Transmission electron microscopes use electrons with wavelengths of a few picometers, potentially capable of imaging individual atoms in solids at a resolution ultimately set by the intrinsic size of ...an atom. However, owing to lens aberrations and multiple scattering of electrons in the sample, the image resolution is reduced by a factor of 3 to 10. By inversely solving the multiple scattering problem and overcoming the electron-probe aberrations using electron ptychography, we demonstrate an instrumental blurring of less than 20 picometers and a linear phase response in thick samples. The measured widths of atomic columns are limited by thermal fluctuations of the atoms. Our method is also capable of locating embedded atomic dopant atoms in all three dimensions with subnanometer precision from only a single projection measurement.
Achieving efficient spatial modulation of phonon transmission is an essential step on the path to phononic circuits using “phonon currents”. With their intrinsic and reconfigurable interfaces, domain ...walls (DWs), ferroelectrics are alluring candidates to be harnessed as dynamic heat modulators. This paper reports the thermal conductivity of single-crystal PbTiO3 thin films over a wide variety of epitaxial-strain-engineered ferroelectric domain configurations. The phonon transport is proved to be strongly affected by the density and type of DWs, achieving a 61% reduction of the room-temperature thermal conductivity compared to the single-domain scenario. The thermal resistance across the ferroelectric DWs is obtained, revealing a very high value (≈5.0 × 10–9 K m2 W–1), comparable to grain boundaries in oxides, explaining the strong modulation of the thermal conductivity in PbTiO3. This low thermal conductance of the DWs is ascribed to the structural mismatch and polarization gradient found between the different types of domains in the PbTiO3 films, resulting in a structural inhomogeneity that extends several unit cells around the DWs. These findings demonstrate the potential of ferroelectric DWs as efficient regulators of heat flow in one single material, overcoming the complexity of multilayers systems and the uncontrolled distribution of grain boundaries, paving the way for applications in phononics.
We provide a comparative study of basic electrical properties of bulk single crystals of transparent semiconducting oxides (TSOs) obtained directly from the melt (9 compounds) and from the gas phase ...(1 compound), including binary (β-Ga
2
O
3
, In
2
O
3
, ZnO, SnO
2
), ternary (ZnSnO
3
, BaSnO
3
, MgGa
2
O
4
, ZnGa
2
O
4
), and quaternary (Zn
1−x
Mg
x
Ga
2
O
4
, InGaZnO
4
) systems. Experimental outcome, covering over 200 samples measured at room temperature, revealed n-type conductivity of all TSOs with free electron concentrations (
n
e
) between 5 × 10
15
and 5 × 10
20
cm
−3
and Hall electron mobilities (
μ
H
) up to 240 cm
2
V
−1
s
−1
. The widest range of
n
e
values was achieved for β-Ga
2
O
3
and In
2
O
3
. The most electrically conducting bulk crystals are InGaZnO
4
and ZnSnO
3
with
n
e
> 10
20
cm
−3
and
μ
H
> 100 cm
2
V
−1
s
−1
. The highest
μ
H
values > 200 cm
2
V
−1
s
−1
were measured for SnO
2
, followed by BaSnO
3
and In
2
O
3
single crystals. In
2
O
3
, ZnO, ZnSnO
3
, and InGaZnO
4
crystals were always conducting, while others could be turned into electrical insulators.
Graphic abstract
Epitaxial strain can unlock enhanced properties in oxide materials, but restricts substrate choice and maximum film thickness, above which lattice relaxation and property degradation occur. Here we ...employ a chemical alternative to epitaxial strain by providing targeted chemical pressure, distinct from random doping, to induce a ferroelectric instability with the strategic introduction of barium into today's best millimetre-wave tuneable dielectric, the epitaxially strained 50-nm-thick n = 6 (SrTiO
)
SrO Ruddlesden-Popper dielectric grown on (110) DyScO
. The defect mitigating nature of (SrTiO
)
SrO results in unprecedented low loss at frequencies up to 125 GHz. No barium-containing Ruddlesden-Popper titanates are known, but the resulting atomically engineered superlattice material, (SrTiO
)
(BaTiO
)
SrO, enables low-loss, tuneable dielectric properties to be achieved with lower epitaxial strain and a 200% improvement in the figure of merit at commercially relevant millimetre-wave frequencies. As tuneable dielectrics are key constituents of emerging millimetre-wave high-frequency devices in telecommunications, our findings could lead to higher performance adaptive and reconfigurable electronics at these frequencies.
