Nanoscale (EOT = 5.6 nm) nonvolatile memory characteristics using n-Si/SiO(2)/HfAlO nanocrystal/Al(2)O(3)/Pt capacitors

The charge storage characteristics of the high-κ HfAlO nanocrystal memory capacitors prepared by atomic layer deposition in an n-Si/SiO(2)/HfAlO/Al(2)O(3)/Pt structure have been investigated after high-temperature annealing treatment. The high-resolution transmission electron microscopy image shows that the diameter of high-κ HfAlO nanocrystal is<2?nm. The high-κ HfAlO nanocrystals have been also confirmed by x-ray photoelectron spectroscopy measurement. Due to the formation of high-κ HfAlO nanocrystals with the high-temperature (～900?°C) annealing treatment, a large hysteresis memory window of 3.7?V at a sweeping gate voltage <10?V is observed as compared to that of the as-deposited memory capacitors. A hysteresis memory window of ～1.7?V with a small sweeping gate voltage of ± 5?V is also observed. A small equivalent oxide thickness (EOT) of 5.6?nm is obtained due to the high-κ memory structure design. A significant memory window of ΔV≈0.7?V at 20?°C and ΔV≈0.6?V at 85?°C is observed after 10(4)?s of retention time, due to the charge confinement in the high-κ HfAlO nanocrystals.     

Preparation and growth mechanism of lead telluride nanocrystals by a modified molten composite-hydroxides method

PbTe nanocrystals were prepared by a modified molten composite-hydroxides method at 180 degrees C for different times, using Pb(NO3)2 and TeO2 as starting materials and KBH4 as a reductant. The nanocrystal structure and morphologies of the synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution TEM (HRTEM), respectively. The results showed that the reaction time has a significant influence on the size and shape of the as-prepared PbTe nanocrystals. As the reaction time increased, the as-prepared products were eventually transformed from nanomaterials (nanocubes, nanorods, and nanosheets) to microcrystals with different morphologies (microcubes, mciroprisms, and microplates). The formation mechanism of the PbTe was proposed, and a one-dimensional oriented attachment growth process combined with two-dimensional oriented attachment growth process was suggested for the growth of nanorods and nanosheets.     

Synthesis of germanium nanocrystals in high temperature supercritical CO(2)

Germanium nanocrystals were synthesized in supercritical (sc) CO(2) by thermolysis of diphenylgermane (DPG) or tetraethylgermane (TEG) with octanol as a capping ligand at 500?°C and 27.6?MPa. The Ge nanocrystals were characterized with high resolution transmission electron microscopy (HRTEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD). On the basis of TEM, the mean diameters of the nanocrystals made from DPG and TEG were 10.1 and 5.6?nm, respectively. The synthesis in sc-CO(2) produced much less organic contamination compared with similar reactions in organic supercritical fluids. When the same reaction of DPG with octanol was performed in the gas phase without CO(2) present, bulk Ge crystals were formed instead of nanocrystals. Thus, the solvation of the hydrocarbon ligands by CO(2) was sufficient to provide steric stabilization. The presence of steric stabilization in CO(2) at a reduced temperature of 2.5, with a reduced solvent density of only 0.4, may be attributed to a reduction in the differences between ligand-ligand interactions and ligand-CO(2) interactions relative to thermal energy.     

Fabrication of multilayered Ge nanocrystals by magnetron sputtering and annealing

Multilayered Ge nanocrystals embedded in Si and Ge oxide films have been fabricated on Si?substrate by a (SiO(2)+Ge)/(SiO(2)+GeO(2)) superlattice approach, using an rf magnetron sputtering technique with a Ge+SiO(2) composite target and subsequent thermal annealing in N(2) ambient at 750?°C for 5?min. X-ray diffraction (XRD) measurements indicated the formation of Ge nanocrystals with an average size estimated to be 9.8?nm. Raman scattering spectra showed a peak of the Ge-Ge vibrational mode shifted downwards to 298.8?cm(-1), which was caused by quantum confinement of phonons in the Ge nanocrystals. X-ray photoemission spectroscopy (XPS) analysis demonstrated that the Ge chemical state is mainly Ge(0) in the (SiO(2)+Ge) layer and Ge(4+) in the (SiO(2)+GeO(2)) layer in the superlattice structure. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (SiO(2)+Ge) layers, and had good crystallinity. This superlattice approach significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the 'Z' growth direction compared with the conventional Ge-ncs fabrication method using a single and thick SiO(2) matrix film.     

