Name: automated delivery of microfabricated targets for intense laser irradiation experiments
Uploaded: 2021-01-28T13:00:00.000+00:00
Duration: 6 min 40 s
Description: Watch this Scientific Journal Video about Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments at JoVE.com

This work has been supported by the Israel Science Foundation, grant No. 1135/15 and by the Zuckerman STEM Leadership Program, Israel, which are gratefully acknowledged. We also acknowledge the support of the Pazy Foundation, Israel grant #27707241, and NSF-BSF grant No. 01025495.&#160;The authors would like to kindly acknowledge Tel Aviv University Center for Nanoscience and Nanotechnolog

1. Target fabrication
NOTE: Figure 2 and Figure 3 illustrate the fabrication process of freestanding gold foils.
<ol>
	<li>Back Side
	<ol>
		<li>Use a 250 &#956;m thick, 100 mm diameter, high-stress silicon wafer in a &#60;100&#62; crystal formation, coated on both sides with silicon nitride.</li>
		<li>Clean the wafer using acetone&#160;followed by isopropanol and dry with nitrogen.&#160; Then spin coat a layer of HMDS&#160;to form an adhesive layer following the steps outlined in Table 1.</li>
		<li>Spin-coat the wafer with an AZ1518&#160;photoresist layer following the steps outlined in&#160;Table 2.</li>
		<li>Bake the wafer at 100 &#176;C for 1 min, then let it cool.</li>
		<li>Photolithograph 1,000 &#956;m x 1,000 &#956;m square openings under vacuum, exposing the wafer in 1 cycle of 4 to 7 seconds&#160;to a 400 nm UV lamp. The wafer is exposed to an overall fluence of 40&#160;J/cm2. Use an AZ726K developer to expose the silicon nitride, and a bath of dehydrated water to stop the process.</li>
		<li>Use Reactive Ion Etcher (RIE) to remove the silicon nitride in the location of the squares.</li>
		<li>Use an N-methyl-2-pyrrolidone (NMP) bath for 20 min to remove the residual resist and photoresist, producing a replica of the mask on the silicon nitride layer. Wash the wafer under fresh water and dry with nitrogen.</li>
		<li>Sink the wafer in a 30%, 90 &#176;C, potassium hydroxide solution to etch the silicon through the square openings. Sink the wafer for 40 min for every 50 &#956;m of silicon that needs to be etched. Because the etch rate in the &#60;100&#62; plane is much higher than in others, the potassium hydroxide reaches the bottom silicon nitride layer through the silicon bulk before etching any significant depth in the silicon nitride mask.</li>
	</ol>
	</li>
	<li>Front Side
	<ol>
		<li>For the front side, repeat steps 1.1.1&#8211;1.1.6 with a mask shaped as three concentric rings.</li>
		<li>Use RIE to remove the silicon nitride where the rings are located, followed by an NMP bath to remove resist and photoresist leftovers.</li>
		<li>Finally, to roughen the silicon rings, sink the wafer in nitric acid and in a solution of 0.02 M silver nitrate and 4 M hydrogen fluoride.</li>
		<li>On the etched side of the wafer, use a physical vapor deposition machine (PVD)18&#160;to sputter a layer of a few hundred nanometers of gold on top of a ~10 nm thin film of adhesive titanium, nickel, or chrome. The sputtered gold layer will become the freestanding membrane target.</li>
	</ol>
	</li>
</ol>
2. Alignment
NOTE: Figure 4 shows the target irradiation setup.
<ol>
	<li>Bring a first arbitrarily chosen target into view under a 100x magnification microscope.</li>
	<li>Point a triangulation ranging sensor (e.g., MTI/MicroTrak 3 LTS 120-20)19 to the roughened ring closest to the target, and record its displacement reading. 
	NOTE: The ranging sensor model used is not intended for high-vacuum applications. Different models, like the MTI-2100 from the same vendor, are compatible with low-outgassing applications.</li>
	<li>While leaving the microscope in place, move the wafer away a known distance to clear the beam path.</li>
	<li>Using two folding mirrors and the off-axis parabolic mirror (OAP), align the beam in low power into the field of view of the microscope.</li>
	<li>Adjust these three mirrors to correct astigmatisms in the beam. The result should be a nearly diffraction-limited focal spot.</li>
	<li>Block the laser beam and bring the target back to the focus of the microscope. Validate its position using the microscope and the ranging sensor&#39;s reading.</li>
	<li>Move the microscope to a position in which it will be kept safe from laser light and debris.</li>
</ol>
3. Irradiation sequence and automated target positioning
<ol>
	<li>Implement a closed-loop feedback between the focal axis manipulator of the target and the displacement sensor reading using software. Use the recorded value from protocol step 2.2 as the setpoint. The main PID20 control sequence, prepared with LabView, is shown in Figure 5.</li>
	<li>Once the closed-loop positioning has reached a desired tolerance distance from the setpoint, irradiate the target with a single high-power laser pulse.</li>
	<li>Translate the IP using the mechanical feedthrough to a new position.</li>
	<li>Repeat the irradiation sequence with the next target brought to focus by the software.</li>
</ol>

