High-resolution Transmission Electron Microscopy Measurements Research Articles

An improved method for preparation of SrTiO 3 nanoparticles

SrTiO 3 nanoparticles were synthesized for the first time via a modified polymeric precursor method. The samples were characterized by thermogravimetry, X-ray diffraction (XRD), BET surface area, micro-Raman spectroscopy, field emission scanning and transmission electron microscopy (FE-SEM and FE-STEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence measurements. It is found that calcination atmosphere (air, nitrogen and oxygen) plays an important role of both crystal size and photolumiscence behavior of the SrTiO 3 nanocrystallites. Results show that the powders obtained in nitrogen/oxygen atmosphere possess controllable particles size of approximately 11 nm presenting the highest photoluminescence emission.

Effect of heat treatment on stability of gold particle modified carbon supported Pt–Ru anode catalysts for a direct methanol fuel cell

Carbon supported Au–PtRu (Au–PtRu/C) catalysts were prepared as the anodic catalysts for the direct methanol fuel cell (DMFC). The procedure involved simple deposition of Au particles on a commercial Pt–Ru/C catalyst, followed by heat treatment of the resultant composite catalyst at 125, 175 and 200 °C in a N 2 atmosphere. High-resolution transmission electron microscopy (HR-TEM) measurements indicated that the Au nanoparticles were attached to the surface of the Pt–Ru nanoparticles. We found that the electrocatalytic activity and stability of the Au–PtRu/C catalysts for methanol oxidation is better than that of the PtRu/C catalyst. An enhanced stability of the electrocatalyst is observed and attributable to the promotion of CO oxidation by the Au nanoparticles adsorbed onto the Pt–Ru particles, by weakening the adsorption of CO, which can strongly adsorb to and poison Pt catalyst. XPS results show that Au–PtRu/C catalysts with heat treatment lead to surface segregation of Pt metal and an increase in the oxidation state of Ru, which militates against the dissolution of Ru. We additionally find that Au–PtRu/C catalysts heat-treated at 175 °C exhibit the highest electrocatalytic stability among the catalysts prepared by heat treatment: this observation is explained as due to the attainment of the highest relative concentration of gold and the highest oxidation state of Ru oxides for the catalyst pretreated at this temperature.

A Novel Characterization Scheme of $\hbox{Si/SiO}_{2}$ Interface Roughness for Surface Roughness Scattering-Limited Mobilities of Electrons and Holes in Unstrained- and Strained-Si MOSFETs

In this paper, a novel method to directly determine the surface roughness scattering-limited mobilities (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sr</sub> ) of electrons and holes in Si MOSFETs from the experimental data of MOS interface roughness is proposed and compared with the experimental μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sr</sub> of Si MOSFETs with and without biaxial tensile strain. This method includes the direct evaluation of the scattering potential from the power spectra of Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface roughness data, which are taken through high-resolution advanced transmission electron microscopy measurements, without assuming any autocorrelation function form of the interface roughness, like a Gaussian or exponential function. It is found, for the first time, that, by employing the present method, experimental electron and hole μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sr</sub> (both unstrained and strained Si) could be presented by a same model. As a result, the difference in strain dependence between electron and hole μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sr</sub> , which has experimentally been observed, is systematically explained by the change of power spectra of the interface roughness due to strain.

Synthesis and characterisations of poly(aniline-co- o / m -toluidine)/Sb 2 O 3 nanocomposites

This study is focused on the preparation and characterisation of conducting poly(aniline-co-o/m-toluidine)/Sb2O3 nanocomposites. These nanocomposites were synthesised by the oxidative chemical polymerisation with peroxydisulphate as an oxidant in aqueous hydrochloric acid (HCl) medium and Sb2O3 as a nanomaterial under different experimental conditions. The nanocomposites were characterised by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis, high-resolution transmission electron microscopy and conductivity measurements. FTIR-based kinetics was proposed based on the relative intensities of FTIR peaks.

