Name: experimental methods for trapping ions using microfabricated surface ion traps
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Description: Watch this Scientific Journal Video about Experimental Methods for Trapping Ions Using Microfabricated Surface Ion Traps at JoVE.com

This research was partially supported by the Ministry of Science, ICT, and Future Planning (MSIP), Korea, under the Information Technology Research Center (ITRC) support program (IITP-2017-2015-0-00385) and the ICT R&#38;D program (10043464, Development of quantum repeater technology for the application to communication systems), supervised by the Institute for Information &#38; Communications Technology Promotion (IITP).

<ol>
	<li>Wineland, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nobel+Lecture:+Superposition,+entanglement,+and+raising+Schr&#246;dinger's+cat.">Nobel Lecture: Superposition, entanglement, and raising Schr&#246;dinger's cat.</a> Rev Mod Phys. 85 (3), 1103 (2013).</li><li>Blatt, R., Wineland, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Entangled+states+of+trapped+atomic+ions.">Entangled states of trapped atomic ions.</a> Nature. 453 (7198), 1008-1015 (2008).</li><li>Leibfried, D., Blatt, R., Monroe, C., Wineland, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+dynamics+of+single+trapped+ions.">Quantum dynamics of single trapped ions.</a> Rev Mod Phys. 75 (1), 281 (2003).</li><li>Paul, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electromagnetic+traps+for+charged+and+neutral+particles.">Electromagnetic traps for charged and neutral particles.</a> Rev Mod Phys. 62 (3), 531 (1990).</li><li>Rosenband, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Frequency+ratio+of+Al++and+Hg++single-ion+optical+clocks;+metrology+at+the+17th+decimal+place.">Frequency ratio of Al+ and Hg+ single-ion optical clocks; metrology at the 17th decimal place.</a> Science. 319 (5871), 1808-1812 (2008).</li><li>Dawson, P. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Quadrupole mass spectrometry and its applications. , (2013).</li><li>Ladd, T. D., Jelezko, F., Laflamme, R., Nakamura, Y., Monroe, C., O'Brien, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+computers.">Quantum computers.</a> Nature. 464 (7285), 45-53 (2010).</li><li>Monz, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Realization+of+a+scalable+Shor+algorithm.">Realization of a scalable Shor algorithm.</a> Science. 351 (6277), 1068-1070 (2016).</li><li>Debnath, S., Linke, N. M., Figgatt, C., Landsman, K. A., Wright, K., Monroe, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Demonstration+of+a+small+programmable+quantum+computer+with+atomic+qubits.">Demonstration of a small programmable quantum computer with atomic qubits.</a> Nature. 536 (7614), 63-66 (2016).</li><li>Blatt, R., Roos, C. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+simulations+with+trapped+ions.">Quantum simulations with trapped ions.</a> Nature Phys. 8 (4), 277-284 (2012).</li><li>Kielpinski, D., Monroe, C., Wineland, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Architecture+for+a+large-scale+ion-trap+quantum+computer.">Architecture for a large-scale ion-trap quantum computer.</a> Nature. 417 (6890), 709-711 (2002).</li><li>Moehring, D. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design,+fabrication+and+experimental+demonstration+of+junction+surface+ion+traps.">Design, fabrication and experimental demonstration of junction surface ion traps.</a> New J Phys. 13 (7), 075018 (2011).</li><li>Wright, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reliable+transport+through+a+microfabricated+X-junction+surface-electrode+ion+trap.">Reliable transport through a microfabricated X-junction surface-electrode ion trap.</a> New J Phys. 15 (3), 033004 (2013).</li><li>Amini, J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toward+scalable+ion+traps+for+quantum+information+processing.">Toward scalable ion traps for quantum information processing.</a> New J Phys. 12 (3), 033031 (2010).</li><li>Sterling, R. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+and+operation+of+a+two-dimensional+ion-trap+lattice+on+a+high-voltage+microchip.">Fabrication and operation of a two-dimensional ion-trap lattice on a high-voltage microchip.</a> Nat Commun. 5, (2014).</li><li>Kumph, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Operation+of+a+planar-electrode+ion-trap+array+with+adjustable+RF+electrodes.">Operation of a planar-electrode ion-trap array with adjustable RF electrodes.</a> New J Phys. 18 (2), 023047 (2016).</li><li>Mielenz, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Arrays+of+individually+controlled+ions+suitable+for+two-dimensional+quantum+simulations.">Arrays of individually controlled ions suitable for two-dimensional quantum simulations.</a> Nat Commun. 7, (2016).</li><li>Stick, D., Hensinger, W. K., Olmschenk, S., Madsen, M. J., Schwab, K., Monroe, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ion+trap+in+a+semiconductor+chip.">Ion trap in a semiconductor chip.</a> Nat Phys. 2 (1), 36-39 (2006).</li><li>Harty, T. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-fidelity+preparation,+gates,+memory,+and+readout+of+a+trapped-ion+quantum+bit.">High-fidelity preparation, gates, memory, and readout of a trapped-ion quantum bit.</a> Phys Rev Lett. 113 (22), 220501 (2014).</li><li>Cho, D., Hong, S., Lee, M., Kim, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+of+silicon+microfabricated+ion+traps+for+quantum+information+processing.">A review of silicon microfabricated ion traps for quantum information processing.</a> Micro Nano Sys Lett. 3 (1), 1-12 (2015).</li><li>Weidt, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Trapped-ion+quantum+logic+with+global+radiation+fields.">Trapped-ion quantum logic with global radiation fields.</a> Phys Rev Lett. 117 (22), 220501 (2016).</li><li>Monroe, C., Kim, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scaling+the+ion+trap+quantum+processor.">Scaling the ion trap quantum processor.</a> Science. 339 (6124), 1164-1169 (2013).</li><li>Brown, K. R., Kim, J., Monroe, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Co-designing+a+scalable+quantum+computer+with+trapped+atomic+ions.">Co-designing a scalable quantum computer with trapped atomic ions.</a> npj Quantum Inf. 2, 16034 (2016).</li><li>Lekitsch, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blueprint+for+a+microwave+trapped-ion+quantum+computer.">Blueprint for a microwave trapped-ion quantum computer.</a> Science Adv. 3 (2), e1601540 (2017).</li><li>Reichel, J., Vuletic, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Atom chips. , (2011).</li><li>Ghosh, P. K., ed, ,. 1. s. t. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Ion Traps. , (1995).</li><li>Wesenberg, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrostatics+of+surface-electrode+ion+traps.">Electrostatics of surface-electrode ion traps.</a> Phys Rev A. 78 (6), 063410 (2008).</li><li>House, M. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analytic+model+for+electrostatic+fields+in+surface-electrode+ion+traps.">Analytic model for electrostatic fields in surface-electrode ion traps.</a> Phys Rev A. 78 (3), 033402 (2008).</li><li>Hong, S., Lee, M., Cheon, H., Kim, T., Cho, D. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Guidelines+for+Designing+Surface+Ion+Traps+Using+the+Boundary+Element+Method.">Guidelines for Designing Surface Ion Traps Using the Boundary Element Method.</a> Sensors. 16 (5), 616 (2016).</li><li>Allcock, D. T. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Implementation+of+a+symmetric+surface-electrode+ion+trap+with+field+compensation+using+a+modulated+Raman+effect.">Implementation of a symmetric surface-electrode ion trap with field compensation using a modulated Raman effect.</a> New J Phys. 12 (5), 053026 (2010).</li><li>Chiaverini, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface-electrode+architecture+for+ion-trap+quantum+information+processing.">Surface-electrode architecture for ion-trap quantum information processing.</a> Quantum Inf Comput. 5 (6), 419-439 (2005).</li><li>Allcock, D. T. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heating+rate+and+electrode+charging+measurements+in+a+scalable,+microfabricated,+surface-electrode+ion+trap.">Heating rate and electrode charging measurements in a scalable, microfabricated, surface-electrode ion trap.</a> Appl Phys B. 107 (4), 913-919 (2012).</li><li>. Demonstration of a microfabricated surface electrode ion trap Available from: <a target="_blank" href="https://arxiv.org/abs/1008.0990">https://arxiv.org/abs/1008.0990</a> (2010)</li><li>Allcock, D. T. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduction+of+heating+rate+in+a+microfabricated+ion+trap+by+pulsed-laser+cleaning.">Reduction of heating rate in a microfabricated ion trap by pulsed-laser cleaning.</a> New J Phys. 13 (12), 123023 (2011).</li><li>Mount, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+qubit+manipulation+in+a+microfabricated+surface+electrode+ion+trap.">Single qubit manipulation in a microfabricated surface electrode ion trap.</a> New J Phys. 15 (9), 093018 (2013).</li><li>Siverns, J. D., Simkins, L. R., Weidt, S., Hensinger, W. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+application+of+radio+frequency+voltages+to+ion+traps+via+helical+resonators.">On the application of radio frequency voltages to ion traps via helical resonators.</a> Appl Phys B. 107 (4), 921-934 (2012).</li><li>Kleinert, M., Dahl, M. E. G., Bergeson, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+the+Yb+I+1S0&#8722;1P1+transition+frequency+at+399+nm+using+an+optical+frequency+comb.">Measurement of the Yb I 1S0&#8722;1P1 transition frequency at 399 nm using an optical frequency comb.</a> Phys Rev A. 94 (5), 052511 (2016).</li><li>Olmschenk, S., Younge, K. C., Moehring, D. L., Matsukevich, D. N., Maunz, P., Monroe, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Manipulation+and+detection+of+a+trapped+Yb++hyperfine+qubit.">Manipulation and detection of a trapped Yb+ hyperfine qubit.</a> Phys Rev A. 76 (5), 052314 (2007).</li><li>Sansonetti, J. E., Martin, W. C., Young, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Handbook of Basic Atomic Spectroscopic Data. , (2013).</li><li>Kern, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Thin film processes II. , (2012).</li><li>Streed, E. W., Weinhold, T. J., Kielpinski, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Frequency+stabilization+of+an+ultraviolet+laser+to+ions+in+a+discharge.">Frequency stabilization of an ultraviolet laser to ions in a discharge.</a> Appl Phys Lett. 93 (7), 071103 (2008).</li></ol>

