Yanhong Lv

Thermoelectric transport of Se-rich Ag2Se in normal phases and phase transitions

Small amount of Se atoms are used to tune the carrier concentrations (nH) and electrical transport in Ag2Se. Significant enhancements in power factor and thermoelectric figure of merit (zT) are observed in the compositions of Ag2Se1.06 and Ag2Se1.08. The excessive Se atoms do not change the intrinsically electron-conducting character in Ag2Se. The detailed analysis reveals the experiment optimum carrier concentration in Ag2Se is around 5 × 1018 cm−3. We also investigate the temperature of maximum zT and the thermoelectric transport during the first order phase transitions using the recently developed measurement system.

Synthesis and characterization of titanium-containing graphite-like carbon films with low internal stress and superior tribological properties

Titanium-containing graphite-like carbon films were deposited on silicon substrates by an unbalanced magnetron sputtering system. The effect of titanium concentration on the film microstructure and properties was subsequently investigated by means of different characterization techniques. It is found that the current carbon films have a graphite-like structure with some fine titanium carbide particles dispersed in an amorphous carbon matrix. With increasing titanium concentration from 0?at% to ?9.6?at%, the sp2 concentration in the film shows a slight increase, while the hardness of the carbon films decreases evidently when a small quantity of titanium (?2.9?at%) is introduced into the film structure, but it does not suffer an obvious change with further increase in titanium concentration until the titanium concentration is up to ?9.6?at%. The increased hardness of the film with a titanium concentration of about 9.6?at% is probably due to the formation of specified dimension titanium carbide crystals in the amorphous carbon matrix. All the current carbon films have low internal stress and rough surface, and the doping of titanium has little influence on their internal stress and root mean square roughness. The friction coefficient of the films decreases distinctly as the titanium concentration increases from 0?at% to ?9.6?at%, but the wear rate does not increase evidently until the titanium concentration exceeds over ?6.2?at% in air tests. The titanium-containing graphite-like carbon films show a stable friction coefficient and extremely low wear under oil lubricated conditions. The unique graphite-like structure, the high hardness and elastic modulus ratio (H/E) and the easy formation of a transfer film are mainly responsible for the superior tribological properties of the resulting titanium-containing graphite-like carbon films.

Composition control of pulsed laser deposited copper (I) chalcogenide thin films via plasma/Ar interactions

We present how the applied Ar background pressure correlates to the cation and anion composition of Cu(I) chalcogenide thin films grown by pulsed laser deposition (PLD). The as-grown films produced at ∼10−2 mbar pAr show a more pronounced deficiency in lighter composition, as compared with using quasi-vacuum or ∼10−1 mbar. The thermoelectric performance of the as-grown Cu2Se varies consistently with the respective changes in Cu/Se ratio vs.pAr. The optimum thermoelectric performance of Cu2Se is achieved by growing in vacuum or quasi-vacuum, where dense and even thin film morphology is obtained while the cation/anion composition is more congruent than at higher pAr.摘要本文阐述了在利用脉冲激光沉积法生长亚铜基硫族化合物薄膜过程中, 所使用的氩气背景气体压力与薄膜化学组分的关系. 当氩气压力在∼10−2 mbar时, 薄膜材料中原子量较轻的成分缺失更为严重. 与之相比, 当利用准真空或∼10−1 mbar时薄膜材料化学组分与所用靶材组分更为接近. 以硒化亚铜为例, 研究结果显示所生长薄膜材料的电输运性能与铜硒组分比例随压力的变化相一致. 当生长条件为真空或准真空时, 所生长的硒化亚铜薄膜具有致密的结构和最佳的化学组分, 因而具有最优的热电性能.

Friction and Wear Properties of Graphite-Like Carbon Films Deposited on Different Substrates with a Different Interlayer Under High Hertzian Contact Stress

Four types of graphite-like carbon (GLC) films were deposited on different substrates (Ti6Al4V, WC-27CrNi) with a different interlayer (TiC/Ti, TiC/Ti/TiN) using an unbalanced magnetron sputtering system. The effect of substrate and interlayer on the microstructure and properties of the studied GLC films was then investigated using different characterization techniques. The results show that both the substrate and interlayer had an obvious influence on the tribological properties of the studied GLC films even though there was no significant structural difference between these films. Specifically, a substrate with a high hardness was propitious to achieving superior tribological behaviors for carbon film even with a different interlayer. However, the interlayer had a distinct influence on the tribological properties of the carbon film deposited on different substrates, and this effect varied with the hardness property of the substrate. For a hard substrate, the wear rate and wear life were similar irrespective of the interlayer. For a soft substrate, the addition of a TiN interlayer improved the wear life sevenfold compared to the film with only a TiC/Ti interlayer, but the wear rate for a film with and without a TiN interlayer was approximately the same. The obvious discrepancy between wear life and wear rate for a carbon film deposited on soft substrate was closely related with the film adhesion strength and plastic deformation of the substrate materials. Based on these results, it can be concluded that the wear life is a better parameter than wear rate in terms of characterization of the wear resistance of carbon film once the applied load causes the plastic deformation of the substrate.

Study on the microstructure and properties of graphite-like carbon films deposited by unbalanced magnetron sputtering

A series of graphite-like amorphous carbon films were deposited by unbalanced magnetron sputtering system with different sputtering currents. The microstructure, morphology, contact angle, and tribological properties of the resultant carbon films were subsequently investigated by means of different characterization techniques. Raman analysis shows that the resultant amorphous carbon films are dominated by sp2 sites, and the intensity ratio of the D and G peaks increases gradually from ∼4.1 to ∼5.4 with decrease in the sputtering current from 16 to 4 A, which is one order of magnitude larger than that of diamond-like carbon films with high sp3 content, indicating a more graphite-like structure. The surface of the resulting carbon films is composed of granular structure with different diameters and heights, and the root mean square roughness of the studied films monotonically increases from 3.5 nm at a sputtering current of 4 A to 8.2 nm at 16 A. The contact angle of graphite-like carbon films with water changes from 43.4° to 89.5° with decrease in the sputtering current. Besides, these graphite-like carbon films demonstrate superior tribological properties with high load-bearing capacity and low friction coefficient in humid atmosphere. The superior tribological behaviors of this graphite-like carbon film are promising for a wide range of applications such as gears, cutting tools, automobile parts, etc.