Physicochemical characterization of Fe3O4/SiO2/Au multilayer nanostructure

The purpose of this research was to synthesize and characterize gold-coated Fe₃O₄/SiO₂ nanoshells for biomedical applications. Magnetite nanoparticles (NPs) were prepared using co-precipitation method. Smaller particles were synthesized by decreasing the NaOH concentration, which in our case this corresponded to 35 nm using 0.9 M of NaOH at 750 rpm with a specific surface area of 41 m² g⁻¹. For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetization range of 80–100 emu g⁻¹ and coercivity of 80–120 Oe for particles between 35 and 96 nm, respectively. The magnetic NPs were modified with a thin layer of silica using Stober method. Small gold colloids (1–3 nm) were synthesized using Duff method and covered the amino functionalized particle surface. Magnetic and optical properties of gold nanoshells were assessed using Brunauer–Emmett–Teller (BET), vibrating sample magnetometer (VSM), UV–Vis spectrophotometer, atomic and magnetic force microscope (AFM, MFM), and transmission electron microscope (TEM). Based on the X-ray diffraction (XRD) results, three main peaks of Au (1 1 1), (2 0 0) and (2 2 0) were identified. The formation of each layer of a nanoshell is also demonstrated by Fourier transform infrared (FTIR) results. The Fe₃O₄/SiO₂/Au nanostructures, with 85 nm as particle size, exhibited an absorption peak at ∼550 nm with a magnetization value of 1.3 emu g⁻¹ with a specific surface area of 71 m² g⁻¹.     

Growth and characterization of nitrogen-doped TiO2 thin films prepared by reactive pulsed laser deposition

Nitrogen-doped titanium dioxide (TiO₂) thin films were grown on (001) SiO₂ substrates by reactive pulsed laser deposition. A KrF* excimer laser source (λ = 248 nm, τ_FWHM ≅ 10 ns, ν = 10 Hz) was used for the irradiations of pressed powder targets composed by both anatase and rutile phase TiO₂. The experiments were performed in a controlled reactive atmosphere consisting of oxygen or mixtures of oxygen and nitrogen gases. The obtained thin film crystal structure was investigated by X-ray diffraction, while their chemical composition as well as chemical bonding states between the elements were studied by X-ray photoelectron spectroscopy. An interrelation was found between nitrogen concentration, crystalline structure, bonding states between the elements, and the formation of titanium oxinitride compounds. Moreover, as a result of the nitrogen incorporation in the films a continuous red-shift of the optical absorption edge accompanied by absorption in the visible spectral range between 400 and 500 nm wavelength was observed.     

NO2 gas sorption studies of Ge33Se67 films using quartz crystal microbalance

A study on the NO₂ gas sorption ability of amorphous Ge₃₃Se₆₇ coated quartz crystal microbalance (QCM) is presented. The thin films have been characterized before and after sorption/desorption processes of NO₂ by energy-dispersive X-ray spectroscopy (EDS), grazing angle X-ray diffraction (GAXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and atom force microscopy (AFM) measurements. These studies indicated that physisorption occurs when NO₂ gas molecules are introduced into the chalcogenide film and the thin film composition or structure do not change. The mass loading due to NO₂ gas sorption was calculated by the resonator’s frequency shift. At the conditions of our experiment, up to 6.8 ng of the gas was sorbed into 200 nm thick Ge₃₃Se₆₇ film at 5000 ppm NO₂ concentration. It has been established that the process of gas molecules sorption is reversible.     

Femtosecond laser deposition of TiO2 by laser induced forward transfer

Femtosecond lasers have been used for laser induced forward transfer (LIFT) of TiO₂, a wide-band semiconductor with many industrial and research applications. TiO₂ polycrystalline thin films on quartz (obtained by pulsed laser deposition) were used as donors and both quartz and fluorine-doped tin dioxide coated glass substrates as acceptors. LIFT was performed at the laser wavelengths of 248 and 800 nm with pulses of 450 and 300 fs respectively. The transferred material was characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction and micro-Raman spectroscopy to determine the composition and crystalline quality, and by scanning electron microscopy and atomic force microscopy to assess the surface morphology. The relation between these properties and the laser transfer conditions, including wavelength, pulse energy and acceptor substrate, are presented.     

Characterization of ultra-thin TiO2 films grown on Mo(112)

Ultra-thin TiO₂ films were grown on a Mo(112) substrate by stepwise vapor depositing of Ti onto the sample surface followed by oxidation at 850 K. X-ray photoelectron spectroscopy showed that the Ti 2p peak position shifts from lower to higher binding energy with an increase in the Ti coverage from sub- to multilayer. The Ti 2p peak of a TiO₂ film with more than a monolayer coverage can be resolved into two peaks, one at 458.1 eV corresponding to the first layer, where Ti atoms bind to the substrate Mo atoms through Ti-O-Mo linkages, and a second feature at 458.8 eV corresponding to multilayer TiO₂ where the Ti atoms are connected via Ti-O-Ti linkages. Based on these assignments, the single Ti 2p_3/2 peak at 455.75 eV observed for the Mo(112)-(8 × 2)-TiO_x monolayer film can be assigned to Ti³⁺, consistent with our previous results obtained with high-resolution electron energy loss spectroscopy.     

