Quasi-one-dimensional (quasi-1D) materials enjoy growing interest due to their unusual physical properties and promise for miniature electronic devices. However, the mechanical exfoliation of quasi-1D materials into thin flakes and nanoribbons received considerably less attention from researchers than the exfoliation of conventional layered crystals. In this study, we investigated the micromechanical exfoliation of representative quasi-1D crystals, TiS3 whiskers, and demonstrate that they typically split into narrow nanoribbons with very smooth, straight edges and clear signatures of 1D TiS3 chains. Theoretical calculations show that the energies required for breaking weak interactions between the two-dimensional (2D) layers and between 1D chains within the layers are comparable and, in turn, are considerably lower than those required for breaking the covalent bonds within the chains. We also emulated macroscopic exfoliation experiments on the nanoscale by applying a local shear force to TiS3 crystals in different crystallographic directions using a tip of an atomic force microscopy (AFM) probe. In the AFM experiments, it was possible to slide the 2D TiS3 layers relative to each other as well as to remove selected 1D chains from the layers. We systematically studied the exfoliated TiS3 crystals by Raman spectroscopy and identified the Raman peaks whose spectral positions were most dependent on the crystals’ thickness. These results could be used to distinguish between TiS3 crystals with thickness ranging from one to about seven monolayers. The conclusions established in this study for the exfoliated TiS3 crystals can be extended to a variety of transition metal trichalcogenide materials as well as other quasi-1D crystals. The possibility of exfoliation of TiS3 into narrow (few-nm wide) crystals with smooth edges could be important for the future realization of miniature device channels with reduced edge scattering of charge carriers.

The on-demand generation and separation of entangled photon pairs are key components of quantum information processing in quantum optics [1][2][3] . In an electronic analogue, the decomposition of electron pairs represents an essential building block for using the quantum state of ballistic electrons in electron quantum optics [4][5][6][7] . The scattering of electrons has been used to probe the particle statistics of stochastic sources in Hanbury Brown and Twiss experiments 8,9 and the recent advent of on-demand sources further offers the possibility to achieve indistinguishability between multiple sources in Hong-Ou-Mandel experiments [10][11][12][13][14][15] . Cooper pairs impinging stochastically at a mesoscopic beamsplitter have been successfully partitioned, as verified by measuring the coincidence of arrival [16][17][18][19][20][21] . Here, we demonstrate the splitting of electron pairs generated on demand. Coincidence correlation measurements allow the reconstruction of the full counting statistics, revealing regimes of statistically independent, distinguishable or correlated partitioning, and have been envisioned as a source of information on the quantum state of the electron pair [22][23][24][25][26] . The high pair-splitting fidelity opens a path to future on-demand generation of spin-entangled electron pairs from a suitably prepared two-electron quantum-dot ground state.The few-electron source is based on a single-parameter non-adiabatic quantized charge pump [27][28][29] , which enables the deterministic generation of single electrons and electron pairs with tunable emission energy 12,30 . Non-equilibrium electrons propagate along the edge of a quantum Hall sample with minimal inelastic scattering. The device and measurement set-up are presented in Fig. 1. An energy-selective detector barrier splits the incoming beam of electrons into two detector paths. The coincidence of arrival of electrons in the two detector channels leads to positive correlation between the time-dependent current signals. These correlations are inferred from a measurement of the zero-frequency cross-correlation shot noise. Although an oscillator-controlled electron source is noiseless 31 , the splitting of electron pairs generates partitioning noise and enables tomography of the probability distribution for the partitioning outcomes within each emission cycle.The generation and energy-selective detection of on-demand non-equilibrium electrons was demonstrated with the electron source configured to emit one electron with charge e and repetition frequency f of 280 MHz. Figure 2 shows the transmitted current I T as a function of barrier energy. The maximum level of I T is 2% below the emission current I P = 1 ef due to residual inelastic scattering events on the 2-µm-long path to the barrier (the emission error of the source is <1 × 10 −4). For energies greater than 57 meV, the current is pinched off as all of the emitted electrons are reflected at the beamsplitter. The emission energy is defined by the exit barrier height and ca...

Abstract:We describe the application of scattering-type near-field optical microscopy to characterize various semiconducting materials using the electron storage ring Metrology Light Source (MLS) as a broadband synchrotron radiation source. For verifying high-resolution imaging and nano-FTIR spectroscopy we performed scans across nanoscale Si-based surface structures. The obtained results demonstrate that a spatial resolution below 40 nm can be achieved, despite the use of a radiation source with an extremely broad emission spectrum. This approach allows not only for the collection of optical information but also enables the acquisition of nearfield spectral data in the mid-infrared range. The high sensitivity for spectroscopic material discrimination using synchrotron radiation is presented by recording near-field spectra from thin films composed of different materials used in semiconductor technology, such as SiO 2 , SiC, Si x N y , and TiO 2 . ©2014 Optical Society of AmericaOCIS codes: (120.0120) Instrumentation, measurement, and metrology; (180.4243) Near-field microscopy; (240.0240) Optics at surfaces; (300.0300) Spectroscopy; (310.6860) Thin films, optical properties. 1248-1262 (2014). 5. S. Kawata and Y. Inouye, "Scanning probe optical microscopy using a metallic probe tip," Ultramicroscopy 57(2-3), 313-317 (1995). 6. F. Zenhausern, Y. Martin, and H. K. Wickramasinghe, "Scanning interferometric apertureless microscopy: References and linksOptical imaging at 10 angstrom resolution," Science 269(5227), 1083-1085 (1995). 7. R. Bachelot, P. Gleyzes, and A. C. Boccara, "Near-field optical microscope based on local perturbation of a diffraction spot," Opt. Lett. 20(18), 1924-1926 (1995). 8. B. Knoll and F. Keilmann, "Near-field probing of vibrational absorption for chemical microscopy," Nature 399(6732), 134-137 (1999 Helm, "Anisotropy contrast in phonon-enhanced apertureless near-field microscopy using a free-electron laser," Phys. Rev. Lett.

Infrared scattering scanning near-field optical microscopy (IR s-SNOM) provides for spectroscopic imaging with nanometer spatial resolution, yet full spatio-spectral imaging is constrained by long measurement times. Here, we demonstrate the application of compressed sensing algorithms to achieve hyperspectral FTIR-based nano-imaging at an order of magnitude faster imaging speed to achieve the same spectral content compared to conventional approaches. At the example of the spectroscopy of a single vibrational resonance, we discuss the relationship of prior knowledge of sparseness of the employed Fourier base functions and sub-sampling. Compressed sensing nano-FTIR spectroscopy promises both rapid and sensitive chemical nano-imaging which is highly relevant in academic and industrial settings for fundamental and applied nano- and bio-materials research.

Nanoscale plasmonic phenomena observed in single and bi-layers of molybdenum disulfide (MoS(2)) on silicon dioxide (SiO(2)) are reported. A scattering type scanning near-field optical microscope (s-SNOM) with a broadband synchrotron radiation (SR) infrared source was used. We also present complementary optical mapping using tunable CO(2)-laser radiation. Specifically, there is a correlation of the topography of well-defined MoS(2) islands grown by chemical vapor deposition, as determined by atomic force microscopy, with the infrared (IR) signature of MoS(2). The influence of MoS(2) islands on the SiO(2) phonon resonance is discussed. The results reveal the plasmonic character of the MoS(2) structures and their interaction with the SiO(2) phonons leading to an enhancement of the hybridized surface plasmon-phonon mode. A theoretical analysis shows that, in the case of monolayer islands, the coupling of the MoS(2) optical plasmon mode to the SiO(2) surface phonons does not affect the infrared spectrum significantly. For two-layer MoS(2), the coupling of the extra inter-plane acoustic plasmon mode with the SiO(2) surface transverse phonon leads to a remarkable increase of the surface phonon peak at 794 cm(-1). This is in agreement with the experimental data. These results show the capability of the s-SNOM technique to study local multiple excitations in complex non-homogeneous structures.