Electron-Induced Reactions of MeCpPtMe 3 Investigated by HREELS M. N. Hedhili, † J. H. Bredeho ¨ft, and P. Swiderek* UniVersita ¨t Bremen, Institute for Applied and Physical Chemistry, Fachbereich 2 (Chemie/Biologie), Leobener Strasse/NW 2, Postfach 330440, 28334 Bremen, Germany ReceiVed: December 9, 2008; ReVised Manuscript ReceiVed: May 27, 2009 Multilayer condensed films of trimethyl(methylcyclopentadienyl)-platinum(IV) (MeCpPtMe 3 ) have been exposed to low-energy electrons at incident electron energies of 15, 30, and 500 eV. The reactions occurring under exposure have been investigated using high-resolution electron energy loss (HREEL) spectroscopy. The observed changes in the HREEL spectra upon exposure are similar for the three different energies. Contrary to previous results obtained for electron irradiation at 500 eV using reflection absorption infrared spectroscopy (RAIRS) and pointing toward a complete loss of hydrogen a comparable electron exposure in the present experiment yields a product that still contains a significant amount of C-H bonds. In accord with results from thermal desorption spectrometry also obtained after exposure to electrons at lower electron energy, a material is obtained that does not evaporate at room temperature. A crude estimate suggests that the overall reaction rate is consistent with previous results. 1. Introduction Electron-beam-induced deposition (EBID) is a versatile technique for the controlled growth of nanostructures of arbitrary shape at surfaces. 1 It relies on the decomposition of volatile organometallic precursors under the effect of a highly focused high-energy electron beam. Low-energy electrons backscattered from the surface are recognized as playing an important role in the decomposition reactions. It is thus of interest to study the chemical reactions of the precursors induced by direct exposure to low-energy electrons. Trimethyl(methylcyclopentadienyl)-platinum(IV) (MeCpPt- Me 3 ) 2,3 is an important precursor for the growth of platinum nanostructures using EBID. In the ideal case, the EBID process would completely remove the organic material, leaving behind pure platinum. Often, though, this is not the case. A recent study of electron-induced chemistry in thin molecular films of MeCpPtMe 3 has been performed under UHV conditions using a combination of temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), mass spectrometry (MS), and reflection absorption infrared spectroscopy (RAIRS). 4 The results suggested that decomposition at an incident electron energy of 500 eV is far from complete with as many as eight carbon atoms remaining per Pt. RAIRS, on the other hand, hinted toward a complete loss of hydrogen at 500 eV. The present results obtained by high-resolution electron energy loss (HREEL) spectroscopy show that exposure at low electron energies (15 and 30 eV) but also at 500 eV leads to a material that still contains a significant amount of C-H bonds. 2. Experimental Section The experiments were performed using a μ-metal-shielded UHV chamber equipped with a HREEL spectrometer consisting of a rotating cylindrical double pass monochromator and a single-pass electron-energy analyzer. 5 The base pressure of the system reaches 10 -11 mbar through the combined action of an ion pump and a titanium sublimation pump. The HREEL chamber is connected to a sample preparation chamber with a base pressure of about 2 × 10 -9 mbar. MeCpPtMe 3 was purchased from Acros Organics at a stated purity of 99% and degassed by repeated freeze-pump-thaw cycles. The experiments were performed on thin molecular films deposited on a polycrystalline Pt substrate (surface area ∼3.8 cm 2 ) cooled by means of a closed-cycle Helium refrigerator (Leybold Vacuum). A small heater unit was used to vary the temperature of the substrate between ∼20 and 30 K and room temperature. Prior to each deposition, the substrate was cleaned by direct resistive heating to an orange glow. To produce thin films of MeCpPtMe 3 , the vapor present in the reservoir containing the solid compound at room temperature was expanded into a small calibrated volume where the absolute pressure is measured with a capacitance manometer. For most experiments a calibrated amount of the vapor corresponding to a pressure drop of 3 μbar was leaked via a stainless steel capillary whose end is located just in front of the metal substrate. By comparison with previous monolayer calibrations for ben- zene 5 and cyclopropane, 6 it was deduced that this amount of vapor produces films with an average thickness of at least 10 monolayers. The samples were exposed to electrons at incident energies (E 0 ) of 15, 30, or 500 eV using a commercial flood gun (estimated resolution of 0.5-1 eV) located in the sample preparation chamber and delivering at these E 0 currents of the order of a few tens of μA/cm 2 as measured at the sample. After deposition and after each exposure the cryostat carrying the sample was transferred to the HREEL chamber for data acquisition. All HREEL spectra were acquired with an incident electron energy of 5.5 eV. The spectrometer was operated with a resolution of 11-13 meV, measured as the fwhm of the elastic peak, for currents transmitted through the samples of the order of 0.2-0.3 nA. The typical acquisition time of a full spectrum was 30 min. Both the incidence and scattering angle were set at 60° from the surface normal. Spectra of the samples annealed to 300 K were actually recorded at this temperature while all * To whom correspondence should be addresssed. E-mail: swiderek@ uni-bremen.de. † Permanent address: Unite ´ de recherche ´ Mate ´riaux Avance ´s et Optro- nique, Faculte ´ des Sciences de Tunis, 1060 Tunis, Tunisia. J. Phys. Chem. C 2009, 113, 13282–13286 13282 10.1021/jp810834r CCC: $40.75  2009 American Chemical Society Published on Web 07/02/2009