Stimulus-responsive fluidic dispersions of rod shaped liquid crystal polymer colloids

Electrically responsive liquid crystal polymer nanorods were fabricated by template synthesis. Liquid crystal monomers are templated by alumina membranes. Molecular ordering of the liquid crystal molecules resulted from the confinement in the sub-micron channels and this ordering can be captured permanently through photo-polymerization. Template removal and sonication result in individual rods that can be reoriented by applied electrical and magnetic fields. Such anisotropic particles have significant potential applications in electro-rheological fluids and in active mixing in microfluidic channels.     

Study of the material properties and suitability of plasma-deposited fluorine-doped silicon dioxides for low dielectric constant interlevel dielectrics

A major challenge for back-end interconnection technology as device geometries shrink is the development of low dielectric constant materials with good gap-filling properties that are suitable for microelectronics manufacturing. Recently, there has been much interest in fluorine-doped silicon dioxides (SiOF) as such a material. The advantages of a silicon dioxide based film from an integration standpoint make these films very attractive for manufacturing.

In this study, SiOF films have been prepared in a conventional parallel-plate dual-frequency plasma-enhanced chemical vapor deposition reactor. By varying the deposition parameters, SiOF films with indices of refraction from 1.38 to 1.46 and corresponding changes of as much as 20% in the dielectric constants have been produced. Fourier transform infrared data for these films have been correlated with fluorine concentration by secondary ion mass spectroscopy measurements. The presence of fluorine can also be observed in the capacitance-voltage (CV) characteristics for the films. Fluorine interface states trap electrons which delay the onset of accumulation in the CV measurements for p-type silicon. In a similar way, the fluorine-induced trap states affect the onset of inversion for n-type silicon.

Some films with high fluorine concentrations have been observed to be unstable with respect to moisture absorption. The reliability and stability data for these films are presented.     

Electrical stability of polyimide siloxane films for interlayer dielectrics in multilevel interconnections

Electrical stability of a polyimide siloxane (PSI) film for ultra-large scale integrated circuit (ULSI) multilevel interconnections is studied. The PSI films, modified by p-aminophenyltrimethoxysilane (APTMS), are designed to have three-dimensional polymer structures through Si–O bonds. It has been revealed that the PSI films are more stable in electrical properties at higher temperatures than 150°C, as compared to the conventional polyimide (PI) films. The electrical conduction mechanism study for the PSI films has revealed that Schottky emission is dominant. Barrier height φ_B obtained from the electrical property for the PSI film was 0.460 eV in the temperatures ranging from 25–250°C. On the other hand, barrier height of 0.422 eV at lower temperatures than 150°C and activation energy of 1.09 eV at higher temperatures than 150°C were obtained for the conventional PI film. The difference in polymer structure is very sensitive to the electrical conduction at high temperature, due to sodium ion migration. The ideal band diagrams of metal-insulator-semiconductor (MIS) structures were also discussed. The optical band gaps for PSI and conventional PI films were 3.320 eV and 3.228 eV, respectively. This result suggests that the band gap of PI films can be enlarged by modification with Si–O components. The differential barrier height between the PSI and conventional PI films is 0.038 eV, and is close to the difference in half of optical band gaps (0.046 eV).     

The effect of metallic barriers in inhibiting copper ion transport in low-k dielectrics: Implications for time-to-failure

In this article we study the effect of metallic barriers in inhibiting copper ion drift/diffusion into low-k dielectrics through a mathematical analysis. We extend our previous drift/diffusion model for copper ion drift without barriers to include the effect of metallic barriers. The addition of the barrier changes the boundary condition at the barrier/dielectric interface and results in a time dependent flux and concentration at the interface. The results show that for a given dielectric, a metallic barrier needs to have both a lower ionic solubility and lower ionic diffusivity for optimal effectiveness.     

