The study compared the influences of silicon materials from different sources on the crystal growth process and geometry of silicon carbide (SiC). As revealed by the results of the study, although the purity of commercial silicon material was as high as 11N, the rate of crystal growth was slow. However, if the silicon material made by electron beam refining metallurgical silicon was utilized for the SiC crystal growth experiment, the morphology of SiC crystal was better and the rate of crystal growth was faster despite its purity being only about 4.5N.

A void free 3C-SiC film grown on Si(100) can be achieved by low pressure chemical vapor deposition using the modified four-step method. The diffusion step plays an important role to enhance the quality of the 3C-SiC buffer layer on Si(100). X-ray photoelectron spectroscopy was used to characterize the bonding characteristics of the 3C-SiC buffer layer of about 10 nm thick. The Si-C bonds are partially formed on the as-carburized Si(100) before the diffusion step. The ratio of C-C to Si-C bonds on the as-carburized Si(100) is about 7:3, which can be lowered to about 1:9 after the diffusion step at 1350 oC for 5 min or at 1300 oC for 7 min. According to XPS data and Fick’s second law, the diffusivity of Si across the 3C-SiC interlayer are determined to be 2.2×10-16 cm2/s and 3.13×10-16 cm2/s at 1300°C and 1350°C, respectively. The derived activation energy is 1.6 eV for the diffusion of Si atoms in the 3C-SiC buffer layer.

In situ chemical polymerization is used to prepare composites of multiwalled carbon nanotubes (MWCNTs) that are either wrapped with polyaniline (PANI) (MWP), or with perpendicular aligned PANI ( MAP). Systematic study of morphology, composition, structure, thermal stability, and electrical properties is performed as a function of temperature to understand the composite formation. Orientation of PANI chains and the direction of electron transport in MWCNTs and PANI play an important role in conductivity. At room temperature (RT), MWP, wherein PANI and MWCNTs are aligned parallel, exhibits high conductivity, which decreases gradually above RT. Contrary in MAP, the conductivity at RT is lower because of the perpendicular alignment of PANI on the MWCNTs. However, it increases with the increase in temperature, as short chains of PANI switchover and get adsorbed onto the MWCNTs forming a near parallel orientation, in which, aromatic amines of PANI graft to the MWCNTs. Eventually, morphology becomes a dominating factor which influences the conductivity and thermoelectric properties of the composites, above 150 degrees C. The results show that the morphology, interfacial contact, and the dopant concentration are the key factors in governing the conductivity of MWP and MAP composites at RT and above. These observations are supported by X-ray diffraction, X-ray photoelectron spectroscopy, and time of flight-secondary ionization mass spectrometry study.

Surface modification of quantum dots (QDs) for improved photo and physicochemical properties is a topic of potential technological interest. Herein, we report on the synthesis of aggregation free 11-mercaptoundecanoic acid and tetraaniline (TA) capped CdS QDs with narrow size distribution (∼2.3nm diameter), which are further characterized using UV–visible spectroscopy, photoluminescence spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The TA capped CdS QDs show improved photoluminescence and photostability, which is attributed to the effective grafting of TA on CdS QDs through N-atoms, changing the surface chemical environment and facilitating charge transfer.

A modified four-step method has been developed to grow a void-free 3C-SiC film of high quality on Si(100) in a mixed gas of SiH4-C3H8-H-2 using low pressure chemical vapor deposition. A diffusion step was added after the carburization step in the traditional three-step method (clean, carburization, growth), and no cooling between each step was required. X-ray photoemission C 1s spectra support that the formation of SiC bonds can be greatly improved in the ascarburized Si(100) surface after diffusion at 1350 degrees C for 300 g. A thick 3C-SiC film of good crystal quality was grown on the as-diffused SiC layer during the growth step, confirmed by both X-ray diffraction and electron diffraction data. Hall effect measurements were used to characterize the electrical properties of SiC films. All the SiC films are n-type. The Hall mobility and carrier concentration of a SiC film of 1.5 mu m thick increase from 320 to 395 cm(2)/(V s) and from 1.6 x 10(17) cm(-3) to 2.7 x 10(17) cm(-2), respectively, when the diffusion step is added.

