Microstructure control of low-resistivity tin-doped indium oxide films grown by photoreaction of nanoparticles using a KrF excimer laser at room temperature

A tin-doped indium oxide (ITO) film on a SiO₂ substrate was prepared by photo-irradiation of spin-coated nanoparticles using a Xe excimer lamp and a KrF excimer laser. The effects of the excimer lamp and the excimer laser on the resistivity, mobility, and carrier concentration of the film were investigated. To better understand how to control the microstructure of the film, we investigated the effect of thickness on the resistivity of a film prepared by the two-step process, and found that the resistivity was higher in a thicker film. Using two-step irradiation plus one-step KrF irradiation in N₂ at room temperature, we produced an ITO film with lowest resistivity of any in this study. The electrical resistivity of this film was 5.94×10⁻⁴ Ω cm. On the other hand, when using a simple thermal process, the resistivity of a film sintered at 500°C in N₂ was 4.10×10⁻³ Ω cm. The differences in resistivity are discussed on the basis of the microstructure of the films using atomic force microscopy and Hall measurements.     

Characterization of porous silicon prepared by powder technology

In this study, we have proposed the powder technology as new method for preparation of bulk porous silicon. Formation of porous silicon by high-energy ball milling followed by pressing and sintering was studied by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy (XPS). A crystalline wafer with (1 1 1) orientation was extensively ball milled up to 72 h leading to a decrease in average crystallite size up to 15 nm. The most significant reduction of crystallite size was observed after milling process for about 24 h. The nanopowders were then pressed into pellets at a pressure up to 400 MPa and sintered at 1173 K for 60 min in a high purity argon atmosphere. Results showed that after sintering the material became porous with uniform porosity in whole volume, independently of the sinter size. It is not possible to prepare such porous materials using the conventional electrochemical etching, where the porous structure depth usually does not exceed tens of micrometers. Core-level XPS studies showed very good agreement between peak positions of the sintered porous silicon and in-situ prepared polycrystalline 20 nm-Si thin film or single-crystalline Si (1 1 1) wafer. Furthermore, the valence band spectra measured for sintered samples are broader compared to those measured for the Si (1 1 1) wafer or polycrystalline Si thin film. On the other hand, the shape and broadening of the valence bands measured for the sintered samples are in very good agreement with those reported for electrochemically prepared porous silicon.     

Effects of oxygen pressures on pulsed laser deposition of ZnO films

Zinc oxide (ZnO) thin films on Si (1 1 1) substrates were deposited by pulsed laser ablation of ZnO target at different oxygen pressures. A pulsed Nd:YAG laser with wavelength of 1064 nm was used as laser source. The deposited thin films have been characterized by X-ray diffraction (XRD), Atomic force microscopy (AFM), and Raman spectroscopy. XRD measurements indicate that the ZnO thin films deposited at the oxygen pressure of 1.3 Pa have the best crystalline quality. AFM results show that the surface roughness of ZnO film increases with the increase of oxygen pressure. The Raman results indicate that oxygen ambient plays an important role in removing defects due to excess zinc.     

Probing the effect of nitrogen gas on electrical conduction phenomena of ZnO and Cu-doped ZnO thin films prepared by spray pyrolysis

Zinc oxide (ZnO) and Cu-doped ZnO (CZO) thin films were prepared on borosilicate glass substrates by spray pyrolysis technique. The X-ray diffraction study revealed that Cu doping caused a reduction in crystallite size. AFM study showed an increase in roughness with doping. This is attributed to the aggregation of particles to form clusters. From transmission electron microscopy analysis, the particle size is measured to be in the range 30–65 nm (average particle size 48 nm) for undoped ZnO, whereas it is in the range 24–56 nm (average particle size 40 nm) for CZO film. The electrical resistivity of the thin films was investigated in the presence of air as well as N₂ mixed air at different temperatures in the range 30–270 °C. The change in resistivity properties was explained on the basis of conduction phenomena within the grain along with the grain boundaries as well as Cu- and N₂-induced defect states. The thermal activation energy of ZnO was found to be in the range 0.04–0.7 eV and dependent on Cu doping and N₂ level in air.     

