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Actuation of thin polymeric films via electron irradiation is a promising avenue to realize devices based on strain engineered two-dimensional materials. Complex strain profiles demand a deep understanding of the mechanics of the polymeric layer under electron irradiation; in this article, we report a detailed investigation on electron-induced stress on a poly-methyl-methacrylate (PMMA) thin film material. After an assessment of stress values using a method based on dielectric cantilevers, we directly investigate the lateral shrinkage of PMMA patterns on epitaxial graphene, which reveals a universal behavior, independent of the electron acceleration energy. By knowing the stress-strain curve, we finally estimate an effective Young's modulus of PMMA on top of graphene, which is a relevant parameter for PMMA-based electron-beam lithography and strain engineering applications. Published under license by AIP Publishing.

Conductive metallic contacts can significantly affect the operation of field effect transistors fabricated starting from semiconductor nanowires deposited on a dielectric substrate. Screening effects can also lead to systematic errors in the estimates of transport parameters obtained on the basis of simple uniform capacitive models. We study the role of contacts in both back- and lateral-gate transistor geometries and provide rules of thumbs to predict screening effects in real devices. Additionally, we show how the contacts influence charge density profiles within the wire, focusing in particular on their evolution when transistors nonlinear properties are addressed.

We explore the use of quantum cascade structures as amplifiers for terahertz radiation. For this purpose, two section devices were fabricated, in which the output from a nu similar to 2.3 THz laser section is amplified in a subsequent stage. For relatively short devices we obtain an amplification of 1.5x, in good agreement with the calculated level. Based on these results we predict that amplifications of up to 13 dB could be obtained for such structures using increased amplifier lengths of a few millimeters.(C) 2007 American Institute of Physics.

The conduction‐band discontinuity in Zn1−xCdxSe/ZnSe multiple‐quantum‐well structures grown by molecular‐beam epitaxy and pseudomorphically strained to ZnSe were evaluated via electrical and intersubband absorption measurements for 0.23≤x≤0.33. A variation between 165±14 and 253±14 meV is found in the cadmium concentrations range analyzed. Our results are consistent with a valence‐band contribution to the band‐gap difference Qv=0.33±0.03 in the alloy series.