Research Article Controlling Terahertz Surface Plasmon Properties on a Periodically Structured Silicon Surface Gagan Kumar Department of Physics, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India Correspondence should be addressed to Gagan Kumar; gk@iitg.ernet.in Received 31 October 2014; Revised 15 January 2015; Accepted 22 January 2015 Academic Editor: Alan C. Samuels Copyright © 2015 Gagan Kumar. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te paper presents experimental and numerical investigations on the terahertz (THz) surface plasmon propagation in a periodically patterned doped silicon substrate. Silicon substrates are periodically patterned with 2D array of vertical structures forming a plasmonic waveguide. Te waveguide confgurations are found to support resonant surface modes at certain frequencies which can occur anywhere depending on the structural parameters. Te 2D pattern of vertical structures is observed to afect the THz surface plasmon propagation along the waveguide confguration. Te periodicities are changed in both directions to examine the change in amplitude and cut-of frequencies of the resonant surface modes. Te results are confrmed independently through fnite element method based numerical simulations and compared with theory. Te present study should fnd applications in facilitating the development of futuristic ultrahigh speed networks and devices operating at the terahertz frequencies. 1. Introduction Recent years have witnessed signifcant developments in the feld of plasmonic metamaterials. Metamaterials are the artifcially designed subwavelength scale structures that have the ability to alter electromagnetic radiation propagation in a controlled fashion [1–7]. Te artifcially designed struc- tures have been shown to guide and manipulate surface electromagnetic waves whose properties can be controlled with structural parameters [8, 9]. Te guided wave devices utilizing plasmonic metamaterials have led to several appli- cations which include nanoimaging [10], nanoscale photonic components [11, 12], slow light systems [13], and biosensing [14–16]. Tere has been immense interest in developing guided wave components which can operate at terahertz frequencies. Terahertz frequency regime of the electromag- netic spectrum has the potential to signifcantly improve the efciency and speed of the devices [17, 18]. In this direction, plasmonic metamaterials have been investigated to play an important role, and guided wave components and devices operating at terahertz frequencies have been developed [19– 21]. Te metals have been favorable choice for this purpose as they exhibit negligible dielectric and ohmic losses [22]. Williams et al. have demonstrated that a two-dimensional array of groove pattern with metal coating can support highly confned terahertz surface modes [23]. Te metal coating is considerably thick (more than skin depth) to reduce the propagation losses. Zhu et al. also later on showed that when a thin metal sheet of stainless steel is periodically patterned with the one-dimensional array of apertures, then it supports high confned terahertz surface modes at certain frequencies which can be defned by the geometrical parameters of the apertures [24]. Subsequently, a signifcant amount of work has been noticed in this direction with diferent shapes of the metallic corrugations [25–29]. It is important to mention that these experimental investigations on guiding surface electromagnetic waves are inspired by Pendry’s seminal work on plasmonic metamaterials [30, 31]. In spite of an extensive research work in the feld of plasmonic metamaterials using metals, we have not been able to achieve active waveguide components such as mod- ulators, ultrafast switches, flters, and active resonators. Tis is because of the difculty in tuning the properties of the metal based waveguides. In order to overcome this issue, recently Kumar et al. demonstrate the planar plasmonic terahertz waveguides based on heavily doped silicon [32]. Tese waveguides can be more readily fabricated using photolithographic techniques in a clean room and properties Hindawi Publishing Corporation Journal of Spectroscopy Volume 2015, Article ID 543985, 8 pages http://dx.doi.org/10.1155/2015/543985