作者想感谢 ESPRC 和 BAE 系统的财政支持, 和 Prof. 布莱恩 a. Korgel 和他的小组供应的 SFLS 生长硅纳米线用于这项工作。

警告: 除非另有规定, 所有的程序都要在干净的房间环境中进行, 并进行风险评估, 以确保纳米线和化学品处理过程中的安全。纳米材料可能有许多健康方面的影响, 这是未知的, 所以应该处理适当的照顾21。
注: 该过程从基板的制备开始, 然后是第一个光刻和金属沉积步骤来定义 DEP 接触。然后通过 DEP 组装纳米线, 再选择一个可选的光刻和金属沉积步骤, 将顶端接触物沉积到纳米线上。纳米线晶体管器件的电流电压特性, 然后使用半导体表征套件测量。
1. 基板的制备
<ol><li>将掺杂的 n 型硅/二氧化硅晶片切割成合适的尺寸,例如, 2.5 厘米2。</li>
	<li>在切割过程中, 确保晶片的顶面不被触及或划伤。</li>
	<li>在一个连续的运动中, 用一个钻石划线在表面上进行切割。</li>
	<li>沿切口拆下晶片。</li>
	<li>将样品放在基板上, 在超音波浴中几种5分钟, 在100% 功率 (450 W), 先是在去离子水中, 然后是丙酮, 最后是异丙醇 (国际音标)。 注意: 请参阅 CAS 编号和供应商的材料表。</li>
	<li>用氮气枪擦干基板, 去除表面上的任何残留的国际音标或灰尘。</li>
	<li>血浆灰分在氧等离子体中的样品在 100 W 为5分钟, 除去任何残留的有机残渣。</li>
</ol>2. 接触用光刻双层工艺
注: 双层光刻工艺用于制造电极。光刻工艺在一个黄色的房间进行, 以防止光刻胶材料的衰变。
<ol><li>用板将样品在150° c 下加热15分钟, 从表面除去任何剩余的水分。 注: 这是为了保证光刻胶的附着力;然而化学底漆例如 HMDS 也可能使用。</li>
	<li>从热板中取出样品, 并将其放在旋转涂布机上。</li>
	<li>使用吸管, 下降约1毫升的光刻胶在表面上, 直到整个样品被统一覆盖。 注: 有关所用的精确光刻胶, 请参见材料表。</li>
	<li>旋转样品在 4000 rpm 为四十五年代, 生产大约250毫微米的影片厚度。如果要沉积的电极厚度大于 150 nm, 请更改此配方。</li>
	<li>将样品从自旋涂布机上取出, 放在150° c 的板上5分钟。</li>
	<li>从板中取出样品, 并将样品留在50% 湿度箱中休息5分钟。这是为了确保抗蚀剂的复水性22。 注: 如果实验室的湿度大于 50%, 则可以将样品留在空气中休息。</li>
	<li>将样品放回自旋涂布机上, 将大约1毫升的抗蚀剂 B 放在基板表面。</li>
	<li>旋转样品在 3500 rpm 为四十五年代, 给影片厚度大约500毫微米。</li>
	<li>将样品放在120° c 的板上2分钟。</li>
	<li>从板中取出样品, 在50% 的湿度箱中休息5分钟。</li>
	<li>暴露样品使用面罩-器和掩紫外线的6.7 秒, 共180兆焦耳的曝光。 注意: 确切的曝光剂量可能需要根据特定型号的面膜器进行调整。</li>
	<li>从面具器中取出样品, 并在三十年代将其浸入光刻胶显影液中进行开发。 注意: 有关确切的开发人员, 请参见材料表。</li>
	<li>从显影液中取出样品, 将样品浸入去离子水中, 冲洗, 以停止开发过程。</li>
	<li>使用光学显微镜检查影印。偏光片可以用来检查双层咬边, 它应该出现在通道周围的微弱线上。如果达到太多或两个小的缺口, 则可以调整时间。</li>
</ol>3. 金属接触物的沉积
注: 电子束 (电子束) 沉积用于将电极沉积在所制备的光刻胶上。这个过程也可以使用热蒸发器或其他类型的金属薄膜沉积技术。
<ol><li>将样品放在电子束室中;把它抽下去直到达到高真空。在这种情况下, 达到了大约 1 x 10-6 mTorr 的真空。</li>
	<li>沉积 2-6 纳米钛, 作为一个黏附层, 其次为30纳米黄金的 DEP 接触。</li>
