Nanoparicles smaller than 100 nm have been expected to reveal the novel physical and chemical properties that differ from the corresponding bulk materials. And nanoparticles are to be used as constituents for many applications in the various fields. These applications include the electronic, magnetic, optoelectronic and electric materials. In this article, we review the research work for expected and ongoing nanoparticle electronic device developments of current interest. And we briefly refer to the research activities on the shape and array control of nanoparticles as a new class of materials, although the device usages have not yet proposed.
Mesoporous silica particles with hexagonal or spherical structure were synthesized by a sol-gel method using tetraethoxysilane (TEOS) as a silica source, P123 (EO20PO70EO20) as a surfactant, and cetyltrimethylammonium bromide (CTMABr) as the co-surfactant. And the experiment was carried out at the molar ratio of TEOS/P123/CTMABr (1:0.011:0.031). The effect of aging time on properties of mesoporous silica particles was studied and the obtained particles were also characterized by SEM, TEM, BET, TGA, and XRD. As a result, the particle size, surface area, and pore size of hexagonal mesoporous silica particles were similar to those of spherical mesoporous silica particles, and the pore size of all samples increased with aging time. N2 adsorption/desorption isotherms for the mesoporous silica particles prepared by changing the aging time (0–14 h) were obtained and all the samples exhibited type IV isotherms. In addition, it was found that the difference between adsorption and desorption increased with aging time.
MgO is a well-known additive to BaTiO3 powder for MLCC application. A nano-coating process was investigated to produce an MgO shell layer onto BaTiO3 core powder. Several deposition reaction routes were examined to find out that a magnesium nitrate-urea system worked very well, if not the best. The solution-state reaction gave Mg5(CO3)4(OH)2·4H2O as confirmed by XRD, which later turned to MgO upon calcination at 600°C. The core-shell morphology was characterized using SEM and TEM whereas the composition of the shell layer was determined via ICP-AES and XRF. The composition of the MgO shell layer was rather easily controlled by adjusting initial amounts of reactants.
Manganese-doped zinc sulfide (ZnS:Mn) nanoparticles were synthesized by mixing aqueous solutions of zinc nitrate and manganese nitrate with sodium sulfide. The photoluminescence (PL) of ZnS:Mn nanoparticles (NPs) dispersed in the aqueous solution was observed at 590 nm using extinction light 320 nm in wavelength. When the S and Zn ion concentrations were equal (equimolar condition), the Mn content in NPs increased with the molar ratio Mn/Zn in the feed solution. PL intensity and PL quantum efficiency were proportional to the Mn content in NPs. The particle size of ZnS:Mn increased with the time elapsed after preparation, although the Mn content was constant. NP absorbance at 320 nm increased with elapsed time due to increasing NP size so that PL intensity increased because of increasing absorbed light energy. However, the quantum efficiency remained almost constant. When the S ion concentration exceeded the Zn ion concentration (excess S ion condition), the particle size and absorbance at 320 nm increased with elapsed time, exhibiting trends similar to those observed in NPs prepared under the equimolar condition. On the other hand, the quantum efficiency under an excess S ion condition increased with the elapsed time.
This study presents the effects of particle size on the monolayer structure of silica nanoparticles in the diameter range between 10 and 100 nm via a wet-coating process. Suspensions of silica nanoparticles coated on a solid substrate by a bar coater are dried to give a monolayer. For the comprehension of dominant factors in the formation process, the experimental results are compared with the results obtained by numerical simulations. Dense monolayers can be obtained in the diameter range of silica nanoparticles from 10 to 100 nm via the wet-coating process; however, the monolayers of the nanoparticles, the diameter of which is 11 nm, cannot be obtained at the coverage over 0.7. The pair correlation function of the monolayer shows that the 11-nm nanoparticles are arranged with the inter-particle separation of about 1–2 nm. A feasible model for the formation process suggests that the hydration force between silica surfaces retains the nanoparticles with a constant separation.
The objective of this study was to find the effect of the initial droplet size in the ASES (aerosol solvent extraction system) process. We prepared poly(L-lactic acid) (PLLA) nano- and micro-particles using ASES process. The experiments were carried out on various conditions. We got PLLA particles that had mean particle diameter from 0.54 to 1.28 μm. And we calculated theoretical initial droplet size with the equation derived by Lorenzetto and Lefebvre and investigated the relation between the initial droplet size and particle size. The results show that there is a linear relationship between the initial droplet size and particle diameter.