Effects of (NH4)2Sx treatment on the electrical and optical properties of indium tin oxide/conducting polymer electrodes

In this study, the effects of (NH₄)₂S_x treatment on the electrical and optical properties of the indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) electrodes were researched. The authors found that (NH₄)₂S_x treatment could result in suppressing the hysteresis-type current-voltage characteristics related to the interfacial capacitance variation and a reduction in the equivalent refractive index of the ITO/PEDOT:PSS electrodes, owing to the improvement in the interfacial stability of the ITO/PEDOT:PSS electrodes and a reduction in the interface trap-states related charge store at the ITO/PEDOT:PSS interface. This implies that the ITO/PEDOT:PSS electrodes fabricated using the (NH₄)₂S_x-treated ITO may produce a higher extraction efficiency for ITO/PEDOT:PSS-based optoelectronic devices.     

Preliminary evaluation of interfacial stability of surface modified porous methyl silsesquioxane by ion implantation for copper metallization scheme

Thin films of ultra-low-κ materials such as porous methyl silsesquioxane (MSQ) (κ=2.2) were implanted with argon 1×10¹⁶ cm⁻² dose at energies varying from 20 to 50 keV at room temperature. This work shows that the surface hardness of the porous films can be improved five times as compared to the as-deposited porous films by implanting Ar with 1×10¹⁶ cm⁻² doses at 20 keV, sacrificing only a slight increase (∼9%) in dielectric constant (e.g., from 2.2 to 2.4). The hardness persists after 450 °C annealing. In this current work, an ion implantation strategy was pursued to create a SiO₂-like surface on MSQ. The effects of implantation parameters on the barrier property and bulk stability of MSQ were then studied. The results reveal one possible route to attain the “zero barrier thickness” requirement for interconnects systems.     

Synthesis of magnetic nanostructures: Shape tuning by the addition of a polymer at low temperature

We report a simple method for shape-controlled synthesis of iron oxide spinels such as magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) nanostructures using a thermoresponsive polymer poly(vinyl methyl ether) (PVME) by the alkaline hydrolysis of iron salt at low temperature (20 °C). Microscopic analysis confirmed the formation of needle- and flower-shaped iron oxide nanostructures depending on reaction conditions. High-resolution transmission electron microscopic analysis of the needle- and flower-shaped nanostructures as well as their corresponding selected area electron diffraction patterns revealed that the formed nanostructures are crystalline in nature. X-ray diffraction study reveals the formation of well-crystalline pure Fe₃O₄ and γ-Fe₂O₃ nanostructures under different reaction conditions. Fourier transform Infra-red spectroscopic analysis confirms the adsorption of PVME on the surface of iron oxide nanostructures. Finally, the magnetic properties of γ-Fe₂O₃ and Fe₃O₄ nanostructures is studied that shows the superparamagnetic behavior of the formed iron oxide nanostructures.     

Ferromagnetic and microwave absorption properties of copper oxide/cobalt/carbon fiber multilayer film composites

The copper oxide/cobalt/carbon fiber multilayer film composites were synthesized by thermal oxidation route. In order to investigate the intrinsic reasons for microwave absorption properties of absorbers, the complex permittivity, complex permeability and the microwave absorption properties of composites were studied in the 1-18 GHz range. The strongest reflectivity loss (RL) of microwave absorber was further enhanced to − 42.7 dB (microwave absorption rate > 99.9%) at 10.8 GHz for a layer of 2.0 mm thickness, and the strong absorption (RL < − 10 dB) was obtained between 8.72 and 18 GHz for the thickness of 1.3-2.2 mm. The results indicated that the dielectric loss and magnetic loss led to the excellent microwave absorption property of CuO/Co/CF composites. It is believed to be ideal for making a lightweight, strong absorption and wide-frequency microwave absorbing material.     

Growth of SrTiO3 thin films on LaAlO3(001) substrates; the influence of growth temperature on composition, orientation, and surface morphology

SrTiO₃ films have been grown on LaAlO₃(001) single crystal substrates using rf-sputtering. The substrates were held at temperatures ranging from 100 to 850°C. For growth temperatures as low as 350°C epitaxial growth is observed. Below 350°C the films are polycrystalline and three different orientations (100), (110), and (111) can be observed using X-ray diffraction. Atomic force microscopy shows that films deposited at temperatures below 350°C and above 650°C are smooth while the surfaces of the films made at intermediate temperatures are rough and faceted. As growth temperatures decrease below 250°C, the films show decreasing amount of Sr.     

