Two-Dimensional Surface Topological Nanolayers and Dirac Fermions in Single Crystals of the Diluted Magnetic Semiconductor (Cd1−x−yZnxMny)3As2 (x + y = 0.3)

Features in the transverse magnetoresistance of single-crystalline diluted magnetic semiconductors of a (Cd1−x−yZnxMny)3As2 system with x + y = 0.3 have been found and analyzed in detail. Two groups of samples have been examined. The samples of the first group were thermally annealed for a long time, whereas the samples of the second group were not thermally annealed. The Shubnikov–de Haas (SdH) oscillations were observed for both groups of the samples within a 4.2 ÷ 30 K temperature range and under transverse magnetic field sweeping from 0 up to 11 T. The value of a phase shift, according to the SdH oscillations, was found to be a characteristic of the Berry phase existing in all the samples, except the unannealed sample with y = 0.08. Thickness of 2D surface topological nanolayers for all the samples was estimated. The thickness substantially depended on Mn concentration. The experimental dependence of reduced cyclotron mass on the Fermi wave vector, extracted from the SdH oscillations for the samples with different doping levels, is in satisfactory agreement with the predicted theoretical linear dependence. The existence of the Dirac fermions in all the samples studied (except the unannealed sample with y = 0.08) can be concluded from this result.

Effect of Thermal Annealing on Thermoluminescence Glow Curves of KY3F10:Ho3+

The effect of thermal annealing on thermoluminescence (TL) glow curves of commercially obtained KY3F10:Ho3+ phosphor is investigated, and the result is compared with that of unannealed sample. The samples were annealed at different annealing temperatures: namely, 400, 500, and 600 ∘C. The activation energy (trap depth), which is one of the TL kinetic parameters, is calculated for the annealed and unannealed samples using the variable heating rate (VHR) method. The results show that the thermal annealing has a clear effect on the TL intensities of the glow curves. The maxima of the TL glow curves shift toward a higher temperature region, as the annealing temperature increases. Moreover, the higher the annealing temperature, the shallower the position of the trap beneath the edge of the conduction band. The X-ray diffraction (XRD) pattern of the sample shows a monoclinic structure with unit cell dimensions (in Angstr¨om) a = 10.41, b = 6.73, c = 12.46 match with JCPDS card No. 21-1458.

Photonic upconversion in solution-processed Gd-based thin films for delayed quantum efficiency roll-off in a-Si flat panel image detectors

ABSTRACTAmorphous Si (a-Si) is used for fabrication of commercial low-cost flat panel image detectors for radiographic applications such as computed tomography (CT) imaging. a-Si photodiodes are known to exhibit a rapid decrease in quantum efficiency near 750nm. While crystalline Si does not suffer from such an early decline, the large-area and low-cost constraints of medical imagers make it challenging and costly to use crystalline Si for such devices. In this work, we report on the development of a sensitive layer for upconversion from 785 nm to green region of the spectrum, which nearly matches the peak quantum efficiency of a-Si detectors. Various host materials have been extensively studied in literature with rare earth ions such as Er3+(emission: green+red), Tm3+(emission: blue), Ho3+(emission: red+green) along with Yb3+ as a sensitizer for upconversion to the visible regime at high incident optical power (∼100 mW) for colloidal solutions. We carried out a thermal decomposition synthesis of NaYF4:Yb(18%),Er(2%),Gd(15%) at moderate temperature (∼320°C), resulting in a nearly pure hexagonal phase material. This is confirmed by powder X-ray diffraction (PXRD) of the unannealed sample with a lattice constant (∼5.17 Å). High-resolution transmission electron microscopy (HRTEM) measurements reveal the formation of nearly spherical nanoparticles. The observed plane ([100]) inferred from lattice fringes in TEM data with a visibly estimated interplanar distance (4.4±1.6 Å) is in reasonable agreement with standard data (∼5.17 Å) for comparable NaYF4-based materials. Excitation (785 nm) of the deposited thin films of Gd-doped unannealed material at relatively low incident power (∼0.4 mW) exhibits a PL response in green (539 nm) and red (665 nm) region of the spectrum. Gd-based upconversion material based thin films are thus a feasible photonic material for potential effective extension of high quantum efficiency range in a-Si for flat panel image detectors.