<ol>
	<li>Snavely, R. A., 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=Intense+High-Energy+Proton+Beams+from+Petawatt-Laser+Irradiation+of+Solids.">Intense High-Energy Proton Beams from Petawatt-Laser Irradiation of Solids.</a> Physical Review Letters. 85, 4945 (2000).</li><li>Tosaki, 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=Evaluation+of+laser-driven+ion+energies+for+fusion+fast-ignition+research.">Evaluation of laser-driven ion energies for fusion fast-ignition research.</a> Progress of Theoretical and Experimental Physics. 2017 (10), 103 (2017).</li><li>Borghesi, 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=Proton+imaging:+a+diagnostic+for+inertial+confinement+fusion/fast+ignitor+studies+Related+content+Inertial+confinement+fusion+and+fast+ignitor+studies.">Proton imaging: a diagnostic for inertial confinement fusion/fast ignitor studies Related content Inertial confinement fusion and fast ignitor studies.</a> Plasma Physics and Controlled Fusion. 43, 12 (2001).</li><li>Malka, V., 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=Practicability+of+proton+therapy+using+compact+laser+systems.">Practicability of proton therapy using compact laser systems.</a> Medical Physics. 31 (6), 1587-1592 (2004).</li><li>Roth, 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=Laser-Driven+Neutron+Source+Based+on+the+Relativistic+Transparency+of+Solids.">Laser-Driven Neutron Source Based on the Relativistic Transparency of Solids.</a> Physical Review Letters. 110, 044802 (2013).</li><li>Noaman-Ul-Haq, 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=Statistical+analysis+of+laser+driven+protons+using+a+high-repetition-rate+tape+drive+target+system.">Statistical analysis of laser driven protons using a high-repetition-rate tape drive target system.</a> Physical Review Accelerators and Beams. 20 (4), 41301 (2017).</li><li>Li, Z., 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=Protons+and+electrons+generated+from+a+5-&#956;m+thick+copper+tape+target+irradiated+by+s-,+circularly-,+and+p-polarized+55-fs+laser+pulses.">Protons and electrons generated from a 5-&#956;m thick copper tape target irradiated by s-, circularly-, and p-polarized 55-fs laser pulses.</a> Physics Letters, Section A: General, Atomic and Solid State Physics. 369 (5-6), 483-487 (2007).</li><li>Shaw, B. H., 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-peak-power+surface+high-harmonic+generation+at+extreme+ultra-violet+wavelengths+from+a+tape.">High-peak-power surface high-harmonic generation at extreme ultra-violet wavelengths from a tape.</a> Journal of Applied Physics. 114 (4), 43106 (2013).</li><li>Fill, E., Bayerl, J., Tommasini, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+tape+target+for+use+with+repetitively+pulsed+lasers.">A novel tape target for use with repetitively pulsed lasers.</a> Review of Scientific Instruments. 73 (5), 2190-2192 (2002).</li><li>Morrison, J. 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=MeV+proton+acceleration+at+kHz+repetition+rate+from+ultra-intense+laser+liquid+interaction.">MeV proton acceleration at kHz repetition rate from ultra-intense laser liquid interaction.</a> New Journal of Physics. 20 (2), 22001 (2018).</li><li>Margarone, D., 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=Proton+Acceleration+Driven+by+a+Nanosecond+Laser+from+a+Cryogenic+Thin+Solid-Hydrogen+Ribbon.">Proton Acceleration Driven by a Nanosecond Laser from a Cryogenic Thin Solid-Hydrogen Ribbon.</a> Physical Review X. 6, 041030 (2016).</li><li>Prencipe, I., 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=Targets+for+high+repetition+rate+laser+facilities:+needs,+challenges+and+perspectives.">Targets for high repetition rate laser facilities: needs, challenges and perspectives.</a> High Power Laser Science and Engineering. 5, 17 (2017).</li><li>Porat, 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=Towards+direct-laser-production+of+relativistic+surface+harmonics.">Towards direct-laser-production of relativistic surface harmonics.</a> Proceedings Volume 11036, Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources III. , 110360 (2019).