Ag Ultrafine Particles Research Articles

Molecular Approach To Enhance Thermal Conductivity in Electrically Conductive Adhesives

Significant heat generation in modern high-speed electronic devices requires elevated thermal conductivity of electrically conductive adhesives (ECAs), but the gap between discrete filler materials significantly interrupts the pathway of heat transport. In this work, we demonstrated the 587% enhancement of thermal conductivity by adding a silver–organic complex (i.e., silver 2-ethylhexanoate) in an epoxy-based ECA with the optimal value of 4.7 W/mK at a low curing temperature of 180 °C. After the postannealing at 200 °C, the thermal conductivity can be further enhanced to 6.2 W/mK with high stability. In the presence of the silver–organic complex, the optimal die shear strength can be increased to 179% (38.06 MPa) compared to that of the blank samples. The silver–organic complex is capable of molecule-scale blending and forming ultrafine Ag particles (13–47 nm) well-distributed in the epoxy matrix, enabling gap-filling and bulky network sintering to achieve thermal conductivity enhancement.

Effect of Ultrafine Ag Particles on Superconducting Properties and Water Resistance of Eu-Ba-Cu-O Thick Films

Effect of Ultrafine Ag Particles on Superconducting Properties and Water Resistance of Eu-Ba-Cu-O Thick Films

Synthesis and electrochemical properties of composite films based on poly-3,4-ethylenedioxythiophene with inclusions of silver particles

The electrochemical behavior of PEDOT/Ag composite films obtained by chemical deposition of ultrafine Ag particles into the poly-3,4-ethylenedioxythiophene (PEDOT) matrix was studied. The film morphology was characterized by transmission electron microscopy (TEM). The changes in the mass of the films during the chemical deposition of silver into the polymer structure were evaluated microgravimetrically. The mass of the included metallic silver particles depends on the synthesis time and the initial concentration of silver ions in solution. The cyclic voltammograms (CVs) of PEDOT/Ag films in sodium nitrate solutions and sodium nitrate solutions with additions of chloride ions were studied. The cyclic voltammograms of PEDOT/Ag films in chloride-containing solutions showed the peaks of the oxidation of silver and reduction of the oxidation product, which were absent on the CVs of the starting PEDOT film.

An investigation on the application of process control agents in the preparation and consolidation behavior of nanocrystalline silver by mechanochemical method

In this paper, the effect of various amounts and types of process control agent (PCA), i.e., stearic acid (SA) and ethylene bis-stearamide (EBS), in the production and consolidation behavior of nanocrystalline silver prepared by mechanochemical reduction of Ag2O by graphite was studied. The structural evolution and morphology of powders were investigated using XRD, HRSEM and particle size analyzer techniques. The results showed the nanocrystalline Ag formed after 25h of milling and the addition of PCA prolonged the synthesis process time. Also, the effect of EBS on prevention of the excessive cold welding of ultra-fine Ag particles in the final stages of milling was more serious than SA. In fact, the presence of PCA effectively inhibited the creation of coarse Ag particles and finally decreased the crystallite size to 14nm. Moreover, with the addition of PCAs, the Brinell hardness of sintered Ag samples was considerably increased.

Fabrication of a Pure, Uniform Electroless Silver Film Using Ultrafine Silver Aerosol Particles

To obtain evenly distributed pure Ag particles with a narrow size distribution on a polymer membrane, a novel activation procedure with an environmentally friendly, cost-effective method was utilized as a pretreatment before electroless Ag deposition. The pretreatment was first performed on an untreated membrane surface by collecting ultrafine ambient spark-generated Ag aerosol particles. After annealing, the electroless Ag film was fabricated on the collected aerosol particles in the Ag electroless bath. Experimental characterizations showed that the ultrafine Ag particles were uniformly anchored onto the membrane surface through pretreatment, resulting in a pure Ag film of closely packed particles with a narrow size distribution on the membrane, and the properties were comparable to those of an Ag film on wet Sn-Ag-activated membranes.

