SIMS Applications
16Pages

SIMS APPLICATIONS SIMS Applications

SIMS Applications Secondary Ion Mass Spectrometry (SIMS) is an analytical technique where the specimen surface is bombarded by a stream of high energy ions causing sputtering of the surface. The resultant secondary ions are analysed by a mass spectrometer. This provides highly sensitive compositional analysis with extremely good depth resolution and mass resolved imaging. Secondary ions analysed by mass spectrometry STATIC SIMS The most surface sensitive analysis is termed static SIMS. Under conditions where the total dose of ions is under 1012 per square cm, only the top monolayer is...

Contamination with silicone – top monolayer specific analysis Electronic materials – depth profiling layer structures and ppm sensitivity for dopants Flexible solar cell – multicomponent complex depth profiles collecting both matrix and dopant level elements Isotopically labelled material – depth profiling to determine ion exchange and fundamental materials research Surgical stent – imaging, depth profiling and surface specific analysis to characterise the near surface SNMS of magnetic storage materials – depth profiling and quantified composition of alloys using SNMS 10. Nuclear materials...

Contamination with silicone Polydimethylsiloxane (PDMS) is inert, non-toxic and nonflammable and used extensively as a lubricant, in cosmetics, as a food additive [E900] and in sealants. However, it can break down to silicon dioxide (glass) and form an insulating layer in electronics as well as forming a barrier to adhesion when bonding surfaces – it is also difficult to remove. SIMS can easily detect monolayer quantities of this important industrial contaminant. The positive secondary ion spectra below are from an aluminium foil before and after contact with a protective glove. A residue...

Electronic materials Ion implantation and diffusion is used to deliver dopants into semiconductors, SIMS accurately measures the dopant concentration for process development and monitoring. The examples below show quantified depth profiles in silicon substrates CVD grown SiGe layer structure O2+ primary ions positive secondary ions Arsenic ion implant in silicon Cs+ primary ions negative secondary ions Dopant (C and Si) concentration / atoms cm -3 Boron ion implant in silicon O2+ primary ions positive secondary ions III-V MBE grown quantum well structure analysed using Cs+ primary ions....

Flexible solar cell Depth profile through a Copper Indium Gallium Selenide (CIGS) solar cell showing high dynamic range and good depth resolution. The depth scale is left as analytical cycles, showing that high data density can be achieved even when a large number of elements are detected. The overall depth is around 4 microns. Using caesium primary ions, the species of interest is measured as a molecule together with a Cs+ ion. For some elements, such as Zn, the ion ZnCs+ is actually more sensitive than detecting either Zn+ or Zn- ions.

Isotopically labelled material Being a mass spectrometry technique, SIMS can determine the isotopic composition of a material. This is particularly useful when investigating diffusion within layers. Here a very sharp isotopically pure 54Fe layer is clearly defined with excellent depth resolution, grown within a thicker layer of natural isotopic abundance. Nuclear fusion produces very high energy protons which implant in the reactor walls. Here SIMS has been used to detect deuterium implanted into tungsten as a simulation for the material effects in a fusion reactor wall.

Surgical stent Stents are wireframe scaffolds, typically laser cut from stainless steel, use to hold narrowed arteries open. Inserted via a catheter, the mesh is placed in the narrow area and expanded using a small balloon which is then withdrawn. Surface condition of the stent is very important and SIMS can be used to examine the nanometre thick protective chromium dioxide layer which naturally forms on the material. The depth profiles below show how treating with a chlorine based disinfecting product leaves the surface iron rich and open to corrosion, potentially causing failure or tissue...

Stents may be coated with polymer layers for protection or to elute drugs into the region to prevent future blockage. Static SIMS can detect and characterise this layer. ION BEAM POLARITY AND CHEMISTRY The secondary ions emitted from the specimen usually have a favoured polarity. For instance, alkali metals are emitted as positive ions and halogens as negative. The probability of ion formation is also enhanced by using oxygen for electropositive elements and caesium for electronegative elements. In addition, caesium can be used in the CsM+ mode, where the element of interest, M, is detected...

SNMS of magnetic storage materials SNMS provides excellent depth resolution and quantification to analyse the layer structure of the hard disc head material (left) and the active region of the platter surface itself (right). SPUTTERED NEUTRAL MASS SPECTROMETRY SNMS Sputtered Neutral mass Spectrometry separates the ionisation event from the sputtering and thus overcomes the matrix effect which makes high concentration quantification difficult in conventional SIMS analysis. The MAXIM spectrometer uses a high efficiency electron impact ioniser to detect the sputtered neutral flux after...

OXYGEN FLOOD Low energy beams give improved depth resolution but can also induce surface topography. A directional jet of pure oxygen is provided over the sample surface, fully oxidising the surface via a stainless steel capillary. The gives enhancements in sensitivity for the analysis of electropositive species such as metals and semiconductor dopants, as well as reductions in surface roughness in low beam energy, high depth resolution analyses. The examples show the improvements in surface topography given by the use of the localised oxygen flood in a 3.6 nm multilayer Si/Fe sample....

Nuclear materials The isotopic sensitivity, and ability to analyse small particles, makes SIMS the ideal technique for the study of nuclear materials. The spectrum below was measured from a uranium containing glass (under 1% wt.) using a 5keV oxygen primary ion beam and 500eV electron beam charge compensation. The 235U fraction is determined to be 0.55 ±0.02%; less than the 0.72% abundance expected from natural material. QUANTIFICATION DEPTH SIMS depth profile data is collected as a function of sputter time which comprises the time taken for individual raster scanned frames and the number...