The authors are grateful to the University of California and the NANO3 facility at UC San Diego for provision of funds and facilities in support of this work. This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI) of UCSD, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (Grant ECCS&#8722;1542148). The work presented here was generously supported by a research grant from the W.M. Keck Foundation. The authors are also grateful for the support of this work by the Office of Naval Research (via Grant 12368098).

1. Thickness mode transducer fabrication via DC sputtering
<ol>
	<li>Wafer preparation
	<ol>
		<li>Place a 100 mm 128YX LN wafer in a clean glass dish of at least 125 mm diameter. Sonicate the wafer in at least 200 mL of acetone for 5 min.</li>
		<li>Repeat sonication with isopropyl alcohol and again with deionized water for 5 min each.</li>
		<li>Remove visible water from the surface using dry nitrogen.</li>
		<li>Completely remove water from the surface by placing the wafer on a hotplate at 100 &#176;C for 5 min. Ensure that there is a sheet of aluminum foil on the hotplate as this helps in dissipation of charge buildup on the wafer.</li>
	</ol>
	</li>
	<li>Electrode deposition
	<ol>
		<li>Place the wafer in the vacuum chamber of the sputter deposition system and pump down the chamber to 5 x 10-6 mTorr. Set the argon pressure to 2.3 mTorr and the rotation speed to 13 rpm. 
		NOTE: If parameters for the speci&#64257;c instrument being used have been established that result in high quality &#64257;lms, then use those instead.</li>
		<li>Deposit 5&#8722;10 nm of titanium at 1.2&#8722;1.6 A/s. 
		NOTE: Before beginning this process with the intended wafer, test the deposition rate with the plasma power set to 200 W and depositing for 1 min. Then measure the height of the layer with a pro&#64257;lometer. Do this separately for each metal. Set the power according to this test in order to achieve the stated deposition rate.</li>
		<li>Deposit 1-1.2 &#181;m of gold at 7&#8722;9 A/s. 
		NOTE: Deposition at a higher rate due to increased plasma power or increased argon partial pressure may reduce &#64257;lm quality.</li>
		<li>Remove the wafer and repeat steps 1.2.1&#8722;1.2.3 for the second side of the wafer.</li>
	</ol>
	</li>
	<li>Dicing
	<ol>
		<li>Use a dicing saw to dice the entire wafer as needed. 
		NOTE: A protective resist can be applied on the substrate prior to dicing, and the system (Table of Materials) used here applies a UV curable &#64257;lm just before the samples are loaded on the dicing stage. It is found that dicing the samples with an automated dicing saw does not compromise the integrity of the samples. Hand-scribe dicing of LN is possible, though tedious and prone to inconsistencies.</li>
	</ol>
	</li>
</ol>
2. Making electrical and mechanical contact with the transducer
NOTE: Several methods are described below (steps 2.1&#8722;2.4), and it is highlighted later in the protocol which method is most appropriate for each subsequent step.
<ol>
	<li>Place a diced transducer &#64258;at on a magnetic steel plate. Mount one pogo-probe in contact with the plate and another pogo-probe in contact with the top surface of the transducer. Hereafter this will be referred to as pogo-plate contact.</li>
	<li>Place the transducer between two pogo-probes. Hereafter referred to as pogo-pogo contact.</li>
	<li>Solder wire to each face of the transducer. Hereafter referred to as solder contact.</li>
	<li>Assemble a custom transducer holder.
	<ol>
		<li>Order the custom printed circuit boards (PCBs) whose Gerber &#64257;les have been provided.</li>
		<li>Solder two surface mount spring contacts(Table of Materials) to each custom PCB. Press &#64257;t the spikes into the plated holes on the custom PCBs such that they point away from each other.</li>
		<li>Connect the two custom PCBs with board spacers and screws so that the contacts are just in contact with each other. Adjust the spacing with plastic washers if necessary.</li>
		<li>Slide a 3 mm x 10 mm transducer in between the inner pair of contacts. Clip the outer contacts so they do not short the circuit. 
		NOTE: Figure 1 shows the entire assembly.</li>
	</ol>
	</li>
</ol>
3. Resonance frequency identi&#64257;cation via impedance analysis
<ol>
	<li>Ensure that a port calibration has been performed according to the manufacturer&#8217;s instructions for the speci&#64257;c contact method being used.</li>
	<li>Connect a transducer to the open port of the network analyzer (Table of Materials) with one of the contact methods described in steps 2.1&#8722;2.4. 