Among many deposition techniques, atomic layer deposition (ALD) is well suited for highly conformal and uniform ultrathin films with accurate thickness control over a large area. A number of ALD deposition processes have been used to grow mixed oxides like Hf or Zr silicate and aluminate thin films for high-k gate dielectrics needed in the next generation silicon transistors. Nano laminate mixing of each oxide by switching between two metal precursors with an oxidant like water can be used and film composition can be controlled by adjusting the number of each single oxide cycles. An alternating injection of metal alkoxides and chlorides without the injection of extra oxidants is another method. Single metal source, which contains both metal and Si (or Al), also can be adopted to form silicate or aluminate films. These processes will be overviewed in this article with our recent work on atomic layer deposition (ALD) of high-k gate dielectrics. It is important to select a proper set of precursors and each process should be evaluated and compared in terms of the reliability and film properties. In-situ diagnostic technique such as FT-IR is also helpful for the process development.
White organic light-emitting diodes (OLEDs) based on a multilayer structure were fabricated, in which the red emission is from [2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo [ij] quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene]propane-dinitrile (DCM2) doped 4,4′-bis[N-1-naphthyl-N-phenyl-amino]biphenyl (NPB) layer and the blue-green emission from 4,4′-bis[2-(3-N-ethylcarbazoryl)vinyl]biphenyl (BCzVBi) doped 4,4′-bis(2,2-diphenylvinyl)biphenyl (DPVBi) layer. White light emission was obtained by controlling the doping concentration of each dopant material in a hole-transporting layer and an emitting layer. But in this white device, electroluminescence spectra depend on the applied voltage. By inserting a tris-(8-hydroxyquinoline)aluminum (Alq3) layer as an electron-transporting layer, voltage-independent white emission of the CIE coordinates (0.31, 0.32) was obtained. The luminance of this device was 10,600 cd/m2 at 15 V and the power efficiency was 1.50 lm/W at 7.75 V. This voltage independence is believed to result from efficient electron injection and a narrowing effect of the width of the recombination zone by insertion of an Alq3 layer.
Amorphous carbon thin films are deposited by RF pulsed plasma chemical vapor deposition (CVD) on Si wafers at 15°C. The depositions are carried out using a mixture of methane and hydrogen by changing DC self-bias voltage from –100 to –400 V. The morphologies of the deposited films are observed by atomic force microscopy (AFM). The structure and the properties of the deposited films are analyzed by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). With an increase in the DC self-bias voltage value to –400V, a needle-like surface morphology forms, which indicates that clusters of sp2-coordinated carbon atoms originate in the film and their amount increases. Raman and XPS spectra are analyzed in more details by deconvolution using the Gaussian and Lorentz curve fitting. Raman and XPS analyses showed that diamond-like films with highest sp3 are formed at –300 V while at higher DC self-bias voltage (>–400 V), films with a little decrease of sp3 contents are formed due to high ion bombardment.
Copper phthalocyanine (CuPc), a widely-used semiconductor material, was deposited onto quarts substrates via a vacuum process. SEM and XRD analyses were employed to characterize the structure-controlled CuPc films. As-deposited CuPc thin films were weakly oriented according to the XRD result and were homogeneous. The conductivity of a CuPc thin film was estimated using a four-point probe measurement technique and the values of the conductivity were 8.0 × 10–8–3.5 × 10–7 Ω–1 cm–1. It was observed that thermal annealing had CuPc film well-aligned since thermal annealing could participate to increase the interaction among the CuPc molecules. The interaction between the CuPc molecule and the surface of the substrate may lead to closer stacking of CuPc molecules as well. For well-aligned CuPc thin films, the threshold voltage in the current-voltage characteristics of the ITO/CuPc/Al device was decreased by 20% compared to those of as-deposited CuPc thin films. The current density-voltage (J-V) and luminance-voltage (L-V) characteristics of the present ITO/CuPc/NPD/Alq3/LiF/Al devices were measured to investigate the effect of the alignment of CuPc molecules on the enhancement of hole injection from ITO (Indium Tin Oxide) into HTL (Hole Transporting Layer) through a well-aligned CuPc layer. The luminance is proportional to the current density in the present devices as a similar discrepancy in the L-V characteristic is expected. The higher current density and luminance at a given voltage are shown when a thermally-annealed CuPc layer was placed in the present multilayer devices.
This review provides an overview of polymer gels with various intelligent functional elements. Information about the functions as well as the physical and chemical characteristics of the polymer gels acts as a guiding principle for a wide variety of technological applications in polymer gels. This article provides descriptions of the history of polymer gels, their current research and a review of noteworthy contributions in the polymer gel system in which gel networks are utilized as reaction and/or separation media.