One-pot synthesis of Zn xCd 1− xS nanocrystals with tunable optical properties from molecular precursors

We have reported a non-injection one-pot synthesis of the alloyed Zn x Cd 1− x S semiconductor nanocrystals (SNCs) with controlled shapes and compositions. This non-injection approach involves heating two molecular precursors (cadmium ethylxanthate and zinc ethylxanthate) as metal and S sources in organic solvents at 320 °C for 30 min, which results in the thermal decompositions of the molecular precursors to produce Zn x Cd 1− x S. The effects of solvents and compositions on the shapes and structures of Zn x Cd 1− x S SNCs have been investigated. The mixture solvent containing oleic acid, paraffin oil and oleylamine (such as a volume ratio: 1/2/1) results in the preparation of uniform Zn x Cd 1− x S nanoparticles with diameters of 7–13 nm, while pure oleylamine or the mixture of oleylamine and paraffin oil as the solvent leads to the formation of uniform Zn x Cd 1− x S nanorods. Monodisperse wurtzite Zn x Cd 1− x S nanorods with different compositions have been prepared in pure oleylamine, and no obvious effects of the compositions on their shapes are found. Their alloying nature is consistently confirmed by the results of high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and optical measurements. These alloyed Zn x Cd 1− x S nanorods exhibit composition-dependent absorption and emission properties, and therefore they can be promising candidates as emitting materials.

Microstructure and field emission characteristics of ZnO nanoneedles grown by physical vapor deposition

Single crystalline zinc oxide (ZnO) nanoneedles have been grown on Au coated Si (1 0 0) substrates in an inert gas atmosphere by physical vapor deposition (PVD) process. A mixture of ZnO and graphite powder was used as precursor for the production of nanoneedles. Their structure has been assessed by a range of techniques including scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The synthesized ZnO nanoneedles have tip diameter around 30 nm and average length of ∼5 μm. The XRD patterns and HRTEM measurements revealed the highly crystalline phase of wurtzite single crystalline structure, with a preferred 〈0 0 0 1〉 growth direction. Field emission from these nanoneedles was investigated and a low turn on voltage of 5.07 V μm −1 at a current density of 10 μA cm −2 was observed.

Modifying growth conditions of ZnO nanorods for solar cell applications

AbstractWe show that the size of nanorods grown by a vapour phase transport method on different substrates can be easily changed by an order of magnitude. This allows producing customized nanorod arrays that can improve the efficiency of Grätzel‐type solar cells as well as polymer hybrid solar cells. Luminescence measurements show that doping is possible simply by the choice of the substrate. The crystalline quality is examined by high resolution TEM measurements (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Pre-Heating Effect on the Catalytic Growth of Partially Filled Carbon Nanotubes by Chemical Vapor Deposition

The surface reconstruction of the Fe catalyst films due to high temperature processing in hydrogen prior to nanotube nucleation and its effect on the growth morphologies of partially filled carbon nanotubes (CNTs) synthesized using atmospheric pressure chemical vapor deposition (APCVD) of propane was investigated. Results show that pre-heating of the catalyst film deeply influences the particle size distribution, which governs the growth morphologies of the corresponding CNTs. The distribution of the catalyst particles over the Si substrate was analyzed before and after the heat treatment by atomic force microscopy (AFM) which reveals that heat treatment causes clusters of catalyst to coalesce and form macroscopic islands. The X-ray diffraction (XRD) pattern of the grown material indicates that they are graphitic in nature. Scanning electron microscopy (SEM) analysis suggested that the growth density strongly depends on the pre heat treatment of the Fe catalyst film. Multiwalled CNTs with partial catalyst filling were observed via high-resolution transmission electron microscopy (HRTEM) measurements. The degree of graphitization of the CNTs also depends on the pre heating as demonstrated by Raman analysis. A simple model for the growth of partially catalyst filled nanotubes is proposed.

Formation and characterization of iron oxide nanoparticles loaded on self-organized TiO2 nanotubes

Abstract The iron oxide nanoparticles were loaded onto self-organized TiO2 nanotube layers grown by anodization of Ti in fluoride containing electrolytes. The nanoparticles were obtained by electrodepositing method in glycerol/water/FeCl3·6H2O electrolytes at room temperature. The X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) measurements showed that the nanoparticles consisted of iron nanocrystalline (Fe) and magnetite (Fe3O4). The hematite (α-Fe2O3) structure was obtained by annealing in air at 450 °C. The growth mechanism of the nanoparticles and their morphology were also described. Furthermore, the nanoparticles exhibited good ferromagnetic properties at room temperature.

