Tongkui Li

Bio: Tongkui Li is an academic researcher. The author has contributed to research in topics: Coercivity & Crystallite. The author has an hindex of 1, co-authored 1 publications receiving 5 citations.

Effect of the Sputtering Power on the Structure, Morphology and Magnetic Properties of Fe Films

Abstract: In this paper, the radio frequency (RF) magnetron sputtering (MS) method was utilized to fabricate multiple sets of the iron film samples under different sputtering powers. With the help of X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and vibrating sample magnetometer (VSM), how the sputtering power affected the structure, morphology and magnetic properties of the iron film was studied. XRD results showed that all Fe films have a polycrystalline bcc structure and (110) preferred orientation. According to the Bragg equation calculation, the larger the sputtering power, the larger the average grain size, which is consistent with the results of AFM particle size analysis. The main reason is that the sputtering power affects the grain growth mode. As the sputtering power increases, it gradually changes from a small island-like growth to a thick columnar growth. However, from the surface morphology and height profile, we saw that the iron film deposited under 230 W had the most uniform grain size distribution and the grain size was relatively small. This is why thin films deposited under this condition have the best soft magnetic properties. The saturation magnetization (Ms) reaches 1566 emu/cm3, coercivity (Hc) is 112 Oe, and squareness ratio (Mr/Ms) is 0.40. Therefore, iron film prepared under 230 W has good comprehensive properties (highest Ms, lower Hc and Mr/Ms) that provide an experimental basis for further thin film research work.

Effect of RF Power on the Physical Properties of Sputtered ZnSe Nanostructured Thin Films for Photovoltaic Applications.

Abstract: Zinc selenide (ZnSe) thin films were deposited by RF magnetron sputtering in specific conditions, onto optical glass substrates, at different RF plasma power. The prepared ZnSe layers were afterwards subjected to a series of structural, morphological, optical and electrical characterizations. The obtained results pointed out the optimal sputtering conditions to obtain ZnSe films of excellent quality, especially in terms of better optical properties, lower superficial roughness, reduced micro-strain and a band gap value closer to the one reported for the ZnSe bulk semiconducting material. Electrical characterization were afterwards carried out by measuring the current–voltage (I-V) characteristics at room temperature, of prepared “sandwich”-like Au/ZnSe/Au structures. The analysis of I-V characteristics have shown that at low injection levels there is an Ohmic conduction, followed at high injection levels, after a well-defined transition voltage, by a Space Charge Limited Current (SCLC) in the presence of an exponential trap distribution in the band gap of the ZnSe thin films. The results obtained from all the characterization techniques presented, demonstrated thus the potential of ZnSe thin films sputtered under optimized RF plasma conditions, to be used as alternative environmentally-friendly Cd-free window layers within photovoltaic cells manufacturing.

Analysis of mechanical and thermal stresses due to TiN coating of Fe substrate by physical vapor deposition

Abstract: The residual stress generated after thin layer TiN coating by Physical Vapor Deposition is reducing the mechanical and tribological properties of TiN. Thermal stresses are one of the residual stress components which can cause failure modes of proper coatings. In this article, a validated computational simulation was developed to investigate the effect of physical and thermal properties on the thermal stresses of the coating, including the deposition temperature, Young's modulus of coating, the thermal expansion coefficient of coating, and the thicknesses of coating and substrate. An analytical method using Stoney & Tsui model was used to verify the simulation result by Abaqus software 6.14–5, and very good agreement was achieved. Results show that the thermal stress distribution is discontinued large difference between high stresses in the coating and low stress in the substrate. Also, increasing the deposition temperature from 100 oC to 500 oC increases the thermal stresses from 214 MPa to 1355 MPa linearly. Analysis of the coating thickness in the range of 1–5 µm slightly reduces the thermal stress from 1362 MPa to 1342 MPa, while an increase of the substrate thickness in the range of 1–5 mm increases the thermal stress from 1330 MPa to 1360 MPa. It is also realized that an increase in Young's modulus of TiN from 250 GPa to 600 GPa linearly increases the thermal stress from 567 MPa to 1355 MPa, while an increase of the coefficient of thermal expansion of TiN from 3.92×10−6 °C−1 to 9.40 × 10−6 °C−1 reduces the thermal stress from 3418 MPa to 1355 MPa.

A novel soft deposition methodology for textured ZnO:Al thin films as efficient transparent conductive oxide layers

Abstract: In this paper, a novel soft deposition methodology was developed for depositing Al-doped ZnO (AZO) thin films as Transparent Conducting Oxide (TCO) layer. The new proposed methodology could help in reducing the process time and cost that could subsequently be useful for industrial scalability purposes. In general, the effect of substrate distance (dTS), Ar gas flow (FAr), and sputtering power (PW) were analyzed on structural, morphological, optical, and electrical properties. Films exhibiting the best electrical values (3.2 × 10−4 Ω*cm, 21.3 cm2 V−1 s−1, and 9.2 × 1020 cm−3) were deposited at FAr of 5 sccm, PW of 45 W, and room temperature. Additionally, AZO thin films deposited inside the high-density zone (HDZ, dTS < 6 cm) of the plasma sputtering exhibited a textured surface with crater-like morphology, and it was found to be more evident in films deposited at reduced FAr (5 sccm) and low PW (45 W) values. The present methodology could be of great interest for the low-cost production of AZO thin films with a textured surface obtained in a one-step DC sputtering process for modern optoelectronic applications such as flexible solar cells and electroluminescent devices.

Tuning the microstructure and mechanical properties in nanocrystalline Cr coatings by sputtering power

Abstract: A significant sputtering power effect on the microstructure and mechanical properties was investigated in the nanocrystalline Cr coatings that were prepared by employing magnetron sputtering. Experimental results demonstrated that all the Cr coatings exhibited a columnar grain structure with preferred (110) out-of-plane orientation. However, with raising the sputtering power from 50 to 250 W, the surface morphology changed from the faceted pyramid to vermiform-like shape due to the anisotropy of growth rate along different crystallographic plane. Meanwhile, raising sputtering power also increased the grain size and coating thickness, between of which followed a power-law relationship, indicative of an evolutionary overgrowth mechanism. In addition, both the nanoindentation hardness and elastic modulus of Cr coatings exhibited a monotonic increment with reducing the grain size. This size-dependent strengthening behavior was rationally interpreted by the classical Hall-Petch theory, and a grain coalescence model for columnar grain morphology was developed to quantitatively describe the size effect on elastic modulus of nanocrystalline Cr coatings.