Single Molecular Precursor Research Articles

Mn2O3–4TiO2 semiconducting composite thin films for photo-electrochemical water splitting

Mn2O3–4TiO2 composite thin films were deposited on fluorine doped tin oxide (FTO) coated glass substrates from a solution of a newly synthesised hexanuclear single source molecular precursor [Mn2Ti4(TFA)8(THF)6(OH)4(O)2]·0.4THF 1 (where TFA=trifluoroacetato and THF=tetrahydrofuran) by aerosol-assisted chemical vapour deposition (AACVD) technique. The precursor 1 was characterised by melting point, elemental analysis, Fourier transform infra-red (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR) spectroscopy, thermogravimetry/derivative thermogravimetry (TG/DTG) and single crystal X-ray analysis. The chemical composition and surface morphology of the fabricated thin film which have been determined by X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), suggest the formation of impurity-free nanocrystalline mixtures of Mn2O3–4TiO2 composite with well-defined and evenly distributed particles in the size range of 112–308nm. The indirect optical band gap energies of 1.20 and 2.81eV were estimated by UV–Vis spectrophotometry. The current–voltage characterisation proved that the composite Mn2O3–4TiO2 electrodes exhibit n-type semiconducting behaviour. The maximum photocurrent density of 343μA/cm2 at 0.7V versus Ag/AgCl/3M KCl (∼1.23V versus RHE) was obtained for the Mn2O3–4TiO2 photoelectrode deposited at 450°C for 45min from 0.006M solution of 1 in THF.

Surface functionalized bare and core–shell quantum dots in poly(ethylene-co-vinyl acetate) for light selective nanocomposite films

Light-selective polymer films based on poly(ethylene-vinyl acetate) (PEVA) are of significant interest in emerging solar materials, including PV encapsulants and greenhouse plastic films. Quantum dots (QDs) have been shown to absorb UV light while transmitting light of higher wavelengths which potentially can be advantageous for enhancing PV efficiencies or in the case of greenhouse films, controlling plant growth. However, a simple procedure for integration of the QD nanocrystals into PEVA films with retention of the light selective properties has been elusive. In this work we report a simple procedure for loading QD nanocrystals into PEVA using a novel silane functionalized QD approach by simple melt-mixing in a twin-screw extruder. Both bare CdS and core–shell CdS–ZnS QDs were synthesized by colloidal chemistry using a facile single-molecular precursor method, and then functionalized with (3-mercaptopropyl)trimethoxysilane to improve their compatibility with PEVA. These nanocrystals were then melt-mixed into PEVA in a mini-compounder, with the resulting blends extruded and pressed into thin films using a Universal Film Maker and a Carver hydraulic press. Both experimental and commercial greenhouse films were analyzed by electron, confocal and atomic force microscopy, showing that the silane ligand enhanced dispersibility of QDs throughout the PEVA. The bare and core–shell QDs were studied at various loading levels from 0.1% to 0.5%, showing high light transmissions (90%) and decreased UV transmission with increased QD loading.

Synthesis, characterization and p–n type gas sensing behaviour of CuFeO2 delafossite type inorganic wires using Fe and Cu complexes as single source molecular precursors

CuFeO2 delafossite type nanowires with a diameter of 180 nm were successfully synthesized by electrospinning using an equimolar mixture of molecular copper and iron precursors and polyacrylnitrile as polymer template followed by calcination. This mixture was electrospun under ambient conditions. The copper and iron precursor complexes diaqua-bis[2-(methoxyimino)-propanato] M(II) (M = Cu, Fe) were fully characterized by spectroscopic and electrochemistry methods (NMR, IR, cyclovoltammetry) as well as by single crystal structure and by thermogravimetric analysis (TGA). The pre-ceramic electrospun composite fiber mats were subsequently heat treated in a two step procedure to yield the final CuFeO2 delafossite type nanowires agglomerated as microsized ceramic mats. Intermediate oxide phases as well as the finally obtained CuFeO2 fibrous mats composed of delafossite type nanowires were characterized analytically by temperature dependent powder X-ray crystallography (PXRD). Their topological morphology was studied by scanning electron microscopy (SEM). The obtained CuFeO2 fibrous mats were studied with respect to their O2 gas sensing behaviour and variable p and n-type semiconducting behaviour depending on temperature was observed.