Synthesis of ZnO–Pt nanoflowers and their photocatalytic applications

The photocatalytic behaviors of ZnO nanoparticles have been intensively studied recently.However, the photocatalytic efficiency of pure ZnO nanoparticles always suffers from thequick recombination of photoexcited electrons and holes. In order to suppressthe electron–hole recombination and then raise the photocatalytic efficiency ofZnO, metal nanoparticles have been combined with ZnO to form ZnO–metalheterostructures. In this work, the feasibility of synthesizing ZnO–Pt composite nanoflowersfor optimized catalytic properties was studied. Three different Pt nanocrystals,i.e. cubic Pt nanocrystals enclosed by {100} facets, octahedral Pt nanocrystals enclosedby {111} facets, and truncated octahedral Pt nanocrystals enclosed by both {111}and {100} facets, were selected as seeds for epitaxial growth of ZnO. A ZnO–Ptflowerlike nanostructure was formed by selective growth of ZnO nanolobes at {111}facets of the truncated octahedral Pt nanocrystals. The resultant nanoflowershad well defined ZnO–Pt interfaces and exposed Pt {100} facets, as confirmed bytransmission electron microscopy (TEM) and high-resolution TEM (HRTEM)measurements. The photocatalytic behaviors of the resultant ZnO–Pt nanoflowers weredemonstrated in the photodegradation of ethyl violet. In comparison with the commercialTiO2 photocatalyst P25, the ZnO–Pt flowerlike nanostructures showed improved catalyticefficiency. Notable ferromagnetism of the obtained ZnO–Pt flowerlike nanostructures wasalso observed. It is believed that the ZnO–Pt interface played an important role in theenlarged magnetic coercivity of the ZnO–Pt nanoflowers.

Effect of Internal Interfaces on Hardness and Thermal Stability of Nanocrystalline Ti0.5Al0.5N Coatings

The effect of microstructure on the thermal stability and hardness of the cathodic arc evaporated Ti0.5Al0.5N coatings was investigated with the aid of the in-situ high-temperature X-ray diffraction experiments, which were accompanied by high-resolution transmission electron microscopy (HRTEM) and nanoindentation measurements. The microstructure of the coatings was modified through the choice of the bias voltage in the deposition process. It was found that the bias voltage affects strongly the uniformity of the local distribution of titanium and aluminum in the coatings. The nonuniform distribution of the elements contributes to the formation of lattice strains at the crystallite and phase boundaries. The lattice strains at the crystallite boundaries increase the hardness of the coatings; the lattice strains at the phase boundaries improve their thermal stability. A certain nonuniformity of the distribution of the metallic species in the coatings is regarded as advantageous. However, a great nonuniformity in the distribution of the metallic species accelerates the degradation of the coatings at high temperatures. As a measure for the nonuniformity of the distribution of the atomic species in the as-deposited (Ti, Al) N samples, the stress-free lattice parameter of fcc-(Ti, Al) N is suggested.

Improved performance of dye-sensitized solar cells with TiO 2/alumina core–shell formation using atomic layer deposition

Alumina (Al 2O 3) shell formation on TiO 2 core nanoparticles by atomic layer deposition (ALD) is studied to suppress the recombination of charge carriers generated in a dye-sensitized solar cell (DSSC). It is relatively easy to control the shell thickness using the ALD method by controlling the number of cycles. An optimum thickness can be identified, which allows tunneling of the forward current while suppressing recombination. High-resolution TEM measurements show that a uniform Al 2O 3 shell is formed around the TiO 2 core particles and elemental mapping of the porous TiO 2 layer reveals that the Al 2O 3 distribution is uniform throughout the layer. The amount of dye absorption is increased with increase in the shell thickness but electrochemical impedance spectroscopic (EIS) measurement shows a drastic increase in the resistance. With an optimum Al 2O 3 thickness of 2 nm deposited by ALD, a 35% improvement in the cell efficiency (from 6.2 to 8.4%) is achieved.

