Wenli Zhou

Formation and characteristics of Pb(Zr,Ti)O3 field-effect transistor with a SiO2 buffer layer

Ferroelectric heterostructures of Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si and Au/Pb(Zr0.52Ti0.48)O3/Si have been fabricated by using laser ablation technique. Electrical properties of these ferroelectric field-effect transistors have been characterized through both the current vs voltage and capacitance vs voltage (C–V) measurements. The C–V characteristics of Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si heterostructures demonstrate a polarization switching behavior, showing a memory window as much as 1 V at 1 kHz. In addition, the experimental results reveal that a SiO2 buffer layer is essential for memory properties in the Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si gate structure.

Ultrafast room temperature wiping-rubbing fabrication of graphene nanosheets as flexible transparent conductive films with high surface stability

In this letter, we developed an original innovative wiping-rubbing method to fabricate flexible transparent conductive films (TCFs) based on graphene nanosheets. We achieved this by using only commercial graphite block and polycarbonate film as raw materials, through a cost effective and ultrafast room temperature wiping-rubbing process (within 2 min). The properties of our flexible TCFs were competitive when comparing with literature reported graphene TCFs. Our flexible TCFs showed enough surface stability under a series of surface destructive treatments. The physical mechanism aspects of wiping-rubbing processes and surface stability were discussed.

Room temperature rubbing for few-layer two-dimensional thin flakes directly on flexible polymer substrates.

The functional layers of few-layer two-dimensional (2-D) thin flakes on flexible polymers for stretchable applications have attracted much interest. However, most fabrication methods are “indirect” processes that require transfer steps. Moreover, previously reported “transfer-free” methods are only suitable for graphene and not for other few-layer 2-D thin flakes. Here, a friction based room temperature rubbing method is proposed for fabricating different types of few-layer 2-D thin flakes (graphene, hexagonal boron nitride (h-BN), molybdenum disulphide (MoS2), and tungsten disulphide (WS2)) on flexible polymer substrates. Commercial 2-D raw materials (graphite, h-BN, MoS2, and WS2) that contain thousands of atom layers were used. After several minutes, different types of few-layer 2-D thin flakes were fabricated directly on the flexible polymer substrates by rubbing procedures at room temperature and without any transfer step. These few-layer 2-D thin flakes strongly adhere to the flexible polymer substrates. This strong adhesion is beneficial for future applications.

Stress analysis and ferroelectric properties of Pb(Zr0.52Ti0.48)0.96Nb0.04O3 thin film grown on different thickness of BaPbO3 electrodes

Pb(Zr0.52Ti0.48)0.96Nb0.04O3 (PZTN) thin films were deposited on BaPbO3 (BPO) electrodes by rf-magnetron sputtering. 34, 68, 135, and 270 nm thick BPOs were adopted in this study. The preferred orientation changes from slightly (100)/(001) to slightly (101)/(110) as the BPO thickness increased. The mean grain sizes obtained by Williamson–Hall plots are 81 nm, 120 nm, 146 nm, and 90 nm, respectively. The same tendency was observed by atomic force microscopy method. In residual stress analysis, tensile stress was observed in every film. The stress magnitude is the maximum in the film with 135 nm thick BPO. Through a simple calculation, we suggest that the tensile stress in our films mainly originates from the phase transformation stresses. We also note that the ferroelectric and dielectrics properties are improved with the raise of tensile stresses. A possible reason is that the tensile stress benefits the tetragonal–monoclinic phase transition in the PZTN films with composition near morphotropic phase boun...

The influence of the thickness of TiO2 seeding layer on structural and electrical properties of Bi3.15Nd0.85Ti3O12 thin films

Thin films of Bi3.15Nd0.85Ti3O12(BNT) and BNT with various TiO2 seeding layer thicknesses BNT-Tx (x = 10, 20, 30 nm) were fabricated on Pt/Ti/SiO2/Si substrates by the sol–gel method. The influence of the TiO2 seeding layer thickness on the structural and the electrical properties of BNT thin films was investigated. The x-ray diffraction pattern indicated that the BNT thin film with a TiO2 seeding layer showed a-axis preference orientation. The Pr value was a maximum for the BNT-T20 film and decreased with both decreasing and increasing thickness. The BNT-T20 film had the largest er and the lowest tanδ. The leakage current density of the BNT thin films with various TiO2 seeding layer thicknesses was generally in the order of 10−6–10−5 A cm−2. The surface micrograph of BNT-Tx films was more homogeneous and dense than that without a seeding layer.

Surface fractal evolution induced rubbing for rapid room temperature and transfer-free fabrication of graphene on flexible polymer substrate

Graphene as functional layer on flexible polymers for stretchable applications have attracted much research interests, and the fabrication methods are of great importance. In this letter, rapid room temperature and transfer-free fabrication of few-layer graphene on flexible polymer substrates has been realized by rubbing method. This is achieved by the surface fractal evolution rubbing step which can evolve sandpaper surface to form relatively large area of smooth parts as self-lubricated smooth surface. The graphene displayed strong adhesion with flexible polymer substrates, which is benefit for applications. Physical mechanisms of rubbing steps and fabrication of graphene on polymers are studied.

Numerical simulation of CZTS thin film solar cell

The performance of CZTS (Cu2ZnSnS4) thin film solar cell is numerically simulated in this paper. The influences of structural and physical parameters are studied, including thickness, carrier density and defect density of CZTS absorber, thickness of CdS buffer layer. It can be found in the simulation results that to reach high conversion efficiency, the cell should have a thin buffer layer and a thick absorber layer. It is necessary to control the defect density in the absorber one order lower than carrier density. The effect of operating temperature on the cell performance shows that increased temperature will strongly affect the efficiency. The presence of low band gap interfacial layer between CZTS absorber and Mo back contact may lower the open circuit voltage.

One-Minute Room-Temperature Transfer-Free Production of Mono- and Few-Layer Polycrystalline Graphene on Various Substrates.

Graphene deposited on various substrates has attracted the attention of the scientific and technical communities for use in a wide range of applications. Graphene on substrates is commonly produced by two types of methods, namely, methods that require a transfer step and transfer-free methods. Compared with methods that require a transfer step, transfer-free methods have a simpler procedure and a lower cost. Thus, transfer-free methods have considerable potential to meet the industrial and commercial demands of production methods. However, some limitations of the current transfer-free methods must be overcome, such as the high temperatures encountered during production, the relatively long manufacturing times, incompatibilities for both rigid and flexible substrates, and an inability to extend the process to other two-dimensional (2-D) atomic crystals. In this work, a room-temperature rubbing method is developed for the rapid transfer-free production of defect-free polycrystalline graphene on rigid and flexible substrates. Starting with inexpensive commercially obtained graphite powder, mono- and few-layer graphene can be fabricated directly on various substrates, with an average production time of less than one minute (from raw graphite to graphene on the substrate). Importantly, this method can be extended to other 2-D atomic crystals.

Universal ultrafast sandpaper assisting rubbing method for room temperature fabrication of two-dimensional nanosheets directly on flexible polymer substrate

In this letter, a universal ultrafast sandpaper assisting rubbing method was proposed to fabricate two-dimensional nanosheets (graphene, hexagonal boron nitride, tungsten disulfide, molybdenum disulfide) directly on flexible polymer substrate under room temperature. By two steps of rubbing progresses totally within 2 min, raw materials could be evolved to be thinner and to be attached onto polymer substrate. The final products showed high surface stability, which would be very useful during applications, and the physical mechanisms of surface stability were discussed. The micro-morphology evolutions of two-dimensional powders and sandpapers were tested to study the physical mechanisms of the method.

Characteristics of Pb(Zr0.52Ti0.48)O3 Thin Films on p-Si with a Buffer Layer of Bi4Ti3O12 Prepared by Pulsed Laser Deposition

The Pb(Zr0.52Ti0.48)O3 ferroelectric films with a c-axis oriented Bi4Ti3O12 buffer layer were deposited on p-Si(100) substrate by pulsed laser deposition (PLD) technique. The Pb(Zr0.52Ti0.48)O3 films were found to grow with a preferred orientation along (110) direction. Good ferroelectric properties were obtained for a 400 nm thick Pb(Zr0.52Ti0.48)O3/Bi4Ti3O12 film system with Au electrodes: Pr and Ec were 20 µC/cm2 and 48 kV/cm respectively. The memory window of capacitance–voltage (C–V) charactristics enlarged obviously and the current density reduced nearly two orders of magnitude after introducing the BIT buffer layer. The decay in remnant polarization was only 10% up to at least 109 bipolar switching cycles.