Preparation of triethylamine stabilized silver nanoparticles for low-temperature sintering

In this article, silver nanoparticles were synthesized by chemical reduction from silver nitrate using triethylamine as the protecting and reducing agents simultaneously. The average size of the silver nanoparticles was about 2.10–4.65 nm, which allowed low-temperature sintering of the metal. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and energy dispersive spectrometric (EDS) analysis results indicate that silver nitrate has been converted to silver nanoparticles completely. Using a 20 wt% silver nanoparticles suspension with thermal treatment at 150 °C, silver films with a resistivity of 8.09 × 10⁻⁵ Ω cm have been produced, which is close to the resistivity of bulk silver.     

Inkjet-printed gold nanoparticulate patterns for surface finish in electronic package

Gold (Au) pads for surface finish in electronic package were developed by the inkjet printing method. The Au ink for printing was prepared by Au nanoparticles (NPs) coated with capping molecules of dodecylamine (C₁₂H₂₅NH₂). The microstructures of the inkjet-printed Au films were characterized after sintering in various gas flows. The film sintered in air showed that bonding between NPs was not enough for further grain growth due to the incomplete decomposition of the capping layer. The film sintered under nitrogen (N₂) had NPs existing on the surface and the bottom which did not participate in sintering. When the film was sintered under N₂-bubbled through formic acid (FA/N₂), a large portion of the pores were observed to make a holey pancake-like structure of the film. The microstructures of the inkjet-printed Au film became denser with grain growth when Au NPs were sintered under mixed gas flows of FA/N₂ and N₂. The resistivity of film was 4.79 μΩ cm, about twice the bulk value. Organic analysis showed that about 0.43% of residual organics was left in the film. Therefore, this Au film was chosen for solder ball shear test because the microstructure was denser compared to the films sintered under other gasses such as N₂ or FA/N₂ and less organic residue was found from organic analyses. Even though the film sintered under N₂ showed the best electrical property (4.35 μΩ cm), it was not adopted in the shear test because NPs remaining on the bottom of the film could lead to the poor adhesion between the film and substrate and show low shear strength. The shear force was 8.04 newton (N) on average and the strength was 64 MPa. This shear strength is good enough to substitute the inkjet-printed Au nanoparticulate film for electroplating in electronic package.     

Direct writing of conductive silver micropatterns on flexible polyimide film by laser-induced pyrolysis of silver nanoparticle-dispersed film

This article describes fabrication of Ag micropatterns on a flexible polyimide (PI) film by laser direct writing using an Ag nanoparticle-dispersed film as a precursor. Ag micropatterns are characterized by optical microscopy, atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), surface profilometry, and resistivity measurements. The line width of Ag micropatterns can be effectively controlled by altering the experimental parameters of laser direct writing especially laser intensity, objective lens, and laser beam scanning speed etc. Using an objective lens of 100× and laser intensity of 170.50 kW/cm², Ag micropatterns with a line width of about 6 μm have been achieved. The Ag micropatterns show strong adhesion to polyimide surface as evaluated by Scotch-tape test. The resistivity of the Ag micropatterns is determined to be 4.1 × 10⁻⁶ Ω cm using two-point probe method. This value is comparable with the resistivity of bulk Ag (1.6 × 10⁻⁶ Ω cm).     

Effects of metal doping on the physical properties of ZnTe thin films

Zinc telluride (ZnTe) thin films were sublimated on a glass substrate using closed space sublimation (CSS) technique. ZnTe thin films of same thickness were tailored with copper (Cu) & silver (Ag) doping, considered for comparative study. X-ray diffraction (XRD) patterns of as-deposited ZnTe thin film and doped ZnTe samples exhibited polycrystalline behavior. The preferred orientation of (111) having cubic phase was observed. XRD patterns indicated that the crystallite size had increased after silver and copper immersion in as-deposited ZnTe thin films. Scanning electron microscopy (SEM) was used to observe the change of as-deposited and doped sample's grains sizes. EDX confirmed the presence of Cu and Ag in the ZnTe thin films after doping respectively. The optical studies showed the decreasing trend in energy band gap after Cu and Ag-doping. Transmission also decreased after doping. Resistivity of as-deposited ZnTe thin film was about 10⁶ Ω cm. The resistivity was reduced to 68.97 Ω cm after Cu immersion, and 10⁴ Ω cm after Ag immersion. Raman spectra were used to check the crystallinity of as-deposited, Cu and Ag-doped ZnTe thin film samples.     