Solution-phase synthesis of germanium nanoclusters using sulfur

Sulfur is used to promote the formation of germanium nanocrystals from the robust organometallic precursor, triphenylgermanium chloride, at elevated temperatures (300?°C) in the surfactant/solvent hexadecylamine. Transmission electron microscopy shows that 8?nm germanium nanocrystals are produced that self-assemble into uniform-sized 60?nm germanium nanoclusters after purification. Electron diffraction studies show that the germanium nanoclusters have a diamond germanium crystal structure and energy dispersive x-ray spectroscopy shows that the nanoclusters are primarily composed of pure germanium.     

A general aqueous sol-gel route to Ln(2)Sn(2)O(7) nanocrystals

This paper describes a general aqueous sol-gel route for the synthesis of a series of rare earth stannates, Ln(2)Sn(2)O(7) (Ln = Y, La, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu), with pure pyrochlore phase via the assistance of a cetyltrimethyl ammonium bromide (CTAB) surfactant. The route involves first the formation of CTAB-inorganic lamellar structures and then their thermal decomposition at 800?°C to yield the pyrochlore Ln(2)Sn(2)O(7) nanocrystals. Techniques using a thermo-gravimetric/differential thermal analyzer (TG-DTA), x-ray diffraction (XRD) and transmission electron microscopy (TEM) as well as selected-area electron diffraction (SAED) have been employed to characterize the as-synthesized Ln(2)Sn(2)O(7) nanocrystals. Furthermore, photoluminescence (PL) of the 5% Eu(3+) activated Ln(2)Sn(2)O(7) nanocrystals and carbon monoxide catalytic oxidation over the as-obtained Ln(2)Sn(2)O(7) nanocrystals were investigated. The results indicate that the PL properties as well as the catalytic activity changes significantly with the ionic radii of the rare earth elements.     

Gold island films on indium tin oxide for localized surface plasmon sensing

Mechanically, chemically and optically stable gold island films were prepared on indium tin oxide (ITO) substrates by direct thermal evaporation of thin gold films (2-6?nm) without the need for pre-?or post-coating. The effect of mild thermal annealing (150?°C, 12?h) or short high temperature annealing (500?°C, 1?min) on the morphology of the gold nanostructures was investigated. ITO covered with 2?nm gold nanoislands and annealed at 500?°C for 1?min was investigated for its ability to detect the adsorption of biotinylated bovine serum albumin using local surface plasmon resonance (LSPR), and its subsequent molecular recognition of avidin.     

Influence of hydrogen on thermally induced phase separation in GeO/SiO2 multilayers

The influence of the annealing atmosphere on the temperature induced phase separation of Ge oxide in GeO(x)/SiO(2) multilayers (x≈1), leading to size controlled growth of Ge nanocrystals, is explored by means of x-ray absorption spectroscopy at the Ge K-edge. Ge sub-oxides contained in the as-deposited multilayers diminish with increasing annealing temperature, showing complete phase separation at approximately 450?°C using inert N(2) ambient. The use of reducing H(2) in the annealing atmosphere influences the phase separation even at an early stage of the disproportionation. In particular, the temperature regime where the phase separation occurs is lowered by at least 50?°C. At temperatures above 400?°C the sublayer composition, and thus the density of the Ge nanocrystals, can be altered by making use of the reduction of GeO(2) by H(2).     

From cobalt nitrate carbonate hydroxide hydrate nanowires to porous Co(3)O(4) nanorods for high performance lithium-ion battery electrodes

We have developed a simple approach for the large-scale synthesis of cobalt nitrate carbonate hydroxide hydrate (Co(CO(3))(0.35)(NO(3))(0.2)(OH)(1.1)·1.74H(2)O) nanowires via the hydrothermal process using sodium hydroxide and formaldehyde as mineralizers at 120?°C. The porous Co(3)O(4) nanorods 10-30?nm in diameter and hundreds of nanometres in length have been fabricated from the above-mentioned multicomponent nanowires by calcination at 400?°C. The morphology and structure of cobalt nitrate carbonate hydroxide hydrate nanowires and Co(3)O(4) nanorods have been characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and x-ray powder diffraction (XRD). Moreover, the porous Co(3)O(4) nanorods have been applied in the negative electrode materials for lithium ion batteries, which exhibit high electrochemical performance.     

Ge-Si-O phase separation and Ge nanocrystal growth in Ge:SiO(x)/SiO(2) multilayers--a new dc magnetron approach

Ge:SiO(x)/SiO(2) multilayers are fabricated using a new reactive dc magnetron sputtering approach. The influence of the multilayer stoichiometry on the ternary Ge-Si-O phase separation and the subsequent size-controlled Ge nanocrystal formation is explored by means of x-ray absorption spectroscopy, x-ray diffraction, electron microscopy and Raman spectroscopy. The ternary system Ge-Si-O reveals complete Ge-O phase separation at 400?°C which does not differ significantly to the binary Ge-O system. Ge nanocrystals of < 5?nm size are generated after subsequent annealing below 700?°C. It is shown that Ge oxides contained in the as-deposited multilayers are reduced by a surrounding unsaturated silica matrix. A stoichiometric regime was found where almost no GeO(2) is present after annealing. Thus, the Ge nanocrystals become completely embedded in a stoichiometric silica matrix favouring the use for photovoltaic applications.     

