1. Substrate Preparation 
<ol>
 <li>Cut 1 cm x 1 cm silicon substrates from a Si wafer, Silicon is good for SEM characterization (plane view and cross section).</li>
 <li>Cut 1 cm x 1 cm glass (soda-lime, 1 mm thick), glass is optimal for optical and electrical characterization.</li>
 <li>If contacts are needed on glass substrates, Au contacts can be evaporated in vacuum by using a mask. Deposit 10 nm of Cr as an interlayer to improve adhesion of Au, deposit 50 nm of Au.</li>
 <li>Cut 1 cm x 1 cm polymer sample (e.g. Ethylene Tetrafluoroethylene, ETFE).</li>
 <li>Clean the substrates by sonicating in isopropanol for 5-10 min and rinse in isopropanol, dry using a N2 flow.</li>
</ol>
2. Laser Alignment and Selection of Laser Parameters 
<ol>
 <li>Warm-up the Nd:YAG laser and select IV harmonic emission (266 nm wavelength) by using a fourth harmonic generator (FHG) constituted by two second harmonic generators (SHG) in cascade.</li>
 <li>Mount a 2%wt. Al2O3:ZnO circular target (2" diameter) on the target manipulator. Align the laser spot at the center of the target, start target rotation and translation and set the maximum vertical range. Check that the laser spot never touches the external steel ring used to fix the target. The target is moved with a roto-translational motion to have uniform ablation of the whole target surface.</li>
 <li>Select repetition rate (e.g. 10 Hz) and pulse energy (e.g. 75 mJ). Adjust pulse energy and monitor laser stability by a power meter.</li>
 <li>Move the focusing lens to a selected position and use a piece of sensitive paper attached to the target to measure the spot size. For any position of the focusing lens fire 1-5 laser shots on the paper. Select a lens position to have a laser fluence of about 1 J/cm2.</li>
</ol>
3. Setting up PLD and Selection of Deposition Parameters
<ol>
 <li>Alignment of substrate position
 <ol>
 <li>Mount a circular paper sheet about 2" diameter as a substrate for alignment tests.</li>
 <li>Move the substrate holder to a target-to-substrate distance dTS = 50 mm.</li>
 <li>Start pumping down the chamber with primary and turbomolecular pumps until the vacuum level reaches 10-2 Pa.</li>
 <li>Select a gas type (i.e. oxygen) and adjust pumping speed and gas flow to have the proper gas pressure (see sections 4 and 5). Adjust x-y position of the substrate manipulator off-axis with respect to the plume center to obtain uniform film thickness over a circular corona.</li>
 <li>Start ablation by removing the beam stopper/power meter. If the target is new or if it was not used for long time, this pre-ablation is necessary to clean the target.</li>
 <li>Stop ablation when a deposit can be seen on the paper looking from a viewport.</li>
 </ol>
 </li>
 <li>Determination of plasma plume length
 <ol>
 <li>Follow steps 3.1.1. to 3.1.5, during ablation take pictures with a digital camera with 0.5 - 1 sec accumulation time to average over different plasma plumes.</li>
 <li>Measure the visible plasma plume length from the pictures taking dTS as a reference (see Figure 3).</li>
 </ol>
 </li>
 <li>Calibration of the film thickness
 <ol>
 <li>Move the substrate far from the target (i.e. 100 mm and more) and move the Quartz Micro-Balance (QCM) at a distance equal to dTS from the target.</li>
 <li>Deposit 1000 laser shots (i.e. 1' 40'') and measure the deposited mass value, then move the QCM away.</li>
 <li>Mount a Si substrate as in 1.1.</li>
 <li>Deposit a test sample (e.g. 18,000 laser shots, i.e. 30' ) and use cross sectional SEM images to calibrate the deposition rate (nm/pulse).</li>
 </ol>
 </li>
</ol>
 4. Deposition of Nanoengineered AZO Films 
<ol>
 <li>Mount the substrates prepared as in section 1 on the sample holder manipulator by using adhesive tape.</li>
 <li>Follow steps 3.1.2 - 3.1.3.</li>
 <li>Start substrate rotation.</li>
 <li>Deposition of compact AZO films
 <ol>
 <li>Switch on the ion gun and set ion energy at 100 eV, RF power at 75-100 W and Ar gas flux at 20 sccm (the pressure is in the 10-2 Pa range). Clean substrates with Ar+ ion gun for 5-10 min. After the cleaning treatment close gas inlet and pump down the chamber to remove Argon.</li>
 <li>Insert oxygen gas and adjust pumping speed and gas flux to have 2 Pa oxygen.</li>
 <li>start ablation and deposit for 18,000 shots (30'). During ablation check that the plume length is the same as determined in step 3.2.</li>
 <li>stop ablation, close gas inlet, pump down the chamber.</li>
 </ol>
 </li>
 <li>Deposition of hierarchically structured AZO films
 <ol>
 <li>Insert oxygen gas and adjust pumping speed and gas flow to have 160 Pa oxygen.</li>
 <li>start ablation and deposit for 18,000 shots (30'). During ablation check that the plume length is the same as determined in step 3.2.</li>
 <li>stop ablation, close gas inlet, pump down the chamber.</li>
 </ol>
 </li>
 <li>Vent the chamber and remove samples</li>
</ol>
5. Electrical and Optical Characterization
<ol>
 <li>Measure the in-plane transport properties using four-probe techniques (i.e. Van der Pauw method). See Figure 4 for a scheme of the contacts. Typical values of the probe current are in the 1 &mu;A to 10 mA range. The measurements is performed over a sample area reduced to 0.7 cm x 0.7 cm to ensure a better thickness uniformity (about 5%).</li>
 <li>Measure the optical transmittance of the sample and of the bare substrate. Correct the spectra for the substrate contribution by setting to 1 the intensity at the glass/film interface. For a precise correction procedure make sure that the sample is mounted with the glass substrate facing the incident beam. Determine the visible light transparency by calculating the average transmittance in the 400-700 nm range. Use a 150 mm diameter integrating sphere to measure the scattered fraction of the light, the Haze factor can be calculated by dividing the scattered fraction by the total transmitted light (i.e. scattered and forward transmitted), see Figure 5.</li>
</ol>

<ol>
	<li>Chrisey, D. B., Hubler, G. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Pulsed Laser Deposition of Thin Films. , (1994).</li><li>Lowndes, D. H., Geohegan, D. B., Puretzky, A. A., Norton, D. P., Rouleau, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+novel+thin-film+materials+by+pulsed+laser+deposition.">Synthesis of novel thin-film materials by pulsed laser deposition.</a> Science. 273, 898 (1996).</li><li>Di Fonzo, F., Bailini, A., Russo, V., Baserga, A., Cattaneo, D., Beghi, M. G., Ossi, P. M., Casari, C. S., Li Bassi, A., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+characterization+of+nanostructured+tungsten+and+tungsten+oxide+films.">Synthesis and characterization of nanostructured tungsten and tungsten oxide films.</a> Catalysis Today. 116, 69-73 (2006).</li><li>Casari, C. S., Foglio, S., Passoni, M., Siviero, F., Bottani, C. E., Li Bassi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Energetic+regimes+and+growth+mechanisms+of+pulsed+laser+deposited+Pd+clusters+on+Au(111)+investigated+by+in+situ+Scanning+Tunneling+Microscopy.">Energetic regimes and growth mechanisms of pulsed laser deposited Pd clusters on Au(111) investigated by in situ Scanning Tunneling Microscopy.</a> Physical Review B. 84 (111), 155441 (2011).</li><li>Cattaneo, D., Foglio, S., Casari, C. S., Li Bassi, A., Passoni, M., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Different+W+cluster+deposition+regimes+in+pulsed+laser+ablation+observed+by+in+situ+Scanning+Tunneling+Microscopy.">Different W cluster deposition regimes in pulsed laser ablation observed by in situ Scanning Tunneling Microscopy.</a> Surface Science. 601, 1892-1897 (2007).</li><li>Bailini, A., Di Fonzo, F., Fusi, M., Casari, C. S., Li Bassi, A., Russo, V., Baserga, A., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pulsed+laser+deposition+of+tungsten+and+tungsten+oxide+thin+films+with+tailored+structure+at+the+nano-+and+mesoscale.">Pulsed laser deposition of tungsten and tungsten oxide thin films with tailored structure at the nano- and mesoscale.</a> Applied Surface Science. 253, 8130-8135 (2007).</li><li>Fusi, M., Russo, V., Casari, C. S., Li Bassi, A., A, C. E., Bottani, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Titanium+oxide+nanostructured+films+by+reactive+pulsed+laser+deposition.">Titanium oxide nanostructured films by reactive pulsed laser deposition.</a> Applied Surface Science. 255 (10), 5334-5337 (2009).</li><li>Dellasega, D., Facibeni, A., Fonzo, F. D. i., Russo, V., Conti, C., Ducati, C., Casari, C. S., Li Bassi, A., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanostructured+High+Valence+Silver+Oxide+Produced+by+Pulsed+laser+Deposition.">Nanostructured High Valence Silver Oxide Produced by Pulsed laser Deposition.</a> Applied Surface Science. 255 (10), 5248-5251 (2009).</li><li>Di Fonzo, F., Tonini, D., Li Bassi, A., Casari, C. S., Beghi, M. G., Bottani, C. E., Gastaldi, D., Vena, P., Contro, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+regimes+in+pulsed+laser+deposition+of+alumina+films.">Growth regimes in pulsed laser deposition of alumina films.</a> Applied Physics A. 93, 765-769 (2008).</li><li>Bailini, A., Donati, F., Zamboni, M., Russo, V., Passoni, M., Casari, C. S., Li Bassi, A., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pulsed+Laser+Deposition+of+Bi2Te3+Thermoelectric+Films.">Pulsed Laser Deposition of Bi2Te3 Thermoelectric Films.</a> Applied Surface Science. 254, 1249-1254 (2007).</li><li>Baserga, A., Russo, V., Fonzo, F. D. i., Bailini, A., Cattaneo, D., Casari, C. S., Li Bassi, A., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanostructured+Tungsten+Oxide+With+Controlled+Properties:+Synthesis+And+Raman+Characterization.">Nanostructured Tungsten Oxide With Controlled Properties: Synthesis And Raman Characterization.</a> Thin Solid Films. 515, 6465-6469 (2007).</li><li>Dellasega, D., Facibeni, A., Di Fonzo, F., Bogana, M., Polissi, A., Conti, C., Ducati, C., Casari, C. S., Li Bassi, A., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanostructured+Ag4O4+films+with+enhanced+antibacterial+activity.">Nanostructured Ag4O4 films with enhanced antibacterial activity.</a> Nanotechnology. 19, 475602 (2008).</li><li>Fonzo, F. D. i., Casari, C. S., Russo, V., Brunella, M. F., Li Bassi, A., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hierarchically+organized+nanostructured+TiO2+for+photocatalysis+applications.">Hierarchically organized nanostructured TiO2 for photocatalysis applications.</a> Nanotechnology. 20, 015604 (2009).</li><li>Torta, F., Fusi, M., Casari, C. S., Bottani, C. E., Bachi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Titanium+Dioxide+Coated+MALDI+plate+for+on+target+Analysis+of+Phosphopeptides.">Titanium Dioxide Coated MALDI plate for on target Analysis of Phosphopeptides.</a> Journal of Proteome Research. 8, 1932-1942 (2009).</li><li>Ponzoni, A., Russo, V., Bailini, A., Casari, C. S., Ferroni, M., Li Bassi, A., Migliori, A., Morandi, V., Ortolani, L., Sberveglieri, G., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Structural And Gas-Sensing Characterization Of Tungsten Oxide Nanorods And Nanoparticles. Sensors &amp; Actuators: B. Chemical B. 153, 340-346 (2011).</li><li>Li Bassi, A., Bailini, A., Donati, F., Russo, V., Passoni, M., Mantegazza, A., Casari, C. S., Bottani, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermoelectric+properties+of+Bi-Te+Films+with+controlled+structure+and+morphology.">Thermoelectric properties of Bi-Te Films with controlled structure and morphology.</a> Journal of Applied Physics. 105, 124307 (2009).</li><li>Sauvage, F., Di Fonzo, F., Li Bassi, A., Casari, C. S., Russo, V., Divitini, G., Ducati, C., Bottani, C. E., Comte, P., Graetzel, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bio-inspired+hierarchical+TiO2+photo-anode+for+dye-sensitized+solar+cells.">Bio-inspired hierarchical TiO2 photo-anode for dye-sensitized solar cells.</a> Nano Letters. 10, 2562-2567 (2010).</li><li>Grankvist, C. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transparent+conductors+as+solar+energy+materials:+A+panoramic+review.">Transparent conductors as solar energy materials: A panoramic review.</a> Solar Energy Materials &amp; Solar Cells. 91, 1529 (2007).</li><li>Minami, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transparent+conducting+oxide+semiconductors+for+transparent+electrodes.">Transparent conducting oxide semiconductors for transparent electrodes.</a> Semicond. Sci. Technol. 20, S35 (2005).</li><li>Fortunato, 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=Transparent+Conducting+Oxides+for+Photovoltaics.">Transparent Conducting Oxides for Photovoltaics.</a> MRS Bulletin. 32, 242 (2007).</li><li>Exarhos, G. 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=Discovery-based+design+of+transparent+conducting+oxide+films.">Discovery-based design of transparent conducting oxide films.</a> Thin Solid Films. 515, 7025 (2007).</li><li>Gondoni, P., Ghidelli, M., Fonzo, F. D. i., Russo, V., Bruno, P., Mart-Rujas, J., Bottani, C. E., Li Bassi, A., Casari, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+and+functional+properties+of+Al:ZnO+thin+films+grown+by+Pulsed+Laser+Deposition+at+room+temperature.">Structural and functional properties of Al:ZnO thin films grown by Pulsed Laser Deposition at room temperature.</a> Thin Solid Films. 520, 4707-4711 (2012).</li><li>Gondoni, P., Ghidelli, M., Fonzo, F. D. i., Carminati, M., Russo, V., Li Bassi, A., Casari, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure-dependent+optical+and+electrical+transport+properties+of+nanostructured+Al-doped+ZnO.">Structure-dependent optical and electrical transport properties of nanostructured Al-doped ZnO.</a> Nanotechnology. 23, 365706 (2012).</li><li>Casari, C. S., Li Bassi, A., Arkin, W. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pulsed+Laser+Deposition+of+Nanostructured+Oxides:+from+Clusters+to+Functional+Films.">Pulsed Laser Deposition of Nanostructured Oxides: from Clusters to Functional Films.</a> Advances in Laser and Optics Research. 7, 65-100 (2012).</li><li>Amoruso, S., Sambri, A., Vitiello, M., Wang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plume+expansion+dynamics+during+laser+ablation+of+manganates+in+oxygen+atmosphere.">Plume expansion dynamics during laser ablation of manganates in oxygen atmosphere.</a> Applied Surface Science. 252, 4712-4716 (2006).</li><li>Uccello, A., Dellasega, D., Perissinotto, S., Lecis, N., Passoni, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanostructured+Rhodium+Films+for+Advanced+Mirrors+Produced+by+Pulsed+Laser+Deposition.">Nanostructured Rhodium Films for Advanced Mirrors Produced by Pulsed Laser Deposition.</a> Journal of Nuclear Materials. , (2013).</li><li>Gondoni, P., Ghidelli, M., Fonzo, F. D. i., Russo, V., Bruno, P., Mart&#237;-Rujas, J., Bottani, C. E., Li Bassi, A., Casari, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+Performing+Al:ZnO+Thin+Films+grown+by+Pulsed+Laser+Deposition+at+Room+Temperature.">Highly Performing Al:ZnO Thin Films grown by Pulsed Laser Deposition at Room Temperature.</a> Nanoscience and Nanotechnology. , (2013).</li></ol>

No conflicts of interest declared.

The plasma plume shape is closely related to the ablation process, especially in the presence of a gas; monitoring the plasma plume by visual inspection is important to control the deposition. When depositing a metal oxide by ablating an oxide target, oxygen is needed to support oxygen losses during the ablation process. At lower oxygen background gas pressure, the deposited material may have oxygen vacancies. This effect is reduced by increasing the gas pressure. To separate stoichiometry from morphology gas mixt...

Pulsed Laser Deposition (PLD) employs laser ablation of a solid target which results in the formation of a plasma of ablated species which can be deposited on a substrate to grow a film (see Figure 1) 1. Interaction with a background atmosphere (inert or reactive) can be used to induce homogeneous cluster nucleation in the gas phase (see Figure 2) 2,3. Our strategy for material synthesis by PLD is based on the tuning of material properties in a bottom-up approach by carefully controlling the plasma dynamics generated in the PLD process. Cluster size, kinetic energy and composition can be varied by a proper setting of deposition parameters which affect film growth and result in morphological and structural changes 4,5. By exploiting the method described here we demonstrated, for a number of oxides (e.g. WO3, Ag4O4, Al2O3 and TiO2), the capability to tune morphology, density, porosity, degree of structural order, stoichiometry and phase by modifying the material structure at the nanoscale 6-11. This allows the design of materials for specific applications 12-16. With reference to photovoltaic applications, we synthesized nanostructured TiO2 hierarchically organized by assembling nanoparticles (&lt;10 nm) in a nano- and mesostructure that resembles a 'forest of trees' 13 showing interesting results when employed as photoanodes in dye sensitized solar cells (DSSC) 17. Based on these previous results we describe the protocol for the deposition of Al-doped ZnO (AZO) films as a transparent conducting oxide.
Transparent conducting oxides (TCOs) are high bandgap (&gt;3 eV) materials converted into conductors by heavy doping, displaying resistivity &lt;10-3 ohm-cm and more than 80% optical transmittance in the visible range. They are a key element for many applications such as touch screens and solar cells 18-21 and they are typically grown by different techniques such as sputtering, pulsed laser deposition, chemical vapour deposition, spray pyrolysis and with solution-based chemical methods. Among TCOs, indium-tin-oxide (ITO) has been widely studied for its low resistivity but suffers from the drawback of the high cost and low availability of indium. Research is now moving towards indium-free systems such as F-doped SnO2 (FTO), Al-doped ZnO (AZO) and F-doped ZnO (FZO).
Electrodes capable of providing an intelligent management of the incident light (light trapping) are particularly interesting for photovoltaic applications. To exploit the possibility to scatter visible light via structures and morphologies modulated at a scale comparable to the wavelength of light (e.g. 300-1,000 nm), a good control on the film morphology and on cluster assembly architectures is needed.
In particular we describe how to tune morphology and structure of AZO films. Compact AZO deposited at low pressure (2 Pa oxygen) and at room temperature is characterized by low resistivity (4.5 x 10-4 ohm cm) and visible light transparency (&gt; 90%) which is competitive with AZO deposited at high temperatures, while AZO hierarchical structures are obtained by ablating at O2 pressures above 100 Pa. These structures display a strong light scattering capability with haze factor up to 80% and more 22,23.

<table border="1">
 <tbody>
 <tr>
 <td>Name of Reagent/Material</td>
 <td>Company</td>
 <td>Catalog Number</td>
 </tr>
 <tr>
 <td>Pulsed Laser</td>
 <td>Continuum-Quantronix </td>
 <td>Powerlite 8010</td>
 </tr>
 <tr>
 <td>Power meter</td>
 <td>Coherent</td>
 <td>FieldMaxII-TO</td>
 </tr>
 <tr>
 <td>Ion Gun</td>
 <td>Mantis Dep</td>
 <td>RFMax60</td>
 </tr>
 <tr>
 <td>Mass flow controller</td>
 <td>Mks</td>
 <td>2179 &deg;</td>
 </tr>
 <tr>
 <td>Quartz Crystal Microbalance</td>
 <td>Infcon</td>
 <td>XTC/2</td>
 </tr>
 <tr>
 <td>Background gas</td>
 <td>Rivoira-Praxair</td>
 <td>5.0 oxygen</td>
 </tr>
 <tr>
 <td>Target</td>
 <td>Kurt Lesker</td>
 <td>(made on request)</td>
 </tr>
 <tr>
 <td>Isopropanol</td>
 <td>Sigma Aldrich</td>
 <td>190764-2L</td>
 </tr>
 <tr>
 <td>Source meter</td>
 <td>Keithley</td>
 <td>K2400</td>
 </tr>
 <tr>
 <td>Magnet Kit</td>
 <td>Ecopia</td>
 <td>0.55T-Kit</td>
 </tr>
 <tr>
 <td>Spectrophotometer</td>
 <td>PerkinElmer</td>
 <td>Lambda 1050</td>
 </tr>
 </tbody>
</table>

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.

The deposition of AZO by PLD in oxygen atmosphere produces compact transparent conducting films at low background gas pressure (i.e. 2 Pa) and mesoporous forest-like structures constituted by hierarchically assembled clusters at high pressures (i.e. 160 Pa). The material is constituted by nanocrystalline domains whose size is maximum (30 nm) at 2 Pa 22.
Due to collisions between the ablated species and the background gas, the shape and length of the plasma p...

