This study was financially supported by the National Key Scientific Instrument and Equipment Development Projects (Grant No. 2014YQ120351), the Youth Innovation Promotion Association of CAS (Grant No. 2014136), and the China Innovative Talent Promotion Plans for Innovation Team in Priority Fields (Grant No. 2014RA4051).

1. Preparation of Standard Samples
NOTE: This step is not essential.
<ol>
	<li>Prepare raw material (Table 1). To make a 100 kg of sample #1, add 12.82 kg of Cr, 3.39 kg of Mo, 4.79 kg of Al, 1.00 kg of Ti, 0.60 kg of Cu, and approximately 77.4 kg of Ni to the crucible. During the melting process, some elements will be burned. The final ingredient is determined by the melting temperature, melting duration, and other working parameters. The ingredient test shows the quantity of each element inside the alloys.</li>
	<li>Perform vacuum induction melting at approximately 1,700 &#176;C for approximately 45 min for each standard sample. The furnace used to make standard samples can melt approximately 100 kg alloys each time for 2 sets of standard samples.</li>
	<li>Pour all molten liquid steel into a sticky mold to make standard samples, and naturally cool for at least 4 h. The size of the standard samples is determined by the furnace in the experiment. Use rod-shaped standard samples in the experiments with a rod diameter of 100 mm. The shape of the crucible in the furnace is a frustum cone with a cup-like container. The diameter of the rim is 150 mm, the bottom is 100 mm, and the depth is 200 mm. Chunked standard samples can also be employed.</li>
	<li>Use an electric saw to cut standard samples for the experiment. The length of the standard rod sample is determined by the furnace. Use a length of 150 mm for the experimental smelting system. Melt a piece of the samples for each experiment.</li>
	<li>Repeat these steps and make all standard samples. Ten samples are employed in this experiment.</li>
</ol>
2. Test Ingredient of Standard Alloy Samples
<ol>
	<li>Use a chemical analysis method to test the composition of all standard alloy samples. Test all elements in each sample. 
	NOTE: We strongly recommend sending these samples to an authority organization to perform the analysis. These samples are sent to the Central Iron &#38; Steel Research Institute of China for the ingredients test. The test results for these samples are listed in Table 2.</li>
</ol>
3. Smelt Samples
<ol>
	<li>Check the security of the smelting system, which includes the power supply, availability of each pump, vacuum hold ability of the experimental furnace, cooling water, and current.</li>
	<li>Place the standard samples into the smelting system. To ensure that a small amount of each sample is ablated by the laser, use small samples for the experiment. Due to the size of the crucible in the furnace, smelt approximately 10 kg samples each time.</li>
	<li>Open the vacuum pump until the pressure is lower than 0.1 Pa. Use 2 levels of pump to make the vacuum: mechanical pump and diffusion pump. The mechanical pump can reach approximately 1 Pa in 15 min, and the diffusion pump can reach 0.01 Pa after 40 min.</li>
	<li>Melt samples. Increase the furnace working current to approximately 130 A; this parameter is determined by the ingredients of the samples and the size of the furnace. A standard sample requires approximately 15 min to become molten. Due to oxidation or nitridation, the ingredients of liquid steel slowly change during the course of smelting.
	<ol>
		<li>To ensure precision of the experiment, determine the spectrum within 15 min after the standard samples are molten.</li>
	</ol>
	</li>
</ol>
4. Determine Laser Breakdown Spectra of Standard Samples
<ol>
	<li>Check availability of laser focusing and spectrum gathering system, laser generator, and spectrometer.</li>
	<li>Set the spectrometer and laser generator to work synchronously. Use a spectrometer output synchronization signal and laser passive working method in the system. The method of laser generator synchronization signal or method of synchronizer output synchronization signal can also be employed to control the laser generator and spectrometer.</li>
	<li>Open the laser generator and spectrometer; prepare to generate the pulse laser. The pulse width is 20 ns, the frequency is 5 Hz, and the energy of each pulse is 90 mJ.</li>