Fine-tuning longitudinal plasmon resonances of nanorods by thermal reshaping in aqueous media

Metallic nanoparticles that support surface plasmons are potential building units for future nanophotonic circuits, metamaterials, high-density optical data storage, etc. Many of these applications require the ability to 'dial-up' the desired plasmonic resonance modes and frequencies with high precision. Here, we demonstrate a thermal reshaping route that can be used to tailor longitudinal plasmon resonance energies of gold nanorods almost continuously from ~800 to ~560 nm. The longitudinal plasmon resonance wavelength exhibits an exponential decay function of the thermal annealing time at a given temperature. This correlates with the transmission electron microscopy characterization (TEM) which showed that the nanorod aspect ratio decreases exponentially with time, accompanying a gradual shape transformation from rod to sphere. The exponential decay half-time decreases with increasing annealing temperatures, with a value of 1.43 × 10(5) s at 50?°C down to 0.02 × 10(5) s at 100?°C. Our experimental results show that the shape transformation could be attributed to desorption of silver ions and side facet-binding Ag-Br-CTA ligands, which therefore promote the side growth leading to nanorod fattening. Compared to other synthetic methodologies to tune plasmonics, our thermal reshaping approach presents a straightforward paradigm for precisely tailoring plasmon resonance energy with a single parameter.     

Microstructural changes in CdSe-coated ZnO nanowires evaluated by in situ annealing in transmission electron microscopy and x-ray diffraction

We report on the crystallite growth and phase change of electrodeposited CdSe coatings on ZnO nanowires during annealing. Both in situ transmission electron microscopy (TEM) and x-ray diffraction (XRD) reveal that the nanocrystal size increases from ～3?to ～10?nm upon annealing at 350?°C for 1?h and then to more than 30?nm during another 1?h at 400?°C, exhibiting two distinct growth regimes. Nanocrystal growth occurs together with a structural change from zinc blende to wurtzite. The structural transition begins at 350?°C, which results in the formation of stacking faults. Increased crystallite size, comparable to the coating thickness, can improve charge separation in extremely thin absorber solar cells. We demonstrate a nearly two-fold improvement in power conversion efficiency upon annealing.     

Rare earth ions and Ge nanocrystals in SiO(2)

Experimental studies of Ge nanocrystals embedded in SiO(2) films doped with Er and Yb deposited by rf-magnetron sputtering are presented. Although inter-band photoluminescence (PL) from the Ge nanocrystals is not observed, it is nevertheless found that the presence of Ge nanocrystals is crucial for obtaining light emission from Er(3+) and Yb(3+). For both kinds of rare earth ions, the intensity of the related PL line has a maximum after heat treatment at 800?°C, and the PL excitation spectra for the two cases are very similar. This suggests that the presence and the structure of the nanocrystals are important for the efficiency of PL from Er(3+) and Yb(3+). Experiments performed with multilayer structures of Ge nanocrystals and SiO(2) show that the optically active rare earth ions are located in the SiO(2) layers, and not inside the Ge nanocrystals. The mechanism of energy transfer from Ge nanocrystals to the rare earth ions is found to be non-optical.     

In situ synthesis and characterization of GaN nanorods through thermal decomposition of pre-grown GaN films

Herein we describe a thermal treatment route to synthesize gallium nitride (GaN) nanorods. In this method, GaN nanorods were synthesized by thermal treatment of GaN films at a temperature of 800?°C. The morphology and structure of GaN nanorods were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that GaN nanorods have a hexagonal wurtzite structure with diameters ranging from 30 to 50?nm. Additionally, GaN nanoplates are also founded in the products. The growth process of GaN nanostructures was investigated and a thermal decomposition mechanism was proposed. Our method provides a cost-effective route to fabricate GaN nanorods, which will benefit the fabrication of one-dimensional nanomaterials and device applications.     

Deterministic shape-selective synthesis of nanowires, nanoribbons and nanosaws by steady-state vapour-transport

We demonstrate the deterministic shape-selective synthesis and growth of CdSe nanowires, nanosaws and nanoribbons by a simple vapour-transport process in a tube furnace. The key step, in order to achieve reproducible shape selectivity for a given set of deposition parameters, is to exclude any effects of the temperature ramping. We prove that an efficient precursor-flow shutter is achieved just by varying the total furnace pressure. We then present a shape-diagram linking the different nanocrystals morphologies to only two parameters: powder and substrate temperature. These are varied in the 550-700?°C and 400-600?°C range, respectively. A model explaining the shape control is discussed.     