Synthesis of SnO<Subscript>2</Subscript> tubular nanostructures on top of a silicon nitride surface using polymeric templates and their characterization as gas sensor

Uniform polycrystalline SnO₂ microtubes formed by sintered nanoparticles (fixed to a surface or in free standing form) were obtained with the infiltration technique using SnCl₄ as precursor and a porous polycarbonate (PC) film as template. The advantage of this synthesis method was based on its simplicity, reproducibility, low cost, and the possible applicability to other complex oxides. The morphology and crystal structure of SnO₂ tubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The crystalline sizes of the nanoparticles assembled in the tube walls obtained at 600 °C were in the range of 5–7 nm, calculated from both the XRD and the TEM data. The length of the microtubes fixed to a silicon nitride surface ranged between 2 and 7 μm. Sensors fabricated with this material showed unusual sensitivity to ethanol at room temperature and fast reversible response, as compared to those obtained by the deposition of metallic tin film and further oxidation (Rheotaxial Growth and Thermal Oxidation method).     

Effect of lithium salt concentration in PVAc/PMMA-based gel polymer electrolytes

Hybrid solid polymer electrolyte films comprising of poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA), LiClO₄, and propylene carbonate are prepared by solution casting technique by varying the salt concentration. In this study, PVAc/PMMA polymer blend ratio is fixed as 25:75 on the basis of conductivity and mechanical stability of the film. X-ray diffraction, Fourier transform infrared impedance, thermogravimetry/differential thermal analysis and scanning electron microscopy studies are carried out for the polymer electrolytes. The maximum ionic conductivity is found to be 4.511 × 10⁻⁴ S cm⁻¹ at 303 K for the plasticized polymer electrolyte with 8 wt.% of LiClO₄. The ionic conductivity is found to decrease with an increase of LiClO₄ concentration.     

A wet chemical preparation of transparent conducting thin films of Al-doped ZnO nanoparticles

A wet chemical deposition method for preparing transparent conductive thin films on the base of Al-doped ZnO (AZO) nanoparticles has been demonstrated. AZO nanoparticles with a size of 7 nm have been synthesised by a simple precipitation method in refluxed conditions in ethanol using zinc acetate and Al-isopropylate. The presence of Al in ZnO was revealed by the EDX elemental analysis (1.8 at.%) and UV–Vis spectroscopy (a blue shift due to Burstein–Moss effect). The obtained colloid solution with the AZO nanoparticles was used for preparing by spin-coating thin films on glass substrates. The film demonstrated excellent homogeneity and transparency (T > 90%) in the visible spectrum after heating at 400 °C. Its resistivity turned to be excessively high (ρ = 2.6 Ω cm) that we ascribe to a poor charge percolation due to a high film porosity revealed by SEM observations. To improve the percolation via reducing the porosity, a sol–gel solution was deposited “layer-by-layer” in alternation with layers derived from the AZO colloid followed by heating. As it was shown by optical spectroscopy measurements, the density of thus prepared film was increased more than twice leading to a significant decrease in resistivity to 1.3 × 10⁻² Ω cm.     

The relationship between refractive index-energy gap and the film thickness effect on the characteristic parameters of CdSe thin films

CdSe thin films were deposited on glass substrates using Successive Ionic Layer Adsorption and Reaction (SILAR) method at room temperature and ambient pressure. The relationship between refractive index and energy bandgap was investigated. The film thickness effect on the structural, morphological, optical and electrical properties of CdSe thin films was investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies showed that all the films exhibit polycrystalline nature with hexagonal structure and are covered well with glass substrates. The crystalline and surface properties of the films improved with increasing film thickness. The optical absorption studies revealed that the films are found to be a direct allowed transition. The energy bandgap values were changed from 1.93 to 1.87 eV depending on the film thickness. The electron effective mass (m_e^?/m_o), refractive index (n), optical static and high frequency dielectric constant (ε_o, ε_∞) values were calculated by using the energy bandgap values as a function of the film thickness. The resistivity of the films changed between 10⁶ and 10² Ω-cm with increasing film thickness at room temperature.     

