Multi-technique Investigation Research Articles

A Multi-Technique Investigation of the Pulsed Plasma and Plasma Polymers of Acrylic Acid: Millisecond Pulse Regime

Acrylic acid plasma polymers have been fabricated from pulsed 13.56 MHz RF plasmas in a “capacitively” coupled plasma deposition chamber. Plasma “on” and “off” (ton/off) times in the millisecond (ms) pulse time regime have been investigated using a peak plasma power of 50 W. Employing a fixed ton (5 ms), the effect of toff (2−1000 ms) on the solid-phase plasma polymer has been investigated using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF SIMS). For the first time, mass spectrometry has been employed to monitor the neutral and charged species in pulsed plasma (gas-phase) as a function of toff. These measurements are supported by quartz crystal mass balance (QCMB) deposition rate measurements. Throughout the study, comparison with continuous (CW) wave plasmas of equivalent “average” power has been made.XPS analyses revealed that with increased toff (i.e., lower “average” power) the extent of carboxyl retention increased from <33% at a toff of 5 ms to ca. 6...

The Mesoproterozoic Supercontinent Atlantica in the Brazilian Shield - Review of Geological and U-Pb Zircon and Sm-Nd Isotopic Evidence

Supercontinent Atlantica was formed in South America by the orogenies of the Trans-Amazonian Cycle, namely the accretionary Encantadas Orogeny (2250-2100 Ma) and the collisional Camboriú Orogeny (2100-2000 Ma). Large belts 500 to more than1000 km long formed during the Trans-Amazonian Cycle in the three major cratons of South America, in the northern part of the Amazon Craton, in the São Francisco Craton and in the Rio de la Plata Craton. However, other large (1000 km) segments of Archean crust remained little deformed in the cratonic interior of Supercontinent Atlantica, such as a major portion of the Tocantins Province in central Brazil. In addition, smaller fragments, up to 100 km, of Trans-Amazonian Cycle continental crust are present inside the Neoproterozoic Brasiliano Cycle orogenic belts in the eastern half of extra-Andean South America. In contrast, the dominant volume, about 90%, of Neoproterozoic belts was formed by reworking of Archean and Paleoproterozoic crust. Zircon U-Pb geochronology, associated with Nd isotopes, indicates the widespread presence of Supercontinent Atlantica crust in South America and sensitive high-mass resolution ion microprobe investigation of zircons indicates that crust in southern Brazil was formed mostly in the Trans-Amazonian Cycle. Zircon geochronology also reveals that Supercontinent Atlantica was preceded by an intra-cratonic period lasting about 300 my and was succeeded by an intra-cratonic period of about 1000 to 1300 my. Many of the Trans-Amazonian Cycle belts and crustal fragments may have been accreted to South America during the Neoproterozoic. The demonstration that they all were once part of Supercontinent Atlantica must await further multi-technique investigations.

A chemical and morphological study of fullerene derivatives Langmuir–Blodgett films

We present here a multi-technique investigation of C 60-based Langmuir–Blodgett films. C 60–(CH 2) 2–N–(CH 2–CH 2–O) 3–CH 3 films were investigated with atomic force microscopy (AFM), static secondary ion mass spectroscopy (SSIMS) and X-ray photoelectron spectroscopy (XPS) measurements. The aim was to test the ability of this fullerene-derivative to form a stable monolayer to be transferred to a solid substrate. In fact, AFM measurements revealed a clustering of molecules when a single dipping was done. The C 60-derivative could be detected by SSIMS as a whole and as separated fragments of C 60 and hydrophilic heads and, finally, XPS enabled to measure the film thickness and to chemically characterize the film surface.

Oxidation States of Copper Ions in ZSM-5 Zeolites. A Multitechnique Investigation.

The redox behavior of Cu/ZSM-5 zeolites prepared by ion exchange from Cu2+ aqueous solutions has been followed by a variety of spectroscopic techniques to provide a thorough picture of the so-called "self-reduction" of cupric ions, which occurs upon dehydration of the hydrated system at various temperatures, and of the reverse process of reoxidation as well. Conflicting hypotheses on both these processes are, in fact, present in the literature. The experimental techniques employed in this work are electron paramagnetic resonance (EPR), IR, and optical spectroscopies, extended X-ray absorption fine structure, and X-ray absorption near-edge structure. The early stages of dehydration (from room temperature to about 470 K) involve cupric ion migration and formation of EPR silent moieties but no reduction to Cu+. The onset of this latter phenomenon starts at 470 K and, in the range 470-670 K, involves the majority of copper ions present in the system. Rehydration of Cu+-containing samples does not cause direct Cu+ oxidation to Cu2+ but favor this latter process when O2 is used as oxidant. Oxidation of Cu+ to Cu2+ by molecular oxygen, in fact, does not take place at room temperature if O2 is contacted with the dehydrated material but easily occurs when oxygen is adsorbed on rehydrated samples at the same temperature.

