We present a study on the growth and characterization of high-quality single-layer MoS 2 with a single orientation, i.e. without the presence of mirror domains. This single orientation of the MoS 2 layer is established by means of x-ray photoelectron diffraction. The high quality is evidenced by combining scanning tunneling microscopy with x-ray photoelectron spectroscopy measurements.Spin-and angle-resolved photoemission experiments performed on the sample revealed complete spin-polarization of the valence band states near the K and -K points of the Brillouin zone. These findings open up the possibility to exploit the spin and valley degrees of freedom for encoding and processing information in devices that are based on epitaxially grown materials.
The characterization of thermal and elastic properties at the nanometer length scale is fundamental for the implementation of materials in nanotechnology. Here, we show how four-wave mixing of extreme ultraviolet ultrashort pulses allows for high-precision measurements of nanoscale elasticity in thin suspended silicon nitride membranes through the generation and detection of Lamb waves at 10's of nm wavelengths. Our approach is contact-free and nondestructive, and it provides an estimate of both shear and longitudinal elastic moduli, without the need of nanopatterning. The data provide important information on nanoscale thermal transport and reveal a heat carrier behavior compatible with the diffusive regime. By controlling the fluence of the free-electron laser excitation pulses, we study the dependence of elastic moduli and the thermal relaxation rate on the sample temperature, which increases by hundreds of kelvins due to radiation absorption. At the same time, the experimental data allow us to estimate the characteristic time of phonon attenuation. The capability of determining this parameter, as well as the elastic moduli, at nanoscale wavelengths is a key aspect for the fundamental understanding of solids without translational invariance.
Ultrafast
control of magnetization on the nanometer length scale,
in particular all-optical switching, is key to putting ultrafast magnetism
on the path toward future technological application in data storage
technology. However, magnetization manipulation with light on this
length scale is challenging due to the wavelength limitations of optical
radiation. Here, we excite transient magnetic gratings in a GdFe alloy
with a periodicity of 87 nm by the interference of two coherent femtosecond
light pulses in the extreme ultraviolet spectral range. The subsequent
ultrafast evolution of the magnetization pattern is probed by diffraction
of a third, time-delayed pulse tuned to the Gd N-edge
at a wavelength of 8.3 nm. By examining the simultaneously recorded
first and second order diffractions and by performing reference real-space
measurements with a wide-field magneto-optical microscope with femtosecond
time resolution, we can conclusively demonstrate the ultrafast emergence
of all-optical switching on the nanometer length scale.
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