</li><li>Gershuni, Y., 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=A+gatling-gun+target+delivery+system+for+high-intensity+laser+irradiation+experiments.">A gatling-gun target delivery system for high-intensity laser irradiation experiments.</a> Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 934, 58-62 (2019).</li><li>Jung, D., 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=Development+of+a+high+resolution+and+high+dispersion+Thomson+parabola.">Development of a high resolution and high dispersion Thomson parabola.</a> Review of Scientific Instruments. 82 (1), 13306 (2011).</li><li>Cobble, J. A., 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-resolution+Thomson+parabola+for+ion+analysis.">High-resolution Thomson parabola for ion analysis.</a> Review of Scientific Instruments. 82 (11), 113504 (2011).</li><li>Man&#269;i&#263;, A., Fuchs, J., Antici, P., Gaillard, S. A., Audebert, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Absolute+calibration+of+photostimulable+image+plate+detectors+used+as+high-energy+proton+detectors.">Absolute calibration of photostimulable image plate detectors used as high-energy proton detectors.</a> Review of Scientific Instruments. 79, 73301 (2008).</li><li>Mattox, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Processing. Handbook of Physical Vapor Deposition (PVD) Processing. , (2007).</li><li>Astrom, K. J., Murray, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Feedback Systems: An Introduction for Scientists and Engineers. , (2006).</li><li>Passoni, M., Bertagna, L., Zani, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Target+normal+sheath+acceleration:+Theory,+comparison+with+experiments+and+future+perspectives.">Target normal sheath acceleration: Theory, comparison with experiments and future perspectives.</a> New Journal of Physics. 12, 045012 (2010).</li><li>Roth, M., Schollmeier, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ion+Acceleration:+TNSA.">Ion Acceleration: TNSA.</a> Laser-Plasma Interactions and Applications. , 303-350 (2013).</li><li>Zaffino, R., 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=Efficient+proton+acceleration+from+a+3+TW+table-top+laser+interacting+with+submicrometric+mass-produced+solid+targets.">Efficient proton acceleration from a 3 TW table-top laser interacting with submicrometric mass-produced solid targets.</a> Journal of Physics Communications. 2 (4), 41001 (2018).</li><li>Harres, 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=Development+and+calibration+of+a+Thomson+parabola+with+microchannel+plate+for+the+detection+of+laser-accelerated+MeV+ions.">Development and calibration of a Thomson parabola with microchannel plate for the detection of laser-accelerated MeV ions.</a> Review of Scientific Instruments. 79 (9), 93306 (2008).</li><li>Robinson, A. P. 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=Spectral+modification+of+laser-accelerated+proton+beams+by+self-generated+magnetic+fields+Related+content+New+Journal+of+Physics+Spectral+modification+of+laser-accelerated+proton+beams+by+self-generated+magnetic+fields.">Spectral modification of laser-accelerated proton beams by self-generated magnetic fields Related content New Journal of Physics Spectral modification of laser-accelerated proton beams by self-generated magnetic fields.</a> New Journal of Physics. 11 (15), 83018 (2009).</li><li>Treffert, F., 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+and+implementation+of+a+Thomson+parabola+for+fluence+dependent+energy-loss+measurements+at+the+Neutralized+Drift+Compression+experiment.">Design and implementation of a Thomson parabola for fluence dependent energy-loss measurements at the Neutralized Drift Compression experiment.</a> Review of Scientific Instruments. 89 (10), 103302 (2018).</li><li>Pappalardo, A., Cosentino, L., Finocchiaro, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+imaging+technique+for+detection+and+absolute+calibration+of+scintillation+light.">An imaging technique for detection and absolute calibration of scintillation light.</a> Review of Scientific Instruments. 81 (3), 33308 (2010).</li></ol>

