# Study on Nitrogen-Doped Graphene Ink and Its Effects on the Heat Dissipation for the LED Lamps
## 5 Conclusions  
The application of the NDG ink for the thermal management of the LED lamps was studied in this paper. The NDG ink was also tested for adhesion and electrical resistance. The corresponding inspections including XPS, AFM, and Raman spectroscopy were used to investigate the characterization of the NDG powder in this study. The results can be concluded as follows:  
1. As a result of the XPS inspection, it was found that the content of the detected nitrogen component in NDG was 3.8%.
2. The AFM test results for the NDG powder showed that the height of the stacked NDG layers was 1.277 nm. The roughness Rq can be an index of wrinkles and defects for the graphene film. The roughness Rq of the NDG sample in this study was 0.9 nm, the same as that of graphene on glass with a Ti coating thickness of about 4 nm in [22].
3. In the Raman analysis, the intensity ratio of D and G bands (i.e., (\(I_{\text{D}}\)/\(I_{\text{G}}\) ratio) showed the defects of the NDG samples where a higher ratio produced more defects on NDG. The result of the NDG in this study was 0.729 (436/597.9). In addition, the NDG in this study belonged to the multi-layer graphene with a layer number over 10.
4. When the NDG ink was spray-baked, the cross-cut adhesion test was performed in accordance with ASTM D3359. The results showed that small pieces of peeling were found at the intersection of the cuts. The actual damage in the grid area was less than 5%, which was judged to be class 4B for the NDG, according to ASTM D3359.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Point** & **Original Lamp** & **Fin-Removed Lamp** & **NGC Lamp** \\ \hline
1 & 52.2 & 67.7 & 47 \\
2 & 53.8 & 63.7 & 49.6 \\
3 & 50.4 & 69.1 & 50.5 \\
4 & 51.1 & 65.7 & 52.2 \\
5 & 68.9 & 75.6 & 67.9 \\
6 & 69.3 & 82.5 & 68.6 \\
7 & 75.7 & 85.9 & 70.7 \\
8 & 74.7 & 76.1 & 68.1 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Stable temperature distribution for the different LED lamps (Unit: \({}^{\circ}\)C).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Lamp Type** & **Original** & **Fin-Removed** & **NGC** \\ \hline Power (W) & 8.35 & 8.35 & 8.35 \\ Lumen (lm) & 753.99 & 717.02 & 781.42 \\ Light efficiency (lm/W) & 90.29 & 85.87 & 93.58 \\ Color rendering Index & 69.7 & 70.6 & 71.4 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Properties for the different LED types.  
In the four-point probe resistance experiment, the NDG ink had a high electrical resistance, and its volumetric resistance was greater than \(10^{9}\)\(\Omega\)-cm, which was in the range of an insulator. This proved that the NDG ink was suitable for the LED lamp coating, which is required to have high electrical resistance.
* According to the PCBA temperature measurements, the results showed that the performance of the NGC lamp was the best among the tested LED lamps. Compared to the fin-removed LED lamp, the temperature drop ratio was 17.9% for the NGC lamp and 11.9% for the original lamp (heat transfer enhancement with fins).
* In the integrating sphere experiment, compared to the original lamp with the luminous efficiency of 90.29 lm/W, the NGC lamp improved the effective luminous efficiency with a value of 93.58 lm/W.  
Conceptualization: A.-D.L., W.-K.Y. and C.-M.H.; Data curation: A.-D.L., W.-K.Y. and S.Z.P.; Formal analysis: A.-D.L. and W.-K.Y.; Funding acquisition: A.-D.L., C.-Y.C. and C.-M.H.; Investigation: A.-D.L., W.-K.Y. and C.-M.H.; Methodology: A.-D.L. and W.-K.Y.; Project administration: A.-D.L., W.-K.Y., S.Z.P., C.-X.C. and C.-M.H.; Resources: A.-D.L.; Software: W.-K.Y.; Supervision: A.-D.L., W.-K.Y., S.Z.P. and C.-Y.C.; Validation: W.-K.Y.; Writing--original draft: A.-D.L. and W.-K.Y.; Writing--review & editing: A.-D.L., W.-K.Y., S.Z.P., C.-Y.C. and C.-M.H. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.