Chemically alternating langmuir-blodgett thin films as a model for molecular depth profiling by mass spectrometry

Abstract

Langmuir-Blodgett multilayers of alternating barium arachidate and barium dimyristoyl phosphatidate are characterized by secondary ion mass spectrometry employing a 40 keV buckminsterfullerene (C 60 ) ion source. These films exhibit well-defined structures with minimal chemical mixing between layers, making them an intriguing platform to study fundamental issues associated with molecular depth profiling. The experiments were performed using three different substrates of 306 nm, 177 nm, and 90 nm in thickness, each containing six subunits with alternating chemistry. The molecular subunits are successfully resolved for the 306 nm and 177 nm films by cluster ion depth profiling at cryogenic temperatures. In the depth profile, very little degradation was found for the molecular ion signal of the underneath layers compared with that of the top layer, indicating that the formation of chemical damage is removed as rapidly as it is formed. The resolving power decreases as the thickness of the alternating subunits decrease, allowing a depth resolution of 20 to 25 nm to be achieved. The results show the potential of LB films as an experimental model system for studying fundamental features of molecular depth profiling. (J Am Soc Mass Spectrom 2008, 19, 96 -102)

Cluster secondary ion mass spectrometry of polymers and related materials

“…PS depth profiling was unsuccessful at all temperatures, similar to what was observed with SF þ 5 (Mahoney et al, 2006a). Though low temperatures did not appear to help with the PMMA samples when employing C þ 60 , low temperatures are still turning out to be ideal in some organic systems (Zheng, Wucher, & Winograd, 2008).…”

“…In the second case, the sputter rate at the interface is expected to be reduced because the material being removed from the interface is a highly damaged overlayer with significantly reduced sputter rates as compared to the original polymer. In such cases, there is a slightly increased probability of More recent work has been published on the preparation of model multilayer films, which can serve as organic ''delta-layers'' (commonly used reference samples for dynamic SIMS in the semiconductor industry), thus allowing for more direct comparisons (Shard et al, 2008;Zheng, Wucher, & Winograd, 2008). In these films, the sputter rates and densities of the materials are very similar such that accurate depth resolutions can be obtained and compared.…”

A Computational Investigation of C60 Depth Profiling of Ag: Molecular Dynamics of Multiple Impact Events

“…[3][4][5][6][7][8][9][10][11][12] For example, it is possible to analyze multilayered structures used in the electronics/semiconductor industry, 6,13 as well as perform molecular specific depth profiles of cells and other biologically important systems. [13][14][15][16][17][18][19][20] The critical issue for quantitative interpretation of depth profiles is the interface width, a quantity that reflects how precisely one can measure a change in composition. The depth profiling experiments utilizing C 60 in which interface widths between similar materials such as two metals 11,12 or two Langmuir-Blodgett films 14,15 give values of 8.7 and ∼23 nm, respectively.…”

“…[13][14][15][16][17][18][19][20] The critical issue for quantitative interpretation of depth profiles is the interface width, a quantity that reflects how precisely one can measure a change in composition. The depth profiling experiments utilizing C 60 in which interface widths between similar materials such as two metals 11,12 or two Langmuir-Blodgett films 14,15 give values of 8.7 and ∼23 nm, respectively. The molecular dynamics simulations in which the depth of origin of ejected material has been investigated, [21][22][23][24][25] however, consistently indicate that ejected material originates from the top 2-3 nm, values much smaller than experimental interface widths.…”

Latest applications of 3D ToF-SIMS bio-imaging

“…Analysis of the sample at cryogenic temperatures produced the best result. When analyzed at 100 K, a depth resolution of 17-35 nm was achieved, 23,24 suggesting the possibility to probe lipid bilayer composition in biological samples and laboratory cell mimics as a function of depth. An example depth profile plot of a six layer film is presented in Fig.…”