Effect of Oxide Particles on δ-γ Transformation and Austenite Grain Growth

表面技术第52卷第5期镀锌热成形钢表面颜色及氧化物形成规律卢岳，张彩东，齐建军，孙力，马成，刘艳丽，熊自柳（河钢材料技术研究院，石家庄 050023）摘要：目的研究保温时间对热成形钢镀锌层颜色及氧化物组成的影响。

方法通过改变镀锌热成形22MnB5钢热处理保温时间，利用色差、辉光实验、X射线光电子能谱、粗糙度检测、扫描电子显微镜和透射电子显微镜对镀层表面及截面进行观察，利用电子探针进行元素分析，研究保温前后镀层表面氧化物形貌及镀层元素分布规律。

结果随着保温时间的增加，色差值ΔE逐渐增大。

当温度处在945 ℃时，镀层连续性受到破坏，逐渐脱落。

880 ℃加热过程后，镀层表面由排列均匀连贯的圆球状氧化物组成，连续覆盖表面，且呈聚集存在趋势，镀层表面氧化物厚度出现明显差异。

当热加工时间超过6 min后，氧化物明显增多，表面厚度起伏大，呈现出不均匀分布趋势，裂纹萌生，并逐渐加深扩散。

随着加热时间的增加，整体Zn浓度有降低的趋势。

结论镀层表面主要由ZnO、FeO、Al2O3组成，ZnO连续铺满表面，并呈现连续分布的趋势，有效避免了在高温下镀层表面Zn的挥发。

保持Zn含量在一定范围内，使得镀层具有阴极保护的作用。

关键词：热成形钢；GI镀层；色差；辉光；TEM；氧化物；粗糙度中图分类号：TG306 文献标识码：A 文章编号：1001-3660(2023)05-0208-10DOI：10.16490/ki.issn.1001-3660.2023.05.020Surface Color and Oxide Formation Rule of Galvanized Hot-formed Steel LU Yue, ZHANG Cai-dong, QI Jian-jun, SUN Li, MA Cheng, LIU Yan-li, XIONG Zi-liu(HBIS Material Technology Research Institute, Shijiazhuang 050023, China)ABSTRACT:This paper took the hot-dip galvanized hot-formed steel 22MnB5 as the research object. The morphology and element composition of the surface oxides in hot-dip galvanized hot-formed steel under different heat treatment time was compared. The mechanism of the surface oxides of the hot-dip galvanized steel with the holding time was summarized, to provide a practical reference for subsequent coating and welding production.22MnB5 galvanized sheet with a thickness of 1.4 mm was used and processed into a sample of 60 mm× 60 mm. Before the test, acetone was used to clean the oil stains and attachments on the surface of the sample. The sample and place was dried in an oven. The SX2-16-13 box-type resistance furnace was used for the heat treatment. The initial heating temperature of the heat treatment was 850 ℃. The sample was taken out and water-cooled immediately. The experiment was carried out under standard atmospheric pressure, the ambient temperature was 25 ℃ and the humidity was 10%. The sample was prepared into a metallographic sample of 10×10 mm with a inlaid cross section, and was then ground and polished. The metallographic sample was corroded with 4% nitric acid alcohol solution for about 15 s. The color difference experiment was carried out on the收稿日期：2022–03–31；修订日期：2022–08–15Received：2022-03-31；Revised：2022-08-15作者简介：卢岳（1995—），男，硕士，工程师，主要研究方向为钢铁焊接及镀层材料开发。

氧分压对IWO薄膜表面形貌及光电性能的影响张远鹏（北京航空航天大学物理科学与核能工程学院，北京100191，中国）指导教师：王文文摘要：掺钨氧化铟（In2O3:W, IWO）薄膜是一种新型的透明导电氧化物（TCO）薄膜，其中W与In之间存在着较高的价态差，使得IWO薄膜与其他TCO薄膜相比，在相同的电阻率条件下具有载流子浓度低、迁移率高和近红外区透射率高的特点。

本文利用直流反应磁控溅射法制备了IWO薄膜，利用扫描电子显微镜、Hall效应及分光光度计表征了薄膜的表面形貌及光电性能。

在氧分压为2.4×10- 1Pa的条件下，实验中制备的IWO薄膜最佳电阻率为6.3 10-4Ω·cm,最高载流子迁移率为34 cm2V-1s-1 ,载流子浓度达到2.9×1020 cm-3, 可见光平均透射率约为85%，近红外平均透射率大于80%。

关键词：In2O3:W薄膜；直流磁控溅射；氧分压；表面形貌；光电性能1 薄膜制备及性能测试透明导电氧化物薄膜的制备方法有多种,如磁控溅射、脉冲激光沉积( PLD)、喷涂热分解、溶胶-凝胶( SOL-GEL)法等[1]，本文采用的直流磁控溅射法，是磁控溅射法中的一种，与其他方法相比，直流磁控溅射法具有成膜速率大、可控性强、可大面积制备等优点[2]，在试验研究以及工业生产当中得到了广泛的应用。

影响薄膜光电性能的因素有很多，本文主要讨论氧分压对IWO薄膜性能的影响，研究过程中选择的实验条件为：溅射功率42W，溅射时间10MIN，掺钨量6.4 %（WT%），衬底温度275℃，溅射气压1.0PA，以上溅射参数保持不变的条件下，1-4号样品的氧分压分别为8×10- 2 PA、1.6×10- 1 PA、2.4×10- 1 PA、3.2×10- 1 PA。

利用X射线衍射法（XRD）表征了薄膜的晶体结构和结晶性能，利用扫描电子显微镜（SEM）表征薄膜表面形貌，利用台阶仪测量薄膜厚度，利用霍尔效应测量薄膜电阻率、迁移率等电学性能，使用分光光度计测定了薄膜在紫外、可见和近红外光区的透过率。

基于氧化石墨烯－微纳光纤的微加热器制备及其性能研究杨剑鑫;史可樟;李锡均;郑嘉鹏;史萌;蔡祥;朱德斌;邢晓波【摘要】利用近红外光在微纳光纤传输时产生的强烈倏逝场效应将氧化石墨烯沉积在微纳光纤表面，组装成具有优异光热转换性能的氧化石墨烯－微纳光纤，得到一种新型的光驱动微加热器。

