Magnetic properties of ferromagnetic/antiferromagnetic thin-films structures for spin-valve applications have been studied. Multilayer structures of Ta/Co/IrMn/Ta and Ta/FeNi/IrMn/Ta were deposited on Si substrate at room temperature by DC magnetron sputtering. Thickness of the antiferromagnetic layer changed from 10 to 50 nm. The coercive force was found to be non-monotonic function of the antiferromagnetic layer thickness. The exchange bias for 30-50 nm antiferromagnetic layers (73 Oe) is about 10 Oe larger than for 10-20 nm antiferromagnetic layers. Moreover, it was demonstrated that the alternative sequence of the deposition (antiferromagnetic layer on the top or below the ferromagnetic layer) leads to dramatic changes of structures magnetic properties.
We report on an extensive structural and electrical characterization of undergate dielectric oxide insulators Al_2O_3 and HfO_2 grown by atomic layer deposition. We elaborate the atomic layer deposition growth window for these oxides, finding that the 40-100 nm thick layers of both oxides exhibit fine surface flatness and required amorphous structure. These layers constitute a base for further metallic gate evaporation to complete the metal-insulator-semiconductor structure. Our best devices survive energizing up to ≈ 3 MV/cm at 77 K with the leakage current staying below the state-of-the-art level of 1 nA. At these conditions the displaced charge corresponds to a change of the sheet carrier density of 3 × 10^{13} cm^{-2}, which promises an effective modulation of the micromagnetic properties in diluted ferromagnetic semiconductors.
The signal coming from SiO_{2} layer of MOS structure have large noise-to-signal ratio. This has two reasons - first: the dielectric layers have small Raman efficiency, second: the thickness of the dielectric layers are of the order of 10 nm, so the volume of the material irradiated with laser light is small. At the other side spectroscopic and optical data carry the information about important properties of the structure like mechanical stress. Distribution of mechanical stress introduce an important contribution to the electric properties of the electronic systems based on the MOS structures. Therefore, it is important to "distillate" the optical data from the noise. In this contribution the authors discuss some methods of denoising of the Raman signal. The discussed methods compare treatments like wavelet analysis or convolution. The work is illustrated with some examples of the extraction of the data coming from thin layers. The examples of application of the optical data in the description of the properties of the studied structures are presented.
Ionic diffusion of (H_2O)_{n}^{+} and CO¯_3 on SiO_2 surfaces has been quantified using Kelvin force microscopy measurement of ion distribution change after small spot corona charge. For both positive and negative ionic species, the concentration profiles versus time follow the two-dimensional surface diffusion enabling a determination of corresponding diffusion coefficients. On a thermally grown SiO_2 surface, diffusion coefficients of (H_2O)_{n}^{+} and CO¯_3 ions were 2.2 × 10^{-11} cm^2/s and 4.8 × 10^{-12} cm^2/s, respectively. On a chemically cleaned SiO_2 surface, diffusion coefficients of (H_2O)_{n}^{+} and CO¯_3 ions were 7.5 × 10^{-9} cm^2/s and 2.4 × 10^{-9} cm^2/s, respectively. Mathematical analysis of the surface potential decay yields an additional parameter - capacitance equivalent thickness.
The optical properties of lead oxide samples prepared using thermal evaporation technique on unheated glass substrates with different film thicknesses have been studied. The structural characteristics of a lead oxide sample was investigated using X-ray diffraction and it is confirmed to be in the amorphous state. The optical properties of the prepared films were studied by transmittance and reflectance measurements, and the integrated transmittance (T_{UV}, T_{VIS} and T_{Sol}) in ultraviolet, visible and solar regions was calculated and found to be affected by film thickness. The dependence of absorption coefficient on wavelength was also reported. The energy gap was calculated and has been observed around 3.7 eV.
