selective-area-modification-silicon-surface-wettability-pulsed-uv

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Université de Sherbrooke

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. 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.

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

Observed properties of thiol self-assembled monolayers (SAMs) on GaAs (001) surfaces can be explained by the presence of surface reconstructions, but their exact form is generally unknown. We propose a new approach to modeling the SAM-surface interface based on using alkanethiol dense packing structures as a starting point and adjusting the surface reconstruction to accommodate them. Obtained in such a way, model SAMs adsorb along the trenches in the [110] direction and exhibit a 19 degrees tilt and +/- 45 degrees twist angles, in agreement with available experimental data. The molecules of the SAM bind to both Ga and As, and cover only 50% of the available surface sites. The requirements for the SAM formation process to achieve the proposed structures are discussed.

Structure of thiol self-assembled monolayers commensurate with the GaAs (001) surface.

Using alkanethiol dense packing as a starting point, we have found six prototypical packing structures commensurate with the (3x2 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(4x2) self-assembled monolayers involving thiolate-adatom and thiolate-adatom-thiolate species and to propose a new model with four gold adatoms per unit cell.

c(4x2) structures of alkanethiol monolayers on Au (111) compatible with the constraint of dense packing.

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 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.

Surface plasmon effects induced by uncollimated emission of semiconductor microstructures.

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 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.

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

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.

Surface dipole layer potential induced ir absorption enhancement in n-alkanethiol SAMs on GaAs(001).

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 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.

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

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 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.

Iterative bandgap engineering at selected areas of quantum semiconductor wafers.

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 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.

Hyperspectral imaging of diffracted surface plasmons.

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 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.

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

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.

Plasmonic propagations distances for interferometric surface plasmon resonance biosensing.

The concept of a portable, inexpensive and semi-automated biosensing platform, or lab-on-a-chip, is a vision shared by many researchers and venture industries. Under this scope, we have investigated the application of optical emission from quantum well (QW) microstructures for monitoring surface phenomena on gold layers remaining in proximity (<300 nm) with QW microstructures. The uncollimated QW radiation excites surface plasmons (SP) and through the surface plasmon resonance (SPR) effect allows for detection of small perturbation in the density surface adsorbates. The SPR technology is already commonly used for biochemical characterization in pharmaceutical industries, but the reduction of the distance between the SP exciting source and the biosensing platform to a few hundreds of nanometers is an innovative approach enabling us to achieve an ultimate miniaturization of the device. We evaluate the signal quality of this nanophotonic QW-SPR device using hyperspectral-imaging technology, and we compare its performance with that of a standard prism-based commercial system. Two standard biochemical agents are employed for this characterization study: bovine serum albumin and inactivated influenza A virus. With an innovative conical method of SPR data collection, we demonstrate that individually collected SPR scan, each in less than 2.2 s, yield a resolution of the detection at 1.5 × 10-6 RIU.

Miniaturized quantum semiconductor surface plasmon resonance platform for detection of biological molecules.

Excimer (ultraviolet) laser-induced quantum well intermixing (UV-Laser-QWI) is an attractive technique for wafer level post-growth processing and fabrication of a variety of monolithically integrated photonic devices. The results of UV-Laser-QWI employed for the fabrication of multibandgap III-V semiconductor wafers have demonstrated the attractive character of this approach although the process accuracy and reproducibility have remained relatively weakly covered in related literature. We report on a systematic investigation of the reproducibility of this process induced with a KrF excimer laser. The influence of both the irradiation with different laser doses and the annealing temperatures on the amplitude of intermixing in InGaAs/InGaAsP/InP quantum well heterostructures has been evaluated based on the photoluminescence measurements. Under optimized conditions, the process allows to blue shift the bandgap of a heterostructure by more than 100 nm with a remarkable 5.3% relative standard deviation.

Excimer laser induced quantum well intermixing: a reproducibility study of the process for fabrication of photonic integrated devices.

Compact and portable surface plasmon resonance (SPR) biosensors of high sensitivities can be made through integration of discrete components in a single device. We report on a device comprising a vertical cavity light emitting diode (VLED) integrated with gold-based biosensing nanostructures fabricated atop its surface. Coupling of surface plasmon waves was achieved by the introduction of a spacer SiO<sub>2</sub> layer located between the light source and the functionalized Au thin film. The SPR signal was extracted in far field with a Au-based nanograting and detected using a custom designed hyperspectral imager. We discuss the performance of a VLED-based SPR device employed for detection of different concentration saltwater solutions.

Integrated electrically driven surface plasmon resonance device for biosensing applications.

We report on the fast wavelength switching in V-cavity laser (VCL) with quantum well intermixed tuning section. The laser wavelength can be switched between 32 channels at 100 GHz spacing using a single electrode control. The fabrication process involves a quantum well intermixing (QWI) process using KrF laser irradiation and rapid thermal annealing (RTA). The tuning current is less than 40 mA, much lower than previously demonstrated tunable VCL based on electro-thermal-optic effect. The wavelength switching is also faster by three orders of magnitude. The dynamic switching characteristics between two channels with different numbers of intermediate channels are investigated. It shows that the switching time is about 1 ns between adjacent channels and increases up to 12 ns with increasing number of intermediate channels.

Article	Year
Structure, bonding nature, and binding energy of alkanethiolate on As-rich GaAs (001) surface: a density functional theory study. The journal of physical chemistry. B\| PubMed ID: 17125316	2006
Structure of thiol self-assembled monolayers commensurate with the GaAs (001) surface. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 18975925	2008
c(4x2) structures of alkanethiol monolayers on Au (111) compatible with the constraint of dense packing. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 19466814	2009
Surface plasmon effects induced by uncollimated emission of semiconductor microstructures. Optics express\| PubMed ID: 19506696	2009
The role of gold adatoms and stereochemistry in self-assembly of methylthiolate on Au(111). Journal of the American Chemical Society\| PubMed ID: 19737018	2009
Surface dipole layer potential induced ir absorption enhancement in n-alkanethiol SAMs on GaAs(001). Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 19874009	2009
Specific immobilization of influenza A virus on GaAs (001) surface. Journal of biomedical optics\| PubMed ID: 19895143	2009
Iterative bandgap engineering at selected areas of quantum semiconductor wafers. Optics express\| PubMed ID: 19997205	2009
Hyperspectral imaging of diffracted surface plasmons. Optics express\| PubMed ID: 21197011	2010
Electro-optic investigation of the surface trapping efficiency in n-alkanethiol SAM passivated GaAs(001). Nanotechnology\| PubMed ID: 21490389	2011
Plasmonic propagations distances for interferometric surface plasmon resonance biosensing. Nanoscale research letters\| PubMed ID: 21711921	2011
Miniaturized quantum semiconductor surface plasmon resonance platform for detection of biological molecules. Biosensors\| PubMed ID: 25586127	2013
Excimer laser induced quantum well intermixing: a reproducibility study of the process for fabrication of photonic integrated devices. Optics express\| PubMed ID: 25835867	2015
Integrated electrically driven surface plasmon resonance device for biosensing applications. Optics express\| PubMed ID: 26367633	2015
Carrier-induced fast wavelength switching in tunable V-cavity laser with quantum well intermixed tuning section. Optics express\| PubMed ID: 26480147	2015

Jan J. Dubowski

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