The authors have nothing to disclose.

This paper presented a method for trapping ions using microfabricated surface ion traps. The construction of an ion trapping system requires experiences in various research fields but has not previously been described in detail. This paper provided detailed procedures for microfabricating a trap chip as well as for constructing an experimental setup to trap ions for the first time. This paper also provided detailed procedures for trapping 174Yb+ ions and experimenting with trapped ions.
A significant obstacle faced in the microfabrication procedures is the deposition of the dielectric layer, with a thickness of over 10 &#181;m. During the deposition process of the thick dielectric layer, residual stress can build up, which can cause damage to the dielectric film or even break the wafer. To reduce the residual stress, which is generally compressive, a slow deposition rate should be used40. In our case, a compressive stress of 110.4 MPa was measured with the deposition conditions of 540 sccm of SiH4 gas flow rate, 140 W of RF power, and 1.9 Torr of pressure at 5-&#181;m film thickness. However, these process conditions provide only a rough reference, since these conditions can vary significantly for different equipment. In order to reduce the effects of accumulated stress, 3.5 &#181;m-thick SiO2 films were deposited alternatingly on both sides of the wafer in the presented method. The required thickness of the dielectric layer can be reduced if a smaller RF voltage amplitude and hence a shallower trap depth is chosen. However, a shallower trap depth easily leads to the escape of trapped ions, so the fabrication of thicker dielectric layers, which can withstand higher RF voltages, is more desirable.
There are some limitations to the fabrication method presented in this paper. The lengths of the overhangs are not sufficient to completely hide the dielectric sidewalls from the trapped ions, as shown in Figure 7f. Furthermore, the sidewalls of the oxide pillars are jagged, increasing the exposed area of the dielectric sidewalls compared to the vertical oxide pillar. For example, in the case of the sidewall of the inner DC rail near the loading slot with a 5 &#181;m uniform overhang, it is calculated that 33% of the dielectric surface is exposed to the trapped ion position of the vertical sidewall. In the jagged-edge case, more than 70% of the sidewall area is exposed. These non-ideal fabrication results can induce additional stray fields from the exposed dielectrics, but the effects have not been quantitatively measured. Nevertheless, the fabricated chip as reported above has been successfully used in ion trapping and qubit manipulation experiments. In addition, the trap chip presented in this paper has exposed silicon sidewalls near the loading slot. Native oxide can grow on the silicon surfaces and can result in additional stray fields. Therefore, it is recommended to protect the silicon substrate with an additional metal layer, as in33.
To trap 174Yb+ ions, the frequencies of the lasers should be stabilized within a few tens of MHz, and a few different methods are discussed in advanced setups38,41. However, for the simple setup discussed in this paper, initial trapping is possible only with stabilization using a wavelength meter.
This paper provided a protocol to trap 174Yb+ ions using a microfabricated surface ion-trap chip. Although the protocol for trapping 171Yb+ ions is not specifically discussed, the experimental setup described in this paper can be also used to trap 171Yb+ ions and to manipulate the qubit state of the 171Yb+ ions to obtain Rabi oscillation results (shown in Figure 10). This can be done by adding several optical modulators to the output of the lasers and by using a microwave setup, as described in the Supplementary Document.
In conclusion, the experimental methods and results presented in this paper can be used to develop various quantum information applications using surface ion traps.

