Name: epitaxial growth of perovskite strontium titanate on germanium via atomic layer deposition
Uploaded: 2016-07-26T14:00:00.000+00:00
Duration: 9 min 45 s
Description: Watch this Scientific Journal Video about Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition at JoVE.com

This research was supported by the National Science Foundation (Awards CMMI-1437050 and DMR-1207342), the Office of Naval Research (Grant N00014-10-10489), and the Air Force Office of Scientific Research (Grant FA9550-14-1-0090).

1.准备锶，钛前兆ALD实验<ol><li>加载清洁，干燥湿润和新的前体到一个手套箱的前室。按照手套箱的装载程序，以确保空气和水分的正确清洗。转移材料到主腔室中。 注:本集团还采用了房子建湿润（ 见图3）购得的部件。饱和器组件的细节可以在特定的试剂和仪器的清单中找到。 </li><li>存储锶前体（锶双（triisopropylcyclopentadienyl）[锶（ⅰPR 3的Cp）2]）和钛前体（四异丙氧基钛钛[Ti（O- 我镨）4]，TTIP）在惰性环境（ 例如 ，一个手套箱）在打开由制造商提供的原始包装之后。 注:本组使用手套箱带有水分含量不摹于5ppm reater。 </li><li>加载前体进入饱和器，使得前体占据大约2/3的饱和（约5g）的玻璃部分。 </li><li>重新组装湿润，并保证良好的防漏密封的实现。 注:本组使用金属垫片端面密封接头实现防漏密封。 </li><li>从手套箱中取出填充湿润和填充湿润连接到ALD歧管。 注意:装载前体可在较长时间内多次使用。在这组系统的前体一般需要每半年加气，因为他们成为消费。锶（ⅰPR 3的Cp）2是在RT和在工作温度为这项研究棕色液体（130 - 140℃）。 TTIP是一种透明的液体。当TTIP劣化，通常是由于湿气和/或空气污染，前体将转成白色固体。目前还没有VISI为锶前体恶化的BLE指标（PR 我 三个 CP）2本组观察。锶的前体恶化，一般通过在利用锶一个可重复的ALD生长锶含量显著减少（大于10％）检测到（ⅰPR 3的Cp）2。 </li></ol> 2.清洁戈（001）衬底<ol><li>放置一个锗（001）衬底（18毫米×20 MM），抛光的侧朝上，成一个小烧杯（25-50毫升）。填充烧杯至约1厘米的高度，用丙酮。放置烧杯在水浴超声和超声处理10分钟。 注意:此组使用单面抛光-4-锗晶 ​​片，切成使用切割锯18×20 平方毫米碎片。如果需要该膜的电气测量用重掺杂n型Ge（本研究使用锑掺杂锗晶片与ρ≈0.04Ω-cm）的，否则所有的掺杂水平和掺杂剂类型是可以接受的。 </li><li>倒出大部分丙酮进入废物容器中，注意不要倒出来或翻转Ge衬底。冲洗用异丙醇（IPA）的烧杯的壁和填充到约1cm的高度。倒多数的IPA到废物容器，笔芯烧杯1厘米与IPA和超声处理另外10分钟。 </li><li>重复步骤2.2，但与去离子水代替IPA。 </li><li>从用镊子烧杯除去基板。干燥用氮气枪或其他干燥的惰性气体流中的衬底。 </li><li>放置在UV臭氧清洁器基板和运行清洁30分钟。 </li><li>紫外线臭氧清洗后，立即装入基板进入真空系统。 </li></ol> 3.装载Ge衬底<ol><li>移动至输送管线样品载体推车进入负载锁定。关闭门阀以隔离负载锁定。 </li><li>关闭负载锁涡轮分子泵，并打开氮气管线泄装载锁定。完成步骤3.3在等待负载锁定完全排出。 </li><li>基板，磨光面朝向下，放置到20毫米×20毫米的样本保持器。 注意:所有的沉积与样品朝下进行。确保在基板与支架的底部齐平;否则RHEED实验可能会遇到困难和电影可能不会均匀沉积。这个组采用的样品保持器示于图4。 </li><li>打开装载锁定后，它已经完全排空。通过用开放车位置的通道对准样品架的标签和降低到位放置样本保持到打开载波车位置。 </li><li>关闭负载锁和打开负载锁定涡轮分子泵。关闭氮气管线。 </li><li>等到在负载锁定的压力是约5.0×10 -7乇通过传输线打开负载锁定闸阀和移动推车之前。 </li></ol> 4.脱氧葛<ol><li>在Ge衬底转移到MBE室。 </li><li>斜坡锗衬底温度达到550℃以20℃•分钟-1，然后在10至700℃℃，•分钟-1。保持在700℃将样品1小时后，冷却样品至200℃，用30℃•分钟-1斜率。 </li><li>使用RHEED作为代表性的成果节所述确认2×1重构表面。26,39 </li><li>可选:使用XPS确保锗（001）基片是自由的氧化物（在第8部分所述）。 </li></ol> STO对Ge衬底5薄膜ALD增长<ol><li>调整ALD反应器温度为225ºC。 </li><li>热锶（ⅰPR 3的Cp）2至130℃，并TTIP至40℃。在RT（20和25℃之间）保持水。调节水蒸汽流入ALD系统通过附连到饱和，使得水的计量压力为大约1乇针阀。保持恒定的前体的温度在整个沉积过程。 </li><li> 在真空下转移样品至已预热到225℃的ALD反应器，并等待15分钟的样品，以达到热平衡。 </li><li>从涡轮分子泵的机械泵切换ALD反应器的排气口。 </li><li>转流控制器上，以允许惰性气体流（此组使用氩气）。保持1乇的在整个生长过程中的操作压力。 </li><li>设置的锶与Ti的单元周期比为2:1。设置的Sr和钛的单元周期2秒剂量Sr或Ti前体的，随后是15秒的氩气清洗，然后水1秒的剂量，紧接着又15秒的氩吹扫。 </li><li>调整单元的周期数，以获得所需的厚度。确保ALD循环序列包含个别锶或Ti单元周期尽可能少重复。例如，一个2:当1-锶，1-钛，接着1-锶，2-钛，而不是2-锶接着3-钛执行3锶到钛循环序列会取得更好的效果。 注:本组采用36单位周期的锗矿床有2纳米厚的薄膜STO。 </li><li>可选:使用XPS验证膜组成（第8节所述）。 </li></ol> 6.退火STO电影<ol><li>转移沉积样品在真空中进退火室。 </li><li>加热样品到650℃的速率20℃•分钟UHV条件下（10 -9 - 10 -8乇）下-1。保持在650ºC该温度5分钟，然后以相同的速率冷却样品至200℃。 注意:使用RHEED评估退火结果，如代表结果部分描述26,39。 </li></ol> 7.福申通快递的rther增长<ol><li>重复5.1 - 5.5。 </li><li>设置单元周期比为1:1至4:3。保持每个单位周期内的相同给药/吹扫组件。根据步骤5.6中提到的原则的序列。 </li><li>调整单元的周期数，以达到预定的厚度。 </li><li>根据议定书第6退火的沉积膜。 </li></ol> 8. XPS测量<ol><li>加载样品进入该XPS分析室，并转动X射线源上。确保所有适当的门/门关闭，以防止意外X射线曝光。 </li><li>通过选择期望的用于分析的元素（结合能范围）创建新的扫描，或选择预先存在的扫描程序。 注:绑定能量范围可以手动更改，如果需要的话。设置其他设置，例如通过能量，激发能量，步骤能量，和步骤时间，以优化信噪比，但仍在所有元素的扫描恒定维持元素光谱间的可比性。 表1示出由该组使用的扫描设置。 </li><li>检查是否有任何的充电是通过观察一个已知元素的峰的结合能，如O 1秒在531 eV的发生在基板上。 注:如果峰值已经从它的已知值转移充电发生。 </li><li>将洪水枪扔到了XPS室，如果充电发生打开流枪。调整来自样品的流枪的能量输出和距离，使得所选择的峰移回到其正确的结合能。 </li><li>操纵台上的位置，最大限度已知元素的峰下观察到的区域（通常是O 1■在531伏特峰值）。 </li><li>运行XPS扫描和收集数据。 </li><li>关闭X射线源，并从该XPS取出样品。 </li></ol>

