Atomic Layer Deposition for Fiber Surface Modification and Nanosheet Fabrication

Atomic layer deposition (ALD) is a vapor phase thin film deposition technique based upon the sequential dosing of precursor species. This sequential precursor delivery process affords precise control over thin film thickness in sub-nanometer resolution. Moreover, it is possible to vary film composition or create junctions by altering precursor chemistries in successive ALD processes.;We present the mechanism for wetting transition with X-ray photoelectron spectroscopy (XPS), in situ Fourier-transform infrared spectroscopy (in situ FTIR), and scanning electron microscope (SEM). The wetting property of cotton was modified only with a few number of ALD cycles. In situ FTIR and XPS suggest that Al-(O-C-)3 bonding on the fiber surface bring about the change from hydrophilicity to hydrophobicity. Induced hydrophobicity is promoted from an increase in surface roughness after small number of Al2O3 cycles.;We show a new strategy to nanosheet synthesis that uses atomic layer deposition (ALD) and allows vast control over nanosheet composition and thickness. Nanosheets are twodimensional (2D) materials with micro- to macro-scale lateral dimensions and nanometer to subnanometer thickness with unique electrical and mechanical properties. The two common routes to nanosheet synthesis, which are mechanical or chemical exfoliation from layered compounds, and vapor-phase or hydrothermal growth using morphologically constrained systems, suffer from limited control over nanosheet thickness or restriction to layered materials. We use metal oxide ALD films on a polymer sacrificial layer followed by dissolution to create nanosheets with controlled thickness and show the photocatalytic activity of TiO2 and ZnO nanosheets under UV light. Surface area and thickness of nanosheets as well as UV light intensity affect dye photodegradation rate according to the kinetic equation. More importantly, TiO2/ZnO bilayer nanosheets from two successive ALD processes promote dye photodegradation > 5 times than TiO2 nanosheets under UV light.;Cu2O films are grown by electrodeposition. They all have pyramidal triangular grain in shape but the size depends on deposition temperature, pH of the solution, and deposition time. To increase electrochemical stability, TiO2 ALD film with Al-doped ZnO buffer layer is deposited on Cu 2O films but the expected increase in stability is not observed.;Free-standing Cu2O sheets are obtained using flexible ITO-PET substrates. Simple bending after electrodeposition isolates Cu2O film from the substrates. Dye molecules are degraded with Cu2O sheets for the first 30 min but it is recovered after 30 min under UV light while Cu2O sheets with ZnO ALD layer prevent dye reduction showing continuous degradation. Under visible light, however, dye recovery is not observed with Cu2O sheets. Although ZnO film prevents reduction of dye molecules, photocatalytic activity of Cu2O sheets is decreased after ALD.