	<li>Use spectrum deposit software to trigger the laser output and gather the spectrum. Set the integration time of the spectrometer to 10 ms, and each laser pulse generates a frame of the spectrum. If the integration time is too short, the spectrum signal intensity will be too weak. If the integration time is too long, more background signals will be gathered.</li>
	<li>Adjust the laser focusing position, and effectively ablate the sample. Optimize the focusing position until the strongest spectrum signal is obtained. This process is used to adjust the focusing point. The spectrometer numerical divided signal intensity ranges from 0 to 65,535. In most cases, the intensity of a signal should exceed 15% of the saturation signal, which indicates that the highest peak intensity should exceed 10,000. If the signal intensity is too small, the quantitative analysis will have low precision.</li>
	<li>Optimize the delay time. Choose the delay after bremsstrahlung, and the strength of the signal need with the optimized delay time should be sufficient.</li>
	<li>Use the spectrometer to gather a spectrum for the analysis. Gather 20 frames of the spectrum, and obtain the average for LIBS analysis.</li>
	<li>Shut off the working current of the furnace and cool the samples. Solidification of the samples requires approximately 15 min.</li>
	<li>Inject nitrogen into the experimental furnace to break the vacuum.</li>
	<li>Open the lid of the experimental furnace and remove the solidification samples.</li>
	<li>Repeat step 3.3 to 4.10 until all samples are measured.</li>
</ol>
5. Construct Calibration Curve of Quantitative Analysis
<ol>
	<li>Spectrum pretreatment
	<ol>
		<li>Background correction. Delete the background effect caused by braking radiation. The method of baseline correction is employed in the experiment.</li>
		<li>Spectrum-peak searching. Use a two-order derivative method to identify peaks of each element; local minimum points are weighted.</li>
		<li>Spectrum fitting. Apply a Lorentz spectra overlay to the selected peaks to prevent self-corrosion or overlap. The spectral peak intensity, stretch status, and center wavelength is obtained by a fitting algorithm.</li>
	</ol>
	</li>
	<li>Import the chemical ingredient analysis results of all standard samples.</li>
	<li>Construct the calibration curve.
	<ol>
		<li>Choose an inner relative standard wavelength. The main element spectral lines are always selected.</li>
		<li>Choose a calibration wavelength. Select from the NIST spectrum database15.</li>
		<li>Fit the curve. Use linear fitting or quadratic fitting.</li>
	</ol>
	</li>
	<li>Achieve analysis precision. Calculate the fitting factor and relative standard error after fitting. A program is used to automatically select the best relative standard wavelength and calibration wavelength from the wavelength base of NIST15.</li>
</ol>
6. Elemental Composition Analysis of Molten Alloy
NOTE: The experimental setup has been divided to two parts, namely, the detector head and the control cabinet, as shown in Figure 1. The same laser and spectrometer parameters, moulting, and spectrum gathering process employed in the previous process are utilized to ensure accurate quantitative analysis results.
<ol>
	<li>Put the unknown sample into the smelting system.</li>
	<li>Vacuum the experimental system.</li>
	<li>Increase the smelting current until the sample is molten. The melting temperature is approximately 1,700 &#176;C, and the melting time is approximately 45 min.</li>
	<li>Open the laser generator and realize the pulse laser output. Use the following laser parameters: pulse width is 20 ns, frequency is 5 Hz, and energy of each pulse is 90 mJ.</li>
	<li>Open the spectrometer and the spectrum deposit software to determine the spectrum. Employ the same spectrometer with a spectral range from 190 to 600 nm and resolution of 0.06 nm at a wavelength of 200 nm. The integration time of the spectrometer is 10 ms. The spectrometer is used to trigger the laser and determine the spectrum.</li>
	<li>Adjust laser focusing position. Optimize focusing position until the strongest spectrum signal is attained; the value of the highest peak should exceed 10,000.</li>
	<li>Determine laser breakdown spectrum. Each laser pulse generates a frame of the spectrum; 20 frames of the spectrum are obtained and averaged for the analysis.</li>
	<li>Spectrum pretreatment. Perform background correction, such as deleting the background effect caused by braking radiation, as mentioned in 5.1.3, to perform spectrum fitting.</li>
	<li>Elemental concentration calculation. Perform analysis elemental concentration by the internal standard method from the calibration curve.</li>
</ol>