通入较小功率的近红外光，微加热器能诱导各种液体（例如N，N-二甲基甲酰胺、去离子水）产生高温相变进而产生微泡，显示了良好的光热转换效应。

结果表明，在N，N-二甲基甲酰胺中，微泡按一定周期循环生长，重复搅动液体。

在微流芯片中，这些微泡可用于操控微纳米颗粒、微纳米线等。

在去离子水中，产生的微泡结构稳定、不易破裂，可用于聚集微粒等。

该微加热器具有制备简单、尺寸小、损耗低、激发功率小、效率高等优良特性，在微机电系统、微流控芯片等领域具有良好的应用前景。

%An optical technique is developed by depositing graphene oxide ( GO) onto a micro/nanofiber ( MNF) , which can act as a novel light-driven microheater based on the strong evanescent field from MNF and the photother-mal property of GO.Excited by the low-power near-infrared light, GO-MNF is capable of initiating the phase transi-tion of surrounding solvent ( such as N,N-dimethylformamide, deionized water) to generate photothermal microbub-bles.As a result, in the N,N-dimethylformamide, the microbubbles grows in a certain cycle, and stirs the liquid repeated.In the microfluidic chip, the microbubbles can manipulate micro/nano particles and wires.In the deion-ized water, the microbubble is stable and not easy to break, which can be used to gather particles.The microheater has the superiorities of easy fabrication, small size, low loss, low excitation power,and high efficiency, which would have prospective applications in micro-electromechanical systems, lab-on-a-chip, and other techniques.【期刊名称】《华南师范大学学报（自然科学版）》【年(卷),期】2015(000)004【总页数】5页(P30-34)【关键词】氧化石墨烯;微纳光纤;微加热器;光热效应;光热微泡【作者】杨剑鑫;史可樟;李锡均;郑嘉鹏;史萌;蔡祥;朱德斌;邢晓波【作者单位】华南师范大学华南先进光电子研究院，光及电磁波中心，广州510006; 华南师范大学物理与电信工程学院，广州 510006;华南师范大学华南先进光电子研究院，光及电磁波中心，广州510006; 华南师范大学物理与电信工程学院，广州 510006;华南师范大学物理与电信工程学院，广州 510006;华南师范大学华南先进光电子研究院，光及电磁波中心，广州510006;华南师范大学华南先进光电子研究院，光及电磁波中心，广州510006;广东职业技术学院轻化工程系，佛山528041;华南师范大学生物光子学研究院，激光生命科学教育部重点实验室，广州510631;华南师范大学华南先进光电子研究院，光及电磁波中心，广州510006; 华南师范大学生物光子学研究院，激光生命科学教育部重点实验室，广州510631【正文语种】中文【中图分类】O421世纪中期，随着光子器件向集成化和小型化方向发展，研究光与物质的相互作用受到越来越多的关注. 微纳光纤(MNF)作为一种典型的微纳光波导，具有强倏逝场效应、强光场约束、传输损耗低、制备工艺简易等优异特性，是构建微纳米级器件的重要元件[1]. 随着研究的逐渐深入，MNF与各种功能化材料(如荧光染料[2]、金属纳米颗粒[3]等)相结合，成功制备了功能化微光子器件. 通光后，MNF表面的强倏逝场与功能化纳米材料相互作用，产生诸如光致发光、等离子体共振等效应[2-3]，极大扩展了MNF微光子器件的研究与应用领域. 因此，将具有光波导的MNF巧妙地与功能化纳米材料结合起来，制备光激发MNF器件的方法，对于纳米光子学的发展具有重要意义.氧化石墨烯(GO)作为石墨烯的衍生物，既包含有导电的sp2杂化碳晶格，又含有绝缘的sp3杂化碳基体，使其具有非凡的光电、光热以及机械性能，在诸如光学、光电子学以及生物医学等领域具有潜在应用[4]. 最近研究表明，在近红外波段，GO具有强烈的光热效应，使之成为一种潜在的光疗药剂[5]. Zhang等[6]通过使用GO作为光疗药剂，提高了癌症的治疗效能. Markovic等[7]证明对于相同的辐射条件，GO展示出了比碳纳米管更优良的光热性能. 基于MNF倏逝场的微粒捕获技术已经成熟[8]，为MNF功能化器件的制作提供了新的思路.直径在微米量级的气泡，简称微泡. 它具有存在时间长、传输效率高、界面电位高等优良性质[9-10]，在微流阀、微流混合、微流泵等研究领域[11]有着广泛的应用. 常见的光热微泡是通过聚焦激光照射吸收性液体[12]、金属纳米颗粒[13]、金属薄膜[14]等发生光热效应或等离子体效应，从而诱发液体剧烈相变产生的. 然而，产生效率较低且所需的激光功率较大. 本文基于MNF的倏逝场效应和GO的光热效应，利用GO-MNF微加热器产生的热量诱导周围液体相变产生微泡，所需的激发能量仅40 mW，远小于其他案例[12-14]. 这里，N,N-二甲基甲酰胺(DMF)的沸点为152.8 ℃，证明沉积少量GO的MNF能产生152.8 ℃的高温. 因此，GO-MNF 是一种性能优异、光驱动的微加热器.1.1 微纳光纤的制备及其倏势场效应通过熔拉法[15]拉制普通二氧化硅单模光纤得到MNF. 将单模光纤上的外层涂覆层剥离，并用酒精将裸纤上残留的碎屑、灰尘洗净. 此后将其固定在酒精灯外焰处加热至熔融态，同时开动步进电机往两端匀速水平拉制光纤. 如图1中插图所示，拉制出来的MNF表面光滑呈锥形. 与普通光纤以全反射的方式传输光信号不同，MNF将有大部分能量以倏逝场形式在纤芯外部传输. Tong等[16]从理论上证明了随着MNF直径的减小，以倏逝场形式传输的能量将会变强，相应的约束在光纤直径范围内的能量将会减弱. 本文用时域有限差分法(FDTD)，对锥形MNF(长为150 μm、最大直径5 μm、端面直径2 μm)的光传输特性进行了分析，模拟区域是1个250 μm×100 μm的矩形. 这里，MNF长150 μm，最大直径5 μm，端面直径2 μm,工作波长为1 550 nm，锥形光纤的折射率为1.47，矩形区域的折射率定为DMF的折射率1.428. 通过模拟可以看出，光场以MNF为轴线呈对称分布(图1). 光能量分为2部分，一部分将沿MNF表面以倏逝场的形式传播，随着MNF 直径的减小，倏逝场效应会越来越强；另一部分在MNF内部传播并汇聚在MNF 端面处，产生较强的光强梯度. 已有文献证明，倏逝场对其作用范围内的微粒存在梯度力，可应用于微粒的捕获与聚集[17-18]. 同时，光从光纤末端射出，端面附近的光也对微粒产生梯度力，用于光操控[19]. 这种捕捉微粒的效用与光镊相似，而光镊需要复杂的透镜系统对激光束进行聚焦准直. 基于MNF的捕获具有成本低、操作简便的优势，能弥补光镊捕获的不足. 本文利用锥形MNF的倏逝场以及末端出射的光场将功能化材料吸附在其表面，从而实现功能化材料与MNF的融合. 1.2 氧化石墨烯的制备及其表征通过改进汉姆法制备得到氧化石墨烯[20-21]. 首先在80 ℃水浴加热条件下，将天然鳞片状石墨加入盛有浓硫酸、过硫酸钾和五氧化二磷混合液的三口烧瓶中，搅拌2 h，随后自然冷却，再用去离子水(DW)洗至中性，并用0.2 μm微孔滤膜过滤，所得产品放入干燥箱中，在室温下干燥24 h，得到纯化的石墨. 将纯化后的石墨放入盛有浓硫酸的三口烧瓶中，在冰浴条件下，边搅拌边加高锰酸钾，反应2 h后，用DW稀释；接着，在50 ℃下，将体积分数为30%的双氧水加入到上述混合物中，释出GO. 用1∶10的盐酸溶液去除混合物中的残酸和金属离子，用离心机在8 000 r/min的条件下离心5 min，去除未反应的天然鳞片状石墨，即可得到纯化的GO. 将上述GO经透析、离心、干燥工序制成粉末状. 将GO粉末溶于DMF溶剂中，经过3 h的水浴超声(KQ218, 60 W)处理，即制成实验所需的GO-DMF悬浮液. 图2描述了在1 200～1 600 nm波段浓度分别为0、0.05、0.20、0.50mg/mL的GO-DMF悬浮液的吸收光谱图. 随着浓度的增加，悬浮液对光的吸收显著增强. 表明在近红外波段，所制备的GO具有优异的光热转换性能.1.3 器件的组装、原理和过程图3为组装GO-MNF微加热器的实验装置. 光源由自发辐射光源(ASE)连接掺铒光纤放大器(EDFA)而成，输出功率≤100 mW、波长范围在1 527～1 566 nm的近红外光. 利用装有CCD的倒置荧光显微镜作为观察工具，清晰观察并记录实验现象. 光纤被固定在三维微调整架(MR)上，一端与光源相连接，另一端被拉制成MNF并浸没在GO悬浮液中.图4为GO-MNF的组装过程. 打开光源初期,在MNF尖端的光场作用下，悬浮液中的GO汇聚移动并排列成一条线，之后向两边扩展. t=25 s时，GO开始附着在MNF的尖端(图4B). 由于激光被GO吸收和散射，激光对悬浮GO的作用力减弱，因而无法驱动GO微粒. 由于GO的光热效应，GO不断吸收光并产生热量，形成温度梯度，诱导产生自然对流[22]. 自然对流作为新的驱动源，不断驱使悬浮的GO进行环流运动，其驱动的速度远大于光场梯度力的驱动速度. 在此过程中，悬浮的GO微粒靠近光滑的MNF时，散射产生的倏逝场将GO捕获[19]. 因此，GO 沿着光源传播的反方向不断沉积. t=50 s时，在MNF上的GO沉积长度为52.5μm(图4C). t=75 s时，断开光源，沉积停止，组装的GO沉积长度达81 μm(图4D). 表明通过控制光源的开关可以简易地控制GO的沉积状态.在范德瓦耳斯力的作用下，GO沉积即使在无光作用下也能紧紧吸附在MNF上.图5为GO-MNF的扫描电子显微镜(SEM)观察形貌的图像，GO在MNF上沉积不均匀，但吸附紧密，不易脱落.本文基于GO的光热效应，利用GO沉积的MNF在小功率红外光射下产生的热量诱导周围液体相变产生微泡.为了定量描述各种液体内光热微泡的生长现象，以光热微泡的直径来表示其生长情况. 由图6A可知，t=0 s时，微泡开始出现，持续生长至t=10 s时达到最大(微泡直径D=129.94 μm). 然后，微泡爆裂并在相同位置重新生长. 按上述生长规律不断地循环. 由图7可知DMF溶液中微泡的生长具有周期性(t=10 s)，直径最大值在128～138 μm范围. 与DMF溶液不同的是，DW微泡始终固定在生长点处，持续生长(图6B). t=10 s时，D=87.14 μm；t=20 s时，D=124.01 μm；t=30 s后，直径基本保持在D=127.14 μm. 如图7所示，DW微泡的生长经历了快速增长与稳定不变2个阶段. 整个生长过程并未发生爆破.通过大量的实验发现，在DMF中产生的微泡，按一定周期循环生长，具有循环周期短、直径大的特性.在短时间内，微泡大范围重复搅动周围液体，因此，可应用于微流操控领域[23]. 而在去离子水中，微泡在生长过程中结构稳定，不易破裂. 当生长到极大值后，长期稳定存在，可用于聚集微粒等领域[14].利用MNF的倏逝场效应成功组装了GO-MNF光控微加热器. 利用GO优异的光热转换性能，在DMF、去离子水等溶剂中生成性质各异的光热微泡. 各类微泡可按其生长规律应用于不同的微操作领域. 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胶体悬液中白云母与铁铝氧化物表面双电层的相互作用王艳平;徐仁扣;李九玉【摘要】@@ 白云母是一种原生矿物,也是土壤中常见的层状硅酸盐矿物,其负电荷主要由四面体结构中的Al置换Si而来[1].在通常的pH条件下,白云母带负电荷,可变电荷土壤中的铁、铝氧化物带正电荷.当白云母与铁、铝氧化物存在于同一悬液体系中时,带相反电荷的胶体颗粒之间可以发生相互作用.Qafoku和Sumner[2]提出可变电荷土壤中带相反电荷的胶体颗粒表面双电层重叠的假说.【期刊名称】《土壤学报》【年(卷),期】2011(048)003【总页数】4页(P650-653)【关键词】扩散双电层;zeta电位;白云母;铁铝氧化物;胶体颗粒相互作用【作者】王艳平;徐仁扣;李九玉【作者单位】土壤与农业可持续发展国家重点实验室(中国科学院南京土壤研究所),南京,210008;中国科学院研究生院,北京,100049;土壤与农业可持续发展国家重点实验室(中国科学院南京土壤研究所),南京,210008;中国科学院研究生院,北京,100049;土壤与农业可持续发展国家重点实验室(中国科学院南京土壤研究所),南京,210008;中国科学院研究生院,北京,100049【正文语种】中文【中图分类】S153白云母是一种原生矿物，也是土壤中常见的层状硅酸盐矿物，其负电荷主要由四面体结构中的Al置换Si而来［1］。

