Direct Laser Writing of Microscale Metal Oxide Gas Sensors from Liquid Precursors.

Fabrication and processing approaches that facilitate the ease of patterning and the integration of nanomaterials into sensor platforms are of significant utility and interest. In this work, we report the use of laser-induced thermal voxels (LITV) to fabricate microscale, planar gas sensors directly from solutions of metal salts. LITV offers a facile platform to directly integrate nanocrystalline metal oxide and mixed metal oxide materials onto heating platforms, with access to a wide variety of compositions and morphologies including many transition metals and noble metals. The unique patterning and synthesis flexibility of LITV enable the fabrication of chemically and spatially tailorable microscale sensing devices. We investigate the sensing performance of a representative set of n-type and p-type LITV-deposited metal oxides and their mixtures (CuO, NiO, CuO/ZnO, and Fe2O3/Pt) in response to reducing and oxidizing gases (H2S, NO2, NH3, ethanol, and acetone). These materials show a broad range of sensitivities and notably a strong response of NiO to ethanol and acetone (407 and 301% R/R0 at 250 °C, respectively), along with a 5- to 20-fold sensitivity enhancement for CuO/ZnO to all gases measured over pure CuO, highlighting the opportunities of LITV for the creation of mixed-material microscale sensors.

Nondestructive Measurements of the Mechanical and Structural Properties of Nanostructured Metalattices.

Metalattices are artificial 3D solids, periodic on sub-100 nm length scales, that enable the functional properties of materials to be tuned. However, because of their complex structure, predicting and characterizing their properties is challenging. Here we demonstrate the first nondestructive measurements of the mechanical and structural properties of metalattices with feature sizes down to 14 nm. By monitoring the time-dependent diffraction of short wavelength light from laser-excited acoustic waves in the metalattices, we extract their acoustic dispersion, Young's modulus, filling fraction, and thicknesses. Our measurements are in excellent agreement with macroscopic predictions and potentially destructive techniques such as nanoindentation and scanning electron microscopy, with increased accuracy over larger areas. This is interesting because the transport properties of these metalattices do not obey bulk predictions. Finally, this approach is the only way to validate the filling fraction of metalattices over macroscopic areas. These combined capabilities can enable accurate synthesis of nanoenhanced materials.