基于Landsat 8 OLI数据的玉米冠层含水量反演研究

植被含水量是作物长势好坏的指示因子,利用遥感技术及时准确监测植被含水量对农业生产、作物估产和干旱状况评价具有重要意义。基于新一代对地观测计划Landsat 8 OLI传感器(Operational Land Imager,陆地成像仪),评价其植被含水量反演的能力与局限性。首先,利用ProSail冠层模型模拟冠层光谱反射率数据集,分析OLI传感器的植被含水量敏感波段以及土壤背景对各波段反射率的影响,然后利用基于Landsat OLI影像计算的植被水分指数和2013年6月1日—8月14日期间采样的植被含水量数据,比较12种植被水分指数与地面实际采样的植被含水量的相关性,评价估算植被含水量的最佳植被水分指数。结果表明：OLI传感器的红、近红外和两个短波红外对植被含水量敏感,其中近红外波段最为敏感;在低植被覆盖度时,土壤背景反射率的太阳辐射将达到光谱传感器影响植被水分指数与植被含水量之间的关系,利用ProSail模拟干湿土壤背景反射率结果也表明土壤背景对植被冠层反射率的影响很大;引入优化土壤调整植被指数(OSAVI)去除土壤背景对植被水分指数的影响;在12种植被水分指数中,MSI2与植被含水量的拟合关系最好(R2=0.948),植被含水量的平均拟合误差为0.52 kg·m-2;在植被生长晚期即植被含水量大于2 kg·m-2时,各植被水分指数出现饱和情况,植被含水量的估算结果不佳。     

Double-layer indium doped zinc oxide for silicon thin-film solar cell prepared by ultrasonic spray pyrolysis

Indium doped zinc oxide(ZnO:In) thin films were prepared by ultrasonic spray pyrolysis on corning eagle 2000 glass substrate.1 and 2 at.% indium doped single-layer ZnO:In thin films with different amounts of acetic acid added in the initial solution were fabricated.The 1 at.% indium doped single-layers have triangle grains.The 2 at.% indium doped single-layer with 0.18 acetic acid adding has the resistivity of 6.82×10-3Ω·cm and particle grains.The doublelayers structure is designed to fabricate the ZnO:In thin film with low resistivity(2.58×10-3Ω·cm) and good surface morphology.It is found that the surface morphology of the double-layer ZnO:In film strongly depends on the substratelayer,and the second-layer plays a large part in the resistivity of the double-layer ZnO:In thin film.Both total and direct transmittances of the double-layer ZnO:In film are above 80% in the visible light region.Single junction a-Si:H solar cell based on the double-layer ZnO:In as front electrode is also investigated.     

Analysis of heating effect on the process of high deposition rate microcrystalline silicon

A possible heating effect on the process of high deposition rate microcrystalline silicon has been studied.It includes the discharge time-accumulating heating effect,discharge power,inter-electrode distance,and total gas flow rate induced heating effect.It is found that the heating effects mentioned above are in some ways quite similar to and in other ways very different from each other.However,all of them will directly or indirectly cause the increase of the substrate surface temperature during the process of depositing microcrystalline silicon thin films,which will affect the properties of the materials with increasing time.This phenomenon is very serious for the high deposition rate of microcrystalline silicon thin films because of the high input power and the relatively small inter-electrode distance needed.Through analysis of the heating effects occurring in the process of depositing microcrystalline silicon,it is proposed that the discharge power and the heating temperature should be as low as possible,and the total gas flow rate and the inter-electrode distance should be suitable so that device-grade high quality deposition rate microcrystalline silicon thin films can be fabricated.     

Superconducting Single-Layer T-Graphene and Novel Synthesis Routes

Single-layer superconductors are ideal materials for fabricating superconducting nano devices.However,up to date,very few single-layer elemental superconductors have been predicted and especially no one has been successfully synthesized yet.Here,using crystal structure search techniques and ab initio calculations,we predict that a single-layer planar carbon sheet with 4-and 8-membered rings called T-graphene is a new intrinsic elemental superconductor with superconducting critical temperature(T_c)up to around 20.8 K.More importantly,we propose a synthesis route to obtain such a single-layer T-graphene,that is,a T-graphene potassium intercalation compound(C_4 K with P4/mmm symmetry)is firstly synthesized at high pressure(11.5 GPa)and then quenched to ambient condition;and finally,the single-layer T-graphene can be either exfoliated using the electrochemical method from the bulk C4 K,or peeled off from bulk T-graphite C4,where C4 can be obtained from C4 K by evaporating the K atoms.Interestingly,we find that the calculated T_c of C4 K is about 30.4 K at 0 GPa,which sets a new record for layered carbon-based superconductors.The present findings add a new class of carbon-based superconductors.In particular,once the single-layer T-graphene is synthesized,it can pave the way for fabricating superconducting devices together with other 2 D materials using the layer-by-layer growth techniques.     