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作者有没有竞争经济利益透露。

生长外延钙钛矿使用ALD当Ge衬底的清洁度是成功的关键。的时间一Ge衬底脱脂和脱氧，和脱氧和STO沉积之间的时间量之间花费的量，应保持在最低限度。样品仍然受到连特高压环境下的污染物暴露。长期接触可能会导致不定碳或再氧化锗的再沉积，导致薄膜生长不良。这个小组已聘请（丙酮/ IPA / DI水随后紫外臭氧接触超声）一种广泛使用的脱脂方法去除碳污染物。超高真空条件下的另一个使用步?...

钙钛矿材料是由于其高度对称的立方或仿立方体的结构和性质的无数越来越具有吸引力。这些材料中，与通式ABO 3，由具有与六个氧原子配位12个氧原子和硼原子配位的原子。由于其结构简单，但广泛的潜在元素，钙钛矿材料为异质器件的理想候选。外延氧化物异质夸铁，1 - 3防/铁电，4多铁，5 - 8超导，7 - 12和磁阻功能13,14许多可取的电子性质是界面，因此依赖于材料间干净的，突然的转变。钙钛矿家族成员之间共享的几乎相同的结构，晶格常数让优秀的升attice匹配，因此，高品质的接口。容易晶格匹配彼此以及一些半导体，钙钛矿型氧化物现在正在转向下一代金属氧化物半导体电子元件。 与硅晶体氧化物，先用钙钛矿型钛酸锶证实的单片集成，的SrTiO 3（STO），由麦基和他的同事，15是在实现具有钙钛矿半导体掺入的电子设备的一个巨大的步骤。分子束外延（MBE）为上，因为层与层之间的生长的硅氧化物的外延生长的主要技术，以及需要控制无定形的，界面的 SiO 2形成的可调氧分压16日 - 19典型MBE生长在Si STO的（001）是由SiO 2构成锶辅助脱氧实现。下的超高真空（UHV）条件下，的SrO是易失性和分JECT热蒸发。自的SrO是热力学优于锶金属和SiO 2，锶的沉积从SiO 2层拾荒氧和所得的SrO从表面蒸发。在此过程中在硅表面经历2×1重构，形成二聚硅原子的行的表面上。交通便利，½重建表面上的锶原子的单层（ML）的覆盖填补这些二聚体行而产生的空白。20 1/2 ML覆盖范围规定，与氧气压力的严格控制，可以防止或控制界面的SiO 2的保护层随后的氧化物生长期间形成的21 - 23在STO的情况下（与类似的晶格匹配的钙钛矿），将所得的晶格旋转45°的面内，使得（001）STO‖（001） 的Si和（100）STO‖ （110） 的Si，从而在Si之间的注册表（3.84埃丝丝的距离）和STO（A = 3.905埃）与申通快递只有轻微的压缩应变。该注册表是必要的高品质的接口和它们具有所需的性质。 硅成为工业显著由于其界面氧化的高品质，但SiO 2的使用正在逐渐被淘汰了能够在更小的特征尺寸同等性能的材料。 的 SiO 2的经验高漏电流时的超薄和这减少设备的性能。对于更小的特征尺寸的需求可以通过具有高介电常数，K钙钛矿氧化物膜，提供相当于SiO 2的性能，并且由系数k /3.9比SiO 2的物理厚来满足。此外，另外的半导体，如锗，提供更快的设备操作的潜力，由于比硅更高的电子和空穴迁移率。24,25锗也有一个INTERFacial氧化物，GeO 2的，但在对比的 SiO 2，它是不稳定的，并受到热脱氧。因此，2×1重构是通过超高真空下简单的热退火实现的，和一个保护锶层是不必要的，以防止钙钛矿沉积期间界面氧化物的生长。26 尽管明显缓解通过MBE提供生长，原子层沉积（ALD）提供用于商业化生产的氧化物材料的比MBE更具扩展性和成本有效的方法。27,28 ALD采用剂量气态前体的对是自基板限制在与衬底表面反应。因此，在理想的ALD工艺，最多一个原子层沉积为任何给定的前体给药周期和相同的前体的持续给药不会沉积附加的材料在表面上。反应性官能恢复与一个共反应物，通常是氧化或还原的前体（ 如，水或氨）。