Juzheng Liu

Surface-bound nanoparticles for initiating metal deposition

An alternative activation method was developed via binding electroless catalysts onto silicon substrates with 3-aminopropyltriethoxysilane (APTS) self-assembled monolayers (SAMs). Atomic force microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy were used to characterize the laden of tin-free Pd(II)-based nanoparticles on silicon surfaces. The results indicate that the formation of coordination bonds between Pd ions and nitrogen atoms of APTS SAMs serves the important binding mechanism. Electroless copper deposition was successfully initiated by the catalyzed substrates and high quality Cu deposition was obtained. Owing to the chemically bound catalyst, this approach has advantages over the conventional Sn–Pd combined activation process, including reduced steps and improved longevity of initiator and enhanced adhesion of the deposition to the substrates. 2003 Elsevier Science B.V. All rights reserved.

Stability of hydrophilic magnetic nanoparticles under biologically relevant conditions.

Hydrophilic 2,3-dimercaptosuccinnic acid (HOOC-CH(SH)-CH(SH)-COOH, DMSA) coated monodisperse magnetic nanoparticles (Fe3O4) were dispersed in water, RPMI-1640 with 10% (v/v) fetal calf serum, RPMI-1640, PBS and MES, respectively, to investigate their stability under biologically relevant conditions. The Photon Correlation Spectroscopy (PCS) results showed that DMSA-Fe3O4 nanoparticles existed as aggregate under biological conditions. UV-vis, MRI and AFM results indicated that DMSA-Fe3O4 nanoparticles dispersed in RPMI-1640, PBS and MES presented poor stability, whereas those dispersed in RPMI-1640 with fetal calf serum exhibited excellent stability, which was due to their adsorption from fetal calf serum, as confirmed by zeta potential and IR results. Additionally, in vitro cell experiments showed that DMSA-Fe3O4 nanoparticles with adsorption from fetal calf serum had higher intracellular uptake than those without adsorption from serum, indicating that fetal calf serum could play a great role in intracellular uptake of nanoparticles.

Pendant thiol groups-attached Pd(II) for initiating metal deposition

A new activation method has been developed for initiating electroless metal deposition on silicon substrates without SnCl2 sensitization and roughening condition. Silicon wafers are first coated with thiol-terminated self-assembled monolayers (SAMs), and then catalyzed with a stable tin-free Pd(II)-based colloidal solution. Atomic force microscopy (AFM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to characterize the step-by-step surfaces and study the binding mechanism of Pd(II) with SAMs onto surfaces. Results show that Pd(II) oligomer particles are chemisorbed on pendant thiol surfaces through S‐Pd bonds. This process involves fewer steps than the conventional Sn/Pd combined activation one. Furthermore, the chemical bound initiator possesses longevity and can be stored for a long time before metallization. # 2003 Elsevier Science B.V. All rights reserved.

Synthesis of double-conjugated-segment molecules and their application as ultra-broad two-photon-absorption optical limiters

A series of novel double-conjugated-segment molecules, in which two conjugated segments are separated by an ether chain, were synthesized; these compounds provide a very broad two-photon absorption spectral range, which satisfies an urgent need in the optical limiting area.

Hyper-Rayleigh scattering of CdS nanoparticles capped with hexametaphosphate

Abstract Hyper-Rayleigh scattering (HRS) technique, an incoherent methodology, was used to measure the first-order hyperpolarizability (β) of CdS nanoparticles capped with hexametaphosphate (HMP). The results show that the “per particle” β value is 1.33x10−26 esu. Two possible contributions to the large β value, bulklike contribution and the one from particle aggregates, are negligible. Contribution from nanoparticle surface emerges as the main HRS mechanism due to the large surface-to-volume ratio and the high density of surface defects.