在通常的 pH条件下，白云母带负电荷，可变电荷土壤中的铁、铝氧化物带正电荷。

当白云母与铁、铝氧化物存在于同一悬液体系中时，带相反电荷的胶体颗粒之间可以发生相互作用。

Qafoku和Sumner［2］提出可变电荷土壤中带相反电荷的胶体颗粒表面双电层重叠的假说。

Hou等［3］在高岭石与铁铝氧化物混合胶体悬液体系中的研究结果表明，带相反电荷胶体颗粒的扩散层的重叠降低了高岭石表面的有效负电荷密度，使得混合体系的zeta电位向正值方向位移。

Tombácz［4］在蒙脱石与氧化铁的混合体系中也观察到类似的现象。

Effect of Crystallographic Structure of MnO2on Its Electrochemical Capacitance PropertiesS.Devaraj and N.Munichandraiah*Department of Inorganic and Physical Chemistry,Indian Institute of Science,Bangalore-560012,IndiaRecei V ed:No V ember14,2007;In Final Form:January7,2008MnO2is currently under extensive investigations for its capacitance properties.MnO2crystallizes into severalcrystallographic structures,namely,R, ,γ,δ,andλstructures.Because these structures differ in the wayMnO6octahedra are interlinked,they possess tunnels or interlayers with gaps of different magnitudes.Becausecapacitance properties are due to intercalation/deintercalation of protons or cations in MnO2,only somecrystallographic structures,which possess sufficient gaps to accommodate these ions,are expected to beuseful for capacitance studies.In order to examine the dependence of capacitance on crystal structure,thepresent study involves preparation of these various crystal phases of MnO2in nanodimensions and to evaluatetheir capacitance properties.Results of R-MnO2prepared by a microemulsion route(R-MnO2(m))are alsoused for comparison.Spherical particles of about50nm,nanorods of30-50nm in diameter,or interlockedfibers of10-20nm in diameters are formed,which depend on the crystal structure and the method ofpreparation.The specific capacitance(SC)measured for MnO2is found to depend strongly on thecrystallographic structure,and it decreases in the following order:R(m)>R=δ>γ>λ> .A SC valueof297F g-1is obtained for R-MnO2(m),whereas it is9F g-1for -MnO2.A wide(∼4.6Å)tunnel size andlarge surface area of R-MnO2(m)are ascribed as favorable factors for its high SC.A large interlayer separation(∼7Å)also facilitates insertion of cations inδ-MnO2resulting in a SC close to236F g-1.A narrow tunnelsize(1.89Å)does not allow intercalation of cations into -MnO2.As a result,it provides a very small SC.1.IntroductionIn recent years,electrochemical capacitors(ECs)have received a great attention in the filed of electrochemical energy storage and conversion because of their high power capability and long cycle-life.An EC is useful as an auxiliary energy device along with a primary power source such as a battery or a fuel cell for power enhancement in short pulse applications.1-4 Charge storage mechanisms in EC capacitor materials include separation of charges at the interface between the electrode and the electrolyte and/or fast faradaic reactions occurring at the electrode.Capacitance,which arises from separation of charges, is generally called electric double-layer capacitance(EDLC). Capacitance due to a faradaic process is known as pseudoca-pacitance.Because the magnitude of capacitance of these types of capacitors is several times greater than that of conventional capacitors,ECs are also known as supercapacitors or ultraca-pacitors.Various materials investigated for ECs include(i)carboneous materials,(ii)conducting polymers,and(iii)transition-metal oxides.3Among transition-metal oxides,amorphous hydrous ruthenium oxide(RuO2‚x H2O)has specific capacitance(SC) as high as760F g-1because of the solid-state pseudofaradaic reaction.5-8However,the high cost,low porosity,and toxic nature of RuO2limit commercialization of supercapacitors employing this material.Therefore,there is a need to investigate alternate transition-metal oxides,which are cheap,available in abundance,nontoxic,and environmentally friendly.Manganese dioxide has attracted much attention9-21because it has these favorable properties and it is widely used as a cathode material in batteries.22However,the SC values reported are lower than the values obtained for RuO2‚x H2O,and studies on various ways of increasing the SC are reported.14,15Hydrous MnO2exhibits pseudocapacitance behavior in several aqueous electrolytes of alkali salts such as Li2SO4,Na2-SO4,K2SO4,and so forth.Transition of Mn4+/Mn3+involving a single electron transfer is responsible for the pseudocapacitance behavior of MnO2.10,23,24MnO2exists in several crystallographic forms,which are known as R, ,γ,δ,andλforms.22,25The R, ,andγforms possess1D tunnels in their structures,theδis a2D layered compound,and theλis a3D spinel structure. The properties of MnO2largely depend on its crystallographic nature.Because of various crystallographic structures,MnO2 is useful as a molecular sieve,26a catalyst,27and an electrode material in batteries22as well as in supercapacitors.9-21Because these structures differ in the way MnO6octahedra are inter-linked,they possess tunnels or interlayers with gaps of different magnitudes.Because capacitance properties are due to intercala-tion/deintercalation of protons or cations in MnO2,only the crystallographic structures,which possess sufficient gaps to accommodate these ions,are anticipated to be useful for capacitance studies.It is expected that the amount of alkali cations or protons intercalated/extracted into/from MnO2lattice and hence its SC largely depends on either the size of the tunnel or the interlayer separation between sheets of MnO6octahedra. MnO2with three different crystallographic forms(R, ,and γ)was prepared by the hydrothermal-electrochemical method, and lithium insertion behavior was studied.28,29R-andγ-MnO2 were prepared by the electrolysis of aqueous MnSO4solution containing various alkali and alkaline earth salts at various pH and potential values.It was found that the crystallographic structure of MnO2depends on the radius of the alkali or alkaline earth metal-ion,the pH,and the potential.30Brousse et al.studied the dependence of capacitance on surface area for various*Corresponding author.Tel:+91-80-22933183.Fax:+91-80-23600683.E-mail:muni@ipc.iisc.ernet.in.4406J.Phys.Chem.C2008,112,4406-441710.1021/jp7108785CCC:$40.75©2008American Chemical SocietyPublished on Web02/26/2008amorphous and crystalline samples of MnO 2.31On the basis of cyclic voltammetric data,SC values were calculated.The SC values obtained for δ-MnO 2were in the range of 80-110F g -1,which was slightly smaller than the values found for amorphous samples.The SC values obtained for -MnO 2(5F g -1),γ-MnO 2(30F g -1),and λ-MnO 2(70F g -1)were smaller than the values obtained for δ-MnO 2.31The present trend of research in many fields is to employ nanosize materials,which are expected to possess better properties than the micrometer-size materials.Studies on the capacitance properties of various crystallographic forms of MnO 2are scarce in the literature.31The intention of the present study is to prepare nanosize particles of R -, -,γ-,δ-,and λ-MnO 2samples and to evaluate their properties with a special interest in supercapacitor behavior.A comparison of the SC values of the various structures of MnO 2is made,and appropri-ate explanations for the variation of SC values are provided.2.Experimental SectionAll chemicals were of analytical grade,and they were used without further purification.MnSO 4‚H 2O,KMnO 4,Na 2SO 4,sodium dodecyl sulfate (SDS),and cyclohexanewere purchasedfrom Merck,n-butanol from SD Fine Chemicals,(NH 4)2S 2O 8from Ranbaxy,Mn(NO 3)2‚4H 2O from Fluka,and LiMn 2O 4from Aldrich.All solutions were prepared in doubly distilled (DD)water.Samples of MnO 2with different crystal structures were synthesized by the following procedures.2.1.Synthesis of R -MnO 2.Nanoparticles of R -MnO 2were synthesized by redox reaction between stoichiometric quantities of MnSO 4and KMnO 4in both aqueous medium 9and a microemulsion medium.15In a typical synthesis in aqueous medium,10mL of 0.1M KMnO 4solution was mixed with 10mL of 0.15M MnSO 4‚H 2O solution and stirred continuously for 6h.A dark-brown precipitate thus formed and was washed several times with DD water,centrifuged,and dried at 70°C in air for 12h.Details of the microemulsion method of synthesis of nanostructured MnO 2is reported elsewhere.15MnO 2samples obtained from aqueous and microemulsion routes are hereafter referred to as R -MnO 2and R -MnO 2(m),respectively.About 300mg of the product was synthesized in each batch.2.2.Synthesis of -MnO 2.Nanorods of -MnO 2were prepared by hydrothermal treatment of aqueous solution of Mn-(NO 3)2‚4H 2O.20Twenty-five milliliters of 0.5M Mn(NO 3)2‚4H 2O solution was loaded into a Teflon-lined stainless-steel autoclave (capacity:40mL)and heated at 190°C for 6h.The autoclave was cooled slowly to room temperature.A dark brown powder was formed.It was washed several times with DD water,centrifuged,and dried at 70°C in air for 12h.Because the amount of product obtained in a batch of synthesis (typically 20mg)was small,the synthesis was repeated several times to get sufficient quantity for the experiments.During this synthesis,it was noticed that a minor variation in temperature caused drastic variations in the properties of the product.After several experiments,the experimental conditions of hydrothermal synthesis were optimized.2.3.Synthesis of γ-MnO 2.Nanowires/nanorods of γ-MnO 2were prepared from MnSO 4using (NH 4)2S 2O 8as an oxidizing agent.21Stoichiometric amounts of MnSO 4‚H 2O and (NH 4)2S 2O 8were dissolved in DD water.They were mixed together and heated at 80°C for 4h.A dark-brown precipitate wasseparated,Figure 1.Crystal structures of R -, -,γ-,δ-,and λ-MnO 2.TABLE 1:Tunnel Size of Different Crystallographic Forms of MnO 234-36crystallographicformtunnel size/ÅR (1×1),(2×2) 1.89,4.6 (1×1)1.89γ(1×1),(1×2) 1.89,2.3δinterlayer distance7.0Figure 2.Powder XRD pattern of R -,R (m)-, -,γ-,δ-,and λ-MnO 2.The (hkl )planes are indicated.The data were recorded at a sweep rate of 0.5°min -1using Cu K R source.TABLE 2:Crystal Radius and Size of the Alkali Cation in Aqueous Solution 37alkali cationcrystal radius/Åin aqueous solution/ÅLi +0.66Na +0.954K + 1.333H +9Effect of Crystallographic Structure of MnO 2J.Phys.Chem.C,Vol.112,No.11,20084407washed,and dried at 70°C.About 3.8g of the product was synthesized in a batch.2.4.Synthesis of δ-MnO 2.Nanoplatelets of δ-MnO 2were prepared by following the same route of synthesis of R -MnO 2,but with double the stoichiometric amount of KMnO 4.The presence of excess K +ion stabilizes the 2D layered δ-structure of MnO 2.The quantity obtained was about 340mg.2.5.Synthesis of λ-MnO 2.λ-MnO 2was prepared by delithia-tion of LiMn 2O 4.32Spinel LiMn 2O 4powder was treated with 0.5M HCl at 25°C for 24h.About 500mg of the product was obtained in a batch.2.6.Characterization.Powder X-ray diffraction (PXRD)patterns of MnO 2were recorded using Philips XRD X’PERT PRO diffractometer using Cu K R radiation (λ)1.54178Å)as the source.The morphology of MnO 2was examined using an FEI scanning electron microscope (SEM)model SIRION and an FEI high-resolution transmission electron microscope (HR-TEM)model TECNAI F 30.The Brunauer -Emmett -Teller (BET)surface area and pore volume were measured by the nitrogen gas adsorption -desorption method at 77K using a Quantachrome surface area analyzer model Nova-1000.The pore size distribution was calculated by the Barrett -Jayner -Halenda (BJH)method using the desorption branch of the isotherm.Samples were heated at 120°C for 2h in air prior to surface property measurements.IR spectra were recorded using a Perkin-Elmer FT-IR spectrophotometer model Spectrum One,using KBr pellets.KBr and samples were heated at 80°C in vacuum overnight prior to measurements.Thermogravimetric analysis (TGA)was performed in the temperature range from ambient to 800°C in air at a heating rate of 10°C/min using a Perkin-Elmer thermal analyzer model Pyris Diamond TG/DTA.2.7.Electrochemical Measurements.Electrodes were pre-pared on high-purity battery-grade Ni foil (0.18mm thick)as the current collector.The Ni foil was polished with successive grades of emery,cleaned with detergent,washed copiously with DD water,rinsed with acetone,dried,and weighed.MnO 2(70wt %),acetylene black (20wt %),and polyvinylidene difluoride (10wt %)were ground in a mortar,and a few drops of 1-methyl-2-pyrrolidinone was added to form a syrup.It was coated on to the pretreated Ni foil (area of coating:2cm 2)and dried at 110°C under vacuum.Coating and drying steps were repeated to get the loading level of the active material close to 0.5mg cm -2.Finally,the electrodes were dried at 110°C under vacuum for 12h.A Sartorious balance model CP22D-OCE with 10µgFigure 3.SEM micrographs of R -,R (m)-,and -MnO 2.1and 2refer to different magnifications of a sample.4408J.Phys.Chem.C,Vol.112,No.11,2008Devaraj andMunichandraiahsensitivity was used for weighing the electrodes.A glass cell of capacity 70mL,which had provisions for introducing a MnO 2working electrode,Pt auxiliary electrodes,and a reference electrode,was employed for electrochemical studies.An aqueous solution of 0.1M Na 2SO 4was used as the electrolyte.A saturated calomel electrode (SCE)was used as the reference electrode,and potential values are reported against SCE.Electrochemical studies were carried out using a potentiostat -galvanostat EG&G model Versastat II or Solartron model SI 1287.All electrochemical experiments were carried out at 20(2°C.3.Results and DiscussionThe reactions involved in the synthesis of different crystal-lographic forms of MnO 2are listed below:We have shown recently that R -MnO 2prepared in a micro-emulsion medium (R -MnO 2(m))possesses electrochemical properties superior to those of the samples prepared in aqueous medium.15Some important results of R -MnO 2(m)are also included here for the purpose of comparison.3.1.XRD Studies.The structural frame work of MnO 2consists of basic MnO 6octahedra units,which are linked in different ways to produce different crystallographic forms.22The different ways of sharing the vertices and edges of MnO 6octahedra units lead to the building of 1D,2D,and 3D tunnel structures.33The different crystallographic forms are described by the size of the tunnel formed with the number ofoctahedraFigure 4.SEM micrographs of γ-,δ-,and λ-MnO 2.1and 2refer to different magnifications of a sample.3MnSO 4+2KMnO 4+2H 2O f 5R -MnO 2+K 2SO 4+2H 2SO 4(1)Mn(NO 3)2+1/2O 2+H 2O f -MnO 2+2HNO 3(2)MnSO 4+(NH 4)2S 2O 8+2H 2O f γ-MnO 2+(NH 4)2SO 4+2H 2SO 4(3)3MnSO 4+2KMnO 4(excess)+2H 2O f 5δ-MnO 2+K 2SO 4+2H 2SO 4(4)2LiMn 2O 4+4HCl f LiCl +3λ-MnO 2+MnCl 2+2H 2O (5)Effect of Crystallographic Structure of MnO 2J.Phys.Chem.C,Vol.112,No.11,20084409subunits (n ×m ).The structures are shown schematically in Figure 1,and the type of tunnel formed as well as the size of tunnels are presented in Table 1.34-36The structure of R -MnO 2(Figure 1R )consists of double chains of edge-sharing MnO 6octahedra,which are linked at corners to form 1D (2×2)and (1×1)tunnels that extend in a direction parallel to the c axis of the tetragonal unit cell.The size of the (2×2)tunnel is ∼4.6Å,which is suitable for insertion/extraction of alkali cations (Table 2).34,37A small amount of cations such as Li +,Na +,K +,NH 4+,Ba 2+,or H 3O +is required to stabilize the (2×2)tunnels in the formation of R -MnO 2.34 -MnO 2(Figure 1 )is composed of single strands of edge-sharing MnO6Figure 5.TEM image (R 1),HRTEM image (R 2),and bright-field (R 3)and dark-field (R 4)TEM image of R -MnO 2.SAD pattern is given as an inset in R 1.Also shown are TEM images at different magnifications (R (m)1,R (m)2,and R (m)3),HRTEM image (R (m)4)of R -MnO 2(m).SAD pattern is given as an inset in R (m)2.4410J.Phys.Chem.C,Vol.112,No.11,2008Devaraj andMunichandraiahoctahedra to form a 1D (1×1)tunnel.Because of the narrow (1×1)tunnel of size (∼1.89Å),35 -MnO 2cannot accom-modate cations.22The structure of γ-MnO 2(Figure 1γ)is random intergrowth of ramsdellite (1×2)and pyrolusite (1×1)domains.38This intergrowth structure can be described in terms of De Wolff disorder and microtwinning.38δ-MnO 2(Figure 1δ)is a 2D layered structure with an interlayer separation of ∼7Å.36It has a significant amount of water and stabilizing cations such as Na +or K +between the sheets of MnO 6octahedra.