Spray deposition and property analysis of anatase phase titania (TiO2) nanostructures

Anatase phase titanium dioxide thin films have been deposited at various substrate temperatures by chemical spray pyrolysis of an aerosol of titanyl acetylacetonate. Deposited TiO₂ films were nanocrystalline and preferentially oriented along [101] direction, uniform and adherent to the glass substrate. Best films processed at 450 °C were characterized to analyze its phase composition, texture, roughness, optical and electrical properties. X-ray photoelectron spectroscopy revealed that the surface of the film has only the Ti⁴⁺ cations to form perfect TiO₂ stoichiometry with less amount of hydration. Atomic force microscopy image demonstrated the existence of homogeneous and rough surface, suitable for electrocatalytic applications. The film has an optical transmittance more than 90% and the refractive index of 2.07 was recorded at the wavelength 633 nm. Due to nano-sized grains, obtained optical band gap (3.65 eV) of the TiO₂ thin film was larger than that of the bulk TiO₂ (3.2 eV). Calculated porosity of the films 0.44, revealed the porous nature of the films. Hall measurements indicated that these materials are p-type and yield a carrier density of the order 8.8 × 10²⁰ cm⁻³ and a carrier mobility of 0.48 × 10⁻⁶ cm²/Vs. The dc electrical conductivity was therefore very low (8.91 × 10⁻⁶ S/cm) because of lower value of mean free path of the charge carriers (4.36 × 10⁻¹¹ cm). It gives an impression that the process of spray pyrolysis provides an easy way to tailor make thin films possessing superior properties.     

Micro-Raman spectroscopy study of surface transformations induced by excimer laser irradiation of TiO2

Pressed disks of TiO₂ powder particles (≈1 μm in size) have been irradiated with a pulsed KrF (248 nm) excimer laser source at fluences between 0.1 and 1 J cm⁻². Surface films (1.5–2 μm thick) have been studied by Raman microprobe spectroscopy and atomic force microscopy (AFM). The Raman study reveals a three-layer structure for the irradiated anatase powders. A dark layer of reduced oxide is sandwiched between a top coating of molten/resolidified rutile and an underlying defective, slightly oxygen-deficient mixed-phase of rutile and anatase. AFM measurements indicate that a smooth surface layer coexisting with the initial rough grain morphology gradually appears with increasing fluence. At low fluence, anatase is reduced in a dark film and further transformed into rutile. At intermediate fluence, a shiny coating of resolidified stoichiometric rutile forms on the dark film. It gets thicker as the fluence increases while darkening of the sublayer intensifies up to a maximum of approximately 700 mJ cm⁻². At high fluence, however, melting and re-oxidation (and eventually ablation) prevail over reduction; the whole layer turns into a greyish crust of mostly resolidified rutile in non-ablated regions. A physico-chemical mechanism is proposed to explain the in-depth distribution of the various components as a function of fluence.     

Studies on morphological and optoelectronic properties of MEH-CN-PPV:TiO2 nanocomposites

Nanosized TiO₂ has been synthesized solvothermally using an autoclave. X-ray diffraction and electron microscopy studies elucidate that the synthesized nanoparticles are strongly crystalline and are dominantly in anatase phase. UV–vis and photoluminescence (PL) spectroscopy studies show a blue shift phenomenon in the synthesized nanoparticle in contrast to the bulk anatase TiO₂ which furnish evidence in support of quantum size effect. The nanocomposites of TiO₂ and MEH-CN-PPV have been prepared and characterized structurally (AFM, TEM) and optically (absorbance and photoluminescence). The nanocomposites have been used in light emitting diodes and electroluminescence (EL) and current density (J–V) of the device has been evaluated. The enhanced EL at elevated voltages for MEH-CN-PPV:5% TiO₂ hybrid device suggests influence of the reduced particle size and modified surface morphology.     

Ion beam modification of TiO2 films prepared by Cat-CVD for solar cell

The effects of nitrogen ion bombardment on TiO₂ films prepared by the Cat-CVD method have been studied to improve the optical and electrical properties of the material for use in Si thin film solar cells. The refractive index n and the dark conductivity of the TiO₂ film increased with irradiation time. The refractive index n of the TiO₂ film was changed from 2.1 to 2.4 and the electrical conductivity was improved from 3.4 × 10^− 2 to 1.2 × 10^− 1 S/cm by the irradiation. These results are due to the formation of Ti-N bonds and oxygen vacancies in the film.     

