DYNAMIC DISORDER AT INTERMEDIATE TEMPERATURE AND ITS EFFECT ON THE MAGNETIC PROPERTIES OF THE ORGANIC SUPERCONDUCTOR κ-(BEDTTTF)2Cu[N(CN)2]Br

The k-(BEDT-TTF)X superconducting salts, [where BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene, abbreviated as ET, and X is a monovalent anion like Cu[N(CN) ]Br 2 , and for either Cu[N(CN) ]Cl 2 or ( )2 Cu NCN and so on], exhibit interestinmagnetic and superconducting phase transitions [1]. They are quasi-two-dimensional and the interplane coupling is very weak. The basic structural unit is a dimer consisting of two BEDTTTF molecules stacked on top of one another. This layered structure leads to highly anisotropic electronic properties. These organic superconductors have similar characteristic superconducting properties including the intrinsic Josephson Effect and the mixed-state properties. This similarity suggests the existence of the vortex phase transition in the organic layered superconductors as observed in HTSC. Because the temperature scale is much lower in organic materials, the thermal fluctuation is expected to be small compared to HTSC. Thus, the comparison between the high-Tc and organic superconductors can give important clues as to the nature of vortex phase transitions. Besides these anomalies around 50 K, unusual time dependencies in magnetic and transport properties have been reported for both deuterated and hydrogenated k-Br near 80 K. For - H - Br 8 k , the superconducting properties have been found to depend on the thermal history, in particular on how fast the sample had been cooled through 80 K. As mentioned above, the ground state of - D - Br 8 k is strongly sample-dependent: both superconducting as well as non-superconducting crystals are found. Furthermore, superconducting as well as insulating (possibly antiferromagnetic) phases in separated volume parts of the same sample have been reported. Their relative volume fraction was found to depend on the cooling rate Vc employed at around 80 K[2-3-4]: in fast cooled samples, a strong decrease of the diamagnetic signal has been observed, which has been interpreted as indicating a suppression of the superconducting in favour of the magnetic phase

Self-assembly of Silver Nanoparticles and Multiwall Carbon Nanotubes on Decomposed GaAs Surfaces

Atomic Force Microscopy complemented by Photoluminescence and Reflection High Energy Electron Diffraction has been used to study self-assembly of silver nanoparticles and multiwall carbon nanotubes on thermally decomposed GaAs (100) surfaces. It has been shown that the decomposition leads to the formation of arsenic plate-like structures. Multiwall carbon nanotubes spin coated on the decomposed surfaces were mostly found to occupy the depressions between the plates and formed boundaries. While direct casting of silver nanoparticles is found to induce microdroplets. Annealing at 300°C was observed to contract the microdroplets into combined structures consisting of silver spots surrounded by silver rings. Moreover, casting of colloidal suspension consists of multiwall carbon nanotubes and silver nanoparticles is observed to cause the formation of 2D compact islands. Depending on the multiwall carbon nanotubes diameter, GaAs/multiwall carbon nanotubes/silver system exhibited photoluminescence with varying strength. Such assembly provides a possible bottom up facile way of roughness controlled fabrication of plasmonic systems on GaAs surfaces

DENSITY OF SURFACE STATES IN Pd/SiGe/Si INTERFACE FROM CAPACITANCE MEASUREMENTS

Pd/Si0.9Ge0.1/Si Schottky barrier diodes subjected to irradiation are characterized using capacitance and conductance measurements performed under forward and reverse bias while varying the temperature and frequency. The C–V technique has been used in particular to determine the carriers profile as well as the interface state density and its energy distribution.Schottky barrier, interface states, capacitance spectroscopy

Defect production in strained p-type Si1-xGex by Er implantation

Strained p-Si1−xGex (x = 5.3%, 10.2%, and 15.4%) was irradiated at room temperature with 160 keV 166Er2+ ions to a fluence of 1×1010 or 3×1013 Er/cm2. The defects induced by ion implantation were investigated experimentally using high-resolution x-ray diffraction, Rutherford backscattering and channeling spectroscopy, and deep level transient spectroscopy. X-ray diffraction indicates that the damage induced by Er implantation produces a slight perpendicular expansion of the SiGe lattice. For all compositions, channeling measurements reveal that Er implantation in p-Si1−xGex to a fluence of 3×1013 Er/cm2 induces an amorphous region below the Si1−xGex surface. Annealing at 850 °C for 30 s, results in a reduction in damage density, a relaxation of the implantation-induced perpendicular expansion of the SiGe lattice in the implanted region, while a more pronounced relaxation of the compressive strain SiGe is observed for higher Ge content (x = 0.10 and 0.15). On the other hand, for the annealed SiGe samples that were implanted with Er at the fluence of 1010 Er/cm2, the compressive strain in the SiGe layer is nearly completely retained. Deep level transient spectroscopy studies indicate that two prominent defects with discrete energy levels above the valence band are introduced during Er implantation. Their activation energy was found to decrease with increasing Ge content. However, the relatively large local strain induced by high fluence Er implantation reduces the activation energy by 40 meV with respect to the low fluence Er implanted p-Si1−xGex. This shift (40 meV) in the activation energy remains constant regardless of the Ge content, suggesting that the Si1−xGex layers remained fully strained after Er implantation. The observed defects are further compared to those introduced by alpha particle irradiation and electron beam metal deposition. The results indicate that defects introduced by Er implantation have similar electronic properties as those of defects detected after electron beam deposition and alpha particle irradiation. Therefore, it is concluded that these defects are due to the Er implantation-induced damage and not to the Er species specifically.The authors acknowledge the Fund for Scientific Research Flanders (FWO), the financial support from the Inter-University Attraction Pole (IUAP P6/42) and the KULeuven (GOA/09/006 and INPAC)

Negatively charged exciton X and donor bound exciton D0X in planar doped CdTe/Cdl-xZnxTe quantum well heterostructures

A comparative luminescence and magneto-transmission study is made of donor bound excitons DoX and negatively charged excitons X- in planar doped CdTe/Cd1-xZnxTe quantum wells of 100Å width. As the dopant plane is removed from the well centres to 450Å distance in the barriers, DoX evolves continuously into an X- species weakly localised in random potential fluctuations. The exciton localisation energy in DoX transforms into the second electron's binding energy in X-

Mn fraction substitutional site and defects induced magnetism in Mn-implanted

International audiencen-type 6H-SiC(0001) single crystal substrates were implanted with three fluences of manganese (Mn+) ions: 5×1015, 1×1016and 5×1016 cm–2 with implantation energy of 80 keV at 365°C to stimulate dynamic annealing. The samples were characterized using Rutherford backscattering channeling spectroscopy (RBS/C), high-resolution X-ray diffraction technique (HRXRD), and Superconducting Quantum Interference Device (SQUID) techniques. Two main defect regions have been identified using RBS/C spectra fitted with the McChasy code combined to SRIM simulations. Intermediate defects depth region is associated with vacancies (DV) and deeper defect (DN) essentially related to the Si and C interstitial defects. The defect concentration and the maximum perpendicular strain exhibit similar increasing trend with the Mn+ fluence. Furthermore, the amount of Mn atoms at Si substitutional sites and the corresponding magnetic moment per Mn atom were found to increase with increasing Mn fluence from 0.7μB to 1.7μB and then collapsing to 0.2μB. Moreover, a strong correlation has been found between the magnetic moment and the combination of both large DV/DN ratio and high Mn at Si sites. These results are corroborated by our ab initio calculations considering the most stable configurations showing that besides the amount of Mn substituting Si sites, local vacancy-rich environment is playing a crucial role in enhancing the magnetism