The study of a new n/p tunnel recombination junction and its application in a-Si：H/μc-Si：H tandem solar cells

This paper reports that a double N layer (a-Si:H/μc-Si:H) is used to substitute the single microcrystalline silicon n layer (n-μc-Si:H) in n/p tunnel recombination junction between subcells in a-Si:H/μc-Si:H tandem solar cells. The electrical transport and optical properties of these tunnel recombination junctions are investigated by current-voltage measurement and transmission measurement. The new n/p tunnel recombination junction shows a better ohmic contact. In addition, the n/p interface is exposed to the air to examine the effect of oxidation on the tunnel recombination junction performance. The open circuit voltage and FF of a-Si:H/μc-Si:H tandem solar cell are all improved and the current leakage of the subcells can be effectively prevented efficiently when the new n/p junction is implemented as tunnel recombination junction.     

TiO2纳米团聚体的制备及在太阳电池中的应用

利用钛酸四丁酯水解反应,结合溶胶-凝胶与水热处理法制备了TiO2纳米团聚体.以该团聚体制备染料敏化太阳电池的光阳极,不但可以保持纳米粉体高比表面积的优点,同时可以提高对太阳光的散射率,简化电池制备工艺.本文研究了水解pH值对粉体物理性质、电池效率的影响规律.结果表明,水解的pH值对TiO2纳米粒子的尺寸、分布以及染料敏化太阳电池光阳极的显微形貌、电池光电特性都有很大影响.当pH值为1时,制备的电池效率最高达到5.77;(Jsc=15.04 mA/cm2,Voc=0.73 V, FF=0.53).     

高速沉积μc-Si:H薄膜生长机制及其微结构的研究

采用高压高功率的超高频等离子体增强化学气相沉积(VHF-PECVD)技术,在腐蚀后的7059玻璃、低晶化和高晶化的微晶硅(μc-Si:H)p型材料3种衬底上,通过改变沉积时间的方法,高速(沉积速率约为1 nm/s)沉积了不同厚度的μc-Si:H薄膜材料.测试其表面形貌及晶化率,比较了不同衬底上高速生长的μc-Si:H薄膜生长机制及微结构的差异,最后得到适于高速沉积pin μc-Si:H太阳电池的μc-Si:H p型材料应具备的条件.     

微晶硅薄膜的制备及结构和稳定性研究

采用甚高频等离子体增强化学气相沉积技术制备了不同衬底温度的微晶硅薄膜.利用傅里叶变换红外吸收对制备薄膜进行了结构方面的测试分析.结果表明：随衬底温度的升高，材料 中的氢含量总的趋势下降；傅里叶变换红外吸收和二次离子质谱测试结果都显示薄膜中氧含 量随衬底温度的升高而增加（在10¹⁹cm^-3量级）；与高衬底温度相 比，低衬底温度制备的材料易于后氧化，这说明低温制备材料的稳定性不好. 关键词： 甚高频等离子体增强化学气相沉积 微晶硅薄膜 傅里叶变换红外吸收     

可穿戴型下肢助力机器人感知系统研究

在分析可穿戴型下肢助力机器人所需要的控制信息的基础上,设计了一套基于CAN总线的人体下肢运动信息感知系统.该系统主要包括可获取人体腿部和脚底状态的力传感器和获取髋关节和踝关节角度信息的编码器.实验结果表明,所设计的多传感器系统稳定,实时性好,满足可穿戴型下肢助力机器人系统控制的需要.     

掺杂室沉积本征微晶硅材料及其在太阳能电池中的应用

在掺杂P室采用甚高频等离子体增强化学气相沉积(VHF-PECVD)技术,制备了不同硅烷浓度条件下的本征微晶硅薄膜.对薄膜电学特性和结构特性的测试结果分析表明:随硅烷浓度的增加,材料的光敏性先略微降低后提高,而晶化率的变化趋势与之相反;X射线衍射(XRD)测试表明材料具有(220)择优晶向.在P腔室中用VHF-PECVD方法制备单结微晶硅太阳能电池的i层和p层,其光电转换效率为4.7%,非晶硅/微晶硅叠层电池(底电池的p层和i层在P室沉积)的效率达8.5%.