Donald P. Land

Associate Professor

Email: dpland@ucdavis.edu

Analytical and Physical Chemistry

B.A., Lawrence University of Wisconsin, 1984. Ph.D., University of California, Irvine, 1989. Postdoctoral Researcher, Institute for Surface and Interface Science, University of California, Irvine, 1989-90. Alexander von Humboldt Postdoctoral Fellow, Institut füer Grenzfläechenforschung und Vakuumphysik, Forschungszentrum, Jülich, 1990-91. Appointed to faculty, UC Davis, 1991-.

Research Interests

For schematics, figures, and more information, please see the  Land Group web page.

Our goal is to understand the details of chemistry at interfaces, and specifically how changes in surface structure bring about changes in the chemistry and bonding of adsorbates. Interfaces play key roles in fuel cells, catalysts, microelectronics manufacturing, corrosion, wear, and waste remediation. In addition, interactions at the interface between biomedical implants and biological fluids play a deciding role in the assimilation of these devices.

Microscopy and molecular kinetics studies of surface reactions are used to elucidate the relationship between structure and function in surface chemistry.  We use a barrage of specialized techniques to analyze the outer-most atomic/molecular layer at interfaces. Because of the infinitesimal amount of sample, this field relies on recent technologies which probe only the surface region. Indeed, a substantial portion of our research includes development and refinement of techniques which provide time resolved information from surfaces.
 

INSTRUMENTATION

The apparatus to carry out the bulk of the experiments are custom-designed instruments combining techniques at the forefront of molecular surface analysis. The design and construction of instrumentation is a continuing process. Virtually every component is specially designed to accommodate the new technologies and approach for our projects. Many items are manufactured entirely here at UC Davis by the graduate students in our machine, glass, and electronics shops.
 

SURFACE MOLECULAR COMPOSITION

Thermal desorption (TDS), laser desorption (LITD), Fourier transform mass spectrometery (FTMS), FT reflection absorption infrared spectroscopy (FTRAIRS), Auger electron (AES) and X-ray photoelectron (XPS) spectroscopies are used to ascertain the molecular composition of adsorbates in ultra-high vacuum for a variety of samples.  The infrared and electron spectroscopies monitor the surface composition in situ, requiring little or no perturbation of the sample.  Of these, FTRAIRS, which bounces an IR beam off the surface at a low angle, is the least perturbing and gives the most chemical information.  When the IR beam interacts with the surface, vibrational modes of adsorbed species can absorb energy, leading to an IR spectrum.  Selection rules can be used to ascertain the molecular identity and orientation on the surface.  Changes can be monitored to infer surface chemistry.

Removal of the adsorbed species (desorption) allows them to be monitored by mass spectrometry, a very powerful moleuclar analysis technique.  Two methods for achieving desorption are used.  One is to simply heat the entire surface with electric current (directly or with and adjacent heater coil) at about 10 K/s and observe the gases that are evolved (TDS).  Mass spectrometry gives the molecular identity of the desorbing species and the temperatures and amounts can be used to infer surface reaction mechanisms. A second method of inducing desorption is to rapidly (10 ns) heat a small (1 mm²) region with a pulsed laser (LITD).  The rapid laser heating can cause species to desorb before they react further, giving a snapshot of the surface composition at the time of the laser firing.  When LITD is coupled with FTMS, the surface molecular composition can be probed rapidly and repeatedly to allow kinetics studies of adsorbed reacting systems.
 

RATES OF FUNDAMENTAL SURFACE PROCESSES

My laboratory in Chemistry at UC Davis is one of the premier laboratories in the world for performing time-resolved molecular analyses of surface chemistry. This allows us to directly measure the rates of adsorbate --> adsorbate transformations. Knowledge of these rates is of paramount importance in modeling catalyst function and leads to insight into the details of the reaction mechanisms for these processes.   My group has also been engaged in the direct measurement of kinetic parameters associated with desorption of species from surfaces. Propene desorption from Pd(111) has been shown to have an unusually low pre-exponential factor (10¹¹/s), while benzene desorption exhibits a very high value (10¹⁷/s). The pre-exponential factor for desorption is often estimated to be 10¹³/s for purposes of estimating activation barriers from conventional thermal desorption spectroscopy. We, however, are able to measure these parameters directly using laser-induced desorption, and find that the prefactor varies considerably from the value often used by rote. In addition to allowing the more accurate calculation of values for the activation energies of desorption, the pre-exponential factors carry information about the nature of the adsorbed species and the transition state to desorption.

SURFACE STRUCTURE

All of the studies below concentrate on using techniques which probe the molecular surface composition and surface structure as a function of time. The Advanced Surface Microscopy Facility at UC Davis incorporates variable temperature scanning tunneling microscopy (VT-UHV-STM), low energy electron microscopy (LEEM), and x-ray photoelectron spectroscopy (XPS) to probe the time-dependent structural features of surfaces. Only a handful of other such facilities currently exist anywhere in the world. With these techniques, we are able to correlate the molecular information obtained from the mass spectrometry and IR experiments described above with time-resolved structural information. In some cases, we expect to be able to monitor the reactions of individual molecules to assess directly the effects of steps, defects, and coadsorbates on surface reactivity. The complementarity of these different techniques leads to unprecedented detail in relating surface structure to chemical reactivity. This instrument is designed so that it can occasionally be transported to the Advanced Light Source at Lawrence Berkeley Laboratory for element- and chemical-state-resolved microscopy using the LEEM in a slightly modified configuration for photoelectron emission microscopy (PEEM). These studies will be carried out in collaboration with Professors Shirley Chiang, Xiangdong Zhu, and Charles Fadley of the Department of Physics at UCD.
 
 

Some Research Specifics

HYDROTREATING MODELS

The removal of heteroatoms from hydrocarbon feedstocks is an important and costly step in refining. It is known that late transition metals promote these reactions, increasing efficiencies by orders of magnitude, yet very few surface studies of heterocycles (the most prevalent and persistent form of heterocompounds) on late transition metals have been performed. We have studied several model compounds on Pd. Furan, pyrrole, and thiophene all decompose near 300 K on Pd(111), but via surprisingly different mechanisms, we have found. Numerous results  have been published(see below).

ALTERNATIVE FUELS

We have also probed the reactions of cyclic pure hydrocarbons on Pd(111) to relate these systems to the now abundant data on Pt(111) with some surprising initial results. An important related technology is the use of liquid hydrocarbons or methanol as convenient stores for hydrogen with on-demand catalytic conversion (methanol or cyclohexane/Pd,PT ---> benzene + hydrogen). The benzene byproduct would be rehydrogenated back to cyclohexane in a separate catalytic process. We are studying the fundamental steps (rates and mechanisms) along both of these pathways.

BIOMEDICAL IMPLANT SURFACE ANALYSIS

A third broad area of research concerns the analysis of complex surfaces exposed to environmental conditions or biological systems. The initial experiments in this area were carried out on oxidized Ti foils, and it was during these studies that we developed the ion deflection technique to allow the analysis of surfaces containing alkali, since alkali is ubiquitous in environmental and biological systems. The original experiments showed that, when ion deflection was used, organic adsorbates such as benzene and ethylene could be detected on oxidized Ti foil surfaces. The hope is that quantitative diagnostics can be developed to ascertain the efficacy of different implant preparation techniques currently employed. This should improve incorporation into living systems and reduce the need for costly animal studies. For example, we have shown that the use of alcohols to wash the surfaces of Ti implants is likely to leave hydrocarbon residues which are stable to high temperature. We are also finding analogy to TiOx catalysts and are able to relate the observed surface species to some published results that looked at evolved gases. We, however, are able to shed light on the formation temperatures for species whose evolution is desorption-rate limited.

REACTION OF METAL-ORGANICS ON SURFACES

Another area of research involves the detailed investigation of the factors controlling the reactions of metal-organics and coordination compounds on transition metal and semiconductor surfaces. These studies relate to metal-organic chemical vapor deposition (MOCVD) for electronic device manufacturing and for the construction of nanoscale metal features with novel magnetic properties. In general, the metal films formed from industrial application of this technique have unacceptably high concentrations of carbon and other impurities from the decomposition of the organic ligands. We are initiating studies to better understand the mechanisms involved in metal deposition and the fate of the organic ligands. We also will study the metal film growth mechanisms (with S. Chiang and X. Zhu, UCD Physics) and novel methods of forming nanostructures using STM tips and energetic particles to initiate the surface chemistry. These projects are just being initiated and we are seeking funding from the NSF Division of Materials Research and from the DOE Basic Energy Sciences Division, in part in collaboration with Professors Chiang and Zhu.

REACTION OF HALOCARBONS ON TRANSITION METALS AND THEIR OXIDES

These studies are aimed at understanding the fundamental factors controlling the rates and mechanisms of dehalogenation and the fate of the organic constituents of these species. This project relates to halocarbon solvent waste remediation, to the formation of surface radical species which may undergo surface polymerization, and to the interaction of polar molecules adsorbed on polar and non-polar surfaces. We are also interested in studying thin-film polymers, particularly fluorinated films, to ascertain details of bonding and reactivty of these films, some of which might be useful as lubricants in magnetic storage disk/head systems.

Selected

Publications

D.M. Jaramillo, D.E. Hunka, and D. P. Land.   Iodobenzene on Pd(111) Studied by TDS and LITD-FTMS.  Surface Science, 445, 23-31 (2000).

N.A. Thornburg, I. M. Abdelrehim, and D. P. Land.   Kinetics of propene desorption from Pd(111) studied by thermal desorption spectroscopy and laser-induced thermal desorption with Fourier transform mass spectrometry.  Journal of Physical Chemistry B, 103, 8894-8898 (1999).

T.E. Caldwell and D. P. Land.   In situ kinetics and mechanism of furan decomposition and desorption with CO formation on Pd(111).  Journal of Physical Chemistry B, 103, 7869-7875 (1999).

M.N. Rocklein and D. P. Land.   Thermal Surface Chemistry of Fe(CO)₅ on Pd(111) studied by FT-TPD and LITD-FTMS.  Surface Science, 436, L702-L706 (1999).

D.E. Hunka, T. Picciotto, D. M. Jaramillo, and D. P. Land.  Dehydrogenation of cyclohexene to benzene on Pd(111).   Surface Science, 421, L166-L170 (1999).

M.N. Rocklein and D.P. Land. Mass spectra of Fe(CO)₅ using FTMS and using laser induced thermal desorption FTMS with electron ionization, charge exchange, and proton transfer. International Journal of Mass Spectrometry and Ion Processes, 177, 83-89 (1998).

J.S. Loring and D.P. Land. Theoretical determination of parameters for optimum surface specificity in overlayer attenuated-total-reflection infrared spectroscopy. Applied Optics, 37, 3515-3526 (1998)

T.E. Caldwell, I.M. Abdelrehim, and D.P. Land. A laser-induced thermal desorption Fourier transform mass spectrometry study of acetylene cyclization on S/Pd(111): The formation and kinetics of benzene, thiophene, and 1,3-butadiene. Langmuir, 14,1407-1410 (1998).

T.E. Caldwell, I.M. Abdelrehim, and D.P. Land. Preadsorbed oxygen atoms affect the product distribution and kinetics of acetylene cyclization to benzene on Pd(111): A laser-induced thermal desorption Fourier transform mass spectrometry study. Journal of Physical Chemistry B, 102, 562-568 (1998).

I.M. Abdelrehim, N.A. Thornburg, and D.P. Land. An Ultrahigh Vacuum Surface Analysis Instrument Incorporating a Fourier Transform Mass Spectrometer and a Fourier Transform Infrared Spectrometer. Review of Scientific Instruments, 12, 4572-4582 (1997).

T.E. Caldwell and D.P. Land. Desulfurization, deoxygenation and denitrogenation of heterocycles by a palladium surface: A mechanistic study of thiophene, furan and pyrrole on Pd(111) using laser-induced thermal desorption with Fourier-transform mass spectrometry. Polyhedron, 16(18), 3197-3211 (1997).

T.E. Caldwell, I.M. Abdelrehim, and D.P. Land. Thiophene Decomposition on Pd(111) Studied by LITD/FTMS: Observation of C₄ Products. Surface Science, 367, L26-L31 (1996).

I.M. Abdelrehim, T.E. Caldwell, and D.P. Land. Coverage Effects on the Kinetics of Benzene Formation from Acetylene on Pd(111): A Laser-Induced Thermal Desorption / Fourier Transform Mass Spectrometry Investigation. Journal of Physical Chemistry, 100, 10265-10268 (1996).

T.E. Caldwell, I.M. Abdelrehim, and D.P. Land. Furan Decomposes on Pd(111) To Form H and CO plus C₃H₃, Which Can Dimerize to Benzene at 350 K. Journal of the American Chemical Society, 118, 907-908 (1996).

I.M. Abdelrehim, N.A. Thornburg, J.T. Sloan, T.E. Caldwell, and D.P. Land. Kinetics and Mechanism of Benzene Formation from Acetylene on Pd(111) Studied by Laser-Induced Thermal Desorption/Fourier Transform Mass Spectrometry. Journal of the American Chemical Society, 117, 9509-9514 (1995).

D.P. Land, I.M. Abdelrehim, N.A. Thornburg, and J.T. Sloan. Laser-Induced Thermal Desorption with Fourier Transform Mass Spectrometry for the Time-Resolved Analysis of Catalyst and Biomedical Implant Model Surface Molecular Composition. Analytica Chimica Acta, 307, 321-331 (1995). (Solicted contribution.)

J.H. Wang, P.W. Tiedemann, D.P. Land, R.T. McIver, Jr., and J.C. Hemminger. Dynamics of Ion Coupling in an FTMS Ion Trap and Resulting Effects on Mass Spectra Including Isotope Ratios. International Journal of Mass Spectrometry and Ion Processes, 134, 11-21 (1994).

N.A. Thornburg, I.M. Abdelrehim, S. Pullins, and D.P. Land. Deflection of Laser-Produced Ions in Laser-Induced Thermal Desorption/Fourier Transform Mass Spectrometry for Surface Analysis. Journal of the American Society for Mass Spectrometry, 5(6), 583-587 (1994).

W. Erley, Y. Li, D.P. Land, and J.C. Hemminger. The Conversion of Ethylene to Ethylidyne on Pt(111): Non-First Order Kinetics and Ensemble Effects. Surface Science, 301, 177-196 (1994).

I.M. Abdelrehim, N. A. Thornburg, J. T. Sloan, and D. P. Land. Benzene and Thiophene Formation from Acetylene on Sulfided Pd(111) studied by LITD/FTMS. Surface Science, 298, L169-L172 (1993).

A Few from Previous Positions:

D.P. Land, W. Erley and H. Ibach. HREELS Investigation of the Orientation and Dehydrogenation of Cyclohexane on Pt(111). Surface Science, 289, 237-246 (1993).

D.P. Land, C.L. Pettiette-Hall, J.C. Hemminger, and R.T. McIver, Jr. Identification of Molecular Adsorbates: A Breakthrough for Surface Chemistry. Accounts of Chemical Research, 24, 42-47 (1991).

D.P. Land, J.C. Hemminger, R.T. McIver, Jr., and I.J. Amster. Chemical Ionization as a Post-Ionization Technique for Laser-Desorbed Neutrals. Advances in Mass Spectrometry, 11, 680-681 (1989).

D.P. Land, C.L. Pettiette-Hall, R.T. McIver, Jr., and J.C. Hemminger. Detection of Reaction Intermediates in the conversion of Cyclohexane to Benzene on Pt(111). Journal of the American Chemistry Society, 111, 5970-5972 (1989).

COMING SOON!

D.E. Hunka and D.P. Land. Reaction of 1,1-dichloroethene on Pd(111). Surface Science, in preparation.

D.C. Herman and D.P. Land. Reaction of trans-1,2-dichloroethene on Pd(111). Surface Science, in preparation.

D. Jaramillo and D.P. Land. Reaction of cis-1,2-dichloroethene on Pd(111). Surface Science, in preparation.

E. Delgado and D.P. Land. FT-TDS and LITD/FTMS of Common Solvents on Oxidized Ti: The Fate of Decomposition Products and Implications for Biomedical Implants. Analytical Chemistry; in preparation.

T.V. Arnold, C.M. Gerth and D.P. Land. The Desorption Kinetics of Flat-Lying Benzene from Pd(111) Studied by LITD/FTMS. Journal of Physical Chemistry, in preparation.