The authors have no competing financial interests.

With some variations, the target fabrication process described in this protocol is common (e.g., Zaffino et al.23). Here, one unique step that is critical to the operation of automatic positioning is the addition of nanometer-scale roughening in ring-shaped areas on the back of the wafer (step 1.2.3). The purpose of this step is to increase the diffused scattering of light incident on the wafer in those areas. The ranging sensor shines a low-power laser beam on the wafer, collects the scattered li...

An erratum was issued for:&#160;<a href="https://www-jove-com.bdigitaluss.remotexs.co/t/61056">Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments</a>. The author list was updated.
The author list was updated from:
Yonatan Gershuni1,2, Michal Elkind1,2, Itamar Cohen1,2, Aviad Tsabary1,2, Deep Sarkar1,2, Ishay Pomerantz1,2 
1The School of Physics and Astronomy, Tel Aviv University, 
2Tel Aviv University Center for Light-Matter Interaction
to:
Yonatan Gershuni1,2, Michal Elkind1,2, Dolev Roitman1,2, Itamar Cohen1,2, Aviad Tsabary1,2, Deep Sarkar1,2, Ishay Pomerantz1,2 
1The School of Physics and Astronomy, Tel Aviv University, 
2Tel Aviv University Center for Light-Matter Interaction

An erratum was issued for:&#160;<a href="https://www-jove-com.bdigitaluss.remotexs.co/t/61056">Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments</a>. The author list was updated.

Erratum: Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments

High-intensity laser irradiation of solid targets generates multiple forms of radiation. One of these is the emission of energetic ions with energies at the Mega electron-volt (MeV) level1. A compact source of MeV ions has potential for many applications, such as proton fast-ignition2, proton radiography3, ion radiotherapy4, and neutron generation5.
A major challenge in making laser-ion acceleration practical is the ability to position micrometer-scale targets accurately within the focus of the laser at a high rate. Few target delivery technologies were developed to answer this challenge. Most common are target systems based on micrometer-scale thick tapes. These targets are simple to replenish and may be easily positioned within the focus of the laser. Tape target has been made using VHS6, copper7, Mylar, and Kapton8 tapes. The tape drive system typically consists of two motorized spools for winding and unwinding and two vertical pins placed between them to keep the tape in position9. The accuracy in positioning the tape surface is typically less than the Rayleigh range of the focusing beam. Another type of replenishable laser target is liquid sheets10. These targets are delivered rapidly to the interaction region and introduce a very low amount of debris. This system comprises a high-pressure syringe pump continuously supplied with liquid from a reservoir. Recently, novel cryogenic hydrogen jets11 were established as means to deliver ultrathin, low-debris, replenishable targets.
The main drawback of all of these replenishable target systems is the limited choice of target materials and geometries, which are dictated by mechanical requirements such as strength, viscosity, and melting temperature.
Here, a system able to bring micromachined targets to the focus of a high intensity laser at a rate of 0.2 Hz is described. Micromachining offers a wide choice of target materials in versatile geometries12. The target positioning is performed by a closed-loop feedback between a commercial displacement sensor and a motorized manipulator.
The target delivery system was tested using a high-contrast, 20 TW laser system that delivers 25 fs-long laser pulses with 500 mJ on target. A review of the laser system&#8217;s architecture is given in Porat et al.13, and a technical description of the target system is given in Gershuni et al.14. This paper presents a detailed method for making and using this type of system and shows representative results of laser-ion acceleration from ultrathin gold foil targets.
The Thomson Parabola ion spectrometer (TPIS)15,16 shown in Figure 1 was used to record the energy spectra of the emitted ions. In a TPIS, accelerated ions pass through parallel electric and magnetic fields, which places them on parabolic trajectories in the focal plane. The parabolic curvature depends on the ion&#8217;s charge-to-mass ratio, and the location along the trajectory is set by the ion&#8217;s energy.
A BAS-TR imaging plate (IP)17 positioned at the focal plane of the TPIS records the impinging ions. The IP is attached to a mechanical feedthrough to allow translation to a fresh area before each shot.

