To understand the near-interface magnetism in manganites, uniform, ultrathin films of La 0.67 Sr 0.33 MnO 3 were grown epitaxially on single crystal (001) LaAlO 3 and (110) NdGaO 3 substrates. The temperature and magnetic field dependent film resistance is used to probe the film's structural and magnetic properties. A surface and/or interface related dead-layer is inferred from the thickness dependent resistance and magnetoresistance. The total thickness of the dead layer is estimated to be ∼ 30Å for films on NdGaO 3 and ∼ 50Å for films on LaAlO 3 .

By lifting an epitaxial thin film off its growth substrate, we directly and quantitatively demonstrate how elastic strain can alter the magnetic and electrical properties of single-domain epitaxial SrRuO3 thin films (1000 Å thick) on vicinal (001) SrTiO3 substrates. Free-standing films were then obtained by selective chemical etching of the SrTiO3. X-ray diffraction analysis shows that the free-standing films are strain free, whereas the original as-grown films on SrTiO3 substrates are strained due to the lattice mismatch at the growth interface. Relaxation of the lattice strain resulted in a 10 K increase in the Curie temperature to 160 K, and a 20% increase in the saturation magnetic moment to 1.45 μB/Ru atom. Both values for the free-standing films are the same as that of the bulk single crystals. Our results provide direct evidence of the crucial role of the strain effect in determining the properties of the technologically important perovskite epitaxial thin films.

Articles you may be interested inCurrent-sensitive electroresistance and the response to a magnetic field in La 0.8 Ca 0.2 MnO 3 epitaxial thin films J. Appl. Phys. 97, 10H706 (2005); 10.1063/1.1847092 Effects of film thickness and lattice mismatch on strain states and magnetic properties of La 0.8 Ca 0.2 MnO 3 thin filmsThe evolution of three-dimensional strain states and crystallographic domain structures of epitaxial colossal magnetoresistive La 0.8 Ca 0.2 MnO 3 films have been studied as a function of film thickness and lattice mismatch with two types of ͑001͒ substrates, SrTiO 3 and LaAlO 3 . In-plane and out-of-plane lattice parameters and strain states of the films were measured directly using normal and grazing incidence x-ray diffraction techniques. The unit cell volume of the films is not conserved, and it exhibits a substrate-dependent variation with film thickness. Films grown on SrTiO 3 substrates with thickness up to ϳ250 Å are strained coherently with a pure (001) T orientation normal to the surface. In contrast, films as thin as 100 Å grown on LaAlO 3 show partial relaxation with a (110) T texture. While thinner films have smoother surfaces and higher crystalline quality, strain relaxation in thicker films leads to mixed (001) T and (110) T textures, mosaic spread, and surface roughening. The magnetic and electrical transport properties, particularly Curie and peak resistivity temperatures, also show systematic variations with respect to film thickness.

We report on the gigahertz radio frequency (RF) performance of chemical vapor deposited (CVD) monolayer MoS2 field-effect transistors (FETs). Initial DC characterizations of fabricated MoS2 FETs yielded current densities exceeding 200 μA/μm and maximum transconductance of 38 μS/μm. A contact resistance corrected low-field mobility of 55 cm(2)/(V s) was achieved. Radio frequency FETs were fabricated in the ground-signal-ground (GSG) layout, and standard de-embedding techniques were applied. Operating at the peak transconductance, we obtain short-circuit current-gain intrinsic cutoff frequency, fT, of 6.7 GHz and maximum intrinsic oscillation frequency, fmax, of 5.3 GHz for a device with a gate length of 250 nm. The MoS2 device afforded an extrinsic voltage gain Av of 6 dB at 100 MHz with voltage amplification until 3 GHz. With the as-measured frequency performance of CVD MoS2, we provide the first demonstration of a common-source (CS) amplifier with voltage gain of 14 dB and an active frequency mixer with conversion gain of -15 dB. Our results of gigahertz frequency performance as well as analog circuit operation show that large area CVD MoS2 may be suitable for industrial-scale electronic applications.

We report the effect of both miscut angle (α) and miscut direction (β) of vicinal substrates on the epitaxial growth and domain structure of isotropic metallic oxide SrRuO3 thin films. The thin films have been grown on vicinal (001) SrTiO3 substrates with α up to 4.1° and β up to 37° away from the in-plane [010] axis. Single-crystal epitaxial (110)o SrRuO3 thin films were obtained on vicinal SrTiO3 substrates with a large miscut angle (α=1.9°, 2.1°, and 4.1°) and miscut direction close to the [010] axis. Decreasing the substrate miscut angle or aligning the miscut direction close to the [110] axis (β=45°) resulted in an increase of 90° domains in the plane. The films grown on vicinal substrates displayed a significant improvement in crystalline quality and in-plane epitaxial alignment as compared to the films grown on exact (001) SrTiO3 substrates. Atomic force microscopy revealed that the growth mechanism changed from two-dimensional nucleation to step flow growth as the miscut angle increased.

Magnetic anisotropy of La0.8Ca0.2MnO3 (LCMO) epitaxial thin films grown on (001) SrTiO3 and LaAlO3 a substrates exhibits strong correlation with substrate-induced strain states as determined by normal and grazing incidence x-ray diffraction. In a 250 Å thick LCMO (001)T film grown on SrTiO3 substrate, an in-plane biaxial magnetic anisotropy is observed, and it is accompanied by a substrate-induced in-plane biaxial tensile strain. In contrast, the observed magnetic easy axis for a 250 Å (110)T film grown on LaAlO3 substrate is perpendicular to the film plane, and the corresponding in-plane strain is biaxial compressive. In both cases the magnetic easy axes are along the crystallographic directions under tensile strain, indicating the presence of a positive magnetostriction. In thicker films (∼4000 Å) grown on both substrates that are nearly strain relaxed, the magnetic easy axis lies in the film plane along the [110] direction of the (001) substrate.

Single domain epitaxial (110) films of SrRuO3 exhibit uniaxial magnetic anisotropy instead of the biaxial anisotropy observed in the bulk material. The magnetic easy axis for the film is along the orthorhombic [010] direction below TC, and it rotates toward the [110] perpendicular direction as temperature decreases. The [100] direction, which is also magnetically “easy” in the bulk, becomes “hard” in the film. X-ray diffraction experiments show that this unique transformation of magnetic anisotropy is related to a distortion from the bulk orthorhombic lattice into a triclinic structure in the epitaxial film, such that the lattice along the [010] direction expands while its [100] counterpart contracts. The distortion appears to arise from rotation and tilt of RuO6 octahedra. The finding indicates that the magnetic anisotropy in epitaxial SrRuO3 films is rooted in the crystalline anisotropy influenced by strong spin–orbit interactions.

Mechanically flexible integrated circuits (ICs) have gained increasing attention in recent years with emerging markets in portable electronics. Although a number of thin-film-transistor (TFT) IC solutions have been reported, challenges still remain for the fabrication of inexpensive, high-performance flexible devices. We report a simple and straightforward solution: mechanically exfoliating a thin Si film containing ICs. Transistors and circuits can be prefabricated on bulk silicon wafer with the conventional complementary metal-oxide-semiconductor (CMOS) process flow without additional temperature or process limitations. The short channel MOSFETs exhibit similar electrical performance before and after exfoliation. This exfoliation process also provides a fast and economical approach to producing thinned silicon wafers, which is a key enabler for three-dimensional (3D) silicon integration based on Through Silicon Vias (TSVs).