以前的工作已经证明各种钙钛矿薄膜，如锐钛矿型的 TiO 2，钛酸锶3 的 BaTiO 3，和LaAlO 3的ALD生长，对已缓冲通过MBE生长四晶胞厚的STO的Si（001）。29 - 34在晶体氧化物纯粹MBE生长，½锶清洁的Si（001）单层覆盖足以原产于技术（〜10 -7托）的压力下，提供针对二氧化硅形成的障碍。然而，在〜1乇的典型的ALD操作压力，以前的工作已经表明，STO四个单元电池是必需的，以避免氧化Si表面29 这里详细介绍的过程利用的GeO 2的不稳定性，实现对通过ALD锗STO的单片集成，而不需要一个MBE生长缓冲层。26。此外，葛优葛原子间距离（3.992 a）在（100）表面允许为与硅（001）观察到的STO类似的外延注册表。虽然这里介绍的程序是特定于戈STO，轻微的修改可以允许多种锗钙钛矿薄膜的单片集成。事实上，结晶SrHfO 3和钛酸钡的电影直接ALD增长已经报道了葛优，35,36其他可能性包括潜在的栅氧化层，SrZr 点¯x钛1-X O 3。37最后，建立在ALD钙钛矿增长以前的研究上的Si的四单元电池的STO膜（001）29 - 34表明可能的STO / Si的平台上生长的任何膜可以在锗一ALD生长的STO缓冲膜，如LaAlO 3和LaCoO生长3，32,38可用于氧化异质结构和钙钛矿型氧化物之间显着的相似性的众多建议这个程序可以利用ŤØ以前的研究与这样一个工业可行的技术困难或不可能的增长组合。 图1描绘了真空系统，该系统包括ALD，MBE，并通过一个12英尺传输线相连的分析腔室的示意图。可将样本在各腔室之间真空转移。输送线的基线压力是由三个离子泵保持在约1.0×10 -9乇。商业角度分辨紫外线和X射线光电子能谱（XPS）系统被保持与离子泵，使得在分析腔室中的压力保持在约1.0×10 -9乇。 所述ALD反应器是矩形定制不锈钢室中460 cm 3的体积和长度为20厘米。所述ALD反应器的示意图示于图2，反应器是一个热壁，连续横流型反应器中。放置在反应器样品具有的所述基板的顶部表面和所述室的天花板和基板的底面和腔室底板在1.9厘米1.7厘米的间隙。加热胶带，搭载专用的电源，从入口室缠到超出排气口约2厘米，提供了反应器壁的温度控制。温度控制器根据由位于加热胶带和外部反应器壁之间的热耦合截取的温度测量来调整输入功率到加热胶带。然后将反应器完全由自耦变压器提供恒定的功率的三个附加加热磁带，和玻璃纤维羊毛用铝箔被覆的最终层提供绝缘，以促进均匀的加热包裹。自耦变压器的功率输出进行调节，使得在反应器的怠速温度（当专用电源关闭）为约175℃。该反应器是PASsively经由环境空气冷却。基板温度是使用线性拟合等式（1），其中T S（℃）是衬底和T C（℃）的温度是反应器壁的温度计算，得到通过直接测量装配有衬底一个热电偶。温度曲线沿着腔室的流动方向上存在由于连接在反应器的输送管线的冷闸阀;垂直于流动方向上的温度分布是忽略的。的温度分布导致在样品的前缘更丰富的锶沉积，而是沿着样品的组成变化是根据XPS小（小于样品的前缘和后缘之间有5％的差异）。31的排气反应器被连接到一个涡轮分子泵和机械泵。在ALD工艺中，反应器是由机械泵泵送保持在约1乇的压力。否则，reactoř压力由涡轮分子泵保持在低于2.0×10 -6乇。 （1）T S = 0.977T C + 3.4 在MBE室保持在约2.0×10 -9乇或低于一个低温泵的基线压力。在MBE室的各种物质的分压是由残余气体分析仪监测。的H 2的背景压力为大约1.0×10 -9乇，而那些的 O 2，CO，N 2，CO 2和H 2 O，小于1.0×10 -10乇。此外，MBE室还配备有六个喷射室，一个四口袋电子束蒸发器，一个原子氮等离子体源和具有高精度的压电泄漏阀的原子氧等离子体源，以及一反射高能电子衍射（RHEED ）系统，用于在原位生长和结晶观察实时性。山姆PLE操纵器允许基板使用耐氧碳化硅加热器被加热到​​1000℃。