Sol–gel transparent nano-glass–ceramics containing Eu 3+-doped NaYF 4 nanocrystals

A spectroscopic study has been carried out in transparent nano-glass–ceramics containing Eu 3+-doped NaYF 4 nanocrystals, successfully developed for the first time by thermal treatment of precursor sol–gel derived glasses. X-ray diffraction and high-resolution transmission electron microscopy measurements confirmed the precipitation of NaYF 4 nanocrystals during heat treatment and their corresponding sizes have been calculated by using Scherrer’s equation and from electron microscopy measurements. Changes in the luminescence spectra with the temperature of the heat treatment have been analyzed and correlated with the crystallinity degree of the samples. In addition, emission spectra have been obtained for selected excitation wavelengths, observing large excitation selectivity among the fraction of the rare-earth ions located in near crystalline environments and those remaining in the silica glassy phase.

Properties of highly crystalline NiO and Ni nanoparticles prepared by high-temperature oxidation and reduction

We describe here the use of high-temperature oxidation and reduction to produce highly crystalline nanoparticles of Ni and NiO. Starting with an amorphous Ni powder, we demonstrate that oxidation at $900\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ produces faceted NiO nanocrystals with sizes ranging from 20 to 60 nm. High-resolution transmission electron microscopy measurements indicate near-perfect atomic order, truncated by (200) surfaces. Magnetization measurements reveal that the N\'eel temperature of these NiO nanoparticles is 480 K, substantially reduced by finite-size effects from the bulk value of 523 K. The magnetization of these faceted NiO nanoparticles does not saturate in fields as large as 14 T while a loop offset is observed which increases from 1000 Oe at 300 K to its maximum value of 3500 Oe at 50 K. We have used high-temperature reduction to transform the faceted NiO nanoparticles into highly ordered Ni nanoparticles, with a Curie temperature of 720 K and blocking temperatures in excess of 350 K. Subsequent efforts to reoxidize these Ni nanoparticles into the core-shell morphology found that the Ni nanoparticles are much more resistant to oxidation than the original Ni powder, perhaps due to the relative crystalline perfection of the former. At $800\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, an unusual surface roughening and subsequent instability was observed, where 50-nm-diameter NiO rods grow from the Ni surfaces. We have demonstrated that high-temperature oxidation and reduction in Ni and NiO are both reversible to some extent and are highly effective for creating the highly crystalline nanomaterials required for applications such as exchange-bias devices.

Synthesis of InP nanoparticles by pulsed laser ablation in ethanol

We have synthesized InP nanoparticles using laser ablation in ethanol using 532 nm and 266 nm pulses of Q-switched Nd: YAG laser operating at repetition rate of 10 Hz. The average particle size estimated from transmission electron microscopy (TEM) is 4–10 nm for 532 nm and 2–3 nm for 266 nm pulses. The optical transmission spectra show large blue shift form nanoparticles prepared with 266 nm laser pulses and confirm the size reduction compared to nanoparticles prepared with 532 nm laser pulses. The structural phases determined from high-resolution transmission electron microscopy (HRTEM) and micro-Raman measurements are found to depend on the wavelength of the laser used in the ablation. The measured binding energies from X-ray photoemission spectra are in agreement with values corresponding to InP and oxidized indium.

Structural and morphological features of concentric iron oxide/carbon nanotubes obtained from phospholipids

Biologically active 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) nanotube-forming phospholipids (PLs) have been utilized as templates to prepare ferromagnetic nanotubes (FMNTs). Combining X-ray diffraction (XRD), selected area electron diffraction (SAD), high-resolution transmission electron microscopy (HRTEM), Raman, and Mössbauer spectroscopy measurements, FMNTs morphological features and chemical composition were determined. These studies showed that FMNTs consist of iron oxide/carbon/iron oxide concentric nanotubes with the amorphous carbon phase sandwiched between two iron oxide layers. The iron oxide phase consists of nanocrystalline magnetite (Fe3O4) which coexist as tetrahedral Fe3+ and octahedral Fe2.5+ sites containing minute quantities of hematite (α-Fe2O3) phase. The carbon phase consists of amorphous carbon forming an amorphous carbon nanotube (ACNT). Magnetic measurements showed that saturation magnetization (Ms) of FMNTs is 79 emu/g, but upon removal of the iron oxide outer and inner layers, ACNTs become paramagnetic. The electrical resistivity (ρ) of single FMNT is 3.3 × 10−2 Ω·m, which decreases to 5.06 × 10−4 Ω·m for ACNT. These magneto-electric properties can be easily tailored, depending upon desired applications and needs.

