We report the fabrication and characterization results of a simple and low-cost pH sensor fabricated using a graphite pencil to define a working electrode and silver paste to define a reference electrode on scotch tape. The sensor operation is based on potentiometric measurement and thereby insensitive to fabrication variations in shape of the electrode unlike amperometric and chemiresistive measurement techniques. The substrate of the disposable sensor is prepared by pasting scotch tape atop a piece of chart paper, and two types of sensors fabricated with 6B and 2B graphite pencils are tested with three solutions with different pH values. The sensor functions as a passive sensing tag without requiring any external power or stimulus, and the measured sensitivities of the pH sensors fabricated using 2B and 6B pencil carbon electrodes (PCEs) are −4.54mV/pH and −4.09mV/pH respectively. Index Terms-pH sensor, pencil carbon electrode (PCE), potentiometry, flexible sensor
Wavelength scale photonic, high-quality factor (Q-factor), cavities are crucial for enhancing light- matter interaction. Such on-chip hybrid devices could potentially provide a route towards scalable quantum technologies with color defects in diamond. A variety of designs for photonic crystal cavities have been proposed; however, the challenging and multi-step fabrication processes required for such designs limit the experimentally observed Q-factors in addition to significant radiation loss. One possible way to minimize the radiation loss in a one-dimensional (1-D) photonic crystal cavity is by introducing a so-called Gaussian defect region around the cavity. In this work, we propose a versatile approach to designing a Gaussian defect region by changing the lattice parameter in a 1-D photonic crystal. Further, to circumvent the problem of creating freestanding cavities for achieving high-Q factor in a 1-D photonic crystal cavity, we propose a novel hybrid diamond-titanium dioxide (TiO2) based materials for color defects in diamond, in particular the nitrogen-vacancy (NV−) center. Our proposed mechanically stable and high-Q cavity could be crucial for on-chip integration of different nanophotonic components for chip-scale photonic devices. We show via simulations that Q-factor > 105 can be achieved with the device.
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