Shift and ballistic photovoltaic currents, previously indistinguishable experimentally, can now be separated.

Thermal properties of single wall carbon nanotube sheets (SWCNT-sheets) are of significant importance in the area of thermal management, as an isolated SWCNT possesses high thermal conductivity of the value about 3000 W m(-1) K(-1). Here we report an indirect method of estimating the thermal conductivity of a nanometer thick suspended SWCNT-sheet by employing the Raman scattering technique. Tube diameter size is examined by the transmissions electron microscopy study. The Raman analysis of the radial breathing modes predicts narrow diameter size distribution with achiral (armchair) symmetry of the constituent SWCNTs. From the first order temperature coefficient of the A1g mode of the G band along with the laser power dependent frequency shifting of this mode, the thermal conductivity of the suspended SWCNT-sheet is estimated to be about ∼18.3 W m(-1) K(-1). Our theoretical study shows that the thermal conductivity of the SWCNT-sheet has contributions simultaneously from the intratube and intertube thermal transport. The intertube thermal conductivity (with contributions from the van der Waals interaction) is merely around 0.7 W m(-1) K(-1), which is three orders smaller than the intratube thermal conductivity, leading to an abrupt decrease in the thermal conductivity of the SWCNT-sheet as compared to the reported value for isolated SWCNT.

Room temperature ferroelectricity in pulsed laser deposited rare-earth doped hafnium oxide (HfO 2 ) thin films is discussed. Maximum values of remnant polarizations (P r ) ∼13.5 and 12 μC/cm 2 along with coercive fields (E C ) ∼334 and 384 kV/cm are observed in 6 mol. % of rare-earth (Sm or Gd) doped-HfO 2 thin films (Sm:HfO 2 and Gd:HfO 2 ), respectively. Piezoresponse force microscopy measurements confirmed ferroelectric nature of films by showing phase hysteresis and butterfly amplitude loops. It is noticed that wake-up cycles improved the remnant polarization and found to be necessary for the forming of well saturated hysteresis loops. Our results showed potential toward realization of future highly scaled non-volatile ferroelectric memories. Ferroelectric materials are engendering considerable interest because of a variety of emerging applications including ferroelectric memories which have promising potentials for next generation high integration density and low power nonvolatile memory technology. 1,2The most studied material for ferroelectric memories, Pb[Zr x Ti 1-x ]O 3 (PZT), 1 is facing severe scaling limitations due to its complicated crystal structure which in turn hinders its applicability toward dense integration in the complementary metal oxide semiconductor (CMOS) technology. The lead (Pb) toxicity in PZT is also a snag due to ecological concerns.Recently, experimental as well as theoretical studies showed ferroelectricity in doped hafnia (HfO 2 ) thin films which are compatible with existing CMOS technology.3-10 Ferroelectric phenomenon in these doped-HfO 2 films deposited by various deposition techniques such as atomic layer deposition, 5-10 chemical solution deposition, 11 and sputtering 12 was mainly explained by the existence of noncentrosymmetric orthorhombic phase (space group of Pca2 1 ). 5,6,12 The dopant incorporation into monoclinic HfO 2 matrix results in a transformation to tetragonal/cubic phase with the appearance of an intermediate metastable orthorhombic (Pca2 1 ) phase. On the other hand, in some of the reports, ferroelectric nature in doped-HfO 2 films was attributed to the influence of "wake-up" effect. [11][12][13] In this paper, we report on the ferroelectric properties of rare earth doped Sm:HfO 2 (SHO) and Gd:HfO 2 (GHO) thin films fabricated by the sequential pulsed laser deposition (SPLD) technique. [14][15][16] The deposition was performed by periodic depositions from HfO 2 and Sm 2 O 3 /Gd 2 O 3 ceramic targets. The dopant concentration was obtained by controlling number of Sm 2 O 3 /Gd 2 O 3 ablation pulses relative to that of HfO 2 . To study the ferroelectric properties of the deposited samples, polarization-voltage (P-V), capacitance-voltage (C-V), and piezoresponse force microscopy (PFM) measurements were performed. ExperimentalPolycrystalline thin films of SHO and GHO of ∼60 nm thickness were fabricated on Pt/TiO 2 /SiO 2 /Si substrates by SPLD technique at a fixed temperature of 650• C and in an oxygen ambient partial pressure of ∼0.5 Pa. The KrF excimer laser...

We have studied ferroelectricity and photovoltaic effects in atomic layer deposited (ALD) 40-nm thick SnTiO x films deposited directly onto p-type (001)Si substrate. These films showed well-saturated, square and repeatable hysteresis loops with remnant polarization of 1.5 µC/cm 2 at room temperature, as detected by out-of-plane polarization versus electric field (P-E) and field cycling measurements. A photo-induced enhancement in ferroelectricity was also observed as the spontaneous polarization increased under white-light illumination. The ferroelectricity exhibits relaxor characteristics with dielectric peak shifting from ca. T = 600K at f = 1 MHz to ca. 500K at 100 Hz. Moreover, our films showed ferroelectric photovoltaic behavior under the illumination of a wide spectrum of light, from visible to ultraviolet regions. A combination of experiment and theoretical calculation provided optical band gap of SnTiO x films which lies in the visible range of white light spectra. Our study leads a way to develop green ferroelectric SnTiO x thin films, which are compatible to semiconducting processes, and can be used for various ferroelectric and dielectric applications.

We studied switchable photovoltaic and photo-diode characteristics of Pt/(Bi 0.9 Sm 0.1 )(Fe 0.97 Hf 0.03 )O 3 /LaNiO 3 (Pt/BSFHO/LNO) heterostructures integrated on Si (100). The directions of photocurrent (J SC ) and rectification are found to be reversibly switchable after applying external poling voltages. In pristine state, metal-ferroelectric-metal capacitor Pt/BSFHO/LNO shows J SC ~32 µA/cm 2 and V OC ~0.04 V, which increase to maximum value of J SC ~ 303 (˗206) µA/cm 2 and V OC ~ ˗0.32 (0.26) V after upward (downward) poling at ±8 V. We believe that Schottky barrier modulation by polarization flipping at Pt/BSFHO interface could be a main driving force behind switchable photovoltaic and rectifying diode characteristics of Pt/BSFHO/LNO heterostructures.