Pulsed laser deposition of Bi2Te3 thin films

A feasibility study of thin stoichiometric Bi₂Te₃ films by pulsed laser deposition (PLD) was performed, the difficulty arising from the differences of vapour pressure between Te and Bi. The films were elaborated using a pulsed Nd:YAG laser under various experimental conditions and were characterized by electron microsprobe, scanning electron microscopy, X-ray diffraction and secondary ion mass spectroscopy analyses. Congruent transfer of stoichiometry occurs from the target to the substrate on several cm² and a good crystallinity can be achieved, even on glass substrates at room temperature, by combining convenient target to substrate facing and distance, respectively. Depletion in Te observed in some films may result from a laser beam-plume interaction that was put forward during elaboration of films on large scale substrates.     

Initial stages of WO3 growth on silicon substrates

Ultrathin films (5 nm, 10 nm and 20 nm effective thickness) of WO₃ have been deposited in high vacuum (10^− 6 Torr) onto single crystal Si(100) substrates and studied with X-ray diffraction, atomic force microscopy, scanning tunneling microscopy and spectroscopy. The experiments have been carried out on “as-deposited” thin films or after 1 h post-deposition annealing at various temperatures (ranging from 300 °C to 500 °C). A size induced increase of the amorphous to crystalline (monoclinic) phase transition has been observed for the 5 nm and 10 nm films, with a critical crystallite size of 25 ± 5 nm and a critical temperature of 345 ± 5 °C. All the experimental evidences show that, upon annealing, there is a diffusion limited aggregation growth of WO₃ that forms large flat two-dimensional islands composed by aggregates of individual crystallites approximately uniform in size and shape. These islands are isolated in the 5 nm thin films, are connected in the 10 nm case and form a uniform patchwork in the 20 nm thin films. Scanning tunneling spectroscopy shows the opening of a large surface band gap (2.7 eV) in the 500 °C annealed films and the significant presence of in gap states for thin films prepared with a lower (below 400 °C) annealing temperature. These findings are discussed in view of the optimization of the best morphological, structural and electronic parameters to fabricate WO₃ gas sensing devices at the sub-micrometer length scale.     

TiO2 thin films using organic liquid materials prepared by Hot-Wire CVD method

TiO₂ thin films prepared by Hot-Wire CVD method have been studied as a protecting material of transparent conducting oxide (TCO) against atomic hydrogen exposures for the fabrications of Si thin film solar cells. It was found that electrical conductivity of the films at room temperature reached a value of 0.4 S/cm. This value is 2-3 orders of magnitude higher than that of TiO₂ films prepared by RF magnetron sputtering and electron-beam evaporation methods in our previous works. The conductivity improvement seems to be partly due to the enlargement of TiO₂ crystallites.     

Size distribution-controlled preparation of graphene oxide nanosheets with different C/O ratios

A convenient and efficient preparation method for separation graphene oxide with well-defined size distribution is developed using a centrifugation technique. The graded profile of graphene oxide nanosheets with narrow size distribution is effectively controlled by varying the centrifugation speed. The results show that the oxygen content of graphene oxide is highly dependent on their size distribution. Graphene oxide nanosheet with large size shows a red-shift in UV–vis absorption spectra, compared to graphene oxide with small size. This phenomenon is interpretation by a density functional theory calculation. The present work will provide a simple method to prepare graphene oxide nanosheets with controllable size distribution and C/O ratio, which will be valuable for the functionalization of graphene-based hybrids and the fabrication of graphene nano-devices.     

Native oxide consumption during the atomic layer deposition of TiO2 films on GaAs (100) surfaces

The consumption of the surface native oxides is studied during the atomic layer deposition of TiO₂ films on GaAs (100) surfaces. Films are deposited at 200 °C from tetrakis dimethyl amido titanium and H₂O. Transmission electron microscopy data show that the starting surface consists of ~2.6 nm of native oxide and X-ray photoelectron spectroscopy indicates a gradual reduction in the thickness of the oxide layer as the thickness of the TiO₂ film increases. Approximately 0.1-0.2 nm of arsenic and gallium suboxide is detected at the interface after 250 process cycles. For depositions on etched GaAs surfaces no interfacial oxidation is observed.     

Controlled modification of octadecyltrichlorosilane self-assembled monolayer by CO2 plasma

CO₂-plasma is used to introduce functional groups on the uppermost surface of an alkoxysilane self-assembled monolayer (SAM). The structural and chemical modifications of the material surface were monitored by X-ray reflectometry, atomic force microscopy, X-ray photoelectrons spectroscopy and water contact angle measurements. Optimization of the plasma parameters is performed in order to achieve a maximum functionalization and to prevent degradation of the SAM. Finally, the ability of grafting organic compounds onto the plasma modified SAMS was demonstrated by the formation of an alkoxysilane bilayer.     