Opportunity of metallic interconnects for solid oxide fuel cells: a status on contact resistance

The status and opportunity of metallic interconnects for an anode-supported solid oxide fuel cell stack is reviewed with special emphasis on the variation of contact resistance of currently developed interconnects at operating temperatures, as well as the prevailing approaches to reduce contact resistance. It appears that without a coating, current metallic interconnects are not suitable for practical applications at 800 °C since they may cause drastic performance degradation of the stack within its expected service lifetime. Some guidelines in designing new metallic interconnects with both excellent oxidation resistance and reasonably low contact resistance in SOFC environments are set forth.     

Synthesis of copper oxalate in ether-water bilayer refluxing system and their conversion to copper oxide nanowires

Copper oxalate nanowires with a mean diameter of 100 nm and a length of 10 µm were synthesized via the reaction of copper acetate and dimethyl oxalate in ether-water bilayer refluxing system. The volume ratio of ether to water and the concentration of copper acetate were used to examine the effects on forming copper oxalate nanowires. Copper oxalate nanowires were obtained only in the case of the greater volume ratio of ether to water and the lower concentration of copper acetate. Copper oxalate nanowires with a dense structure (enclosed by a smooth surface) can be further transformed into highly porous copper oxide nanowires by the decomposition of copper oxalate nanowires at 350 °C.     

A novel technique for fabrication of metallic structures on polyimide by selective electroless copper plating using ion implantation

The successful use of palladium ion implantation into polyimide to seed an electroless plated film of copper on the polyimide surface is reported. Polyimide (Hitachi PIX 3400) was implanted with palladium ions to doses of 1.5 × 10¹⁵ − 1.2 × 10¹⁷ ions cm⁻² using a MEVVA ion implanter. The implanted ions acted as sites for nucleation of copper film. A copper film was then deposited on implanted polyimide using a commercial electroless plating solution. The ion energy was kept low enough to facilitate a low critical ‘seed’ threshold dose that was measured to be 3.6× 10¹⁶ Pd ions cm⁻². Test patterns were made using polyimide to study the adaptability of this technique to form thick structures. Plated films were studied with optical microscopy, Rutherford Backscattering Spectrometry (RBS) and Profilometry. The adhesion of films was qualitatively assessed by a ‘scotch tape test’. The film growth (thickness) was observed to be linear with plating time. A higher implantation dose led to greater plating rates. The adhesion was found to improve with increasing dose.     

Investigation of structural,optical, antibacterial,and dielectric properties of V-doped copper oxide thin films: Comparison with undoped copper oxide thin films

Vanadium doped Copper oxide (CO) thin films were prepared by the sol-gel dip-coating method. The properties of thin films were examined by X-Ray Diffractometer (XRD), UV–Visible-NIR spectrophotometry, and dielectric properties analyzer. The antibacterial and photocatalytic properties were also determined. XRD spectra revealed the dual-phase of copper oxide (cuprite and tenorite) for all percentages of V with no other impurity peak. Tauc's relation is used to probe the optical band gap which is reduced from 1.96 to 1.64 eV with an increase in vanadium doping percentage. The impurity band coalesces with the conduction band of copper oxide to decrease the band gap. Dielectric constant measurements reveal that the Ac conductivity of thin films increases with an increase in V doping percentage.     

Preparation, characterization, and electrochemical application of mesoporous copper oxide

Mesoporous CuO was successfully synthesized via thermal decomposition of CuC₂O₄ precursors. These products had ring-like morphology, which was made up of nanoparticles with the average diameter of 40 nm. The electrochemical experiments showed that the mesoporous CuO decreased the overvoltage of the electrode and increased electron transference in the measurement of dopamine.     

Synthesis and characterization of silica aerogel films for inter-metal dielectrics via ambient drying

Low-dielectric silica aerogel films could be synthesized via solvent exchange-ambient drying of wet gel films that were obtained by spin-coating the isopropanol based silica sol on a p-Si (100) wafer. Using isopropanol as a drying solvent, the thickness and the dielectric constant of silica films significantly changed from 1100 nm to 350 nm and from 2.1 to 3.6, respectively, with the drying pressure of [8 MPa (270 °C)→2.6 MPa (200 °C)]. However, when isopropanol in pores was exchanged with n-heptane followed by ambient drying technique, the aerogel films had 1350 nm thickness, 80% porosity, and 2.0 dielectric constant, regardless of the drying pressure. The degree of planarization and the gap filling capability on 0.7 μm tungsten patterning wafer were excellent. It was proven that the ambient-dried aerogel films have a possibility of an application to IMD (inter-metal dielectrics) materials in the next generation of semiconductor devices beyond the giga level.     

X-ray reflection spectroscopy of the HfO2/SiO2/Si system in the region of the O–K absorption edge

The paper shows the importance of soft X-ray reflection spectroscopy as a non-destructive in-depth characterization tool of the local atomic structure of high-k dielectric planar HfO₂/SiO₂/Si systems. The data obtained in the region of the O–K absorption edge demonstrate that the variation of the glancing angle enables the depth profilometry of the sample. By using the Kramers–Kronig analysis the reflection spectra are transformed into absorption spectra, from which the local physico-chemical environment of oxygen atoms is deduced, allowing also the knowledge of the local atomic structure and point defects associated with a thin superficial layer.     

Effect of sputtering power on the physical properties of dc magnetron sputtered copper oxide thin films

Cuprous oxide films were deposited on glass substrates using dc magnetron sputtering technique by sputtering of pure copper target in a mixture of argon and oxygen atmosphere under various sputtering powers in the range 0.38–1.50 W cm⁻². The influence of sputtering power on the structural, electrical and optical properties was systematically studied. The films were polycrystalline in nature with cubic structure. The films formed at sputtering powers ≤0.76 W cm⁻² exhibited mixed phase of Cu₂O and CuO while those formed at 1.08 W cm⁻² were single phase Cu₂O. The single-phase Cu₂O films formed at a sputtering power of 1.08 W cm⁻² showed electrical resistivity of 46 Ω cm, Hall mobility of 5.7 cm² V⁻¹ s⁻¹ and optical band gap of 2.04 eV.     

Fast and accurate solutions of electromagnetics problems involving lossy dielectric objects with the multilevel fast multipole algorithm

Fast and accurate solutions of electromagnetic scattering problems involving lossy dielectric objects are considered. Problems are formulated with two recently developed formulations, namely, the combined-tangential formulation (CTF) and the electric and magnetic current combined-field integral equation (JMCFIE), and solved iteratively using the multilevel fast multipole algorithm (MLFMA). Iterative solutions and accuracy of the results are investigated in detail for diverse geometries, frequencies, and conductivity values. It is demonstrated that CTF solutions are significantly accelerated as the conductivity increases to moderate values and CTF becomes comparable to JMCFIE in terms of efficiency. Considering also the superior accuracy of this formulation, CTF becomes suitable for fast and accurate analysis of scattering problems involving lossy dielectric objects.     

Catalytic combustion of ethyl acetate on supported copper oxide catalysts

Total oxidation of ethyl acetate on supported copper oxide catalysts was investigated. The catalysts have been prepared by wet impregnation method and characterized by XRD, TEM and XPS. Among the catalysts with the supports of TiO2, CeO2/TiO2 and CeO2-ZrO2/TiO2, CeO2-ZrO2 solid solutions doped TiO2 supported catalyst gives the highest catalytic activity. Catalyst with the composition of 5 wt.% CuO/10 wt.% CeO2-ZrO2-TiO2 shows the total oxidation of ethyl acetate at about 270 degrees C with the 100% CO2 selectivity. The characterization studies of supported copper oxide catalysts showed that the highly dispersed CuO is one of the active phase which contacts intimately with the support, the action of the interface between the components was not be ignored.