Effective mechanical properties of multilayer nano-heterostructures

Two-dimensional and quasi-two-dimensional materials are important nanostructures because of their exciting electronic, optical, thermal, chemical and mechanical properties. However, a single-layer nanomaterial may not possess a particular property adequately, or multiple desired properties simultaneously. Recently a new trend has emerged to develop nano-heterostructures by assembling multiple monolayers of different nanostructures to achieve various tunable desired properties simultaneously. For example, transition metal dichalcogenides such as MoS2 show promising electronic and piezoelectric properties, but their low mechanical strength is a constraint for practical applications. This barrier can be mitigated by considering graphene-MoS2 heterostructure, as graphene possesses strong mechanical properties. We have developed efficient closed-form expressions for the equivalent elastic properties of such multi-layer hexagonal nano-hetrostructures. Based on these physics-based analytical formulae, mechanical properties are investigated for different heterostructures such as graphene-MoS2, graphene-hBN, graphene-stanene and stanene-MoS2. The proposed formulae will enable efficient characterization of mechanical properties in developing a wide range of application-specific nano-heterostructures

Structure of a nonstoichiometric chromium silver sulfide

Ag0.37Crr21S2, rhombohedral, R3m, a = 3.4325 (1), c =- 37.190 (1) A (in hexagonal setting), Z = 6. The structure was determinined using singlecrystalX-ray data from 908 independent reflections; the least-squares refinement of the positional and thermal parameters and the population parameters ofAg and Cr led to a final R e = 0.102. It is a layer compound with hexagonal layers of atoms. Layers of S form a close packing of the type (hcch) 3, forming CrS 2 sandwiches with Cr in octahedral coordination. The gaps between these sandwiches are alternately occupied by Cr (2 x 0.21 Cr per site), also in octahedral coordination, and by Ag in tetrahedral holes. Both tetrahedral holes are partly occupied by 0.37 Ag; Ag is distributed over several sites within the S tetrahedra

The determination of the incommensurately modulated structure of niobium tetratelluride

A complete analysis of the modulated structure of NbTe4 is presented, using the newly developed formalism of de Wolff [Acta Cryst. (1974). A30, 777-785] and Yamamoto [Acta Cryst. (1982). A38, 87-92]. The diffraction pattern was measured at room temperature, including first-order and second-order satellites. The superspace group of the complete structure is |'l/Pa/mcc,, 1 T I 1" The final R~ value is 0.095 (0.044 for main reflections only), for a total of 3894 unique reflections (923 main reflections). The average structure found previously [Selte & Kjekshus (1964). Acta Chem. Scand. 18, 690-696] is confirmed. In addition, the modulation wave is determined; it resides mainly on the Nb atoms, which have an amplitude of 0.33/~. The results show that the displacements are correlated in such a way as to keep the Te-Te bonding distance constant and to minimize the variation in the shortest Nb-Te distance. It is found possible to refine at least up to the fifth harmonic in the modulation wave. However, the values found for higher harmonics do not describe the real modulation wave, but assume values to account for the variation in intensities due to experimental errors. Therefore, only the amplitudes up to the second order are considered to be reliable

High-Sensitivity LC-MS/MS Quantification of Peptides and Proteins in Complex Biological Samples:The Impact of Enzymatic Digestion and Internal Standard Selection on Method Performance

<p>Two important aspects of peptide and protein quantification by LC-MS/MS, the enzymatic digestion step and the internal standardization approach, were systematically investigated with a small protein, salmon calcitonin, which could be analyzed both without and with digestion. Quantification of undigested salmon calcitonin, after solid-phase extraction from plasma, resulted in a lower limit of quantification of 10 pg/mL, while introduction of a tryptic digestion step, followed by quantification of a signature peptide, increased this to 50 pg/mL. The sensitivity was reduced by interferences in the selected reaction monitoring (SRM) transition of the signature peptide due to the increase in sample complexity caused by the digestion and a less selective SRM transition of the signature peptide as compared to undigested salmon calcitonin. Eight internal standardization approaches were compared with respect to accuracy and precision in workflows with and without digestion. Analogue and stable-isotope-labeled (SIL) internal standards were evaluated including an in-house created O-18-labeled peptide, a cleavable SIL peptide, and an internal standard created by differential derivatization of the signature peptide. We conclude that the best internal standard for the workflows both with and without digestion was the SIL form of the analyte, although the use of several SIL signature peptides and a differentially derivatized signature peptide also resulted in methods with performances which meet the FDA guidelines.</p>