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	<li>Radziemski, L., Cremers, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+brief+history+of+laser-induced+breakdown+spectroscopy:+From+the+concept+of+atoms+to+LIBS+2012.">A brief history of laser-induced breakdown spectroscopy: From the concept of atoms to LIBS 2012.</a> Spectrochimica Acta Part B: Atomic Spectroscopy. 87, 3-10 (2013).</li><li>El Haddad, J., Canioni, L., Bousquet, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Good+practices+in+LIBS+analysis:+Review+and+advices.">Good practices in LIBS analysis: Review and advices.</a> Spectrochimica Acta Part B: Atomic Spectroscopy. 101, 171-182 (2014).</li><li>Mueller, M., Gornushkin, I. B., Florek, S., Mory, D., Panne, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Approach+to+Detection+in+Laser-Induced+Breakdown+Spectroscopy.">Approach to Detection in Laser-Induced Breakdown Spectroscopy.</a> Analytical Chemistry. 79 (12), 4419-4426 (2007).</li><li>Noll, R., Fricke-Begemann, C., Brunk, M., Connemann, S., Meinhardt, C., Schsrun, M., Sturm, V., Makowe, J., Gehlen, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser-induced+breakdown+spectroscopy+expands+into+industrial+applications.">Laser-induced breakdown spectroscopy expands into industrial applications.</a> Spectrochimica Acta Part B: Atomic Spectroscopy. 93, 41-51 (2014).</li><li>Leon, R., David, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+brief+history+of+laser-induced+breakdown+spectroscopy:+From+the+concept+of+atoms+to+LIBS+2012.">A brief history of laser-induced breakdown spectroscopy: From the concept of atoms to LIBS 2012.</a> Spectrochimica Acta Part B: Atomic Spectroscopy. 87, 3-10 (2013).</li><li>El Haddad, J., Canioni, L., Bousquet, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Good+practices+in+LIBS+analysis:+Review+and+advices.">Good practices in LIBS analysis: Review and advices.</a> Spectrochimica Acta Part B: Atomic Spectroscopy. 101, 171-182 (2014).</li><li>Gonzaga, B. F., Pasquini, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+compact+and+low+cost+laser+induced+breakdown+spectroscopic+system:+Application+for+simultaneous+determination+of+chromium+and+nickel+in+steel+using+multivariate+calibration.">A compact and low cost laser induced breakdown spectroscopic system: Application for simultaneous determination of chromium and nickel in steel using multivariate calibration.</a> Spectrochimica Acta Part B: Atomic Spectroscopy. 69, 20-24 (2012).</li><li>Peter, L., Sturm, V., Noll, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liquid+steel+analysis+with+laser-induced+breakdown+spectrometry+in+the+vacuum+ultraviolet.">Liquid steel analysis with laser-induced breakdown spectrometry in the vacuum ultraviolet.</a> Applied Optics. 42 (30), 6199-6204 (2003).</li><li>Hubmer, G., Kitzberger, R., M&#246;rwald, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+LIBS+to+the+in-line+process+control+of+liquid+high-alloy+steel+under+pressure.">Application of LIBS to the in-line process control of liquid high-alloy steel under pressure.</a> Analytical and Bioanalytical Chemistry. 385 (2), 219-224 (2006).</li><li>Sun, L. X., Yu, H. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Automatic+estimation+of+varying+continuum+background+emission+in+laser-induced+breakdown+spectroscopy.">Automatic estimation of varying continuum background emission in laser-induced breakdown spectroscopy.</a> Spectrochimica Acta Part B: Atomic Spectroscopy. 64, 278-287 (2009).</li><li>Lin, X. M., Chang, P. H., Chen, G. H., Lin, J. J., Liu, R. X., Yang, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+melting+iron-based+alloy+temperature+on+carbon+content+observed+in+laser-induced+breakdown+spectroscopy.">Effect of melting iron-based alloy temperature on carbon content observed in laser-induced breakdown spectroscopy.</a> Plasma Science &amp; Technology. 17 (11), 933-937 (2015).</li><li>Rai, A. K., Yueh, F. Y., Singh, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser-induced+breakdown+spectroscopy+of+molten+aluminum+alloy.">Laser-induced breakdown spectroscopy of molten aluminum alloy.</a> Applied Optics. 42 (12), 2078-2084 (2003).</li><li>Hanson, C., Phongikaroon, S., Scott, J. 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G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NIST+Chemistry+WebBook,+NIST+Standard+Reference+Database+Number+69.">NIST Chemistry WebBook, NIST Standard Reference Database Number 69.</a> National Institute of Standards and Technology. , 20899 (2018).</li></ol>

The authors have nothing to disclose.

For elemental analysis, popular methods are X-ray fluorescence (XRF), spark discharge optical emission spectrometry (SD-OES), atomic absorption spectroscopy (AAS), and inductive couple plasma (ICP). These methods are mainly suited for a laboratory and industrial online application for molten alloys, which is determined by the characters of these technologies, is difficult. XRF uses X-rays to shock samples, and SD-OES makes sparks on the samples. The working distance of these two methods are always in the range of several centimetres. AAS and ICP yields liquid or powder samples, which requires several tens of minutes for preparation. These methods are not suitable for high-temperature samples or measurements from a distance of several metres. Compared with these analysis methods, LIBS has the advantages of long-distance analysis, fast analysis, and the need to prepare samples. LIBS is the only good method for realizing melting alloys ingredient online analysis.
The protocol includes three critical steps: using a laser to burn the molten alloy, using a spectrometer to determine the spectrum of the plasma, and quantitatively analyzing the elemental composition with the calibration curve. Preparation of the samples with gradient components and construction of the calibration curve to demonstrate the relation between the laser breakdown spectrum intensity and the elemental content are preparative steps.
Use of the LIBS to analyze the elemental composition of molten alloy has some limitations. The precision of the quantitative analysis is the most important problem. The precision of LIBS is expected to improve by an order of magnitude. The gas pressure, surface status of the samples, and focusing precision have a distinct influence on the precision; however, compensation of these errors is difficult1,2,6.
Use of the LIBS system for on-line analysis of elemental composition during vacuum melting is proven by experiments. The experimental results have shown that the plasma spectrum can be determined in a typical industrial vacuum melting furnace situation. The calibration results show that the major components of molten alloys can be quantitatively analysed.

Due to its unique features, such as remote sensing, fast analysis, and no need for sample preparation, laser-induced breakdown spectroscopy (LIBS) offers unique capabilities for on-line concentration determination1,2,3. Although the use of the LIBS technique in different fields has been investigated4,5,6, a considerable attempt to develop its capabilities in industrial applications is ongoing.
Analysis of molten material contents during the course of industrial processes can effectively improve the product quality, which is a promising development direction of LIBS. Experimental findings have been reported about the application of LIBS in the industrial field, such as findings about argon oxygen liquid steel7,8,9,10,11, molten aluminium alloy12, molten salt13, and molten silicon14. The majority of these materials exist in the environment of air or an assistant gas. However, vacuum induction melting (VIM) is another good application field of LIBS to realize processing control. A VIM furnace can realize smelting at temperatures higher than 1,700 &#176;C for alloy refining; it is the most popular method for refining high-purity metal and alloys such as iron-base or nickel-base alloys, high purity alloys, and clean magnetic alloys. During the course of melting, the pressure in a furnace is always in the region of 1-10 Pa, and the composition of air in the furnace mainly includes the air absorbed on the sample or the inner wall of the furnace and some vaporous oxide or nitride metal. These working situations induce quite different LIBS measurement situations for smelting in air. Here, we report an experimental investigation of the analysis of molten alloy during the course of VIM by LIBS.
An optical window is added to a furnace for laser ablation and radiant light detection. A silica glass with a diameter of 80 mm serves as the window. An emitting laser and gathering of radiant light employ the same window; it is a co-axial optical structure that focuses on the same point. The working focal length is approximately 1.8 m, and the focusing length of the experimental setup can be adjusted from 1.5 to 2.5 m.
Based on the practicality of industrial online analysis, precision, repeatability and stability is more important than the low limit of detection (LOD) during molten alloy ingredient analysis. The technical route of a four-channel linear CCD spectrometer is chosen, the spectral range of the spectrometer ranges from 190 to 600 nm, the resolution is 0.06 nm, and the wavelength is 200 nm. A laser diode pumped Q-switched laser (constructed in house) is used to ablate molten alloy, with an output energy of 100 mJ, a frequency of 5 Hz, an FWHM pulse width of 20 ns, and a working wavelength of 1064 nm. The remaining part will present the VIM LIBS-analysing process and live measurement, followed by an introduction of the data processing results.

<table border="0" cellpadding="0" cellspacing="0" style="width:699px;" width="699">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Laser source</td>
			<td style="width:135px;">Gklaser Co.,Ltd.</td>
			<td style="width:119px;"></td>
			<td style="width:229px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Molten alloy to be measured</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Smelting furnace</td>
			<td style="width:135px;">Tianyu Co.,Ltd.</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Spectrometer</td>
			<td style="width:135px;">Avantes</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">standard samples</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td>Well known of its composition</td>
		</tr>
	</tbody>
</table>

quantitative analysis of vacuum induction melting by laser-induced breakdown spectroscopy