Synthesis of nano-sized magnetic colloidal particles from ferrous salts and hydroxylated poly(butyl methacrylate-b-glycidyl methacrylate)

Poly(butyl methacrylate-b-glycidyl methacrylate) is used to prepare magnetic nanoparticles from ferrous salts. The structural identification of synthesized colloidal particles and bulk magnetite is performed via X-ray diffraction. Magnetic hysteresis studies show that the obtained microspheres are specified as soft magnetic materials. Microspheres have a ferrite core and a polymer shell. The size and size dispersion of the microspheres decrease with the total concentration of ferrous salts.

Three-Photon Absorption in a Charge Transfer Compound Pumped with Picosecond and Nanosecond Lasers

A new intramolecular charge transfer compound with an absorption band in the short wavelength range has been synthesized. The measured three-photon absorption coefficient and the corresponding molecular cross-section when pumped by a nanosecond beam are γ=2.2×10-17 cm3/W2 and σ3=6.4×10-74 cm6/s2, respectively. When pumped by a picosecond laser beam, the three-photon absorption cross section is one order of magnitude lower. Three-photon-absorption-induced frequency-upconverted fluorescence emission has been observed by pumping with 8 ns 1.06 µm laser pulses. The emission intensity dependence of the incident intensity obeys the cubic law.

Hyper-Rayleigh scattering of CdS nanoparticles stabilized by inorganic heteropolyanions

Abstract The composite nanoparticles CdS/PW 12 O 40 3− were easily synthesized by arrested precipitation with inorganic heteropolyanion PW 12 O 40 3− as the stabilizer. The obtained nanoparticles were very stable, both in solution and in solid state. The second-order optical non-linearity of the nanoparticles in solution were studied by Hyper-Rayleigh Scattering (HRS) technique. The first-order hyperpolarizability β “per particle” was found to be 2.15×10 −26 esu, which was in the largest values reported for solution species.

Influence of surface-capping molecule exchange on the hyper-Rayleigh scattering of CdS nanoparticles

Hyper-Rayleigh scattering (HRS) or incoherent second harmonic generation (SHG) technique has been used to investigate the second-order optical nonlinearities of nanoparticles and seems sensitive to nanoparticle surfaces. Here, more direct evidence that shows the importance of surfaces for HRS response of nanoparticles was experimentally obtained. Two CdS nanoparticles of 3 nm average diameter with different surface-capping molecules, CdS/AOT-SO3− (AOT-SO3− is anion of bis (2-ethylhexyl) sulfosuccinate, disodium salt) and CdS/Py/AOT-SO3− (Py represents pyridine molecule), were studied by HRS technique. The “per particle” first-order hyperpolarizability β values were evaluated to be 3.98×10−27 esu for the CdS/AOT-SO3− and 2.63×10−27 esu for the CdS/Py/AOT-SO3− nanoparticles. A reduction in β value is found when AOT-SO3− on CdS nanoparticle surface is replaced by pyridine. Similarly, the reduction of HRS signal intensity of a solution containing the CdS/AOT-SO3− nanoparticles was observed when increasing pyridine concentration in the solution. Furthermore, the dynamic process of the surface-capping molecule exchange was studied by detecting both HRS signal intensity and electroconductivity variations with time. Possible effect mechanism is discussed in terms of a two-level model approximation derived from molecular chromophores, when considering the influence of different surface-capping molecules on the polarity of Cd---S bonds at nanoparticle surfaces.

Synthesis and Characterization of CdS Nanoparticles with Strong Electrolyte Behavior

The CdS nanoparticles whose structure is similar to a strong electrolyte were synthesized by the colloidal chemical method. The CdS nanoparticles with Cd2+-rich surface are capped by the electrically neutral ligand of 2,2′-bipyridine (bpy), and the counterion, BPh4-, is adsorbed around the particle as balance charge. The ω donation from 2,2′-bipyridine at 2-position to the Cd2+-rich surface of the CdS nanoparticles was characterized by X-ray photoelectron spectroscopy (XPS). These CdS nanoparticles can redisperse in pyridine (py) or DMF, and have high stability. The determination of electroconductivity and the electrophoresis deposition in dilute solution containing the CdS nanoparticles further prove the rationality of the above electrolyte structure of the CdS nanoparticles.