λ-MnO 2(Figure 1λ)is a 3D spinel structure.32Powder XRD patterns of MnO 2samples are shown in Figure 2.Although the pattern of samples marked R and R (m)exhibitFigure 6.TEM images ( 1, 2),HRTEM image of a single nanorod ( 3),and the corresponding FFT pattern ( 4)of -MnO 2.Also shown are TEM images at different magnifications (γ1,γ2),HRTEM image (γ3),and the corresponding FFT pattern (γ4)of γ-MnO 2.SAD pattern is given as an inset in γ2.Effect of Crystallographic Structure of MnO 2J.Phys.Chem.C,Vol.112,No.11,20084411fluorescence,broad peaks at2θ)11.6and37.3°for R and at 2θ)10.8,37.0,41.7,and65.5°for R(m)are clearly present. It is thus inferred that these samples are in a poorly crystalline state with a short-range R-crystallographic form(JCPDS no. 44-0141).The XRD patterns marked andγ(Figure2)confirm the formation of -(JCPDS no.24-0735)andγ-(JCPDS no. 14-0644)crystallographic forms of MnO2,respectively.Broad peaks at2θ)12.2,24.8,37.0,and65.4°in the pattern marked δ(Figure2)correspond toδ-MnO2(JCPDS no.18-0802),and it is also considered to be in a poorly crystalline phase.Unlikethe above patterns,the diffraction pattern markedλin Figure2 consists of clear peaks,suggesting that this sample possesses a long-range crystalline order.This pattern was indexed to cubic symmetry with space group Fd3m(no.227)using the Appleman program,and the lattice constants were calculated.The lattice constants obtained are a)b)c)8.03Å,and these values are in good agreement with the reported data for the pure phase ofλ-MnO2(JCPDS no.44-0992).323.2.SEM and TEM Studies.SEM images of R-MnO2,R-MnO2(m),and -MnO2(two magnifications for each)are shown in Figure3.R-MnO2and R-MnO2(m)are composed of spherical aggregates of nanoparticles without clear interparticle boundaries(Figure3R1,R2,R(m)1,and R(m)2).Hydrothermal treatment of the aqueous Mn(NO3)2solution yields1D nanorods of -MnO2(Figure3 1and 2),which are about50nm in diameter and several micrometers in length.Adjacent nanorods are fused to each other.SEM images ofγ-,δ-,andλ-MnO2are presented in Figure 4in two magnifications for each.The morphology ofγ-MnO2 consists of spherical brushes with straight and radially grown nanorods.Several nanorods of30-50nm in diameter and a few micrometers in length assemble together to form spherical brushes.δ-MnO2(Figure4)consists of spherical agglomerates made of interlocked short fibers of∼10-20nm in diameter. The particles ofλ-MnO2(Figure4)exhibit random shapes with sizes varying from a few tens of nanometers to a few micrometers.TEM images of R-MnO2and R-MnO2(m)are presented in Figure5.The TEM image(Figure5R1)shows that R-MnO2 consists of agglomerated particles.A selected area diffraction (SAD)pattern is shown in the inset of Figure5R1.It is seen that a couple of weak rings corresponding to the crystal planes of R-MnO2are evolved,indicating the poor crystalline nature of the sample.The HRTEM image(Figure5R2)indicates the crystalline nature of the sample.The bright-field and corre-sponding dark-field TEM images of R-MnO2(Figure5R3and R4)suggest that several nanoparticles of less than5nm are agglomerated.It seen in Figure5R(m)1,R(m)2,and R(m)3that R-MnO2-(m)has a hexagonal shape of∼50nm size.The SAD pattern is shown as the inset to Figure5R(m)2.It is seen that rings corresponding to crystal planes are absent.The spotty diffraction pattern suggests that the nanoparticles of MnO2obtained from microemulsion route possess single-crystal character.The HR-TEM image(Figure5R(m)4)shows the interplanar distance to be2.392Å,which agrees well with separation between the[211] planes of R-MnO2.Shown in Figure6 1and 2are nanorods of -MnO2,which are20-50nm in diameter and several micrometers in length. In the HRTEM(Figure6 3),lattice fringes are clearly seen. The interplanar distance is0.311nm,which agrees well with the separation between the[110]planes of -MnO2.The corresponding FFT pattern(Figure6 4)displays spot lines perpendicular to the lattice fringes of Figure6 3,suggesting the crystalline nature of -MnO2.Furthermore,the length of the nanorod extends along the[110]direction.The TEM images shown in Figure6γ1andγ2suggest that nanorods ofγ-MnO2grow in a random fashion.The SAD pattern shown as inset in Figure6γ2reveals that rings and spots corresponding to crystal planes ofγ-MnO2are better evolved compared to R-MnO2,which is in agreement with the XRD results(Figure2).It is seen in the HRTEM image(Figure6γ3) that several nanowires of less than1nm are self-assembled to form nanorods.The interplanar distance calculated from the lattice fringes of HRTEM is0.212nm,which corresponds to separation of the[200]ttice fringes are inclined at about 60°toward the self-assembled nanowires.It is also seen in the HRTEM that nanorods exhibit better crystalline character at the center of the rod than the outer part.The FFT pattern(Figure 6γ4)corresponding to the HRTEM image ofγ-MnO2shows spot lines perpendicular to lattice fringes confirming the crystalline nature and also indicating that the nanorod extends in the[200]direction.TEM images ofδ-MnO2(Figure7δ1,δ2,andδ3)show that nanofibers with thicknesses less than10nm are agglomer-ated to form interconnected spherical structures ofδ-MnO2.The SAD pattern shown as inset in Figure7δ1supports the partial crystalline nature ofδ-MnO2inferred from the powder XRD pattern.The HRTEM image(Figure7δ4)indicates the crystal-line nature of the sample.TEM images ofλ-MnO2(Figure7λ1andλ2)suggest that the particles grow in different shapes and the adjacent particles fuse to each other.Spots evolved in the FFT pattern(Figure 7λ3)are indexed,and they confirm the highly crystalline nature ofλ-MnO2.Energy-dispersive analysis of the X-ray(EDAX) spectrum shown in Figure7λ4indicates the presence of manganese and oxygen.3.3.Porosity Measurements.Nitrogen adsorption-desorp-tion isotherms for MnO2samples were measured(see Supporting Information,Figure S1).The isotherms of R-,R(m)-,γ-,and δ-MnO2belong to type IV,which indicates the mesoporous nature of the samples with an hysteresis loop.Alternatively, the isotherm ofλ-MnO2belongs to type II,which is a characteristic feature of nonporous solids.39The specific surface area,total pore volume,and average pore diameter for all crystallographic forms of MnO2are listed in Table3.Although R-MnO2and R-MnO2(m)exhibit the same type of adsorption-desorption isotherm,their surface area and pore size distribution are different.The specific surface area of123m2g-1and total pore volume of0.25cm3Å-1g-1obtained for R-MnO2(m)are greater than the specific surface area of17.3m2g-1and pore volume of0.037cm3Å-1g-1obtained for R-MnO2.These differences indicate that R-MnO2(m)is more porous thanR-MnO2,and,hence,it is anticipated that R-MnO2(m)possesses higher electrochemical activity.Lower values of specific surface area and total pore volume are observed forγ-MnO2compared to R-MnO2(m).A high average pore diameter of129Åobtained forδ-MnO2is TABLE3:Specific Surface Area and Total Pore Volume of Polymorphic MnO2crystallographicformspecificsurface area(m2g-1)totalpore volume(cc/Å/g)averagepore diameter(Å) R17.290.0367585.020R(m)123.390.2481180.431γ31.560.0600676.112δ20.930.06750129.014λ 5.210.0087867.4514412J.Phys.Chem.C,Vol.112,No.11,2008Devaraj and Munichandraiahattributed to the wide interlayer separation.The lowest values of specific surface area (5.2m 2g -1)and total pore volume (0.0088cm 3Å-1g -1)are obtained for λ-MnO 2.It is inferred from the adsorption isotherm and Table 3that λ-MnO 2is the least porous among all samples.3.4.Vibrational Spectroscopic Studies.In IR spectra of MnO 2samples (see Supporting Information,Figure S2),a broad band around 400-700cm -1observed for all crystallographic forms of MnO 2is ascribed to Mn -O bending vibration.A broad band around 3400cm -1and a weak band around 1630cm -1observed for R -,R (m)-,γ-,and δ-MnO 2are attributed to stretching and bending vibrations of H -O -H,respectively.40Bands corresponding to vibrations of water molecules are not observed for -and λ-MnO 2,suggesting that these phases do not contain water.This is in agreement with the literature report that -and λ-MnO 2do not contain lattice water.22,32Figure 7.TEM images at different magnifications (δ1,δ2,and δ3)and HRTEM image (δ4)of δ-MnO 2.SAD pattern in given as an inset in δ1.Also shown are TEM images at different magnifications (λ1,λ2),FFT pattern (λ3),and EDAX spectrum (λ4)of λ-MnO 2.Effect of Crystallographic Structure of MnO 2J.Phys.Chem.C,Vol.112,No.11,200844133.5.Thermogravimetric Analysis.TGA thermograms of different crystallographic forms of MnO 2were recorded (see Supporting Information,Figure S3).Progressive weight loss from room temperature to 500°C is observed for R -,R (m)-,γ-,and δ-MnO 2samples.This is due to removal of water.13Weight loss is not observed in the case of -and λ-MnO 2samples because of the absence of water in these phases.22,32At around 550°C,a sudden weight loss is observed for all samples except for δ-MnO 2.This weight loss corresponds to the transformation of MnO 2to Mn 2O 3.41As δ-MnO 2prepared in the presence of excess of K +ions,these ions present between the layers of δ-MnO 2prevent the conversion of MnO 2to Mn 2O 3.The weight loss corresponding to this process is sharp in the case of -MnO 2as it has very narrow (1×1)tunnel in which no stabilizing ions are present.22The weight loss is much less (<2wt %)in the case of R -MnO 2because the stabilizing cations present at low concentration in its (2×2)tunnels prevent the transformation to a large extent.Weight loss values of about 2and 6wt %are observed for R -and R -MnO 2(m),respectively.This difference is ascribed to different amounts of K +ions present in their (2×2)tunnels.All crystallographic forms of MnO 2were annealed in air for 3h at various temperatures ranging from ambient to 800°C at intervals of 200°C,and powder XRD patterns were recorded (not shown).Conversion of MnO 2to Mn 2O 3is observed for all samples annealed at g 400°C except for δ-MnO 2,thus supporting the analysis of TGA data.3.6.Electrochemical Studies.There are two mechanisms proposed for charge storage in MnO 2.The first mechanism involves intercalation/extraction of protons (H 3O +)or alkali cations such as Li +,Na +,K +,and so forth into the bulk of oxide particles with concomitant reduction/oxidation of the Mn ion.10,23The second mechanism is a surface process,which involves the adsorption/desorption of alkali cations.17Although the bulk process (reaction 6)is anticipated to occur in crystalline samples of MnO 2,the surface process (reaction 7)occurs in amorphous samples.24Electrodes,which were fabricated with different crystal-lographic forms of MnO 2,were subjected to electrochemical studies in aqueous 0.1M Na 2SO 4electrolyte.Cyclic voltam-mograms recorded between 0and 1.0V at a sweep rate of 20mV s -1for all electrodes are shown in Figure 8.All voltam-mograms are nearly rectangular in shape.The rectangular shape of the voltammogram is a fingerprint for capacitance behavior.1-3Among all samples,the highest current density is obtained for R -MnO 2(m)(Figure 8),which is attributed to the higher porosity and greater surface area in relation to the rest of the samples.The voltammograms of R -and δ-MnO 2electrodes nearly overlap,suggesting that the SC values of R -and δ-MnO 2are comparable.The voltammetric current of the γ-MnO 2electrode (Figure 8)is lower than the currents of the R -,R (m)-,and δ-MnO 2electrodes.There is an increase in current near 0and also at 1V,suggesting that the overpotentials for the hydrogen evolution reaction (HER)as well as the oxygen evolution reaction (OER)are lower for γ-MnO 2.The current values(Figure 8)for the -and λ-MnO 2electrodes are very low,suggesting that the capacitance values of these samples are very small.Thus,the SC values of MnO 2samples qualitatively decrease in the following order:R (m)>R =δ>γ>λ> .Quantitatively,the SC values were evaluated from galvanostatic charge -discharge cycling as described below.The electrodes were subjected to galvanostatic charge -discharge cycling between 0and 1.0V in aqueous 0.1M Na 2-SO 4electrolyte at several current densities.The variations of potential with time during the first few charge -discharge cycles at a current density of 0.5mA cm -2are shown in Figure 9.Linear variation of potential during both charging and discharg-ing processes are observed for all MnO 2electrodes.The linear variation of potential during charging and discharging processes is another criterion for capacitance behavior of a material in addition to exhibiting rectangular voltammograms.1The dura-tions of charging and discharging are almost equal for each electrode,implying high columbic efficiency of charge -discharge cycling.However,the durations of charge and discharge cycles are different for different crystallographic forms of MnO 2,suggesting that the SC values are different similar to the observation made from cyclic voltammograms (Figure 8).The SC values were calculated from charge -discharge cycles using the following equationwhere,I is the discharge (or charge)current,t is the discharge (or charge)time,∆E ()1.0V)is the potential window of cycling,and m is the mass of MnO 2.The discharge SC values for all electrodes are presented in Figure 10.The variation of SC values follows the order R (m)>R =δ>γ>λ> .The SC values are 240F g -1for R -MnO 2and 236F g -1for δ-MnO 2.Alternatively,they are as low as 9F g -1for -MnO 2and 21F g -1for λ-MnO 2.The SC values are generally expected to follow the trend of surface area if capacitance is due to double-layer charging or adsorption of cations on the surface of active material.In recent studies,it is shown that the surface process is dominant in the amorphous sample of MnO 2.24Because all samples of MnO 2prepared in the present study are in the crystalline or poorly crystalline state of various structures,the low values of SC obtained are not due to the amorphous nature of the samples.In fact,λ-MnO 2has greater crystallinity than the rest of the samples (Figure 2)because of its larger particle size (Figure 4),but its SC is low.It is inferred that SC values largely depend on crystal structure and not on surface area while making comparisons among various structures (within thesameFigure 8.Cyclic voltammograms of R -,R (m)-, -,γ-,δ-,and λ-MnO 2recorded between 0and 1.0V vs SCE in aqueous 0.1M Na 2SO 4at a sweep rate of 20mV s -1.SC )It /(∆Em )(8)MnO 2+M ++e -h MnOOM (M +)Li +,Na +,K +,or H 3O +)(6)(MnO 2)surface +M ++e -h (MnOOM)surface (M +)Li +,Na +,K +,or H 3O +)(7)4414J.Phys.Chem.C,Vol.112,No.11,2008Devaraj andMunichandraiah。

文章编号:167320291(2005)0120074204化学机械抛光中抛光液流动的微极性分析张朝辉1,雒建斌2(1.北京交通大学机械与电子控制工程学院,北京100044;2.清华大学摩擦学国家重点实验室,北京100084)摘　要:化学机械抛光(Chemical Mechanical Polishing ,CMP )是用于获取原子级平面度的一种有效手段,抛光液是其中重要因素之一.目前,CMP 的抛光液通常使用球形纳米级颗粒来加速切除和优化抛光质量,这类流体的流变性能必须考虑微极性效应的影响.本文给出了考虑微极性效应的CMP 运动方程,并进行了数值求解,这有助于了解CMP 的作用机理.数值模拟表明,微极性将提高抛光液的等效粘度从而在一定程度上提高其承载能力,加速材料去除.这在低节距或低转速下尤为明显,体现出尺寸依赖性.关键词:化学机械抛光;微极流体;抛光液;流变特性中图分类号:TH117 文献标识码:AMicro-Polar E ffects of Flow Features of Slurriesin Chemical Mechanical Polishing ProcessZHA N G Chao 2hui 1,L UO Jian 2bi n2(1.School of Mechanical and Electronic Control Engineering ,Beijing Jiaotong University ,Beijing 100044,China ;2.State K ey Laboratory of Tribology ,Tsinghua University ,Beijing 100084,China )Abstract :Chemical mechanical polishing (CMP )is a manufacturing process to achieve the planarity in the level of atom where the slurry makes a great deal of contributions to the CMP performances.Cur 2rently ,the slurry used in CMP usually contains sphere-shaped particles at nano scale to enhance the material removal ratio (MRR )and to optimize the planarity.Micro polar theory will provide a feasible candidate to describe the rheology of these fluids.The flow equation of the slurries in CMP ,based on fluid theories with microstructure ,provide some insights into the mechanism of CMP.The effects on load and moments of micro polarity are simulated.The results indicate that micro-polarity can give rise to an increase in load capacity to a certain degree by increasing the equivalent viscosity of the slurries ,thereby the MRR can be enhanced.The size-depend features can be seen since it becomes more promi 2nent with low pivot height and low pad velocity.K ey w ords :Chemical Mechanical Polishing ;micro-polar fluids ;slurry ;rheology收稿日期:2004207212基金项目:国家自然科学基金资助项目(50390060)作者简介:张朝辉(1972—),男,湖南宁乡人,讲师,博士.em ail :zhangchaohui @ 现代芯片制造领域中有两个相互矛盾的趋势:被加工件的尺寸越来越大,而所需的加工精度要求却越来越高.比如下一代集成电路中的晶片要求直径大于300mm 而表面粗糙度和波纹度要小于几个埃.下一代磁盘也要求表面划痕深度≤1nm ,粗糙度≤0.1nm.这样,有必要对材料进行分子级去除.化学机械抛光(Chemical Mechanical Polishing/Pla 2narization ,CMP )是一种合适的技术[1,2].另外,要获取低介电常数的材料来取代SiO 2材料也需要CMP 技术实现表面抛光[3].因技术的需求,CMP 技术现在已经发展为制造过程中的一个完整手段[4].抛光液对CMP 过程有重要作用[5],据预测,从第29卷第1期2005年2月 北　京　交　通　大　学　学　报JOURNAL OF BEI J IN G J IAO TON G UN IV ERSIT Y Vol.29No.1Feb.20052000年到2005年全世界抛光液市场将扩大3倍[6].在抛光中,其所含的化学物质与晶片表面或亚表面相互作用形成软化层或者弱键,或者对晶片表面产生钝化反应从而使得材料可以以光滑和均匀的方式被切除,其所含的固体(纳米级)颗粒对软化或弱键表面的磨损形成超精表面.事实上,在CMP 中,重要的相互作用就是表层膜的形成与切除(如晶片金属涂层的氧化与切除),切除材料从表面带走等等,所以对抛光液流动规律的了解将有助于理解CMP的机理.Levert等[7]的实验发现了负压的存在,Tichy等[8]提出了一个初步的二维接触模型来解释Levert等的结果,其研究忽略了无直接接触抛光的情形.然而,在某些特殊场合,如进行纳米级超精抛光,或者在通常抛光的最后步骤中,流动效应将完全平衡外加的载荷.Runnels等[9]就通过求解Navier-Stokes方程讨论了润滑性能和磨损率问题. Sundararajan等[10]求解Reynolds方程给出了抛光液的膜厚和压力关系.Cho和Park[11,12]建立了一流动模型来描述硅片CMP过程.张朝辉等[13]建立了三维流动模型,并且研究了CMP中液体的流动规律[14].抛光液的流变性能对去除率和抛光质量有重要作用[15].大多数的抛光液都含有固体粒子,如胶体SiO2抛光液,可达到高的平整度[2,16].这样改变了其流变性能[17].从物理上讲,微极流体是指这样一类流体:它由刚性、随机取向粒子(或者为球体)构成,粒子悬浮于粘性介质中,而粒子本身的变形可忽略不计[18].由于SiO2粒子通常以球形存在,用微极流体来表征这种流体是一个较好的选择[19].本文作者分析了抛光液中纳米级粒子的微极性对流动性能的影响,数值模拟结果表明,微极性将增加等效粘度,从而增强承载能力,并且体现出尺寸依赖性.1　数学模型考虑抛光液中纳米粒子的微极性,其流动方程可导出为・φ(N,l,h)h312η p= ・V1+V22h(1)式中,h为流体膜厚;η为流体粘度;p为压力;V1、V2分别为晶片和抛光垫的速度向量;=55r+5r5θ,其中,r、θ分别代表晶片的径向和周向;φ(N,l,h)=112+l2h2-N l2hcoth N h2l,其中,N为耦合数,l为特征长度.方程(1)的分量形式为55rh3φ(N,l,h)12η5p5r+ 1r55θh3φ(N,l,h)12η1r5p5θ=55rw1+w22h+1r55θu1+u22h(2)式中,w1、w2、u1、u2分别为速度边界条件,表示为w1=ωp d sinθ,u1=(r+d cosθ)ωp,w2=0,u2=rωw.其中,d为晶片和抛光垫之间的中心距离,ωw和ωp分别为晶片和抛光垫的转速.在抛光中,晶片相对抛光垫成一定角度倾斜(由转角α和倾角β决定),以产生收敛楔效应.于是任一点的流体膜厚度为h=h piv-r sinαcosθ-r sinβsinθ(3)式中,h piv是节距高度值.将晶片半径r0和参考压强p0引入,得量纲一量χ=r0h piv,　Λ=χ26ηωpp0, r=rr0,h=hh piv, p=pp0,　D=dr0,l=lh piv,　ξ=ωwωp(4)膜厚方程为h=1-χ r sinαcosθ-χ r sinβsinθ(5)量纲一流动方程为r255 r h35 p5 rφ(N, l, h)+55θ h35 p5θφ(N, l, h)= χΛ r2( r+ξ r+D cosθ)× (sinαsinθ-sinβcosθ)-Λ rD sinθ(6)且有φ(N, l, h)=112+l2h2-N l2 hcoth Nh2 l(7)量纲一载荷和转矩分别为W f=1π∫2π0∫10 p r d r dθ(8) M x=1π∫2π0∫10 p r2sinθd r dθ(9) M y=-1π∫2π0∫10 p r2cosθd r dθ(10)57第1期 张朝辉等:化学机械抛光中抛光液流动的微极性分析 真实载荷和转矩为W f =πp 0r 20 W f ,M x =πp 0r 30 M x ,M y =πp 0r 30 M y ,横轴方向连接晶片和抛光垫的中心.2　计算结果与讨论计算中未指明的变量参数为:ωw =50r/min ,ωp =100r/min ,h piv =100μm ,α=0102°,β=01018°,η=010214Pa ・S ,d =150mm ,r 0=50mm ,p 0=20kPa .图1和图2分别为节距高度对量纲一载荷与力矩的影响.显然,增加节距高度值(即晶片与抛光垫之间的距离),将导致承载能力的降低,所以在CMP 中需要慎重选择合适的间隙值(过大的间隙将降低承载能力,从而降低抛光速率,而过小的间隙将妨碍抛光液中固体颗粒和磨屑的带出,从而恶化抛光质量).另外,纳米粒子引起的微极性将增加承载能力,增加特征长度l 或耦合数N 都将增加承载能力.间隙值越小,这种效应越明显,体现出微极性的尺寸依赖性.图1　载荷与节距高度的关系Fig.1　Relation between loads and pivotheight图2　转矩与节距高度的关系Fig.2　Relation between moments and pivot height抛光垫转速对量纲一载荷与转矩的影响分别见图3和图4所示.一个显著特征即是量纲一载荷与转矩与抛光垫转速呈线性关系变化.另外,微极性同样将增加承载能力.耦合数N 或特征长度l 的增加将提高承载能力,同时增加耦合数N 和特征长度l ,效果更加显著.另外,在低速下这种效应也越明显,体现出微极性的尺寸依赖性.图3　载荷与抛光垫转速的关系Fig.3　Relation between loads and pad rollvelocity图4　转矩与抛光垫转速的关系Fig.4　Relation between moments and pad roll velocity3　结论化学机械抛光技术(CMP )合适于获取高级别平面度.抛光液的流动特性对CMP 的行为有很大的影响.由于抛光液通常含有纳米级的圆形固体颗粒来加速抛光、提高抛光表面质量,利用微极流体可以模拟粒子的微旋运动对抛光性能的影响.模拟结果表明微极性将增加承载能力,从而有利于提高抛光速率.这一特性在低节距或低转速下更为显著,体现出尺寸依赖性.这一分析模型忽略了抛光垫[20]和其他一些因素的影响,因而其结果只有定性意义.参考文献:[1]Hooper B J ,Byrne G ,G alligan S.Pad conditioning inchemical mechanical polishing[J ].J.Materials Processing Technology ,2002,123:107-113.[2]Lei H ,Luo J B ,Pan G S ,et al.Chemical Mechanical Pol 2ishing of Computer Hard Disk Substrate in Colloidal SiO2Slurry[J ].International Journal of Nonlinear Science and67北　京　交　通　大　学　学　报 第29卷Numerical Simulation,2002,3(3-4):455-459.[3]Borst C L,G ill W N,Gutmann R J.Chemical-MechanicalPolishing of low Dielectric Constant Polymers and Organosilicate G lasses:Fundamental Mechanisms and A p2 plication to IC Interconnect Technology[M].London: K luwer Academic Publishers,2002.[4]Braun A E.CMP Becomes G entler,More E fficient[J].Semiconductor Int,2001,11:54-66.[5]Grover G S,Liang H,G aneshkumar S,et al.E ffect ofSlurry Viscosity Modification on Oxide and Tungsten CMP [J].Wear.1998,214:10-13.[6]Market Watch:CMP Slurries:A Wild Ride Ahead[J].S olid State Technology,2000,12:74-76.[7]Levert J A,Mess F M,Salant R F.Mechanisms of Chem2ical-Mechanical Polishing of SiO2Dielectric on Integrated Circuits[J].Tribol.Trans,1998,41(4):593-599. [8]Tichy J,Levert J A,Shan L,et al.Contact Mechanicsand Lubrication Hydrodynamics of Chemical Mechanical Polishing[J].J.Electrochemical S oc.,1999,146(4): 1523-1528.[9]Runnels S R,Eyman L M.Tribology Analysis of Chemi2cal-Mechanical Polishing[J].Journal of the Electrochemi2 cal S ociety,1994,141(6):1698-1701.[10]Sundararajan S,Thakurta D G.Two-Dimensional Wafer-Scale Chemical-Mechanical Planarization Models Based on Lubrication Theory and Mass Transport[J].Journal of the Electrochemical S ociety,1999,146(2):761-766. [11]Cho C H,Park S S,Ahn Y.Three-Dimensional WaferScale Hydrodynamic Modeling for Chemical Mechanical Polishing[J].Thin S olid Films,2001,389(1-2):254-260.[12]Park S S,Cho C H,Ahn Y.Hydrodynamic Analysis ofChemical Mechanical Polishing Process[J].Tribol.Int., 2000,33:723-730.[13]张朝辉,雒建斌,温诗铸.化学机械抛光流动性能分析[J].润滑与密封,2004,(4):31-33.ZHAN G Chao2hui,LUO Jian2bin,WEN Shi2zhu.Anal2ysis on Flow Properties of Chemical Mechanical Polishing Process[J].Lubrication Engineering,2004,(4):31-33.(in Chinese)[14]ZHAN G Chao2hui,LUO Jian2bin,WEN Shi2zhu.Multi2grid Technique Incorporated Algorithm for CMP Lubrica2 tion Equations[J].Progress in Natural Science,2004,14(3):81-84.[15]Grover G S,Liang H,G aneshkumar S,et al.E ffect ofSlurry Viscosity Modification on Oxide and Tungsten CMP[J].Wear.1998,214:10-13.[16]雷红,雒建斌,张朝辉.化学机械抛光技术的研究进展[J].上海大学学报,2003,9(6):494-502.L EI H ong,LUO Jian-bin,ZHANG Chao-hui.Advances in Chemical Mechanical P olishing[J].J.Shanghai University (Natural Science),2003,9(6):494-502.(in Chinese) [17]ZHAN G Chao2hui,LUO Jian2bin,WEN Shi2zhu.Mod2eling Chemical Mechanical Polishing with Couple Stress Fluids[J].Tsinghua Science and Technology,2004,3: 270-273.[18]张朝辉.纳米级薄膜润滑性能数值计算的研究[D].北京:清华大学,2002.ZHAN G Chao2hui.Numerical Analysis on Tribological Performances of Lubricating film in the Nano Scale[D].Beijing:Tsinghua University,2002.(in Chinese) [19]张朝辉,温诗铸,雒建斌.薄膜润滑的微极流体模拟[J].机械工程学报,2001,37(9):4-8.ZHAN G Chao2hui,WEN Shi2zhu,LUO Jian2bin.Simu2 lation of Thin Film Lubrication with Micro polar Fluids [J].Chinese J.Mechanical Engineering,2001,37(9):4-8.(in Chinese)[20]张朝辉,雒建斌,温诗铸.考虑抛光垫特性的CMP流动性能[A].中国机械工程学会年会论文集[C].北京: 2003.162-170.ZHAN G Chao2hui,LUO Jian2bin,WEN Shi2zhu.A Porosity Model for Flows in CMP[A].Proc.Chinese Mech.Engr.S oc[C].Beijing:2003.162-170.(in Chi2 nese)77第1期 张朝辉等:化学机械抛光中抛光液流动的微极性分析。

Abstract—The environmental prevalence of engineered nanomaterials, particularly nanoparticulate silver (AgNP), is expected to increase substantially. The ubiquitous use of commercial products containing AgNP may result in their release to the environment, and the potential for ecological effects is unknown. Detecting engineered nanomaterials is one of the greatest challenges in quantifying their risks. Thus, it is imperative to develop techniques capable of measuring and characterizing exposures, while dealing with the innate difficulties of nanomaterial detection in environmental samples, such as low-engineered nanomaterial concentrations, aggregation, and complex matrices. Here the authors demonstrate the use of inductively coupled plasma–mass spectrometry, operated in a single-particle counting mode (SP-ICP-MS), to detect and quantify AgNP. In the present study, two AgNP products were measured by SP-ICP-MS, including one of precisely manufactured size and shape, as well as a commercial AgNP-containing health food product. Serialdilutions, filtration, and acidification were applied to confirm that the method detected particles. Differentiation of dissolved and particulate silver (Ag) is a feature of the technique. Analysis of two wastewater samples demonstrated the applicability of SP-ICP-MS at nanograms per liter Ag concentrations. In this pilot study, AgNP was found at 100 to 200 ng/L in the presence of 50 to 500 ng/L dissolved Ag. The method provides the analytical capability to monitor Ag and other metal and metal oxide nanoparticles in fate, transport, stability, and toxicity studies using a commonly available laboratory instrument. Rapid throughput and element specificity are additional benefits of SP-ICP-MS as a measurement tool for metal and metal oxide engineered nanoparticles. Environ. Toxicol. Chem. 2012;31:115–121.翻译环境中工程纳米材料的含量，尤其是纳米银，看起来正在增长。

内氧化法制备MgO弥散强化铁基材料徐延龙;罗骥;郭志猛;杨薇薇;于海华【摘要】The MgO dispersion strengthening iron powder was prepared by mechanical alloying, surface oxidation at low temperature, internal oxidation at high temperature and reduction treatment. Then the MgO dispersion strengthening ferrous material was fabricated by spark plasma sintering (SPS). The analysis of SEM and EDS on the microstructure and fracture shows that the MgO particle size is 200 nm~1μm and the MgO is uniformly distributed in the matrix which can refine the grain. The dimple fractures become smaller after the addition of MgO. The mechanical properties at room temperature of the Fe+1.0%MgO are that, the tensile strength is 342.6 MPa, the yield strength is 276.3 MPa, the hardness is 61 HRB, which compared with pure iron are increased by 20.5%, 54.2% and 84.8% respectively.%采用机械合金化—低温表面氧化—高温内氧化—还原处理制备MgO弥散强化铁粉后再经放电等离子(SPS)烧结制备MgO弥散强化铁基材料，并通过SEM和EDS对材料的组织和断口进行分析。