Chenying Wang

Thickness dependent critical strain in submicron Cu films adherent to polymer substrate

For the polymer-supported metal thin films that are finding increasing applications, the critical strain to nucleate microcracks (eC) should be more meaningful than generally measured rupture strain. In this letter, the eC values of polymer-supported Cu films are simply but precisely determined by measurements of both electrical resistance and statistical microcrack density changes on the film surface. Significant thickness dependence of eC, i.e., the thinner the film the lower the eC, has been revealed for the Cu films with a thickness range from 700 down to 60nm, which is suggested to result from the constraint effect of refining grain size on the dislocation movability.

Multiferroic heterostructures of Fe3O4/PMN-PT prepared by atomic layer deposition for enhanced interfacial magnetoelectric couplings

In this work, multiferroic heterostructures have been prepared by in situ growing oxide magnetic films on ferroelectric single crystal substrates using atomic layer deposition (ALD). Strong interfacial mechanical coupling between the magnetic and ferroelectric phases has been created, arising from the formation of chemical bonds at the interface due to the nature of layer-by-layer self-limiting growth mechanism of the ALD technique. An enhanced magnetoelectric (ME) coupling has been achieved, which allows an electric field to robustly switch magnetic anisotropy up to 780 Oe. In addition, electrical impulse non-volatile tuning of magnetism has also been realized through partially coupled ferroelectric/ferroelastic domain switching. The ALD growth of magnetic oxide films onto ferroelectric substrates provides an effective platform for the preparation of multiferroic heterostructures at low temperatures with an improved ME coupling, demonstrating a great potential for applications in 3D spintronics, microele...

Agglomeration and dendritic growth of Cu/Ti/Si thin film

Agglomeration and the transformation from random fractal to dendritic growth have been observed during Cu/Ti/Si thin film annealing. The experimental results show that the annealing temperature, film thickness, and substrate thickness influenced the agglomeration and dendritic growth. Multifractal spectrum is used to characterize the surface morphology quantificationally. The shapes of the multifractal spectra are hook-like to the left. Value of Δα increases with the annealing temperature rising, and Δf increases from 500°C to 700°C but reduces from 700°C to 800°C. The dendritic patterns with symmetrical branches are generated in the surfaces when the thin films were annealed at 800°C.

ALD preparation of high-k HfO2 thin films with enhanced energy density and efficient electrostatic energy storage

High-k dielectric HfO2 thin films with a predominant monoclinic phase were prepared by atomic layer deposition (ALD). The annealed HfO2 films exhibited a large dielectric constant, of up to er = 26 with a high breakdown field of over 4000 kV cm−1. The best performance with a maximum recoverable energy density of 21.3 J cm−3 and energy efficiency of 75% was obtained with the 63 nm HfO2 films. In addition, a well-defined temperature dependence of the energy storage properties from room temperature to 150 °C was demonstrated, indicating a stable energy density variation between 11.0 and 13.0 J cm−3 with a high energy efficiency of about 80%. These achievements provide a platform for synthesizing high-k dielectric thin films with enhanced energy densities and efficiencies.

Buckling and Delamination of Ti/Cu/Si Thin Film During Annealing

In this paper, the formation of buckling and delamination of sandwiched stacking of Ti/Cu/Si thin film are investigated. The crystallization structures, the composition of the Cu/Ti thin films, and the surface morphology are measured during annealing. The results show that the solid-phase reaction between Cu and Ti occurs at the interface. Buckling is initiated in the thin film annealed at 600°C. The volume expansion promotes the buckling and further produces microcracks. With increasing volume expansion, there are cavities formed in the middle layer when the annealing temperature is up to 700°C. Finally, thin film is delaminated from the substrate.

