Support of this work from Office of Naval Research (N000141210603) and the Army Research Office (W911NF1010381) is gratefully acknowledged. Partial support of this work from the National Science Foundation (CBET-0931290, CMMI-0926704, and CBET-0932573) is also acknowledged.

1. Experiment Procedure
<ol>
	<li>Collect sample. In this work, the human head hair samples are collected from a 30-year old healthy Asian female.</li>
	<li>Suspend the sample between two copper electrodes as shown in Figure 1A. Apply silver paste at the sample-electrode contact to reduce the thermal and electrical contact resistances to a negligible level.</li>
	<li>Use a microscope to do the preliminary check of the sample and make sure that the silver paste does not contaminate the suspended sample.</li>
	<li>Since human head hair samples are not electrically conductive, coat the outside of the sample with a very thin layer of gold film (~40 nm) to make it electrically conductive.</li>
	<li>Put the sample in the vacuum chamber and pump it to 1-3 mTorr.</li>
	<li>Feed a step dc current through the sample to introduce electrical heating and the induced voltage-time (V-t) profile will be recorded by using an oscilloscope.</li>
	<li>Get the sample out of the chamber and coat it with another thin layer of gold film (~40 nm), and repeat steps 1.5 and 1.6.</li>
	<li>Prepare a new sample with a different length, and repeat steps 1.2-1.7.</li>
	<li>Use scanning electron microscope (SEM) to characterize the length and diameter of the samples (long and short ones).</li>
</ol>
2. Data Processing
Normalize the experimental temperature rise first, and conduct the theoretical fitting of that by using different trial values of the thermal diffusivity of the sample. This procedure is discussed in Guo&#39;s work1 in detail. Then subtract the effect of radiative losses and parasitic conduction on thermal diffusivity, and calculate the thermal conductivity. Details are given below.
<ol>
	<li>Determine the effective thermal diffusivity 
	A schematic of the TET experiment setup is shown in Figure 1A. In the measurement, feed a step current through the sample to induce joule heating. Use an oscilloscope to record the induced voltage-time (V-t) profile which is presented in Figure 1B. How fast/slow the temperature increases is determined by two competing processes: one is the joule heating, and the other one is the heat conduction from the sample to the electrodes. A higher thermal diffusivity of the sample will lead to a faster temperature evolution, meaning a shorter time to reach the steady state. Therefore, the transient voltage/temperature change can be used to determine the thermal diffusivity. When determining thermal diffusivity of the sample, no real temperature rise is needed. In fact, only the normalized temperature rise based on the voltage increase is used. The processes for determining the thermal diffusivity and thermal conductivity are outlined below.
	<ol>
		<li>Simplify the heat transfer to one-dimensional: Take the heat transfer of the sample in one dimension along the axial direction. Note: The length of the wire must be much longer than its diameter. More details can be referred to Guo&#39;s work1.
		<ol>
			<li>Solve for the normalized temperature rise (T*, also known as the spatial average temperature over the whole sample) over the sample for a one-dimensional heat transfer problem using the following equation: 
			<img alt="1" fo:content-width="1.8in" height="46" src="/files/ftp_upload/51144/51144_clip_image002.gif" width="260" /> (1) 
			&#945; and L are the thermal diffusivity and length of the sample.</li>
			<li>Solve for the normalized temperature rise from the voltage evolution (Vwire) recorded by the oscilloscope, and conduct data fitting to determine the thermal diffusivity. The voltage over the wire is related to its temperature as: 
			<img alt="" fo:content-width="1.3in" height="47" src="/files/ftp_upload/51144/51144_clip_image002_0000.gif" width="160" /> (2) 
			R0 is the resistance of the sample before heating, I the current passing through the sample, and k thermal conductivity. q0 is the electrical heating power per unit volume. It is clear that the measured voltage change is inherently related to the temperature change of the sample. The normalized temperature rise T*exp based on the experimental data can be calculated as T*exp = (Vwire - V0) / (V1 - V0), where V0 and V1 are the initial and final voltages across the sample (as illustrated in Figure 1B). After obtaining T*exp, use different trial values of &#945; to calculate the theoretical T* by applying Equation 1 and fit the experimental results (T*exp). MATLAB is used for programming to compare the experimental and theoretical values by applying the least square fitting technique, and take the value giving the best fit of T*exp as the thermal diffusivity of the sample.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Subtract the effect of radiative losses and gas conduction 
