Comparison of near-interface traps in Al2_2O3_3/4H-SiC and Al2_2O3_3/SiO2_2/4H-SiC structures

Aluminum oxide (Al2O3) has been grown by atomic layer deposition on n-type 4H-SiC with and without a thin silicon dioxide (SiO2) intermediate layer. By means of Capacitance Voltage and Thermal Dielectric Relaxation Current measurements, the interface properties have been investigated. Whereas for the samples with an interfacial SiO2 layer the highest near-interface trap density is found at 0.3 eV below the conduction band edge, Ec, the samples with only the Al2O3 dielectric exhibit a nearly trap free region close to Ec. For the Al2O3/SiC interface, the highest trap density appears between 0.4 to 0.6 eV below Ec. The results indicate the possibility for SiC-based MOSFETs with Al2O3 as the gate dielectric layer in future high performance devices.Comment: 3 figures. Applied Physics Letters, accepted for publicatio

Electrical characterization of amorphous LiAlO2 thin films deposited by atomic layer deposition

LiAlO2 thin films deposited by atomic layer deposition (ALD) have a potential application as an electrolyte in three-dimensional (3D) all-solid-state microbatteries. In this study, Li-ion conductivity of such films is investigated by both in-plane and cross-plane methods. LiAlO2 thin films with a Li composition of [Li]/([Li] + [Al]) = 0.46 and an amorphous structure were grown by ALD with thicknesses of 90, 160 and 235 nm on different substrates. The electrical characterization was conducted by impedance spectroscopy using inert electrodes over a temperature range of 25-200 degrees C in an inert atmosphere. In-plane conductivities were obtained from films on insulating sapphire substrates, whereas cross-plane conductivities were measured from films on conducting titanium substrates. For the first time, comparison of the in-plane and cross-plane conductivities in these ALD LiAlO2 films has been achieved. More comparable results are obtained using a cross-plane method, whereas in-plane conductivity measurements demonstrate a considerable thickness-dependence with thinner film thickness. The room-temperature conductivity of the LiAlO2 films has been determined to be in the order of 10(-10) S cm(-1) with an activation energy of ca. 0.8 eV.Peer reviewe

Thermal, magnetic and structural aspects of transitions in Mn0.63Cr0.37As. Thermodynamic properties from 10 to 350 K

Subambient crystallographic and magnetic structures and heat capacity on Mn0.63Cr0.37As are measured below 350 K. A complex first order magnetic (helimagnetic Ha- to Hc-type) and structural (MnP- to MnP-type) transition, accompanied by a discontinuous unit cell volume change, and a second order magnetic [heli-(Hc) to paramagnetic] transition are observed at 165 and 219 K, respectively. The thermodynamic functions are derived and the thermodynamic characteristics of the transitions are discussed. The enthalpy and entropy of the combined MnP,Ha- to MnP,Hc- and MnP,Hc [right harpoon over left] MnP,P-type transitions are assessed to be 124.8R K and 0.749R, respectively. Two different models for the deconvolution of the magnetic heat-capacity envelope into contributions from the MnP,Ha- to MnP,Hc- and the MnP,Hc [right harpoon over left] MnP,P-type transitions are considered.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26813/1/0000371.pd

Heat capacity of MnAs0.88P0.12 from 10 to 500 K: Thermodynamic properties and transitions