	NOTE: It can be instructive to repeat this analysis with multiple electrical contact methods and compare the results.</li>
	<li>Select the re&#64258;ection coefficient parameter, s11, via the user interface of the network analyzer, choose the frequency range of interest, and perform the frequency sweep. 
	NOTE: s11 is the input re&#64258;ection coefficient and has a minimum value at the resonance frequency of operation. For a typical 500 &#181;m thick 128YX LN wafer, the primary resonance frequency will be near 7 MHz and the second harmonic will be near 21 MHz, as illustrated in Figure 2. The impedance plot in frequency space displayed on the instrument will exhibit local minima at the resonance frequencies.</li>
	<li>Export the data by selecting Save/Recall | Save Trace Data on the user interface for closer inspection using data processing software to identify the precise minima locations.</li>
</ol>
4. Vibration characterization via LDV
<ol>
	<li>Place a transducer in pogo-plate contact on the LDV stage. Connect the pogo-probe leads to the signal generator. Ensure that the objective in use is selected in the acquisition software (Table of Materials) and focus the microscope on the surface of the transducer.</li>
	<li>De&#64257;ne the scan points by selecting De&#64257;ne scan points or proceed to step 4.3 if performing a continuous scan.</li>
	<li>Select the Settings option and under the General tab, select either the FFT or Time option depending on whether the scan is being performed in frequency or time domain.&#160;Select the number of averages in this section. 
	NOTE: The number of averages affects scan time. Five averages for the transducers described in this protocol have shown to give sufficient signal/noise ratio.</li>
	<li>In the Channel tab, make sure that the Active boxes are checked, which correspond to the reference and re&#64258;ected signal from the transducer. Adjust the reference and incident channels by selecting a voltage value from the drop-down menu in order to obtain maximum signal strength from the substrate.</li>
	<li>In the Generator tab, if the measurement is carried out under single frequency signal, select Sine from the Waveform pull down list; if it is under a band signal, select MultiCarrierCW.</li>
	<li>Change the bandwidth and FFT lines in the Frequency tab to adjust the scan resolution for a frequency domain scan. Similarly, change the Sample Frequency in the Time tab when performing time domain measurements. 
	NOTE: The bandwidth typically used is 40 MHz and the number of FFT lines is 32,000. The presentation software (Table of Materials) can be used to process and analyze the data obtained from the scan. A typical displacement spectrum is provided in Figure 3.</li>
</ol>
5. Fluid supply
<ol>
	<li>Obtain a 25 mm long, 1 mm diameter wick composed of a bundle of &#64257;bers of a hydrophilic polymer designed to transport aqueous liquid across its length such as those available for plug-in air fresheners.&#160;Trim one end such that an off center point is formed.</li>
	<li>Insert the wick into a syringe tip with an inner diameter that provides a snug &#64257;t and a length that allows the wick to extend 1&#8722;2 mm beyond each end. Lock the tip onto a syringe with the desired capacity (1&#8722;10 mL).</li>
	<li>Mount the wick/syringe assembly such that the wick is 10&#176;&#8722;90&#176; from horizontal (depending on the desired atomization rate, which also depends on the applied voltage) and the tip of the wick is just in contact with the edge of the transducer as shown in Figure 1C.</li>
	<li>Fill the syringe with water and apply a continuous voltage signal (starting with 20 Vpp) at the resonance frequency determined using the impedance analyzer. Adjust the voltage level until the liquid is atomized continuously without the device &#64258;ooding or drying out.</li>
</ol>
6. Dynamics observation via high-speed imaging
<ol>
	<li>Rigidly mount a high-speed camera horizontally on an optical table, place a transducer in either pogo-pogo contact or pogo-plate contact on an x-y-z stage near the focal length of the camera, and position a diffuse light source at least one focal length on the opposite side of the transducer from the camera.</li>
	<li>For pogo-pogo contact, position the &#64258;uid supply so that it does not block the camera view or the light source. For pogo-plate contact, apply &#64258;uid directly to the substrate with a pipette.</li>
	<li>Adjust the camera focus and the x-y-z position to bring the &#64258;uid sample into sharp focus.</li>
	<li>Estimate the frequency of the speci&#64257;c phenomenon to be studied based on literature. Choose a frame rate at least twice as large as this frequency according to the Nyquist rate in order to avoid aliasing. 
	NOTE: For example, consider capillary waves that occur on a sessile drop at a range of frequencies. Cameras limited in spatial resolution can only distinguish waves with a minimum amplitude. In this case the minimum amplitude occurs around 4 kHz so a frame rate of 8,000 frames per second (fps) is chosen.</li>
	<li>Adjust the light intensity, the camera shutter, or both in order to optimize contrast between the &#64258;uid and the background. 
	NOTE: An opaque dye can be added to the &#64258;uid in order to increase the contrast.</li>
	<li>Connect alligator clips from the ampli&#64257;ed signal generator to the pogo-probes leads.</li>
	<li>Capture video in the camera software simultaneously with actuation via the voltage signal either by manually triggering both at the same time or by connecting a trigger output from the signal generator to the camera. 
	NOTE: The typical frame rate used is 8,000 fps and a CF4 objective is used.</li>
	<li>Save only the frames containing the phenomenon to avoid wasted storage, which is particularly relevant at large frame rates, to produce a result as shown in Figure 4. 
	NOTE: Make sure to save the &#64257;le in a format that is compatible with the image processing software of choice so that useful data can be extracted.</li>
</ol>
7. Droplet size measurement via laser scattering analysis
<ol>
	<li>The laser scattering system (Table of Materials) has a module that transmits the laser and one that receives the scattered laser signal. Position the modules along the rail provided with the system, with a 20&#8722;25 cm gap between them.</li>
	<li>Rigidly mount a platform in this gap such that, when the transducer and &#64258;uid supply assemblies are placed on it, atomized mist will be ejected into the laser beam path. Facilitate this alignment by turning on the laser beam via&#160;selecting Tools | Laser Control... | Laser on as a visual indicator.</li>
	<li>Fix the transducer holder to the platform and &#64257;x the &#64258;uid supply assembly to an articulated arm (Table of Materials). Position the &#64258;uid supply assembly so that the tip of the wick is just in contact with the edge of the transducer.</li>
	<li>Create a standard operating procedure (SOP) in the software by clicking the New SOP icon. Con&#64257;gure the SOP with the following settings: template = Default continuous, sampling period (s) = 0.1, under Data handling, click Edit... and set Spray pro&#64257;le | Path length (mm) to 20.0, click Alarms to uncheck Use default values and set Min transmission (%) to 5 and 1 and set Min scattering to 50 and 10. Leave all other settings as defaults. 
	NOTE: Consult the software manual that came with the instrument.</li>
	<li>Start the measurement within the software by clicking Measure | Start SOP and selecting the SOP created in step 7.4. Wait for background calibrations to complete. Fill the &#64258;uid supply reservoir, the syringe, with water up to the desired level and note the volume. Turn on the voltage signal to begin atomizing the &#64258;uid. Start the stopwatch and start the measurement by clicking Start.</li>
	<li>The software generates a size distribution based on the scattered laser signal at the receiver due to Mie theory and a multiple scattering algorithm. Once the desired volume of &#64258;uid has been atomized, turn off the voltage signal, stop the stopwatch, and record the &#64257;nal volume, and stop recording data by clicking Stop. 
	NOTE: The laser scattering system is capable of measuring as little as 1 &#956;L of fluid and does not have an upper limit for fluid volume. The atomization &#64258;ow rate can simply be calculated by dividing the volume by the time duration.</li>
	<li>In the measurement histogram, select the portion of the data during which the atomization was occurring as expected and the signal at the receiver was strong enough to be statistically significant. Click Average | Ok to generate a distribution based on the selected data. 
	NOTE: All measurements with this technique are statistical averages and thus, if there are too few droplets, then the scattered signal will be weak, and the measurement will be statistically insigni&#64257;cant.</li>
	<li>Save the average distribution&#160;by selecting the window and clicking Edit | Copy text then pasting the result in a text &#64257;le and saving with an appropriate name. 
	NOTE: This distribution data can now be used with other software (e.g., MATLAB) to create the plot in Figure 5.</li>
</ol>

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The authors have nothing to disclose.

The dimensions and aspect ratio of a transducer affects the vibration modes it produces. Because the lateral dimensions are &#64257;nite, there are always lateral modes in addition to the desired thickness modes. The above LDV methods can be used to determine dominant modes in the desired frequency range for a given transducer. A square with dimensions below 10 mm typically gives a close approximation to a thickness mode. Three by ten millimeter rectangles also work well. Movie 1 and Movie 2</str...

Ultrasound atomization has been studied for almost a century and although there are many applications, there are limitations in understanding the underlying physics. The &#64257;rst description of the phenomenon was made by Wood and Loomis in 19271, and since then there have been developments in the &#64257;eld for applications ranging from delivering aerosolized pharmaceutical &#64258;uids2 to fuel injection3. Although the phenomenon works well in these applications, the underlying physics is not well understood4,5,6.
A key limitation in the &#64257;eld of ultrasonic atomization is the choice of material used, lead zirconate titanate (PZT), a hysteretic material prone to heating7 and lead contamination with elemental lead available from the inter-grain boundaries8,9. Grain size and mechanical and electronic properties of grain boundaries also limit the frequency at which PZT can operate10. By contrast, lithium niobate is both lead-free and exhibits no hysteresis11, and can be used to atomize &#64258;uids an order of magnitude more efficiently than commercial atomizers12. The traditional cut of lithium niobate used for operation in the thickness mode is the 36-degree Y-rotated cut, but the 127.86-degree Y-rotated, X-propagating cut (128YX), typically used for surface acoustic wave generation, has been shown to have a higher surface displacement amplitude in comparison with the 36-degree cut13 when operated in resonance and low loss. It has also been shown that thickness mode operation offers an order of magnitude improvement in atomizer efficiency over other modes of vibration13, even when using LN.
The resonance frequency of a piezoelectric device operating in the thickness mode is governed by its thickness t: the wavelength &#955; = 2t/n where n = 1, 2,... is the number of anti-nodes. For a 500 &#181;m thick substrate, this corresponds to a wavelength of 1 mm for the fundamental mode, which can then be used to calculate the fundamental resonance frequency, f = v/&#955; if the wave speed, v, is known. The speed of sound through the thickness of 128YX LN is approximately 7,000 m/s, and so f = 7 MHz. Unlike other forms of vibration, particularly surface-bound modes, it is straightforward to excite higher-order thickness mode harmonics to much higher frequencies, here to 250 MHz or more, though only the odd-numbered modes may be excited by uniform electric &#64257;elds14. Consequently, the second harmonic (n = 2) near 14 MHz cannot be excited, but the third harmonic at 21 MHz (n = 3) can. Fabrication of efficient thickness mode devices requires depositing electrodes onto opposing faces of the transducer. We use direct current (DC) sputtering to accomplish this, but electron-beam deposition and other methods could be used. Impedance analysis is useful to characterize the devices, particularly in &#64257;nding the resonance frequencies and electromechanical coupling at these frequencies. Laser Doppler vibrometry (LDV) is useful to determine the output vibration amplitude and velocity without contact or calibration15, and, via scanning, the LDV provides the spatial distribution of surface deformation, revealing the mode of vibration associated with a given frequency. Finally, for the purposes of studying atomization and &#64258;uid dynamics, high-speed imaging can be employed as a technique to study the development of capillary waves on the surface of a sessile drop16,17. In atomization, like many other acoustofluidic phenomena, small droplets are produced at a rapid rate, over 1 kHz in a given location, too quickly for high-speed cameras to observe with sufficient &#64257;delity and &#64257;eld of view to provide useful information over a sufficiently large droplet sample size. Laser scattering may be used for this purpose, passing the droplets through an expanded laser beam to (Mie) scatter some of the light in re&#64258;ection and refraction to produce a characteristic signal that may be used to statistically estimate the droplet size distribution.
It is straightforward to fabricate piezoelectric thickness mode transducers, but the techniques required in device and atomization characterization have not been clearly stated in the literature to date, hampering progress in the discipline. In order for a thickness mode transducer to be effective in an atomization device, it must be mechanically isolated so that its vibration is not damped and it must have a continuous &#64258;uid supply with a &#64258;ow rate equal to the atomization rate so that neither desiccation nor &#64258;ooding occur. These two practical considerations have not been thoroughly covered in the literature because their solutions are the result of engineering techniques rather than pure scienti&#64257;c novelty, but they are nonetheless critical to studying the phenomenon. We present a transducer holder assembly and a liquid wicking system as solutions. This protocol offers a systematic approach to atomizer fabrication and characterization for facilitating further research in fundamental physics and myriad applications.

<table border="0" cellpadding="0" cellspacing="0" style="width:1452px;" width="1452">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Amplifier</td>
			<td style="width:345px;">Amplifier Research, Souderton, PA, USA</td>
			<td style="width:412px;">5U1000</td>
			<td style="width:483px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Articulating arm</td>
			<td style="width:345px;">Fisso, Zurich, Switzerland</td>
			<td style="width:412px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">CF4 Objective</td>
			<td style="width:345px;">Edmund Optics, Barrington, NJ, USA</td>
			<td></td>
			<td>Objective used for high speed imaging</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Dicing saw</td>
			<td style="width:345px;">Disco, Tokyo, Japan</td>
			<td>Disco Automatic Dicing Saw 3220</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Fiber Fragrance Diffuser Wick</td>
			<td style="width:345px;">Weihai Industry Co., Ltd., Weihai, Shandong, China</td>
			<td colspan="2">https://www.weihaisz.com/Fiber-Fragrance-Diffuser-Wick_p216.html</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">High Speed Camera</td>
			<td style="width:345px;">Photron, San Diego, USA</td>
			<td style="width:412px;">Fastcam Mini</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Laser Doppler Vibrometer</td>
			<td style="width:345px;">Polytec, Waldbronn, Germany</td>
			<td style="width:412px;">UHF120</td>
			<td>Non-contact laser doppler vibrometer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:212px;">Laser Scattering Droplet size measurement system</td>
			<td style="width:345px;">Malvern Panalytical, Malvern, UK</td>
			<td style="width:412px;">STP5315</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Lithium niobate substrate</td>
			<td style="width:345px;">PMOptics,Burlington, MA, USA</td>
			<td style="width:412px;">PWLN-431232</td>
			<td style="width:483px;">4&#8221; double-side polished 0.5 mm thick 128&#176;Y-rotated cut lithium niobate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Luer-lock syringes</td>
			<td style="width:345px;">Becton Dickingson, New Jersey, USA</td>
			<td style="width:412px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Nano3 cleanroom facility</td>
			<td style="width:345px;">UCSD, La Jolla, CA, USA</td>
			<td style="width:412px;"></td>
			<td>Fabrication process is performed in it.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Network Analyzer</td>
			<td style="width:345px;">Keysight Technologies, Santa Rosa, CA, USA</td>
			<td style="width:412px;">5061B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Oscilloscope</td>
			<td style="width:345px;">Keysight Technologies, Santa Rosa, CA, USA</td>
			<td style="width:412px;">InfiniiVision 2000 X-Series</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">PSV Acquistion Software</td>
			<td style="width:345px;">Polytec, Waldbronn, Germany</td>
			<td style="width:412px;">Version 9.4</td>
			<td>LDV Software</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">PSV Presentation Software</td>
			<td style="width:345px;">Polytec, Waldbronn, Germany</td>
			<td style="width:412px;">Version 9.4</td>
			<td>LDV Software</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Signal generator</td>
			<td style="width:345px;">NF Corporation, Yokohama, Japan</td>
			<td style="width:412px;">WF1967 multifunction generator</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Single Post Connector</td>
			<td style="width:345px;">DigiKey, Thief River Falls, MN</td>
			<td>ED1179-ND</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Sputter deposition</td>
			<td style="width:345px;">Denton Vacuum, NJ, USA</td>
			<td style="width:412px;">Denton 18</td>
			<td>Denton Discovery 18 Sputter System</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Surface Mount Spring Contacts</td>
			<td style="width:345px;">DigiKey, Thief River Falls, MN</td>
			<td style="width:412px;">70AAJ-2-M0GCT-ND</td>
			<td style="width:483px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Teflon wafer dipper</td>
			<td style="width:345px;">ShapeMaster, Ogden, IL, USA</td>
			<td style="width:412px;">SM4WD1</td>
			<td>Wafer Dipper 4&#34;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">XYZ Stage</td>
			<td style="width:345px;">Thor Labs, Newton, New Jersey, USA</td>
			<td style="width:412px;">MT3</td>
			<td>Optical table stages</td>
		</tr>
	</tbody>
</table>

fabrication and characterization of thickness mode piezoelectric devices for atomization and acoustofluidics

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid more efficiently, in terms of &#64258;ow rate per power input, than those that rely on Rayleigh waves and other modes of vibration in LN or lead zirconate titanate (PZT). The complete device is composed of a transducer, a transducer holder, and a &#64258;uid supply system. The fundamentals of acoustic liquid atomization are not well known, so techniques to characterize the devices and to study the phenomena are also described. Laser Doppler vibrometry (LDV) provides vibration information essential in comparing acoustic transducers and, in this case, indicates whether a device will perform well in thickness vibration. It can also be used to &#64257;nd the resonance frequency of the device, though this information is obtained more quickly via impedance analysis. Continuous &#64258;uid atomization, as an example application, requires careful &#64258;uid flow control, and we present such a method with high-speed imaging and droplet size distribution measurements via laser scattering.

Thickness mode piezoelectric devices were fabricated from 128YX lithium niobate. Figure 1 shows a complete assembly to hold the transducer in place with a custom transducer holder used with the passive &#64258;uid delivery system developed for continuous atomization. The characterization steps for these devices include determination of the resonant frequency and harmonics using an impedance analyzer (Figure 2). The fundamental frequency of the devices was found ...

Watch this Scientific Journal Video about Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics at JoVE.com

Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

Fabrication of piezoelectric thickness mode transducers via direct current sputtering of plate electrodes on lithium niobate is described. Additionally, reliable operation is achieved with a transducer holder and &#64258;uid supply system and characterization is demonstrated via impedance analysis, laser doppler vibrometry, high-speed imaging, and droplet size distribution using laser scattering.

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid ...

fabrication-characterization-thickness-mode-piezoelectric-devices-for

Research

JoVE Journal

Engineering

6.7K Views.  University of California San Diego. Fabrication of piezoelectric thickness mode transducers via direct current sputtering of plate electrodes on lithium niobate is described. Additionally, reliable operation is achieved with a transducer holder and ﬂuid supply system and characterization is demonstrated via impedance analysis, laser doppler vibrometry, high-speed imaging, and droplet size distribution using laser scattering.

Video: Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

Metamaterials (MM), artificial materials engineered to have properties that may not be found in nature, have been widely explored since the first theoretical1 and experimental demonstration2 of their unique properties. MMs can provide a highly controllable electromagnetic response, and to date have been demonstrated in every technologically relevant spectral range including the optical3, near IR4, mid IR5 , THz6 , mm-wave7 , microwave8 and radio9 bands. Applications include perfect lenses10, sensors11, telecommunications12, invisibility cloaks13 and filters14,15. We have recently developed single band16, dual band17 and broadband18 THz metamaterial absorber devices capable of greater than 80% absorption at the resonance peak. The concept of a MM absorber is especially important at THz frequencies where it is difficult to find strong frequency selective THz absorbers19. In our MM absorber the THz radiation is absorbed in a thickness of ~ &lambda;/20, overcoming the thickness limitation of traditional quarter wavelength absorbers. MM absorbers naturally lend themselves to THz detection applications, such as thermal sensors, and if integrated with suitable THz sources (e.g. QCLs), could lead to compact, highly sensitive, low cost, real time THz imaging systems.

This protocol outlines the simulation, fabrication and characterization of THz metamaterial absorbers. Such absorbers, when coupled with an appropriate sensor, have applications in THz imaging and spectroscopy.

Metamaterials (MM),  artificial materials engineered to have properties that may not be found in  nature, have been widely explored since the first ...

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

Patterning via Optical Saturable Transitions - Fabrication and Characterization

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical Saturable Transitions (POST). In this technique the chemical properties of organic photochromic molecules that undergo single-photon reactions are exploited, enabling rapid top-down nanopatterning over large areas at low light intensities, thereby, allowing for the circumvention of the far-field diffraction barrier.4 Simple, cost-effective, high throughput and resolution alternatives to nanopatterning are being explored, such as, two-photon polymerization5,6, beam pen lithography (BPL)7, scanning electron beam lithography (SEBL), and focused ion beam (FIB) patterning. However, multi-photon approaches require high light intensities, which limit their potential for high throughput and offer low image contrast. Although, electron and ion beam lithographic processes offer increased resolution, the serial nature of the process is limited to slow writing speeds, which also prevents patterning of features over large areas. Beam-pen lithography is an approach towards parallel near-field optical lithography. However, the gap between the source of the beam and the surface of the photoresist needs to be controlled extremely precisely for good pattern uniformity and this is very challenging to accomplish for large arrays of beams. Patterning via Optical Saturable Transitions (POST) is an alternative optical nanopatterning technique for patterning sub-wavelength features1-3. Since this technique uses single photons instead of electrons, it is extremely fast and does not require high light intensities1-3, opening the door to massive parallelization.

We report that the diffraction limit of conventional optical lithography can be overcome by exploiting the transitions of organic photochromic derivatives induced by their photoisomerization at low light intensities.1-3 This paper outlines our fabrication technique and two locking mechanisms, namely: dissolution of one photoisomer and electrochemical oxidation.

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical ...

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene&#8217;s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene&#39;s electronic structure in the presence of a charged impurity.&#160;The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene&#8217;s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

This paper details the fabrication process of a gate-tunable graphene device, decorated with Coulomb impurities for scanning tunneling microscopy studies. Mapping the spatially dependent electronic structure of graphene in the presence of charged impurities unveils the unique behavior of its relativistic charge carriers in response to a local Coulomb potential.

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees ...

Characterization of Full Set Material Constants and Their Temperature Dependence for Piezoelectric Materials Using Resonant Ultrasound Spectroscopy

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the degradation of device performance. In order to evaluate such degradations using computer simulations, full matrix material properties at elevated temperatures are needed as inputs. It is extremely difficult to measure such data for ferroelectric materials due to their strong anisotropic nature and property variation among samples of different geometries. Because the degree of depolarization is boundary condition dependent, data obtained by the IEEE (Institute of Electrical and Electronics Engineers) impedance resonance technique, which requires several samples with drastically different geometries, usually lack self-consistency. The resonant ultrasound spectroscopy (RUS) technique allows the full set material constants to be measured using only one sample, which can eliminate errors caused by sample to sample variation. A detailed RUS procedure is demonstrated here using a lead zirconate titanate (PZT-4) piezoceramic sample. In the example, the complete set of material constants was measured from room temperature to 120 &#176;C. Measured free dielectric constants <img alt="Equation 1" src="/files/ftp_upload/53461/image001.jpg" /> and&#160;<img alt="Equation 2" src="/files/ftp_upload/53461/image002.jpg" /> were compared with calculated ones based on the measured full set data, and piezoelectric constants d15 and d33 were also calculated using different formulas. Excellent agreement was found in the entire range of temperatures, which confirmed the self-consistency of the data set obtained by the RUS.

This protocol describes the procedure of measuring the temperature dependence of the full set material constants of piezoelectric materials using resonant ultrasound spectroscopy (RUS).

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the ...

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

Fabrication and Characterization of Superconducting Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors (MKIDs) for the detection of faint astrophysical signatures, as well as for quantum computing applications and materials characterization. In this paper, procedures are presented for the fabrication and characterization of thin-film superconducting microwave resonators. The fabrication methodology allows for the realization of superconducting transmission-line resonators with features on both sides of an atomically smooth single-crystal silicon dielectric. This work describes the procedure for the installation of resonator devices into a cryogenic microwave testbed and for cool-down below the superconducting transition temperature. The set-up of the cryogenic microwave testbed allows one to do careful measurements of the complex microwave transmission of these resonator devices, enabling the extraction of the properties of the superconducting lines and dielectric substrate (e.g., internal quality factors, loss and kinetic inductance fractions), which are important for device design and performance.

Superconducting microwave resonators are of interest for detection of light, quantum computing applications and materials characterization. This work presents a detailed procedure for fabrication and characterization of superconducting microwave resonator scattering parameters.

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors ...

Characterization of Anisotropic Leaky Mode Modulators for Holovideo

Holovideo displays are based on light-bending spatial light modulators. One such spatial light modulator is the anisotropic leaky mode modulator. This modulator is particularly well suited for holographic video experimentation as it is relatively simple and inexpensive to fabricate1-3. Some additional advantages of leaky mode devices include: large aggregate bandwidth, polarization separation of signal light from noise, large angular deflection and frequency control of color1. In order to realize these advantages, it is necessary to be able to adequately characterize these devices as their operation is strongly dependent on waveguide and transducer parameters4. To characterize the modulators, the authors use a commercial prism coupler as well as a custom characterization apparatus to identify guided modes, calculate waveguide thickness and finally to map the device's frequency input and angular output of leaky mode modulators. This work gives a detailed description of the measurement and characterization of leaky mode modulators suitable for full-color holographic video.

This work describes fabrication and characterization of anisotropic leaky mode modulators for holographic video.

Holovideo displays are based on light-bending spatial light modulators.  One such spatial light modulator is the anisotropic leaky mode modulator.  This ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each thermoplastic of interest. Solvent bonding is a simple and versatile method that can be used to fabricate devices from a variety of plastics. An appropriate solvent is added between two device layers to be bonded, and heat and pressure are applied to the device to facilitate the bonding. By using an appropriate combination of solvent, plastic, heat, and pressure, the device can be sealed with a high quality bond, characterized as having high bond coverage, bond strength, optical clarity, durability over time, and low deformation or damage to microfeature geometry. We describe the procedure for bonding devices made from two popular thermoplastics, poly(methyl-methacrylate) (PMMA), and cyclo-olefin polymer (COP), as well as a variety of methods to characterize the quality of the resulting bonds, and strategies to troubleshoot low quality bonds. These methods can be used to develop new solvent bonding protocols for other plastic-solvent systems.

Solvent bonding is a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds. We describe a protocol to achieve strong, optically clear bonds in PMMA and COP microfluidic devices that preserve microfeature details, by a judicious combination of pressure, temperature, an appropriate solvent, and device geometry.

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each ...