through an efficient four-electron-dominant ORR process. Compared with nanoparticles, the one-dimensional and hollow structure of the nanotubes result in greater diffusion of electrolyte and superior electrical conductivity, and contribute to the greatly improved electrocatalytic performance of the carbon-coated TiN NTs nanocomposites.