A Paul trap can confine charged particles, including ions in empty space, using a combination of a static electric field and a varying electric field oscillating at radio frequency (RF), and the quantum states of the ions confined in the trap can be measured and controlled1,2,3. Such ion traps were originally developed for precise measurement applications, including optical clocks and mass spectroscopy4,5,6. In recent years, these ion traps have also been actively explored as a physical platform to implement the quantum information processing attributed to the desirable characteristics of trapped ions, such as long coherence times, ideal isolation in an ultra-high vacuum (UHV) environment, and the feasibility of individual qubit manipulation7,8,9,10. Since Kielpinski et al.11 proposed a scalable ion-trap architecture that can be used to develop quantum computers, various types of surface traps, including junction traps12,13, multi-zone trap chips14, and 2-d array traps15,16,17, have been developed using semiconductor process-derived microfabrication methods18,19,20,21. Large-scale quantum information processing systems based on the surface traps have also been discussed22,23,24.
This paper presents experimental methods for trapping ions using microfabricated surface ion traps. More specifically, a procedure for fabricating surface ion traps and a detailed procedure for trapping ions using the fabricated traps are described. In addition, detailed descriptions of various practical techniques for setting up the experimental system and trapping ions are provided in the Supplementary Document.
The methodology for microfabricating a surface ion trap is given in step 1. Figure 1 shows a simplified schematic of a surface ion trap. The electric fields generated by the voltage applied to the electrodes in the transverse plane are also shown25. An RF voltage is applied to the pair of RF electrodes, while all other electrodes are kept at RF ground; the ponderomotive potential26 generated by the RF voltage confines the ions to the radial direction. The direct current (DC) voltage applied to the multiple DC electrodes outside the RF electrodes confine the ions to the longitudinal direction. The inner rails between the RF electrodes are designed to help tilt the principal axes of the total potential in the transverse plane. The methodology for designing a DC voltage set is included in the Supplementary Document. In addition, more details for designing the essential geometric parameters of surface ion-trap chips can be found in27,28,29,30,31.
The fabrication method introduced in step 1 was designed considering the following aspects. First, the dielectric layer between the electrode layer and the ground layer should be sufficiently thick to prevent electrical breakdown between the layers. Generally, the thickness should be over 10&#181;m. During the deposition of the thick dielectric layer, the residual stress from the deposited films can cause bowing of the substrate or damages to the deposited films. Thus, controlling the residual stress is one of the key techniques in the fabrication of the surface ion traps. Second, the exposure of the dielectric surfaces to the ion position should be minimized because stray charges can be induced on the dielectric material by scattered ultraviolet (UV) lasers, which in turn results in a random shift of ion position. The exposed area can be reduced by designing overhang electrode structures. It has been reported that surface ion traps with electrode overhangs are resistant to charging under typical experimental conditions32. Third, all the materials, including various deposited films, should be able to withstand 200 &#176;C baking for approximately 2 weeks, and the amount of outgassing from all materials should be compatible with UHV environments. The design of the surface ion-trap chips microfabricated in this paper is based on the trap design from33, which was successfully used in various experiments32,33,34,35. Note that this design includes a slot in the middle of the chip for loading neutral atoms, which are later photo-ionized for trapping.
After the fabrication of the ion-trap chip, the chip is mounted and electrically connected to the chip carrier using gold bonding wires. The chip carrier is then installed in a UHV chamber. A detailed procedure for preparing a trap chip package and the design of the UHV chamber are provided in the Supplementary Document.
Preparation of the optical and electrical equipment, as well as the experimental procedures for trapping ions, are explained in detail in step 2. The ions trapped by the ponderomotive potential are generally subject to the fluctuation of the surrounding electric field, which continuously increases the average kinetic energy of the ions. Laser cooling based on Doppler shift can be used to remove the excess energy from the motion of the ions. Figure 2 shows the simplified energy-level diagrams of a 174Yb+ ion and a neutral 174Yb atom. Doppler cooling of 174Yb+ ions requires a 369.5-nm laser and a 935-nm laser, while photo-ionization of neutral 174Yb atoms requires a 399-nm laser. Steps 2.2 and 2.3 describe an efficient method to align these lasers to the surface ion-trap chip and a procedure to find the proper conditions for photo-ionization. After the optical and electrical components are prepared, trapping ions is relatively straightforward. The experimental sequence for trapping ions is presented in step 2.4.

