Transmission electron microscopy study of platinum clusters on Al₂O₃/NiAl(110) under the influence of electron irradiation

Using transmission electron microscopy we have studied the influence of the electron beam in an electron microscope onto platinum clusters deposited on a thin single crystalline γ-Al2O3 film grown by oxidation of NiAl(110). At electron current densities below j≈1 A/cm2 no influence is observed. Movement and coalescence of clusters occur at electron beam current densities between j=2 and some 10 A/cm2. For current densities around j=50 A/cm2 decoration of steps takes place. Further increase to j=100  A/cm2 and above induces drilling of holes into the substrate by clusters. At such current densities also melting of the clusters may occur. Due to the heat capacity of the system the result does not only depend on the electron current density but also on the irradiation time

A new charge-transfer complex in UHV co-deposited tetramethoxypyrene and tetracyanoquinodimethane

UHV-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP1-TCNQ1) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), X-ray-diffraction (XRD), infrared (IR) spectroscopy and scanning tunnelling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD (d1= 0.894 nm, d2= 0.677 nm). A softening of the CN stretching vibration (red-shift by 7 cm-1) of TCNQ is visible in the IR spectra, being indicative of a CT of the order of 0.3e from TMP to TCNQ in the complex. Characteristic shifts of the electronic level positions occur in UPS and STS that are in reasonable agreement with the prediction of from DFT calculations (Gaussian03 with hybrid functional B3LYP). STS reveals a HOMO-LUMO gap of the CT complex of about 1.25 eV being much smaller than the gaps (>3.0 eV) of the pure moieties. The electron-injection and hole-injection barriers are 0.3 eV and 0.5 eV, respectively. Systematic differences in the positions of the HOMOs determined by UPS and STS are discussed in terms of the different information content of the two methods.Comment: 20 pages, 6 figure

Магніторезистивні властивості нанорозмірних плівкових систем на основі Fe і Pd

Проведені дослідження ефекту магнітоопору в одно- і двошарошарових плівках Pd/Fe/П. Отримано, що залежність магнітоопору від індукції зовнішнього магнітного поля має гістерезисний характер і його величина, як і величина опору, який монотонно зменшується при зростанні індукції. Опір двошарових плівкових систем має більшу величину при вимірюванні в перпендикулярній геометрії у порівнянні із паралельною. Вказана відміна пояснюється різною динамікою руху електронів провідності.Проведены исследования эффекта магнитосопротивления в одно- и двухслойных пленках Pd/Fe/П. Получено, что зависимость магнитосопротивления от индукции внешнего магнитного поля имеет гистерезисный характер и его величина, как и величина сопротивления, монотонно уменьшается при росте индукции. Сопротивление двухслойных пленочных систем имеет большую величину при измерении в перпендикулярной геометрии по сравнению с параллельной. Указанное отличие объясняется разной динамикой движения электронов проводимости.Effect of magnetoresistance researches are carried out in one- and double-layered films Pd/Fe/S. It is received, that magnetoresistance from an induction of an external magnetic field character and its size, as well as resistance size has dependence hysteresis, monotonously decreases at induction growth. Resistance of two-layered film systems has the big size at measurement in perpendicular geometry in comparison with the parallel. The specified difference speaks different dynamics of movement of electrons conductivity

Magnetization dynamics in microscopic spin-valve elements: Shortcomings of the macrospin picture

We have studied ultrafast magnetodynamics in micropatterned spin-valve structures using time-resolved x-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism. Exciting the system with ultrafast field pulses of 250 ps width, we find the dynamic response of the free layer to fall into two distinctly different contributions. On the one hand, it exhibits localized spin wave modes that strongly depend on the shape of the micropattern. A field pulse applied perpendicular to the exchange bias field along the diagonal of a square pattern leads to the excitation of a standing spin wave mode with two nodes along the field direction. This mode is strongly suppressed for a pattern of elliptical shape. On the other hand, the integrated response of the free layer roughly follows a single-spin model with a damping constant of alpha=0.025 independent of the shape and resembles the response of a critically damped forced oscillator

Near-Edge X‐ray Absorption Fine Structure Investigation of the Quasi-One-Dimensional Organic Conductor (TMTSF)2PF6

We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P L2/3 edges, F K edge, C K edge, and Se M2/3 edges of the quasi-one-dimensional (1D) conductor and superconductor (TMTSF)2PF6. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken around RT were also studied as a function of the angle (θ) between the electric field of the X-ray beam and the 1D conducting direction. In contrast with a previous study of the S L2/3-edges spectra in (TMTTF)2AsF6, the Se M2/3 edges of (TMTSF)2PF6 do not exhibit a well-resolved spectrum. Surprisingly, the C K-edge spectra contain three well-defined peaks exhibiting strong and nontrivial θ and temperature dependence. The nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)2PF6 and (TMTTF)2AsF6 exhibit important differences. In contrast with the case of (TMTTF)2AsF6, the F K-edge spectra of (TMTSF)2PF6 do not change with temperature despite stronger donor−anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts

Electrophysical, Magnetoresistivity and Magneto-optical Properties of Multilayer Materials Based on Nanocrystalline and Amorphous Films

In work is presented to the results of complex investigate of phase formation, thermal resistivite, magnetoresistive and magneto-optical properties of multilayers based Fe and Pd, Ag or Ge, which obtained by sequential condensation of the layers with following thermal annealing. Investigation of phase formation processes of thin film systems and established of correlation between this processes and above-mention physical properties. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3500

First-principles thermodynamics of transition metals and alloys: W, NiAl, PdTi

We apply the pseudopotential density functional perturbation theory approach along with the quasiharmonic approximation to calculate the thermal expansion of tungsten and two important metallic alloys, NiAl and PdTi. We derive the theory for anisotropic crystal structures and test the approximation that the anisotropic effects of thermal expansion are equivalent to negative pressure - this simplifies the calculation enormously for complex structures. Throughout, we find excellent agreement with experimental results.Comment: 11 pages 9 fig

Spin texture of time reversal symmetry invariant surface states on W 110

We find in the case of W 110 previously overlooked anomalous surface states having their spin locked at right angle to their momentum using spin resolved momentum microscopy. In addition to the well known Dirac like surface state with Rashba spin texture near the point, we observe a tilted Dirac cone with circularly shaped cross section and a Dirac crossing at 0.28 amp; 8201; amp; 8201; amp; 8201; within the projected bulk band gap of tungsten. This state has eye catching similarities to the spin locked surface state of a topological insulator. The experiments are fortified by a one step photoemission calculation in its density matrix formulatio

Spectral focusing of broadband silver electroluminescence in nanoscopic FRET-LEDs

Few inventions have shaped the world like the incandescent bulb. Edison used thermal radiation from ohmically heated conductors, but some noble metals also exhibit ‘cold’ electroluminescence in percolation films1,2, tunnel diodes3, electromigrated nanoparticle aggregates4,5, optical antennas6 or scanning tunnelling microscopy7,8,9. The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Nanoparticle electroluminescence is particularly intriguing because it involves localized surface-plasmon resonances with large dipole moments. Such plasmons enable very efficient non-radiative fluorescence resonance energy transfer (FRET) coupling to proximal resonant dipole transitions. Here, we demonstrate nanoscopic FRET–light-emitting diodes which exploit the opposite process, energy transfer from silver nanoparticles to exfoliated monolayers of transition-metal dichalcogenides10. In diffraction-limited hotspots showing pronounced photon bunching, broadband silver electroluminescence is focused into the narrow excitonic resonance of the atomically thin overlayer. Such devices may offer alternatives to conventional nano-light-emitting diodes11 in on-chip optical interconnects