Piezoelectricity and charge trapping in ZnO and Co-doped ZnO thin films

Abstract

Highly efficient isolation of waterborne sound by an air-sealed meta-screen AIP Advances 7, 055001 (2017) Piezoelectricity and charge storage of undoped and Co-doped ZnO thin films were investigated by means of PiezoResponse Force Microscopy and Kelvin Probe Force Microscopy. We found that Co-doped ZnO exhibits a large piezoelectric response, with the mean value of piezoelectric matrix element d 33 slightly lower than in the undoped sample. Moreover, we demonstrate that Co-doping affects the homogeneity of the piezoelectric response, probably as a consequence of the lower crystalline degree exhibited by the doped samples. We also investigate the nature of the interface between a metal electrode, made up of the PtIr AFM tip, and the films as well as the phenomenon of charge storage. We find Schottky contacts in both cases, with a barrier value higher in PtIr/ZnO than in PtIr/Co-doped ZnO, indicating an increase in the work function due to Co-doping. © 2017 Author(s)

Role of the carrier density in the transport mechanisms of polycrystalline ZnO films

“…The O 2 partial pressure was 1 Â 10 À5 mbar for S1, 10 À3 mbar for S2, 10 À2 mbar for S3, and 10 À1 mbar for S4. XRD spectra, according to previous reports, [14][15][16][17][18][19][20][21] exhibit only the presence of (00l) reflections, indicating a c-axis oriented structure without appreciable secondary phases. In line four-probe dc resistance vs. T measurements were carried out by means of a Keithley current source and a high-impedance Keithley voltmeter, with the probe insert fitted into a closed-cycle refrigerator system operating in the 20-300 K range.…”

Structural, optical, thermoelectrical, and magnetic study of Zn1‐xCoxO (0 ≤ x ≤ 0.10) nanocrystals

“…Thermoelectric properties can be recovered by reducing thermal conductivity (κ), and increasing electrical conductivity (σ), and Seebeck coefficient ( S ). Experimental and theoretical studies suggest that substitution ZnO with transitional metal elements (M‐ZnO) such as Mn, Ce, Co, Ni, and Al can improve optical, electrical, and thermoelectric properties . Cobalt has received much recognition as a candidate material because the ionic radius of Co 2+ is close to that of Zn 2+ (a Co 2+ = 0.058 nm, a Zn 2+ = 0.06 nm).…”

“…Experimental and theoretical studies suggest that substitution ZnO with transitional metal elements (M-ZnO) such as Mn, Ce, Co, Ni, and Al can improve optical, electrical, and thermoelectric properties. [17][18][19][20][21][22][23][24][25][26][27] Cobalt has received much recognition as a candidate material because the ionic radius of Co 2+ is close to that of Zn 2+ (a Co 2+ = 0.058 nm, a Zn 2+ = 0.06 nm). It can be a substitute in the host lattice without disturbing the crystalline structure.…”

Tuning the Porosity of Piezoelectric Zinc Oxide Thin Films Obtained from Molecular Layer-Deposited “Zincones”

“…However, it should be noted that they obtained significantly higher piezoelectric coefficients for deposition onto flexible substrates and for higher deposition temperatures, which switched the preferred orientation of the PE-ALD ZnO films to (002). A different study, also concerned with nonporous ZnO thin films of a comparable thickness (50 nm), reported a significantly higher piezoelectric coefficient of d 33 = (25 ± 15) pm/V for samples prepared on silicon wafer by pulsed laser deposition (PLD) [ 60 ]. In contrast to the present study, the piezoelectric response of the PLD samples was not assessed with a macroscopic stamp but instead microscopically via piezoresponsive force microscopy.…”