<table><tbody><tr><td>photoresist used for 2-&amp;mu;m spin coating</td><td>AZ Materials</td><td>AZ7220</td><td>Discontinued. Easily replaced by other alternative photoresist product.</td></tr><tr><td>photoresist used for 6-&amp;mu;m spin coating</td><td>AZ Materials</td><td>AZ4620</td><td>Discontinued. Easily replaced by other alternative photoresist product.</td></tr><tr><td>ceramic chip carrier</td><td>NTK</td><td>IPKX0F1-8180BA</td><td></td></tr><tr><td>epoxy compound</td><td>Epotek</td><td>353ND</td><td></td></tr><tr><td>Plasma enhanced chemical vapor deposition (PECVD) system</td><td>Oxford Instruments</td><td>PlasmaPro System100</td><td></td></tr><tr><td>Low pressure chemical vapor deposition (LPCVD) system</td><td>Centrotherm</td><td>E-1200</td><td></td></tr><tr><td>Furnace</td><td>Seltron</td><td>SHF-150</td><td></td></tr><tr><td>Sputter</td><td>Muhan Vacuum</td><td>MHS-1500</td><td></td></tr><tr><td>Manual aligner</td><td>Karl-Suss</td><td>MA-6</td><td></td></tr><tr><td>Deep Si etcher</td><td>Plasma-Therm</td><td>SLR-770-10R-B</td><td></td></tr><tr><td>Inductive coupled plasma (ICP) etcher</td><td>Oxford Instruments</td><td>PlasmaPro System100 Cobra</td><td></td></tr><tr><td>Reactive ion etching (RIE) etcher</td><td>Applied Materials</td><td>P-5000</td><td></td></tr><tr><td>Boundary element method (BEM) software</td><td>CPO Ltd.</td><td>Charged Particle Optics</td><td></td></tr><tr><td>Single crystaline (100) silicon wafer</td><td>STC</td><td>4SWP02</td><td>100 mm / (100) / P-type / SSP / 525&amp;plusmn;25 &amp;mu;m</td></tr><tr><td>metal tubes</td><td>Mcmaster-carr</td><td>89935K69</td><td>316 Stainless Steel Tubing, 0.042&quot; OD, 0.004&quot; Wall Thickness</td></tr><tr><td>Yb piece</td><td>Goodfellow</td><td>YB005110</td><td>Ytterbium wire, purity 99.9%</td></tr><tr><td>enriched &lt;sup&gt;171&lt;/sup&gt;Yb</td><td>Oak Ridge National Laboratory</td><td>Yb-171</td><td>https://www.isotopes.gov/catalog/product.php?element=Ytterbium</td></tr><tr><td>tantalum foil</td><td>The Nilaco Corporation</td><td>TI-453401</td><td>0.25x130x100mm 99.5%</td></tr><tr><td>Kapton-insulated copper wire</td><td>Accu-glass</td><td>18AWG (silver plated copper wire kapton insulted)</td><td></td></tr><tr><td>residual gas analyzer (RGA)</td><td>SRS</td><td>RGA200</td><td></td></tr><tr><td>turbo pump</td><td>Agilent</td><td>Twistorr84 FS</td><td></td></tr><tr><td>all-metal valve</td><td>KJL</td><td>manual SS All-Metal Angle Valves (CF flanged)</td><td></td></tr><tr><td>Leak detector (used as a rough pump)</td><td>Varian</td><td>PD03</td><td></td></tr><tr><td>ion gauges</td><td>Agilent</td><td>UHV-24p</td><td></td></tr><tr><td>ion pump</td><td>Agilent</td><td>VacIon Plus 20</td><td></td></tr><tr><td>NEG pump</td><td>SAES Getters</td><td>CapaciTorr D400</td><td></td></tr><tr><td>spherical octagon</td><td>Kimball Physics</td><td>MCF600-SphOct-F2C8</td><td></td></tr><tr><td>ZIF socket</td><td>Tactic Electronics</td><td>P/N 100-4680-002A</td><td></td></tr><tr><td>multi-pin feedthroughs</td><td>Accu-Glass</td><td>6-100531</td><td></td></tr><tr><td>25 D-sub gender adapters</td><td>Accu-Glass</td><td>104101</td><td></td></tr><tr><td>Recessed viewport</td><td>Culham Centre for Fusion Energy</td><td>100CF 316LN+20.9 Re-Entrant 316 (Custom order)</td><td>Disc material: 60cv Fused Silica 4mm THK, TWE Lambda 1/10, 20/10 Scratch-Dig</td></tr><tr><td>Recessed viewport AR coating</td><td>LaserOptik</td><td>AR355nm/0-6&amp;deg; HT370-650nm/0-36&amp;deg; on UHV (Custom order)</td><td>AR coating was performed in the middle of the fabrication of the recessed viewport</td></tr><tr><td>Digital-analog converter</td><td>AdLink</td><td>PCIe-6216V-GL</td><td></td></tr><tr><td>369.5nm laser</td><td>Toptica</td><td>TA-SHG Pro</td><td></td></tr><tr><td>369.5nm laser</td><td>Moglabs</td><td>ECD004 + 370LD10 + DLC102/HC</td><td></td></tr><tr><td>399nm laser</td><td>Toptica</td><td>DL 100</td><td></td></tr><tr><td>935nm laser</td><td>Toptica</td><td>DL 100</td><td></td></tr><tr><td>369.5nm &amp;amp; 399nm optical fiber</td><td>Coherent</td><td>NUV-320-K1</td><td>Patch cables are connectorized by Costal Connections.</td></tr><tr><td>935nm optical fiber</td><td>GouldFiber Optics</td><td>PSK-000626</td><td>50/50 fiber beam splitter made of Corning HI-780 single mode fiber to combine 935nm and 638nm together.</td></tr><tr><td>Wavelength meter</td><td>High Finesse</td><td>WSU-2</td><td></td></tr><tr><td>temporary mirror</td><td>Thorlabs</td><td>PF10-03-P01</td><td></td></tr><tr><td>Dichroic mirror</td><td>Semrock</td><td>FF647-SDi01-25x36</td><td></td></tr><tr><td>369.5nm &amp;amp; 399nm collimator</td><td>Micro Laser Systems</td><td>FC5-UV-T/A</td><td></td></tr><tr><td>935nm collimator</td><td>Sch&amp;auml;fter + Kirchhoff</td><td>60FC-0-M8-10</td><td></td></tr><tr><td>369.5nm focusing lens</td><td>CVI</td><td>PLCX-25.4-77.3-UV-355-399</td><td>Focal length: ~163mm @ 369.5nm</td></tr><tr><td>399nm &amp;amp; 935nm focusing lens</td><td>CVI</td><td>PLCX-25.4-64.4-UV-355-399</td><td>Focal length: ~137mm @ 399nm, ~143mm @ 935nm</td></tr><tr><td>imaging lens</td><td>Photon Gear</td><td>P/N 15470</td><td></td></tr><tr><td>369.5nm bandpass filter</td><td>Semrock</td><td>FF01-370/6-25</td><td></td></tr><tr><td>399nm bandpass filter</td><td>Semrock</td><td>FF01-395/11-25</td><td></td></tr><tr><td>IR filter</td><td>Semrock</td><td>FF01-650/SP-25</td><td></td></tr><tr><td>EMCCD camera</td><td>Andor Technology</td><td>DU-897U-CS0-EXF</td><td></td></tr><tr><td>PMT</td><td>Hamamatsu</td><td>H10682-210</td><td></td></tr></tbody></table>

experimental methods for trapping ions using microfabricated surface ion traps

Ions trapped in a quadrupole Paul trap have been considered one of the strong physical candidates to implement quantum information processing. This is due to their long coherence time and their capability to manipulate and detect individual quantum bits (qubits). In more recent years, microfabricated surface ion traps have received more attention for large-scale integrated qubit platforms. This paper presents a microfabrication methodology for ion traps using micro-electro-mechanical system (MEMS) technology, including the fabrication method for a 14 &#181;m-thick dielectric layer and metal overhang structures atop the dielectric layer. In addition, an experimental procedure for trapping ytterbium (Yb) ions of isotope 174 (174Yb+) using 369.5 nm, 399 nm, and 935 nm diode lasers is described. These methodologies and procedures involve many scientific and engineering disciplines, and this paper first presents the detailed experimental procedures. The methods discussed in this paper can easily be extended to the trapping of Yb ions of isotope 171 (171Yb+) and to the manipulation of qubits.

