Application of the gas phase condensation to the preparation of nanoparticles

The evaporation of materials in ultra-high vacuum leads to the growth of thin films on appropriated substrates. In the presence of an inert gas (pressure above 10⁻¹ Torr), the evaporated materials lose kinetic energy by collisions with the inert gas molecules in the gas phase and condense in the form of nanometric size crystallites that can be collected on the substrate as an ultrafine powder. In the present communication, we discuss how thin film deposition methods can be modified to collect ultrafine powders instead of continuous films. We describe, with some examples, the use of the gas phase condensation in the preparation of two different types of materials as nanometric powders. On one hand, CdS nanoparticles have been obtained in the form of homogeneous spheres with a mean particle size of 16 nm in diameter. This material, with applications in catalysis and optical devices, has been characterised by UV–VIS Absorption Spectroscopy, Transmission Electron Microscopy and X-ray Diffraction. On the other hand, magnetic nanoparticles of Co have also been prepared as nanostructured materials with an average particle size of 10 nm. Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy and X-ray Diffraction have been used to characterise this sample. The formation of an interesting material, consisting of Co cores covered by an oxide passivation layer, has been demonstrated.     

Structural order and magnetic properties of Fe3Si/Si(100) heterostructures grown by pulsed-laser deposition

The single-phase Fe₃Si thin films with preferred (220) growth orientation were prepared on Si(100) substrates by pulsed-laser deposition. Different states of order were developed by changing the substrate temperature from room temperature to 500 °C. X-ray diffraction, Mössbauer spectroscopy and macroscopic magnetic measurements were used to analyze changes of structural order and magnetic properties with the substrate temperature. The results show that over the whole range of substrate temperatures considered all films are of Fe₃Si single phase, highly oriented along the (220) plane. With increasing the substrate temperature, the structural order type changes from A2 through B2 to DO₃ and the order degree gradually increases. Meanwhile, the saturation magnetization remarkably decreases with the increase of the substrate temperature, induced by Si segregation from the substrate and embedment into the film probably as the amorphous phase. The room temperature grown film has a high saturation magnetization of 917 kA m^− 1, which nearly equals that of bulk DO₃-Fe₃Si.     

X-ray Photoelectron Spectroscopy characterization of native and RCA-treated Si (111) substrates and their influence on surface chemistry of copper phthalocyanine thin films

In this paper native and RCA-treated n- and p-doped Si(111) substrates and ultra-thin 16-nm copper phthalocyanine (CuPc) layers deposited thereon were investigated using X-ray Photoemission Spectroscopy and Angle-Resolved X-ray Photoemission Spectroscopy. The oxide layer thickness was determined to be 1.3 nm on the RCA-treated substrates and 0.8 nm on the native ones. The analysis of substrate carbon contamination showed the existence of C-H, C-OH and COOH components on all substrates. The RCA clean removes more readily the carbon components with the OH group from the n-type Si and causes the segregation of the contaminants. The initial carbon species propagate in the evaporated CuPc layer up to a thickness of about 5 nm affecting the shape of the C1s peak. Additionally, the behavior of the binding energy difference between N1s and Si2p peaks upon the CuPc growth shows that there may occur various CuPc molecule adsorption modes on investigated Si substrates. It could be a useful information, from the technological point of view, especially for low dimensional electronic device preparation.     

Structural and optical properties of high quality ZnO thin film on Si with SiC buffer layer

ZnO thin films are grown on Si substrates with SiC buffer layer using ion plasma high frequency magnetron sputtering. These substrates are fabricated using a technique of solid phase epitaxy. With this technique SiC layer of thickness 20-200 nm had been grown on Si substrates consisting pores of sizes 0.5-5 μm at SiC and Si interface. Due to mismatching in lattice constants as well as thermal expansion coefficients, elastic stresses have been developed in ZnO film. Pores at the interface of SiC and Si are acting as the elastic stress reliever of the ZnO films making them strain free epitaxial. ZnO film grown on this especially fabricated Si substrate with SiC buffer layer exhibits excellent crystalline quality as characterized using X-ray diffraction. Surface topography of the film has been characterized using Atomic Force Microscopy as well as Scanning Electron Microscopy. Chemical compositions of the films have been analyzed using Energy Dispersive X-ray Spectroscopy. Optical properties of the films are investigated using Photoluminescence Spectroscopy which also shows good optical quality.     

Multilayer membranes via layer-by-layer deposition of glucose oxidase and Au nanoparticles on a Pt electrode for glucose sensing

We prepared multilayer membranes by the layer-by-layer deposition of glucose oxidase (GOx) and Au nanoparticles (5, 10, or 50 nm φ) on sensor substrates, such as a Pt electrode and a quartz glass plate, to prepare glucose sensors. The enzyme activity of GOx remained even in alternate assemblies, and the activity increased with the increasing number of depositions. The apparent K_m values of the deposited GOx were 28–32 mM, while a reported value in a solution is 33 mM. These results suggest that Au nanoparticles can be used as binders for the deposition of GOx without significant change in the affinity between GOx and glucose.     

