Adsorption calorimetry during metal vapor deposition on single crystal surfaces: Increased flux, reduced optical radiation, and real-time flux and reflectivity measurements

Abstract

Thin films of metals and other materials are often grown by physical vapor deposition. To understand such processes, it is desirable to measure the adsorption energy of the deposited species as the film grows, especially when grown on single crystal substrates where the structure of the adsorbed species, evolving interface, and thin film are more homogeneous and well-defined in structure. Our group previously described in this journal an adsorption calorimeter capable of such measurements on single-crystal surfaces under the clean conditions of ultrahigh vacuum [J. T. Stuckless, N. A. Frei, and C. T. Campbell, Rev. Sci. Instrum. 69, 2427 (1998)]. Here we describe several improvements to that original design that allow for heat measurements with ~18-fold smaller standard deviation, greater absolute accuracy in energy calibration, and, most importantly, measurements of the adsorption of lower vapor-pressure materials which would have previously been impossible. These improvements are accomplished by: (1) using an electron beam evaporator instead of a Knudsen cell to generate the metal vapor at the source of the pulsed atomic beam, (2) changing the atomic beam design to decrease the relative amount of optical radiation that accompanies evaporation, (3) adding an off-axis quartz crystal microbalance for real-time measurement of the flux of the atomic beam during calorimetry experiments, and (4) adding capabilities for in situ relative diffuse optical reflectivity determinations (necessary for heat signal calibration). These improvements are not limited to adsorption calorimetry during metal deposition, but also could be applied to better study film growth of other elements and even molecular adsorbates.

Ni Nanoparticles on CeO2(111): Energetics, Electron Transfer, and Structure by Ni Adsorption Calorimetry, Spectroscopies, and Density Functional Theory

“…The apparatus and methods for SCAC, XPS, LEIS and LEED have described in detail previously. [25][26][27][28] The CeO2-x(111) thin films (x = 0.05 and 0.2) were grown on a clean Pt(111) single crystal surface up to a thickness of 4 nm, using the same methods as described previously that were shown to produce ordered (111) terraces with ~5% step sites. 29 This is thick enough to give a bulk-like behavior based on the adsorption energy of Ag vapor.…”

Energetics of Ag Adsorption on and Adhesion to Rutile TiO2(100) Studied by Microcalorimetry

“…The SCAC experiments were performed as described previously. 70 The Ag metal beam is generated by evaporating Ag pellets in an e-beam evaporator. The Ag vapor is then collimated through a series of 4.26 mm-diameter apertures and dosed onto the TiO 2 film in 100 ms pulses with a period of 2 s. The flux of the Ag beam is measured with two quartz crystal microbalances (QCMs).…”

“…The SCAC experiments were performed as described previously . The Ag metal beam is generated by evaporating Ag pellets in an e-beam evaporator.…”

Calorimetric measurement of adsorption and adhesion energies of Cu on Pt(111)

“…The calorimetry apparatus has been described in detail previously. [31] The calorimeter was housed in an ultrahigh vacuum chamber (UHV) with a base pressure >2x10 -10 torr. The chamber was equipped with low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), a quadrupole mass spectrometer (QMS), and several quartz crystal microbalances (QCM).…”

“…The single crystal adsorption calorimetry experiments were performed as described in detail elsewhere. [31,32] Briefly, the calorimeter heat detector is a pyroelectric polyvinylidene fluoride ribbon that can be translated into gentle thermal and mechanical contact to the backside of the Pt(111) single crystal sample. A 4-mm diameter beam of Cu atoms is generated using an electron beam evaporator and is chopped and collimated through a series of apertures to produce a spatially and temporally well-defined 100 ms pulse every 2 seconds which is directionally dosed onto the front of the single crystal sample.…”