	<li>从电子束室中取出样品。</li>
	<li>通过去除大部分的光刻胶和多余的金属来执行升降过程。这是通过把样品放入一烧杯的光刻胶卸妆15分钟。</li>
	<li>从光刻胶的烧杯中取出样品, 再将其放入另一干净的光刻胶中15分钟。这是为了防止任何大型金属微粒沉淀在样品上。</li>
	<li>完成 sonicating 的烧杯5分钟, 在50% 功率。</li>
	<li>从浴缸中取出样品, 确保用国际音标冲洗掉任何材料, 防止金属微粒在电极间沉淀。 注: 电极现在为纳米线的 DEP 校准做好准备。</li>
</ol>4. 纳米线的 DEP
<ol><li>在大约1µg/毫升浓度的甲醚中制备硅或其他纳米线的溶液。在这个实验中, 解决方案是简要声十五年代在最低功率设置可能消除任何絮凝。其他溶剂可以使用, 如甲苯和 n, n-胺 (DMF)1。</li>
	<li>通过将纳米线配方的10µL 放在牺牲基底上来检查溶液。</li>
	<li>使用偏光显微镜 (POM) 检查基板的沉积纳米线。硅纳米线是双折射的, 因此可以很容易地在 POM 中看到。如果没有纳米线的团簇可见, 并且大部分的纳米导线在基体上都有很好的分散, 那么下一阶段就可以开始, 否则溶液是重新声的, 并且可能需要调整纳米丝的浓度。它可能需要几次尝试, 以实现正确的纳米线分散。</li>
	<li>将准备好的样品与电极放置在30° (vs. 地平线) 倾斜平台上, 设备通道水平对齐。色散流方向需要垂直于电极边缘, 以使纳米线对齐更加有效。</li>
	<li>使用连接到频率发生器1的微探针与电极接触。</li>
	<li>设置所需的频率和电压在频率发生器上。在本实验中, 使用10伏峰值和 1 MHz 正弦波的 DEP 信号电压。 注: 增加20兆赫的频率可以帮助收集高电导率和低阱密度的纳米线1,2。有关详细讨论, 请参见参考1 。本文所述的 DEP 信号频率范围是通过导电 SFLS 硅纳米线阻抗谱和收集时间分析得到的, 如参考1所示。其他类型的高或低电荷载流子移动性纳米线, 掺杂纳米线, 或其他生长方法获得的纳米线, 可以有不同的 DEP 信号频率范围, 导致收集高质量的纳米线。</li>
	<li>开关-在频率发生器和下降约10µL 纳米线解决方案使用微到设备区域。 注: 将样品置于一个角度 (30 °) 有助于产生重力辅助的液体缓慢流动。或者, 使用玻璃幻灯片的毛细管操作可以使用6。</li>
	<li>应用三十年代的 DEP 信号, 然后关掉频率发生器。</li>
	<li>取出样品, 用国际音标轻轻冲洗。</li>
	<li>用氮气枪轻轻地把样品干掉。偏振光学显微镜可用于检测样品和调整参数 注: DEP 信号的电压、频率和纳米线的色散密度可进行调整, 以实现可重现的纳米导线密度, 从数个纳米线到每设备1,2。</li>
</ol>5. 二次金属层的沉积
<ol><li>为了在 NW fet 中获得改进的电流注入, 在纳米线的顶端应用第二个金属接触。 注: 此接触沉积过程遵循与2和3节完全相同的步骤, 在光刻和金属沉积, 但只有一个金层的沉积。</li>
</ol>6. 纳米线器件的 i-v 特性
注: 样品现已完成, 可用于后续实验或其 i-v 特性可以测量, 以建立纳米线 FET 的电性能。所制备的器件为后门式 fet, 掺杂硅晶片作为共用栅极, 而2层则充当栅极电介质。
<ol><li>要与栅极建立电接点, 请使用菱形划线在试样边缘移除一个小面积的氧化硅。</li>
	<li>使用氮气枪清除任何不需要的二氧化硅粒子。</li>
	<li>安置三探针 (来源、流失和门) 在金子来源-流失电极联络, 与门探针在区域与被去除的一点的2。</li>
	<li>使用半导体表征系统进行 i-v 测量。</li>
	<li>测量传输和输出扫描的 NW fet, 因为这些提供有关设备性能的信息和纳米线的电气性能1,17,23。请注意, 传输测量涉及步进源-漏电压和扫门电压。通过扫源电压和步进门电压来测量输出特性。</li>
</ol>

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作者证实没有利益冲突。

器件的成功制造和性能取决于几个关键因素。这些包括纳米线的密度和在配方中的分布, 溶剂的选择, DEP 的频率, 以及对器件电极上存在的纳米导线数量的控制1。
实现可重复工作装置的关键步骤之一是制备无簇或块状的纳米线配方。该配方可声前, 以减少团簇数量和保持纳米线分散。一个溶液的密度一旦被制造, 也很难控制, 特别是如果纳米线可能凝固, 这可能导致较不致密的配方。表面活性剂可用于制造更分散的配方, 但表面活性剂可能对器件性能产生负面影响。
图 2A显示了一个投影沉积纳米线的例子, 有大量的块状。如果纳米线的团簇难以去除, 或纳米线在超声16期间易受破坏, 建议允许解决方案几秒钟。然后, 该配方的顶部应 pipetted 关闭, 以供使用。均匀分散的纳米线浮在溶液的顶端, 而重纳米丝团簇下沉到底部。
溶剂和纳米材料的选择将影响到沉积阶段的参数。纳米线经历的介力由公式 18:
<img alt="Equation 1" src="/files/ftp_upload/56408/56408eq1v2.jpg">
其中是与纳米线的半径和长度相关的几何因子, 是电场的根均方根的渐变, 是克劳-Mossotti 因子<img alt="Equation 2" src="/files/ftp_upload/56408/56408eq2.jpg"> (公式 2) 的真实部分. <img alt="Equation 3" src="/files/ftp_upload/56408/56408eq3v2.jpg"> <img alt="Equation 4" src="/files/ftp_upload/56408/56408eq4.jpg">
<img alt="Equation 5" src="/files/ftp_upload/56408/56408eq5.jpg">
其中, 和是粒子和介质的介电常数, 和是它们的电导率, 是 DEP 的频率. <img alt="Equation 6" src="/files/ftp_upload/56408/56408eq6.jpg"> <img alt="Equation 7" src="/files/ftp_upload/56408/56408eq7.jpg"> <img alt="Equation 8" src="/files/ftp_upload/56408/56408eq8.jpg"> </img> <img alt="Equation 9" src="/files/ftp_upload/56408/56408eq9.jpg"> <img alt="Equation 10" src="/files/ftp_upload/56408/56408eq10v3.jpg">从方程式 2, 作用力取决于溶剂和纳米材料的导电性和介电常数。如果溶剂改变, 这可能会大大改变频率和力量响应的纳米线组件。同样明显的是, 不同的纳米线材料, 即使在相同的溶剂中, 反应也会有所不同。
<img alt="Equation 11" src="/files/ftp_upload/56408/56408eq11.jpg">表明, 在不同的频率, 粒子可能或多或少极化比介质, 这反过来决定是否纳米线移动到高电场梯度 (积极 DEP) 区域或向低电场区域渐变 (负 DEP)1。
图 5显示了甲醚中硅纳米线所经历的受力的模拟曲线。纳米线的介电常数为 11.9, 电导率为 2.5 x 10-2至 5 x 10-2 s/m. 甲醚有4.33 的介电常数和假设的电导率 2 x 10-6 s/米。在不同的电导率下, 力降到零的频率是不同的。该效应可以通过改变应用频率1,2,24, 来根据它们的相对电导率和介电常数来选择不同的粒子。更高的频率被发现选择高电导率的纳米线和较低的陷阱密度。这一选择导致 FET 设备的电流明显增加每纳米线和改进的次阈值斜率1。
这种效应取决于所使用的电极的类型和基体的倾角。我们建议研究人员希望将这个过程调整到他们的电极, 通过一次只改变一个参数来校准它。
在设备通道区域中存在的纳米线的数量对于实现可重复工作设备也是至关重要的, 因为太多的纳米线将导致出现图 2C中所示的垫, 这可能导致由于纳米线而造成的 i-v 设备特性不佳。相互筛选, 减小栅极场对通道的影响。
为了控制纳米线的密度, 该配方的电压、频率和浓度可能会被改变1。例如, 为了增加纳米线的数量, 可以增加电压, 或者增加纳米丝配方的浓度。DEP 信号的频率是一个非常重要的参数, 因为它对所采集的纳米线的质量有很大的影响, 因此, 如果要制备高性能的纳米丝器件, 不推荐使用频率的降低。还应指出, 在某些情况下, 高电压可能会导致某些类型的高导电纳米线熔化19, 或烧毁接触区域。
总之, dep 纳米线组装是一项非常强大的技术, 当结合阻抗光谱学, 允许评估 dep 信号频率收集高质量的纳米导线。在高 DEP 信号频率, 在 1-20 兆赫范围, 确定为优质 Si 纳米线汇集, 可控制和可再生的纳米线汇编可以获得。在许多情况下, 每台设备面积几十到几百个纳米线的组装都足以证明高性能的纳米丝晶体管。如果每种材料都是根据对 DEP 信号的响应1,2进行检查, 则该方法可以直接扩展到其他类型的纳米线和纳米材料。

纳米粒子在预先定义的基底位置的可控性和可再生性组装是利用半导体或导电纳米粒子的解决方案处理的电子和光子器件的主要挑战之一。对于高性能器件来说, 能够选择具有优先尺寸的纳米粒子, 以及特殊的电子特性, 包括高导电性和低密度的表面陷阱状态, 也是非常有益的。尽管纳米线和纳米管材料的发展有了很大的进展, 但纳米粒子的某些特性始终存在, 选择步骤可以显著改善纳米粒子的性能1 ,2。
在这项工作中演示的流辅助 DEP 方法的目的是通过向高性能纳米线场效应晶体管显示可控的半导体纳米导线组装到金属触点上来解决上述挑战。dep 解决了纳米线器件制造中的几个问题, 包括纳米导线的定位、纳米线的对准/定位、以及所需性能的纳米线的选择via dep 信号频率选择1。DEP 已用于许多其他设备, 从气体传感器3, 晶体管1, 和 RF 开关4,5, 到细菌的定位分析7。
DEP 是通过非均匀电场的应用来操纵极化粒子, 从而使纳米线在电极上的自组装成为8。该方法最初是为操作细菌而开发的9,10 , 但此后已扩展到对纳米线和纳米材料的操作。
纳米粒子的 DEP 解决方案使半导体器件的制造与传统的基于多 photomasking、离子注入、高温14、退火和蚀刻的顶向下技术截然不同。步骤.由于 DEP 操作已经合成的纳米粒子, 所以它是一种低温、自下而上的制作技术11。这种方法允许大型纳米线器件在几乎任何基板上组装, 包括温度敏感、柔性塑料衬底6、12、13。
在这项工作中, 使用流辅助 DEP 制作高性能 p 型硅纳米线场效应晶体管, 并进行 FET 电流电压特性表征。这项工作中使用的硅纳米线是通过超级流体固体 (SFLS) 方法15,16来发展的。纳米线被有意掺杂, 直径约 10-50 µm, 长度为 30-40 nm。SFLS 的生长方法是非常诱人的, 因为它可以提供行业可伸缩的数量的纳米线材料15。所提出的纳米线组装方法直接适用于其他半导体纳米线材料, 如 InAs13、诺23和 GaN18。该技术还可以扩展到对齐导电纳米线19 , 并将纳米粒子置于电极间隙位置20。

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Silicon/silicon dioxide wafer, CZ method growth, 100mm diameter,&#160; 300 nm oxide thermal growth,&#160; n-doped phosphorus</td>
			<td>Si-Mat (Silicon materials)</td>
			<td>-</td>
			<td>http://si-mat.com/</td>
		</tr>
		<tr>
			<td>Acetone (200ml)</td>
			<td>Sigma Aldrich</td>
			<td>W332615</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Isopropanol (200ml)</td>
			<td>Sigma Aldrich</td>
			<td>W292907</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Deionised water (150ml)</td>
			<td>On site supply</td>
			<td>-</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Photoresist (A) SF6 PMGI under etch photoresit (approx 1 ml per sample)</td>
			<td>Microchem&#160;</td>
			<td>-</td>
			<td>http://microchem.com/pdf/PMGI-Resists-data-sheetV-rhcedit-102206.pdf</td>
		</tr>
		<tr>
			<td>Photoresist (B) S1805 photoresit) (approx 1 ml per sample)</td>
			<td>Microchem&#160;</td>
			<td>-</td>
			<td>http://www.microchem.com/PDFs_Dow/S1800.pdf</td>
		</tr>
		<tr>
			<td>Photoresist developer (A) Microposit&#160; MF319&#160; (100ml)</td>
			<td>Microchem&#160;</td>
			<td>-</td>
			<td>http://microchem.com/products/images/uploads/MF_319_Data_Sheet.pdf</td>
		</tr>
		<tr>
			<td>Photoresist remover (A) Microposit remover 1165 (300ml (2 baths 150 each))</td>
			<td>Microchem&#160;</td>
			<td>-</td>
			<td>http://micromaterialstech.com/wp-content/dow_electronic_materials/datasheets/1165_Remover.pdf</td>
		</tr>
	</tbody>
</table>

flow-assisted dielectrophoresis: a low cost method for the fabrication of high performance solution-processable nanowire devices

流辅助介 (DEP) 是一种高效的自组装方法, 可用于纳米线的可控、可重复定位、对准和选择。DEP 用于纳米线的分析、表征以及基于溶液的半导体器件的制造。该方法的工作原理是在金属电极之间应用交流电场。纳米线的配方, 然后下降到电极上, 在一个倾斜的表面, 以创造一个流动的配方使用重力。然后, 纳米线沿着电场的梯度和液体流动的方向排列。该场的频率可以调整, 以选择具有优越的导电率和较低的陷阱密度纳米线。
在这项工作中, 流辅助 DEP 用于创建纳米线场效应晶体管。流动辅助 DEP 有几个优点: 它允许选择纳米线的电学性质;纳米线长度的控制;纳米线在特定区域的放置;纳米线定向的控制;和控制纳米线密度的装置。
该技术可以扩展到许多其他应用, 如气体传感器和微波开关。该技术效率高、速度快、重现性好, 使用了少量的稀溶液, 使其适合于新型纳米材料的测试。纳米线器件的晶片规模组装也可以使用这种技术实现, 允许大量的样品用于测试和大面积电子应用。

双层光刻结果在清洁尖锐定义的电极。在示例 (图 1A) 中, digitated 的手指结构使用了10µm 的通道长度。当应用 DEP 力时, 这些结构允许大面积的纳米线的最大数目聚集。图 1B显示了底部栅纳米线 FET 装置的示意图。
不正确的纳米线分散浓度, 以及不足的超声可能导致质量较差的分散体, 在图 2A和 图 2B中显示的纳米导线的滴铸例子, 具有大量的纳米丝团.沉积非常致密的纳米线的分散体也可以产生不理想的质量层, 如图 2C所示。在这个例子中, 纳米线被沉积得太密, 从而产生了非常重要的纳米丝的筛分效果。一个良好的 DEP 沉积的例子显示在图 2D中, 演示了良好的分散、隔离、对齐的纳米线。
流动辅助纳米线的 DEP 应导致纳米线垂直穿过通道, 并在电极上有几微米的重叠, 如图 3所示。理想的纳米线组装可以近似为一个很好的 "单层"。另外, 纳米线之间的小间隙更倾向于减少纳米丝的筛分效果。一个可控的纳米线组件的流动辅助 DEP 的示例如图 3A和图 3B所示, 其中 dep 信号电压在图 3B中减少, 从而使沉积在电极间隙。
一个典型的硅纳米线场效应晶体管的传输和输出扫描显示在图 4中。结果表明, 该装置具有 p 型行为, 具有良好的门调制特性。这些结果与在文献1,2中使用相同方法制作的其他纳米线晶体管比较好。但是, 这些设备也可以通过诸如表面钝化之类的技术来改进, 这里没有讨论17。解决方案处理过的硅纳米线 fet 在电流上表现为高在毫安级的1;然而, 对于许多应用, fet 与微放大器电流是充足的。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56408/56408fig1.jpg"> 图 1:晶体管的光学图像和示意图(A) 指电极结构的光学显微镜图像, 纳米线与电极之间排列。(B) 底部栅纳米线场效应晶体管的示意图, 它建立在硅/微晶的2硅片上, 具有 si 公共栅极。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56408/56408fig1large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56408/56408fig2.jpg"> 图 2:极化光学显微镜图像的溶液沉积硅纳米线.(A) 纳米线在硅晶片上的优化色散的例子, 显示了大量的纳米丝团簇。(B) 在短超声和少量团簇后丢弃纳米线。(C) 设备在不正确的 DEP 后显示非常高密度的纳米线和块状。(D) 设备在正确的 DEP 沉积后显示出与电极间隙相交的、隔离的纳米线。红色箭头指示流体流动的方向。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56408/56408fig2large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56408/56408fig3.jpg"> 图 3:硅纳米线可控 DEP 沉积的偏振光学显微镜图像(A) 在高 DEP 信号电压 (15 V) 上组装的纳米线, 显示对齐的纳米线的高密度。(B) 在低 DEP 电压 (5 V) 上组装的纳米线, 只有两个纳米线连接电极。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56408/56408fig3large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56408/56408fig4.jpg"> 图 4: 典型的纳米线 FET 器件的特性.(a) 用金电极对硅纳米线底部门控 fet 器件进行 fet 转移扫描。排泄电压从-0.1 到-0.5 v 以-0.1 v 区间和门电压被扫从10到-40 v (B) 输出扫描同一个设备以台阶门电压从0到-40 伏与-5 v 间隔时间和扫漏电压从0到-0.5 五. 纳米线在 DEP 信号处以 2 MHz 和 10 Vpp. FET 显示 5 pA 关闭电流 (vG = 0 v), 5 µΑ在当前 at vD= 0.5 v, 导致 106 -107开/关电流比。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56408/56408fig4large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56408/56408fig5v2.jpg"> 图 5:在不同电导率的甲醚中, 硅纳米线的 DEP 力与频率的模拟图.在模拟中, 纳米线的介电常数为 11.9, 电导率介于 2.5 x 10-2 /m 到 10 x 10-2 /米之间. 甲醚具有4.33 的介电常数和假设的电导率 2 x 10-6 s/米. 注意, 较高的热导率有一个更高的频率, 使力降到零。这一趋势表明高电导率纳米线可以在较高的 DEP 信号频率下采集。<a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56408/56408fig5large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>

Watch this Scientific Journal Video about Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices at JoVE.com

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

本文对纳米线器件的自组装进行了流动辅助介。以硅纳米线场效应晶体管的制备为例。

流动辅助介: 一种低成本的制备高性能溶液可纳米线器件的方法

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of ...

flow-assisted-dielectrophoresis-low-cost-method-for-fabrication-high

Nanyang Technological University

Research

JoVE Journal

Engineering

7.6K 次观看.  University of Surrey. 本文对纳米线器件的自组装进行了流动辅助介。以硅纳米线场效应晶体管的制备为例。

视频: Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

单氮化镓纳米线设备分析接触界面

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

科研

工程学

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each thermoplastic of interest. Solvent bonding is a simple and versatile method that can be used to fabricate devices from a variety of plastics. An appropriate solvent is added between two device layers to be bonded, and heat and pressure are applied to the device to facilitate the bonding. By using an appropriate combination of solvent, plastic, heat, and pressure, the device can be sealed with a high quality bond, characterized as having high bond coverage, bond strength, optical clarity, durability over time, and low deformation or damage to microfeature geometry. We describe the procedure for bonding devices made from two popular thermoplastics, poly(methyl-methacrylate) (PMMA), and cyclo-olefin polymer (COP), as well as a variety of methods to characterize the quality of the resulting bonds, and strategies to troubleshoot low quality bonds. These methods can be used to develop new solvent bonding protocols for other plastic-solvent systems.

Solvent bonding is a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds. We describe a protocol to achieve strong, optically clear bonds in PMMA and COP microfluidic devices that preserve microfeature details, by a judicious combination of pressure, temperature, an appropriate solvent, and device geometry.

溶剂粘接的PMMA的制备和COP微流体装置

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

具有嵌入式金属网的高性能，灵活，透明电极的可扩展解决方案处理制造策略

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

高精度水泥浆水溶氯分布的检测

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

Method for Recording Broadband High Resolution Emission Spectra of Laboratory Lightning Arcs

Lightning is one of the most common and destructive forces in nature and has long been studied using spectroscopic techniques, first with traditional camera film methods and then digital camera technology, from which several important characteristics have been derived. However, such work has always been limited due to the inherently random and non-repeatable nature of natural lightning events in the field. Recent developments in lightning test facilities now allow the reproducible generation of lightning arcs within controlled laboratory environments, providing a test bed for the development of new sensors and diagnostic techniques to understand lightning mechanisms better. One such technique is a spectroscopic system using digital camera technology capable of identifying the chemical elements with which the lightning arc interacts, with these data then being used to derive further characteristics. In this paper, the spectroscopic system is used to obtain the emission spectrum from a 100 kA peak, 100 &#181;s duration lightning arc generated across a pair of hemispherical tungsten electrodes separated by a small air gap. To maintain a spectral resolution of less than 1 nm, several individual spectra were recorded across discrete wavelength ranges, averaged, stitched, and corrected to produce a final composite spectrum in the 450 nm (blue light) to 890 nm (near infrared light) range. Characteristic peaks within the data were then compared to an established publicly available database to identify the chemical element interactions. This method is readily applicable to a variety of other light emitting events, such as fast electrical discharges, partial discharges, and sparking in electrical equipment, apparatus, and systems.

Emission spectroscopy techniques have traditionally been used to analyze inherently random lightning arcs occurring in nature. In this paper, a method developed to obtain the emission spectroscopy from reproducible lightning arcs generated within a laboratory environment is described.

记录实验室闪电弧宽带高分辨率发射光谱的方法

Lightning is one of the most common and destructive forces in nature and has long been studied using spectroscopic techniques, first with traditional ...

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 Refractive-index-matched Devices for Biomedical Microfluidics

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices can be implemented as part of a robust platform capable of making simultaneous complementary measurements. The primary challenge created by the combination of these two techniques is the mismatch in refractive index between the materials traditionally used to make microfluidic devices and the aqueous solutions typically used in biomedicine. This mismatch can create optical artifacts near the channel or device edges. One solution is to reduce the refractive index of the material used to fabricate the device by using a fluorinated polymer such as MY133-V2000 whose refractive index is similar to that of water (n = 1.33). Here, the construction of a microfluidic device made out of MY133-V2000 using soft lithography techniques is demonstrated, using O2 plasma in conjunction with an acrylic holder to increase the adhesion between the MY133-V2000 fabricated device and the polydimethylsiloxane (PDMS) substrate. The device is then tested by incubating it filled with cell culture media for 24 h to demonstrate the ability of the device to maintain cell culture conditions during the course of a typical imaging experiment. Finally, quantitative phase microscopy (QPM) is used to measure the distribution of mass within the live adherent cells in the microchannel. This way, the increased precision, enabled by fabricating the device from a low index of refraction polymer such as MY133-V2000 in lieu of traditional soft lithography materials such as PDMS, is demonstrated. Overall, this approach for fabricating microfluidic devices can be readily integrated into existing soft lithography workflows in order to reduce optical artifacts and increase measurement precision.

This protocol describes the fabrication of microfluidic devices from MY133-V2000 to eliminate artifacts that often arise in microchannels due to the mismatching refractive indices between microchannel structures and an aqueous solution. This protocol uses an acrylic holder to compress the encapsulated device, improving adhesion both chemically and mechanically.

生物医学微流体折射率匹配器件的研制

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices ...

Low-cost Custom Fabrication and Mode-locked Operation of an All-normal-dispersion Femtosecond Fiber Laser for Multiphoton Microscopy

A protocol is presented to build a custom low-cost yet high-performance femtosecond (fs) fiber laser. This all-normal-dispersion (ANDi) ytterbium-doped fiber laser is built completely using commercially available parts, including $8,000 in fiber optic and pump laser components, plus $4,800 in standard optical components and extra-cavity accessories. Researchers new to fiber optic device fabrication may also consider investing in basic fiber splicing and laser pulse characterization equipment (~$63,000). Important for optimal laser operation, methods to verify true versus apparent (partial or noise-like) mode-locked performance are presented. This system achieves 70 fs pulse duration with a center wavelength of approximately 1,070 nm and a pulse repetition rate of 31 MHz. This fiber laser exhibits the peak performance that may be obtained for an easily assembled fiber laser system, which makes this design ideal for research laboratories aiming to develop compact and portable fs laser technologies that enable new implementations of clinical multiphoton microscopy and fs surgery.

A method is presented to build a custom low-cost, mode-locked femtosecond fiber laser for potential applications in multiphoton microscopy, endoscopy, and photomedicine. This laser is built using commercially available parts and basic splicing techniques.

用于多光子显微镜的全正常分散飞秒光纤激光器的低成本定制制造和模式锁定操作

A protocol is presented to build a custom low-cost yet high-performance femtosecond (fs) fiber laser. This all-normal-dispersion (ANDi) ytterbium-doped ...

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone (ITZ)

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect of aggregate surface morphology on the formation of ITZ. First, a model concrete sample is prepared with a spherical ceramic particle in roughly the central part of the cement matrix, acting as a coarse aggregate used in common concrete/mortar. After curing until the designed age, the sample is scanned by X-ray computed tomography to determine the relative location of the ceramic particle inside the cement matrix. Three locations of the ITZ are chosen: above the aggregate, on the side of the aggregate, and below the aggregate. After a series of treatments, the samples are scanned with a SEM-BSE detector. The resultant images were further processed using a digital image processing method (DIP) to obtain quantitative characteristics of the ITZ. The surface morphology is characterized at the pixel level based on the digital image. Thereafter, K-means clustering method is used to illustrate the effect of surface roughness on ITZ formation.

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone ITZ

Hereby, we proposed a protocol to illustrate the effect of aggregate surface morphology on the ITZ microstructure. The SEM-BSE image were quantitatively analyzed to obtain ITZ's porosity gradient via digital image processing and a K-means clustering algorithm was further employed to establish a relationship between porosity gradient and surface roughness.

在界面过渡区（ITZ）的聚合曲面形态测定

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect ...

Fabrication and Design of Wood-Based High-Performance Composites

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber reinforced composites, due to its excellent mechanical properties. Delignified wood, however, is rather fragile in a wet state, which makes handling and shaping challenging. Here we present two fabrication processes, closed-mold densification and vacuum densification, to produce high-performance cellulose composites based on delignified wood, including an assessment of their advantages and limitations. Further, we suggest strategies for how the composites can be re-used or decomposed at the end-of-life cycle. Closed-mold densification has the advantage that no elaborate lab equipment is needed. Simple screw clamps or a press can be used for densification. We recommend this method for small parts with simple geometries and large radii of curvature. Vacuum densification in an open-mold process is suitable for larger objects and complex geometries, including small radii of curvature. Compared to the closed-mold process, the open-mold vacuum approach only needs the manufacture of a single mold cavity.

Delignified densified wood represents a new promising lightweight, high-performance and bio-based material with great potential to partially substitute natural fiber reinforced- or glass fiber reinforced composites in the future. We here present two versatile fabrication routes and demonstrate the possibility to create complex composite parts.

基于木材的高性能复合材料的制造与设计

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber ...