Another way to interpret the results shown in Fig. is through the Langmuir model of mass balance at the surface sites. This model sees through the perspective of local precursor concentration and the consequent impact on precursor molecule occupancy at surface sites for the deposition process. With Xe co-flow, the differential diffusion rates of TEB and Xe result in a concentration gradient along the trench depth, as shown in Fig. of the supplementary information. This, in turn, modifies the local dilution of the TEB molecules at the surface site along the trench depth in addition to the modification in the absolute local influx. At the trench top, a minor thinning of the film, i.e., from 453 nm to 436 nm, suggests a reduced Langmuir adsorption of TEB due to the presence of Xe. Conversely, at the trench bottom, an enhanced concentration of TEB enhances the Langmuir adsorption rate, facilitating more precursor molecules to attach and promote film growth. Furthermore, decrease in film thickness from 453 nm to 442 nm with 50 sccm Xe flow (see supplementary information) aligns with this observation. A similar observation can be made with Ar (Fig. ). However, unlike Xe, Ar does not cause any differential dilution to result an enhancement in the SC. On the other hand, the probability of lighter Ar undergoing collisions with TEB is much less than that of collisions with Ar itself due to the two orders of magnitude higher partial pressure for Ar, preventing possible diminution of the SC. Whereas, in the case of Xe and TEB, the dynamics are reversed, the lighter TEB molecules are benefited from the elastic collisions with the excess heavier Xe with a higher probability than undergoing collisions with TEB molecule itself. The overall pathway that resulting in the observed SC enhancement is likely a result of collective effect of more than one phenomenon. % increase in carbon content was noticed for the films deposited with the Xe co-flow, see supplementary information. We attribute this to a small change in the ratio of β-hydride elimination to hydrogen assisted ligand elimination, which are the two different decomposition pathways for TEB. The β-hydride elimination forms more reactive ethylene (C2H4) which could contribute to higher C in the film, while the hydrogen assisted elimination forms less reactive ethane (C2H6). The addition of Xe induces a small reduction in the hydrogen partial pressure, 4887 Pa H2 and 113 Pa Xe, as compared to 4999 Pa H2 without Xe co-flow, which will affect the gas phase chemistry of TEB. In our previous work, we observed that the boronto-carbon ratio shifted from B4C to B3C when transitioning from purely Hydrogen to purely Argon ambient. While our focus remains on conformality enhancement, we appreciate the broader implications of these phenomena. In addition to higher SC with a Xe co-flow, we also note a more uniform film deposition over a flat substrate surface, as shown by the deposition rate mapped over 10 mm x 100 mm area for films deposited with and without Xe co-flow (Fig. ). The deposition rate distribution ranged from 7.6 nm/min to 0 nm/min without Xe, while the introduction of a Xe co-flow yielded a more uniform film deposition with a deposition rate ranging from 7.3 nm/min to 1.5 nm/min. These results suggest that the Xe co-flow enhances the precursor diffusion also on a lateral macroscale in the CVD reactor, not only on a vertical microscale in the trenches. We attribute the changes in growth rate distribution over the large area to the enhanced diffusion on a reactor scale. Additionally, this could also be due to a reduction in surface residence time for reactive intermediates, caused by the addition of heavy Xe gas, which lead to a higher lateral spread. This implies that reactive species spend lesser time absorbed on the surface, allowing for a more effective lateral spread of the gas mixture across the substrate.