Structure and surface morphology of Mn-implanted TiO2

A study of structure and surface morphology together with magnetic properties of Mn-implanted rutile-type TiO₂ single crystals is performed. Homogenous thin films of about 100 nm with different Mn_xTi_1 − xO₂ (x = 0.03; 0.05 and 0.07) chemical formula were obtained. The Mn ion implanted surface exhibited a dense microstructure with a nano grain size. The dependence of c/a axial ratio on manganese content suggests that Mn³⁺ species substituted tetragonal Ti⁴⁺. The annealing at 873 K caused changes in surface structure, morphology and roughness. A migration of manganese ions into the rutile single crystal takes place and in certain conditions Ti₂O phase occurs. Mn-implanted samples exhibit room temperature ferromagnetism and a Curie temperature of 680 K. Electron spin resonance analysis evidenced that manganese is incorporated by substitution as magnetically isolated Mn⁴⁺, Mn³⁺ and Mn²⁺ species. At 0.07% contents the Mn³⁺ species may enter in interstitial sites contributing to extinction of substitutional magnetic moment.     

Poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate): Correlation between colloidal particles and thin films

We deal with correlation between sizes of colloidal particles and minimum thickness of spin-coated thin films of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) studied by a dynamic light scattering (DLS), a scanning transmission electron microscopy coupled with an energy dispersive X-ray spectroscopy (STEM-EDX), C₆₀-sputtering X-ray photoelectron spectroscopy (XPS), and an atomic force microscopy. Based on the various measurements, it was pointed out that, PEDOT/PSS colloidal dispersion contained majority of primary nanoparticles with mean diameter of 41 nm and 16 nm for BAYTRON P AG (denote P grade) or BAYTRON PH500 (denote PH grade) solutions, respectively, and small amount of clusters aggregated by the primary particles, based on the DLS measurement and STEM observation. On the other hand, PEDOT/PSS thin films with thickness of 44 nm and 16 nm were easily prepared by spin-coating on silicon wafers from the P and PH grade solutions, respectively. Results of STEM-EDX, DLS, and XPS measurements suggested that the PEDOT/PSS thin films consist of the randomly packed primary nanoparticle-“monolayer”.     

Investigation of the growth of In2O3 on Y-stabilized ZrO2(100) by oxygen plasma assisted molecular beam epitaxy

Thin films of In₂O₃ have been grown on Y-stabilised ZrO₂(100) substrates by oxygen plasma assisted molecular beam epitaxy over a range of substrate temperatures between 650 °C and 900 °C. Growth at 650 °C leads to continuous but granular films and complete extinction of substrate core level structure in X-ray photoelectron spectroscopy. However with increasing substrate temperature the films break up into a series of discrete micrometer sized islands. Both the continuous and the island films have excellent epitaxial relationship with the substrate as gauged by X-ray diffraction and selected area electron diffraction and lattice imaging in high resolution transmission electron microscopy.     

Influence of Si(1 0 0) surface pretreatment on the morphology of TiO2 films grown by atomic layer deposition

The effect of water plasma treatment of both hydrophobic and hydrophilic Si(1 0 0) surfaces has been studied using infrared spectroscopy to monitor the various surface species present. Exposure to a water plasma results in a significant increase in the concentration of H-bonded hydroxyls and hydrides. Both atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM) of TiO₂ films deposited by atomic layer deposition at 300 °C, show that the morphology of the films is dependent on the nature of the initial surface. XTEM of the early stages of growth showed that coatings on hydrophilic substrates deposited as initially amorphous and continuous films, which crystallised with further growth. However, the hydrophobic substrate produced island growth of small, crystalline grains. AFM images of 23-nm thick films showed that films deposited on hydrophobic and hydrophilic Si consisted of 35–100 and 150–350 nm crystallites, respectively. A film on water plasma treated Si, closely resembled that on the hydrophilic surface, indicating that hydroxyl groups are responsible for directing the film growth.     

Self-limiting growth of anatase TiO2: A comparison of two deposition techniques

Self-limiting deposition of titanium dioxide thin films was accomplished using pulsed plasma-enhanced chemical vapor deposition (PECVD) and plasma-enhanced atomic layer deposition (PEALD) at low temperatures (T < 200 °C) using TiCl₄ and O₂. TiCl₄ is shown to be inert with molecular oxygen at process conditions, making it a suitable precursor for these processes. The deposition kinetics were examined as a function of TiCl₄ exposure and substrate temperature. The quality of the anatase films produced by the two techniques was nominally identical. The key distinctions are found in precursor utilization and conformality. Pulsed PECVD requires 20 times less TiCl₄, while PEALD must be used to uniformly coat complex topographies.