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves several steps, include drawing samples, cooling, cutting, transport to the laboratory, and analysis. The whole analysis process requires more than 30 minutes, which hinders on-line process control. Laser-induced breakdown spectroscopy is an excellent on-line analysis method that can satisfy the requirements of vacuum induction melting because it is fast and noncontact and does not require sample preparation. The experimental facility uses a lamp-pumped Q-switched laser to ablate melted liquid steel with an output energy of 80 mJ, a frequency of 5 Hz, a FWHM pulse width of 20 ns, and a working wavelength of 1,064 nm. A multi-channel linear charge coupled device (CCD) spectrometer is used to measure the emission spectrum in real time, with a spectral range from 190 to 600 nm and a resolution of 0.06 nm at a wavelength of 200 nm. The protocol includes several steps: standard alloy sample preparation and an ingredient test, smelting of standard samples and determination of the laser breakdown spectrum, and construction of the elements concentration quantitative analysis curve of each element. To realize the concentration analysis of unknown samples, the spectrum of a sample also needs to be measured and disposed with the same process. The composition of all main elements in the melted alloy can be quantitatively analyzed with an internal standard method. The calibration curve shows that the limit of detection of most metal elements ranges from 20-250 ppm. The concentration of elements, such as Ti, Mo, Nb, V, and Cu, can be lower than 100 ppm, and the concentrations of Cr, Al, Co, Fe, Mn, C, and Si range from 100-200 ppm. The R2 of some calibration curves can exceed 0.94.

Ten nickel-based alloy samples (#1-#10) are used to construct internal-standard calibration curves. The compositions of all samples are listed in Table 1. The elemental concentrations of these samples are orthogonally designed to avoid signal interference. The concentration of each element in all samples is measured with chemical analysis methods.
Nickel is the internal standard element. The calibration curves of Cu, Ti, Mo, Al, and Cr are constructed. Figure 2 to Figure 6 show the calibration results. In these figures, the X-axis represents the concentration of the calibrated elements, and the Y-axis represents the relative signal intensity ratio of the calibrated element after the disposal process of background correction and peak fitting. The error bar of each point in these figures shows the fluctuation range of the signal strength with twenty frame measurements. The calibration parameters of these elements are listed in Table 3 to Table 7. The linear curve fitting results, including the residual sum of squares, Pearson&#39;s r, and the linear fitting coefficient R2, are shown from Figure 2 to Figure 6. The intercept and slope of the coefficient of determination are also shown in these figures. The calibration curves show a near-linear relationship between the concentration of the element and the peak intensity. The spectral lines used for each element were introduced in the legend of these figures. These lines are searched by a method of filtration. All signal peaks are filtered by the signal intensity, the central of wavelength, and the Lorenz fitting effect. These selected peaks are chosen by a permutation-combination analysis of the fitting factor R2.
According to the standard of International Union of Pure and Applied Chemistry (IUPAC), 3&#963; limit of detection (LOD) of Cu, Ti, Mo, Al and Cr are calculated and listed in Table 8. Other elements, such as Si, C, and Nb, are analyzed. The RSD ranges from 4-6%, and the R2 exceeds 0.93. The precision can be improved if a better relative standard is employed.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57903/57903fig1.jpg" /> 
Figure 1: Experimental setup of quantitative analysis in the process of vacuum induction melting by laser-induced breakdown spectroscopy. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57903/57903fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57903/57903fig2.jpg" /> 
Figure 2: Calibration curves of Cu. Internal standard lines include Cu: 224.70 nm, Ni: 241.61 nm and 233.75 nm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57903/57903fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57903/57903fig3.jpg" /> 
Figure 3: Calibration curves of Ti. Internal standard lines include Ti: 444.38 nm and 337.22 nm, Ni: 445.90 nm and 313.41 nm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57903/57903fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57903/57903fig4.jpg" /> 
Figure 4: Calibration curves of Mo. Internal standard lines include Mo: 342.23 nm, 346.02 nm, and 277.44 nm, Ni: 440.16 nm and 336.68 nm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57903/57903fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57903/57903fig5.jpg" /> 
Figure 5: Calibration curves of Al. Internal standard lines include Al: 272.31 nm, 231.22 nm, and 334.85 nm, Ni: 221.65 nm, 332.23 nm, and 440.16 nm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57903/57903fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/57903/57903fig6.jpg" /> 
Figure 6: Calibration curves of Cr. Internal standard lines include Cr: 286.51 nm, 302.67 nm and 342.12 nm, Ni: 224.27 nm, 233.75 nm, and 350.08 nm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57903/57903fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Table 1" src="/files/ftp_upload/57903/57903table1.jpg" /> 
Table 1: Raw material ingredients in the experiment.
<img alt="Table 2" src="/files/ftp_upload/57903/57903table2.jpg" /> 
Table 2: Standard nickel-based alloy samples ingredient measured results.
<img alt="Table 3" src="/files/ftp_upload/57903/57903table3.jpg" /> 
Table 3: Calibration data of Cu.
<img alt="Table 4" src="/files/ftp_upload/57903/57903table4.jpg" /> 
Table 4: Calibration data of Ti.
<img alt="Table 5" src="/files/ftp_upload/57903/57903table5.jpg" /> 
Table 5: Calibration data of Mo.
<img alt="Table 6" src="/files/ftp_upload/57903/57903table6.jpg" /> 
Table 6: Calibration data of Al.
<img alt="Table 7" src="/files/ftp_upload/57903/57903table7.jpg" /> 
Table 7: Calibration data of Cr.
<img alt="Table 8" src="/files/ftp_upload/57903/57903table8.jpg" /> 
Table 8: Limit of detection of Cu, Ti, Mo, Al, and Cr.