Truly bulk ZnGa2O4 single crystals were obtained directly from the melt. High melting point of 1900 ± 20 °C and highly incongruent evaporation of the Zn- and Ga-containing species impose restrictions ...on growth conditions. The obtained crystals are characterized by a stoichiometric or near-stoichiometric composition with a normal spinel structure at room temperature and by a narrow full width at half maximum of the rocking curve of the 400 peak of (100)-oriented samples of 23 arcsec. ZnGa2O4 is a single crystalline spinel phase with the Ga/Zn atomic ratio up to about 2.17. Melt-grown ZnGa2O4 single crystals are thermally stable up to 1100 and 700 °C when subjected to annealing for 10 h in oxidizing and reducing atmospheres, respectively. The obtained ZnGa2O4 single crystals were either electrical insulators or n-type semiconductors/degenerate semiconductors depending on growth conditions and starting material composition. The as-grown semiconducting crystals had the resistivity, free electron concentration, and maximum Hall mobility of 0.002–0.1 Ωcm, 3 × 1018–9 × 1019 cm−3, and 107 cm2 V−1 s−1, respectively. The semiconducting crystals could be switched into the electrically insulating state by annealing in the presence of oxygen at temperatures ≥700 °C for at least several hours. The optical absorption edge is steep and originates at 275 nm, followed by full transparency in the visible and near infrared spectral regions. The optical bandgap gathered from the absorption coefficient is direct with a value of about 4.6 eV, close to that of β-Ga2O3. Additionally, with a lattice constant of a = 8.3336 Å, ZnGa2O4 may serve as a good lattice-matched substrate for magnetic Fe-based spinel films.
Electrical conductivity and acoustic loss Q−1 of single crystalline Li(Nb,Ta)O3 solid solutions (LNT) are studied as a function of temperature by means of impedance spectroscopy and resonant ...piezoelectric spectroscopy, respectively. For this purpose, bulk acoustic wave resonators with two different Nb/Ta ratios are investigated. The obtained results are compared to those previously reported for congruent LiNbO3. The temperature dependent electrical conductivity of LNT and LiNbO3 show similar behavior in air at high temperatures from 400 to 700 °C. Therefore, it is concluded that the dominant transport mechanism in LNT is the same as in LN, which is the Li transport via Li vacancies. Further, it is shown that losses in LNT strongly increase above about 500 °C, which is interpreted to originate from conductivity-related relaxation mechanism. Finally, it is shown that LNT bulk acoustic resonators exhibit significantly lower loss, comparing to that of LiNbO3.
SnO2 is a semiconductor with a wide optical bandgap (3.5 eV), which makes it an attractive transparent semiconducting oxide (TSO) for electronic and opto‐electronic applications. At elevated ...temperatures it is, however, much more unstable than other TSOs (such as ZnO, Ga2O3, or In2O3). This leads to a rapid decomposition even under very high oxygen pressures. Our experiments showed that stoichiometric SnO2 does not melt up to 2100 °C, in contradiction to earlier published data. Bulk SnO2 single crystals, that could provide substrates for epitaxial growth, have not been reported so far. Hereby we report on truly bulk SnO2 single crystals of 1 inch diameter grown by physical vapor transport (PVT). The most volatile species during SnO2 decomposition is, in addition to oxygen, SnO, which is stable in the gas phase at high temperature and reacts again with oxygen at lower temperatures to form SnO2. We identified a relatively narrow temperature window, temperature gradients and a ratio of SnO/O2 for providing the best conditions for SnO2 single crystal growth. X‐ray powder diffraction (XRD) proved the single SnO2 phase. Moreover, by selecting a suitable SnO/O2 ratio it was possible to obtain either n‐type conductivity with electron concentrations up to 2 × 1018 cm−3 and electron mobilities up to 200 cm2 V−1 s−1, or insulating behavior. The crystals exhibited an optical absorption edge located at 330–355 nm, depending on the crystal orientation, and a good transparency over visible and near infrared (NIR) spectra.
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