Supplementary Figure S1. Characterization using X-ray diffraction (XRD). (a) Starting titanium (Ti) foil used for the synthesis (JCPDS No. 65-3362). (b) Oxidized Rutile titanium dioxide (TiO 2 ) obtained after heating Ti foil at 750 ºC for 8 hours (JCPDS No. 65-0191). (c) Sodium titanate nanowire arrays used as precursors synthesized on oxidized Ti foil; H denotes the Sodium Hexatitanate (Na 2 Ti 6 O 13 ) peaks (JCPDS No. 73-1398) and T denotes the Sodium Trititanate peaks (JCPDS No. 31-1329).
Supplementary Figure S2. Images of the sensor fabrication process. (a) BaTiO 3 nanowire arrays handled with tweezer with the images on the right showing the SEM of the top surface (scale bar, 10 µm) and the cross-section of the NW arrays (scale bar, 20 µm). (b) Fabrication process starting with the silver epoxy layer applied on borosilicate glass substrate (top left), followed by NW arrays placed on the silver epoxy (bottom left) and then solder film placed on top of the NW arrays and heated to enhance bonding with NWs (right).
Supplementary Figure S3. BaTiO 3 NW arrays between the two electrodes. (a) The crosssectional SEM image of the NWs between the bottom silver epoxy electrode and the top solder foil electrode (scale bar, 20 µm). (b) The SEM image of the NWs contact with the solder foil by adherence from heating during fabrication process (scale bar, 5 µm) with the inset clearly showing the contact (scale bar, 1 µm). (c) Photographic image of the sensor structure held upside down with tweezers to show the solder foil adhered to the NWs after the completion of heating during the sensor fabrication process.
Supplementary Figure S4. Experimental setup for BaTiO 3 NWs NEMS sensor. (a) BaTiO 3 NWs based acceleration sensing device. (b) Experimental Setup. (c) Experimental Arrangement inside Faraday cage.
Supplementary Figure S5. The schematic of the circuit representation. The piezoelectric BaTiO 3 NW Sensor is modeled as a charge source (q) in parallel with the source capacitance (C p ) and insulation resistance (R p ). The high input resistance (R i = 1TΩ) of the unity gain voltage follower (LTC 6240CS8) 10 reduces the loading effect. In addition, it tracks and converts the high input impedance voltage signal (V i ) from the sensor into a low output impedance voltage signal (V 0 ) measured using the data acquisition system (DAQ).
Supplementary Figure S6. Voltage noise floor and Acceleration spectral density. a, Showing the voltage noise floor spectral density that corresponds to a mean of 430 from 500 Hz - 10 khz. b, Showing the input rms acceleration spectral applied to the sensor for FRF characterization.
Supplementary Figure S7. Sinusoidal input/output analysis of BaTiO 3 NW NEMS sensor. a, Detailed plot of the acceleration input and output voltage at 100 Hz. b, Detailed plot showing the output voltage obtained near resonance at 450 Hz that clearly shows the 90º phase lag between the output piezoelectric voltage and the input acceleration applied to the sensor.
Supplementary Figure S8. Poling/depoling/repoling analysis of BaTiO 3 NW NEMS sensor. The magnitude of frequency response function (FRF) from white noise excitation from poled state by supplying DC field of 75 kv/cm for 12 hours, depoled state after heating at 150 ºC for 3 hours (Curie temperature, T C = 120 ºC) shows the loss in piezoelectric behavior as the electric dipoles in the NWs have been relaxed from their oriented poled state to random directions, and from re-poled state of again poling at 75 kv/cm for 30 minutes clearly demonstrating the return of the resonant peak thereby validating the piezoelectric behavior from the novel ferroelectric BaTiO 3 NW arrays.
Supplementary Figure S9. Switching polarity test on BaTiO 3 NW NEMS Sensor. The BaTiO 3 NW NEMS is subjected to pulse input at 10 Hz when forward connected and backward connected to the voltage follower to demonstrate the reversing voltage signal which confirms that the measured response is generated by BaTiO 3 NW arrays.
Supplementary Figure S10. SEM of ZnO NW arrays and Sinusoidal input/output analysis of ZnO NW sensor. a, Cross-sectional SEM image of ZnO NW arrays. b, c Detailed plot of the acceleration input and output voltage at 100 Hz (b) and 200 Hz (c) showing in-phase relationship. d, Detailed plot showing the output voltage obtained near resonant frequency at 500 Hz is associated with the 90º phase lag between the output piezoelectric voltage and the input acceleration applied to the ZnO sensor.
Supplementary Figure S11. Characterization of NWs sensor made of annealed BaTiO 3 NWs. (a) Frequency response function (FRF) illustrated by magnitude in decibel (db) scale of (V/g), (b) phase angle in degree, and (c) the coherence function (γ 2 (f)) from BaTiO 3 NW sensor fabricated from annealed NW arrays at 700 C for 1 hour when excited with white noise.
Supplementary Tables Solder Dimension = 4 X 4 (mm) 2 BaTiO 3 NWs area located below Solder = 6 X 6 (mm) 2 Seismic mass (Solder) = 16 mg Supplementary Table S1. Properties of BaTiO 3 Sensor with Solder acting as top electrode Solder Dimension = 4 X 4 (mm) 2 Seismic mass (Solder) = 16 mg Supplementary Table S2. Properties of ZnO Sensor with Solder acting as top electrode