<table><tbody><tr><td>MBE</td><td>DCA</td><td>M600</td><td></td></tr><tr><td>Cryopump for MBE</td><td>Brooks Automation, Inc.</td><td>On-Board 8</td><td></td></tr><tr><td>Residual Gas Analyzer for MBE</td><td>Extorr, Inc.</td><td>XT200M</td><td></td></tr><tr><td>ALD Reaction Chamber</td><td>Huntington Mechanical Laboratories</td><td></td><td>Custom manufactured, hot-wall, stainless steel, rectangular (~20&amp;nbsp;cm long, 460 cm&lt;sup&gt;3&lt;/sup&gt;)</td></tr><tr><td>ALD Saturator</td><td>Swagelok/Larson Electronic Glass</td><td>See comments</td><td>Custom-built from parts supplied by Swagelok and Larson Electronic Glass. The saturator is made out of 316 stainless steel and Pyrex. All parts are connected via butt welding. Swagelok catalog numbers: SS-4-VCR-7-8VCRF, SS-4-VCR-1, SS-8-VCR-1-03816, SS-8-VCR-3-8MTW, 316L-12TB7-6-8, SS-8-VCR-9, SS-4-VCR-3-4MTW, SS-T2-S-028-20. Larson Electronic Glass catalog number: SP-075-T.</td></tr><tr><td>Manual Valves for Saturators</td><td>Swagelok</td><td>SS-DLVCR4-P and 6LVV-DPFR4-P</td><td>Both diaphragm-sealed valves are used interchangably by this group. The specific connectors (VCR male/female/&lt;em&gt;etc.&lt;/em&gt;) to use will depend on the actual system design.</td></tr><tr><td>ALD Valves</td><td>Swagelok</td><td>6LVV-ALD3TC333P-CV</td><td></td></tr><tr><td>ALD System Tubing</td><td>Swagelok</td><td></td><td>316L tubing of various sizes. This group uses inner diameter of 1/4&quot;</td></tr><tr><td>ALD power supply</td><td>AMETEK Programmable Power, Inc.</td><td>Sorensen DCS80-13E</td><td></td></tr><tr><td>ALD Temperature Controller</td><td>Schneider Electric</td><td>Eurotherm 818P4</td><td></td></tr><tr><td>ALD Valve Controller&amp;nbsp;</td><td>National Instruments</td><td>LabView</td><td>Program developed within the group</td></tr><tr><td>XPS</td><td>VG Scienta</td><td></td><td></td></tr><tr><td>RHEED</td><td>Staib Instruments</td><td>CB801420</td><td>18 keV at ~3&amp;deg; incident angle</td></tr><tr><td>RHEED Analysis System</td><td>k-Space Associates</td><td>kSA 400</td><td></td></tr><tr><td>Digital UV Ozone System</td><td>Novascan</td><td>PSD-UV 6</td><td></td></tr><tr><td>Ozone Elimination System</td><td>Novascan</td><td>PSD-UV OES-1000D</td><td></td></tr><tr><td>Titanium tetraisopropoxide (TTIP)</td><td>Sigma-Aldrich</td><td>87560</td><td>Flammable in liquid and vapor phase&lt;br /&gt;&amp;nbsp;&lt;br /&gt;&amp;nbsp;</td></tr><tr><td colspan="4">[header]</td></tr><tr><td>Strontium bis(triisopropylcyclopentadienyl)</td><td>Air Liquide</td><td>HyperSr</td><td>Mildly reactive to air and water. Further information supplied by Air Liquide can be found at https://www.airliquide.de/inc/dokument.php/standard/1148/airliquide-hypersr-datasheet.pdf</td></tr><tr><td>Ge (001) wafer</td><td>MTI Corporation</td><td>GESBA100D05C1</td><td>4&quot;, single-side polished Sb-doped wafer with &amp;rho; &amp;asymp; 0.04 &amp;Omega;-cm</td></tr><tr><td>Argon (UHP)</td><td>Praxair</td><td></td><td></td></tr><tr><td>Deionized Water</td><td></td><td></td><td>18.2 M&amp;Omega;-cm</td></tr></tbody></table>

epitaxial growth of perovskite strontium titanate on germanium via atomic layer deposition

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2&#215;1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

图5和6示出典型的X-射线光电子光谱和RHEED图像从清洗和脱氧Ge衬底。 26,39另外一个成功脱氧Ge衬底的特征在于它的"笑脸"2×1重构的RHEED图案中，菊池线也在RHEED图像，这表明该清洁和试样的长程有序观察。40锐度和衍射图案的强度也证明了表面的清洁度。葛三维 X射线光电子能谱应该是免费的氧化戈峰，在​​30 eV的观察戈...

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Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition

这个工作详细直接结晶的SrTiO 3的锗基板通过原子层沉积的生长和表征的程序。该过程示出了一个全化学生长方法来单片集成氧化物到半导体金属氧化物半导体器件的能力。

锗通过原子层沉积钙钛矿型钛酸锶的外延生长

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and ...

epitaxial-growth-perovskite-strontium-titanate-on-germanium-via

Research

JoVE Journal

Chemistry

12.3K 次观看.  The University of Texas at Austin. 这个工作详细直接结晶的SrTiO 3的锗基板通过原子层沉积的生长和表征的程序。该过程示出了一个全化学生长方法来单片集成氧化物到半导体金属氧化物半导体器件的能力。 

视频: Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10- nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

Various procedures are outlined to prepare atomically defined templates for epitaxial growth of complex oxide thin films. Chemical treatments of single crystalline SrTiO3 (001) and DyScO3 (110) substrates were performed to obtain atomically smooth, single terminated surfaces. Ca2 Nb3 O10- nanosheets were used to create atomically defined templates on arbitrary substrates.

原子定义模板复合氧化物薄膜的外延生长

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain ...

科研

化学

Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical properties. The possibility of doping was investigated by adding monovalent cation halides with similar ionic radii to Pb2+, including Cu+, Na+, and Ag+. A shift in the Fermi level and a remarkable decrease of sub-bandgap optical absorption, along with a lower energetic disorder in the perovskite, was achieved. An order-of-magnitude enhancement in the bulk hole mobility and a significant reduction of transport activation energy within an additive-based perovskite device was attained. The confluence of the aforementioned improved properties in the presence of these cations led to an enhancement in the photovoltaic parameters of the perovskite solar cell. An increase of 70 mV in open circuit voltage for AgI and a 2 mA/cm2 improvement in photocurrent density for NaI- and CuBr-based solar cells were achieved compared to the pristine device. Our work paves the way for further improvements in the optoelectronic quality of CH3NH3PbI3 perovskite and subsequent devices. It highlights a new avenue for investigations on the role of dopant impurities in crystallization and controls the electronic defect density in perovskite structures.

Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

Here, we present a protocol to adjust the properties of solution-processed CH3NH3PbI3 through the incorporation of monovalent cation additives in order to achieve highly efficient perovskite solar cells.

CH的单价阳离子兴奋剂<sub&gt; 3</sub&gt; NH<sub&gt; 3</sub&gt;碘化铅<sub&gt; 3</sub&gt;对钙钛矿型高效太阳能电池

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical ...

工程学

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

We fabricate metal/LaAlO3/SrTiO3 heterostructures using a combination of pulsed laser deposition and in situ magnetron sputtering. Through magnetotransport and in situ X-ray photoelectron spectroscopy experiments, we investigate the interplay between electrostatic and chemical phenomena of the quasi two-dimensional electron gas formed in this system.

金属/LaAlO 的生长和静电/化学性质3/SrTiO3异

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide ...

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its well-balanced ferroelectricity, piezoelectricity, and dielectric constant. In addition, BT does not contain any toxic elements. Therefore, it is considered to be an eco-friendly material, which has attracted considerable interest as a replacement for lead zirconate titanate (PZT). However, bulk BT loses its ferroelectricity at approximately 130 &#176;C, thus, it cannot be used at high temperatures. Because of the growing demand for high-temperature ferroelectric materials, it is important to enhance the thermal stability of ferroelectricity in BT. In previous studies, strain originating from the lattice mismatch at hetero-interfaces has been used. However, the sample preparation in this approach requires complicated and expensive physical processes, which are undesirable for practical applications.
In this study, we propose a chemical synthesis of a porous material as an alternative means of introducing strain. We synthesized a porous BT thin film using a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles were used as an organic template. Through a series of studies, we clarified that the introduction of pores had a similar effect on distorting the BT crystal lattice, to that of a hetero-interface, leading to the enhancement and stabilization of ferroelectricity. Owing to its simplicity and cost effectiveness, this fabrication process has considerable advantages over conventional methods.

Here, we present a protocol for the synthesis of porous barium titanate (BaTiO3) thin film by a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles are used as an organic template.

孔隙诱导应变法合成多孔钛酸钡薄膜及铁电相热稳定性

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its ...

A Fabrication and Measurement Method for a Flexible Ferroelectric Element Based on Van Der Waals Heteroepitaxy

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on high-density data storage and low-power consumption capabilities. However, the high-quality oxide based nonvolatile memory on flexible substrates is often constrained by the material characteristics and the inevitable high-temperature fabrication process. In this paper, a protocol is proposed to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica. The versatile deposition technique and measurement method enable the fabrication of flexible yet single-crystalline non-volatile memory elements necessary for the next generation of smart devices.

In this paper, we present a protocol to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica.

基于范德华 Heteroepitaxy 的柔性铁电元件制备及测量方法

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on ...

Fabrication of Schottky Diodes on Zn-polar BeMgZnO/ZnO Heterostructure Grown by Plasma-assisted Molecular Beam Epitaxy

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device applications. Zinc oxide (ZnO), a semiconductor with a wide bandgap (3.4 eV) and high electron saturation velocity has gained a great deal of attention as an attractive material for high speed devices. Efficient gate modulation, however, requires high-quality Schottky contacts on the barrier layer. In this article, we present our Schottky diode fabrication procedure on Zn-polar BeMgZnO/ZnO heterostructure with high density 2DEG which is achieved through strain modulation and incorporation of a few percent Be into the MgZnO-based barrier during growth by molecular beam epitaxy (MBE). To achieve high crystalline quality, nearly lattice-matched high-resistivity GaN templates grown by metal-organic chemical vapor deposition (MOCVD) are used as the substrate for the subsequent MBE growth of the oxide layers. To obtain the requisite Zn-polarity, careful surface treatment of GaN templates and control over the VI/II ratio during the growth of low temperature ZnO nucleation layer are utilized. Ti/Au electrodes serve as Ohmic contacts, and Ag electrodes deposited on the O2 plasma pretreated BeMgZnO surface are used for Schottky contacts.

Attainment of high-quality Schottky contacts is imperative for achieving efficient gate modulation in heterostructure field effect transistors (HFETs). We present the fabrication methodology and characteristics of Schottky diodes on Zn-polar BeMgZnO/ZnO heterostructures with high-density two dimensional electron gas (2DEG), grown by plasma-assisted molecular beam epitaxy on GaN templates.

等离子体辅助分子束外延法制备的锌极性 BeMgZnO/氧化锌异质结构肖特基二极管的制备

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device ...

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Reduction of threading dislocation density (TDD) in epitaxial germanium (Ge) on silicon (Si) has been one of the most important challenges for the realization of monolithically integrated photonics circuits. The present paper describes methods of theoretical calculation and experimental verification of a novel model for the reduction of TDD. The method of theoretical calculation describes the bending of threading dislocations (TDs) based on the interaction of TDs and non-planar growth surfaces of selective epitaxial growth (SEG) in terms of dislocation image force. The calculation reveals that the presence of voids on SiO2 masks help to reduce TDD. Experimental verification is described by germanium (Ge) SEG, using an ultra-high vacuum chemical vapor deposition method and TD observations of the grown Ge via etching and cross-sectional transmission electron microscope (TEM). It is strongly suggested that the TDD reduction would be due to the presence of semicylindrical voids over the SiO2 SEG masks and growth temperature. For experimental verification, epitaxial Ge layers with semicylindrical voids are formed as the result of SEG of Ge layers and their coalescence. The experimentally obtained TDDs reproduce the calculated TDDs based on the theoretical model. Cross-sectional TEM observations reveal that both the termination and generation of TDs occur at semicylindrical voids. Plan-view TEM observations reveal a unique behavior of TDs in Ge with semicylindrical voids (i.e., TDs are bent to be parallel to the SEG masks and the Si substrate).

Theoretical calculation and experimental verification are proposed for a reduction of threading dislocation (TD) density in germanium epitaxial layers with semicylindrical voids on silicon. Calculations based on the interaction of TDs and surface via image force, TD measurements, and transmission electron microscope observations of TDs are presented.

硅上半圆柱空隙锗外延层位错还原的理论计算和实验验证

Reduction of threading dislocation density (TDD) in epitaxial germanium (Ge) on silicon (Si) has been one of the most important challenges for the ...

Epitaxial Nanostructured &alpha;-Quartz Films on Silicon: From the Material to New Devices

In this work, we show a detailed engineering route of the first piezoelectric nanostructured epitaxial quartz-based microcantilever. We will explain all the steps in the process starting from the material to the device fabrication. The epitaxial growth of &#945;-quartz film on SOI (100) substrate starts with the preparation of a strontium doped silica sol-gel and continues with the deposition of this gel into the SOI substrate in a thin film form using the dip-coating technique under atmospheric conditions at room temperature. Before crystallization of the gel film, nanostructuration is performed onto the film surface by nanoimprint lithography (NIL). Epitaxial film growth is reached at 1000 &#176;C, inducing a perfect crystallization of the patterned gel film. Fabrication of quartz crystal cantilever devices is a four-step process based on microfabrication techniques. The process starts with shaping the quartz surface, and then metal deposition for electrodes follows it. After removing the silicone, the cantilever is released from SOI substrate eliminating SiO2 between silicon and quartz. The device performance is analyzed by non-contact laser vibrometer (LDV) and atomic force microscopy (AFM). Among the different cantilever&#8217;s dimensions included in the fabricated chip, the nanostructured cantilever analyzed in this work exhibited a dimension of 40 &#181;m large and 100 &#181;m long and was fabricated with a 600 nm thick patterned quartz layer (nanopillar diameter and separation distance of 400 nm and 1 &#181;m, respectively) epitaxially grown on a 2 &#181;m thick Si device layer. The&#160;measured&#160;resonance frequency was&#160;267 kHz and the estimated quality factor, Q, of the whole mechanical structure was Q ~ 398 under low vacuum conditions. We observed the voltage-dependent linear displacement of cantilever with both techniques (i.e., AFM contact measurement and LDV). Therefore, proving that these devices can be activated through the indirect piezoelectric effect.