The Effect of Annealing Temperatures on the Dielectric Constant of PVDF/MgO Nanocomposites Thin Films

Poly(vinylidene flouride)/nano-magnesium oxide (PVDF/MgO) nanocomposites with MgO loading percentage of (7% wt. %) were annealed with various annealing temperatures ranging from 70°C to 170°C with rapid removal from the oven. From dielectric constant, the samples annealed at temperature of 70°C showed an improvement in the dielectric constant from 21 to 23 at frequency 103 Hz for UN and AN70 respectively. However, as the temperatures were increased, the dielectric constant of PVDF/MgO (7%) was found to decrease. XRD showed the presence of β-phase for PVDF/MgO(7%) sample annealed at 70°C in comparison to unannealed sample, hence PVDF/MgO(7%) film is suitable to be used for low frequency capacitor application.

Dielectric Properties of PVDF/MgO Nanocomposites Thin Film with Various Annealing Temperatures

Poly (vinylideneflouride)/nanomagnesium oxide (PVDF/MgO) nanocomposites with MgO loading percentage of 7% were annealed with various annealing temperatures ranging from 70oC to 170oC. The PVDF/MgO(7%) thin films were fabricated using spin coating technique with MIM structure. The dielectric constant of PVDF/MgO(7%) was studied over a wide range of annealing temperatures with rapid removal from the oven once the annealing was utilized. The nanocomposites thin films annealed at temperature of 70oC (AN70) shows an improvement in the dielectric constant of 23 at 103 Hz compared to unannealed sample (UN), which was 21 at the same frequency. However, as the annealing temperatures were increased from 90oC (AN90) to 170o C (AN170), the dielectric constant of PVDF/MgO(7%) were found to decrease from 16 to 7 respectively, which were lower than the UN thin films. AN70 also produced low value of tangent loss at low frequency˼˰˸̱̈́̾˰δ˹˰̴̷̹̹̳̱̹̾̈́̾˰̸̱̈́̈́˼˰̵̷̱̱̼̹̾̾̾˰̱̈́˰temperatures 70oC is favourable temperature used to improve the dielectric constant of PVDF/MgO(7%).

Experimental Investigation of Ultrafast Thermalization Dynamics on Nickel Thin Films

In order to break the limitation of the speed of magnetic installation due to magnetic layer transfer characteristics, the ultrafast thermalization dynamic of Ni films and its composite films were studied by femtosecond laser pump-probe technique. The paper focuses on the research of the effect of cooling layer and annealing on the transient reflectivity curves. And the transient reflectivity signals of Ni films prepared under different parameters were measured. The results show that the cooling layer with the larger electron heat capacity constant and the stronger electron-phonon coupling constant can enhance the scattering efficiency of transient heat conduction. Compared to the unannealed sample, the composite film sample after annealing has faster recovery process.

A Correlation Study of Thermal Stability on Porous Low k

The thermal stability of organic porous low k, porous SiLK with a dielectric constant of 2.4, has been studied. Organic low k material SiLKTM, non-porous SiLK, with a dielectric constant 2.8 is used as a baseline for comparison. Each sample was subjected to annealing cycles, where each cycle was conducted in a vertical furnace for one hour in an N2 ambient. The annealing temperature was set at either 430°C or 450°C. After every alternate cycle, the film properties were measured and compared to the unannealed sample for changes in film shrinkage, refractive index, dielectric constant, roughness, breakdown voltage, pore size, hardness and Young's modulus. Changes in film properties were investigated and evaluated by using opti-probe, FTIR, XPS, AFM, mercury probe, nano-indentation, SEM and TEM techniques.

X-Ray Diffraction Studies of Annealed SiGe/Si SLS

We have done x-ray diffraction to study the affect of annealing on a SiGe/Si strained-layer superlattice (SLS). The post anneal spatial distribution of the Ge and Si atoms within the alloy layer is of particular interest. X-ray data taken from an annealed sample along the superlattice direction (100) show two sharp and well separated superlattice envelope functions. In contrast to the unannealed sample, and what would be a typical scattering spectra for a superlattice, the envelopes bisect the position of the unannealed sample's envelope function. The position of the envelope function is related to the tetragonal distortion εT in the SiGe alloy layers. The two separate envelopes (α and β) show that the SiGe alloy (100) planes have divided themselves into two groups with different interplanar spacings after the anneal. Each group with a tetragonal distortion such that and where εT is the tetragonal distortion in the unannealed sample. This is strong evidence for coherent phase separation perpendicular to the growth direction, along the SiGe alloy layer. In another investigation a search of reciprocal space for the 2 × 2 {… SiSiGeGe…} (111) chemically ordered state showed no evidence for the existence of such an ordered state.