	During TET thermal characterization, the effect of radiative losses could be significant if the sample has a very large aspect ratio (L/D, D: sample diameter), especially for samples of low thermal conductivity. Also if the pressure of the vacuum chamber is not very low, the heat transfer to the air will affect the measurement to some certain extent. The heat transfer rate of radiation from the sample surface can be expressed as: 
	<img alt="" fo:content-width="3.1in" height="29" src="/files/ftp_upload/51144/51144_clip_image002_0001.gif" width="390" />, (3) 
	where &#949; is the effective emissivity of the sample, As the surface area, T the surface temperature, T0 the temperature of the environment (vacuum chamber), and &#952; = T-T0. In most cases, &#952; &#60;&#60; T0, then: 
	<img alt="" fo:content-width="1.05in" height="23" src="/files/ftp_upload/51144/51144_clip_image002_0002.gif" width="138" />&#160;(4) 
	By converting the surface radiation and gas conduction to body cooling source, the heat transfer governing equation for the sample becomes: 
	<img alt="" fo:content-width="2.25in" height="49" src="/files/ftp_upload/51144/51144_clip_image002_0003.gif" width="345" />, (5) 
	where h is the coefficient of gas conduction. In our physical model, since the electrodes are much larger than the sample and have excellent heat conduction, the sample&#39;s temperature is taken at room temperature at the contact. Because &#952; (x, t) = T (x, t)-T0, the boundary condition is &#952; (0, t) = &#952; (L, t) = &#952; (x, 0) = 0. 
	The solution to Equation 5 is: 
	<img alt="" fo:content-width="3.5in" src="/files/ftp_upload/51144/51144_clip_image002_0004.gif" width="489" />&#160;(6) 
	Here f is defined as -(16&#949;&#948;T03 / D+4h / D)L2 / &#960;2k, which is dimensionless. It is a type of Biot number whose size indicates the amount of heat loss from the sides of the sample. Integrate this equation along the x-direction and the average temperature can be obtained: 
	<img alt="" fo:content-width="3in" src="/files/ftp_upload/51144/51144_clip_image002_0005.gif" width="408" />&#160;(7) 
	So the normalized average temperature is: 
	<img alt="" fo:content-width="4.2in" src="/files/ftp_upload/51144/51144_clip_image004_0005.gif" width="510px" />(8) 
	After careful numerical and mathematic study, with &#945;eff =&#945; (1-f ), T* can be approximated as 
	<img alt="" fo:content-width="2.2in" height="48" src="/files/ftp_upload/51144/51144_clip_image008.gif" width="288" />&#160;(9) 
	Numeric calculations have been conducted to study the accuracy of the above approximation. Please note that, when f is less than 0, the maximum absolute difference in the whole transient state is less than 0.014 (shown in Figure 2). Finally: 
	<img alt="" fo:content-width="1.7in" height="50" src="/files/ftp_upload/51144/51144_clip_image010.gif" width="218" />&#160;(10) 
	Because the experiment is conducted in vacuum chamber at very low pressure (1-3 mTorr), the gas conduction effect (h) is negligible. So simplify Equation 10 as: 
	<img alt="" fo:content-width="1.4in" height="49" src="/files/ftp_upload/51144/51144_clip_image012.gif" width="173" />&#160;(11) 
	This equation demonstrates that the measured thermal diffusivity using the TET technique has a linear relation with the effect of radiative losses (4&#949;&#963;T03). Use such theoretical background to subtract the effect of radiative losses and gas conduction.</li>
	<li>Determine real thermal diffusivity and conductivity 
	The determined thermal diffusivity (&#945;) in Equation 11 still has the effect of parasitic conduction if the tested sample is coated with a thin gold film. The thermal transport effect caused by the coated layer can be subtracted using the Wiedemann-Franz law with negligible uncertainty. The real thermal diffusivity (&#945;) of the sample is determined as1: 
	<img alt="" fo:content-width="1.1in" height="47" src="/files/ftp_upload/51144/51144_clip_image002_0006.gif" width="134" />, (12) 
	&#961;cp is volume-based specific heat, which can be obtained from calibration, noncontact photo-thermal technique or measuring the density and specific heat separately. LLorenz, T, and A are the Lorenz number, sample&#39;s temperature and cross-sectional area, respectively. 
	Because <img alt="" fo:content-width="2.4in" height="46" src="/files/ftp_upload/51144/51144_clip_image004_0006.gif" width="343" />, it is apparent that &#945;eff has a linear relationship with 1/R, so in the experiment, coating one sample with gold film twice (which will cause the change of 1/R) and testing twice can eliminate the effect of parasitic conduction by curve fitting. For real thermal conductivity k, it can be easily evaluated by using k =&#961;cp&#945;.</li>
</ol>

<ol>
	<li>Guo, J. Q., Wang, X. W., Wang, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+characterization+of+microscale+conductive+and+nonconductive+wires+using+transient+electrothermal+technique.">Thermal characterization of microscale conductive and nonconductive wires using transient electrothermal technique.</a> J. Appl. Phys. 101, (2007).</li><li>Lu, L., Yi, W., Zhang, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=3+omega+method+for+specific+heat+and+thermal+conductivity+measurements.">3 omega method for specific heat and thermal conductivity measurements.</a> Rev. Sci. Instrum. 72, 2996-3003 (2001).</li><li>Choi, T. Y., Poulikakos, D., Tharian, J., Sennhauser, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+the+thermal+conductivity+of+individual+carbon+nanotubes+by+the+four-point+three-omega+method.">Measurement of the thermal conductivity of individual carbon nanotubes by the four-point three-omega method.</a> Nano Lett. 6, 1589-1593 (2006).</li><li>Hou, J. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+characterization+of+single-wall+carbon+nanotube+bundles+using+the+self-heating+3-omega+technique.">Thermal characterization of single-wall carbon nanotube bundles using the self-heating 3-omega technique.</a> J. Appl. Phys. 100, (2006).</li><li>Kim, P., Shi, L., Majumdar, A., McEuen, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+transport+measurements+of+individual+multiwalled+nanotubes.">Thermal transport measurements of individual multiwalled nanotubes.</a> Phys. Rev. Lett. 87, (2001).</li><li>Kim, P., Shi, L., Majumdar, A., McEuen, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mesoscopic+thermal+transport+and+energy+dissipation+in+carbon+nanotubes.">Mesoscopic thermal transport and energy dissipation in carbon nanotubes.</a> Physica B Condens. Matter. 323, 67-70 (2002).</li><li>Shi, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measuring+thermal+and+thermoelectric+properties+of+one-dimensional+nanostructures+using+a+microfabricated+device.">Measuring thermal and thermoelectric properties of one-dimensional nanostructures using a microfabricated device.</a> J. Heat Transfer. 125, 881-888 (2003).</li><li>Li, D. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+conductivity+of+individual+silicon+nanowires.">Thermal conductivity of individual silicon nanowires.</a> Appl. Phys. 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J., Wang, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+thermal+characterization+of+micro/submicroscale+polyacrylonitrile+wires.">Transient thermal characterization of micro/submicroscale polyacrylonitrile wires.</a> Appl. Phys. A Mater. Sci. Process. 89, 153-156 (2007).</li><li>Hu, H. P., Wang, X. W., Xu, X. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generalized+theory+of+the+photoacoustic+effect+in+a+multilayer+material.">Generalized theory of the photoacoustic effect in a multilayer material.</a> J. Appl. Phys. 86, 3953-3958 (1999).</li><li>Wang, X. W., Hu, H. P., Xu, X. 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There is nothing to disclose.

In the experiment procedure, three steps [step 2), 3) and 5)] are very critical for the success of characterizing thermal properties accurately. For step 2) and 3), much attention needs to be paid on applying silver paste only at the sample-electrode contact. It is very easy to contaminate the suspended sample with silver paste, and the thermal properties will increase if this happens. So in step 3), check the sample with microscope carefully, if any contamination-the silver paste is applied or extended to the suspended sample-is noticed, a new sample needs to be prepared for the experiment.
When Equation 10 is simplified to Equation 11, it is assumed that the experiment is conducted in a vacuum chamber at very low pressure (1-3 mTorr), so the gas conduction effect is negligible. After doing a series of test at different pressures, it is confirmed that, in Equation 10, the gas conduction coefficient h is proportional to the pressure p as h=&#947;p. The coefficient &#947; is related to a parameter called thermal accommodation coefficient that reflects the energy coupling/exchange coefficient when the gas molecules strike the material surface. &#947; can be calculated as &#958;&#960;2D&#961;cP / (4L2) where &#958; is the slope of the thermal diffusivity against pressure. &#947; varies from sample to sample. This gas conduction factor can be strongly affected by the material surface structure and the spatial configuration in the chamber during TET characterization. For step 5), conducting the experiment at very low pressure (1-3 mTorr) will make sure that this complicated gas conduction effect is negligible.
Surface emissivity (&#949;) of the samples measured by this technique can also be calculated with the given value of volume-based specific heat (&#961;cp), which can be obtained from calibration, noncontact photo-thermal technique13-15 or measuring the density and specific heat separately. After subtracting the effect of parasitic conduction, the thermal diffusivity (&#945;real+rad) shown in Figure 6 only has the effect of radiative losses, <img alt="" fo:content-width="2in" height="60" src="/files/ftp_upload/51144/51144_clip_image002_0011.gif" width="342" />. It is easy to know that: 
<img alt="" fo:content-width="1.7in" height="59" src="/files/ftp_upload/51144/51144_clip_image004_0010.gif" width="244" />&#160;(13) 
Here T0 is the room temperature, L the diameter of tested samples, and D the diameter of the sample.
There are several limitations of the TET technique. First, the characteristic time &#8710;tc for the thermal transport in the sample, which equals to 0.2026L2/&#945;1, should be much larger than the rise time (about 2 &#181;sec) of the current source. Otherwise, the accuracy of the voltage evolution will be affected significantly. So it requires that the sample length L should not be too small or the thermal diffusivity &#945; should not too big. Second, the temperature of the sample will rise by about 20-30&#176;&#160;in the experiment. Within this range, the resistance of the sample should have a linear relationship to temperature. That is because in the part of theoretical background, it is known that the measured voltage change is inherently related to the temperature change of the sample. If the resistance of the sample does not have a linear relationship to temperature, the voltage evolution cannot stand for the temperature evolution. Third, the voltage of the sample should have a linear relationship to the DC current fed during the experiment. This means at a certain temperature, the resistance will not change when the DC current changes. It is well known that semiconductors do not have this property.
In conclusion, the TET technique is a very effective and robust approach to measuring the thermal properties of various types of materials. For the same material, just test two samples with different length each twice, all the important thermal properties of the materials, such as thermal diffusivity, thermal conductivity, and surface emissivity (if &#961;cp is given), can be characterized.

The TET technique1 is an effective approach developed to measure the thermal diffusivity of solid materials, including conductive, semi-conductive or nonconductive one-dimensional structures. In the past, the single wire 3&#969; method2-4 and the micro-fabricated device method5-9 have been developed to measure the thermal properties of one dimensional structures at the micro/nanoscale. In order to broaden the measurement scope of materials (conductive and nonconductive) and improve the accuracy and stability, the transient electro-thermal (TET) technique has been developed for characterization of thermophysical properties of micro/nanoscale wires. This technique has been used successfully for thermal characterization of free-standing micrometer-thick Poly (3-hexylthiophene) films10, thin films composed of anatase TiO2 nanofibers11, single-wall carbon nanotubes1, micro/submicroscale polyacrylonitrile wires12, and protein fibers. After eliminating the effect of parasitic conduction (if the sample is coated with a layer of gold to make it electronically conductive) and radiative losses, the real thermal diffusivity can be obtained. Then the real thermal conductivity can be calculated with a given value of volume-based specific heat (&#961;cp), which can be obtained from calibration, noncontact photo-thermal technique, or measuring the density and specific heat separately.

<table border="0" cellpadding="0" cellspacing="0" width="985">
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			<td height="21" style="height:21px;width:260px;">Digital Phosphor Oscilloscope</td>
			<td style="width:275px;">Tektronix</td>
			<td style="width:119px;">DPO 3052</td>
			<td style="width:331px;"> </td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Sputter Coater</td>
			<td style="width:275px;">Denton Vacuum</td>
			<td style="width:119px;">DESK V</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">AC and DC Current Source</td>
			<td style="width:275px;">KEITHLEY</td>
			<td style="width:119px;">Model 6221</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Laboratory Microscope</td>
			<td style="width:275px;">Olympus</td>
			<td style="width:119px;">BX41</td>
			<td></td>
		</tr>
		<tr height="27">
			<td height="27" style="height:27px;width:260px;">Dual Stage Rotary Vane Vacuum Pump</td>
			<td style="width:275px;">Varian</td>
			<td style="width:119px;">DS102</td>
			<td></td>
		</tr>
		<tr height="71">
			<td height="71" style="height:71px;width:260px;">Vacuum Chamber</td>
			<td style="width:275px;">Huntington Mechanical Laboratories</td>
			<td style="width:119px;">Customized Product</td>
			<td style="width:331px;">The pressure in the chamber should be as low as 1-3 mTorr 
			when working with the vacuum pump</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Colloidal Silver Liquid</td>
			<td style="width:275px;">Ted Pella</td>
			<td style="width:119px;">16031</td>
			<td></td>
		</tr>
	</tbody>
</table>

characterization of thermal transport in one-dimensional solid materials

The TET (transient electro-thermal) technique is an effective approach developed to measure the thermal diffusivity of solid materials, including conductive, semi-conductive or nonconductive one-dimensional structures. This technique broadens the measurement scope of materials (conductive and nonconductive) and improves the accuracy and stability. If the sample (especially biomaterials, such as human head hair, spider silk, and silkworm silk) is not conductive, it will be coated with a gold layer to make it electronically conductive. The effect of parasitic conduction and radiative losses on the thermal diffusivity can be subtracted during data processing. Then the real thermal conductivity can be calculated with the given value of volume-based specific heat (&#961;cp), which can be obtained from calibration, noncontact photo-thermal technique or measuring the density and specific heat separately. In this work, human head hair samples are used to show how to set up the experiment, process the experimental data, and subtract the effect of parasitic conduction and radiative losses.

Fitting of the experimental data for human head hair sample 1 (length 0.788 mm, coated with gold film only once) is shown in Figure 3. Its thermal diffusivity is determined at 1.67 x 10-7 m2/sec, which includes the effect of radiative losses and parasitic conduction. Figure 4 is a typical SEM image of human head hair. The short and long samples are coated with gold film twice and tested twice, respectively, based on Equation 12, the effect of parasitic conduction can be easily subtracted by curve fitting as shown in Figure 5. The point where the fitting curve intersects with the &#945;eff-axis is the value of &#945;eff when the resistance is infinite, which means the effect of parasitic conduction in Equation 12 is 0. Two human head hair samples with different lengths are measured to obtain two intersects. Details about the experimental conditions and measurement results are summarized in Table 1. By combining these two points, the relationship between &#945;eff and L2/D can be revealed. From the measured pairs of ( &#945;1, L12 / D1 ) and ( &#945;2, L22 / D2 ), linear extrapolation (as shown in Figure 6) is done to the point of L=0 (meaning no effect of radiative losses), and thermal diffusivity at that point is 1.42 x 10-7 m2/sec&#160;[=&#945;1 - (&#945;1-&#945;2 ) * L12 / D1 / (L12 / D1-L22 / D2) ]. This value reflects the thermal diffusivity of the sample without the effect of radiative losses and parasitic conduction.
For human head hair, the density is characterized by weighting several strands of hair and measuring their volume, and is measured at 1,100 kg/m3. The specific heat is measured by using DSC (Differential Scanning Calorimetry) and is measured at 1.602 kJ/kg&#160;K. So the real thermal conductivity is 0.25 W/m&#160;K. Details of experimental parameters and results for human head hair sample 1 and 2 are shown in Table 1.
<img alt="Figure 1" fo:content-width="6in" fo:src="/files/ftp_upload/51144/51144fig1highres.jpg" src="/files/ftp_upload/51144/51144fig1.jpg" width="500px" /> 
Figure 1. A) schematic of the TET experiment setup and B) a typical V&#8211;t profile. <a href="https://www.jove.com/files/ftp_upload/51144/51144fig1highres.jpg" target="_blank">Click here to view larger image</a>.
<img alt="Figure 2" fo:content-width="6in" fo:src="/files/ftp_upload/51144/51144fig2highres.jpg" src="/files/ftp_upload/51144/51144fig2.jpg" width="500px" /> 
Figure 2. The difference between T* and its approximation using Equation 9. <a href="https://www.jove.com/files/ftp_upload/51144/51144fig2highres.jpg" target="_blank">Click here to view larger image</a>.
<img alt="Figure 3" fo:content-width="6in" fo:src="/files/ftp_upload/51144/51144fig3highres.jpg" src="/files/ftp_upload/51144/51144fig3.jpg" width="500px" /> 
Figure 3. Comparison between the experimental data and theoretical fitting result for the normalized temperature rise versus time (human head hair sample 1). <a href="https://www.jove.com/files/ftp_upload/51144/51144fig3highres.jpg" target="_blank">Click here to view larger image</a>.
<img alt="Figure 4" fo:content-width="6in" fo:src="/files/ftp_upload/51144/51144fig4highres.jpg" src="/files/ftp_upload/51144/51144fig4.jpg" width="500px" /> 
Figure 4. A typical SEM image of human head hair. <a href="https://www.jove.com/files/ftp_upload/51144/51144fig4highres.jpg" target="_blank">Click here to view larger image</a>.
<img alt="Figure 5" fo:content-width="6in" fo:src="/files/ftp_upload/51144/51144fig5highres.jpg" src="/files/ftp_upload/51144/51144fig5.jpg" width="500px" /> 
Figure 5. The fitting results for the thermal diffusivity change against 1/R for the human head hair sample 1 and 2. <a href="https://www.jove.com/files/ftp_upload/51144/51144fig5highres.jpg" target="_blank">Click here to view larger image</a>.
<img alt="Figure 6" fo:content-width="6in" fo:src="/files/ftp_upload/51144/51144fig6highres.jpg" src="/files/ftp_upload/51144/51144fig6.jpg" width="600px" /> 
Figure 6. The fitting result for the real thermal diffusivity of human head hair samples. <a href="https://www.jove.com/files/ftp_upload/51144/51144fig6highres.jpg" target="_blank">Click here to view larger image</a>.
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		<col />
	</colgroup>
	<tbody>
		<tr height="52">
			<td height="52" style="height:52px;width:249px;">Human head hair samples</td>
			<td style="width:111px;">Sample 1 
			(short)</td>
			<td style="width:115px;">Sample 2 
			(long)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Length (mm)</td>
			<td>0.788</td>
			<td style="width:115px;">1.468</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Diameter (mm)</td>
			<td>74.0</td>
			<td style="width:115px;">77.8</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">&#945;real+radiation (x 10-7 m2/sec)</td>
			<td>1.48</td>
			<td style="width:115px;">1.62</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">&#945;real (x 10-7 m2/sec)</td>
			<td colspan="2">1.42</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">&#961;cp (x 106 J/m3 K)</td>
			<td colspan="2">1.76</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Real thermal conductivity (W/m&#160;K)</td>
			<td colspan="2">0.25</td>
		</tr>
	</tbody>
</table>
Table 1: Details of experimental parameters and results for human head hair.