Honey mediated green synthesis of silver nanoparticles

The paper reports the pH controlled synthesis of silver nanoparticles using honey as reducing and stabilizing agents. By adjusting the pH of the aqueous solution containing metal ions and honey, nanoparticles of various size could be obtained at room temperature. The nanoparticles were characterized by UV–visible, high-resolution TEM, XRD and FTIR measurements. The colloid obtained at a pH of 8.5 is found to consist of monodispersed and nearly spherical silver nanoparticles of size ∼4 nm which is a significant advancement in biosynthesis. The high crystallinity with fcc phase is evidenced by clear lattice fringes in the high-resolution TEM image and peaks in the XRD pattern corresponding to (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) planes. FTIR spectrum indicates that the nanoparticles are bound to protein through the carboxylate ion group.

Structural and electrical properties of HfO 2/Dy 2O 3 gate stacks on Ge substrates

In the present work we report on the structural and electrical properties of metal–oxide–semiconductor (MOS) devices with HfO 2/Dy 2O 3 gate stack dielectrics, deposited by molecular beam deposition on p-type germanium (Ge) substrates. Structural characterization by means of high-resolution Transmission Electron Microscopy (TEM) and X-ray diffraction measurements demonstrate the nanocrystalline nature of the films. Moreover, the interpretation of the X-ray reflectivity measurements reveals the spontaneous growth of an ultrathin germanium oxide interfacial layer which was also confirmed by TEM. Subsequent electrical characterization measurements on Pt/HfO 2/Dy 2O 3/p-Ge MOS diodes show that a combination of a thin Dy 2O 3 buffer layer with a thicker HfO 2 on top can give very good results, such as equivalent oxide thickness values as low as 1.9 nm, low density of interfacial defects (2–5 × 10 12 eV − 1 cm − 2 ) and leakage currents with typical current density values around 15 nA/cm 2 at V g = V FB − 1 V.

Microwave Rapid Synthesis of Nanoporous Fe3O4 Magnetic Microspheres

Nanoporous Fe3O4 magnetic microspheres have been successfully synthesized by the way of microwave heating. The experimental process is expeditious, simple and environmentally friendly. The obtained sample is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Teller analysis (BET), Fourier transform infrared (FT-IR), high-resolution transmission electron microscopy (HRTEM) and magnetic measurements. The average size of Fe3O4 microspheres is ∼100nm and shows well-dispersed quality in aqueous solution. More importantly, the microspheres possess both nanoporous structure and superparamagnetic behaviour, which endow them powerful application potentials in chemical, biological/biomedical, physical and environmental engineering fields, for example, catalyst or drug carrier, absorption, separation and contrast agents, etc. Keywords: Solvothermal synthesis, microwave heating, nanoporous magnetic microspheres

Synthesis and Gas Sensing Properties of Urchin-Like CuO Self-Assembled by Nanorods through a Poly(ethylene glycol)-Assisted Hydrothermal Process

Urchin-like CuO, consisting of closely packed nanorods with a diameter of 10nm, have been successfully synthesized by a poly(ethylene glycol) (PEG)-assisted hydrothermal route at low temperature of 100°C. The as-obtained Urchin-like CuO were thoroughly characterized by X-ray diffraction (XRD) study, Field emission scanning electron microscope (FESEM), High-resolution transmission electron microscopy (HRTEM) and Gas sensor measurements. From the XRD pattern, all the peaks detected can be assigned to CuO in a monoclinic structure with lattice parameters a=4.662, b=3.416 and c=5.118 (JCPDS card no. 65-2309). The FESEM and TEM showed that the diameter of the urchin-like CuO sphere is about 1µm. Further investigation of the formation mechanism reveals that the PEG-assisted hydrothermal process is vital to the formation of 3D structures. Besides the template function, PEG often plays as a reductant while reacting with Cu(+2). In our case, no impurity peaks of Cu2O were observed in the XRD pattern, implying that PEG did not reduce Cu(+2) to Cu(+1). We attribute this to the high concentration of PEG. The sensor based on the urchin-like CuO nanostructures exhibit excellent ethanol-sensing properties at reduced working temperature (200°C), which shows a sensitivity two times higher than that of CuO particles(about 100nm, made from calcinations of Cu(NO3)2 at 400°C). The enhancement in sensitivity of the as-prepared CuO may be contributed to the fancy 3D nanostructures.