This work was funded by the Office of Naval Research (ONR) through the Naval Research Laboratory Basic Research Program.

1. Making Donor Substrates
<ol>
	<li>Mask the edges of a glass slide with tape leaving a central region of uncovered glass.</li>
	<li>Submerge the slide in Buffered HF (6:1 ratio of 40% NH4F in water to 48% HF in water) for 3-15 min. Note: This will etch the center of the slide which is unmasked, creating a well. The depth of the well should be between 1 and 5 &#181;m, which can be determined through a stylus profilometer or AFM using manufacturer&#39;s instructions.</li>
	<li>Remove the tape mask.</li>
</ol>
2. Creating the Ink Ribbon
<ol>
	<li>Spread a small amount of Ag paste at one side of the well. Ensure that there is enough to fill the well, roughly in the 10 mg range. It is not necessary to measure the amount first, however.</li>
	<li>Firmly drag a straight metal blade across the well, spreading a thin layer of paste across its entirety. Uniformly distribute the paste without any thin spots. The final product of this process &#8212; a small well containing Ag ink&#160;&#8212; is called the &#34;ribbon&#34;.</li>
	<li>Wipe away any paste that spread outside the well with a lab wipe.</li>
</ol>
3. Drying the Ribbon
<ol>
	<li>Place the ribbon face-up in a low-humidity environment. A box filled with dry nitrogen works best.</li>
	<li>Leave the ribbon for at least 2 hr at RT. At this point, the ink viscosity should be high enough to print. 
	Note: After sufficient drying, ink ribbons can be stored for roughly a month by placing the well face-down on another glass slide and storing it in a dry-nitrogen environment. Once stored this way, it is alright to leave the ink ribbons unattended for long periods of time.</li>
</ol>
4. Printing Voxels
<ol>
	<li>Attach the receiver substrate to an XY translational stage using a vacuum chuck or double-sided tape. Note: The receiver substrate must be flat, but there are no other limitations. Silicon wafers, glass slides, or 200 &#176;C compatible polymers are all acceptable receiver substrates.</li>
	<li>Place the ink ribbon face-down upon the receiver substrate.</li>
	<li>Focus the optical setup through the back of the donor substrate, onto the back surface of the ink within the well. 
	NOTE: There are many ways to arrange the optics for this process, but the following steps/components are necessary:
	<ol>
		<li>Use a pulsed UV laser with a beam having a &#34;top-hat&#34; spatial energy distribution (as opposed to Gaussian). Use a laser capable of controllably firing individual pulses, which may require an acousto-optic modulator. The acousto-optic modulator allows the user to control the firing of individual pulses.</li>
		<li>Pass the beam through an aperture, shaping the cross section of the beam into the desired shape. Note that the shape of the aperture determines the shape of the voxel. That is to say, the aperture is essentially imaged onto the donor substrate, analogous to mask projection.</li>
		<li>Use a microscopic objective to reduce the size of the beam cross section, which determines the size of the printed voxel. For example, if a 10X objective yields square voxels with 50 &#181;m lateral dimensions, then a 50X objective will print the same shape (square) voxels with 10 &#181;m lateral dimensions.</li>
		<li>Place a video camera in line (via beam splitter) with the microscopic objective. This allows active monitoring of the ink ribbon.</li>
	</ol>
	</li>
	<li>Fire a single laser pulse onto the donor substrate. A reasonable starting value for laser fluence is in the range of 40-60 mJ/cm2. Ensure that there is a visible hole in the shape of the laser beam cross section where the voxel was ejected. If the hole is not visible, there are several possible reasons:
	<ol>
		<li>Out of Focus.
		<ol>
			<li>Adjust the height of the focusing objective. This may bring the hole into focus.</li>
		</ol>
		</li>
		<li>Low Energy.
		<ol>
			<li>Slowly increase the energy of the laser up to a fluence of 60-80 mJ/cm2. Thicker ink ribbons may require high fluence values.</li>
		</ol>
		</li>
		<li>Ink Viscosity Too Low.
		<ol>
			<li>If a voxel is ejected but the hole in the ink ribbon immediately refills, then the ink viscosity is still too low, therefore dry the ribbon for another 30 min based on the instructions in step 3 and then begin step 4 again.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Move the XY translational stage along the X and Y axes to a new spot.</li>
	<li>Fire a single laser pulse onto the donor substrate again, ejecting a voxel and leaving a sharply-defined hole where the voxel was ejected from the ink ribbon.</li>
</ol>
5. Printing Complex Structures
<ol>
	<li>Create lines by linking together adjacent voxels in the following way:
	<ol>
		<li>Transfer a voxel as described in 4.1-4.4.</li>
		<li>Move the XY translational stage one voxel length along the X or Y direction.</li>
		<li>Transfer a voxel as described in 4.1-4.4.</li>
		<li>Repeat this process until a sufficiently long line is obtained.</li>
	</ol>
	</li>
	<li>Create bridging or cantilever structures in the following way:
	<ol>
		<li>Align the beam such that the ejected voxel will bridge a geometric gap on the donor substrate OR such that a portion of the voxel will overhang past the edge of a geometric gap.</li>
		<li>Transfer a voxel as described in 4.1-4.4. Note: If the paste viscosity is too low, the voxel may conform to the features beneath it instead of creating a bridge or cantilever.</li>
	</ol>
	</li>
	<li>Create high aspect ratio structures in the following way:
	<ol>
		<li>Transfer a voxel as described in 4.1-4.4.</li>
		<li>Without moving the receiver substrate, move the donor substrate to a fresh spot on the ink ribbon.</li>
		<li>Transfer a voxel as described in 4.1-4.4.</li>
		<li>Repeat steps 5.3.2 and 5.3.3 until a feature of sufficient height is obtained. If the structure is built taller than ~3-5 &#181;m, periodically insert spacers between the donor and receiver substrate so that the voxel stack and ink ribbon do not come into direct contact. Note that the optics will need to be refocused as described in section 4.4.1 to account for the change in donor substrate height.</li>
	</ol>
	</li>
</ol>
6. Printing Complex Images via DMD Chip
<ol>
	<li>Draw or upload image of desired voxel shape. Ensure that the format of the image file is a bitmap. Note: It is crucial to use the demagnification factor of the optical system to scale the drawing to the size of the voxel to be printed. The DMD essentially replaces the aperture, so instead of imaging the beam with what is essentially mask projection, an array of micromirrors is used to shape the beam.</li>
	<li>Select appropriate laser (UV or green).</li>
	<li>Turn on DMD and open DMD software.
	<ol>
		<li>Click &#34;Open Image&#34; and load bitmap pattern. Select Load and Reset.</li>
		<li>Click &#34;Add&#34;. Name of bitmap file should appear in the right panel.</li>
		<li>Click &#34;Run Once&#34;. Bitmap pattern is now loaded onto DMD.</li>
	</ol>
	</li>
	<li>Arrange the donor and receiver substrates as outlined in steps 4.1 to 4.3. Transfer ink as outlined in steps 4.4 to 4.6.</li>
	<li>Once transfers are successful, repeat steps 6.3 to 6.4 if needed; then proceed to step 7.</li>
</ol>
7. Furnace
Once all the voxels are printed, cure them in a furnace.
<ol>
	<li>Place the receiver substrate face-up in the furnace.</li>
	<li>Leave to cure at 180 &#176;C for 2 hr.</li>
</ol>

<ol>
	<li>Park, J. U., 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+electrohydrodynamic+jet+printing.">High-resolution electrohydrodynamic jet printing.</a> Nature Mater. 6, 782-789 (2007).</li><li>Hon, K. K. B., Li, L., Hutchings, I. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+writing+technology+-+Advances+and+developments.">Direct writing technology - Advances and developments.</a> CIRP Ann. 57, 601-620 (2008).</li><li>Calvert, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inkjet+Printing+for+Materials+and+Devices.">Inkjet Printing for Materials and Devices.</a> Chem. Mater. 13, 3299-3305 (2001).</li><li>Arnold, C. B., Serra, P., Piqu&#233;, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+direct-write+techniques+for+printing+of+complex+materials.">Laser direct-write techniques for printing of complex materials.</a> MRS Bulletin. 32, 23-31 (2007).</li><li>Park, J. U., 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+electrohydrodynamic+jet+printing.">High-resolution electrohydrodynamic jet printing.</a> Nature Mater. 6, 782-789 (2007).</li><li>Hon, K. K. B., Li, L., Hutchings, I. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+writing+technology+-+Advances+and+developments.">Direct writing technology - Advances and developments.</a> CIRP Ann. 57, 601-620 (2008).</li><li>Calvert, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inkjet+Printing+for+Materials+and+Devices.">Inkjet Printing for Materials and Devices.</a> Chem. Mater. 13, 3299-3305 (2001).</li><li>Arnold, C. B., Serra, P., Piqu&#233;, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+direct-write+techniques+for+printing+of+complex+materials.">Laser direct-write techniques for printing of complex materials.</a> MRS Bulletin. 32, 23-31 (2007).</li><li>Piqu&#233;, A., Auyeung, R. C. Y., Kim, H. K., Metkus, M., Mathews, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Digital+microfabrication+by+laser+decal+transfer.">Digital microfabrication by laser decal transfer.</a> J. Laser. Micro. Nanoeng. 3, 163-168 (2008).</li><li>Auyeung, R. C. Y., Kim, H., Birnbaum, A. J., Zalalutdinov, M., Mathews, S. A., Piqu&#233;, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+decal+transfer+of+freestanding+microcantilevers+and+microbridges.">Laser decal transfer of freestanding microcantilevers and microbridges.</a> Appl. Phys. A. 97, 513-519 (2009).</li><li>Kim, H., Melinger, J. S., Khachatrian, A., Charipar, N. A., Auyeung, R. C. Y., Piqu&#233;, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+terahertz+metamaterials+by+laser+printing.">Fabrication of terahertz metamaterials by laser printing.</a> Opt. Lett. 35, 4039-4041 (2010).</li><li>Wang, J., Auyeung, R. C. Y., Kim, H., Charipar, N. A., Piqu&#233;, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+printing+of+interconnects+by+laser+direct-write+of+silver+nanopastes.">Three-dimensional printing of interconnects by laser direct-write of silver nanopastes.</a> Adv. Mater. 22, 4462-4466 (2010).</li><li>Mathews, S. A., Auyeung, R. C. Y., Kim, H., Charipar, N. A., Piqu&#233;, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-speed+video+study+of+laser-induced+forward+transfer+of+silver+nano-suspensions.">High-speed video study of laser-induced forward transfer of silver nano-suspensions.</a> J. Appl. Phys. 114, 064910 (2013).</li><li>King, B. H., Dimos, D., Yang, P., Morissette, 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=Direct-write+fabrication+of+integrated,+multilayer+ceramic+components.">Direct-write fabrication of integrated, multilayer ceramic components.</a> J. Electroceram. 3, 173-178 (1999).</li><li>Lewis, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+ink+writing+of+3D+functional+materials.">Direct ink writing of 3D functional materials.</a> Adv. Funct. Mater. 16, 2193-2204 (2006).</li><li>Calvert, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inkjet+printing+for+materials+and+devices.">Inkjet printing for materials and devices.</a> Chem. Mater. 13, 3299-3305 (2001).</li><li>Kang, H., Soltman, D., Subramanian, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrostatic+Optimization+of+Inkjet-Printed+Films.">Hydrostatic Optimization of Inkjet-Printed Films.</a> Langmuir. 26, 11568-11573 (2010).</li><li>Piqu&#233;, 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=Laser+decal+transfer+of+electronic+materials+with+thin+film+characteristics.">Laser decal transfer of electronic materials with thin film characteristics.</a> Proc. SPIE. 6879, 687911 (2008).</li><li>Auyeung, R. C. Y., Kim, H., Birnbaum, A. J., Zalalutdinov, M., Mathews, S. A., Piqu&#233;, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+decal+transfer+of+freestanding+microcantilevers+and+microbridges.">Laser decal transfer of freestanding microcantilevers and microbridges.</a> Appl. Phys. A: Mater. Sci. Process. 97, 513-519 (2009).</li><li>Soltman, D., Smith, V., Kang, H., Morris, S. J. S., Subramanian, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methodology+for+inkjet+printing+of+partially+wetting+films.">Methodology for inkjet printing of partially wetting films.</a> Langmuir. 26, 15686-15693 (2010).</li><li>Auyeung, R. C. Y., Kim, H., Charipar, N., Birnbaum, A., Mathews, S., Piqu&#233;, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+forward+transfer+based+on+a+spatial+light+modulator.">Laser forward transfer based on a spatial light modulator.</a> Appl. Phys. A: Mater. Sci. Process. 102, 21-26 (2011).</li><li>Duocastella, M., Fernandez-Pradas, J. M., Serra, P., Morenza, 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=Jet+formation+in+the+laser+forward+transfer+of+liquids.">Jet formation in the laser forward transfer of liquids.</a> Appl. Phys. A: Mater. Sci. Process. 93, 453-456 (2008).</li><li>Feinaueugle, M., Alloncle, A. P., Delaporte, P., Sones, C. L., Eason, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-resolved+shadowgraph+imaging+of+femtosecond+laser-induced+forward+transfer+of+solid+materials.">Time-resolved shadowgraph imaging of femtosecond laser-induced forward transfer of solid materials.</a> Appl. Surf. Science. 258, 8475-8483 (2012).</li><li>Breckenfeld, E., Kim, H., Auyeung, R. C. Y., Charipar, N., Serra, P., Piqu&#233;, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser-induced+forward+transfer+of+silver+nanopaste+for+microwave+interconnects,+A.">Laser-induced forward transfer of silver nanopaste for microwave interconnects, A.</a> Appl. Surf. Science. 331, 254-261 (2015).</li></ol>

The authors have nothing to disclose.

In this paper, we have demonstrated a process for non-contact, three-dimensional printing as well as single-laser-shot, large area printing (via DMD chip) of high-viscosity Ag nanopaste. Unlike other direct-write techniques, such as inkjet, the LDT technique described here allows for the printing of complex voxel shapes with one laser pulse, i.e., in one single step. While many aspects of the procedure may seem straightforward, there are multiple steps that require iterative testing in order to optimize. First, paste dryness and viscosity are the most important factors for successful transfer. Although these points have been already been emphasized repeatedly in the text, we reiterate the point here to underline the importance. If the ink viscosity is too low, then it will be impossible to print sharp, well-defined voxel shapes. A telltale sign that the ink viscosity is too low occurs when attempting to eject a voxel. When the laser pulse is fired, the voxel will appear to momentarily eject, but the ink will fill back quickly in the hole left in the donor substrate. In this case, the user should stop firing the laser and the ink should be further treated as outlined in steps 3.1 and 3.2. If the ink viscosity is too high, the voxel transfer process will appear successful on the ribbon. However, when examining the voxels on the receiver substrate, there will be significant tearing, fracturing, or debris. In this case, the user needs to dispose of the current ribbon and make a new ribbon as outlined in section 2. Optimization of ink viscosity and drying time should be accomplished by evaluating the quality of voxel transfer attempts. We do not recommend trying to measure the viscosity of the paste at any point. Second, the laser fluence is almost as important as ink viscosity and very small changes in fluence can have a significant effect on the process. It should be very clear when the energy is too low&#160;&#8212; the voxel will not eject from the donor substrate. It is recommended to begin with the fluence range suggested in step 4.4, and then very incrementally increase the value. The lowest energy that results in a full transfer is called the &#34;threshold fluence&#34;. It is often best to operate at or near the threshold fluence because higher fluence values will tend to fracture or tear the voxels. Finally, depending on the variety of laser used for the process, there could be hot spots in the laser profile. This may require an adjustment of the aperture to sample a more homogeneous region of the beam. If the shape of the ejected voxel is warped or poorly matches the shape of the beam cross section, laser hotspots or ink layer thickness or uniformity could be responsible.
Beyond troubleshooting, there are a few limitations to the technique. The final furnace curing step makes it difficult or impossible to achieve voxels with the desired functional properties on non-high-temperature compatible substrates. Generally, the Ag nanopaste used in this manuscript requires a curing temperature of at least 150 &#176;C in order to obtain reasonable conductivity values. The fabrication of the ink layer on the donor substrate needs to be further optimized to improve thickness uniformity, areal coverage and processing time. The ink layer thickness has a dramatic effect on the threshold fluence and transfer quality, and inhomogeneous thickness can make the transfer process difficult, especially when transferring voxels smaller than 20 &#181;m x 20 &#181;m. The current design for the donor substrate makes it difficult to create ribbons larger than 10s of cm, which limits large-area throughput. Thus, the development of alternate donor substrate designs, such as reel-to-reel or rotating disc, would be required for enhanced automation and larger area processing.
The strength of the LDT technique lies in the ability to transfer fluids with high viscosities that other drop-on-demand techniques cannot handle. The advantages of LDT can be separated into two situations where firstly, printing high viscosity paste offers an improvement in quality or speed over printing low viscosity paste and secondly, in situations where printing with high viscosity paste enables structures that are not accessible to low viscosity printing. Examples of advantages in the first category are: minimal voxel variability from wetting effects, high degree of control over voxel shape and size, minimal shrinkage during curing, and low laser energy compared to other LIFT processes (and thus low transfer velocity). Examples in the second category are: printing of high-aspect-ratio structures, bridging structures, cantilevers, and any other structure that requires good voxel-shape-retention. By combining the LDT process with the DMD chip, parallel printing of complex shapes and patterns is enabled, which greatly speeds up the overall process. Furthermore, the use of a DMD to shape the voxels allows designs to be updated between laser pulses, enabling rapid printing of dynamically reconfigurable voxels. Generally speaking, the refresh rate of the DMD (33 kHz) is slightly slower than the max repetition rate of the laser (100 kHz or higher), but the rate limiting factor for printing speed is the stage translation.
The primary avenues for advancement with the LDT system are the continued development of additional materials, improving the ribbon fabrication process, and continuing to scale up the process through integrating digital light processing (DLP) technology such as the DMD chip. Although metallic and insulating materials have been successfully transferred through this process, few active materials have been developed. The ability to print piezoelectric, magnetic, or optoelectronic materials with the LDT process could open up enormous technological possibilities. As it stands, the geometry of the donor substrate limits scalability. The development of reel-to-reel or rotating disc donor substrates would streamline the processes considerably. Finally, combination of LDT with DLP technology is a potentially disruptive development for the field of digital fabrication, turning a previously serial process into a highly parallel process. A key challenge toward this goal is the ability to print voxels with good feature resolution at multiple scales. That is to say, voxels with lateral dimensions on the order of 10 sec or 100 sec of &#181;m containing features on the order of 1-5 &#181;m. Taken together, these developments offer significant opportunities for large-area additive manufacturing of electronic components.

Additive printing techniques are of considerable interest for the patterning of functional materials onto a variety of substrates. These so-called &#34;direct-write&#34; processes, including micropen10, direct-write assembly11, inkjet12, and LIFT4, are well suited for the fabrication of a variety of feature sizes ranging from sub-micron to macroscale1,2. The primary advantages of these techniques are low cost, environmental friendliness, and fast turnaround from concept to prototype. Indeed, rapid prototyping is a primary use for such processes. The materials utilized by these processes typically consist of a nanoparticle suspension within a solvent, and generally require a furnace curing step after deposition in order to realize their functional properties. Although micropen and direct-write assembly are relatively simple to implement, both rely on a continuous filament contact with the receiving substrate during dispensing. Although inkjet is a simple, non-contact direct-write method, it is usually limited to the transfer of low viscosity, chemically benign nanoparticle suspensions in order to avoid clogging and/or corrosion of the dispensing nozzles. In addition, printing patterns with well-defined edge features by inkjet is very difficult given the variable behavior of fluids on different surfaces and their resulting instability due to wetting effects13. Regardless, inkjet has enjoyed the most attention from researchers thus far.
LIFT, on the other hand, is a non-contact, nozzle-free additive process which is capable of transferring high-viscosity paste with well-defined edges. In this process, controlled amounts of complex materials are transferred from a donor substrate (or &#34;ribbon&#34;) to a receiving substrate by using laser pulses4 as shown schematically in Figure 1. When using high viscosity paste, it is possible for the printed voxel to match the size and shape of the incident laser pulse cross section5. This process has been referred to as laser decal transfer (LDT), and offers a unique approach to direct-writing in which voxel shape and size are readily controllable parameters, allowing the non-lithographic generation of structures for a wide range of applications such as circuit repair14, metamaterials7, interconnects8, and free-standing structures15. The ability to deposit complex shapes in one transfer step greatly reduces the processing time and avoids problems related to the merging of multiple voxels, a common problem in most digital printing techniques. The ability to dynamically adjust the spatial profile of individual laser pulses17 serves to increase the writing speed of LDT as compared to other laser direct write (LDW) techniques. As a result of these processing advantages, we refer to the LDT process as being &#34;partially parallelized&#34; since it allows the combination of multiple serial writing steps into a single parallel one. The degree of parallelization ultimately depends on the ability to rapidly alter the laser cross-section profile, and therefore the shape of the resultant voxel, and on the speed by which the ribbon and substrate can be translated.
To help visualize the process, the behavior of a material during the LIFT process is depicted schematically in Figures 2A, 2C, and 2E for three different paste viscosities. For low viscosity inks (Figure 2A)9, the transfer process follows jetting behavior, resulting in the formation of rounded, hemispherical voxels (Figure 2B)18. Figure 2C depicts the transfer for very high viscosity suspensions, in which the ejected voxel experiences fragmentation similar to what is observed with LIFT of solid ceramic layers19. Figure 2E depicts the LDT transfer of nanopaste with a suitable, intermediate viscosity, wherein the released voxel is not subject to shape deformation due to surface tension effects and reaches the receiving substrate intact. The effect of viscosity on the shape of the transferred voxels is shown in the atomic force microscopy (AFM) images in Figures 2B, 2D, and 2F. As Figure 2F demonstrates, it is possible to obtain sharp, well-defined voxels for an appropriate range of viscosities, usually ~100 Pa&#183;sec for Ag nanopaste5.
Overall, there have been few reports of methods that combine non-contact printing with the potential for micron resolution 3D structures. The LDT method offers a freeform process capable of fabricating interconnects with ultra-fine pitch bonding capabilities. A number of applications including delicate electronic devices, organic electronics, and microelectromechanical systems (MEMS) could benefit from such a process. Here we demonstrate a process for non-contact, three-dimensional printing as well as single-laser-shot, large area printing (via DMD chip) of high-viscosity Ag nanopaste.

<table border="0" cellpadding="0" cellspacing="0" width="1206">
	<tbody>
		<tr height="84">
			<td height="84" style="height:84px;width:248px;">Silver Nano-paste for Screen Printing</td>
			<td style="width:171px;">Harima Chemicals Group, http://www.harima.co.jp/en/</td>
			<td style="width:119px;">NPS Type HP</td>
			<td style="width:669px;">Store at 10 C, do not allow to freeze; before using, wait 1 hour for paste to reach room temperature</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:248px;">Buffered HF Solution</td>
			<td style="width:171px;">http://transene.com/sio2/</td>
			<td style="width:119px;">BUFFER HF IMPROVED</td>
			<td>Etch rate may vary depending on material structure</td>
		</tr>
	</tbody>
</table>

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.

Figure 3 shows a representative donor substrate with a well in its center. A standard glass slide was used for the donor substrate, and the depth of the well in this case is 1 &#181;m. Note that all of the Ag nanopaste is confined to the rectangular well and the rest of the substrate is clean. It is also important to note that the coloration is uniform, indicating roughly uniform paste thickness. Regions with lighter coloration indicate thin spots, which are best avoided. Figure 4 shows a 20X optical image of the donor substrate after a 6x6 array of 20 &#181;m x 20 &#181;m square voxels have been ejected. In this ideal case, there is no paste residue in the gaps and all voxels were fully ejected from the ribbon. If the energy is insufficient or if there are significant hotspots in the beam profile, voxels will only partially detach and remain stuck to the backside of the ribbon.
Voxels ejected from pastes with different viscosities can be found in Figure 59. When the paste viscosity is low, i.e., has not been sufficiently dried, surface tension will cause the voxels to become more rounded, losing their original shape (as seen in Figure 5A and B). Note how the shapes of the voxels in Figure 5B are different from the beam shapes (displayed in the inset of Figure 5B). On the other extreme, when the paste viscosity is high, i.e., has been over-dried, voxels have a tendency to fracture when ejected as seen in Figure 5C and D. Thus, there is an intermediate viscosity range which allows transfer of unfractured voxels that retain the shape of the beam profile as seen in Figure 5E and F. We demonstrate two varieties of voxel chains which form long conductive lines. The first was a simple end-to-end chain in which 40 x 60 &#181;m2 voxels were transferred adjacent to one another (Figure 6A and B)20. Generally, this linking method was somewhat unreliable, with partially or completely broken interfaces appearing after a soft cure at 100 &#176;C (as seen in Figure 6B). The second method used notched, interlocking voxels transferred end-to-end (Figure 6C and D). The dotted lines in Figure 6C outline the original shape of the voxels, as the high quality of the interface makes it difficult to visually resolve the individual shapes. This effect is very clear in Figure 6D, where the seam between voxels is nearly invisible. The notched geometry was more reliable than the simple end-to-end, with nearly all interfaces remaining continuous after a 100 &#176;C cure. Figure 7 demonstrates various stacking geometries, patterns and aspect ratios. A single voxel traversing a 100 &#181;m wide Si trench can be found in Figure 7A. Obtaining the right viscosity is of the utmost importance for bridging or freestanding applications in order to prevent the voxel from sagging or conforming to the geometry of the receiver substrate. Complex, multi-layer structures can be seen in Figure 7B-D, including two stacked pyramids and high aspect ratio micro pillars. These geometries are important for applications requiring vertical and spanning interconnects. Finally, Figure 8A shows an alternate optical setup which uses a commercial DMD chip, referred to as a &#34;digital mirror device&#34; in the diagram. As described in step 6, large, complex images can be loaded onto the computer and transferred with a single laser pulse. A successfully printed NRL logo can be found in Figure 8B. We note that with a single shot, we can transfer a paste structure with a length of 1 mm and a feature resolution of ~20 &#181;m.
<img alt="Figure 1" src="/files/ftp_upload/53728/53728fig1.jpg" /> 
Figure 1. Schematic diagram of LDT setup. Note that the voxel shape is determined by the cross-sectional beam shape only for high-viscosity ink. <a href="https://www.jove.com/files/ftp_upload/53728/53728fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53728/53728fig2.jpg" /> 
Figure 2. Schematic diagram voxel ejection. Diagrams illustrate evolution of transfer for (A) low viscosity, (C) high viscosity, and (E) intermediate viscosity. AFM plots of the resultant voxels are provided in (B), (D), and (F), respectively. This figure has been modified from [9]. <a href="https://www.jove.com/files/ftp_upload/53728/53728fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53728/53728fig3.jpg" /> 
Figure 3. Picture of Ag nanopaste donor substrate. The substrate itself is a glass slide with a 1 &#181;m deep well in the center. <a href="https://www.jove.com/files/ftp_upload/53728/53728fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/53728/53728fig4.jpg" /> 
Figure 4. 20X optical image of the paste layer on the ribbon (donor substrate) after voxel transfer. Sharp, well-defined edges and lack of residue indicate sufficient paste drying and complete transfer of material from the ribbon. <a href="https://www.jove.com/files/ftp_upload/53728/53728fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/53728/53728fig5.jpg" /> 
Figure 5. Scanning electron microscopy (SEM) images of several different voxels. Beam profiles are depicted in the inset (B). Three different voxel shapes were printed from low viscosity (A,B), high viscosity (C,D), and intermediate viscosity (E,F). Note that low viscosity leads to a loss of shape and voxel sharpness while high viscosity leads to voxel fracturing. This figure has been modified from [9]. <a href="https://www.jove.com/files/ftp_upload/53728/53728fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/53728/53728fig6.jpg" /> 
Figure 6. SEM images of conjoined voxel chains. Two linking geometries are depicted: simple end-to-end (A,B) and notched-interlocking (C,D). In general, notched-interlocking geometries are found to be more reliable while simple end-to-end have a tendency to crack due to shrinkage during the furnace steps. This figure has been modified from [20]. <a href="https://www.jove.com/files/ftp_upload/53728/53728fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/53728/53728fig7.jpg" /> 
Figure 7. SEM images of multiple complex voxel structures. Geometries include: A rectangular voxel bridging a 100 &#181;m wide trench (A), a multilayer scaffold (B), a high aspect ratio pyramid (C), and several high aspect ratio micro pillars (D). This figure has been modified from [8]. <a href="https://www.jove.com/files/ftp_upload/53728/53728fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" src="/files/ftp_upload/53728/53728fig8.jpg" /> 
Figure 8. Schematic diagram and results of LDT via DMD chip. In the schematic diagram (A), the laser aperture has been replaced with the DMD chip, which is a large assembly of micro-mirrors. The pattern from an image file can be faithfully imaged onto the donor substrate, ejecting an exact replica of the pattern of voxels in a single shot. As an example, an NRL logo (B) has been transferred by a single laser shot. <a href="https://www.jove.com/files/ftp_upload/53728/53728fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Laser-induced Forward Transfer of Ag Nanopaste at JoVE.com

Laser-induced Forward Transfer of Ag Nanopaste

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 ...

laser-induced-forward-transfer-of-ag-nanopaste

Research

JoVE Journal

Engineering

11.2K Views.  Naval Research Laboratory. 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.

Video: Laser-induced Forward Transfer of Ag Nanopaste

Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement is used. Here we operate a Nd:YAG laser at a frequency of 10 Hz at the fundamental wavelength of 1,064 nm. The 14 nsec pulses with anenergy of 190 mJ/pulse are focused to a 50 &#181;m spot size to generate a plasma from optical breakdown or laser ablation in air. The microplasma is imaged onto the entrance slit of a 0.6 m spectrometer, and spectra are recorded using an 1,800 grooves/mm grating an intensified linear diode array and optical multichannel analyzer (OMA) or an ICCD. Of interest are Stark-broadened atomic lines of the hydrogen Balmer series to infer electron density. We also elaborate on temperature measurements from diatomic emission spectra of aluminum monoxide (AlO), carbon (C2), cyanogen (CN), and titanium monoxide (TiO).
The experimental procedures include wavelength and sensitivity calibrations. Analysis of the recorded molecular spectra is accomplished by the fitting of data with tabulated line strengths. Furthermore, Monte-Carlo type simulations are performed to estimate the error margins. Time-resolved measurements are essential for the transient plasma commonly encountered in LIBS.

Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown

Time-resolved atomic and diatomic molecular species are measured using LIBS. The spectra are collected at various time delays following the generation of optical breakdown plasma with Nd:YAG laser radiation&#160;and are analyzed to infer electron density and temperature.

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement ...

Laser-induced Breakdown Spectroscopy: A New Approach for Nanoparticle's Mapping and Quantification in Organ Tissue

Emission spectroscopy of laser-induced plasma was applied to elemental analysis of biological samples. Laser-induced breakdown spectroscopy (LIBS) performed on thin sections of rodent tissues: kidneys and tumor, allows the detection of inorganic elements such as (i) Na, Ca, Cu, Mg, P, and Fe, naturally present in the body and (ii) Si and Gd, detected after the injection of gadolinium-based nanoparticles. The animals were euthanized 1&#160;to 24 hr&#160;after intravenous injection of particles. A two-dimensional scan of the sample, performed using a motorized micrometric 3D-stage, allowed the infrared laser beam exploring the surface with a lateral resolution less than 100 &#956;m. Quantitative chemical images of Gd element inside the organ were obtained with sub-mM sensitivity. LIBS offers a simple and robust method to study the distribution of inorganic materials without any specific labeling. Moreover, the compatibility of the setup with standard optical microscopy emphasizes its potential to provide multiple images of the same biological tissue with different types of response:&#160;elemental, molecular, or cellular.

Laser-induced breakdown spectroscopy performed on thin organ and tumor tissue successfully detected natural elements and artificially injected gadolinium (Gd), issued from Gd-based nanoparticles. Images of chemical elements reached a resolution of 100 &#956;m and quantitative sub-mM sensitivity. The compatibility of the setup with standard optical microscopy emphasizes its potential to provide multiple images of a same biological tissue.

Emission spectroscopy of laser-induced plasma was applied to elemental analysis of biological samples. Laser-induced breakdown spectroscopy (LIBS) ...

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO2-Ag nanowires with a diameter of 200 nm and a length of 6-20 &#181;m were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO2 phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO2-Ag nanowires, a TiO2 gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO2 gel resulted in the formation of crystalline TiO2 nanotubes. A subsequent Ag electrodeposition step inside the TiO2 nanotubes resulted in formation of coaxial TiO2-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO2) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H2 gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min&#160;of illumination, approximately 0.2 vol% H2 gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Procedures are outlined to prepare segmented and coaxial nanowires via templated electrodeposition in nanopores. As examples, segmented nanowires consisting of Ag and ZnO segments, and coaxial nanowires consisting of a TiO2 shell and a Ag core were made. The nanowires were used in photocatalytic hydrogen formation experiments.

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and ...

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 ...

Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly known as plasmonic effects, play an important role. Research in this field has, however, been impeded owing to the difficulty of fabricating devices containing the desired functional metal nanostructures. In order to provide a viable strategy to this issue, we herein show a transfer printing-based approach that allows the quick and low-cost integration of designed metal nanostructures with a variety of device architectures, including solar cells. Nanopillar poly(dimethylsiloxane) (PDMS) stamps were fabricated from a commercially available nanohole plastic film as a master mold. On this nanopatterned PDMS stamps, Ag films were deposited, which were then transfer-printed onto block copolymer (binding layer)-coated hydrogenated microcrystalline Si (&#181;c-Si:H) surface to afford ordered Ag nanodisk structures. It was confirmed that the resulting Ag nanodisk-incorporated &#181;c-Si:H solar cells show higher performances compared to a cell without the transfer-printed Ag nanodisks, thanks to plasmonic light trapping effect derived from the Ag nanodisks. Because of the simplicity and versatility, further device application would also be feasible thorough this approach.

A viable transfer printing-based methodology to introduce plasmonic metal nanostructures in solar cells is described. Using nanopillar poly(dimethylsiloxane) stamps, an Ag-based ordered nanodisk array was integrated with standard hydrogenated microcrystalline Si solar cells, which led to improved device performances due to plasmonic light trapping.

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly ...

Nanostructured Ag-zeolite Composites as Luminescence-based Humidity Sensors

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high external quantum efficiencies (EQE) and spans the whole visible spectrum. It has been recently reported that the UV excited luminescence of partially Li-exchanged sodium Linde type A zeolites [LTA(Na)] containing luminescent silver clusters can be controlled by adjusting the water content of the zeolite. These samples showed a dynamic change in their emission color from blue to green and yellow upon an increase of the hydration level of the zeolite, showing the great potential that these materials can have as luminescence-based humidity sensors at the macro and micro scale. Here, we describe the detailed procedure to fabricate a humidity sensor prototype using silver-exchanged zeolite composites. The sensor is produced by suspending the luminescent Ag-zeolites in an aqueous solution of polyethylenimine (PEI) to subsequently deposit a film of the material onto a quartz plate. The coated plate is subjected to several hydration/dehydration cycles to show the functionality of the sensing film.

A protocol for the synthesis of moisture-responsive luminescent Ag-zeolite composites is described in this report.

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high ...

Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed that, under the proper conditions, ice can be produced when water is introduced to a bath of cold brine. To make ice form, in addition to having the brine and water mix, the rate of heat transfer must bypass that of mass transfer. When water is introduced in the form of tiny droplets to the brine surface, the mode of heat and mass transfer is by diffusion. The buoyancy stops water from mixing with the brine underneath, but as the ice grows thicker, it slows down the rate of heat transfer, making ice more difficult to grow as a result. When water is introduced inside the brine in the form of a flow, a number of factors are found to influence how much ice can form. Brine temperature and concentration, which are the driving forces of heat and mass transfer, respectively, can affect the water-to-ice conversion ratio; lower bath temperatures and brine concentrations encourage more ice to form. The flow rheology, which can directly affect both the heat and mass transfer coefficients, is also a key factor. In addition, the flow rheology changes the area of contact of the flow with the bulk fluid.

Here, we present a protocol to demonstrate the generation of ice when water is introduced to a cold bath of brine, as a secondary refrigerant, at a range of temperatures well below the freezing point of water. It can be used as an alternative way of producing ice for industry.

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed ...

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 ...

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool-boiling heat-transfer experiments were carried out to observe the effects of hybrid wettable patterns on the heat-transfer coefficient (HTC). The parameters of investigation are the number of interlines and the pattern orientation of the modified wettable surface.

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360&#176; rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

This protocol describes the scanning light scattering profiler (SLSP) that enables the full-angle quantitative evaluation of forward and backward scattering of light from intraocular lenses (IOLs) using goniophotometer principles.

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light ...