The Relationships of Microscopic Evolution to Resistivity Variation of a FIB-Deposited Platinum Interconnector.

Depositing platinum (Pt) interconnectors during the sample preparation process via a focused ion beam (FIB) system is an inescapable procedure for in situ transmission electron microscopy (TEM) investigations. To achieve good electrical contact and avoid irreversible damage in practical samples, the microscopic evolution mechanism of FIB-deposited Pt interconnectors need a more comprehensive understanding, though it is known that its resistivity could be affected by thermal annealing. In this work, an electron-beam FIB-deposited Pt interconnector was studied by advanced spherical aberration (Cs)-corrected TEM combined with an in situ heating and biasing system to clarify the relationship of microscopic evolution to resistivity variation. During the heating process, the Pt interconnector underwent crystallization, organic matter decomposition, Pt nanocrystal growth, grain connection, and conductive path formation, which are combined actions to cause several orders of magnitude of resistivity reduction. The comprehensive understanding of the microscopic evolution of FIB-deposited Pt material is beneficial, not only for optimizing the resistance performance of Pt as an interconnector, but also for understanding the role of C impurities with metal materials. For the purpose of wiring, annealed electron-beam (EB)-deposited Pt material can be recommended for use as an interconnector in devices for research purposes.

Plan-view sample preparation of a buried nanodots array by FIB with accurate EDS positioning in thickness direction.

Recently, there are growing demands on focus ion beam (FIB) sample preparation technique in plan-view geometry because it can provide the in-plane microstructure information of thin film and allows direct correlations of the atomic structure via transmission electron microscopy with micrometer-scale property measurements. However, one main technical difficulty is to position the buried thin film accurately in a sandwich structure. In this paper, an on-line positioning method based on the thickness monitoring by EDS is introduced, where the intensities of the characteristic X-ray peaks from different layers are proportional to the relative thickness of them at the same acquisition conditions. A high density array of ∼100 nm squares BiFeO3 nanodots with ∼ 25 nm thickness grown on a 20 nm thick SrRuO3 bottom electrode and (001)-oriented SrTiO3 substrate is selected for demonstration. By monitoring the intensities of Pt-M, Sr-L, Ti-K, Ru-L, Fe-K and Bi-M peaks, the relative thickness of Pt protection layer, the BiFeO3, SrRuO3 and SrTiO3 can be obtained, which provide accurate position of the BFO nanodots array in the thickness direction. With these information, the cutting parameters are optimized and a high quality plan-view specimen of BFO nanodots array is prepared, which is confirmed by high resolution transmission electron microscopy. This positioning method should have a wide application for material science.

High Mobilities in Layered InSe Transistors with Indium-Encapsulation-Induced Surface Charge Doping.

Tunability and stability in the electrical properties of 2D semiconductors pave the way for their practical applications in logic devices. A robust layered indium selenide (InSe) field-effect transistor (FET) with superior controlled stability is demonstrated by depositing an indium (In) doping layer. The optimized InSe FETs deliver an unprecedented high electron mobility up to 3700 cm2 V-1 s-1 at room temperature, which can be retained with 60% after 1 month. Further insight into the evolution of the position of the Fermi level and the microscopic device structure with different In thicknesses demonstrates an enhanced electron-doping behavior at the In/InSe interface. Furthermore, the contact resistance is also improved through the In insertion between InSe and Au electrodes, which coincides with the analysis of the low-frequency noise. The carrier fluctuation is attributed to the dominance of the phonon scattering events, which agrees with the observation of the temperature-dependent mobility. Finally, the flexible functionalities of the logic-circuit applications, for instance, inverter and not-and (NAND)/not-or (NOR) gates, are determined with these surface-doping InSe FETs, which establish a paradigm for 2D-based materials to overcome the bottleneck in the development of electronic devices.

Formation and dispersion of organometal halide perovskite nanocrystals in various solvents.

The solvent-induced precipitation in a mixture of good and poor solvents was often used to synthesize organometal halide perovskite nanocrystals (OMHP NCs). Here we investigate the formation of OMHP NCs by using HBr based precursors in various solvents. Various emission colors and morphologies of perovskite NCs were obtained depending on the solvents used. The nanoplatelets with blue emission were produced for the low polar solvents, such as toluene, PhCl and EtOAc. The increase in polarity of poor solvents results in the red shift of emission of obtained NCs. The much more polar solvents like acetone and CH3CN lead to formation of CH3NH3PbBr3 NCs (MaPbBr3) with cubic phase. The dispersion behaviors of MaPbBr3 NCs in different solvents was also investigated. MaPbBr3 NCs can exist stably in most unpolar solvents. However, they will be dissolved in polar solvents, like acetone and acetonitrile, to give rise to a clear solution with red emission of Pb2+. By injecting this clear solution to unpolar solvents, OMHP NCs can be reproduced.