The heat capacity of MnAs0.88P0.12 has been measured by adiabatic shield calorimetry from 10 to 500 K. It is shown that very small energy changes are connected with two magnetic order-order transitions, indicating that these can be regarded as mainly "noncoupled" magnetic transitions. At higher temperatures contributions to the excess heat capacity arises from a magnetic order-disorder transition, a conversion from low- to high-spin state for manganese, and a MnP- to NiAs-type structural transition. The observed heat capacity is resolved into contributions from the different physical phenomena, and the character of the transitions is discussed. In particular it is substantiated that the dilational contribution, which includes magnetoelastic and magnetovolume terms as well as normal anharmonicity terms, plays a major role in MnAs0.88P0.12. The entropy of the magnetic order-disorder transition is smaller than should be expected from a complete randomization of the spins, assuming a purely magnetic transition. Thermodynamic functions have been evaluated and the respective values of Cp, {SOm(T) - SOm(0)}, and -{GOm(T) - HOm(0)}/T at 298.15 K are 68.74, 72.09, and 32.30 J K-1 mole-1, and at 500 K 56.05, 108.12, and 56.64 J K-1 mole-1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26552/1/0000091.pd

ZrTe5 and HfTe5: The heat capacity and derived thermophysical properties from 6 to 350 K

The heat capacities of ZrTe5 and HfTe5 have been measured by adiabatic shield calorimetry from 6 to 350 K on samples carefully shielded to minimize the contact between the sample and oxygen during all stages of preparation and measurements. Since ZrTe5 and HfTe5 are isostructural and their molecular volumes are almost identical, the small differences between their heat capacities are due essentially solely to mass effects. There is absolutely no indication of any excess contribution to the heat capacities of these compounds below 350 K. The effective thermodynamic dimension of ZrTe5 and HfTe5 is estimated to be between one and two. The molar heat capacity, entropy, and enthalpy at 298.15 K are 18.32R, 31.96R, and 4155.7R [middle dot] K for ZrTe5, and 18.77R, 32.99R, and 4276.8R [middle dot] K for HfTe5.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27862/1/0000275.pd

Phase stability and structural properties of Ni7 +/- [delta]S6 and Ni9S8 Heat capacity and thermodynamic properties of Ni7S6 at temperatures from 5 K to 970 K and of Ni9S8 from 5 K to 673 K

Two stable solid phases with composition in the range from (45 to 48) moles per cent of S exist for (nickel + sulfur): Ni9S8 which disproportionates to Ni1 - [delta]S and Ni7 +/- [delta]S6 above T = (709 +/- 5) K, and Ni7 +/- [delta]S6. The latter non-stoichiometric phase forms eutectoidally from Ni9S8 and Ni3S2 at T = (675 +/- 3) K. It is stable in a rather narrow temperature interval and disproportionates to Ni1 - [delta]S and Ni3 +/- [delta]S2 at T = (850 +/- 2) K. The phases are characterized structurally, and a revised phase diagram is presented. The heat capacity of a sample with composition Ni7S6 was determined over the temperature range T = 5 K to 970 K by adiabatic calorimetry. Effects from metastable modifications of the high-temperature phase were observed during thermal analysis, X-ray diffraction, and calorimetry on incompletely equilibrated samples. Thermodynamic-function values for Ni7S6 and Ni9S8 are presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31376/1/0000289.pd

Exotic Compositional Ordering in Manganese–Nickel–Arsenic (Mn-Ni-As) Intermetallics

International audienceIn this work we benefited from recent advances in tools for crystal-structure analysis that enabled us to describe an exotic nanoscale phenomenon in structural chemistry. The Mn0.60Ni0.40As sample of the Mn1−xNixAs solid solution, exhibits an incommensurate compositional modulation intimately coupled with positional modulations. The average structure is of the simple NiAs type, but in contrast to a normal solid solution, we observe that manganese and nickel segregate periodically at the nano-level into ordered MnAs and NiAs layers with thickness of 2–4 face-shared octahedra. The detailed description was obtained by combination of 3D electron diffraction, scanning transmission electron microscopy, and neutron diffraction. The distribution of the manganese and nickel layers is perfectly described by a modulation vector q=0.360(3) c*. Displacive modulations are observed for all elements as a consequence of the occupational modulation, and as a means to achieve acceptable Ni–As and Mn–As distances. This modulated evolution of magnetic MnAs and non-magnetic NiAs-layers with periodicity at approximately 10 Å level, may provide an avenue for spintronics