Carbon-based nanostructured materials via cluster beam deposition: a multi-technique investigation

The use of clusters as elemental building blocks can open new routes towards the creation of a new class of architectures and nanostructures. We report the synthesis of nanocrystalline carbon thin films produced by depositing supersonic clusters. An optimized version of a pulsed arc cluster ion source (PACIS) was utilized for the production of intense and stable ionized and neutral cluster supersonic beams. Laser photoionization and mass spectrometric techniques have been used to characterize the source, the cluster mass distribution and energy. A set of techniques was then applied to evaluate the structural and electronic properties of the thus-grown nanocrystalline carbon films encompassing Raman and C 1s X-ray photoemission spectroscopies (XPS).

Structural and noise characterization of VO2 films on SiO2/Si substrates

Multi-technique structural and electrophysical investigations of VO2 films on SiO2/Si substrates are carried out to study the microscopic nature of fluctuator defects — sources of lowfrequency flicker noise. It is established that the noise intensity is determined by the magnitude of the microstress fluctuations 〈e 〉={〈(δc/c)2〉}, where c is the lattice parameter along the c-axis parallel to [011] direction in the blocks of which the film is formed. The dimensions of the blocks were determined in the direction of the c-axis (tc∼1000 A). The suggestion is put forward that the samples contain two types of fluctuator defects: 1) V atoms jumping between the two nearest interstitial sites and 2) V atoms jumping between these interstitial sites near lattice defects.

A multitechnique investigation of sodium-doped poly( p-phenylene vinylene)

Dopant uptake in sodium-doped poly( p-phenylene vinylene) (PPV) has been measured, and e.s.r. spectroscopy has been used to follow the changes in unpaired spin concentration as the doping reaction proceeds. 2H n.m.r. line shapes of sodium-doped, ring-deuterated PPV (PPV-d 4) have also been studied to observe the effects of doping. They contain two distinct components, one of which is attributed to hydride formation. The overall pattern is insensitive to temperature changes.

Investigation of Rubber/Metal Bond Failures by Surface-Analysis Techniques

Abstract Surface-analysis techniques including ISS, SIMS, XPS, and SEM are highly complementary and are essential for detailed investigations of rubber/metal bond failures. Multitechnique investigations offer the most effective means of solving problems in bonding applications. EDS, a near-surface analysis technique usually associated with SEM, is a versatile supporting technique for comprehensive studies. Contamination of materials used in bonding applications, especially by silicones, is a commonly encountered factor in bond failures. However, the extent and role of the contamination is often difficult to assess. Prepared test coupons exposed to silicone spray mist considered significant in this study exhibit isolated regions of silicone contamination that did not severely influence peel-test failure modes or maximum peel-load values. The techniques used in this study can be used independently or together to identify surface-treatment effects, determine failure locus, verify the presence of conversion coatings, primers, and adhesives, and identify contaminants in rubber/metal bonding studies. Failure characteristics of bonded assemblies vary and are often complex. Failure investigations of a high-performance mount that exhibits regions of apparent interfacial failure show silicone contamination is present in the failure regions. Intact regions of the same mount failed by fracturing in liquid nitrogen do not contain silicone and show a different failure locus. This suggests that only limited areas of the part were initially contaminated to the extent that bonding was affected; or the regions disbonded in service were exposed to silicone contamination after the failure was initiated.

Oxidation of clean and Pt covered Ni(111)

In this paper a multi-technique investigation into the high temperature oxidation, up to 400°C, of Ni(111), both clean and Pt-covered, is reported. The oxidation has been monitored in situ with ellipsometry, calibrated for absolute oxygen coverages with Nuclear Reaction Analysis. Depth profiles are obtained using Auger Electron Spectroscopy. Above 250°C, oxygen diffusion into the Ni bulk is observed. After Pt deposition, oxidation at 250°C results in a NiO layer on top of the Pt layer, while no oxygen can pass through the Pt layer into the bulk of the Ni.

Instrument combining x-ray photoelectron spectroscopy and secondary ion mass spectrometry for surface studies

X-ray Photoelectron Spectroscopy (XPS) or (ESCA) and Secondary Ion Mass Spectrometry (SIMS) have been combined in the same ultrahigh vacuum system to facilitate a new approach to studying clean and reacted surfaces. The design philosophy is to connect two satellite vacuum systems via a set of magnetically driven sample transfer devices. The advantages and capabilities of this approach are discussed with respect to its flexibility and its ability to couple to other surface techniques. XPS and static SIMS spectra of an oxidized polycrystalline indium film are presented to exemplify the type of information which can be gleaned from a multitechnique investigation of surfaces. The additional ability to prepare sample surfaces in our system by ion implantation is demonstrated by a positive-ion SIMS analysis of a gold-implanted aluminum foil.