Binding states of hydrogen and of nitrogen on the (100) plane of molybdenum

Abstract

The binding states and desorption kinetics of hydrogen and nitrogen on the (100) plane of Mo are examined by flash desorption mass spectrometry, and the results are compared with the adsorption of these gases on (100) W. Since molybdenum and tungsten are isoelectronic and have the same crystal structure and lattice constant, differences must be attributed to differences in the electronic properties of the substrates. It is found that, while there is a good correlation between the binding states of these gases and between the binding states of each gas on the substrates, there are several interesting differences. There is an extra binding state observed for hydrogen on (100)Mo which is not observed on (100)W. It is suggested that this state may also exist on (100)W but not be observed in flash desorption. It is also found that there are significant differences between the binding energies on the substrates. Hydrogen is much more strongly bound on W while nitrogen is more strongly bound on Mo. The difference in hydrogen adsorption is interpreted in terms of the greater bonding capabilities of the 5d vs. 4d electrons of the substrates, while the strength of the nitrogen adsorption bond on Mo is attributed to the lateral interaction in the plane of the substrates which should be stronger for Mo than for W.(1) This work partially supported by ARPA under Grant DAHC15-69-G6.(2) (a)

Surface spectroscopic studies of the deposition of TiN thin films from tetrakis-(dimethylamido)-titanium and ammonia

“…At 1000 K, a broad gaseousnitrogen ͑N 2 ͒ feature was observed. This state resembled the recombinative desorption of nitrogen-adatoms from tungsten surfaces 14,15 ͑1200-1500 K͒. Post-desorption analyses by XPS and AES revealed that a significant amount of carbon and titanium residue remained on the surface after heating to 1400 K. Similar results are observed from Ta and Re substrates.…”

Design of Active Centers in Ammonia Synthesis on Mo-Based Catalysts: A Theoretical Study

“…The strongly bound N states inhibit the formation of lower-coordinated active states and thus suppress the catalytic activity of the Mo bcc planes (100), (111), and (211). In contrast to these planes, the most active site 6 Mo 3 2 gives E des = 359.6 kJ/mol that is close to the experimental E des of 361.6 kJ/mol at the same coverage θ N = 0.5 ML [36]. The Q N and E diff resulted from the DFT and MIB calculations are in agreement for the plane Mo(111), and show the same sequence but disagree for the plane Mo(100) (ESM), probably due to the rearrangement of near-surface Mo atoms (Table 3).…”

“…The activation energy E diff for N diffusion was estimated as the minimum difference between the Q N of the dominant site [having the maximum θ N provided by the maximum Q N (2), for example, M 4 and M 3 on the face-centered cubic (fcc) planes (100) and (111), respectively] and the Q N of the adjacent site (for example, M 2 on the same planes). The rate of N 2 desorption from metal surfaces is mainly determined by N diffusion [36,44], so the activation energy of second order recombinative N 2 desorption was estimated as E des ≈ 2E diff [45]. Reliability of the calculations was tested by conformity between the calculated and reference E diff and E des .…”

The chemisorption of O2, CO, D2 and C2H4 over epitaxially grown rhenium crystalline films

“…This means that some dissociation of CO may take place at room temperature, contrary to the results obtained by Ducros et al [1]. [26,27], and the multiple states observed in the Mo and W(OOl) and Re (0001) surfaces [28,29].…”