الكتابة وانخفاض درجة الحرارة توصيف أكسيد النانو
Summary
Oxide nanostructures provide new opportunities for science and technology. The interfacial conductivity between LaAlO3 and SrTiO3 can be controlled with near-atomic precision using a conductive atomic force microscopy technique. The protocol for creating and measuring conductive nanostructures at LaAlO3/SrTiO3 interfaces is demonstrated.
Abstract
Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions. Oxide interfaces exhibit a wide range of properties that can be controlled include conduction, piezoelectric behavior, ferromagnetism, superconductivity and nonlinear optical properties. Recently, methods for controlling these properties at extreme nanoscale dimensions have been discovered and developed. Here are described explicit step-by-step procedures for creating LaAlO3/SrTiO3 nanostructures using a reversible conductive atomic force microscopy technique. The processing steps for creating electrical contacts to the LaAlO3/SrTiO3 interface are first described. Conductive nanostructures are created by applying voltages to a conductive atomic force microscope tip and locally switching the LaAlO3/SrTiO3 interface to a conductive state. A versatile nanolithography toolkit has been developed expressly for the purpose of controlling the atomic force microscope (AFM) tip path and voltage. Then, these nanostructures are placed in a cryostat and transport measurements are performed. The procedures described here should be useful to others wishing to conduct research in oxide nanoelectronics.
Introduction
heterostructures أكسيد 1-5 المعرض تشكيلة واسعة من الظواهر الفيزيائية بشكل ملحوظ الناشئة التي هي على حد سواء مثيرة للاهتمام علميا ويمكن أن تكون مفيدة للتطبيقات 4. على وجه الخصوص، يمكن التفاعل بين LaAlO 3 (لاو) وSrTiO 3 (STO) 6 يحمل العازلة، وإجراء، فائقة التوصيل 7، متعلق بالعازل الكهربائي الشفاف مثل 8 و 9 المغناطيسية السلوك. في عام 2006، ثيل وآخرون أظهرت أن هناك 10 انتقال حاد عازل إلى المعادن مثل سمك طبقة لاو هو زيادة، مع سمك الحرجة من 4 وحدة الخلايا (4uc). وقد تبين لاحقا أن الهياكل 3uc-LAO/STO يحمل الانتقال hysteretic التي يمكن السيطرة عليها محليا مع موصل ذرية قوة المجهر (ج فؤاد) التحقيق 11.
خصائص واجهات أكسيد مثل LaAlO 3/3 SrTiO تعتمد على غياب أو وجود إجراءالإلكترونات في واجهة. هذه الالكترونات يمكن السيطرة عليها باستخدام أعلى أقطاب بوابة 12،13، والعودة بوابات 10، سطح adsorbates و14، طبقات متعلق بالعازل الكهربائي الشفاف 15،16 وج فؤاد الطباعة الحجرية 11. ومن المزايا الفريدة لج فؤاد الطباعة الحجرية هي أن ميزات النانو صغيرة جدا يمكن أن تنشأ.
تبوب الأعلى الكهربائية، جنبا إلى جنب مع الحبس ثنائية الأبعاد، وغالبا ما يتم استخدامه لإنشاء نقاط الكم في أشباه الموصلات III-V 17. بدلا من ذلك، أسلاك شبه الموصلة شبه أحادية البعد يمكن بوابات كهربائيا بواسطة القرب. طرق لإنتاج هذه الهياكل هي مضيعة للوقت وعموما لا رجعة فيه. على النقيض من ذلك، فإن تقنية الطباعة الحجرية ج فؤاد هو عكسها، بمعنى أن البنية النانوية يمكن أن تنشأ عن تجربة واحدة، ثم "مسح" (على غرار لوحة بيضاء). عموما، يتم تنفيذ ج فؤاد الكتابة مع الفولتية الإيجابية تطبيقها على الطرف فؤاد، في حين، ومحويتم تنفيذ باستخدام الفولتية السلبية. الوقت اللازم لإنشاء بنية خاصة تعتمد على تعقيد الجهاز ولكن عادة ما يكون أقل من 30 دقيقة؛ وقضى معظم ذلك الوقت محو قماش. القرار المكانية النموذجي هو حوالي 10 نانومتر، ولكن مع ضبط السليم ملامح صغيرة مثل 2 نانومتر يمكن إنشاء 18.
وصف مفصل للإجراءات النانو تلفيق التالي. التفاصيل المقدمة هنا ينبغي أن يكون كافيا للسماح التجارب المماثلة التي يتعين القيام بها من قبل الباحثين المهتمين. الطريقة الموضحة هنا العديد من المزايا على النهج معدني التقليدية المستخدمة في إنشاء النانو الإلكترونية في أشباه الموصلات.
طريقة الطباعة الحجرية ج فؤاد الموصوفة هنا هي جزء من فئة أوسع بكثير من الجهود الطباعة الحجرية القائمة على المسح الضوئي مسبار، بما في ذلك المسح انوديك الأكسدة 19، وتراجع من ركلة جزاء nanolithography إرادة 20، الزخرفة كهرضغطية21، وهلم جرا. تقنية ج فؤاد الموصوفة هنا، إلى جانب استخدام واجهات أكسيد الرواية، يمكن أن تنتج بعض الهياكل الإلكترونية أعلى الدقة مع مجموعة غير مسبوقة من الخصائص الفيزيائية.
Protocol
Representative Results
Discussion
Successful creation of nanostructures depends on several critical steps. It is important that the LAO/STO samples are grown with a thickness that is known to be at the boundary between the insulating and conductive phase. (Details of sample growth fall outside the scope of this paper, but are crucial for overall success.) Second, it is important to have relative humidity within the range 25-45% for successful c-AFM writing. Values below 25% are unlikely to produce conductive nanostructures, while too high humidity will generally produce uncontrollably large features. Also, temperature control of the AFM is important if the c-AFM tip needs to achieve precise registry over long periods of time. Once the nanostructures are created, they must be placed in a vacuum environment if experiments lasting longer than a few hours are to be performed. For the experiments described here, the structure is created and within minutes transferred to a vacuum environment.
It is recommend before writing that a “writing test” be performed on all relevant electrodes. In such a test, two virtual electrodes are first created, and a single nanowire is written while simultaneously monitoring the conductance. A similar test of erasure can be performed by “cutting” the nanowire shortly afterwards. If the nanostructure is decaying rapidly, the issue is most likely due either to the interfacial contacts or the canvas itself. To distinguish between these two effects, a four-terminal measurement of the conductance should be performed, and the two-terminal conductance should be compared with the four-terminal conductance as a function of time. If the two-terminal conductance is decaying more rapidly than the four-terminal conductance, then the issue is related to the electrical contacts to the interface. If the four-terminal conductance is decaying at a comparable rate, then most likely the canvas is not suitable and should be replaced.
There are natural limitations of the current method for creating nanostructures. Specifically, the writing speed for the smallest devices is limited to a few hundred nanometers per second. Speeds far above that value lead to unpredictable results. Use of parallel writing techniques are possible27,28, but are not highly developed and have their own drawbacks. The size of nanostructures that can be created is naturally limited by the scan range of the AFM being used. A high-quality AFM with closed-loop feedback in the two scan directions is highly recommended. Tracking of point-like objects on the sample surface should be performed to monitor temporal drift of the sample.
Once creation of conductive nanostructures at oxide interfaces has been mastered, there are a wide range of experimental directions that can be explored. Using this technique, a wide variety of nanostructures and devices have already been demonstrated, including nanowires18, tunnel barriers29, rectifying junctions30, field-effect transistors18, single-electron transistors31, superconducting nanowires32, nanoscale optical detectors33, and nanoscale THz emitters and detectors34.
Disclosures
The authors have nothing to disclose.
Acknowledgements
The long-standing collaboration with Chang-Beom Eom at the University of Wisconsin-Madison, who provided the LAO/STO samples, is gratefully acknowledged. Video editing assistance from Christopher Solis is greatly appreciated. This work is supported by NSF (DMR-1104191, DMR-1124131), ARO (W911NF-08-1-0317), and AFOSR (FA9550-10-1-0524, FA9550-12-1-0268, FA9550-12-1-0057).
Materials
| Name | Company | Catalog Number | Comments |
| Equipment | |||
| Contact Aligner | Karl-Suss | MA6 | |
| Spinner | Solitec | 5110C | |
| Ion Mill | Commonwealth Scientific | 8C | |
| Sputtering System | Leybold-Heraeus | Z-650 | |
| Barrel Etcher | Branson/IPC | 3000C | |
| Wire Bonder | Westbond | 7700E | |
| AFM | Asylum Research | MFP-3D | |
| Dilution Refrigerator | Quantum Design | P850 | |
| Ultrasonic Wash Machine | Fisher Scientific | 15-335-6 | |
| Current Amplifier | Femto | DLPCA-200 | |
| Materials | |||
| LaAlO3/SrTiO3 | Prof. Chang-Beom Eom | N/A | 5mm x 1mm with ~3.4 unit cells of LAO (See Reference 18) |
| Photoresist | AZ Electronic Materials | P4210 | |
| Developer | AZ Electronic Materials | 400K | |
| Acetone | Fisher Scientific | A929SK-4 | |
| Isopropyl Alcohol | Fisher Scientific | A459-1 | |
| Deionized Water | Fisher Scientific | 23-290-065 | |
| Gold Wire | DuPont | 5771 | 1 mil diameter |
| Chip Carrier | NTK Technologies | IRK28F1-5451D |
References
- Sulpizio, J. A., Ilani, S., Irvin, P., Levy, J. i. . Annual Review of Materials Research, in press. , (2014).
- Mannhart, J., Blank, D. H. A., Hwang, H. Y., Millis, A. J., Triscone, J. M. Two-Dimensional Electron Gases at Oxide Interfaces. Mrs Bulletin. 33, 1027-1034 (2008).
- Zubko, P., Gariglio, S., Gabay, M., Ghosez, P., Triscone, J. -. M., Langer, J. S. Annual Review of Condensed Matter Physics. Interface Physics in Complex Oxide Heterostructures. , 141-165 (2011).
- Bogorin, D. F., Irvin, P., Cen, C., Levy, J. i., Tsymbal, E. Y., Dagotto, E. R. A., Chang-Beom, E., Ramesh, R. . Multifunctional Oxide Heterostructures. 13, (2012).
- Granozio, F. M., Koster, G., Rijnders, G. Functional Oxide Interfaces. MRS Bulletin. 38, 1017-1023 (2013).
- Ohtomo, A., Hwang, H. Y. A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface. Nature. 427, 423-426 (2004).
- Reyren, N., et al. Superconducting interfaces between insulating oxides. Science. 317, 1196-1199 (2007).
- Bark, C. W., et al. Switchable Induced Polarization in LaAlO3/SrTiO3 Heterostructures. Nano Letters. 12, 1765-1771 (2012).
- Brinkman, A., et al. Magnetic effects at the interface between non-magnetic oxides. Nature Materials. 6, 493-496 (2007).
- Thiel, S., Hammerl, G., Schmehl, A., Schneider, C. W., Mannhart, J. Tunable quasi-two-dimensional electron gases in oxide heterostructures. Science. 313, 1942-1945 (2006).
- Cen, C., et al. Nanoscale control of an interfacial metal-insulator transition at room temperature. Nature Materials. 7, 298-302 (2008).
- Singh-Bhalla, G., et al. Built-in and induced polarization across LaAlO3/SrTiO3 heterojunctions. Nature Physics. 7, 80-86 (2011).
- Li, L., et al. Very Large Capacitance Enhancement in a Two-Dimensional Electron System. Science. 332, 825-828 (2011).
- Xie, Y., Hikita, Y., Bell, C., Hwang, H. Y. Control of electronic conduction at an oxide heterointerface using surface polar adsorbates. Nature Communications. 2, 494 (2011).
- Bark, C. W., et al. Tailoring a two-dimensional electron gas at the LaAlO3/SrTiO3 (001) interface by epitaxial strain. PNAS. 108, 4720-4724 (2011).
- Tra, V. T., et al. . Adv Mater. 25, 3357-3364 (2013).
- Cronenwett, S. M., Oosterkamp, T. H., Kouwenhoven, L. P. A Tunable Kondo Effect in Quantum Dots. Science. 281, 540-544 (1998).
- Cen, C., Thiel, S., Mannhart, J., Levy, J. Oxide Nanoelectronics on Demand. Science. 323, 1026-1030 (2009).
- Kalinin, S. V., Gruverman, A. . Scanning probe microscopy: electrical and electromechanical phenomena at the nanoscale. 1, (2007).
- Piner, R. D., Zhu, J., Xu, F., Hong, S. H., Mirkin, C. A. ‘Dip-pen’ nanolithography. Science. 283, 661-663 (1999).
- Ahn, C. H., et al. Nonvolatile Electronic Writing of Epitaxial Pb(Zr0.52Ti0.48)O3/SrRuO3 Heterostructures. Science. 276, 1100-1103 (1997).
- Bi, F., et al. ‘Water-cycle’ mechanism for writing and erasing nanostructures at the LaAlO3/SrTiO3 interface. Applied Physics Letters. 97, 173110 (2010).
- Cheng, G., et al. Anomalous Transport in Sketched Nanostructures at the LaAlO3/SrTiO3 Interface. Phys Rev X. 3, 011021 (2013).
- Veazey, J. P., et al. Nonlocal current-voltage characteristics of gated superconducting sketched oxide nanostructures. Europhys Lett. 103, 57001 (2013).
- Veazey, J. P., et al. Oxide-based platform for reconfigurable superconducting nanoelectronics. Nanotechnology. 24, 375201 (2013).
- Irvin, P., et al. Anomalous High Mobility in LaAlO3/SrTiO3 Nanowires. Nano Letters. 13, 364-368 (2013).
- Salaita, K., et al. Massively Parallel Dip–Pen Nanolithography with 55 Two-Dimensional Arrays. Angewandte Chemie. 118, 7378-7381 (2006).
- Li, S., et al. Parallel Conductive-AFM Lithography on LaAlO3/SrTiO3 Interfaces. Ieee T Nanotechnol. 12, 518-520 (2013).
- Cen, C., Bogorin, D. F., Levy, J. Thermal activation and quantum field emission in a sketch-based oxide nanotransistor. Nanotechnology. 21, 475201 (2010).
- Bogorin, D. F., et al. Nanoscale rectification at the LaAlO3/SrTiO3 interface. Applied Physics Letters. 97, 013102 (2010).
- Cheng, G., et al. Sketched Oxide Single-Electron Transistor. Nature Nanotech. 6, 343-347 (2011).
- Joshua, A., Ruhman, J., Pecker, S., Altman, E., Ilani, S. Gate-tunable polarized phase of two-dimensional electrons at the LaAlO3/SrTiO3 interface. PNAS. 110, 9633 (2013).
- Irvin, P., et al. Rewritable Nanoscale Oxide Photodetector. Nature Photon. 4, 849-852 (2010).
- Ma, Y., et al. Broadband Terahertz Generation and Detection at 10 nm Scale. Nano Letters. 13, 2884-2888 (2013).