<table><tbody><tr><td>76.2 x 127mm EFL 90&amp;deg; Protected Gold 100&amp;Aring; Off-Axis Parabolic Mirror</td><td>Edmund optics</td><td>35-535</td><td></td></tr><tr><td>MicroTrak 3 LTS 120-20</td><td>MTI Instruments</td><td></td><td></td></tr><tr><td>Ultrafast high power dielectric mirrors for 800 nm</td><td>Thorlabs</td><td></td><td></td></tr></tbody></table>

automated delivery of microfabricated targets for intense laser irradiation experiments

Described is an experimental procedure that enables high-power laser irradiation of microfabricated targets. Targets are brought to the laser focus by a closed feedback loop that operates between the target manipulator and a ranging sensor. The target fabrication process is explained in detail. Representative results of MeV-level proton beams generated by irradiation of 600 nm thick gold foils at a rate of 0.2 Hz are given. The method is compared with other replenishable target systems and the prospects of increasing the shot rates to above 10 Hz are discussed.

This target delivery system was employed to accelerate ions from the back side of 600 nm thick gold foils. When irradiated with a normalized laser intensity of a0 = 5.6, these ions were accelerated by the target normal sheath acceleration (TNSA) mechanism21. In TNSA, the lower-intensity light that preceded the main laser pulse ionized the front surface of the target foil. The ponderomotive force exerted by the main laser pulse drove hot electrons through the bulk matter. A charge separa...

Watch this Scientific Journal Video about Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments at JoVE.com

Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments

A protocol is presented for automated irradiation of thin gold foils with high intensity laser pulses. The protocol includes a step-by-step description of the micromachining target fabrication process and a detailed guide for how targets are brought to the laser&#39;s focus at a rate of 0.2 Hz.

Described is an experimental procedure that enables high-power laser irradiation of microfabricated targets. Targets are brought to the laser focus by a ...

automated-delivery-microfabricated-targets-for-intense-laser

Universidad San Sebastian

Research

JoVE Journal

Engineering

4.3K Views.  Tel Aviv University. A protocol is presented for automated irradiation of thin gold foils with high intensity laser pulses. The protocol includes a step-by-step description of the micromachining target fabrication process and a detailed guide for how targets are brought to the laser's focus at a rate of 0.2 Hz.

Video: Automated Delivery of Microfabricated Targets for Intense Laser Irradiation Experiments

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Laser-induced Forward Transfer for Flip-chip Packaging of Single Dies

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics industry. In this technique the chip and/or the substrate is bumped and the two are bonded via these conductive bumps. Many bumping techniques have been developed and intensively investigated since the introduction of the FC technology in 19601 such as stencil printing, stud bumping, evaporation and electroless/electroplating2. Despite the progress that these methods have made they all suffer from one or more than one drawbacks that need to be addressed such as cost, complex processing steps, high processing temperatures, manufacturing time and most importantly the lack of flexibility. In this paper, we demonstrate a simple and cost-effective laser-based bump forming technique known as Laser-induced Forward Transfer (LIFT)3. Using the LIFT technique a wide range of bump materials can be printed in a single-step with great flexibility, high speed and accuracy at RT. In addition, LIFT enables the bumping and bonding down to chip-scale, which is critical for fabricating ultra-miniature circuitry.

We demonstrate the use of the Laser-induced Forward Transfer (LIFT) technique for flip-chip assembly of optoelectronic components. This approach provides a simple, cost-effective, low-temperature, fast and flexible solution for fine-pitch bumping and bonding on chip-scale for achieving high-density circuits for optoelectronic applications.

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics ...

Microfabrication of Chip-sized Scaffolds for Three-dimensional Cell cultivation

Using microfabrication technologies is a prerequisite to create scaffolds of reproducible geometry and constant quality for three-dimensional cell cultivation. These technologies offer a wide spectrum of advantages not only for manufacturing but also for different applications. The size and shape of formed cell clusters can be influenced by the exact and reproducible architecture of the microfabricated scaffold and, therefore, the diffusion path length of nutrients and gases can be controlled.1 This is unquestionably a useful tool to prevent apoptosis and necrosis of cells due to an insufficient nutrient and gas supply or removal of cellular metabolites.
Our polymer chip, called CellChip, has the outer dimensions of 2 x 2 cm with a central microstructured area. This area is subdivided into an array of up to 1156 microcontainers with a typical dimension of 300 m edge length for the cubic design (cp- or cf-chip) or of 300 m diameter and depth for the round design (r-chip).2
So far, hot embossing or micro injection moulding (in combination with subsequent laborious machining of the parts) was used for the fabrication of the microstructured chips. Basically, micro injection moulding is one of the only polymer based replication techniques that, up to now, is capable for mass production of polymer microstructures.3 However, both techniques have certain unwanted limitations due to the processing of a viscous polymer melt with the generation of very thin walls or integrated through holes. In case of the CellChip, thin bottom layers are necessary to perforate the polymer and provide small pores of defined size to supply cells with culture medium e.g. by microfluidic perfusion of the containers.
In order to overcome these limitations and to reduce the manufacturing costs we have developed a new microtechnical approach on the basis of a down-scaled thermoforming process. For the manufacturing of highly porous and thin walled polymer chips, we use a combination of heavy ion irradiation, microthermoforming and track etching. In this so called "SMART" process (Substrate Modification And Replication by Thermoforming) thin polymer films are irradiated with energetic heavy projectiles of several hundred MeV introducing so-called "latent tracks" Subsequently, the film in a rubber elastic state is formed into three dimensional parts without modifying or annealing the tracks. After the forming process, selective chemical etching finally converts the tracks into cylindrical pores of adjustable diameter.

We present two processes for the microfabrication of porous polymer chips for three-dimensional cell cultivation. The first one is hot embossing combined with a solvent vapour welding process. The second one uses a recently developed microthermoforming process combined with ion track technology leading to a significant simplification of manufacture.

Using microfabrication technologies is a prerequisite to create scaffolds of reproducible geometry and constant quality for three-dimensional cell ...

Biology

Laser-induced Forward Transfer of Ag Nanopaste

Over the past decade, there has been much development of non-lithographic methods1-3 for printing metallic inks or other functional materials. Many of these processes such as inkjet3 and laser-induced forward transfer (LIFT)4 have become increasingly popular as interest in printable electronics and maskless patterning has grown. These additive manufacturing processes are inexpensive, environmentally friendly, and well suited for rapid prototyping, when compared to more traditional semiconductor processing techniques. While most direct-write processes are confined to two-dimensional structures and cannot handle materials with high viscosity (particularly inkjet), LIFT can transcend both constraints if performed properly. Congruent transfer of three dimensional pixels (called voxels), also referred to as laser decal transfer (LDT)5-9, has recently been demonstrated with the LIFT technique using highly viscous Ag nanopastes to fabricate freestanding interconnects, complex voxel shapes, and high-aspect-ratio structures. In this paper, we demonstrate a simple yet versatile process for fabricating a variety of micro- and macroscale Ag structures. Structures include simple shapes for patterning electrical contacts, bridging and cantilever structures, high-aspect-ratio structures, and single-shot, large area transfers using a commercial digital micromirror device (DMD) chip.

We demonstrate the use of the Laser-induced forward transfer technique (LIFT) for the printing of high-viscosity Ag paste. This technique offers a simple, low temperature, robust process for non-lithographically printing microscale 2D and 3D structures.

Over the past decade, there has been much development of non-lithographic methods1-3 for printing metallic inks or other functional materials. Many of ...

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

We fabricate metal/LaAlO3/SrTiO3 heterostructures using a combination of pulsed laser deposition and in situ magnetron sputtering. Through magnetotransport and in situ X-ray photoelectron spectroscopy experiments, we investigate the interplay between electrostatic and chemical phenomena of the quasi two-dimensional electron gas formed in this system.

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide ...

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...

Femtosecond Laser Filaments for Use in Sub-Diffraction-Limited Imaging and Remote Sensing

Probing remote matter with laser light is a ubiquitous technique used in circumstances as diverse as laser-induced breakdown spectroscopy and barcode scanners. In classical optics, the intensity that can be brought to bear on a remote target is limited by the spot size of the laser at the distance of the target. This spot size has a lower bound determined by the diffraction limit of classical optics. However, amplified femtosecond laser pulses generate intensity sufficient to modify the refractive index of the ambient air and undergo self-focusing. This self-focusing effect leads to the generation of highly intense laser filaments which maintain their intensity and small sub-millimeter diameter size at distances well beyond the classical Rayleigh length. Such intensity provides the capability of remote scanning, imaging, sensing, and spectroscopy with enhanced spatial resolution. We describe a technique for generating filaments with a femtosecond regenerative chirped-pulse amplifier, and for using the resulting filament to conduct imaging and spectroscopic measurements at remote distances of at least several meters.