Watch this Scientific Journal Video about Characterization of Thermal Transport in One-dimensional Solid Materials at JoVE.com

Characterization of Thermal Transport in One-dimensional Solid Materials

The TET (transient electro-thermal) technique is an effective approach developed to measure the thermal diffusivity of solid materials.

The TET (transient electro-thermal) technique is an effective approach developed to measure the thermal diffusivity of solid materials, including ...

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17.1K Views.  Iowa State University. The TET (transient electro-thermal) technique is an effective approach developed to measure the thermal diffusivity of solid materials.

Video: Characterization of Thermal Transport in One-dimensional Solid Materials

Solid-state Graft Copolymer Electrolytes for Lithium Battery Applications

Battery safety has been a very important research area over the past decade. Commercially available lithium ion batteries employ low flash point (&lt;80 &deg;C), flammable, and volatile organic electrolytes. These organic based electrolyte systems are viable at ambient temperatures, but require a cooling system to ensure that temperatures do not exceed 80 &deg;C. These cooling systems tend to increase battery costs and can malfunction which can lead to battery malfunction and explosions, thus endangering human life. Increases in petroleum prices lead to a huge demand for safe, electric hybrid vehicles that are more economically viable to operate as oil prices continue to rise. Existing organic based electrolytes used in lithium ion batteries are not applicable to high temperature automotive applications. A safer alternative to organic electrolytes is solid polymer electrolytes. This work will highlight the synthesis for a graft copolymer electrolyte (GCE) poly(oxyethylene) methacrylate (POEM) to a block with a lower glass transition temperature (Tg) poly(oxyethylene) acrylate (POEA). The conduction mechanism has been discussed and it has been demonstrated the relationship between polymer segmental motion and ionic conductivity indeed has a Vogel-Tammann-Fulcher (VTF) dependence. Batteries containing commercially available LP30 organic (LiPF6 in ethylene carbonate (EC):dimethyl carbonate (DMC) at a 1:1 ratio) and GCE were cycled at ambient temperature. It was found that at ambient temperature, the batteries containing GCE showed a greater overpotential when compared to LP30 electrolyte. However at temperatures greater than 60 &deg;C, the GCE cell exhibited much lower overpotential due to fast polymer electrolyte conductivity and nearly the full theoretical specific capacity of 170 mAh/g was accessed.

Lithium ion batteries employ flammable and volatile organic electrolytes that are suitable for ambient temperature applications. A safer alternative to organic electrolytes are solid polymer batteries. Solid polymer batteries operate safely at high temperatures (&gt;120 &deg;C), thus making them applicable to high temperature applications such as deep oil drilling and hybrid electric vehicles. This paper will discuss (a) the polymer synthesis, (b) the polymer conduction mechanism, and (c) provide temperature cycling for both solid polymer and organic electrolytes.

Battery safety has been a very important research area over the past decade. Commercially available lithium ion batteries employ low flash point (&lt;80 ...

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. During insertion or removal of alkali metal ions, the redox states of transition metals in the compounds change and structural transformations such as phase transitions and/or lattice parameter increases or decreases occur. These behaviors in turn determine important characteristics of the batteries such as the potential profiles, rate capabilities, and cycle lives. The extremely bright and tunable x-rays produced by synchrotron radiation allow rapid acquisition of high-resolution data that provide information about these processes. Transformations in the bulk materials, such as phase transitions, can be directly observed using X-ray diffraction (XRD), while X-ray absorption spectroscopy (XAS) gives information about the local electronic and geometric structures (e.g.&#160;changes in redox states and bond lengths). In situ experiments carried out on operating cells are particularly useful because they allow direct correlation between the electrochemical and structural properties of the materials. These experiments are time-consuming and can be challenging to design due to the reactivity and air-sensitivity of the alkali metal anodes used in the half-cell configurations, and/or the possibility of signal interference from other cell components and hardware. For these reasons, it is appropriate to carry out ex situ experiments (e.g.&#160;on electrodes harvested from partially charged or cycled cells) in some cases. Here, we present detailed protocols for the preparation of both ex situ and in situ samples for experiments involving synchrotron radiation and demonstrate how these experiments are done.