Figure 7 shows the scanning electron micrographs (SEM)&#160;of the fabricated ion-trap chip. The RF electrodes, inner DC electrodes, outer DC electrodes, and loading slot were successfully fabricated. The sidewall profile of the dielectric pillar became jagged because the PECVD oxide was deposited in several steps. The multiple deposition steps were used to minimize the effects of residual stress from thick oxide films. This is further described in the Discussion.

Figure 8 shows the EMCCD image of five 174Yb+ ions trapped using the microfabricated ion-trap chip. The trapped ions can last for more than 24 h with continuous Doppler cooling. The number of trapped ions can be adjusted between 1 and 20 by changing the applied DC voltage set. This experimental setup is very reliable and robust and has currently been in operation for 50 months.
Figure 9 shows the shuttling of trapped ions along the axial direction. The ion position in Figure 9b is displaced from that in Figure 9a through the adjustment of the position of the DC potential minimum by changing the DC voltages.
Figure 10 shows preliminary results of Rabi oscillation experiments with a 171Yb+ ion. To obtain the results, the additional setups described in the Supplementary Document were used. The results were included to show a potential application of the experimental setup explained in this paper.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56060/56060fig1.jpg" /> 
Figure 1: Schematic of the surface ion trap. (a) The red dots represent the trapped ions. The brown and yellow electrodes indicate the RF and DC electrodes, respectively. The gray arrows show the direction of the electric field during the positive phase of the RF voltage. Note that the schematic is not drawn to scale. (b) The vertical dimensions of the electrode structure. (c) The lateral dimensions of the electrode structure. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56060/56060fig2.jpg" /> 
Figure 2: Simplified energy-level diagrams of a 174Yb+ ion and a neutral 174Yb atom. (a) When a 369.5 nm laser is detuned to the red side (lower frequency) of the resonance, a cycling transition between 2P1/2 and 2S1/2 reduces the kinetic energy of the ion because of the Doppler effect. Occasionally, a small but finite branching ratio makes the electron decay from 2P1/2 to 2D3/2, and a 935-nm laser is required to return the electron back to the main cycling transition. The electron can also decay into a 2F7/2 state once per hour, on average, and a 638 nm laser can pump it out of the 2F7/2 state, but this is not necessary for a simple system38. The values in the ket notation represent the projections of the total angular momenta J along the quantization axis mJ. (b) To ionize neutral atoms evaporated from the oven, a two-photon absorption process was used39. A 399 nm laser excited an electron to 1P1 state, and the 369.5 nm photon for Doppler cooling had more energy than necessary to remove the excited electron from the ion. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56060/56060fig3.jpg" /> 
Figure 3: Fabrication process flow of a surface ion trap. (a) Thermal oxidation to grow a 5,000 &#197;-thick SiO2 layer and LPCVD of a 2,000 &#197;-thick Si3N4 layer. (b) Deposition and ICP etching of a 1.5 &#181;m-thick sputtered Al layer. (c) Deposition of a 14 &#181;m-thick SiO2 layer on the both sides of the wafer using PECVD processes. (d) Patterning of the 14 &#181;m-thick SiO2 layer deposited on the front of the wafer using an RIE process (e) Patterning of the 14 &#181;m-thick SiO2 layer deposited on the back of the wafer using an RIE process. (f) Deposition of a 1.5 &#181;m-thick sputtered Al layer and a 1 &#181;m-thick PECVD SiO2 layer. (g) Patterning of the 1.5 &#181;m-thick Al layer using an ICP process and the 1 &#181;m-thick SiO2 layer using an RIE process. (h) Patterning of the 14 &#181;m-thick SiO2 layer deposited on the front of the wafer using an RIE process. (i) Patterning of the 5,000 &#197;-thick SiO2 layer and the 2,000 &#197;-thick Si3N4 layer using an RIE process. (j) DRIE of the silicon substrate 450 &#181;m from the back of the wafer. (k) Wet-etching of the SiO2 layer on the Al electrodes and the sidewalls of the dielectric pillars. (l) Penetration of the silicon substrate from the front through a DRIE process. Note that the schematics are not drawn to scale. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56060/56060fig4.jpg" /> 
Figure 4: An example of the DC voltage set used to trap ions. The voltages applied to the inner rails can compensate for the asymmetric electric field in the horizontal direction to tilt the principal axes of the total potential in the transverse plane. The axial trap frequency generated by the voltage set was 550 kHz. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56060/56060fig5v2.jpg" /> 
Figure 5: Schematic of the optical setup. Three diode lasers are aligned to overlap at the trapping position. The recessed viewport of the UHV chamber allows the imaging lens to be placed as close as possible to the chip surface. A flip-mirror placed between the imaging lens and the EMCCD allows for the selective monitoring of the ion fluorescence using either a photon multiplied tube (PMT) or an EMCCD. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig5v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56060/56060fig6.jpg" /> 
Figure 6: Images of the constructed optical setup. (a) A coil is wound around the front viewport of the chamber to generate a magnetic field, which can break degenerate energy levels of ytterbium ions. (b) The optical setup for steering the 399 nm and 935 nm beams. The red and green lines indicate the beam path of the 935 nm and 399 nm lasers, respectively. (c) The configuration of the imaging system, including the flip-mirror, the imaging lens, the EMCCD, and the PMT. The path of the fluorescence emitted from the trapped ions can be determined by the flip-mirror. The green and white arrows indicate the path of the fluorescence when being monitored by the EMCCD and the PMT, respectively. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/56060/56060fig7.jpg" /> 
Figure 7: Fabrication results of the surface ion trap. (a) Overview of the chip layout. (b) A magnified view of the chip layout, which shows the multiple outer DC electrodes. (c) A magnified view of chip layout, which shows the loading slot. (d) A cross-sectional view of the trapping region before penetrating the loading slot. (e) A cross-sectional view of the trapping region after penetrating the loading slot. (f) A magnified cross-sectional view of the oxide pillar. The oxide pillars have jagged walls, and the lengths of the overhang are not sufficient, which is attributed to the non-uniform etch rate of the SiO2 at the interfaces between the separately deposited 3.5 &#181;m-thick SiO2 layers. (g) A top view of a wire-bonding pad of a DC electrode. (h) A cross-sectional view of a via. Inclined profiles of the oxide pillars allow for the connection of the DC electrode and the ground layer during the deposition of the Al layer on the sidewall of the oxide pillar instead of filling the via holes with an electroplating process. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/56060/56060fig8.jpg" /> 
Figure 8: An EMCCD image of five 174Yb+ ions trapped on the microfabricated ion-trap chip. The image of the surface trap electrode structure was taken separately, and the images of the trapped ion and of the electrodes were combined for clarity. The intensity legend applies only to the pixels in the box. The thick arrow shows the beam path of the 369.5 nm laser and the thin arrows represent the x- and z-components of the momentum of the photon. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/56060/56060fig9.jpg" /> 
Figure 9: Adjustment of the axial potential of the trapped ions in a linear chain. (a) Seven ions at the center of the trap. (b) The ions were shuttled tens of micrometers. (c) The ion string squeezed in the axial direction. This figure is best viewed as a movie, which is separately uploaded. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/56060/56060fig10.jpg" /> 
Figure 10: Experimental results of Rabi oscillations between the |0<img alt="Image 1" src="/files/ftp_upload/56060/56060img1.jpg" /> and |1<img alt="Image 1" src="/files/ftp_upload/56060/56060img1.jpg" /> states. |0<img alt="Image 1" src="/files/ftp_upload/56060/56060img1.jpg" /> is defined as the 2S1/2|F=0, mF=0<img alt="Image 1" src="/files/ftp_upload/56060/56060img1.jpg" /> state of the 171Yb+ ion, and |1<img alt="Image 1" src="/files/ftp_upload/56060/56060img1.jpg" /> is defined as the 2S1/2|F=1, mF=0<img alt="Image 1" src="/files/ftp_upload/56060/56060img1.jpg" /> state. The Rabi oscillation is induced by a 12.6428-GHz microwave. Bloch spheres above the plot show the corresponding quantum states at different times. <a href="https://cloudflare.jove.com/files/ftp_upload/56060/56060fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplementary Document: <a href="https://cloudflare.jove.com/files/ftp_upload/56060/jove-56060_Supplementary_Document.pdf" target="_blank">Please click here to download this document.</a>

Watch this Scientific Journal Video about Experimental Methods for Trapping Ions Using Microfabricated Surface Ion Traps at JoVE.com

Experimental Methods for Trapping Ions Using Microfabricated Surface Ion Traps

This paper presents a microfabrication methodology for surface ion traps, as well as a detailed experimental procedure for trapping ytterbium ions in a room-temperature environment.

Ions trapped in a quadrupole Paul trap have been considered one of the strong physical candidates to implement quantum information processing. This is due ...

experimental-methods-for-trapping-ions-using-microfabricated-surface

Research

JoVE Journal

Engineering

13.6K Views.  Seoul National University. This paper presents a microfabrication methodology for surface ion traps, as well as a detailed experimental procedure for trapping ytterbium ions in a room-temperature environment.

Video: Experimental Methods for Trapping Ions Using Microfabricated Surface Ion Traps

A Microfluidic-based Hydrodynamic Trap for Single Particles

The ability to confine and manipulate single particles in free solution is a key enabling technology for fundamental and applied science. Methods for particle trapping based on optical, magnetic, electrokinetic, and acoustic techniques have led to major advancements in physics and biology ranging from the molecular to cellular level. In this article, we introduce a new microfluidic-based technique for particle trapping and manipulation based solely on hydrodynamic fluid flow. Using this method, we demonstrate trapping of micro- and nano-scale particles in aqueous solutions for long time scales. The hydrodynamic trap consists of an integrated microfluidic device with a cross-slot channel geometry where two opposing laminar streams converge, thereby generating a planar extensional flow with a fluid stagnation point (zero-velocity point). In this device, particles are confined at the trap center by active control of the flow field to maintain particle position at the fluid stagnation point. In this manner, particles are effectively trapped in free solution using a feedback control algorithm implemented with a custom-built LabVIEW code. The control algorithm consists of image acquisition for a particle in the microfluidic device, followed by particle tracking, determination of particle centroid position, and active adjustment of fluid flow by regulating the pressure applied to an on-chip pneumatic valve using a pressure regulator. In this way, the on-chip dynamic metering valve functions to regulate the relative flow rates in the outlet channels, thereby enabling fine-scale control of stagnation point position and particle trapping. The microfluidic-based hydrodynamic trap exhibits several advantages as a method for particle trapping. Hydrodynamic trapping is possible for any arbitrary particle without specific requirements on the physical or chemical properties of the trapped object. In addition, hydrodynamic trapping enables confinement of a "single" target object in concentrated or crowded particle suspensions, which is difficult using alternative force field-based trapping methods. The hydrodynamic trap is user-friendly, straightforward to implement and may be added to existing microfluidic devices to facilitate trapping and long-time analysis of particles. Overall, the hydrodynamic trap is a new platform for confinement, micromanipulation, and observation of particles without surface immobilization and eliminates the need for potentially perturbative optical, magnetic, and electric fields in the free-solution trapping of small particles.

In this article, we present a microfluidic-based method for particle confinement based on hydrodynamic flow. We demonstrate stable particle trapping at a fluid stagnation point using a feedback control mechanism, thereby enabling confinement and micromanipulation of arbitrary particles in an integrated microdevice.

The ability to confine and manipulate single particles in free solution is a key enabling technology for fundamental and applied science.  Methods for ...