Epitaxial Nanostructured &#945;-Quartz Films on Silicon: From the Material to New Devices

This work presents a detailed protocol for the microfabrication of nanostructured &#945;-quartz cantilever on a Silicon-On-Insulator(SOI) technology substrate starting from the epitaxial growth of quartz film with the dip coating method and then nanostructuration of the thin film via nanoimprint lithography.

硅上显性纳米结构α石英薄膜:从材料到新设备

In this work, we show a detailed engineering route of the first piezoelectric nanostructured epitaxial quartz-based microcantilever. We will explain all ...

Tuning Oxide Properties by Oxygen Vacancy Control During Growth and Annealing

Electrical, optical, and magnetic properties of oxide materials can often be controlled by varying the oxygen content. Here we outline two approaches for varying the oxygen content and provide concrete examples for tuning the electrical properties of SrTiO3-based heterostructures. In the first approach, the oxygen content is controlled by varying the deposition parameters during a pulsed laser deposition. In the second approach, the oxygen content is tuned by subjecting the samples to annealing in oxygen at elevated temperatures after the film growth. The approaches can be used for a wide range of oxides and nonoxide materials where the properties are sensitive to a change in the oxidation state.
The approaches differ significantly from electrostatic gating, which is often used to change the electronic properties of confined electronic systems such as those observed in SrTiO3-based heterostructures. By controlling the oxygen vacancy concentration, we are able to control the carrier density over many orders of magnitude, even in nonconfined electronic systems. Moreover, properties can be controlled, which are not sensitive to the density of itinerant electrons.

Oxide materials show many exotic properties that can be controlled by tuning the oxygen content. Here, we demonstrate the tuning of oxygen content in oxides by varying the pulsed laser deposition parameters and by performing postannealing. As an example, electronic properties of SrTiO3-based heterostructures are tuned by growth modifications and annealing.

通过生长和退火过程中的氧空位控制来调整氧化物性能

Electrical, optical, and magnetic properties of oxide materials can often be controlled by varying the oxygen content. Here we outline two approaches for ...

Synthesis of Nine-atom Deltahedral Zintl Ions of Germanium and their Functionalization with Organic Groups

Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later.1,2 Their redox chemistry is even younger, just about ten years old, but despite this short history these deltahedral clusters ions E9n- (E = Si, Ge, Sn, Pb; n = 2, 3, 4) have already shown interesting and diverse reactivity and have been at the forefront of rapidly developing and exciting new chemistry.3-6 Notable milestones are the oxidative coupling of Ge94- clusters to oligomers and infinite chains,7-19 their metallation,14-16,20-25 capping by transition-metal organometallic fragments,26-34 insertion of a transition-metal atom at the center of the cluster which is sometimes combined with capping and oligomerization,35-47 addition of main-group organometallic fragments as exo-bonded substituents,48-50 and functionalization with various organic residues by reactions with organic halides and alkynes.51-58 
This latter development of attaching organic fragments directly to the clusters has opened up a new field, namely organo-Zintl chemistry, that is potentially fertile for further synthetic explorations, and it is the step-by-step procedure for the synthesis of germanium-divinyl clusters described herein. The initial steps outline the synthesis of an intermetallic precursor of K4Ge9 from which the Ge94- clusters are extracted later in solution. This involves fused-silica glass blowing, arc-welding of niobium containers, and handling of highly air-sensitive materials in a glove box. The air-sensitive K4Ge9 is then dissolved in ethylenediamine in the box and then alkenylated by a reaction with Me3SiC&equiv;CSiMe3. The reaction is followed by electrospray mass spectrometry while the resulting solution is used for obtaining single crystals containing the functionalized clusters [H2C=CH-Ge9-CH=CH2]2-. For this purpose the solution is centrifuged, filtered, and carefully layered with a toluene solution of 18-crown-6. Left undisturbed for a few days, the so-layered solutions produced orange crystalline blocks of [K(18-crown-6)]2[Ge9(HCCH2)2]&bull;en which were characterized by single-crystal X-ray diffraction. 
The process highlights standard reaction techniques, work-up, and analysis towards functionalized deltahedral Zintl clusters. It is hoped that it will help towards further development and understanding of these compounds in the community at large.

We present the high-temperature synthesis of intermetallic precursors K4Ge9, their dissolution in ethylenediamine to form Ge94- deltahedral Zintl ions, and the reaction of the clusters with alkynes to form organo-Zintl ions. The latter are characterized by electrospray mass spectrometry in solutions and by single-crystal X-ray diffraction in the solid state.

九的原子Deltahedral Zintl离子锗和他们的官能合成有机基团

Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later.1,2 ...

锗通过原子层沉积钙钛矿型钛酸锶的外延生长

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