Fabrication of atomically smooth SrRuO3 thin films by laser molecular beam epitaxy

High-quality SrRuO₃ (SRO) thin films and SrTiO₃/SRO bilayer were grown epitaxially on SrTiO₃ (STO)(001) substrates by laser molecular beam epitaxy. The results of in situ observation of reflection high-energy electron diffraction and ex situ X-ray diffraction ϑ-2ϑ scan indicate that the SRO thin films have good crystallinity. The measurements of atomic force microscopy and scan tunneling microscopy reveal that the surface of the SRO thin film is atomically smooth. The resistivity of the SRO thin film is 300 μΘ·cm at room temperature. Furthermore, the transmission electron microscopy study shows that the interfaces of STO/SRO and SRO/STO are very clear and no interfacial reaction layer was observed. The experimental results show that the SRO thin film is an excellent electrode material for devices based on perovskite oxide materials. Supported by the National Natural Science Foundation of China (Grant No. 10334070)     

Fabrication and characterization of GaP/polymer nanocomposites for advanced light emissive device structures

GaP nanoparticles have been prepared using white P and a mild aqueous synthesis at decreased temperature followed by ultrasonication and stored as the suspension in water–ethanol mixture. They were characterized by standard methods of X-ray diffraction, transmission electron microscopy, Raman light scattering, and photoluminescence. Properties of GaP nanoparticles were compared with industrial and specially grown perfect GaP single crystals. It was shown that the GaP nanoparticles in suspension are the most suitable for high quality GaP/polymers nanocomposites because only they are uniform with dimensions of about 10 nm which is optimal for appearance of the pronounced quantum confinement effect. Polyglycidyl methacrylate (PGMA), polyglycidyl methacrylate-co-polyoligoethyleneglycol methacrylate (PGMA-co-POEGMA), and biphenyl vinyl ether (BPVE) polymers were used to prepare GaP polymer nanocomposites. The thickness of the polymer nanocomposite film was about 250–300 nm defined from AFM scratch experiment. The resulting nanocomposites yielded a bright luminescence at room temperature in a broad band with the maximum ranging from 2.5 to 3.2 eV and showed pronounced quantum confinement effects and other interesting and important for application phenomena leading to dramatic 1 eV expansion of GaP luminescence to the UV spectral region.     

Enhancement of conductivity in La2Mo2O9 ceramics fabricated by a novel three-stage thermal processing method

Pure and dense La₂Mo₂O₉ ceramic electrolytes with grain sizes of 1–3 μm were fabricated from nanocrystalline powders by a novel three-stage, one-cycle, pressureless thermal processing method at temperatures as low as 600 °C. Phase formation, microstructure and grain size of the samples were examined using X-ray diffraction and scanning electron microscopy. Density of the sintered samples was determined as in the range of 94–96% of the theoretical density by weight/geometric measurements. Impedance spectroscopy was used to characterize the electrical properties of the sintered samples. The conductivity of the three-stage sintered samples reaches a value of 0.018 S/cm at 600 °C and 0.05 S/cm at 700 °C, much higher than that of the samples fabricated by conventional solid-state reaction method, but similar to that of the samples sintered at 950 °C for 12 h from the same nanocrystalline powders. The high conductivity of these samples was attributed to the co-operation of the excellent performance of nanocrystalline powders and the advantages of the novel three-stage low-temperature thermal processing.     

Electrical performance of Ti/Pt thin films on glass-ceramic substrates after high temperature loading

In this study, the influence of post-deposition annealings (PDA) up to temperatures of T _PDA=700°C on the room-temperature resistivity of e-beam evaporated titanium/platinum (Ti/Pt) bi-layers on low temperature co-fired (LTCC) substrates covered with a glass encapsulate is investigated. The thickness of the platinum top layer is varied between 24 and 95 nm (titanium film thickness: 5 nm) and between 23 and 90 nm (titanium film thickness: 15 nm), respectively. In the “as-deposited” state and up to post-deposition annealing temperatures of T _PDA=450°C, the film resistivity is linearly correlated with the reciprocal value of the platinum film thickness according to the size effect. When applying, however, solely the Fuchs-Sondheimer model for evaluation, the effective mean free path for electrons is substantially above the value reported for crystalline platinum at room temperature. Compared to similar investigations on smooth Si/SiO₂ substrates yielding interpretable results within this theoretical approach, this is due to the increase of the thickness-dependent fraction in film resistivity which is strongly affected by the enhanced LTCC/glass surface roughness. At T _PDA>600°C, diffusion of titanium into the platinum top layer and the roughening of the LTCC/glass substrate dominate the electrical behavior, both causing an increase in film resistivity above average. In contrast to Si/SiO₂ substrates, thermal induced grooving effects in the Pt top layer play a minor role as the temperature coefficients of expansion of metallization and glass-ceramic substrate match better and the effective temperature difference for stress generation is lower due a glass softening temperature of about 450°C.     