Bioengineering

Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

In Situ SIMS and IR Spectroscopy of Well-defined Surfaces Prepared by Soft Landing of Mass-selected Ions

Soft landing of mass-selected ions onto surfaces is a powerful approach for the highly-controlled preparation of materials that are inaccessible using conventional synthesis techniques. Coupling soft landing with in situ characterization using secondary ion mass spectrometry (SIMS) and infrared reflection absorption spectroscopy (IRRAS) enables analysis of well-defined surfaces under clean vacuum conditions. The capabilities of three soft-landing instruments constructed in our laboratory are illustrated for the representative system of surface-bound organometallics prepared by soft landing of mass-selected ruthenium tris(bipyridine) dications, [Ru(bpy)3]2+ (bpy = bipyridine), onto carboxylic acid terminated self-assembled monolayer surfaces on gold (COOH-SAMs). In situ time-of-flight (TOF)-SIMS provides insight into the reactivity of the soft-landed ions. In addition, the kinetics of charge reduction, neutralization and desorption occurring on the COOH-SAM both during and after ion soft landing are studied using in situ Fourier transform ion cyclotron resonance (FT-ICR)-SIMS measurements. In situ IRRAS experiments provide insight into how the structure of organic ligands surrounding metal centers is perturbed through immobilization of organometallic ions on COOH-SAM surfaces by soft landing. Collectively, the three instruments provide complementary information about the chemical composition, reactivity and structure of well-defined species supported on surfaces.

In Situ SIMS and IR Spectroscopy of Well-defined Surfaces Prepared by Soft Landing of Mass-selected Ions

Soft landing of mass-selected ions onto surfaces is a powerful approach for the highly-controlled preparation of novel materials. Coupled with analysis by in situ secondary ion mass spectrometry (SIMS) and infrared reflection absorption spectroscopy (IRRAS), soft landing provides unprecedented insights into the interactions of well-defined species with surfaces.

Soft landing of mass-selected ions onto surfaces is a powerful approach for the highly-controlled preparation of materials that are inaccessible using ...

Chemistry

On-chip Isotachophoresis for Separation of Ions and Purification of Nucleic Acids

Electrokinetic techniques are a staple of microscale applications because of their unique ability to perform a variety of fluidic and electrophoretic processes in simple, compact systems with no moving parts. Isotachophoresis (ITP) is a simple and very robust electrokinetic technique that can achieve million-fold preconcentration1,2 and efficient separation and extraction based on ionic mobility.3 For example, we have demonstrated the application of ITP to separation and sensitive detection of unlabeled ionic molecules (e.g. toxins, DNA, rRNA, miRNA) with little or no sample preparation4-8 and to extraction and purification of nucleic acids from complex matrices including cell culture, urine, and blood.9-12
ITP achieves focusing and separation using an applied electric field and two buffers within a fluidic channel system. For anionic analytes, the leading electrolyte (LE) buffer is chosen such that its anions have higher effective electrophoretic mobility than the anions of the trailing electrolyte (TE) buffer (Effective mobility describes the observable drift velocity of an ion and takes into account the ionization state of the ion, as described in detail by Persat et al.13). After establishing an interface between the TE and LE, an electric field is applied such that LE ions move away from the region occupied by TE ions. Sample ions of intermediate effective mobility race ahead of TE ions but cannot overtake LE ions, and so they focus at the LE-TE interface (hereafter called the "ITP interface"). Further, the TE and LE form regions of respectively low and high conductivity, which establish a steep electric field gradient at the ITP interface. This field gradient preconcentrates sample species as they focus. Proper choice of TE and LE results in focusing and purification of target species from other non-focused species and, eventually, separation and segregation of sample species.
We here review the physical principles underlying ITP and discuss two standard modes of operation: "peak" and "plateau" modes. In peak mode, relatively dilute sample ions focus together within overlapping narrow peaks at the ITP interface. In plateau mode, more abundant sample ions reach a steady-state concentration and segregate into adjoining plateau-like zones ordered by their effective mobility. Peak and plateau modes arise out of the same underlying physics, but represent distinct regimes differentiated by the initial analyte concentration and/or the amount of time allotted for sample accumulation.
We first describe in detail a model peak mode experiment and then demonstrate a peak mode assay for the extraction of nucleic acids from E. coli cell culture. We conclude by presenting a plateau mode assay, where we use a non-focusing tracer (NFT) species to visualize the separation and perform quantitation of amino acids.

Isotachophoresis (ITP) is a robust electrokinetic separation and preconcentration technique with applications ranging from toxin detection to sample preparation. We review the physical principles of ITP and the methodology of applying this technique to two specific example applications: separation and detection of small molecules and purification of nucleic acids from cell culture lysate.

Electrokinetic techniques are a staple of microscale applications because of their unique ability to perform a variety of fluidic and electrophoretic ...

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor performance, which suggest a new direction for the development of next-generation ultrathin and flexible photonic and electronic devices. Enhanced luminescence quantum efficiency has been widely observed in these atomically thin 2D crystals. However, dimension effects beyond quantum confinement thicknesses or even at the micrometer scale are not expected and have rarely been observed. In this study, molybdenum diselenide (MoSe2) layer crystals with a thickness range of 6-2,700 nm were fabricated as two- or four-terminal devices. Ohmic contact formation was successfully achieved by the focused-ion beam (FIB) deposition method using platinum (Pt) as a contact metal. Layer crystals with various thicknesses were prepared through simple mechanical exfoliation by using dicing tape. Current-voltage curve measurements were performed to determine the conductivity value of the layer nanocrystals. In addition, high-resolution transmission electron microscopy, selected-area electron diffractometry, and energy-dispersive X-ray spectroscopy were used to characterize the interface of the metal&#8211;semiconductor contact of the FIB-fabricated MoSe2 devices. After applying the approaches, the substantial thickness-dependent electrical conductivity in a wide thickness range for the MoSe2-layer semiconductor was observed. The conductivity increased by over two orders of magnitude from 4.6 to 1,500 &#937;&#8722;1 cm&#8722;1, with a decrease in the thickness from 2,700 to 6 nm. In addition, the temperature-dependent conductivity indicated that the thin MoSe2 multilayers exhibited considerably weak semiconducting behavior with activation energies of 3.5-8.5 meV, which are considerably smaller than those (36-38 meV) of the bulk. Probable surface-dominant transport properties and the presence of a high surface electron concentration in MoSe2 are proposed. Similar results can be obtained for other layer semiconductor materials such as MoS2 and WS2.

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

Microfluidic Pneumatic Cages: A Novel Approach for In-chip Crystal Trapping, Manipulation and Controlled Chemical Treatment

The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. Herein, we introduce a microfluidic-based technology, employing a double-layer microfluidic device, which can trap and localize in situ and ex situ synthesized structures on microfluidic channel surfaces. Crucially, we show how such a device can be used to conduct controlled chemical reactions onto on-chip trapped structures and we demonstrate how the synthetic pathway of a crystalline molecular material and its positioning inside a microfluidic channel can be precisely modified with this technology. This approach provides new opportunities for the controlled assembly of structures on surface and for their subsequent treatment.

Herein, we describe the fabrication and operation of a double-layer microfluidic system made of polydimethylsiloxane (PDMS). We demonstrate the potential of this device for trapping, directing the coordination pathway of a crystalline molecular material and controlling chemical reactions onto on-chip trapped structures.

The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. ...

Optical Trap Loading of Dielectric Microparticles In Air

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. 
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly ...

Plasmonic Trapping and Release of Nanoparticles in a Monitoring Environment

Plasmonic tweezers use surface plasmon polaritons to confine polarizable nanoscale objects. Among the various designs of plasmonic tweezers, only a few can observe immobilized particles. Moreover, a limited number of studies have experimentally measured the exertable forces on the particles. The designs can be classified as the protruding nanodisk type or the suppressed nanohole type. For the latter, microscopic observation is extremely challenging. In this paper, a new plasmonic tweezer system is introduced to monitor particles, both in directions parallel and orthogonal to the symmetric axis of a plasmonic nanohole structure. This feature enables us to observe the movement of each particle near the rim of the nanohole. Furthermore, we can quantitatively estimate the maximal trapping forces using a new fluidic channel.

A microchip fabrication process that incorporates plasmonic tweezers is presented here. The microchip enables the imaging of a trapped particle to measure maximal trapping forces.

Plasmonic tweezers use surface plasmon polaritons to confine polarizable nanoscale objects. Among the various designs of plasmonic tweezers, only a few ...

Double-barreled and Concentric Microelectrodes for Measurement of Extracellular Ion Signals in Brain Tissue

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular concentration of all major ions. As these ion shifts bear significant functional consequences, their quantitative determination is often required to understand the function and dysfunction of neural networks under physiological and pathophysiological conditions. In the present study, we demonstrate the fabrication and calibration of double-barreled ion-selective microelectrodes, which have proven to be excellent tools for such measurements in brain tissue. Moreover, so-called &#8220;concentric&#8221; ion-selective microelectrodes are also described, which, based on their different design, offer a far better temporal resolution of fast ion changes. We then show how these electrodes can be employed in acute brain slice preparations of the mouse hippocampus. Using double-barreled, potassium-selective microelectrodes, changes in the extracellular potassium concentration ([K+]o) in response to exogenous application of glutamate receptor agonists or during epileptiform activity are demonstrated. Furthermore, we illustrate the response characteristics of sodium-sensitive, double-barreled and concentric electrodes and compare their detection of changes in the extracellular sodium concentration ([Na+]o) evoked by bath or pressure application of drugs. These measurements show that while response amplitudes are similar, the concentric sodium microelectrodes display a superior signal-to-noise ratio and response time as compared to the double-barreled design. Generally, the demonstrated procedures will be easily transferable to measurement of other ions species, including pH or calcium, and will also be applicable to other preparations.

We demonstrate the fabrication, calibration and properties of two types of ion-selective microelectrodes (double-barreled and concentric) for measurement of ion concentrations in brain tissue. These are then used in the mouse hippocampal slice preparation to show that excitatory activity changes both extracellular potassium and sodium concentrations.

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular ...

Neuroscience

Real-time Iontophoresis with Tetramethylammonium to Quantify Volume Fraction and Tortuosity of Brain Extracellular Space

This review describes the basic concepts and protocol to perform the real-time iontophoresis (RTI) method, the gold-standard to explore and quantify the extracellular space (ECS) of the living brain. The ECS surrounds all brain cells and contains both interstitial fluid and extracellular matrix. The transport of many substances required for brain activity, including neurotransmitters, hormones, and nutrients, occurs by diffusion through the ECS. Changes in the volume and geometry of this space occur during normal brain processes, like sleep, and pathological conditions, like ischemia. However, the structure and regulation of brain ECS, particularly in diseased states, remains largely unexplored. The RTI method measures two physical parameters of living brain: volume fraction and tortuosity. Volume fraction is the proportion of tissue volume occupied by ECS. Tortuosity is a measure of the relative hindrance a substance encounters when diffusing through a brain region as compared to a medium with no obstructions. In RTI, an inert molecule is pulsed from a source microelectrode into the brain ECS. As molecules diffuse away from this source, the changing concentration of the ion is measured over time using an ion-selective microelectrode positioned roughly 100 &#181;m away. From the resulting diffusion curve, both volume fraction and tortuosity can be calculated. This technique has been used in brain slices from multiple species (including humans) and in vivo to study acute and chronic changes to ECS. Unlike other methods, RTI can be used to examine both reversible and irreversible changes to the brain ECS in real time.

This protocol describes real-time iontophoresis, a method that measures physical parameters of the extracellular space (ECS) of living brains. The diffusion of an inert molecule released into the ECS is used to calculate the ECS volume fraction and tortuosity. It is ideal for studying acute reversible changes to brain ECS.

This review describes the basic concepts and protocol to perform the real-time iontophoresis (RTI) method, the gold-standard to explore and quantify the ...

Experimental Methods for Trapping Ions Using Microfabricated Surface Ion Traps

Summary

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Chapters in this video

A Microfluidic-based Hydrodynamic Trap for Single Particles

Optical Trapping of Nanoparticles

In Situ SIMS and IR Spectroscopy of Well-defined Surfaces Prepared by Soft Landing of Mass-selected Ions

On-chip Isotachophoresis for Separation of Ions and Purification of Nucleic Acids

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Microfluidic Pneumatic Cages: A Novel Approach for In-chip Crystal Trapping, Manipulation and Controlled Chemical Treatment

Optical Trap Loading of Dielectric Microparticles In Air

Plasmonic Trapping and Release of Nanoparticles in a Monitoring Environment

Double-barreled and Concentric Microelectrodes for Measurement of Extracellular Ion Signals in Brain Tissue

Real-time Iontophoresis with Tetramethylammonium to Quantify Volume Fraction and Tortuosity of Brain Extracellular Space