分类： 材料科学 >> 纳米科学和纳米技术 提交时间： 2017-01-10
摘要： Spongy graphene paper with inside foldable corrugated structure is fabricated by electrothermal reduction of the oxygen-containing groups inside RGO paper. Reversible macroscopical length contraction of the spongy graphene paper with strain of 2.4% under 10V voltage is exhibited, mostly attributed to the deformation of corrugated structures.
分类： 材料科学 >> 纳米科学和纳米技术 提交时间： 2017-01-10
摘要： Bimorph actuators, consisting of two layers with asymmetric expansion and generating bending displacement, have been widely researched. Their actuation performances greatly rely on the differences of coefficient of thermal expansion (CTE) between the two material layers. Here, by introducing a spongy graphene (sG) paper with large negative CTE as well as highly electrical-to-thermal property, an electromechanical sG/PDMS bimorph actuator is designed and fabricated, showing ultra-large bending displacement output under the low voltage stimulation (curvature of about 1.2cm-1 under 10V voltage for 3s), high displacement-to-length ratio (~0.79), and vibration motion under AC voltage (up to 10Hz), which is much larger and faster than that of the other electromechanical bimorph actuators. Based on the sG/PDMS bimorph serving as the “finger”, a mechanical gripper is constructed to realize the fast manipulation of the objects under 0.1 Hz square wave voltage stimulation (0~8V). The designed bimorph actuator coupled with ultra-large bending displacement, low driven voltage, and ease fabrication, may open up substantial possibilities for the utilization of the electromechanical actuator in practical biomimetic device applications.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-01-10
摘要： We argue microscopically that helium-4 superflows carry heat unavoidably. We then show that a heterogeneous helium-4 superflow loop can be used to realize an entropy-decreasing process, thus providing an exception to the second law of thermodynamics. This exception is a quantum effect for its essential dependence on the quantum phenomenon of superfluidity.
分类： 材料科学 >> 纳米科学和纳米技术 提交时间： 2017-01-10
摘要： 采用低温 AlN 成核层在 Si(111)衬底上用金属有机化学气相沉积(MOCVD)设备摘要：采用低温 AlN 成核层在 Si(111)衬底上用金属有机化学气相沉积(MOCVD)设备生长了 GaN 薄膜。采用高分辨 X 射线衍射、椭圆偏振光谱仪和原子力显微镜研究了 AlN成核层的厚度对 GaN 外延层的影响。对 AlN 的测试表明，AlN 的表面粗糙度随着厚度增加而变大。对 GaN 的测试表明，所有 GaN 样品在垂直方向处于压应变状态，并且随 AlN 厚度增加而略有减弱。GaN 的(0002) ω扫描的峰值半宽(FWHM)随着 AlN 成核层厚度增加而略有升高，GaN(10-12) ω扫描的峰值半宽随着厚度增加而有所下降。(10-12) ω扫描的峰值半宽与 GaN 的刃型穿透位错密度相关。说明 AlN 成核层的厚度较大时，会降低刃型穿透位错密度，并减弱 c 轴方向的压应变状态。
分类： 材料科学 >> 纳米科学和纳米技术 提交时间： 2017-01-10
摘要： 摘要:在 Si(111)衬底上用金属有机化学气相沉积(MOCVD)设备生长了 AlN 和GaN 薄膜。采用高分辨 X 射线衍射、椭圆偏振光谱仪和原子力显微镜研究了AlN 缓冲层生长时的载气(H2)流量变化对 GaN 外延层的影响。椭圆偏振仪测试表明，相同生长时间内 AlN 的厚度随着 H2流量的增加而增加，即 H2流量增加会导致 AlN 的生长速率提高。原子力显微镜测试表明，随着 H2 流量的增加，AlN 表面粗糙度也呈上升趋势。对 GaN 的测试表明，随着 AlN 生长时的 H2流量增加，GaN 的(0002)和(10-12)的峰值半宽增加，即螺型穿透位错密度和刃型穿透位错密度增加。可能是由于 AlN 缓冲层厚度较大，导致 GaN 的晶体质量有所下降。实验表明，采用较低的 H2 流量生长 AlN 缓冲层可以控制 AlN 的生长速率，在一定程度上有助于提高 GaN 的晶体质量。
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