We report recent advances in material characterization on the nanometer scale using scanning microwave microscopy. This combines atomic force microscopy and a vector network analyzer using microwave tip sample interaction to characterize dielectric and electronic material properties on the nanometer scale. We present the methods for calibration as well as applications. Scanning microwave microscopy features calibrated measurements of: (1) capacitance with attofarad sensitivity. For calibration a well characterized array of capacitors (0.1 fF to 10 fF) is used. The method is applied to determine the dielectric properties of thin organic films, (2) Semiconductor dopant density. Calibration is performed by imaging the cross-section of a standard sample with differently doped layers (dopant stair case) from 10^{16} atoms/cm^3 to 10^{20} atoms/cm^3.
We report study of current density-voltage (J-V) and capacitance-voltage (C-V) characteristics of Al/Ta_2O_5/Al metal-insulator-metal structures prepared by electron beam deposition. At low bias voltages the J-V characteristics of Al/Ta_2O_5/Al structures show ohmic conduction. At higher voltages the conductivity becomes limited by space charge. The space charge limited conductivity is due to carrier trap centers located within the energy gap of Ta_2O_5. The distribution of the trap appears to be exponential above the valence band. Basing on the comparison of the measured temperature dependences of the current density with the theoretical model one can determine important material parameters, such as the trap density. The density of states at the Fermi level N(E_{F}) for the Ta_2O_5 film is found to be 2.75 × 10^{19} eV^{-1} cm^{-3}. The capacitance-voltage-temperature (C-V-T) characteristics of Al/Ta_2O_5/Al structures were carried out in the bias range -5 to +5 V and at temperatures from 300 to 550 K. The capacitance of Al/Ta_2O_5/Al structures increases with the increasing temperature.
Methods to modify gate dielectrics of MIS structures by irradiation treatments and high-field electron injection into dielectric are considered. In addition, distinctive features of these methods used to correct parameters of MIS devices are studied. It was found out that negative charge, accumulating in the thin film of phosphosilicate glass (PSG) of the MIS structure having a two-layer gate dielectric SiO_2-PSG under the high-field injection or during the irradiation treatment can be used to correct the threshold voltage to improve the charge stability and raise the voltage of breakdown for the MIS devices. It is proved that the density of electron traps rises with the increasing thickness of the PSG film. In this paper a method to modify electrophysical characteristics of MIS structures by the high-field tunnel injection of electrons into the gate dielectric under the mode of controlled current stress is proposed. The method allows to monitor changing of MIS structure parameters directly during the modification process.
This paper presents a model of molecular ultrathin crystalline film and analysis of dielectric properties of these spatially very restricted structures. Using the two-time dependent Green functions the energy spectrum and possible exciton states were determined and the dynamic permittivity was calculated. It was shown that the appearance of localized states in the boundary layers of the film depend on the thickness and the changing values of parameters in the border areas of the film. These localized states define schedule and determine the number of resonant absorption lines in the infrared area of the external electromagnetic radiation.
The aim of this work was the evaluation of ion-beam induced luminescence for the characterization of luminescent oxide materials containing rare earth elements. The yttrium aluminium garnet epilayers doped with Nd, Pr, Ho, and Tm atoms were used. The ion-beam induced luminescence spectra were excited using 100 keV H_2^{+} ion beam and were recorded in the wavelengths ranging from 300 nm up to 1000 nm. The separate parts of the surface of the same samples were used for ion-beam induced luminescence and cathodoluminescence experiments. Cathodoluminescence spectra have been recorded in the range from 370 nm up to 850 nm at 20 keV e-beam in scanning electron microscope equipped with a grating spectrometer coupled with a photomultiplier. The observed narrow ion-beam induced luminescence lines can be ascribed to the well known radiative transitions in the rare-earth ions in the YAG crystals. The cathodoluminescence spectra reveal essentially the same emission lines as ion-beam induced luminescence. The decrease of the ion-beam induced luminescence lines intensity has been observed under the increasing ion fluences. The ion-beam induced luminescence may be used for characterization of transparent luminescent materials as an alternative method for cathodoluminescence and can be especially useful for observation of ion-beam damage formation in crystals.
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