Surface characterization of Cu/Ti thin films by fractal analysis

Copper/Titanium (Cu/Ti) metallic thin bilayer films, xCu/10nmTi/Si and xCu/30nmTi/Si (x=10nm, 20nm, 30nm, respectively), were deposited by DC magnetron sputtering technique. An atomic force microscopy (AFM) was used to measure the surface morphology. The height-height correlation function, described by the surface parameter of roughness exponent α, together with the evolutions of the familiar parameters of roughness w and autocorrelation length ξ, was used to describe the surface quantitatively. The fractal dimension Df of the surface was calculated. The values of Df reduce with the Cu film thickness increasing for the samples of Cu/10nmTi/Si and increase for the samples of Cu/30nmTi/Si. The surface will be rougher for the samples of Cu/10nmTi/Si as the Cu film increasing from 10nm to 30nm and become smoother for the samples of Cu/10nmTi/Si.

Temperature induced interface and optical properties of the multi-layer nanotube network

The ever-increasing demand for larger surface area, well-defined, and conformal multi-layer nanostructures in gas sensor, catalyst and solar cell applications has propelled the exploration of such nanostructures within an atomic resolution. The atomic layer deposition (ALD) technique is ideal for the synthesis of these nanostructures due to its excellent step coverage ability on high aspect ratio nanostructures. In this work, different coaxial nanotube networks are successfully fabricated by electrospinning and ALD, with a well-controlled phase. We systematically studied the temperature-induced microstructures and photoluminescence property evolution of the nanotube network. The Al2O3/ZnO/Al2O3 tri-layer nanotube network is obtained by sintering at 400 °C, and a ZnAl2O4 core-shell nanotube structure has formed by the Kirkendall effect by further post-annealing at 700 °C. Oxygen accumulation is clearly observed at the small neck feature, but the Zn and Al elements are uniformly distributed along the whole ...

Voltage Control of Magnetic Anisotropy through Ionic Gel Gating for Flexible Spintronics

In spite of recent rapid development of flexible electronics, voltage-tunable spintronic structures and devices on flexible substrates have been rarely studied. Here, voltage control of magnetic anisotropy (VCMA) is demonstrated via ionic gel (IG) gating on flexible polyimide substrates with a circuit operating voltage of 1.8 V. A reversible, nonvolatile VCMA switching of 114 Oe is achieved in Pt/Fe/Pt multilayer, where the spatial magnetic anisotropy distribution is determined quantitatively by electron spin resonance technique. This IG gating process is repeatable as the substrates are under different bending conditions. The voltage modulation of magnetic anisotropy through IG gating with excellent flexibility proposes potential applications in low-power wearable spintronic devices.

FORMATION OF TRIANGULAR Cu MICROCRYSTALS IN Ti/Cu/Si THIN FILMS DURING ANNEALING

Sandwich stacked Ti/Cu/Si thin films were deposited on a single-side polished Si(111) substrate using DC magnetron sputtering system and annealed using a rapid thermal annealing (RTA) system. Complex dendritic patterns, whose branches are composed of Cu rods and triangular Cu microcrystals were obtained on Ti/Cu thin film annealed at 700∘C. The shape of one triangular Cu microcrystal is a truncated equilateral triangular pyramid with a flat top. Triangular Cu microcrystals grow in the number when Ti/Cu thin films are annealed at 800∘C. Experimental results show that anisotropy affects the growth of surface patterns and the top Ti capping layer works as a protection for the underlying Cu layer from oxidation.

In-plane calibration for AFM

Currently, the x, y scale and the orthogonality of atomic force microscopy (AFM) was independently calibrated by the traditional in-plane calibration methods. There exist theoretical errors because the other two error terms are neglected during the calibration of a certain error term. It has been found that the traditional calibration methods have a rather big theoretical error which is unbearable for nanometrology. In this paper, we propose a calibration method based on multi-measurement of a one-dimensional grating. The x, y scale and the orthogonality can be calibrated simultaneously. This new calibration method was also modified to eliminate the effect of AFM drift by keeping the parallelism between the slow scan direction of AFM and the grating lines of the one-dimensional grating.