Molecules intercalating two-dimensional (2D) materials form complex structures that have been mostly characterized by spatially averaged techniques. Here we use aberration-corrected scanning transmission electron microscopy and densityfunctional-theory (DFT) calculations to study the atomic structure of bilayer graphene (BLG) and few-layer graphene (FLG) intercalated with FeCl3. In BLG we discover two distinct intercalated structures that we identify as monolayer-FeCl3 and monolayer-FeCl2. The two structures are separated by atomically sharp boundaries and induce large but different free-carrier densities in the graphene layers, 7.1 × 10 cm -2 and 7.8 × 10 cm -2 respectively. In FLG, we observe multiple FeCl3 layers stacked in a variety of possible configurations with respect to one another. Finally, we find that the microscope's electron beam can convert the FeCl3 monolayer into FeOCl monolayers in a rectangular lattice. These results reveal the need for a combination of atomically-resolved microscopy, spectroscopy, and DFT calculations to identify intercalated structures and study their properties.
Superatomic molecular orbitals (SAMO) in C 60 are ideal building blocks for functional nanostructures. However, imaging them spatially in the gas phase has been unsuccessful. It is found experimentally that if C 60 is excited by an 800-nm laser, the photoelectron casts an anisotropic velocity image, but the image becomes isotropic if excited at a 400-nm wavelength. This diffuse image difference has been attributed to electron thermal ionization, but more recent experiments (800 nm) reveal a clear non-diffuse image superimposed on the diffuse image, whose origin remains a mystery. Here we show that the non-diffuse anisotropic image is the precursor of the f SAMO.We predict that four 800-nm photons can directly access the 1f SAMO, and with one more photon, can image the orbital, with the photoelectron angular distribution having two maxima at 0 • and 180 • and two humps separated by 56.5 • . Since two 400-nm photons only resonantly excite the spherical 1s SAMO and four 800-nm photon excite the anisotropic 1f SAMO, our finding gives a natural explanation of the non-diffuse image difference, complementing the thermal scenario.
Phenanthrenequinone doped poly(methyl methacrylate) is a well-known holographic polymer used in many applications. It is important to consider the refractive index modulation (Δn) when designing a phase grating, as it heavily influences the diffraction efficiency. However, due to the behavior of the electric susceptibility in this material, the Δn will be different at varying reconstructed wavelengths. Here, we report on the observation of the difference in this modulation for various wavelengths. We develop a model for a two-level approximation of the electric susceptibility, based on the absorption spectrum of the material, to estimate the read wavelength dependence of the modulation for a given sample, and find our results to be in good agreement with this model.
A point source interferometer (PSI) is a device where atoms are split and recombined by applying a temporal sequence of Raman pulses during the expansion of a cloud of cold atoms behaving approximately as a point source. The PSI can work as a sensitive multi-axes gyroscope that can automatically filter out the signal from accelerations. The phase shift arising from the rotations is proportional to the momentum transferred to each atom from the Raman pulses. Therefore, by increasing the momentum transfer, it should be possible to enhance the sensitivity of the PSI. Here, we investigate the degree of enhancement in sensitivity that could be achieved by augmenting the PSI with large momentum transfer (LMT) employing a sequence of many Raman pulses with alternating directions. We analyze how factors such as Doppler detuning, spontaneous emission, and the finite initial size of the atomic cloud compromise the advantage of LMT and how to find the optimal momentum transfer under these limitations, with both the semi-classical model and a model under which the motion of the center of mass of each atom is described quantum mechanically. We identify a set of realistic parameters for which LMT can improve the PSI by a factor of nearly 40.
We realized superluminal Raman lasing via electromagnetically induced transparency. Compared to a conventional Raman laser with similar operating parameters, the spectral sensitivity of this approach is demonstrated to be enhanced by a factor of ~15.4.
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