High-intensity femtosecond pulses of laser light can undergo cycles of Kerr self-focusing and plasma defocusing, propagating an intense sub-millimeter-diameter beam over long distances. We describe a technique for generating and using these filaments to perform remote imaging and sensing beyond the classical diffraction limits of linear optics.

Probing remote matter with laser light is a ubiquitous technique used in circumstances as diverse as laser-induced breakdown spectroscopy and barcode ...

Fixed Target Serial Data Collection at Diamond Light Source

Serial data collection is a relatively new technique for synchrotron users. A user manual for fixed target data collection at I24, Diamond Light Source is presented with detailed step-by-step instructions, figures, and videos for smooth data collection.

We present a comprehensive guide to fixed target sample preparation, data collection, and data processing for serial synchrotron crystallography at Diamond beamline I24.

Serial data collection is a relatively new technique for synchrotron users. A user manual for fixed target data collection at I24, Diamond Light Source is ...

Biochemistry

Automated Robotic Dispensing Technique for Surface Guidance and Bioprinting of Cells

This manuscript describes the introduction of cell guidance features followed by the direct delivery of cells to these features in a hydrogel bioink using an automated robotic dispensing system. The particular bioink was selected as it allows cells to sediment towards and sense the features. The dispensing system bioprints viable cells in hydrogel bioinks using a backpressure assisted print head. However, by replacing the print head with a sharpened stylus or scalpel, the dispensing system can also be employed to create topographical cues through surface etching. The stylus movement can be programmed in steps of 10 &#181;m in the X, Y and Z directions. The patterned grooves were able to orientate mesenchymal stem cells, influencing them to adopt an elongated morphology in alignment with the grooves&#39; direction. The patterning could be designed using plotting software in straight lines, concentric circles, and sinusoidal waves. In a subsequent procedure, fibroblasts and mesenchymal stem cells were suspended in a 2% gelatin bioink, for bioprinting in a backpressure driven extrusion printhead. The cell bearing bioink was then printed using the same programmed coordinates used for the etching. The bioprinted cells were able to sense and react to the etched features as demonstrated by their elongated orientation along the direction of the etched grooves.

This protocol describes a bioprinting methodology using an automated robotic depositing system that incorporates etched topographical guidance cues with the precision deposition of a cell bearing hydrogel bioink. The printed cells are directly delivered to the etched features and are able to sense and orientate with them.

This manuscript describes the introduction of cell guidance features followed by the direct delivery of cells to these features in a hydrogel bioink using ...

Bioengineering

Control of Cell Geometry through Infrared Laser Assisted Micropatterning

Micropatterning is an established technique in the cell biology community used to study connections between the morphology and function of cellular compartments while circumventing complications arising from natural cell-to-cell variations. To standardize cell shape, cells are either confined in 3D molds or controlled for adhesive geometry through adhesive islands. However, traditional micropatterning techniques based on photolithography and deep UV etching heavily depend on clean rooms or specialized equipment. Here we present an infrared laser assisted micropatterning technique (microphotopatterning) modified from Doyle et al. that can be conveniently set up with commercially available imaging systems. In this protocol, we use a Nikon A1R MP+ imaging system to generate micropatterns with micron precision through an infrared (IR) laser that ablates preset regions on poly-vinyl alcohol coated coverslips. We employ a custom script to enable automated pattern fabrication with high efficiency and accuracy in systems not equipped with a hardware autofocus. We show that this IR laser assisted micropatterning (microphotopatterning) protocol results in defined patterns to which cells attach exclusively and take on the desired shape. Furthermore, data from a large number of cells can be averaged due to the standardization of cell shape. Patterns generated with this protocol, combined with high resolution imaging and quantitative analysis, can be used for relatively high throughput screens to identify molecular players mediating the link between form and function.

The protocol presented here enables automated fabrication of micropatterns that standardizes cell shape to study cytoskeletal structures within mammalian cells. This user-friendly technique can be set up with commercially available imaging systems and does not require specialized equipment inaccessible to standard cell biology laboratories.

Micropatterning is an established technique in the cell biology community used to study connections between the morphology and function of cellular ...