对于新材料的低温磁输运测量先进的实验方法
Summary
We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.
Abstract
Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.
Introduction
先进的电子技术的追求材料的平台要求的高通量材料的合成和随后的表征方法。在这种追求兴趣的新型材料，可以产生散装直接反应合成1,2-，电化学生长3,4-，和其他方法5以更快速的方式相比，如分子束外延或更多参与单晶薄膜沉积技术化学气相沉积。测量块状晶体样品的输运性质的常规方法是切割的矩形棱柱形的片段约为1毫米×1毫米×6毫米的尺寸和连接线导致在一个霍尔棒构6的样品。
某些材料构成挑战，其中传统的散装霍尔棒装置的制造方法是不足以产生一个可测量的装置，用于传输样品测量。这可以是导致产生的结晶太小附加引线到，即使是一个功能强大的光学显微镜下，因为所需的样品厚度是1的量级，以只有几个单层，或因为一个目的是衡量一叠层状二维材料与近或亚纳米厚度。第一类包括，例如纳米线和氧化钼的某些制剂铜器7。第二类包括单对极少数的二维材料，例如石墨烯8层 ，TMDS（ 二硫化钼，WTE 2等），和拓扑绝缘体（ 的 Bi 2硒3，铋锑x 1-X 3碲等 ）。第三类包括制备由经由层转移，的hBN-石墨烯的hBN 9的最显着的一个三层堆积层叠的二维材料的各层通过手工装配异质结构。
新型Ë的探索性研究lectronic原材料的需求，足够制造方法上难以测量的样品设备。通常情况下，第一批直接反应或电化学生长合成新材料的产量非常小的单晶微米尺寸级的尺寸。这种样品在历史上被证明极为困难附加金属接触到，因此有必要改善样品生长参数以实现较大的晶体，以方便运输装置制造，呈现的障碍物的新材料的高通量研究。为了使材料的快速表征，器件制造为非常小的样品的方法，已被设计成只要初步批次已经产生允许新材料的表征。这种方法的细微变化是适用于制造使用二维材料，例如石墨烯，的hBN，和TMDS剥离样品，设备以及这种毫安的多层异质结构terials。设备被附着和引线键合到一个包，用于插入一个商业超导磁体，干燥氦气靠近循环低温恒温器磁输运系统。传输测量是在温度下降到0.300 K和磁场高达12吨
Protocol
Representative Results
Discussion
采集高质量大块样品，其特征在于，以确保适当的组成和结构的后，将样品经图案化成为通过剥离样品的薄片中描绘的几何上1厘米×1厘米的片基片的。基板重p掺杂Si构成覆盖约300nm 的 SiO 2是优选的，因为它们增加了实验参数空间通过使背栅的应用。样品必须足够薄 – 少于10纳米 – 以产生足够的场效应调谐在霍尔棒装置的导电沟道的整体的化学势。样品厚度由适当使用标准的晶片切割用胶?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work is supported by the National Institute of Standards and Technology of the United States Department of Commerce.
Materials
| Cryogenic Limited 12T CFMS | Cryogen Limited | CFM-12T-H3- IVTI-25 | Magnetotransport system customized with modulated field magnet (step 4) |
| 7270 DSP Lock-in amplifier | Signal Recovery | 7270 | lock-in amplifier for source/drain and voltage measurements (step 4) |
| GS200 DC Voltage/Current Source | Yokogawa | GS200 | Voltage source for gate voltage application (step 4) |
| 2636B System Sourcemeter | Keithley | 2636B | Sourcemeter for source/drain and voltage measurements |
| DWL 2000 Laser Pattern Generator | Heidelberg Instruments | DWL 2000 | Generate chrome mask for lithography of substrate location/alignment feature pattern (step 1.3) |
| Suss MicroTec MA6/BA6 Contact Aligner | Suss | MA6 | Used for the lithography of substrate location/alignment feature pattern (step 1.4.12) |
| JEOL Direct Write Electron Beam Lithography System | JEOL | JBX 6300-FS | Perform high-resolution lithography of devices |
| Discovery 550 Sputtering System | Denton Vacuum | Discovery 550 | Perform SiO2 sputtering (step 2.5) |
| Infinity 22 Electron Beam Evaporator | Denton Vacuum | Infinty 22 | Perform Cr/Au deposition (steps 1.5 and 3.7) |
| Unaxis 790 Reactive Ion Etcher | Unaxis | Unaxis 790 | Etch sample into Hall bar structure (step 3.4) |
| Name | Company | Catalog Number | Comments |
| PMMA 495 A4 | MicroChem | PMMA 495 A4 | Polymer coating/electron beam mask for lithography (step 3.5.1) |
| PMMA 950 A4 | MicroChem | PMMA 950 A4 | Polymer coating/electron beam mask for sample dicing and lithography (steps 1.7.3, 3.3.1, and 3.5.2) |
| S1813 positive photoresist | MicroChem | S1813 G2 | Positive photoresist (step 1.4.8) |
| LOR resist | MicroChem | LOR 3A | Lift off resist (step 1.4.3) |
| 1:3 MIBK:IPA PMMA developer | MicroChem | 1:3 MIBK:IPA | PMMA developer |
| MF-321 Developer | MicroChem | MF-321 | Novolac positive photoresist-compatible developer solution (step 1.4.15) |
| Diglycidiyl ether-terminated polydimethylsiloxane | Sigma Aldrich | SA 480282 | For layered material stacking (step 2.6.1) |
| Polypropylene carbonate | Sigma Aldrich | SA 389021 | For layered material stacking (step 2.6.2) |
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