The two different types of precursors, poly(amic acid) and polyisoimide, were prepared from 4,4′-(1,4-phenylenebis(1-methylethylidene))bisbenzenamine and 4-4′-oxydiphthalic anhydride for synthesis of polyimides. The FTIR spectroscopy was used to investigate the imidization reaction progress of poly(amic acid) and polyisoimide. Thermal properties were investigated using DSC and TGA. Stress behaviors during and after imidization processes of the two precursors were analyzed and compared using a bending beam curvature measurement system equipped with an in situ film thickness measurement system, the interferometer. The stress behaviors were significantly affected by the types of precursors, as water molecules evolved during the imidization process of poly(amic acid), being different from polyisoimide. They were also affected by temperature scanning rate for imidization and the annealing process.
The cure kinetics of blends of epoxy resin (4,4′-tetraglycidyl diaminodiphenyl methane; TGDDM)/curing agent (diaminodiphenyl sulfone; DDS) with ATPEI-CTBN-ATPEI triblock copolymer (ABA type) were studied using differential scanning calorimetry under isothermal conditions to determine the reaction parameters such as activation energy and reaction constants. By increasing the amount of ABA in the blends, the final cure conversion was decreased. Lower values of the final cure conversions in the epoxy/ABA blends indicated that ABA hinders the cure reaction between the epoxy and the curing agent. The value of the reaction order m for the initial autocatalytic reaction was not affected by blending ABA with epoxy resin, i.e., the value was approximately 1.0. The value of n for the n-th order component in the autocatalytic analysis was increased from 2.0 to 3.4 by increasing the amount of ABA in the blends. A diffusion controlled reaction was observed as the cure conversion increased and the curing reaction was successfully analyzed by incorporating the diffusion control term in the rate equation for the epoxy/DDS/ABA blends. The glass transition temperature of the cured blend was improved from 187 to 205°C and the value of the fracture toughness was also improved by about 400% compared to that of the unmodified resin at 30 wt% of ABA triblock copolymer. This is attributed to the formation of co-continuous morphology between the epoxy phase and ABA triblock copolymer phase. By increasing the amount of ABA, compressive strain, tensile stress and strain of the cured blends were increased, but the compressive stress was reduced due to the presence of CTBN rubbery phases.
Molecular imprinted thermosensitive gels adsorb and/or desorb a specific heavy metal by taking advantage of temperature swing, resulting from the reconstruction/destruction of a multi-point adsorption site corresponding to the shrinking/swelling of the gel network. Imprinted gels were prepared by copolymerizing N-isopropylacrylamide (NIPA) as a thermosensitive component, a chelating monomer and a cross-linker by means of a molecular imprinting technique using Cu(II) ions as a template. Two types of chelating monomers were used in this study, N-4-(vinylbenzyl)ethylenediamine (VBEDA) and N,N′-di(4-vinyl)benzylethylenediamine (DVBEDA), which contain single and dual vinyl groups, respectively. DVBEDA, a novel chelating monomer, was developed to improve the performance of the gel, and the performances of the NIPA-DVBEDA and NIPA-VBEDA gels were compared. Both imprinted gels repeatedly adsorbed and desorbed Cu by virtue of a temperature swing between 30 and 10°C, where the variations in the amounts of Cu adsorbed on the NIPA-DVBEDA gels were larger than those on the NIPA-VBEDA gels. Both of the imprinted gels selectively adsorbed Cu, which was used as a template molecule, from a solution of Cu, Ni and Zn, where NIPA-DVBEDA had a higher selectivity than NIPA-VBEDA. The improved performance of the NIPA-DVBEDA gels can be attributed to critical control of the reconstruction/destruction of the multi-point adsorption site given by the cross-linking of the DVBEDA on the gel network. The Langmuir parameter describing the equilibria of temperature swing adsorption also indicated that the imprinted NIPA-DVBEDA gels were high-performance in nature.
In order to predict the behavior of polyimides and to optimize their fabrication, it is important to understand the relationship between polyimide’s structure and their surface properties. The surface properties (water sorption and repellency, adhesion) are closely related to the surface tension of polymer solid. Critical surface tension γC and surface tension γS of a polymer solid have generally been estimated by the contact angle method. BPDA (3,3′,4,4′-biphenyltetracarboxylic dianhydride)–BAPE (1,2-di(4-aminophenoxy) ethane) polyimide was successfully synthesized. Testing liquids, e.g., dispersion, polar, hydrogen bonding liquids were used to measure the contact angle θ whose values were determined by a quantitative imaging system. Unlikely the existed contact angle measurements, our lab-made quantitative imaging system could provide accurate and reproducible values of the contact angles. The critical surface tensions γC were analyzed by a Zisman plot, a Young-Dupré-Good-Girifalco plot, and a log(1 + cos θ) vs log γL plot. The surface tension γS of BPDA-BAPE polyimide was calculated using the geometric mean equation and multiple regression analysis. The Zisman plot is essentially a downwardly convex curve with polar and hydrogen bonding liquids having γC << γL. The calculated values of γSd (a dispersion component), γSp (a polar component), γSh (a hydrogen bonding component), and γS are 29.69, 13.17, 0.25, and 43.11 mN·m–1, respectively. The γS of BPDA-BAPE polyimide is 43.11 mN·m–1 which is 1.05 and 1.14 times higher than those of Kapton® H films, respectively. The polarity of BPDA-BAPE polyimide is 0.311 whose value was located between 0.87 and 1.39 magnitudes of Kapton® H films’ polarity, respectively.
Manufacturing C/SiC composites from the reaction of methyltrichlorosilane (MTS) and hydrogen by the pulse CVI (Chemical Vapor Infiltration) was studied. In the pulse CVI, three steps such as evacuation of the reactor (te), injection of reactant gases (ti), and infiltration and deposition reaction during a hold-on period (tr) were repeated. Effects of each step were studied by changing the duration of each step. As the evacuation time increased and the reaction time decreased during the same total actual reaction time, the amount of deposition in the preform increased. Effects of the changes of evacuation time were greater than those of reaction time. The same results were confirmed with the thermal analysis data, porosimeter, and SEM.
N-Isopropylacrylamide (NIPA) hydrogel was successfully incorporated with tributyl phosphate (TBP) which works as an extractant species of phenols. NIPA hydrogel was found to be favorable to prepare a monolithic hydrogel in the coexistence of TBP which requires using methanol as the polymerization medium. The hydrogel was found to be stably obtained at 333 K in methanol and the concentration of crosslinker (N,N′-methylenebisacrylamide) of 86 mM. The TBP-incorporated NIPA hydrogel was used for experiments for removal of phenol from aqueous solution. The removed amount of phenol using the NIPA hydrogel was markedly enhanced in proportion to the amount of incorporated TBP. Liquid–liquid solvent extraction of phenol using TBP dissolved in n-octane was examined for comparison of the distribution ratio D. From the proportional dependence of the distribution ratio on the amount of the incorporated TBP, phenol was found to form a 1:1 complex with TBP both in the cases of NIPA gel and liquid–liquid solvent extraction. At the corresponding concentration of phosphate moiety, the phenol removal performance by the TBP-incorporated NIPA hydrogel was found to be comparable to that by conventional liquid–liquid extraction.
Hybrid Langmuir-Blodgett films of an amphiphilic ruthenium tris-bipyridine complex (DCnRu, n = 7, 13 and 19) and vanadium oxide gel were fabricated and characterized. Langmuir monolayers of the amphiphilic molecules hybridized and stabilized with layered vanadium oxide were transferred onto a solid substrate as z-type multilayers with a transfer ratio close to unity. AFM observation revealed that the monolayer had a smooth surface with roughness of 5 nm over 1 μm2. The hybrid monolayer of the vanadium oxide and DCnRu showed photo-induced electron transfer to methyl viologens through the conduction band of the vanadium oxide.
In order to investigate the adsorptive properties for As(III) and As(V) at 303 K, the magnetite was prepared by adding the aqueous sodium hydroxide solution to the mixture solution of Fe2+:Fe3+ = 1:2 using iron chloride. The adsorption of As(III) and As(V) was dependent on equilibrium pH and showed a maximum value at pH 6 and 5, respectively. From their chemical species existing at each pH and the pH of the zero point of charge of the magnetite surface, As(V) was probably adsorbed on the surface of the magnetite through the electrostatic force, while the adsorption of As(III) was different from that of As(V). It is probable that As(III) was absorbed through an ester reaction on the magnetite. The adsorption capacities of As(III) and As(V) were 2.77 × 10–1 mmol·g–1 and 2.28 × 10–1 mmol·g–1, respectively. The adsorption equilibrium constants for As(III) and As(V) were 4.74 dm3·mmol–1 and 12.1 dm3·mmol–1, respectively, suggesting that the magnetite has higher affinity to As(V). An aqueous sodium hydroxide solution was useful as an eluent for desorption of As(III) and As(V).