Lattice location and stability of ion implanted Cu in Si

We report on the lattice location of ion implanted Cu in Si using the emission channeling technique. The angular distribution of beta(-) particles emitted by the radioactive isotope 67Cu was monitored following room temperature implantation into Si single crystals and annealing up to 600 degrees C. The majority of Cu was found close to substitutional sites, however, with a significant displacement, most likely 0.50(8) A along the <111> directions towards the bond center position. The activation energy for the dissociation of near-substitutional Cu is estimated to be 1.8-2.2 eV.     

Recent Emission Channeling Studies in Wide Band Gap Semiconductors

We present results of recent emission channeling experiments on the lattice location of implanted Fe and rare earths in wurtzite GaN and ZnO. In both cases the majority of implanted atoms are found on substitutional cation sites. The root mean square displacements from the ideal substitutional Ga and Zn sites are given and the stability of the Fe and rare earth lattice location against thermal annealing is discussed.     

Lift‐off protocols for thin films for use in EXAFS experiments

Lift‐off protocols for thin films for improved extended X‐ray absorption fine structure (EXAFS) measurements are presented. Using wet chemical etching of the substrate or the interlayer between the thin film and the substrate, stand‐alone high‐quality micrometer‐thin films are obtained. Protocols for the single‐crystalline semiconductors GeSi, InGaAs, InGaP, InP and GaAs, the amorphous semiconductors GaAs, GeSi and InP and the dielectric materials SiO₂ and Si₃N₄ are presented. The removal of the substrate and the ability to stack the thin films yield benefits for EXAFS experiments in transmission as well as in fluorescence mode. Several cases are presented where this improved sample preparation procedure results in higher‐quality EXAFS data compared with conventional sample preparation methods. This lift‐off procedure can also be advantageous for other experimental techniques (e.g. small‐angle X‐ray scattering) that benefit from removing undesired contributions from the substrate.     

Controlling the Length of Cooperative Supramolecular Polymers with Chain Cappers

The design and the characterization of supramolecular additives to control the chain length of benzene-1,3,5-tricarboxamide (BTA) cooperative supramolecular polymers under thermodynamic equilibrium is unraveled. These additives act as chain cappers of supramolecular polymers and feature one face as reactive as the BTA discotic to interact strongly with the polymer end, whereas the other face is nonreactive and therefore impedes further polymerization. Such a design requires fine tuning of the conformational preorganization of the amides and the steric hindrance of the motif. The chain cappers studied are monotopic derivatives of BTA, modified by partial N-methylation of the amides or by positioning of a bulky cyclotriveratrylene cage on one face of the BTA unit. This study not only clarifies the interplay between structural variations and supramolecular interactions, but it also highlights the necessity to combine orthogonal characterization methods, spectroscopy and light scattering, to elucidate the structures and compositions of supramolecular systems.     

The effect of dendritic pendants on the folding of amphiphilic copolymers via supramolecular interactions

The supramolecular folding of amphiphilic heterograft copolymers equipped with dendritic pendants is investigated using a combination of proton nuclear magnetic resonance (¹H NMR) spectroscopy, small‐angle X‐ray scattering, and circular dichroism spectroscopy. Hereto, the linear poly(ethylene glycol) pendants normally used to convey water compatibility are partially substituted with branched analogues. For one set of copolymers, second‐generation polyglycerol dendrons are directly attached to the polymer backbone, while for the other a hydrophilic linker is placed in between. The results show that the branching of the hydrophilic pendants affects the local structure of the folded copolymer but does not influence the overall conformation and single‐chain character of the folded copolymers in solution. All copolymers fold into 4–5 nm single‐chain polymeric nanoparticles with a very compact spherical morphology, independent of the dendritic content of the copolymer. Intriguingly, the incorporation of the dendritic pendants affects the formation of a structured interior even at low incorporation ratios. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 411–421     

Low temperature ion beam mixing of Co/Si systems

Co/Si systems were ion beam mixed at 77 K using a 100 keV Ar beam. The formation of different phases as a function of irradiation dose has been studied, using Mössbauer spectroscopy (MS) and Rutherford backscattering spectroscopy (RBS). It was found that Co₂Si, CoSi and CoSi₂ are formed subsequently in parallel layers. After high dose irradiation, a phase with stoichiometry Co∶Si equal to 1∶3 was observed, suggesting CoSi₃ has been formed. However, MS gave clear evidence that this phase consists of precipitates of CoSi₂ and Si. Finally, we found that the amount of mixing scales linearly with the square root of the fluence, with a mixing rate of 1.0×10⁴Å⁴.     

Formation and microstructure of cubic metastable iron silicides synthesized during pulsed laser annealing

Hyperfine Interactions - The phase formation and crystallization processes of metastable [CsCl]Fe1?x Si phases were investigated by irradiating?-FeSi/Si(111) thin films with a pulsed...     

Mutual quenching of Er photoluminescence under two laser excitation in GaN:Er

Erbium photoluminescence in GaN:Er was studied with above-band-gap excitation, provided by a He–Cd laser and below-band-gap excitation by a tunable Ti–Sa laser. The spectra obtained with these two lasers exhibit different spectral shapes. When both lasers are used at the same time, we observe that the Er³⁺ photoluminescence induced by each of the lasers is partly quenched by the illumination of the other laser. In this experiment, one of the lasers is modulated and a lock-in amplifier is used to filter the corresponding photoluminescence signal. The spectra recorded this way are found to be linear combinations of spectra obtained with each of the lasers used separately. This effect is explained by the presence of defects mediating the excitation towards the Er³⁺ ions. These defects act as electron traps, which can be populated by one specific laser excitation and are photo-ionized by the other laser leading to a large quenching of Er³⁺ emission.     

Compound Phase Formation in Thin Film Structures

Thin film compound formation during solid phase reaction, reactive deposition, ion-beam synthesis, and ion beam mixing is discussed in terms of the Effective Heat of Formation (EHF) model. This model defines an effective heat of formation ΔH′, which is concentration dependent. By choosing the effective concentration of the interacting species at the growth interface during solid phase reaction, to be that of the liquidus minimum, the model correctly predicts first phase formation during formation of silicides, germanides, aluminides, and other metal-metal binary systems. The ability to predict phase formation sequence and phase decomposition is also illustrated. The EHF model is also used to describe amorphous and metastable phase formation as well as the effect of impurities and diffusion barriers on phase formation. In the case of reactive deposition, the effective concentration is controlled by the rate at which thin film deposition is carried out and the temperature of the substrate. In this way epitaxial phases such as CoSi₂ and NiSi₂ can be formed directly at temperatures much lower than normally needed during solid phase reaction. During ion-beam synthesis silicon-rich compounds are expected to form during metal implantation into silicon- and metal-rich compounds for silicon implantation into a metal substrate. For ion-beam mixing, the effective concentration is not controlled by the mixing process at low temperatures, but by the liquidus minimum of the system at higher temperatures. For both ion-beam mixing and ion-beam synthesis, however, much work still needs to be done to correlate effective concentration with the various experimental parameters. The general trends of compound formation in these systems do, however, also correlate well with the predictions of the EHF model.