A facile single-source route to CdS nanorods

CdS nanorods were synthesized on a large scale by thermolyzing a single-source precursor, (Me(4)N)(4)[S(4)Cd(10)(SPh)(16)], in a single surfactant system. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and x-ray powder diffraction (XRD) have been used to characterize the morphology and crystal structure of the sample. The TEM images show that the CdS nanorods are uniform with an aspect ratio of about 9:1. The XRD result demonstrates that the nanorods are in a wurtzite structure. The nanorods exhibit quantum size effects from the optical absorption spectrum. The influence of reaction conditions on the growth of CdS nanorods demonstrates that high precursor concentration and high reaction temperature (>190?°C) are favorable for the formation of CdS nanorods.     

Cluster synthesis of branched CdTe nanocrystals for use in light-emitting diodes

Highly luminescent cadmium telluride (CdTe) nanocrystals were synthesized using Li(2)[Cd(4)(SPh)(10)] as a reactive Cd cluster compound at relatively low temperature, making it a safe precursor for the large scale synthesis of CdTe nanocrystals. Transmission electron microscopy (TEM) showed that the shape of the CdTe nanocrystals changes from nanorods to branched structures with increasing reaction time. The nanocrystals show high luminescent quantum yields up to 37% for CdTe branched nanostructures, and as high as 52% for CdTe/CdS core-shell heterostructures. CdTe/CdS nanocrystals were used to make light-emitting diodes in combination with organic layers for electron and hole injection. The devices show a maximum luminance efficiency of 0.35?cd?A(-1).     

Preparation, microstructure and hydrogen sorption properties of nanoporous carbon aerogels under ambient drying

Organic aerogels are prepared by the sol-gel method from polymerization of resorcinol with furfural. These aerogels are further carbonized in nitrogen in order to obtain their corresponding carbon aerogels (CA); a sample which was carbonized at 900?°C was also activated in a carbon dioxide atmosphere at 900?°C. The chemical reaction mechanism and optimum synthesis conditions are investigated by means of Fourier transform infrared spectroscopy and thermoanalyses (thermogravimetric/differential thermal analyses) with a focus on the sol-gel process. The carbon aerogels were investigated with respect to their microstructures, using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM) and nitrogen adsorption measurements at 77?K. SAXS studies showed that micropores with a radius of gyration of <0.35 ± 0.07 to 0.55 ± 0.05?nm were present, and TEM measurements and nitrogen adsorption showed that larger mesopores were also present. Hydrogen storage properties of the CA were also investigated. An activated sample with a Brunauer-Emmett-Teller surface area of 1539 ± 20?m(2)?g(-1) displayed a reasonably high hydrogen uptake at 77?K with a maximum hydrogen sorption of 3.6?wt% at 2.5?MPa. These results suggest that CA are promising candidate hydrogen storage materials.     

Preparation and characterization of thermosensitive PNIPAA-coated iron oxide nanoparticles

A new and facile approach was established to fabricate thermoresponsive poly(N-isopropylacrylamide) (PNIPAA) coated iron oxide nanoparticles in a non-aqueous medium. The morphology and structure of the nanoparticle-doped composite were analyzed by?means of transmission electron microscopy (TEM), x-ray powder diffraction (XRD), and Fourier transformation infrared spectrometry (FTIR). The thermosensitivity of the composite was also investigated. Results indicated that the oil-soluble iron oxide nanoparticles encapsulated with PNIPAA, composed of an inorganic iron oxide core and biocompatible PNIPAA shell, were dispersed well in water and had a sphere-like shape. The PNIPAA-coated iron oxide nanoparticles with such a kind of core-shell structure showed excellent thermosensitivity. Namely, the aqueous suspension of PNIPAA-coated iron oxide nanoparticles dramatically changed from transparent to opaque as the temperature increased from room temperature to 38?°C, showing potential as optical transmittance switch materials and their significance in the fields of protein adsorption and purification controlled release, and drug?delivery.     

Effect of Sulfur Precursor on Dimensions of One-dimensional CdS Nanocrystals

One-dimensional CdS nanocrystals have been prepared by solvothermal method using cadmium acetate as a cadmium precursor,elemental sulfur and Na2S,as a sulfur precursor,and ethylenediamine as a solvent at 150℃ for 5 h.The nanocrystals were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM) and UV-Vis absorption spectroscopy.XRD patterns indicate that both Na2S and elemental sulfur as the sulfur precursor result in CdS nanorods with wurtzite phase(h...