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As scaling becomes increasingly difficult, there is growing interest in vertical or three-dimensional stacking of transistors and especially memory. Ferroelectric semiconductor field effect transistors can be key enablers to improve energy efficiency and overall chip and memory performance. In this work, low-temperature processed, back-end-of-the-line compatible transistors were demonstrated by depositing a layered chalcogenide ferroelectric semiconductor, beta-phase In2Se3, at temperature as low as 400 °C. Top gate n-channel In2Se3 thin film transistors were fabricated with field-effect mobility ∼1 cm2 V−1 s−1, and simple polarization switching based memory results are presented.

In the last decade, important research efforts have been posed towards the fabrication of novel carbon polymorphs with controlled sp3/sp2 properties. Nucleation of novel carbon polymorphs has been reported with the use of (1) cold compression experiments and (2) high temperature annealing. In the latter, the formation of a novel foam-like carbon (CFM) material has been reported as the result of an unusual spontaneous process of high temperature fusion of Fe3C-filled carbon nano-onions (Fe3C@CNOs). Being interested in investigating further such CNOs-fusion mechanism we have considered the use of Cu crystals as catalyst for the formation of the filled CNOs to be used as precursor for the CFM nucleation. The choice of these CNOs as precursors relies on their characteristic mass transport properties. This kind of effect is of important interest also for electrochemical battery-related processes. Specifically, we find that a complete conversion of the filled CNOs-precursors into CFM can be achieved within very short timescales of 6 h of annealing. This implies the presence of fast diffusion and mass transport dynamics. In addition, through the use of multiple characterization techniques, such as TEM, HRTEM, XRD, Raman Spectroscopy and XPS we investigate the variation of structural and surface characteristics of the Cu@CNOs and we demonstrate the formation of a sp3-rich mm-scale CFM material completely filled with crystalline copper after the annealing stage. Further investigations are then performed at high pressures of 5 GPa. These measurements reveal a substantial change in the CFM network-morphology and a comprehensive increase in the sp3-content.

We report the observation of novel temperature-driven structural-memory-effects in carbon nanotubes (CNTs) filled with Fe3C nano-crystals. These structural-transitions were measured by means of temperature (T) dependent X-ray diffraction (XRD) in the T-range from 298 K to 12 K. A clear reversible 2theta-shift in the 002-peak of the graphitic-CNTs-walls is found with the decrease of the temperature. As determined by Rietveld refinement, such 2theta-shift translates in a not previously reported decrease in the value of the CNT graphitic c-axis with the decrease of the temperature (from 298 K to 12 K). Also, a clear reversible 2theta-shift in the 031 and 131 diffraction-peaks of Fe3C is observed within the same T-range. Rietveld refinements confirm the existence of such memory-effect and also reveal a gradual decrease of the 010-axis of Fe3C with the decrease of the temperature. These observations imply that the observed structural-memory-effect is a characteristic of CNTs when Fe3C is the encapsulated ferromagnet. The generality of such memory-effects was further confirmed by additional measurements performed on other types of CNTs characterized by continuous Fe3C-filling. XRD measurements in the T-range from 298 K to 673 K revealed also an unusual reversible decrease of the Fe3C-peak intensities with the increase of the temperature. These observations can have important implications on the magnetic data recording applications of these nanostructures by helping in better understanding the unusual temperature-dependent magnetic instabilities of iron-based nano-crystals which have been recently reported in literature

Various low-temperature (LT) ultra-thin buffer layers have been fabricated on the GaAs (001) substrate. The buffer layer is decoupled from the host substrate by introducing low-temperature defects. The 400 nm In0.25Ga0.75As films were grown on these substrates to test the 'compliant' effects of the buffer layers. Atomic force microscopy, photoluminescence, double crystal x-ray diffraction and transmission electron microscopy were used to estimate the quality of the ln(0.25)Ga(0.75)As layer. The measurements indicated that the misfit strains in the epilayer can be accommodated by the LT ultra-thin buffer layer. The strain accommodation effects of the LT defects have been discussed in detail.

We have studied the angular magnetoresistance of iron pnictides BaFe2−x Ni x As2, which shows clear 180 degree periodicity as fitted by a cosine function. In the x = 0.065 sample, the phase of the two-fold symmetry changes 90 degrees above the tetragonal-to-orthorhombic structural transition temperature T s. Since the phase at low temperature is associated with the rotation of orthorhombic domains by magnetic field, we show that even vacuum grease can push the presence of orthorhombic domains at temperatures much higher than T s. Our results suggest that residual stress may have significant effects in studying the nematic orders and its fluctuations in iron pnictides.

Optic phonons and lattice vibrations of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals near the morphotropic phase boundary (MPB) are determined by terahertz (THz) reflectance spectra in a temperature range of 5.5–300 K. Raman scattering is measured with a He–Ne laser with a wavelength of 632.8 nm as the exciting source. On cooling from 300 K, the A1 component of the splitting TO1 mode hardens, which follows the Cochran law with a critical softening temperature of 761–861 K. Moreover, the E component of the soft mode is heavily damped around 0.81 THz (27 cm − 1). Additional polar phonon modes, which are forbidden in the cubic structure, are activated due to the broken cubic symmetry in polar clusters.