We describe the use of synchrotron X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques to probe details of intercalation/deintercalation processes in electrode materials for Li-ion and Na-ion batteries. Both in situ and ex situ experiments are used to understand structural behavior relevant to the operation of devices

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications ...

High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings

Micro-electronic devices often undergo significant self-heating when biased to their typical operating conditions. This paper describes a convenient optical micro-imaging technique which can be used to map and quantify such behavior. Europium thenoyltrifluoroacetonate (EuTFC) has a 612 nm luminescence line whose activation efficiency drops strongly with increasing temperature, due to T-dependent interactions between the Eu3+ ion and the organic chelating compound. This material may be readily coated on to a sample surface by thermal sublimation in vacuum. When the coating is excited with ultraviolet light (337 nm) an optical micro-image of the 612 nm luminescent response can be converted directly into a map of the sample surface temperature. This technique offers spatial resolution limited only by the microscope optics (about 1 micron) and time resolution limited by the speed of the camera employed. It offers the additional advantages of only requiring comparatively simple and non-specialized equipment, and giving a quantitative probe of sample temperature.

Europium thenoyltrifluoroacetonate (EuTFC) has an optical luminescence line at 612 nm, whose activation efficiency decreases strongly with temperature. If a sample coated with a thin film of this material is micro-imaged, the 612 nm luminescent response intensity may be converted into a direct map of sample surface temperature.

Micro-electronic devices often undergo significant self-heating when biased to their typical operating conditions. This paper describes a convenient ...

Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and nanocrystalline materials. The traditional techniques associated with scanning electron microscopy (SEM), such as electron backscatter diffraction (EBSD), do not possess the required spatial resolution due to the large interaction volume between the electrons from the beam and the atoms of the material. Transmission electron microscopy (TEM) has the required spatial resolution. However, due to a lack of automation in the analysis system, the rate of data acquisition is slow which limits the area of the specimen that can be characterized. This paper presents a new characterization technique, Transmission Kikuchi Diffraction (TKD), which enables the analysis of the microstructure of UFG and nanocrystalline materials using an SEM equipped with a standard EBSD system. The spatial resolution of this technique can reach 2 nm. This technique can be applied to a large range of materials that would be difficult to analyze using traditional EBSD. After presenting the experimental set up and describing the different steps necessary to realize a TKD analysis, examples of its use on metal alloys and minerals are shown to illustrate the resolution of the technique and its flexibility in term of material to be characterized.

This paper provides a detailed method to characterize the microstructure of ultra-fine grained and nanocrystalline materials using a scanning electron microscope equipped with a standard electron backscatter diffraction system. Metal alloys and minerals presenting refined microstructures are analyzed using this technique, showing the diversity of its possible applications.

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of ...

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape method or individual WS2 nanotubes by dispersing the suspension of WS2 nanotubes. The selected samples have been fabricated into devices by the use of the electron beam lithography and electrolyte is put on the devices. We have characterized the electronic properties of the devices under applying the gate voltage. In the small gate voltage region, ions in the electrolyte are accumulated on the surface of the samples which leads to the large electric potential drop and resultant electrostatic carrier doping at the interface. Ambipolar transfer curve has been observed in this electrostatic doping region. When the gate voltage is further increased, we met another drastic increase of source-drain current which implies that ions are intercalated into layers of WS2 and electrochemical carrier doping is realized. In such electrochemical doping region, superconductivity has been observed. The focused technique provides a powerful strategy for achieving the electric-filed-induced quantum phase transition.

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

Here, we present a protocol to control the carrier number in solids by using the electrolyte.

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape ...