A robust plasmonic semiconductor-based Mach-Zehnder interferometer (MZI), which consists of a semiconductor layer with a microslit flanked by two identical microgrooves, is proposed and investigated for the terahertz sensing. The microgrooves reflect the surface plasmon polariton waves toward the microslit, where they interfere with the transmitted terahertz wave. The interference pattern is determined by the permittivities of the sensing material and semiconductor (i.e., temperature dependent), making the structure useful for the refractive index (RI) and temperature detection. A quantitative theoretical model is also developed for performance prediction and validated with a finite element method. The numerical results show that the Mach-Zehnder interferometer sensor possesses an RI sensitivity as high as 140000  nm/RIU (or 0.42  THz/RIU) and a relative intensity sensitivity of 1200%RIU^-1. In addition, a temperature sensitivity of 1470  nm/K (or 4.7×10^-3 THz/K) is determined. Theoretical calculations indicate that the further improvement in sensing performance is still possible through optimization of the structure. The proposed sensing scheme may pave the way for applications in terahertz sensing and integrated terahertz circuits.

A novel dimer, tetraethyl 2,2',3,3'-tetramethyl-1,1',2,2'-tetrahydro-4H, 4 'H-2 , 2 ' -b i p y r r o l y l -5 , 5 , 5 ' , 5 ' -tetracarboxylate, has been isolated as an impurity (0.4% yield) from a Knorr reaction for the synthesis of ethyl 3,5-dimethylpyrrole-2-carboxylate from 2,4-pentanedione and diethyl oximinomalonate in a dissolving zinc reduction. The solid-state structure of this novel dimer was determined by X-ray crystallography. Knorr reactions typically rely upon the requisite pyrrole being the only water-insoluble crystalline material present in the reaction mixture, and so work-up and purification procedures for Knorr reactions should be monitored carefully given the water-insolubility of this dimer. Investigations regarding mechanistic implications and reductive dimerization are underway.

An original asymptotic method is developed and used to find closed-form approximations to the symmetric thin-film three- and multi-layer plasmonic dispersion equations. Closed-form analysis of three-layer metal-insulator-metal (MIM: "M" is metal and "I" is insulator) and IMI devices shows a complementary physics underpinning their properties. Analysis of multi-layer symmetric devices, considered for a seven-layer MIMIMIM example, uncovers a remarkable departure from the physics governing MIM and IMI features. Multi-layer propagation length and attenuation are determined by proximity, in the space of cladding thickness and wavelength, to singularities that exist in the limit of vanishing imaginary part of the cladding dielectric constant. Exploitation of this phenomenon will expand the development of a broader range of thin-film applications in optoelectronics.

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