Effect of Ag Particle Size in Thick-Film Ag Paste on the Electrical and Physical Properties of Screen Printed Contacts and Silicon Solar Cells

The impact of the Ag particle (metal powder in the screen printed paste) size on the quality of Ag thick-film ohmic contacts to high-sheet-resistance emitters of Si solar cells is investigated. Spherical particle size was varied in the range of (ultrafine to large). Even though ultrathin glass regions are achieved for the large particle paste, giving low specific contact resistance , secondary ion mass spectroscopy measurements showed a higher Ag concentration at the p–n junction that increased the junction leakage current and decreased the by and fill factor (FF) by . Pastes with ultrafine Ag particles generally produced a thick glass layer at the Ag–Si contact interface, which increased and series resistance , and lowered the FF by . Small to medium size Ag particles in the paste produced thin glass regions and many regularly distributed Ag crystallites at the contact interface. This resulted in low , high shunt resistance , low , and high FF (0.781). Cell efficiencies of were achieved on untextured float zone Si with emitter by rapid firing of screen printed contacts in a lamp-heated belt furnace.

Structural evolution of sol–gel SiO 2 heated glasses containing silver particles

SiO 2 based glasses added with nanometric-silver particles have been prepared by the traditional sol–gel process, using the tetraethyl-orthosilicate alkoxide. The Ag particles were prepared using a new method described in this article, the method uses a cementation reaction between Ag ions and an iron electrode. The size of the particles, measured in the dried glass, was in the range of 100–200 nm. The observed structural changes depend on the annealing conditions, such as the annealing temperature, the amount of silver particles and the type of acid (HCl or HNO 3) used to catalyze the hydrolysis/condensation reactions during the sol–gel process. Samples prepared using both acids crystallized into the cristobalite phase after thermal annealing at 800 °C. The amount of SiO 2 crystallized depends on the amount of Ag present in the glass. Samples prepared from solutions catalyzed with HCl acid show the formation of nanometric Ag particles after thermal annealing at 500 °C, these small particles are not observed after similar treatments when HNO 3 is used as the catalytic acid. HCl and Ag 2O form AgCl which is reduced by residual carbon to form Ag ultrafine particles. The diffusion of the reduced Ag spices, which form these particles, is facilitated by the opened structure of the glasses added with Ag, as indicated by IR measurements.

The Disturbance of Solitary Wave in the Diffusion Process of Ag Ultrafine Particles

With an example of Ag ultrafine particles, the “diffusion-trapping-reaction aggregation” model of ultrafine particles is proposed, and the spontaneous evolution of ultrafine particles is described. The evolution kinetic equation is established and the solitary wave solution of evolution kinetic equation is found and discussed in detail.

A Morphologic Study on the Fate of Ultrafine Silver Particles: Distribution Pattern of Phagocytized Metallic Silver in Vitro and in Vivo

The distribution pattern of inhaled particles is an important factor for the evaluation of health effects. In this study, we morphologically investigated the fate of agglomerated ultrafine particles in macrophages in vitro and in vivo. Metallic silver (Ag) was chosen as a test particle, since it can be easily produced and detected by elemental and morphologic analyses. Ultrafine Ag particles generated by an electric spark generator in an argon atmosphere were collected on PTFE filters. The particles were suspended in distilled water and adjusted to different concentrations (10 μg/ml to 1 mg/ml) with phosphate-buffered saline (PBS). For the in vitro study, 1774 macrophage cell suspensions (200,000 cells in 400 μl medium) were plated in small chambers. Six hours later, 100 μl of the silver-PBS suspension was added to each chamber. For the next 9 days, the chamber slides were examined daily with an inverted microscope in order to detect agglomerated particles in the cell. The medium was changed every day, and Ag in the medium was checked by inductively coupled plasma mass spectrometry (ICP-MS). On days 1, 3, 5, 7, and 9, cells in the chambers were fixed with 2.5% buffered glutaraldehyde and examined ultrastructurally. For the in vivo study using F344 rats, 50 μg Ag particles were instilled intratracheally. On days 1, 4, and 7 following instillation, rats were sacrificed and the lungs were examined morphologically. The Ag content in the lung, liver, and lung-associated lymph nodes was analysed by ICP-MS. In the in vitro study, the dose-dependent presence of agglomerated particles was observed in 1774 cells. The size and form of particles remained unchanged throughout the observation period. Electron microscopy with x-ray microanalysis showed that both single and agglomerated Ag particles were observed in the dilated phagolysosome of 1774 cells. In the in vivo study, focal accumulation of Ag-particle-laden alveolar macrophages was found. Ag particles were also observed in the alveolar wall. Ag content in the lung was constant between day 1 and day 7, indicating that no rapid particle translocation from the lung to other organs had taken place in this time period. In vitro and in vivo studies suggested that agglomerated Ag particles remained in targets for a given period of time—at least up to 7 days.

Preparation of ultrafine composite particles of Ag+AlN/Al by nitrogen plasma metal reaction

Abstract Pure Ag and Al were melted simultaneously by nitrogen arc plasma in a common chamber using two electrodes. Ultrafine composite particles consisting of fcc-Ag, fcc-Al and hexagonal AlN are obtained together with 17% mixture of hexagonal Ag 2 Al ultrafine particles. Ag, Al and AlN ultrafine particles are formed through the condensation of element vapor, but Ag 2 Al ultrafine particles are formed through a solid reaction between Al and Ag ultrafine particles.

Study of optical transient relaxation of an Ag-O-Ba thin film

Under the action of laser pulses with a wavelength of 647 nm and a pulse duration of 150 fs, the optical transient response of an Ag−O−Ba thin film was obtained by the pump-probe method. Optical relaxation is a process in which non-equilibrium electrons, excited by laser pulses and originating from metallic ultrafine particles, return to the equilibrium state. The optical transient relaxation of an Ag−O−Ba thin film consists of fast and slow parts. The fast part occurs in 200 fs and is caused by non-equilibrium electrons entering the matrix. The slow part occurs in 1.6 ps and is caused by non-equilibrium electrons scattering within the lattice and interface between the Ag ultrafine particles and the matrix.

OPTICAL TRANSIENT RESPONSE OF METALLIC ULTRAFINE PARTICLES EMBEDDED IN SEMICONDUCTOR THIN FILM

The femtosecond laser pulses and pump-probe method have been used to measure the transient change of transmissivity of metallic ultrafine particles(UFPs) embedded in semiconductor thin film (Ag-BaO). The phenomena that the optical absorption of the films decreases and then restores within 2ps have been observed. The phenomena are due to the fact that electrons near the Fermi energy level in Ag UFPs are excited by femtosecond laser pulses and then the generated nonequilibrium electrons undergo a transient relaxation. The relaxation includes includes two parts: first, nonequilibrium electrons from Ag UFPs enter the matrix;then,nonequilibrium electrons are scattered by the lattice and inter-face between the Ag UFPs and the matrix. The different diameters of Ag UFPs affter the relaxation time of nonequilibrium electrons.

Synthesis of hybrid metal–semiconductor ultrafine particles. Photochemical deposition of silver on a ZnO colloid surface

Hybrid ZnO–Ag ultrafine particles have been synthesized via photochemical reduction of silver ions on ZnO colloids (ca. 3.8 nm mean diameter) in deaerated ethanol. The excess surface ions such as Zn2+ or OH–, which determine the charge and the structure of the double layer of ZnO particles, greatly affect the deposition behaviour of silver. When the excess ions were Zn2+, upon UV irradiation, Ag+ ions in solution were photoreduced on the ZnO surface with kinetics that accord with a mode where the acceleration of silver is proportional to the increase in the number of silver particles, resulting in the formation of very big hybrid particles (up to ca. 15 nm in diameter). When the excess ions were OH–, Ag+ ions were initially attracted to the negatively charged ZnO surface, then Ag2O was generated after UV irradiation. Further reaction results in the transformation of Ag2O into silver, leading to a damping of the exciton band of ZnO ultrafine particles, the silver being referred to as an electron trap. A combined investigation via UV–VIS and fluorescence spectrometry indicated that the interaction between the silver formed and the surface of ZnO occurred in both the above cases.

