In situ temperature-time effect on MetA-S-SIMS

Abstract

Metal-assisted (MetA) static secondary ion mass spectrometry (S-SIMS) is one of several ion yield enhancing methods developed for S-SIMS in the last decades. MetA-S-SIMS uses a very thin coating of gold or silver on the sample. Earlier experiments revealed dependence of the ion yield enhancement on the applied metal, the nature of the studied sample, the time after metallization, and the heating temperature (ex situ, i.e., under atmospheric pressure). This paper reports on the effects of time and temperature when samples are heated to temperatures between 30 and 80°C inside the S-SIMS vacuum chamber (in situ). Thick layers of poly(vinylbutyral-co-vinylalcohol-co-vinylacetate) (PVB) containing dihydroxybenzophenone (DHBPh) were coated with a nm-thin-layer of gold. The S-SIMS analysis was performed over a period of several hours while samples were kept at a constant elevated temperature. Compared to ex situ heating in an oven, heating in the analysis chamber provided more rapid signal enhancement, but the magnitude of the enhancement was less (by a factor of two). Furthermore, additional experiments on ex situ heated samples revealed that storage of samples with enhanced ion yields at Ϫ8°C is not sufficient to "stabilize" the enhancement. T he continuing search for improved detection limits in static secondary ion mass spectrometry (S-SIMS) has triggered exploration of several approaches for ion yield enhancement, such as the deposition of (sub)-monolayers on noble metal substrates [1], polyatomic primary ion bombardment [2][3][4][5][6], and samples in matrices typically used in matrix assisted laser desorption/ionization (MALDI) MS [7]. The recent MetA-S-SIMS methodology is based on the deposition of a nm-thick gold or silver layer on the sample via evaporation or sputtering [8 -10]; a variant uses metal nanoparticle deposition [11]. The method has been successfully applied in several fields ranging from biological and polymer samples to paper research [12][13][14][15][16].In contrast to the use of MALDI-matrices or monolayers on noble metal substrates, MetA-S-SIMS does not require dissolution of the sample. Moreover, the metal layer facilitates charge compensation for thick insulating samples, and often electron flooding and the associated risk of sample damage [17] can be avoided completely [8]. However, more research is needed to develop and understand the MetA-S-SIMS phenomenon. Problems arise with the detection of components with molecular weight ϾkDa [8]. Expectedly, the ion yield enhancement not only depends on the analyte under study [16] and the applied metal [10,18] but also on the specific sample in which it occurs. Examples hereof include the suppression of the Ca ϩ detection in paper fibers [13], different ion yield enhancement factors for positive and negative ions from the same analyte [10]. The apparent sensitivity of the ion yield enhancement on the exact conditions used for sample preparation and storage [18] aggravates the problem.Previous experiments on gold or silver coated samples of carbocy...

Ion yield improvement for static secondary ion mass spectrometry by use of polyatomic primary ions

“…With the advent of time‐of‐flight (TOF) S‐SIMS and the availability of adequate fast electronics, the limits of instrumental improvements seem to have been reached and further progress with respect to limit of detection (LOD) and molecular specificity is now being pursued by the development of new approaches, involving fundamental optimisation of the desorption‐ionisation (DI) process. Deposition of a thin layer of gold on the sample has been shown to improve ion yields dramatically in a variety of cases, but this involves the risk of modifying the composition of the pristine surface 1, 2. Polyatomic primary ion (P.I.)…”

“…Deposition of a thin layer of gold on the sample has been shown to improve ion yields dramatically in a variety of cases, but this involves the risk of modifying the composition of the pristine surface. 1,2 Polyatomic primary ion (P.I.) bombardment, as an alternative to the traditionally used monoatomic projectiles, has been shown to allow ion yields to be increased non-linearly.…”