The octadecyl-trimethoxysiloxane self-assembled monolayers (SAMs) exhibit better uniformity and smoothness on hydrogenated amorphous carbon (a-C:H) films than on indium tin oxide glasses. The liquid crystal alignment on the SAM/a-C:H can be greatly improved by Ar plasma beam scanning. The pretilt angle increases abruptly with Ar plasma beam scanning time within 5 s and reaches a maximum value of about 5 degrees at a longer scanning time. The surface roughness of SAM slightly increases from 0.10 to 0.13 nm after Ar plasma beam scanning. This implies that bond breaking occurs on the SAM surface during the plasma beam scanning. Fourier transform infrared spectrometer and X-ray photoemission spectroscope data indicate that plasma beam scanning can sputter off the CH2 bonds in the alkyl chain of SAM. The amount of oxygen on the SAM surface increases after plasma beam scanning and the increase of oxygen is attributed to the formation of C-O bonds during air exposure after plasma beam scanning. (C) The Electrochemical Society.

The surface of highly ordered pyrolytic graphite (HOPG) was modified by Ar plasma beam scanning at a controllable angle of incidence. The characteristics of plasma modified HOPG were investigated by atomic force microscope (AFM), micro-Raman, X-ray photoemission spectroscopy (XPS), and grazing incident angle of X-ray diffraction (GIAXRD). A smooth surface of HOPG can be obtained by adjusting the incident angles of Ar plasma beam scanning. The surfaces of HOPG become smoother with increasing angle of incidence after Ar plasma beam scanning. Raman spectra indicate that the plasma beam scanning breaks the hexagonal structures of sp2 C=C bonds near the surface of HOPG. The broken hexagonal network structures can form C–O bonds that increase the amount of oxygen on the surface of HOPG, supported by C1s and O1s XPS spectra. GIAXRD data support that the co-existence of both crystalline structures of 2H and 3R in HOPG. The carbon bond breaking in 2H and 3R is different and depends on the angle of incidence. Most broken carbon bonds form damaged aromatic rings near the surface of HOPG.

A model organic light-emitting diodes (OLEDs) with structure of tris(8-hydroxyquinoline) aluminum (Alq3)/N,N′-diphenyl-N,N′-bis[1-naphthy-(1,1′-diphenyl)]-4,4′-diamine (NPB)/indium tin oxide (ITO)-coated glass was fabricated for diffusion study by ToF-SIMS. The results demonstrate that ToF-SIMS is capable of delineating the structure of multi-organic layers in OLEDs and providing specific molecular information to aid deciphering the diffusion phenomena. Upon heat treatment, the solidity or hardness of the device was reduced. Complicated chemical reaction might occur at the NPB/ITO interface and results in the formation of a buffer layer, which terminates the upper diffusion of ions from underlying ITO.

A single hair sample preparation protocol modified from reported method was developed and used to prepare longitudinally sectioned hair for ToF-SIMS analysis. Preliminary results demonstrate that ToF-SIMS is capable of providing molecular distribution of fragment ions from intrinsic constituents as well as external chemicals like the hair dye ingredients used in this study. The observation of pPDA and H2PO4− penetrating into the internal region of hair might initiate a renewed interest in exposure study.

