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Past research aimed at increasing the sensitivity of capacitive pressure sensors has mostly focused on developing dielectric layers with surface/porous structures or higher dielectric constants. However, such strategies have only been effective in improving sensitivities at low pressure ranges (e.g., up to 3 kPa). To overcome this well‐known obstacle, herein, a flexible hybrid‐response pressure sensor (HRPS) composed of an electrically conductive porous nanocomposite (PNC) laminated with an ultrathin dielectric layer is devised. Using a nickel foam template, the PNC is fabricated with carbon nanotubes (CNTs)‐doped Ecoflex to be 86% porous and electrically conductive. The PNC exhibits hybrid piezoresistive and piezocapacitive responses, resulting in significantly enhanced sensitivities (i.e., more than 400%) over wide pressure ranges, from 3.13 kPa−1 within 0–1 kPa to 0.43 kPa−1 within 30–50 kPa. The effect of the hybrid responses is differentiated from the effect of porosity or high dielectric constants by comparing the HRPS with its purely piezocapacitive counterparts. Fundamental understanding of the HRPS and the prediction of optimal CNT doping are achieved through simplified analytical models. The HRPS is able to measure pressures from as subtle as the temporal arterial pulse to as large as footsteps.

Much attention has been focused recently on the preparation of macroporous materials by templating with colloidal crystals. This interest stems from the important properties of such microstructures, which have a wide range of applications including sensors, catalysts, and photonic crystals. Various macroporous and mesoporous materials have been made via this process, including ceramics, [1±9] carbon, [10,11] chalcogenides, [12±14] NaCl, [3] polymers, [15±19] and silica±gold. [20] The extension of such a material patterning method to metals is particularly attractive, as metals with ordered microstructures exhibit unique optical, electrical, magnetic, and catalytic properties. For example, surface enhancement of Raman scattering in porous gold films has been demonstrated by Tessire et al. [21] In a recent study, Baumberg and coworkers reported the observation of confined plasmons in gold nanocavities. [22] Although the adaptation of the templating method to the preparation of porous metal films is limited, several strategies have been reported, including precipitation/chemical conversion, [23,24] direct penetration of metal nanocrystals, [25] electroless deposition, [26,27] and electrochemical reduction methods. [28] When monodispersed silica spheres are used as the sacrificial elements, annealing of the colloidal crystal is usually performed at high temperatures. This results in the formation of small necks between neighboring spheres, which makes the template stable during the material patterning process.[26±28] A complete filtration of metal into the free spaces of the template has been successfully demonstrated using these approaches, which result in macroporous metal films that are an exact replica of the sacrificial templates. In this communication we report for the first time the preparation of ordered arrays of hollow metal spheres by colloidal crystal templating. However, instead of using annealed silica colloidal crystals as templates, [26±28] we use polymer colloidal crystals. Moreover, the template is confined between two substrates in order to preserve its ordering in the material-patterning process, as described by Xia and coworkers. [29] We combine a seeded growth technique for metal coatings on isolated colloids in solution and the confined template-directed synthesis method for material patterning. The samples we obtain are were two-dimensional (2D) and three-dimensional (3D) ordered hollow silver spheres prepared by templating against the monolayer or the multilayer of hexagonal close packed polymer beads, respectively. The schematic procedure of our experiment is depicted in Figure 1. The starting material is an ordered colloidal crystal consisting of polystyrene (PS) beads, which was prepared using a modification of the micromolding method reported by Kim et al. [30] Specifically, a microchannel was first formed between two glass slides that were separated with two identical spacers. Upon dipping into a colloidal dispersion solution, the microchannel was spontaneously filled with the colloi...

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