New horizons in sputter depth profiling inorganics with giant gas cluster sources: Niobium oxide thin films

Abstract

X‐ray photoelectron spectroscopy is used to study a wide variety of material systems as a function of depth (“depth profiling”). Historically, Ar+ has been the primary ion of choice, but even at low kinetic energies, Ar+ ion beams can damage materials by creating, for example, nonstoichiometric oxides. Here, we show that the depth profiles of inorganic oxides can be greatly improved using Ar giant gas cluster beams. For NbOx thin films, we demonstrate that using Arx+ (x = 1000‐2500) gas cluster beams with kinetic energies per projectile atom from 5 to 20 eV, there is significantly less preferential oxygen sputtering than 500 eV Ar+ sputtering leading to improvements in the measured steady state O/Nb ratio. However, there is significant sputter‐induced sample roughness. Depending on the experimental conditions, the surface roughness is up to 20× that of the initial NbOx surface. In general, higher kinetic energies per rojectile atom (E/n) lead to higher sputter yields (Y/n) and less sputter‐induced roughness and consequently better quality depth profiles. We demonstrate that the best‐quality depth profiles are obtained by increasing the sample temperature; the chemical damage and the crater rms roughness is reduced. The best experimental conditions for depth profiling were found to be using a 20 keV Ar2500+ primary ion beam at a sample temperature of 44°C. At this temperature, there is no, or very little, reduction of the niobium oxide layer and the crater rms roughness is close to that of the original surface.

Hybrid Perovskites Depth Profiling with Variable-Size Argon Clusters and Monatomic Ions Beams

“…On the one hand, by lowering the cluster energy ( E or E/n ), one would expect to reduce the ion beam induced mixing and thus improve the depth resolution. On the other hand, lowering the cluster energy would result in the lowering of the sputtering rate (profile duration), possibly resulting in the roughening and/or in the accumulation of damages during the profile (induced by both the analysis and the sputtering beam) [ 27 , 28 , 29 , 30 ]. For model hybrid samples ( Irganox ) and biological samples, increasing the cluster energy up to 40 keV was shown as beneficial to improve the molecular signals intensities and the lateral resolution [ 31 ].…”

Femtosecond Laser Desorption Postionization MS vs ToF-SIMS Imaging for Uncovering Biomarkers Buried in Geological Samples

“…17,25,43,44 The work presented here demonstrates that the advantages of fs-LDPI-MS extend into the realm of depth profiling of geological samples. ToF-SIMS is the standard technique for MS imaging of organics in geological samples, 11−15 but it is limited by the nm/min removal rates for overlayer material by gaseous cluster ion beams 45 and high fragmentation of species during analysis. By contrast, fs-LDPI-MS allows removal rates of on the order of μm/s.…”

“…LDPI-MS using nanosecond pulsed laser desorption has been studied for three decades, ,, and new instrumental designs continue to be introduced. , However, the advantages of fs-LDPI-MS for universal ablation and high spatial resolution have only recently begun to be explored. ,,, The work presented here demonstrates that the advantages of fs-LDPI-MS extend into the realm of depth profiling of geological samples. ToF-SIMS is the standard technique for MS imaging of organics in geological samples, − but it is limited by the nm/min removal rates for overlayer material by gaseous cluster ion beams and high fragmentation of species during analysis. By contrast, fs-LDPI-MS allows removal rates of on the order of μm/s.…”

Materials Analysis Using Secondary Ion Mass Spectrometry: Challenges and Opportunities

“…Polyatomic ion beams, particularly SF 5 + , C 60 + and Ar GCIB, have enabled the development of molecular depth profiling for organic materials, such as polymers and molecular layers [7,8], and led to improvements in the depth profiling of inorganic materials by reducing preferential sputtering and surface roughening effects [9]. When a primary ion strikes a substrate, material is sputtered from the outermost 10-20 Å, and upon repeated striking the same spot multiple times SIMS can provide chemical information as a function of depth (a "depth profile") if the rate of sample erosion is known.…”

“…Using atomic primary ions molecular depth profiles could not be obtained because the collision cascade caused by the primary ion impact penetrated deep into the sample leading to chemical damage and intermixing of the layers. Cluster ion beams do not penetrate as deep into the samples and have high sputter rates leading to less interlayer mixing and significantly reduced chemical damage [9]. The unique properties of cluster ion beam SIMS -greatly reduced sample damage, relatively flat crater bottoms and significantly enhanced secondary ion production -have also led to the development of 3d chemical imaging in which SIMS two-dimensional SIMS imaging and depth profiling have been combined [2].…”