Multifunctional Nanosheets for Electromagnetic Interference Shielding and Infrared Detection

We report our recent results on developing multi-functional materials for electromagnetic interference (EMI) shielding and infrared detection. The work is motivated by the increasing use of devices that saturate the environment with radio-frequency (RF) electromagnetic radiation. RF radiation can disrupt the operation of electronic components, including sources and detectors of infrared (IR) radiation that are widely used in communication systems and night-vision cameras. Our work focuses on integrating a front-end shield of radio waves with an optoelectronic IR detector in a sheet that can conform to non-planar surfaces, such as windows on an aircraft and domes in IR cameras. In our design, a single-crystalline and highly doped III-As nanomembrane (NM) serves as the IR-transparent shield of EMI. The optoelectronic IR detector is based on black phosphorous (bP). Here, we present our effort in the characterization of IR transmittance and shielding effectiveness of III-As NMs. In addition, we show preliminary results on the integration of bP IR absorbers with III-As NMs. We fabricate III-As NMs with a thickness of a few hundred nanometers and a nominal doping level ranging between 10¹⁹ and 10²⁰ cm^-3. The NMs are grown by molecular beam epitaxy onto GaAs substrates coated with lattice-matched sacrificial layers or etch stop layers (e.g., AlAs or AlGaAs). Freestanding NMs are isolated either by selective etching of the sacrificial layer or by removal of the growth substrate and etch-stop layer. After transfer to a new host (e.g., Kapton film), we measure the optical transmittance of the NMs above 1 µm. We extract the shielding effectiveness of the NM from measured s-parameters of frequencies ranging from 60 to 90 GHz. The extracted shield effectiveness is benchmarked against theoretical calculations to identify shielding mechanisms in the NM. Theoretical calculations use measured DC conductivities of the released NMs. We identify primary reflection (i.e., reflection of the RF radiation by the front surface of the NMs) as the dominant shielding mechanism in NMs. In addition, we quantify the effect of multiple internal reflections on shielding effectiveness.<br/> <br/><i>This research was supported by an appointment to the Intelligence Community Postdoctoral Research Fellowship Program at </i>University of New Mexico<i> administered by Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the U.S. Department of Energy and the Office of the Director of National Intelligence (ODNI). This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the US Department of Energy (DOE) Office of Science by Los Alamos National Laboratory (Contract 89233218CNA000001) and Sandia National Laboratories (Contract DE-NA-0003525).</i>