Watch this Scientific Journal Video about Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition at JoVE.com

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

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, ...

fabrication-nano-engineered-transparent-conducting-oxides-pulsed

Research

JoVE Journal

Engineering

15.4K Views.  Politecnico di Milano. 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.

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

Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses

Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a significant role in laser-material interaction, especially in the air environment1-11.
Early plasma evolution has been captured through pump-probe shadowgraphy1-3 and interferometry1,4-7. However, the studied time frames and applied laser parameter ranges are limited. For example, direct examinations of plasma front locations and electron number densities within a delay time of 100 picosecond (ps) with respect to the laser pulse peak are still very few, especially for the ultrashort pulse of a duration around 100 femtosecond (fs) and a low power density around 1014 W/cm2. Early plasma generated under these conditions has only been captured recently with high temporal and spatial resolutions12. The detailed setup strategy and procedures of this high precision measurement will be illustrated in this paper. The rationale of the measurement is optical pump-probe shadowgraphy: one ultrashort laser pulse is split to a pump pulse and a probe pulse, while the delay time between them can be adjusted by changing their beam path lengths. The pump pulse ablates the target and generates the early plasma, and the probe pulse propagates through the plasma region and detects the non-uniformity of electron number density. In addition, animations are generated using the calculated results from the simulation model of Ref. 12 to illustrate the plasma formation and evolution with a very high resolution (0.04 ~ 1 ps).
Both the experimental method and the simulation method can be applied to a broad range of time frames and laser parameters. These methods can be used to examine the early plasma generated not only from metals, but also from semiconductors and insulators.

An experimental method to examine the early plasma evolution induced by ultrashort laser pulses is described. Using this method, high quality images of early plasma are obtained with high temporal and spatial resolutions. A novel integrated atomistic model is used to simulate and explain the mechanisms of early plasma.

Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a ...

Fabrication of Spatially Confined Complex Oxides

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from the inherent strong electron correlations that reside within them. These materials can also possess electronic phase separation in which regions of vastly different resistive and magnetic behavior can coexist within a single crystal alloy material. By reducing the scale of these materials to length scales at and below the inherent size of the electronic domains, novel behaviors can be exposed. Because of this and the fact that spin-charge-lattice-orbital order parameters each involve correlation lengths, spatially reducing these materials for transport measurements is a critical step in understanding the fundamental physics that drives complex behaviors. These materials also offer great potential to become the next generation of electronic devices 1-3. Thus, the fabrication of low dimensional nano- or micro-structures is extremely important to achieve new functionality. This involves multiple controllable processes from high quality thin film growth to accurate electronic property characterization. Here, we present fabrication protocols of high quality microstructures for complex oxide manganite devices. Detailed descriptions and required equipment of thin film growth, photo-lithography, and wire-bonding are presented.

We describe the use of pulsed laser deposition (PLD), photolithography and wire-bonding techniques to create micrometer scale complex oxides devices. The PLD is utilized to grow epitaxial thin films. Photolithography and wire-bonding techniques are introduced to create practical devices for measurement purposes.

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from ...

Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent thermal evaporation, and it absorbs visible light strongly. However, for a long time the record power conversion efficiency of SnS solar cells remained below 2%. Recently we demonstrated new certified record efficiencies of 4.36% using SnS deposited by atomic layer deposition, and 3.88% using thermal evaporation. Here the fabrication procedure for these record solar cells is described, and the statistical distribution of the fabrication process is reported. The standard deviation of efficiency measured on a single substrate is typically over 0.5%. All steps including substrate selection and cleaning, Mo sputtering for the rear contact (cathode), SnS deposition, annealing, surface passivation, Zn(O,S) buffer layer selection and deposition, transparent conductor (anode) deposition, and metallization are described. On each substrate we fabricate 11 individual devices, each with active area 0.25 cm2. Further, a system for high throughput measurements of current-voltage curves under simulated solar light, and external quantum efficiency measurement with variable light bias is described. With this system we are able to measure full data sets on all 11 devices in an automated manner and in minimal time. These results illustrate the value of studying large sample sets, rather than focusing narrowly on the highest performing devices. Large data sets help us to distinguish and remedy individual loss mechanisms affecting our devices.

Tin sulfide (SnS) is a candidate material for Earth-abundant, non-toxic solar cells. Here, we demonstrate the fabrication procedure of the SnS solar cells employing atomic layer deposition, which yields 4.36% certified power conversion efficiency, and thermal evaporation which yields 3.88%.

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Fabrication of 1-D Photonic Crystal Cavity on a Nanofiber Using Femtosecond Laser-induced Ablation

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using femtosecond laser-induced ablation. We show that thousands of periodic nano-craters are fabricated on an optical nanofiber by irradiating with just a single femtosecond laser pulse. For a typical sample, periodic nano-craters with a period of 350 nm and with diameter gradually varying from 50 - 250 nm over a length of 1 mm are fabricated on a nanofiber with diameter around 450 - 550 nm. A key aspect of such a nanofabrication is that the nanofiber itself acts as a cylindrical lens and focuses the femtosecond laser beam on its shadow surface. Moreover, the single-shot fabrication makes it immune to mechanical instabilities and other fabrication imperfections. Such periodic nano-craters on nanofiber, act as a 1-D PhC and enable strong and broadband reflection while maintaining the high transmission out of the stopband. We also present a method to control the profile of the nano-crater array to fabricate apodized and defect-induced PhC cavities on the nanofiber. The strong confinement of the field, both transverse and longitudinal, in the nanofiber-based PhC cavities and the efficient integration to the fiber networks, may open new possibilities for nanophotonic applications and quantum information science.

We present a protocol for fabricating 1-D photonic crystal cavities on subwavelength diameter silica fibers (optical nanofibers) using femtosecond laser-induced ablation.

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

Production of Single Tracks of Ti-6Al-4V by Directed Energy Deposition to Determine the Layer Thickness for Multilayer Deposition

Directed Energy Deposition (DED), which is an additive manufacturing technique, involves the creation of a molten pool with a laser beam where metal powder is injected as particles. In general, this technique is employed to either fabricate or repair different components. In this technique, the final characteristics are affected by many factors. Indeed, one of the main tasks in building components by DED is the optimization of process parameters (such as laser power, laser speed, focus, etc.) which is usually carried out through an extensive experimental investigation. However, this sort of experiment is extremely lengthy and costly. Thus, in order to accelerate the optimization process, an investigation was conducted to develop a method based on the melt pool characterizations. In fact, in these experiments, single tracks of Ti-6Al-4V were deposited by a DED process with multiple combinations of laser power and laser speed. Surface morphology and dimensions of single tracks were analyzed, and geometrical characteristics of melt pools were evaluated after polishing and etching the cross-sections. Helpful information regarding the selection of optimal process parameters can be achieved by examining the melt pool features. These experiments are being extended to characterize the larger blocks with multiple layers. Indeed, this manuscript describes how it would be possible to quickly determine the layer thickness for the massive deposition, and avoid over or under-deposition according to the calculated energy density of the optimum parameters. Apart from the over or under-deposition, time and materials saving are the other great advantages of this approach in which the deposition of multilayer components can be started without any parameter optimization in terms of layer thickness.

In this research, a rapid method based on melt pool characterization is developed to estimate the layer thickness of Ti-6Al-4V components produced by directed energy deposition.

Directed Energy Deposition (DED), which is an additive manufacturing technique, involves the creation of a molten pool with a laser beam where metal ...

Generation and Coherent Control of Pulsed Quantum Frequency Combs

We present a method for the generation and coherent manipulation of pulsed quantum frequency combs. Until now, methods of preparing high-dimensional states on-chip in a practical way have remained elusive due to the increasing complexity of the quantum circuitry needed to prepare and process such states. Here, we outline how high-dimensional, frequency-bin entangled, two-photon states can be generated at a stable, high generation rate by using a nested-cavity, actively mode-locked excitation of a nonlinear micro-cavity. This technique is used to produce pulsed quantum frequency combs. Moreover, we present how the quantum states can be coherently manipulated using standard telecommunications components such as programmable filters and electro-optic modulators. In particular, we show in detail how to accomplish state characterization measurements such as density matrix reconstruction, coincidence detection, and single photon spectrum determination. The presented methods form an accessible, reconfigurable, and scalable foundation for complex high-dimensional state preparation and manipulation protocols in the frequency domain.

A protocol is presented for the practical generation and coherent manipulation of high-dimensional frequency-bin entangled photon states using integrated micro-cavities and standard telecommunications components, respectively.

We present a method for the generation and coherent manipulation of pulsed quantum frequency combs. Until now, methods of preparing high-dimensional ...