Current Research

Multivariate Curve Resolution analysis of thermal desorption data (click to see full manual)

The substantial amount of information carried in temperature-programmed desorption (TPD) experiments is often difficult to mine due to the occurrence of competing reaction pathways that produce compounds with similar mass spectrometric features. Multivariate curve resolution (MCR) is introduced as a tool capable of overcoming this problem by mathematically detecting spectral variations and correlations between several m/z traces, which is later translated into the extraction of the cracking pattern and the desorption profile for each desorbate. Different from the elegant (though complex) methods currently available to analyze TPD data, MCR analysis is applicable even when no information regarding the specific surface reaction/desorption process or the nature of the desorbing species is available. See the SAMPLE TPD ANALYSIS FILE and the MCR MANUAL available online.

Relevant Publication:

  1. Rodríguez-Reyes, J. C. F., Teplyakov, A. V. and Brown, S. D. Qualitative and quantitative analysis of complex temperature-programmed desorption data by multivariate curve resolution. Surf. Sci. 2010.

 

Thin Solid Films

TEM Image

Cross-sectional TEM image of 3.0 x 104 L TiCN film. Two distinct regions can be seen: the TiCN layer and the 4140 steel substrate. A carbon layer was used to protect the TiCN layer while cutting [2].

The main goal of this project is to develop molecular-level understanding, control, and predict chemical reactions relevant for the formation and properties of complex thin solid films. The potential applications for these films range from microelectronics where their thickness approaches a few nanometers to hard coatings, where 20-100 micron thick films are required. Therefore the questions of scaling the physical properties of the films enter a qualitatively new era: their properties now have to be analyzed and understood at the atomic level. The key objective of this project is to promote desired surface chemical reactions for clean Ta- and Ti-based film deposition and sharp stable interface between the film material and a substrate, while preventing impurity incorporation (C, O, F) at the interfaces formed during this process. Our group employs numerous thermal and photochemical methods to achieve this control. The structure of these amorphous or polycrystalline films presents many challenges. Our group has developed a novel approach to understand their properties. It combines a newly established experimental strategy with novel computational models designed recently in our laboratory to investigate local interactions in these complex systems. Modern deposition and characterization techniques designed for and tested on Ti-based films will be further applied to investigate the poorly characterized Ta-, Hf-, and W-based materials.

Cross-sectional TEM image of 3.0 x 104 L TiCN film.  Two distinct regions can be seen: the TiCN layer and the 4140 steel substrate.  A carbon layer was used to protect the TiCN layer while cutting [3].

Relevant Publications:

  1. Miller, T.; Pirolli, L.; Deng, F., Ni, C. and Teplyakov, A. V. Structurally Different Interfaces between Electrospark-Deposited Titanium Carbonitride and Tungsten Carbide Films on Steel. Surf. Coat. Technol. 2014, DOI: 10.1016/j.surfcoat.2014.07.076..
  2. Lin, J.-M.; Rodríguez-Reyes, J. C. F. and Teplyakov, A. V. Competing reactions during metalorganic deposition: Ligand-exchange versus direct reaction with the substrate surface. J. Vac. Sci. Technol. A. 2013, 31(2), 021401-1-021401-17.
  3. Miller, T.; Lin, J.-M.; Pirolli, L.; Coquilleau, L.; Luharuka, R. and Teplyakov, A. V. Investigation of thin titanium carbonitride coatings deposited onto stainless steel. Thin Solid Films 2012, 522, 193-198.
  4. Perrine, K. A., Rodríguez-Reyes, J. C. F. and Teplyakov, A. V. Simulating the reactivity of disordered surface of the TiCN thin film. J. Phys. Chem. C 2011, 115, 15432-15439.

 

Surface Modification of Semiconductor Materials

Summary of the approaches to form a Si−N bond on silicon surfaces with N-containing compounds.

Semiconductor substrates are widely used in many applications. Multiple practical uses involving these materials require the ability to tune their physical (bandgap, electron mobility) and chemical (functionalization, passivation) properties to adjust those to a specific application. The goal of this research direction is to develop new strategies for manipulating the surface properties of semiconductor materials in a controlled way. Our expertise allows us to selectively tune the chemical and physical properties of semiconductor surfaces by an appropriate choice of elemental or III-V semiconductor, or by chemical modification. Our approach focuses on chemical passivation, on molecular switches and on the use of a variety of functionalized self-assembled monolayers. The findings of these investigations will be relevant for future applications in molecular and nanoelectronics, sensing, and solar energy conversion.

 

Summary of the approaches to form an Si-N bond on silicon surfaces with N-containing compounds, including ammonia, alkyl or aryl amines, nitro-, nitroso-, and azido-compounds, starting from clean, H-terminated, and Cl-terminated Si surfaces by vacuum or wet-chemistry methods. Substituent R group could be hydrogen, alkyl, or aryl functionality. x=0, 1, 2. Selected reactions will be explained in details in the following sections.

Relevant Publications:

  1. Tian, F. and Teplyakov, A. V. Silicon surface functionalization targeting Si-N linkages. Langmuir 2013, 29(1), 13-28. Invited Feature Article, Image featured on the cover of the journal.
  2. Tian, F., Taber, D. F. and Teplyakov, A. V. –NH- termination on Si(111) surface by wet chemistry. J. Am. Chem. Soc. 2011, 133, 20769-20777.
  3. Leftwich, T. R. and Teplyakov, A. V. Chemical manipulation of multifunctional hydrocarbons on silicon surfaces. Invited Review. Surf. Sci. Rep. 2008, 63, 1-71. This review article received Top Cited Author Surface Science Reports Award based on Scopus citations from 2005-2009.

 

Covalent Attachment of Large Molecules to Surfaces and Nanostructures

Image

Biotin-DNA-modified Si(111) surface after exposure to streptavidin-coated gold nanoparticles followed by surface passivation with octadecanethiol (ODT).

We have used C60 Buckminster fullerenes as spectroscopic and microscopic probes to establish the covalent nature of their binding to appropriately terminated self-assembled monolayers on silicon. We have investigated this chemistry using multiple spectroscopic and microscopic techniques and have verified the formation of a covalent link using computational investigation of core level energy shifts in N 1s spectral region and vibrational signatures of covalently bonded fullerenes. Current studies focus on the use of PCBM (modified buckyball) and other nanostructures for making full monolayers and design multilayer systems.

Relevant Publications:

  1. Miller, T. and Teplyakov, A. V. Attachment Chemistry of PCBM to a Primary-Amine-Terminated Organic Monolayer on a Si(111) Surface. Langmuir, 2014, 30, 5105-5114.
  2. Liu, Y.; Chen, J. and Teplyakov, A. V. Chemical passivation processes for biofunctionalization schemes on semiconductors surfaces. Langmuir 2012, 28 (44), 15521-15528.
  3. Liu, Y. and Teplyakov, A. V. Using a Combination of Microscopy and Spectroscopy to Confirm Covalent Bonding of DNA on Functionalized Semiconductor Surfaces, SurFACTS in Biomaterials, 2012, 17 (4), 10-11.