## 3 Results & Discussion  
### Analysis of Glass Envelope  
XPS point scans from eight positions on the interior and one position on the exterior of the glass envelope are shown in Figure 3. Arbitrary vertical shifts were applied to facilitate plotting multiple spectra. Full scans (850-0 eV) are generally dominated by the Ba-, O-, and C- peaks above 400 eV. Peaks below 400 eV are highlighted in a separate spectra; both are included in Figure 3b. The location of each point scan is indicated in Figure 3a. G7 is above the cathodes opposite the anode plate, which has pinholes with \(\sim\)0.5 mm diameters directly in line with the cathodes (see Figures 1 and 2). G1 and G2 are adjacent to the cathode assembly, and G6 is within the Ba-Al flash region. G3, G4, and G5 are behind the cathodes (see Figure 1). G8 is a reference interior point opposite the sealed opening, and G9 is a similarly located exterior reference. Peak binding energies, background-deducted counts, S/N ratios, spectral lines, and species identification for each position can be found in tables located in the Appendix A. Six elements were observed in XPS scans at various points on the glass envelope: Al, Ba, Ca, K, Mg, and Si. Ba signal, likely originating from BaO and BaCO\({}_{3}\), was observed on all interior surfaces, but were absent from the exterior reference point (G9). The strongest Ba signal was observed at G6, which is directly opposite the Ba-Al flash pans, while trace Ba signal was observed at G8, an interior point far from the flash pans and the cathodes. Moderate SiO\({}_{2}\) signal was observed everywhere except at point G6 (Ba-Al flash region), and its strength decreased noticeably at G7 (interior point in front of cathodes). Trace K, Mg, and Ca signal appeared everywhere SiO\({}_{2}\) is present; however, K is absent at G7 and Mg signal is significantly enhanced at G1-G5. Al signal was observed at all points. Signal plausibly originating from Sc was only observed at G2, where its S/N ratio = 4. However, it is important to note that the Mo 3p3/2 peak overlaps that of Sc 2p3/2. As Mo is the primary component of the anode, it cannot be asserted with absolute certainty that it is absent on the glass. Results from G9 give a baseline for the glass envelope itself: Al, Ca, K, Mg, and Si are all present. These results indicate a standard aluminosilicate glass with K, Ca, and Mg dopants [17]. Ca and Al are also both present in the impregnate (known from processing history), but K, Mg, and Si are unique to the glass. Therefore, the absence of K, Mg, and Si at G6 shows that the layer deposited by the Ba-Al flash in this region is thicker than 10 nm, the sampling depth for XPS. The spectrum at G8 differs from that of G9 only by the presence of moderate Ba signal, showing that Ba from the Ba-Al flash and/or impregnate desorption condenses onto all interior glass surfaces. The remaining points show BaO/BaCO\({}_{3}\) peaks increasing in strength from G1/G2 to G3-G5, and reaching a maximum signal (excepting point G6) at G7, a point on the glass envelope in front of the cathodes. The implication is that the thickness of deposited Ba-containing layers in these regions is no more than 10 nm, as signal from elements present only in the glass substrate is observed. While points G3-G5 and G7 are all 90\({}^{\circ}\) away from the flash pans, point G7, in front of the cathodes, is associated with greater Ba signal than points G3-G5, which are located behind the cathodes. The MgO signal is dramatically enhanced at points G3-G5 and somewhat enhanced at G1-G2. This is likely due to Auger enhancement of the Mg signal due to fluorescence from C-containing layers atop the MgO-containing glass [18]. C-containing layers less than a monolayer thick would yield minimal Auger enhancement of MgO emission (due to reduced intensity of C fluorescence) from the glass, while thicker overlayers (e.g., multiple monolayers) of C-containing material would absorb MgO  
Figure 3: (**a**) A diagram of the glass envelope introduced in Figure 1 plotted with each examined point, G1–G9.