Nano-cube MgO formed on silicon substrate using pulsed laser deposition

Nano-cube MgO particles were formed on Si substrates by deposition of an MgO target using pulsed laser deposition method. An epitaxial film grows on Si(001) substrate with its contraction of lattice constants. In this study, expecting high quality MgO film, the MgO film prepared in the oxygen pressure ranging from 75-400 mTorr at the high temperature of -750 degrees C. The deposited MgO showed the growth of (001) preferred orientation on the Si(001) substrate. However, X-ray Photoelectron Spectroscopy (XPS) indicated the MgO film did not form a continuous film on the Si surface. Interestingly, the surface morphology observed by an Atomic Force Microscopy (AFM) showed nano-cube MgO particles scattered on the smooth surface of Si substrate. After annealing the nano-cube MgO, the shape of MgO particles were changed from nano-cube to round shaped particles. The AFM image of the surface showed round shaped MgO nanoparticles scattered on rough surface. X-ray Diffraction (XRD) revealed the epitaxial growth of MgO(001) with cubic on cubic arrangement on the Si(001) substrate (MgO[100] parallel to Si[100]).     

Phase separated AlSi thin films prepared by filtered cathodic arc deposition

Phase separated AlSi films composed of Al cylinders embedded in an amorphous Si matrix were prepared on conducting Si substrates by filtered cathodic arc deposition. The compositional dependence of AlSi films on a negative substrate bias showed a different trend depending on the cathode composition because of the self-sputtering process during the deposition. The porous structure was obtained from the phase separated AlSi film after removal of Al cylinders by wet etching in an ammonia solution. Scanning electron microscope images of the etched AlSi films showed that the average diameter of pores was increased from 3 nm to 7 nm by applying a negative substrate bias voltage during the deposition. The honeycomb ordered arrangement of pores was observed at 0 V and − 25 V substrate bias. The substrate temperature during the depositions had almost the same effect on the film morphologies as the negative substrate bias.     

Textured strontium titanate layers on platinum by atomic layer deposition

Formation of textured strontium titanate (STO) layers with large lateral grain size (0.2-1 μm) and low X-ray reflectivity roughness (~ 1.36 nm) on Pt electrodes by industry proven atomic layer deposition (ALD) method is demonstrated. Sr(t-Bu₃Cp)₂, Ti(OMe)₄ and O₃ precursors at 250 °C were used to deposit Sr rich STO on Pt/Ti/SiO₂/Si ∅200 mm substrates. After crystallization post deposition annealing at 600 °C in air, most of the STO grains showed a preferential orientation of the {001} plane parallel to the substrate surface, although other orientations were also present. Cross sectional and plan view transmission electron microscopy and electron diffraction analysis revealed more than an order of magnitude larger lateral grain sizes for the STO compared to the underlying multicrystalline {111} oriented platinum electrode. The combination of platinum bottom electrodes with ALD STO(O₃) shows a promising path towards the formation of single oriented STO film.     

High-rate deposition of nanostructured SiC films by thermal plasma PVD

With ultrafine SiC powder as starting material, thermal plasma physical vapor deposition has been applied successfully to the deposition of SiC films on Si substrates. The control of processing parameters such as substrate temperature, powder feeding rate and composition of plasma gases, permits the deposition of SiC films on a wide area of around 400 cm² with a variety of microstructures from amorphous to nanostructured and with various morphologies from dense to columnar. For the nanostructured case, the crystallite size was between 3 and 15 nm and the maximum deposition rate calculated based on the actual deposition duty time reached 200 nm/s. The deposition mechanism is discussed briefly.     

Analysis of nanostructured coatings synthesized by ballistic impaction of nanoparticles

SiC nanostructured coatings were synthesized by ballistic impaction of nanoparticles using a process called hypersonic plasma particle deposition (HPPD). X-ray diffraction spectra of typical samples showed the presence of crystalline SiC and Si. Grain sizes obtained through transmission electron microscopy showed particles in the sub 10 nm range with primarily crystalline β-SiC and some crystalline Si particles present. These results correlate well with particle size distributions measured using an aerosol sampling probe coupled to a scanning electrical mobility spectrometer. Interestingly, particle size distributions indicated only small changes in the particle size distributions when Si deposition was compared to SiC. Examination of adhesion characteristics highlighted the importance of a chemically bound interlayer during SiC deposition on Mo and steel substrates.     