Characteristics of sculptured Cu thin films and their optical properties as a function of deposition rate

Sculptured copper thin films were deposited on glass substrates, using different deposition rates. The nano-structure and morphology of the films were obtained, using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Their optical properties were measured by spectrophotometry in the spectral range of 340-850 nm. The real and imaginary refractive indices, film thickness and fraction of metal inclusion in the film structure were obtained from optical fitting of the spectrophotometer data.     

Synthesis and electrical transport of SrHfO3 thin films grown on a SrTiO3 (001) substrate using a pulsed laser deposition

We report the deposition of epitaxial SrHfO₃ thin films on a SrTiO₃ (001) substrate in different substrate temperatures by using a pulsed laser deposition (PLD) method. We carried out X-ray diffraction (XRD), X-ray reflectivity (XRR), reciprocal space mapping (RSM), atomic force microscopy (AFM), resistivity, and Hall measurements to examine the crystallinity, morphology and electrical properties of these films. All films showed smooth and uniform morphology with small root mean square (RMS) roughness. While the SrHfO₃ sample grown at 750 °C is metallic, the films deposited at 600 °C, 650 °C, and 700 °C show an upturn at low temperatures. The temperature dependence of the metallic parts was analyzed based on the parallel resistor model that includes resistivity saturation. On the other hand, the low-temperature upturn was found to be well described by a weak localization mechanism. We also observed the possible emergence of non-Fermi liquid behavior when the upturn disappeared. All SrHfO₃ films have p-type charge carriers.     

Formation of Polyvinyl Alcohol film with graphene nanoplatelets and carbon black for electrostatic discharge protective packaging

This research investigated the synergic effect of graphene nanoplatelets (GNPs) and carbon black (CB) as a blended conductive filler for polymer film used as electrostatic discharge (ESD) packaging materials. Various weight ratios of GNPs/CB and combined filler concentrations were mixed and processed into Polyvinyl Alcohol (PVOH) based film. The surface resistivity and volume resistivity of the resulting film was measured under three different humidity environments. The study found that the composite with GNPs/CB ratios of 10:90 and 30:70 resulted in a sharp drop in surface resistivity by 5–8 orders of magnitude at the filler loading 8-10 wt%. The volume resistivity of the resulting film exhibited steady and consistent ranges within 10⁸–10¹² Ω cm across all loadings. The difference in conductivity between surface and volume made the film possible to be used in protecting equipment against electrostatic discharges inside of a package. The high loading of GNPs in hybrid GNPs/CB had no effect on enhancing both surface and volume conductivity of the composite film.     

Temperature dependence of the electrical resistivity and the anisotropic magnetoresistance (AMR) of electrodeposited Ni-Co alloys

The electrical resistivity and the anisotropic magnetoresistance (AMR) was investigated for Ni-Co alloys at and below room temperature. The Ni-Co alloy layers having a thickness of about 2 μm were prepared by electrodeposition on Si wafers with evaporated Cr and Cu underlayers. The alloy composition was varied in the whole concentration range by varying the ratio of Ni-sulfate and Co-sulfate in the electrolyte. The Ni-Co alloy deposits were investigated first in the as-deposited state on the substrates and then, by mechanically stripping them from the substrates, as self-supporting layers both without and after annealing. According to an X-ray diffraction study, a strongly textured face-centered cubic (fcc) structure was formed in the as-deposited state with an average grain size of about 10 nm. Upon annealing, the crystal structure was retained whereas the grain size increased by a factor of 3 to 5, depending on alloy composition. The zero-field resistivity decreased strongly by annealing due to the increased grain size. The annealing hardly changed the AMR below 50 at.% Co but strongly decreased it above this concentration. The composition dependence of the resistivity and the AMR of the annealed Ni-Co alloy deposits was in good quantitative agreement with the available literature data both at 13 K and at room temperature. Both transport parameters were found to exhibit a pronounced maximum in the composition range between 20 and 30 at.% Co and the data of the Ni-Co alloys fitted well to the limiting values of the pure component metals (fcc-Ni and fcc-Co). The only theoretical calculation reported formerly on fcc Ni-Co alloys yielded at T = 0 K a resistivity value smaller by a factor of 5 and an AMR value larger by a factor of about 2 than the corresponding low-temperature experimental data, although the theoretical study properly reproduced the composition dependence of both quantities.