Yazma ve Oksit Nanoyapıların Düşük Sıcaklık Karakterizasyonu
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
Oksit heteroyapılar 1-5 sergi hem bilimsel ilginç ve uygulamaları 4 için potansiyel olarak yararlı olan acil fiziksel fenomenlerin oldukça geniş bir çeşitlilik. Özellikle, LaAlO 3 (LAO) ve SrTiO 3 (STO) 6 arasındaki arayüz, 8 ferroelektrik gibi ve ferromanyetik 9 davranış 7 süperiletken, iletken, yalıtkan sergileyebilir. 2006 yılında, Thiel ve diğerleri LAO tabakasının kalınlığı gibi keskin bir yalıtkan-metal geçiş olduğunu göstermiştir 4 10 birim hücreler (4uc) önemli bir kalınlık ile artar. Bu, daha sonra 3uc-LAO/STO yapılar iletken bir atomik kuvvet mikroskopu (c-AFM) probu 11 ile yerel olarak kontrol edilebilir bir histeretik geçiş sergiledikleri gösterilmiştir.
Bu tür LaAlO 3/3 SrTiO gibi oksit arabirimleri özellikleri yapma varlığı veya yokluğu bağlıdırarayüzde elektronlar. Bu elektronlar geri üst geçit elektrotları 12,13, kapıları 10 kullanılarak kontrol edilebilir, yüzey 14 adzorbatlar, ferroelektrik katmanlar 15,16 ve c-AFM litografi 11. C-AFM litografi benzersiz bir özelliği, çok küçük nano özellikleri oluşturulabilir olmasıdır.
Iki boyutlu hapsi ile birlikte elektrik üst geçit, çoğu zaman III-V yarı iletkenler 17 kuantum noktaları oluşturmak için kullanılır. Alternatif olarak, yarı-tek boyutlu yarı iletken nanotellerdir elektriksel yakınlığı ile Geçitli edilebilir. Bu yapıların üretilmesi için yöntemler zaman alıcıdır ve genel olarak geri dönüşümsüzdür. Buna karşılık, c-AFM litografi tekniği nanoyapılarını bir deney için yaratıldı ve sonra (bir beyaz tahtaya benzer) "silinebilir" olabilir anlamda geri dönüşümlüdür. Silme sırasında Genel c-AFM yazma, AFM ucuna uygulanan pozitif gerilimleri ile yapılırnegatif voltajları kullanılarak gerçekleştirilir. , Belirli bir yapı oluşturmak için gerekli süre, cihazın karmaşıklığına bağlıdır, ancak genellikle en az 30 dk; O zaman çoğu tuval silme harcanmaktadır. Tipik uzaysal çözünürlüğü yaklaşık 10 nanometre olduğunu, ancak 2 nanometre 18 olarak oluşturulabilir ile uygun ayarlama gibi küçük özellikler.
Nano ölçekli üretim prosedürün ayrıntılı bir açıklaması yer almaktadır. Burada sağlanan ayrıntılı benzer deneyler ilgi araştırmacılar tarafından gerçekleştirilen izin vermek için yeterli olmalıdır. Burada anlatılan yöntemi, yarıiletkenlerin elektronik nanoyapıları oluşturmak için kullanılan geleneksel taşbaskı yaklaşımlar üzerinde birçok avantajı vardır.
Burada anlatılan c-AFM litografi yöntemi tarama anodik oksidasyon 19, dip-kalem nanolitografi 20, piezoelektrik desenleme dahil tarama-prob-tabanlı litografi çabaları, çok daha geniş bir sınıfın bir parçası21, vb. Yeni arabirimleri oksit kullanımı ile birlikte, burada açıklanan c-AFM teknik, fiziksel özelliklerin benzersiz bir çeşitliliği ile en yüksek hassasiyete sahip, elektronik yapıların bazı üretebilir.
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).