Structure and electrical properties of Ag-ultrafine-particle–polymer thin films

Toluylene 2,4-dicarbamidonitrite (TDCN) and Ag-ultrafine-particle–TDCN thin films were prepared by using an ionized-cluster-beam (ICB) deposition method. TDCN is a newly synthesized conjugated polymer with novel properties. These thin films were characterized by transmission electron microscopy (TEM). The TEM results indicate that the crystalline structure of the organic thin films can be controlled by the parameters of the ICB and the ultrathin crystalline TDCN film can be achieved by using the ICB deposition method. Results also demonstrated that amounts of Ag ultrafine particles embedded in the organic thin films may play an important role in the functional properties of the composite thin films. The electrical bistability of the Ag-ultrafine-particle–TDCN thin films was also achieved, and the possible conductive mechanism of the films was suggested qualitatively.

微粉砕‐複合体プロセスによる酸化物高温超電導体の微細構造制御

A synthetic process for the nano-composite of a Ba2YCu3O7-y superconductor and Ag was examined. Hybridization through grinding promoted the uniform dispersion of Ag ultrafine particles (10nm order of diameter) in the Ba2YCu3O7-y matrix. HIP sintering surpressed the undesirable grain growth of Ag on the order of 100-300nm in the sintered body. Enhancement for both the superconducting transport current property and magnetic flux pinning properties was promoted by the control of the post annealing condition of the HIP sintered body.

Preparation of Composite Ultrafine Particles Consisting of Different Kinds of Particles in a Gas

The preparation of composite ultrafine particles (UFP) consisting of two different kinds of particles in a gas environment is described. Two kinds of NaCl and Ag UFP, having different shapes and TEM image brightnesses, were used to distinguish each one during TEM observation. The electrostatic force was utilized to prepare the composite UFP from the two kinds of UFP. They were oppositely charged and subsequently passed through a mixing device with electrodes to promote the coalescence of the particles. The prepared composite UFP have been found to consist of two or three constituent particles which contain the two different kinds of particles. In addition, a unique feature at the interface formed between the constituent particles is discussed.

Response time of photoemission of ultrafine particle thin film

The response time of photoemissive materials is required for detecting ultrashort duration laser pulses. In this paper, the response time of photoemission in ultrafine particle thin film is studied, and the transit time spread (TTS) and response time of peak value (tM) are discussed. The photoelectron's response time will increase with increasing energy of photons. If the surface potential barrier of thin film declines, the photoemissive sensitivity or quantum yield will rise, however the response time will also increase, which means that response-time characteristic gets worse. As an example, the response time for Ag-O-Cs thin film is calculated for different cases when photoelectrons, excited in Ag ultrafine particles, travel through Cs2O semiconductor layer to the surface and escape into vacuum. The calculated response time is about 50 fs if this thin film is irradiated by infrared rays of wavelength 1.06 μm.

Studies on the Size Distribution of Ag Ultrafine Particles Prepared by Sputtering

Abstract In this paper, the sputtering processes of Ag ultrafine particles (Ag UFP) have been theoretically analyzed, and the random field equation satisfied by the size distribution function of Ag UFP has been established. Moreover, the general solution of the random field equation is applied to our sputtering conditions. We used this concrete solution to simulate the sputtering-experiment data of Ag UFP.

NEW PHOTOEMISSIVE THIN FILM FOR ULTRASHORT DURATION LASER PULSE DETECTION

A kind of photoemissive thin films which can be exposed to or stored in the atmosphere and can be used again in a vacuum system without any activation process for laser pulse detection is presented. They are different from usual photoemissive materials, since they do not contain alkali elements. They consist of metallic oxide thin film or other material thin film embedded with metallic ultrafine particles. A main interesting material is barium oxide thin film embedded with Ag ultrafine particles. The phenomenon that photoemissive sensitivity of this kind of ultrafine particle thin film rose up under the action of laser pulses was discovered.

Vaporazation and condensation of metals in a flowing gas with high velocity

Ultrafine Ag particles were prepared by evaporation and condensation in a forced flowing He gas with a high velocity up to 30m/s. From electron microscopic observation, followed by statistical analysis of particle size distributions for specimens collected at various positions in the gas stream, the condensation process occurred in two regions having different morphology; film formation region and particle growth region. The particle growth region is divided into three subregions having different mechanisms of particle growth: absorption growth, coalescence growth, and intermediate or combined growth. By applying a low-temperature plasma generated by microwave, A1N films and particles having wurtzite-type structure were formed. This technique is widely applicable to produce pure compound films and particles.