Sunday, February 14, 2016

Surface-enhanced Raman spectroscopy (SERS) for studying ALD growth used for the first time

Here is a recent paper from Prof. Stairs and Prof. Van Duyne research groups at North Western University on using surface-enhanced Raman spectroscopy (SERS) for studying ALD growth for the first time. Thanks Vincent Vandalon for sending me this information!
  • SERS overcomes the sensitivity limitations of normal Raman scattering because of excitation of localized surface plasmon resonances (LSPRs) that result in enhanced electromagnetic fields around noble metal nanostructures such as Ag, Au, and Cu.
  • The high sensitivity and distance dependence of SERS make it possible to evaluate the location of ALD deposits with respect to the enhancing substrate.

The ALD system at Van Duyne Research Group at North Western University. The ALD reactor can monitor ALD surface reactions in-situ using SERS and quartz crystal microbalance. The reactor will be connected to a GC for in-situ catalytic studies. The GC is equipped with a Thermal Conductivity and Flame Ionization detector so both permanent gases and hydrocarbons can be detected. (Picture and information form Van Duyne Research Group page)

Prof. Richard P. Van Duyne is the discoverer of Surface-enhanced Raman Spectroscopy (1977), the inventor of Nanosphere Lithography (1995) and Localized Surface Plasmon Resonance Spectroscopy (2000). More information can be found here.

Prof. Richard P. Van Duyne

Probing the Chemistry of Alumina Atomic Layer Deposition Using Operando Surface-Enhanced Raman Spectroscopy

Sicelo Simon Masango, Ryan A. Hackler, Anne-Isabelle Henry, Michael O. McAnally, George C. Schatz, Peter C. Stair, and Richard P. Van Duyne
J. Phys. Chem. C, Just Accepted Manuscript
DOI: 10.1021/acs.jpcc.5b11487
Publication Date (Web): January 28, 2016

This work demonstrates for the first time the capability of measuring surface vibrational spectra for adsorbates during atomic layer deposition (ALD) reactions using operando surface-enhanced Raman spectroscopy (SERS). We use SERS to study alumina ALD growth at 55 °C on bare silver film-over nanosphere (AgFON) substrates as well as AgFONs functionalized with thiol self-assembled monolayers (SAMs). On bare AgFONs, we observe the growth of Al-C stretches, symmetric C-H and asymmetric C-H stretches during the trimethylaluminum (TMA) dose half-cycle and their subsequent decay after dosing H2O. Al-C and C-H vibrational modes decay in intensity with time even without H2O exposure providing evidence that residual H2O in the ALD chamber reacts with –CH3 groups on AgFONs. The observed Al-C stretches are attributed to TMA dimeric species on the AgFON surface in agreement with density functional theory (DFT) studies. We observe Al-C stretches and no thiol vibrational frequency shifts after dosing TMA on AgFONs functionalized with toluenethiol and benzenethiol SAMs. Conversely, we observe thiol vibrational frequency shifts and no Al-C stretches for AgFONs functionalized with 4-mercaptobenzoic acid and 4-mercaptophenol SAMs. Lack of observed Al-C stretches for COOH- and OH-terminated SAMs is explained by the spacing of Al-(CH3)x groups from the SERS substrate. TMA penetrates through SAMs and reacts directly with Ag for benzenethiol and toluenethiol SAMs and selectively reacts with the –COOH and –OH groups for 4-mercaptobenzoic acid and 4-mercaptophenol SAMs, respectively. The high sensitivity and chemical specificity of SERS provides valuable information about the location of ALD deposits with respect to the enhancing substrate. This information can be used to evaluate the efficacy of SAMs in blocking or allowing ALD deposition on metal surfaces. The ability to probe ALD reactions using SERS under realistic reaction conditions will lead to a better understanding of the mechanisms of ALD reactions.

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