New ternary compounds containing Zn–Cu and Zn–Ag from single molecular source precursors

Heterobimetallic complexes [(PPh3)Cu(SCOPh)3Zn(PPh3)] and [(PPh3)2Ag(SCOPh)2Zn(SCOPh)(0.5H2O)] were used as single molecular sources for the syntheses of ternary compounds. These complexes upon pyrolysis at 350 °C in the solid state yielded ZnS/CuS and ZnS/Ag2S alloys respectively. In oleylamine solution decomposition of the complexes took place at 165 °C only leading to the formation of the corresponding sulfide nanoparticles. The bulk sulfide materials have been characterized by SEM-EDX, XPS and powder X-ray diffraction techniques. The nanoparticles have been characterized by EDS-elemental mapping and HRTEM.

Synthesis of iron selenide nanocrystals and thin films from bis(tetraisopropyldiselenoimidodiphosphinato)iron(ii) and bis(tetraphenyldiselenoimidodiphosphinato)iron(ii) complexes

Iron selenide nanocrystals (NCs) were synthesised by the thermolysis of single molecular precursors, bis(tetraisopropyldiselenoimidodiphosphinato)iron(II) (3) and bis(tetraphenyldiselenoimidodiphosphinato)iron(II) (4) in oleylamine and hexadecylamine at different growth temperatures. TEM images of the NCs showed the rod and plate-like crystallites. Both complexes were also used for the deposition of thin films by Aerosol Assisted Chemical Vapour Deposition (AACVD) onto silicon substrates. SEM images of thin films deposited from complex (3) and (4) showed significantly different morphologies under similar conditions. X-ray single crystal structures of complexes [Fe{(SePPh2)2N}2] (4) and [(SePPh2)2N)–O–(SePPh2)2N)] (5) were also determined.

Synthesis and nonlinear optical switching of Bi2S3 nanorods and enhancement in the NLO response of Bi2S3@Au nanorod-composites

Organic solvent dispersible bismuth(III) sulfide (Bi2S3) nanorods were prepared by the chemical decomposition of tris(monothiobenzoato) bismuth(III), [Bi(SCOPh)3] as a single molecular precursor in the presence of trioctylphosphine oxide (TOPO) and 1-dodecanethiol (DdT). The rod surfaces of the as-prepared Bi2S3 nanorods were attached to Au nanoparticles (NPs) via direct reduction of KAuCl4·2H2O in the presence of octylamine (OTA) and oleic acid (OA). The attachment of the Au NPs onto the Bi2S3 rod surfaces was found to be relatively stable. The prepared samples (both Bi2S3 and Bi2S3@Au) were characterized by powder X-ray diffraction (PXRD), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) analysis and UV-vis spectroscopy. Their nonlinear-absorption (NLA) responses were studied using laser pulses at 532, 780 and 1064 nm, and the observed enhancement in the NLO response of Bi2S3@Au was discussed. Optical switching behaviour was observed at all the wavelengths.

Hydrogen Adsorption Study upon Ni/Al2O3 Nano-composite Synthesized by MOCVD Technique

The hydrogen adsorption (storage) studies upon M/AI2O3 nano-composite prepared by metal organic chemical vapor deposition technique (MOCVD) exploiting single source molecular precursor (SSP) approach were carried out. The Ni/Al2O3nano-composite is prepared in cold walled MOCVD reactor by the decomposition of SSP, [H2Al(OtBu)]2, on a substrate holding Ni(acac)2 powder. The SSP is a reducing agent which reduces Ni+2 to Ni0 and works as source for Al2O3 matrix in which the Ni0 is dispersed. The resulting Ni/Al2O3 nano-composite is characterized by XRD, SEM, TEM, and EDX. The hydrogen adsorption (storage) studies are performed using home-made Sievert's type apparatus. The hydrogen storage studies reveal that approximately 2.9% (mass ratio) hydrogen can be stored in the Ni/Al2O3 nano-composite. The results show that Ni/Al2O3 nano-composite can be a potential candidate for hydrogen storage which can be used for onboard fuel purposes.

Synthesis and characterization of functionalized dithiocarbamates: New single-source precursors for CdS

Novel single-molecular precursors for CdS are prepared by reacting functionalized secondary amine and CS2 with cadmium acetate dihydrate. All these precursors are characterized by elemental analysis, infrared spectroscopy and solid-state 13C NMR. CdS semiconductor nanoparticles are synthesized using these precursors by a single-step solvothermal method with ethylenediamine at 117°C. The synthesized semiconductor nanoparticles are investigated by infra-red spectroscopy, powder X-ray diffraction analysis, energy-dispersive X-ray spectroscopy analysis, scanning electron microscopy, field emission scanning electron microscopy, transmission electron microscopy, high resolution transmission microscopy, selected area electron diffraction analysis and Raman spectroscopy. The synthesized CdS are hexagonal (zinc wurtzite) crystalline material, which are indicative of the reduction of particles. Comparison with the CdS and the mixture of CdS/CdS⋅0.5gl revealed that the CdS/CdS⋅0.5gl exhibited a well crystalline structure.

High quantum-yield CdSexS1−x/ZnS core/shell quantum dots for warm white light-emitting diodes with good color rendering

Composition-controllable ternary CdSexS1−x quantum dots (QDs) with multiple emission colors were obtained via a hot-injection-like method at a relatively low injection temperature (230 ° C) in octadecene. Then highly fluorescent CdSexS1−x/ZnS core/shell (CS) QDs were synthesized by a facile single-molecular precursor approach. The fluorescent quantum yield of the resulting green (λem = 523 nm), yellow (λem = 565 nm) and red (λem = 621 nm) emission of CS QDs in toluene reached up to 85%, 55% and 39%, respectively. Moreover, a QDs white light-emitting diode (QDs-WLED) was fabricated by hybridizing green-, yellow- and red-emitting CdSexS1−x/ZnS CS QDs/epoxy composites on a blue InGaN chip. The resulting four-band RYGB QDs-WLED showed good performance with CIE-1931 coordinates of (0.4137, 0.3955), an Ra of 81, and a Tc of 3360 K at 30 mA, which indicated the combination of multiple-color QDs with high fluorescence QYs in LEDs as a promising approach to obtain warm WLEDs with good color rendering.

Tuning the Microstructure of γ-Ba4Nb2O9 Polymorph Prepared from Single-Molecular Precursor

Although γ-Ba4Nb2O9 was considered to be metastable at room temperature (RT) and, therefore, prepared only by quenching from high temperatures, a new procedure for preparation of pure γ-Ba4Nb2O9 from a single-molecular precursor, the oxalate-based complex {Ba2(H2O)5[NbO(C2O4)3]HC2O4}·H2O, is described. This study focuses on controlling the phase composition and the crystallite domain lengths by altering preparation conditions, namely, (i) the time for which samples were held at the given temperature and (ii) the cooling rate. The high-temperature γ-Ba4Nb2O9 polymorph has been successfully retained and stabilized at RT; the desired crystallite size in the nanoscale regime, ranging from ∼5 to 20 nm, can easily be tuned. The crystallite domain length and lattice strain were calculated from X-ray diffraction line-broadening analysis performed during Rietveld structure refinement.

Conclusive Growth of CdTe Nanorods by Solvothermal Decomposition Using Single Source Precursors

CdTe nanorods are synthesized by solvothermal decomposition, using single source molecular precursors (SSMP) cadmium (II), complex of bis-(aminopropyl telluride) (SSMP-I) and cadmium (II) bis-(isopropyl telluro) propane (SSMP-II) and quinoline as solvent at relatively low temperature (210°C). As synthesized nanomaterials are structurally characterized by XRD and SEM, SEM micrographs revealed formation of rod shapes structures whose dimensions change with the source precursor molecule. The average crystallite size estimated from XRD data is 29.78 and 28.94 nm respectively using Precursors I and II. The average size of nanorods is 1.237 μm and 0.15μm respectively, estimated from SEM micrographs. These are much larger than the average crystallite size estimated from XRD data. This is attributed to the agglomeration of nanocrystallites as quinoline is not a good capping agent.

A Single Source Precursor Route to Group 13 Homo‐ and Heterometallic Oxides as Highly Active Supports for Gold‐Catalyzed Aerobic Epoxidation of trans‐Stilbene

AbstractA new Mitsubishi‐type of star‐shaped homoleptic derivative of indium(III), In4(mdea)6 (2, mdeaH2 = N‐methyldiethanolamine), was synthesized by the chloro–aminoalkoxo exchange reaction of a heteroleptic complex In6Cl6(mdea)6 (1) and used as a facile single source molecular precursor for the sol–gel preparation of high surface area indium oxide. Successful deposition of gold nanoparticles (1 wt.‐%) of average size 3.3 nm on the above metal oxide by using HAuCl4·3H2O afforded a highly efficient Au/In2O3 catalyst for the aerobic epoxidation of trans‐stilbene at low temperature. The above single source precursor approach was further extended to obtain other group 13 homo‐ and heterometallic oxides, namely, α‐Ga2O3, β‐Ga2O3 and Al4Ga2O9, as highly active supports for gold catalysts. The obtained Au/M2O3 (M = Ga, In) and Au/Al4Ga2O9 catalysts were thoroughly characterized by using several physicochemical techniques such as XRD, high resolution transmission electron microscopy (HR‐TEM), energy‐dispersive X‐ray (EDX) spectroscopy, and X‐ray photoelectron spectroscopy (XPS). A comparative study of the above catalysts for the model aerobic oxidation of stilbene in methylcyclohexane was undertaken.

Thermochemical Vapor Growth of β-SiC Nanospheres

SiC nanospheres have been grown successfully via thermochemical decomposition of tetramethylsilane as a single molecular precursor for Si and C free from halogen. The growth temperature was varied from 700 to 900 degrees C in presence of H2, Ar, and N2 as process gases. XRD analyses showed that the synthesized nanoparticles under various experimental conditions are mainly composed of SiC phase and have broad and low intensity diffraction peaks implying its tiny size characteristics. SEM and TEM images confirmed the formation of SiC nanospheres in the size range of 100-250 nm. Denser cluster formation was observed for the sample deposited in presence of N2 gas. FTIR spectrum showed that the stretching vibration band corresponding to Si-O bond was observed whereas that corresponding to Si-H bond disappeared for the sample deposited in presence of N2 gas. This indicated the formation of oxygen-containing SiC layer on the nanospheres surface. Slight positive and negative weight changes (1.5-7 wt.%) were observed upon heating of SiC nanospheres in dynamic nitrogen atmosphere upto 500 degrees C. This slight changes might be due to the removal of residual un-disproportionated materials and/or formation of N2-dopped SiC nanospheres.

P‐67: Enhanced Photoluminescence Property of Single‐Molecular Precursor CdSe/ZnS Quantum Rod

AbstractIn this paper, an effective synthesis route for CdSe/ZnS core/shell quantum rod fabricated by a single‐molecular precursor is introduced. From the experiment results, the optimum volume ratio of as‐prepared CdSe to ZnS raw material can be achieved of 1:1.7. The photoluminescence intensity of CdSe/ZnS increases to 3‐fold compared to CdSe.

Synthesis of TiO2 thin films using single molecular precursors by MOCVD method for dye-sensitized solar cells application and study on film growth mechanism

For dye-sensitized solar cells application, in this study, we have synthesized TiO2 thin films at deposition temperature in the range of 300–750°C by metalorganic chemical vapor deposition (MOCVD) method. Titanium(IV) isopropoxide, {TIP, Ti(OiPr)4} and Bis(dimethylamido)titanium diisopropoxide, {BTDIP, (Me2N)2Ti(OiPr)2} were used as single source precursors that contain Ti and O atoms in the same molecule, respectively. Crack-free, highly oriented TiO2 polycrystalline thin films with anatase phase were deposited on Si(100) with TIP at temperature as low as 450°C. XRD and TED data showed that below 500°C, the TiO2 thin films were dominantly grown in the [211] direction on Si(100), whereas with increasing the deposition temperature to 700°C, the main film growth direction was changed to [200]. Above 700°C, however, rutile phase TiO2 thin films have only been obtained. In the case of BTDIP, on the other hand, only amorphous film was grown on Si(100) below 450°C while a highly oriented anatase TiO2 film in the [200] direction was obtained at 500°C. With further increasing deposition temperatures over 600°C, the main film growth direction shows a sequential change from rutile [101] to rutile [400], indicating a possibility of getting single crystalline TiO2 film with rutile phase. This means that the precursor together with deposition temperature can be one of important parameters to influence film growth direction, crystallinity as well as crystal structure. To investigate the CVD mechanism of both precursors in detail, temperature dependence of growth rate was also carried out, and we then obtained different activation energy of deposition to be 77.9 and 55.4kJ/mol for TIP and BTDIP, respectively. Also, we are tested some TiO2 film synthesized with BTDIP precursor to apply dye-sensitized solar cell.

High-throughput route to Cu2−xS nanoparticles from single molecular precursor

The copper(II) complex of 1,1,5,5-tetra-iso-propyl-2-thiobiuret was used as a single source precursor for the synthesis of copper sulfide nanoparticles in a continuous flow process. The nanoparticles had a spherical morphology and were produced either as a pure Cu7S4 or Cu7S4 with minor impurities of Cu9S5.

Synthesis and characteristics of NH2-functionalized polymer films to align and immobilize DNA molecules

We developed a method to use NH2-functionalized polymer films to align and immobilize DNA molecules on a Si substrate. The plasma-polymerized cyclohexane film was deposited on the Si substrate according to the radio frequency plasma-enhanced chemical vapor deposition method using a single molecular precursor, and it was then treated by the dielectric barrier discharge method in a nitrogen environment under atmospheric pressure. Changes in the chemistry of the surface functional groups were studied using X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy. The wettability of the surfaces was examined using dynamic contact angle measurements, and the surface morphology was evaluated using atomic force microscopy.We utilized a tilting method to align λ-DNA molecules that were immobilized by the electrostatic interaction between the amine groups in NH2-functionalized polymer films and the phosphate groups in the DNA. The DNA was treated with positively charged gold nanoparticles to make a conductive nanowire that uses the DNA as a template. We observed that the NH2-functionalized polymer film was useful for aligning and immobilizing the DNA, and thus the DNA-templated nanowires.

Magnetic properties of nanosized γ-Fe2O3 and α-(Fe2/3Cr1/3)2O3, prepared by thermal decomposition of heterometallic single-molecular precursor

Thermal decomposition of the trinuclear complex [Fe2CrO(CH3COO)6(H2O)3]NO3 at 300, 400 and 500°C gave γ-Fe2O3 nanoparticles along with amorphous chromium oxide, while decomposition of the same starting compound at 600 and 700°C led to the formation of α-(Fe2/3Cr1/3)2O3 nanoparticles. Size of γ-Fe2O3 nanoparticles, determined by X-ray diffraction, was in the range from 9 to 11nm and increased with formation temperature growth. Average size of α-(Fe2/3Cr1/3)2O3 nanoparticles was about 40nm and almost did not depend on the temperature of its formation. γ-Fe2O3 nanoparticles possessed superparamagnetic behavior with blocking temperature 180–250K, saturation magnetization 29–35emu/g at 5K, 44–49emu/g at 300K and coercivity 400–600Oe at 5K. α-(Fe2/3Cr1/3)2O3 nanoparticles were characterized by low magnetization values (2.7emu/g at 70kOe). Such magnetic properties can be caused by non-compensated spins and defects present on the surface of these nanoparticles. The increase of α-(Fe2/3Cr1/3)2O3 formation temperature led to decrease of magnetization (being compared for the same fields), which may be caused by decrease of the quantity of defects or non-compensated spins (due to decrease of particles' surface).

Highly luminescent blue emitting CdS/ZnS core/shell quantum dots via a single-molecular precursor for shell growth

Highly luminescent blue-emitting CdS/ZnS core/shell quantum dots (QDs) were synthesized in N-oleoylmorpholine by two facile steps: first, the CdS core QDs were prepared via a simple one-pot method involving a direct reaction of Cd precursor cadmium stearate and S precursor S powder in solvent N-oleoylmorpholine; second, ZnS shells were successively overcoated on CdS core through the decomposition of single molecular precursor zinc diethyldithiocarbamate. The thickness of shell was precisely tuned by controlling drip feed speed and amount of shell precursor. The obtained CdS/ZnS core/shell QDs showed the maximum photoluminescent quantum yield of 54.8% and narrow spectra bandwidth, exhibiting high monodispersity, good color purity and long fluorescent lifetimes. The CdS/ZnS core/shell QDs with tunable emission wavelength of 424–470 nm were obtained by controlling the thickness of ZnS shell overgrown on different-sized CdS QDs, which are promising materials for blue light-emitting devices.

Hierarchically structured meso-macroporous aluminosilicates with high tetrahedral aluminium content in acid catalysed esterification of fatty acids

A simple synthesis pathway has been developed for the design of hierarchically structured spongy or spherical voids assembled meso-macroporous aluminosilicates with high tetrahedral aluminium content on the basis of the aqueous polymerisation of new stabilized alkoxy-bridged single molecular precursors. The intimate mixing of an aluminosilicate ester (sec-BuO)2–Al–O–Si(OEt)3 and a silica co-reactant (tetramethoxysilane, TMOS) with variable ratios and the use of alkaline solutions (pH 13.0 and 13.5) improve significantly the heterocondensation rates between the highly reactive aluminium alkoxide part of the single precursor and added silica co-reactant, leading to aluminosilicate materials with high intra-framework aluminium content and low Si/Al ratios. The spherically-shaped meso-macroporosity was spontaneously generated by the release of high amount of liquid by-products (water/alcohol molecules) produced during the rapid hydrolysis and condensation processes of this double alkoxide and the TMOS co-reactant. It has been observed that both pH value and Al–Si/TMOS molar ratio can strongly affect the macroporous structure formation. Increasing pH value, even slightly from 13 to 13.5, can significantly favour the incorporation of Al atoms in tetrahedral position of the framework. After the total ionic exchange of Na+ compensating cations, catalytic tests of obtained materials were realised in the esterification reaction of high free fatty acid (FFA) oils, showing their higher catalytic activity compared to commercial Bentonite clay, and their potential applications as catalyst supports in acid catalysed reactions.