Jan J Dubowski

Publications of Jan J Dubowski

• Electro-optic investigation of the surface trapping efficiency in n-alkanethiol SAM passivated GaAs(001).

  Authors: Gregory M Marshall, Gregory P Lopinski, Farid Bensebaa, Jan J Dubowski

  Nanotechnology. 06/2011; 22(23):235704.

  The electro-optic characteristics of the semi-insulating and n(+)-type GaAs(001) surfaces passivated with n-alkanethiol self-assembled monolayers were investigated using Kelvin probe surfaceThe electro-optic characteristics of the semi-insulating and n(+)-type GaAs(001) surfaces passivated with n-alkanethiol self-assembled monolayers were investigated using Kelvin probe surface photovoltage (SPV) and photoluminescence (PL) techniques. Referencing the equilibrium surface barrier height established in an earlier report, SPV measurements demonstrated a significant (>100 mV) increase in the non-equilibrium band-bending potential observed under low-level photo-injection. Modeling of the SPV accounts for these observations in terms of a large (>10(4)) decrease in the hole/electron ratio of surface carrier capture cross-sections, which is suggested to result from the electrostatic potential of the interfacial dipole layer formed upon thiol chemisorption. The cross-section effects are verified in the high-injection regime based on carrier transport modeling of the PL enhancement manifested as a reduction of the surface recombination velocity.

• Plasmonic propagations distances for interferometric surface plasmon resonance biosensing.

  Authors: Dominic Lepage, Dominic Carrier, Alvaro Jiménez, Jacques Beauvais, Jan J Dubowski

  Nanoscale research letters. 01/2011; 6(1):388.

  ABSTRACT: A surface plasmon resonance (SPR) scheme is proposed in which the local phase modulations of the coupled plasmons can interfere and yield phase-sensitive intensity modulations in theABSTRACT: A surface plasmon resonance (SPR) scheme is proposed in which the local phase modulations of the coupled plasmons can interfere and yield phase-sensitive intensity modulations in the measured signal. The result is an increased traceability of the SPR shifts for biosensing applications. The main system limitation is the propagation distance of the coupled plasmon modes. This aspect is therefore studied for thin film microstructures operating in the visible and near-infrared spectral regions. The surface roughness of the substrate layer is examined for different dielectrics and deposition methods. The Au layer, on which the plasmonic modes are propagating and the biosensing occurs, is also examined. The surface roughness and dielectric values for various deposition rates of very thin Au films are measured. We also investigate an interferometric SPR setup where, due to the power flux transfer between plasmon modes, the specific choice of grating coupler can either decrease or increase the plasmon propagation length.

• Hyperspectral imaging of diffracted surface plasmons.

  Authors: Dominic Lepage, Alvaro Jiménez, Dominic Carrier, Jacques Beauvais, Jan J Dubowski

  Optics express. 12/2010; 18(26):27327-35.

  We present the results of far field measurements of the complete 3D dispersion relation of a surface plasmon resonance (SPR) effect induced by an integrated quantum well nanodevice. The lightWe present the results of far field measurements of the complete 3D dispersion relation of a surface plasmon resonance (SPR) effect induced by an integrated quantum well nanodevice. The light modulations in the far field, where the surface plasmons are extracted by a grating, has been calculated for a continuum of energies and wavevectors injected by the luminescent substrate. We introduce a novel experimental method for direct mapping of the EM wave dispersion that enables the monitoring of massive amounts of light-scattering related information. The quasi-real time method is applied for tracking, in the E(k) space, the SPR peak surfaces generated by the investigated nanodevice. Those additional dimensions, measured with scalable tracking precision, reveal anisotropic surficial interactions and provide spectroscopic response for SPR.

• Molecular self-assembly and passivation of GaAs (001) with alkanethiol monolayers: A view towards bio-functionalization

  Authors: Jan J. Dubowski, Oleksandr Voznyy, G.M. Marshall

  Applied Surface Science. 04/2010; 256:5714-5721.

  Properties of as prepared or nanoengineered III–V semiconductor surfaces provide attractive means for photonic detection of different adsorbants from surrounding gaseous or liquid environments. To beProperties of as prepared or nanoengineered III–V semiconductor surfaces provide attractive means for photonic detection of different adsorbants from surrounding gaseous or liquid environments. To be prac- tical, this approach requires that the surface is made selectively sensitive (functionalized) to targeted species. In addition, such surface has also to stay stable over extended period of time to make it available for rapid testing. Numerous reports demonstrate attractive properties of GaAs for sensing applications. One of the most fundamental issues relevant to these applications concerns the ability to functionalize chemically, or biologically, the surface of GaAs. The most studied method of GaAs surface functionaliza- tion is based on formation of self-assembled monolayers (SAMs) of various n-alkanethiols, HS-(CH2)n-T (T=CH3, COOH, NH2, etc.). In spite of multi-year research concerning this issue, it has only been recently that a comprehensive picture of SAMs formation on GaAs and an understand

• Formation dynamics of hexadecanethiol self-assembled monolayers on (001) GaAs observed with photoluminescence and Fourier transform infrared spectroscopies

  Authors: Chan-Kyu Kim, Gregory M. Marshall, Matthieu Martin, Michel Bisson-Viens, Zbigniew Wasilewski, Jan J. Dubowski

  Journal of Applied Physics. 11/2009;

  The dynamics of hexadecanethiol (HDT) [ HS ( CH ₂)₁₅ CH ₃] chemisorption and the formation of a self-assembled monolayer (SAM) on the GaAs(001) surface was studied inThe dynamics of hexadecanethiol (HDT) [ HS ( CH ₂)₁₅ CH ₃] chemisorption and the formation of a self-assembled monolayer (SAM) on the GaAs(001) surface was studied in situ by monitoring the photoluminescence (PL) intensity over a 20 h period. Comparing the PL time series in HDT solution with that of the bare GaAs surface similarly exposed to the ethanol solvent, we observed a two-phased evolution of the associated PL enhancement. Time-commensurate changes in the absorption frequency and intensity of the C–H stretching mode vibrations were then recorded using Fourier transform infrared spectroscopy, supporting that the PL enhancement corresponds directly with known mechanisms of ordered SAM formation. These results highlight the sensitivity with which in situ PL monitoring can reflect surface processes and underscores its potential for use in sensor applications.

• The role of gold adatoms and stereochemistry in self-assembly of methylthiolate on Au(111).

  Authors: Oleksandr Voznyy, Jan J Dubowski, J T Yates, Peter Maksymovych

  Journal of the American Chemical Society. 10/2009; 131(36):12989-93.

  On the basis of high resolution STM images and DFT modeling, we have resolved low- and high-coverage structures of methylthiolate (CH(3)S) self-assembled on the Au(111) surface. The key new findingOn the basis of high resolution STM images and DFT modeling, we have resolved low- and high-coverage structures of methylthiolate (CH(3)S) self-assembled on the Au(111) surface. The key new finding is that the building block of all these structures has the same stoichiometry of two thiolate species joined by a gold adatom. The self-arrangement of the methylthiolate-adatom complexes on the surface depends critically on their stereochemical properties. Variations of the latter can produce local ordering of adatom complexes with either (3 x 4) or (3 x 4 square root(3)) periodicity. A possible structural connection between the (3 x 4 square root(3)) structure and commonly observed (square root(3) x square root(3))R30 degrees phase in methylthiolate self-assembled monolayers is developed by taking into account the reduction in the long-range order and stereochemical isomerization at high coverage. We also suggest how the observed self-arrangements of methylthiolate may be related to the c(4 x 2) phase of its longer homologues.

• Surface Dipole Layer Potential Induced IR Absorption Enhancement in n-Alkanethiol SAMs on GaAs(001).

  Authors: Gregory M Marshall, Gregory P Lopinski, Farid Bensebaa, Jan J Dubowski

  Langmuir : the ACS journal of surfaces and colloids. 10/2009;

  The work function of n-alkanethiol self-assembled monolayers (SAMs) prepared on the GaAs(001) surface was measured using the Kelvin probe technique yielding the SAM 2D dipole layer potential (DLP).The work function of n-alkanethiol self-assembled monolayers (SAMs) prepared on the GaAs(001) surface was measured using the Kelvin probe technique yielding the SAM 2D dipole layer potential (DLP). Direct n-dependent proportionality between the DLP values and the C-H stretching mode infrared (IR) absorption intensities was observed, which supports a correspondence of reported IR enhancements with the electrostatic properties of the interface. X-ray photoelectron spectroscopy is also used to verify the work function measurements. In addition, the principal components of the refractive index tensor are shown to be n-invariant in the ordered SAM phase. Our results suggest that a local field correction to the transition dipole moment accounts for the observed increase in IR activity through an increase to the electronic polarizability.

• Iterative bandgap engineering at selected areas of quantum semiconductor wafers.

  Authors: Radoslaw Stanowski, Matthieu Martin, Richard Ares, Jan J Dubowski

  Optics express. 10/2009; 17(22):19842-7.

  We report on the application of a laser rapid thermal annealing technique for iterative bandgap engineering at selected areas of quantum semiconductor wafers. The approach takes advantage of theWe report on the application of a laser rapid thermal annealing technique for iterative bandgap engineering at selected areas of quantum semiconductor wafers. The approach takes advantage of the quantum well intermixing (QWI) effect for achieving targeted values of the bandgap in a series of small annealing steps. Each QWI step is monitored by collecting a photoluminescence map and, consequently, choosing the annealing strategy of the next step. An array of eight sites, 280 mum in diameter, each emitting at 1480 nm, has been fabricated with a spectral accuracy of better than 2 nm in a standard InGaAs/InGaAsP QW heterostructure that originally emitted at 1550 nm.

• Surface plasmon effects induced by uncollimated emission of semiconductor microstructures.

  Authors: Dominic Lepage, Jan J Dubowski

  Optics express. 07/2009; 17(12):10411-8.

  We have recently proposed an innovative microstructure for a monolithically integrated surface plasmon resonance (SPR) device comprising a metal coated SiO(2) layer deposited atop a photoluminescenceWe have recently proposed an innovative microstructure for a monolithically integrated surface plasmon resonance (SPR) device comprising a metal coated SiO(2) layer deposited atop a photoluminescence emitting quantum well (QW) wafer. The functioning of such a device is based on the uncollimated and incoherent emission of semiconductors. We discuss the results of our calculations aimed at the description of SPs coupling in QW semiconductor-based SPR architectures designed for biosensing applications. Two SPs modes could be coupled in the 0(th) diffraction order where the injected in-plane wavevectors from the QW structures can always meet SPR conditions. This results in increasing the SPs coupling efficiency up to 100 times higher than in case of indirect SPs injection.

• c(4 x 2) Structures of Alkanethiol Monolayers on Au (111) Compatible with the Constraint of Dense Packing.

  Authors: Oleksandr Voznyy, Jan J Dubowski

  Langmuir : the ACS journal of surfaces and colloids. 06/2009;

  Using alkanethiol dense packing as a starting point, we have found six prototypical packing structures commensurate with the (3 x 2 radical3) supercell of the Au (111) surface. Five of the sixUsing alkanethiol dense packing as a starting point, we have found six prototypical packing structures commensurate with the (3 x 2 radical3) supercell of the Au (111) surface. Five of the six structures are not compatible with the flat surface conditions but can be fitted to a reconstructed surface. Combined with density functional theory calculations and simulations of grazing incidence X-ray diffraction maps and of scanning tunneling microscopy images, this allowed us to refine and assess the recently proposed models of the c(4 x 2) self-assembled monolayers involving thiolate-adatom and thiolate-adatom-thiolate species and to propose a new model with four gold adatoms per unit cell.

• Observation of surface enhanced IR absorption coefficient in alkanethiol based self-assembled monolayers on GaAs(001)

  Authors: Gregory M. Marshall, Farid Bensebaa, Jan J. Dubowski

  Journal of Applied Physics. 06/2009;

  Alkanethiol self-assembled monolayers (SAMs) of various methylene group chain lengths [ HS –( CH ₂)_n– CH ₃] (n=9,11,13,15,17) were fabricated on the GaAs(001) surfaceAlkanethiol self-assembled monolayers (SAMs) of various methylene group chain lengths [ HS –( CH ₂)_n– CH ₃] (n=9,11,13,15,17) were fabricated on the GaAs(001) surface followed by characterization using Fourier transform infrared spectroscopy. Modal analysis of the CH ₂ stretching mode region (2800–3000 cm ^-1) showed that linear scaling of the n -dependent factors accurately reproduced the spectral data, supporting a chain-length consistent physical model upon which a measurement of the absorption coefficient was based. Evaluated from the linearity of the absorbance data, a peak coefficient of 3.5×10⁴ cm ^-1 was obtained and a domain for ordered self-assembly was assigned for values n≫9 . Compared with measurements of the absorption coefficient made in the liquid phase, the SAM phase coefficient was determined to be about six times greater. This enhancement effect is discussed in terms of contributions relating to the locally ordered environment and is largely attributed to the chemical properties of the interface. We believe this to be the first demonstration of IR spectral enhancement of a molecular species chemisorbed on the semiconductor surface.

• Adsorption Kinetics of Hydrogen Sulfide and Thiols on GaAs (001) Surfaces in a Vacuum

  Authors: Oleksandr Voznyy, Jan J. Dubowski

  J. Phys. Chem. C. 03/2008; 112:3726-3733.

  Adsorption mechanisms of hydrogen sulfide and alkanethiols on GaAs (001) surfaces prepared in a vacuum were studied using first principles calculations. The need for a physisorbed precursor wasAdsorption mechanisms of hydrogen sulfide and alkanethiols on GaAs (001) surfaces prepared in a vacuum were studied using first principles calculations. The need for a physisorbed precursor was confirmed based on energetic arguments and molecular dynamics simulations of the transition from a physisorption to a chemisorption state. The preference for S−Ga bond formation was found, resulting from a weak non-dissociative chemisorption state formed by the overlap of a sulfur lone pair orbital with an empty Ga dangling bond. Physisorption energies and the height of the transition barrier from physisorption to chemisorption on GaAs were found to be very similar to those on gold, while the main difference from gold was that hydrogen remains on the GaAs surface upon S−H cleavage. Obtained results allowed for a more advanced interpretation of experimental data concerning H2S and thiol adsorption on GaAs.

• Structure, bonding nature, and binding energy of alkanethiolate on As-rich GaAs (001) surface: a density functional theory study.

  Authors: Oleksandr Voznyy, Jan J Dubowski

  The journal of physical chemistry. B. 12/2006; 110(47):23619-22.

  Chemisorption of alkanethiols on As-rich GaAs (001) surface under a low coverage condition was studied using first principles density functional calculations in a periodic supercell approach. TheChemisorption of alkanethiols on As-rich GaAs (001) surface under a low coverage condition was studied using first principles density functional calculations in a periodic supercell approach. The thiolate adsorption site, tilt angle and its direction are dictated by the high directionality of As dangling bond and sulfur 3p orbital participating in bonding and steric repulsion of the first three CH2 units from the surface. Small charge transfer between thiolate and surface, strong dependence of total energy on tilt angle, and a relatively short length of 2.28 A of the S-As bond indicate the highly covalent nature of the bonding. Calculated binding energy of 2.1 eV is consistent with the available experimental data.

• Multibandgap quantum well wafers by IR laser quantum well intermixing : simulation of the lateral resolution of the process

  Authors: Oleksandr Voznyy, Radoslaw Stanowski, Jan J. Dubowski

  Journal of Laser Micro/Nanoengineering. 01/2006; 1:48-48.

  Post-growth selective-area bandgap tuning of quantum well (QW) microstructures has been investigated using Finite Element Method computer simulations. Laser fast scanning is proposed as a way toPost-growth selective-area bandgap tuning of quantum well (QW) microstructures has been investigated using Finite Element Method computer simulations. Laser fast scanning is proposed as a way to overcome the problem of damaging the surface with a small spot needed to obtain better spatial resolution. Influence of laser parameters, background heating, beam scanning speed and properties of QW microstructures on the ability to achieve sharp bandgap profiles in the laser- written intermixed material are investigated. Lateral resolution of 2 µm is expected to be achievable with a 12-µm beam laser rapid thermal annealing.

• Specific immobilization of influenza A virus on GaAs (001) surface.

  Authors: Valerie Duplan, Yannick Miron, Eric Frost, Michel Grandbois, Jan J Dubowski

  Journal of biomedical optics. 14(5):054042.

  In the quest for the development of an all-optical biosensor for rapid detection and typing of viral pathogens, we investigate biosensing architectures that take advantage of strong photoluminescenceIn the quest for the development of an all-optical biosensor for rapid detection and typing of viral pathogens, we investigate biosensing architectures that take advantage of strong photoluminescence emission from III-V quantum semiconductors (QS). One of the key elements in the development of such a biosensor is the ability to attach various analytes to GaAs--a material of choice for capping III-V QS of our interest. We report on the study of biofunctionalization of GaAs (001) with polyethylene-glycol (PEG) thiols and the successful immobilization of influenza A virus. A diluted solution of biotinylated PEG thiols in OH-terminated PEG thiols is used to form a network of sites for the attachment of neutravidin. Biotinylated polyclonal influenza A antibodies are applied to investigate the process of the immobilization of inactivated influenza A virus. The successful immobilization is demonstrated using atomic force microscopy and fluorescence microscopy measurements.

• Quantitation of influenza A virus in the presence of extraneous protein using electrochemical impedance spectroscopy

  Authors: Walid Mohamed Hassen, Valérie Duplan, Eric Frost, Jan J. Dubowski

  Electrochimica Acta. 56(24):8325-8328.

  In an attempt to provide an insight into detection of specific viruses in biological samples, we report on quantitation of influenza A virus (IAV) in samples containing large amounts of extraneousIn an attempt to provide an insight into detection of specific viruses in biological samples, we report on quantitation of influenza A virus (IAV) in samples containing large amounts of extraneous bovine serum albumin (BSA), foetal bovine serum (FBS) and hepatitis B virus (HBV) vaccine. Detection was carried out using electrochemical impedance spectroscopy (EIS) with an antibody-neutravidin-thiol architecture immobilized on the surface of an Au electrode. A linear response of the EIS signal was observed for IAV concentrations ranging from 0 to almost 64 ng/mL. However, saturation of the EIS response was recorded for greater concentrations and only a 6% increase in signal occurred when the IAV concentration increased to 128 ng/mL. The limit of detection, determined at 8 ng/mL, remained relatively unaffected by the environment composed of 50 ng/mL of HBV and 12.5% of FBS.