The atomic distribution in the monolayer of two different Mn-doped CdS quantum dots (QDs) was studied first time with ToF-SIMS. The model Cd:Mn QDs were immobilized on Au substrate by use of a self-assembled monolayer via 1,10-decanedithiol. Morphological analysis by SPM and TEM indicates larger particle size of in situ synthesizing CdS:Mn. ToF-SIMS depth profile and 3D-images reveal that Mn atoms reside on the surface of in situ synthesizing CdS:Mn and are uniformly embedded in capped CdS:Mn. The results obtained by SPM, TEM, and ToF-SIMS are comparable, indicating that ToF-SIMS might find potential applications in surface and interface study of semiconductor nanocrystals.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used for an in situ thermal decomposition study of Zn(CH3COO)(2).2H(2)O forming ZnO nanoparticles. TOF-SIMS spectra were recorded at regular temperature intervals of 25degreesC in positive and negative detection modes in a dynamic thermal process. Controlled heating (5degreesC min(-1)) of Zn(CH3COO)(2)(.)2H(2)O was also carried out using thermogravimetric analysis (TGA) in an oxygen atmosphere (20 ml min(-1)). Nearly spherical ZnO nanoparticles with no agglomeration and a narrow size distribution (diameter similar to50 nm) were observed, which were characterized using scanning electron microscopy, transmission electron microscopy and x-ray diffraction. In situ thermo-TOF-SIMS was used to monitor the Zn-64(+) and Zn-66(+) ion abundances as a function of temperature, which showed a similar profile to that observed for weight loss in TGA during decomposition. Based on the experimental results, a possible decomposition mechanism for the formation of ZnO is proposed. Copyright (C) 2004 John Wiley Sons, Ltd.

The Ni–P-based coatings, including binary Ni–P, ternary Ni–P–Cr and Ni–P–W, were fabricated by the RF magnetron sputtering technique with dual target of electroless Ni–P alloy and a third metal element. To evaluate the influence of the doping element in Ni–P deposit, differential scanning calorimeter (DSC) analysis was employed to characterize the temperature of phase transformation. The phase transition during thermal evolution under heat-treatment was analyzed by X-ray diffractometry (XRD). Crystallization behavior in binary and ternary Ni–P-based coatings was quite distinct due to the addition of Cr and W. Microhardness tests indicated that the sputtered Ni–P–Cr and Ni–P–W coatings exhibited superior hardness and excellent thermal stability than the Ni–P coating. In addition, chromium exhibited compatible thermal characteristics with the tungsten for the ternary Ni–P-based system. The strengthening mechanism in the sputtered Ni–P–Cr and Ni–P–W deposits is also discussed.

Binary Ni–P and ternary Ni–P–Cr alloy coatings were fabricated by the RF magnetron sputtering technique with dual targets of electroless nickel alloy and a third element metal. The compositions of the as-deposited alloy were measured by electron probe microanalysis. The phase identification was carried out by X-ray diffraction technique. The as-deposited Ni–P and Ni–P–Cr coating exhibited amorphous structure. The thermal property of coating was investigated by the annealing test for 4 h and by the cycling test for 30 min in N2 atmosphere at 400 and 450 °C. The related mechanical properties were evaluated by Knoop microhardness test, and measured microhardness was employed to evaluate the thermal stability of the binary and ternary alloy. The microhardnesses were 1250 and 1380 HK for both the Ni–P alloys at 400 °C and ternary Ni–P–Cr at 450 °C, respectively, after 4-h annealing. For cycling test over 8 times cycles at 400 °C, the microhardness of Ni–P–Cr deposit was 1200 HK, in which full phase of Ni3P precipitation was not completed. The influence of adding element Cr on the thermal properties of Ni–P-based alloy coating was also discussed.

ToF-SIMS with Ga+ ion as primary source is used to analyze plasticizers like bis(2-ethylhexyl) phthalate (DEHP) from the inner surface of the blood bags and their migration into the blood. Food packing materials were also analyzed for the presence of DEHP. The simplicity of using ToF-SIMS with high mass resolution as an aid in the identification and analysis are discussed. The ToF-SIMS results, the fragmentation pattern, and the ratio of ions were comparable to those obtained from traditional GC–MS analysis. This indicates that ToF-SIMS could be a promising technique for direct detection of DEHP (and phthalates in general) in blood bags and food packaging polymeric materials.

A polyaniline (PANT) film was successfully prepared on multiwall carbon nanotubes (CNTs) by modifying the CNTs with aromatic amine group (CNTs-(NC6H6)(n)) followed by aniline polymerization. TOF-SIMS was used to monitor C6H6N-, C2H3Cl-, C8H- and C-10(-) to reveal the interfacial change at PANT film/CNTs-(NC6H6)(n). The functionalized group of CNTs modified with aniline was determined to be C6H6N-, which showed positive effect on polymerization of aniline as shown by the TOF-SIMS ion image. (C) 2004 Elsevier B.V. All rights reserved.