# Compositional Analysis of Chalcopyrite Using Calibration-Free Laser-Induced Breakdown Spectroscopy
## 3 Results  
### Qualitative Analysis  
The recorded optical emission spectrum of the chalcopyrite sample is shown in Figure 2. By comparing the values of the wavelength in units of nm with spectroscopic data available online from the National Institute of Standard and Technology, USA, (NIST), the spectral lines belonging to different elements were identified [33]. It was found that the chalcopyrite spectrum is dominated by the spectral lines of just two elements, Fe and Cu. This result was expected because of the chemical composition of chalcopyrite, i.e., CuFeS\({}_{2}\). However, sulfur (S) was not identified in the spectrum, which was not surprising because of the spectral limitation of the detection system. Most of the intense lines of S lie in vacuum ultraviolet (VUV) region, 10-200 nm and these lines fall outside the spectral range of spectrometer used in this study [24]. Iron is known for its busy spectrum, having almost 13,114 lines in the region of 200-700 nm [28]. Thus, it was very difficult to identify each Fe line in the spectrum, however, a large number of Fe lines were identified. Overall, 66 lines emitted from the  
Figure 1: Schematic arrangement for LIBS2000+ detection system, showing the laser focused beam, plasma plume, and optical routing and detection of emission line from the plasma. neutral Fe-I atoms and 9 coming from the singly ionized Fe-II atoms were recognized. The spectral line at 438.58 nm was the strongest line observed for Fe-I in the spectrum. Total of 25 Cu-I lines and 8 Cu-II lines were identified and the spectral line of Cu-I at 521.80 nm was found to be the most intense line in the entire spectrum. In addition to Fe and Cu, the spectrum also contained 5 low-intensity lines of Ca-I and 2 lines of Ca-II, with the most intense line at 397.01 nm, belonging to Ca-II. Minor sodium-D lines at 588.96 nm and 589.54 nm were also noticed. One hydrogen (H) line at 656.42 nm, known as H\({}_{\alpha}\), was identified. This line may have appeared from air contribution or hydrogen content within the sample. All of the identified spectral lines of various elements are listed in Table 1. The presence of any element in a material can be confirmed by appearance of its few strong and persistent lines in optical emission spectrum and these lines can be termed as fingerprints of that element. Figure 3a,b displays a few strong lines belonging to Fe and Cu respectively, which are the fingerprints of these two elements. These lines include Fe-I lines at 438.58 nm and 440.60 nm and Cu-I lines at 510.82, 515.30, and 521.80 nm. \begin{table}
\begin{tabular}{c c} \hline
**Element** & **\(\boldsymbol{\Lambda\) (nm)** \\ \hline \multirow{4}{*}{Fe-I} & 229.43, 246.30, 252.71, 253.87, 266.48, 271.52, 276.70, 278.49, 283.15, 284.15, 285.88, 294.80, 302.30, \\  & 340.90, 342.82, 344.20, 346.71, 347.68, 349.24, 352.78, 355.70, 356.67, 357.15, 358.31, 361.02, 362.00, \\  & 363.26, 364.91, 371.02, 372.08, 373.64, 375.09, 375.96, 376.53, 376.93, 379.65, 381.4, 381.78, 382.66, \\  & 384.21, 386.06, 387.90, 388.77, 400.84, 404.82, 406.56, 407.34, 412.09, 413.45, 414.61, 420.14, 425.28, \\  & 426.25, 427.41, 430.91, 432.75, 438.58, 440.60, 441.67, 446.82, 487.41, 489.35, 492.25, 495.94, \\  & 516.75, 537.12 \\ \hline \multirow{2}{*}{Cu-I} & 228.24, 239.59, 240.53, 258.70, 259.98, 261.24, 263.17, 274.62, 275.60 \\  & 222.84, 224.78, 244.55, 249.38,310.16, 324.90, 327.52, 329.16, 330.82, 451.14, 453.07, 454.24, 458.89, \\  & 465.38, 470.72, 510.82, 515.30, 521.80, 522.66, 523.32, 529.26, 570.01, 578.19, 667.82, 674.23 \\ \hline \multirow{2}{*}{Cu-II} & 368.88, 467.72, 557.25, 558.60, 561.51, 613.72, 639.49, 640.10 \\  & 422.85, 526.93, 643.98, 646.30, 649.61 \\ \hline \multirow{2}{*}{Na-I} & 393.52, 397.01 \\  & Na-I \\ \hline \multirow{2}{*}{H} & 656.42 \\  & 42.85, 526.93, 643.98, 646.30, 649.61 \\ \hline \multirow{2}{*}{Ca-II} & 393.52, 397.01 \\  & Na-I \\ \hline \multirow{2}{*}{Na-I} & 588.96, 589.54 \\  & 656.42 \\ \hline \end{tabular}
\end{table}