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Quantitative Analysis of Vacuum Induction Melting by Laser-induced Breakdown Spectroscopy

During vacuum induction melting, laser-induced breakdown spectroscopy is used to perform real-time quantitative analysis of the main-ingredient elements of a molten alloy.

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves ...

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7.2K Views.  Chinese Academy of Sciences. During vacuum induction melting, laser-induced breakdown spectroscopy is used to perform real-time quantitative analysis of the main-ingredient elements of a molten alloy.

Video: Quantitative Analysis of Vacuum Induction Melting by Laser-induced Breakdown Spectroscopy

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

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

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

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

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

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

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

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

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

Investigating Single Molecule Adhesion by Atomic Force Spectroscopy

Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment.

A protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. Procedures and examples to determine the adhesion force and free energy of these molecules on solid supports and bio-interfaces are provided.

Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single ...

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

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

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

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

Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. Conventionally reserved for the fabrication of metal thin films, thermal evaporation deposits bismuth into an array of vertical single crystalline nanowires over a flat thin film of vanadium held at RT, which is freshly deposited by magnetron sputtering or thermal evaporation. By controlling the temperature of the growth substrate the length and width of the nanowires can be tuned over a wide range. Responsible for this novel technique is a previously unknown nanowire growth mechanism that roots in the mild porosity of the vanadium thin film. Infiltrated into the vanadium pores, the bismuth domains (~ 1 nm) carry excessive surface energy that suppresses their melting point and continuously expels them out of the vanadium matrix to form nanowires. This discovery demonstrates the feasibility of scalable vapor phase synthesis of high purity nanomaterials without using any catalysts.

A protocol for seedless and high yield growth of bismuth nanowire arrays through vacuum thermal evaporation technique is presented.

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. ...

Laser-induced Forward Transfer of Ag Nanopaste

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

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

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

Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted ...

Quantitative Hardness Measurement by Instrumented AFM-indentation

In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness measurements on an Au(111) surface with atomistic resolution of single plasticity events. A careful experimental procedure is described that includes the force sensor selection, its calibration, the calibration of the cantilever deflection detection system, and the minimization of instrumental drift for accurate and reproducible force-distance measurements. Also, a method for the data analysis is presented that allows the extraction of force-penetration curves from recorded force-distance curves. A typical curve displays a clear elastic deformation regime up to the first plasticity event, or pop-in, with a length in the range of one to two Burger's vectors. Later plasticity events exhibit the same magnitude. The work of plasticity is further extracted from the measurements. Finally, the hardness is determined in combination with the indentation curve using non-contact atomic force microscopy images of the remaining indents.

This experimental protocol describes how atomic force microscopy can be used to measure hardness at the true nanometer scale and to detect single atomistic plasticity events.

In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness ...

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

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

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

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

Production and Characterization of Vacuum Deposited Organic Light Emitting Diodes

A method for producing simple and efficient thermally-activated delayed fluorescence organic light-emitting diodes (OLEDs) based on guest-host or exciplex donor-acceptor emitters is presented. With a step-by-step procedure, readers will be able to repeat and produce OLED devices based on simple organic emitters. A patterning procedure allowing the creation of personalized indium tin oxide (ITO) shape is shown. This is followed by the evaporation of all layers, encapsulation and characterization of each individual device. The end goal is to present a procedure that will give the opportunity to repeat the information presented in cited publication but also using different compounds and structures in order to prepare efficient OLEDs.

A protocol for the production of simple structured organic light-emitting diodes (OLEDs) is presented.

A method for producing simple and efficient thermally-activated delayed fluorescence organic light-emitting diodes (OLEDs) based on guest-host or exciplex ...