Study of the morphology of ultra-thin Pt films as the anode of an organic light emitting display

An ultra-thin Pt layer could be used as a transparent conducting anode to replace the ITO used today in a top-emitting OLED. A proper thickness of Pt thin layer is needed to avoid large leakage current while still keeping the high transparency for visible light. X-ray reflectivity and AFM were used to measure the morphology of e-gun deposition Pt thin films grown on glass substrates. The islands grown on the glass coalesced at the thickness of less than 4 nm. For the sample of 4 nm thickness, the sheet resistance is 800 Ω/□ with a transparency of 65%.     

Fabrication of highly c-axis textured ZnO thin films piezoelectric transducers by RF sputtering

The influence of fabrication parameters on ZnO film properties has been analyzed through conducting several experiment processes to develop an appropriate deposition condition for obtaining highly c-axis textured films. A transducer with the structure of Al/ZnO/Al/Si was fabricated at low deposition rate and under a temperature of 380 °C in a mixture of gases Ar:O₂ = 1:3, and RF power of 178 W. Pt/Ti was employed as the bottom electrode of the transducer fabricated in a suitable substrate temperature, which starts increasing at 380 °C with an increment of 20 °C for each 2 h stage of the deposition. Highly c-axis textured ZnO films have been successfully deposited on Pt/Ti/SiO₂/Si substrate under feasible conditions, including RF power of 178 W, substrate temperature of 380 °C, deposition pressure of 1.3 Pa and Ar:O₂ gas flow ratio of 50%. These conditions have been proposed and confirmed through investigating the influences of the sputtering parameters, such as substrate temperature, RF power and Ar:O₂ gas flow ratio, on the properties of ZnO films.     

Nanocrystalline diamond growth on different substrates

Nanocomposite films consisting of diamond nanoparticles of 3-5 nm diameter embedded in an amorphous carbon matrix have been deposited by means of microwave plasma chemical vapour deposition (MWCVD) from CH₄/N₂ gas mixtures. Si wafers, Si coated with TiN, polycrystalline diamond (PCD) and cubic boron nitride films, and Ti-6Al-4V alloy have been used as substrates. Some of the substrates have been pretreated ultrasonically with diamond powder in order to enhance the nucleation density n_nuc. It turned out that n_nuc depends critically on the chemical nature of the substrate, its smoothness and the pretreatment applied. No differences to the nucleation behaviour of CVD PCD films were observed. On the other hand, the growth process seems to be not affected by the substrate material. The crystallinity (studied by X-ray diffraction) and the bonding environment (investigated by Raman spectroscopy) show no significant differences for the various substrates. The mechanical and tribological properties, finally, reflect again the influence of the substrate material: on TiN, a lower hardness was measured as compared to Si, PCD and c-BN, whereas the adhesion of c-BN/nanocrystalline diamond (NCD) system was determined by that of the c-BN film on the underlying Si substrate.     

Effects of substrate parameters on structure and optical properties of ZnO thin films fabricated by pulsed laser deposition

Highly oriented zinc oxide thin films have been grown on quartz, Si (1 1 1) and sapphire substrates by pulsed laser deposition (PLD). The effect of temperature and substrate parameter on structural and optical properties of ZnO thin films has been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission spectra and PL spectra. The experimental results show that the best crystalline thin films grown on different substrate with hexagonal wurtzite structure were achieved at growth temperature 400–500 °C. The growth temperature of ZnO thin film deposited on Si (1 1 1) substrate is lower than that of sapphire and quartz. The band gaps are increasing from 3.2 to 3.31 eV for ZnO thin film fabricated on quartz substrate at growth temperature from 100 to 600 °C. The crystalline quality and UV emission of ZnO thin film grown on sapphire substrate are significantly higher than those of other ZnO thin films grown on different substrates.     

Effect of substrate temperature on structural, optical and electrical properties of ZnO thin films deposited by pulsed laser deposition

ZnO thin films were grown by the pulse laser deposition (PLD) method using Si (100) substrates at various substrate temperatures. The influence of the substrate temperature on the structural, optical, and electrical properties of the ZnO thin films was investigated. All of the thin films showed c-axis growth perpendicular to the substrate surface. At a substrate temperature of 500 °C, the ZnO thin film showed the highest (002) peak with a full width at half maximum (FWHM) of 0.39°. The X-ray Photoelectron Spectroscopy (XPS) study showed that Zn was in excess irrespective of the substrate temperature and that the thin film had a nearly stoichiometrical composition at a substrate temperature of 500 °C. The photoluminescence (PL) investigation showed that the narrowest UV FWHM of 15.8 nm and the largest ratio of the UV peak to the deep-level peak of 32.9 were observed at 500 °C. Hall effect measurement systems provided information about the carrier concentration, mobility and resistivity. At a substrate temperature of 500 °C, the Hall mobility was the value of 37.4 cm²/Vs with carrier concentration of 1.36 × 10¹⁸ cm⁻³ and resistivity of 2.08 × 10⁻¹ Ω cm.     

激光脉冲沉积制备钛酸锶钡薄膜及其介电调协特性

在Pt（111）／Ti／SiO2／Si（100）衬底上,用脉冲激光沉积工艺制备出了高度a轴取向生长的（Ba0.65Sr0．35）TiO3（BsT）薄膜。薄膜为柱状生长的纳米晶粒,平均晶粒尺寸为50nm。在外加电场254kV／cm时,BST薄膜的相对介电常数与介电调谐率为810和76．3％。高的介电调谐率主要是BST薄膜具有高度a轴取向的柱状生长晶粒,因为来自沿平面c轴极化而产生的内部应力,在电场作用下,获得了高介电调谐率。     

New method for synthesis of Pt nanoparticles embedded in a carbon matrix

Platinum (Pt) nanoparticles embedded in a carbon matrix were synthesized for the first time in benzene by an electric plasma discharge generated in the cavitation field of benzene due to an ultrasonic horn. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to study the particle size, structure and morphology of the synthesized nanoparticles. The Pt nanoparticles have FCC bulk Pt crystal structure. On the average Pt nanoparticle diameter ranged from 8 nm to 40 nm when synthesized at 4.1 kV and from 5 nm to 25 nm when synthesized at 3.4 kV. X-ray photoelectron Spectroscopy (XPS) and Energy dispersive X-ray Spectroscopy (EDX) were used to study the chemical composition of the synthesized nanoparticles. A cost effective new method for carbon supported Pt nanoparticles will be of potential interest in fuel cell and catalysis applications.     

Substrate dependent structural and magnetic properties of pulsed laser deposited Fe3O4 thin films

Nanocrystalline iron oxide thin films have been deposited on various substrates such as quartz, MgO(100), and Si(100) by pulsed laser deposition technique using excimer KrF laser (248 nm). The orientations, crystallite size and lattice parameters were studied using X-ray diffraction. The XRD results show that the films deposited on MgO and Si substrates are highly oriented and show only (400) and (311) reflections respectively. On the other hand, the orientation of the films deposited on quarts substrate changed from (311) to (400) with an increase in the substrate temperature from 400 degrees C to 600 degrees C, indicating thereby that the film growth direction is highly affected with nature of substrate and substrate temperature. The surface morphology of the deposited films was studied using Atomic Force Microscopy (AFM) and spherical ball like regular features of nanometer size grains were obtained. The magnetic properties were studied by Superconducting Quantum Interference Device (SQUID) magnetometer in the magnetic field +/- 6 Tesla. The magnetic field dependent magnetization (M-H) curves of all the Fe3O4 thin films measured at 5 K and 300 K show the ferrimagnetic nature. The electrochemical sensing of dopamine studied for these films shows that the film deposited on MgO substrate can be used as a sensing electrode.     

Diamond thin film nucleation on silicon by ultrasonication in various mixtures

Nucleation is a very important step in synthetic diamond thin film growth process and generally the incubation time for the stable diamond nuclei formation is very long. We can consider it to be a pre-treatment of the Si substrate surface before diamond film deposition.In this study we have investigated the synthetic diamond thin film nucleation mainly on Si substrates by the ultrasonication in different mixtures of isopropanol, deionized water, n-methylpyrrolidon (NMP) or sodiumdodecylsulphate (SDS) containing nanosized diamond powder (≤10 nm, Sigma-Aldrich) and micro-or nanosized metals (Nickel, Cobalt, Yttrium). Liquids NMP and SDS have a special property to separate nanoparticles.     

Influence of growth parameters on the microstructures of erbium films deposited on Si(111) substrates

Erbium films were grown on single crystal Si(111) substrates by electron beam vapor deposition. The microstructures of the erbium films were systematically investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Results indicate that the surface morphologies and microstructures of the erbium films with Si as substrates are susceptible to the substrate temperatures when the deposition rates are fixed. The pure erbium films with columnar grains were obtained at temperatures below 200 °C, but in the films grown at temperatures higher than 350 °C, some pinholes that are composed of erbium silicides were found. The pinholes have triangular shapes which is in accordance with the geometry of the underlying Si(111) substrate. The films grown at a substrate temperature equal or greater than 450 °C have cracks which would be formed due to the different shrinkage degree of erbium and silicon when the substrate temperature was cooled down to room temperature. The films grown at 200 °C show the (002) preferred orientation, which is consistent to the prediction by the theory of surface energy minimization. The deposition rate and deposition time are considered as factors to affect the reaction of the erbium film and the silicon substrate.