Molecular control over single-crystalline GaAs(hkl) surface electronic properties by using bio-thiols Project: PN-II-ID-PCE-2011-3-0304 financed by UEFISCDI (Contract No 91/2011) Project leader : Dr. Valentina Lazarescu

Project description

The project aims to explore the control exerted by the adsorbed cysteine over the electronic properties of the GaAs (hkl) surfaces. Beside the thiol group that binds to substrate with high affinity, this small highly polar molecule owns carboxyl and amino functional groups whose intramolecular and intermolecular interactions with themselves or other ions present in its environment play a key role in determining adsorbate conformation and overlayer structure. The complexity of the interfacial phenomena accompanying its binding to GaAs (hkl) requires an interdisciplinary approach. This is mainly achieved by correlating the information concerning the interplay of the semiconductor surface states and field-effects supplied by electrochemical impedance spectroscopy with that referring to the changes in the surface chemistry furnished by XPS and surface morphology provided by the fractal analysis of the AFM / STM images. UV-VIS-NIR and IR spectroellipsometry investigations on the surface morphology are also considered. Special attention will be focused on pH and doping effects as well as on the influence exerted by the metal cations (e.g. Ca2+/Mg+/ Ni2+), anions (e.g. Cl-) and redox probes (e.g. Fe(CN)63-/4- on the electrochemical properties of the self assembled monolayer of cysteine epinephrine) will be also examined.

on GaAs(hkl) electrodes.

Electrochemical response of the cysteine-modified GaAs (hkl) electrodes in the presence of two important neurotransmitters (dopamine /

Main milestones:



2012:

Preparation of the cysteine modified GaAs(hkl) electrodes & exploration of pH- and doping-effects on the electrochemical behavior of the cysteine adsorbed on GaAs(hkl) electrodes 

2013:

(e.g.

Examination of the influence exerted by metal cations Ca 2+ /Mg 2+ /Ni 2+ ) and cysteine on GaAs(hkl) electrodes anions (e.g.

Cl ) on the electrochemical properties of the self-assembled monolayers of 

2014:

Evaluation of the electrochemical response of the cysteine-modified GaAs(hkl) electrodes in the presence of dopamine / epinephrine 

2015:

Evaluation of the electrochemical response of the cysteine-modified GaAs(hkl) electrodes in the presence of epinephrine and examination of the influence exerted by redox probes (e.g. Fe(CN) the self-assembled monolayers of cysteine on GaAs(hkl) electrodes 6 3-/4 ) on the electrochemical properties of

Budget

Budget chapter 2012 (lei) (expenses) Salaries 150 000 Inventory Mobility Overhead Total 254 067.13 45 932.87 90 000 540 000 2013 (lei) 132 400 86 343.48 27 319.04 2014 (lei) 70 000 37 500 20 000 49 212.50 25 500 295 275. 02 153 000 2015 (lei) Total (lei) 100 000 452 000 272 370.35 650 280.96 54 067.13 147 319. 04 85 287.50 511 724.98 250 000 1 500 000

2012: Objectives

      Preparation of GaAs(hkl) electrodes from n- and p-doped wafers Chemical modification of GaAs(hkl) electrodes with self assembled monolayers (SAM) of cysteine Microstructural (STM/AFM, VASE, fractal analysis) investigations on GaAs(hkl) substrate before and after the chemical modification with cysteine Electrochemical investigations (CV, EIS) on pH-and doping-effects at cysteine-modified GaAs(hkl) electrodes XPS investigations on the chemical composition of the cysteine modified electrodes after the electrochemical measurements Microstructural (STM/AFM, VASE, fractal analysis) investigations on the morphology of the cysteine-modified electrodes after the electrochemical measurements

2012: Working team

        Dr. Mirela Enache Dr. Loredana Preda Dr. Ana Maria Toader Dr. Mihai Anastasescu Dr. Gianina Dobrescu Dr. Sorana Ionescu (University of Bucharest) Hermine Stroescu (PhD student) Cornelia Penea (Technician)

2012: Scientific cooperation



INCFM- Bucharest:

Dr. Mihail F. Lazarescu; Dr. Catalin Negrila (GaAs(hkl) electrodes preparation and XPS investigations)  Instituto de Quimica Fisica “Rocasolano” – Madrid (Spain) Dr. Angel Cuesta (EC-STM investigations)

2012: Activity Report

   

GaAs(100) electrodes prepared from p- and n-doped wafers were chemically modified with self-assembled monolayers of L-cysteine from aqueous and ethanol solutions Microstructural (VASE, AFM coupled with fractal analysis) and XPS investigations pointed to significant effects of both the dopant and the solvent type on the overlayer chemistry and structure Electrochemical investigations (CV, EIS) on the pH effects at L-cysteine-modified p-GaAs(100) electrode revealed an electric field driven process of H + transfer inside the L-cysteine-thiolate film resulting in significant charge diminution both in the organic overlayer and in the semiconductor depletion region; this process observed both during the direct and forward potential scans at L-cysteine thiolate/p-GaAs(100) was found to occur only in the backward potential scan at L-cysteine thiolate/n-GaAs(100) Additional EIS, XPS & AFM investigations coupled with DFT calculations on thiolate formation prevailing on the semiconducting surface at GaAs(111)-Ga and GaAs(111)-As provided evidence that both As and Ga atoms are involved in the chemisorptive bonding no matter which one is

2012: Papers & Communications

 (a) Papers

Ga and As Competition for Thiolate Formation at p-GaAs (111)

L. Preda, C. Negrila, M. F. Lazarescu, M. Enache, M. Anastasescu, A. M. Toader, S. Ionescu, V. Lazarescu Electrochimica Acta 104 (2013) 1-11 (IF: 3.777)  (b) Communications: 1.

Self-assembled monolayers of L-cysteine on GaAs(100) electrodes,

M. Enache, L. Preda, M. Anastasescu, C. Negrila, M.F. Lazarescu, V. Lazarescu, Third Regional Symposium on Electrochemistry: South-East Europe RSE-SEE, May 13-17, 2012, Bucharest, Romania 2. Potential-induced conformational changes in self-assembled monolayers of L-cysteine at p-GaAs(100) electrodes, M. Enache, L. Preda, V. Lazarescu, C. Negrila, M. F. Lazarescu, 222nd ECS Meeting PRIME 2012, Honolulu (SUA) 7-12 Oct. 2012 3.

Molecular self-assembling control over the surface states and field-

effects at n-GaAs(100) electrodes, V. Lazarescu, M. Enache, G. Dobrescu, M. Gartner, C. Negrila, M. F. Lazarescu, 222nd ECS Meeting PRIME 2012, Honolulu (SUA) 7-12 Oct. 2012.

2013: Objectives

      Electrochemical investigations (CV,EIS) on the metallic cation effects XPS investigations on the metallic cation effects Microstructural investigations (AFM, Fractal Analysis) on the metallic cation effects Electrochemical investigations (CV,EIS) on the anion effects XPS investigations on the anion effects Microstructural investigations (AFM, Fractal Analysis) on the cation effects

2013: Working team

      Dr. Mirela Enache Dr. Loredana Preda Dr. Ana Maria Toader Dr. Mihai Anastasescu Dr. Gianina Dobrescu Cornelia Penea (Technician)

2013: Scientific cooperation



INCFM- Bucharest:

Dr. Mihail F. Lazarescu; Dr. Catalin Negrila (GaAs(hkl) electrodes preparation and XPS investigations) 

Universität Ulm, Institut für Theoretische Chemie:

Dr. Elizabeth Santos (theoretical estimation of the cysteine-thiolate bonding at GaAs(100) substrates)

2013: Activity Report

  

CV, EIS, XPS & AFM investigations revealed that Mg to n-GaAs(100) substrate 2+ ions have only minor effects on the electrochemical, chemical and fractal behavior of the L-cysteine thiolate formed at p-GaAs(100) surface but they influence both the electrochemical, chemical and structural properties of the L-cysteine thiolate bound CV, EIS, XPS & AFM studies pointed out that unlike Cl ions which do not bring significant changes in the surface chemistry and morphology as well as the electrochemical activity in solutions with low or high pH, CH 3 (CH 2 ) 11 SO 4 ions have a strong influence on the interfacial properties of both L-cysteine-thiolate formed at p-GaAs(100) and n-GaAs(100) surfaces and the bare substrates investigated supplementary Additional interaction Ga 7 As 8 H 12 DFT of between them calculations L-cysteine showed on with the Ga 8 As 7 H 12 significant chemical and clusters modeling the As-rich and Ga-rich differences



2013: Papers & Communications

(a) Papers

EIS investigations on the L-cysteine-thiolate self-assembled

monolayers formed at p-GaAs (100) electrodes,

V.Lazarescu, M. Enache, M. Anastasescu, G. Dobrescu, C. Negrila, M. F. Lazarescu, Electrochimica Acta 131 (2014) 42-51 (IF: 4.09)  (b) Communications:

1. Ion Effects on self-assembled monolayers of L-cysteine on

p-GaAs (100) Electrodes, M. Enache, M. Anastasescu, C. Negrila, M.F. Lazarescu, V. Lazarescu, Fourth Regional Symposium on Electrochemistry, South East Europe (RSE-SEE), Ljubljana, Slovenia, May, 26-30, 2013

2. EIS Investigations on the L-Cysteine-thiolate Self Assembled Monolayers Formed at p-GaAs (100) Electrodes,

V. Lazarescu, M. Enache, M. Anastasescu, G. Dobrescu, C. Negrila, M. F. Lazarescu, 9th International Symposium on Electrochemical Impedance Spectroscopy (EIS2013) in Okinawa, Japan, June 16-21, 2013

2014: Objectives

Evaluation of the electrochemical response of the cysteine-modified GaAs(hkl) electrodes in the presence of the neuro-transmitter dopamine

 Electrochemical investigations (CV, EIS)  XPS investigations  Microstructural investigations (AFM, fractal analysis)

2014: Working team

     Dr. Mirela Enache Dr. Loredana Preda Dr. Ana Maria Toader Dr. Mihai Anastasescu Dr. Gianina Dobrescu

2014: Scientific cooperation



INCFM- Bucharest:

Dr. Mihail F. Lazarescu; Dr. Catalin Negrila (GaAs(hkl) electrodes preparation and XPS investigations)



Universität Ulm, Institut für Theoretische Chemie:

Dr. Elizabeth Santos; Dr. Fernanda Juarez (theoretical estimation of the cysteine-thiolate bonding at GaAs(100) substrates)

2014: Activity Report

  

CV & EIS investigations revealed that dopamine interacts differently with L-Cysteine-thiolate covered p- and n-doped GaAs(100) electrodes at low pH: there are opposite effects on both the interfacial impedance at the two limits of the potential window and the potential-induced proton transfer taking place within the overlayer XPS & AFM measurements also pointed out distinct chemical and structural changes brought about by the dopamine interaction with L-cysteine-thiolate formed at p- and n-GaAs(100) both before and after the electrochemical bias Additional CV, EIS, XPS and AFM studies were performed on the chemical and electrochemical interaction of dopamine with the bare p- and n GaAs(100) surfaces

2014: Papers & Communications



(a) Papers

Field - dipole interactions in L-cysteine-thiolate self assembled at p-

and n-GaAs(100) electrodes,

V. Lazarescu, M. Enache, A. M. Toader, L. Preda, M. Anastasescu, G. Dobrescu, C. Negrila, M. F. Lazarescu Electrochim. Acta (submitted) (IF: 4.09)  (b) Oral Communications:

1.SDS influence on the surface states and field effects of n GaAs(100),

M. Enache, M.Anastasescu, G. Dobrescu, C. Negrila, M. F. Lazarescu, V. Lazarescu, 47th Heyrovský Discussion Trest, Czech Republic, May 25 – 29, 2014

2. Field - Dipole Interactions in L-Cysteine-Thiolate Self Assembled at

p- and n-GaAs(100) Electrodes,

V. Lazarescu, M. Enache, L. Preda, M. Anastasescu, G. Dobrescu, C. Negrila, M. F. Lazarescu, 15th Topical Meeting of the International Society of Electrochemistry) in Niagara Falls, Canada, April 27- May, 1, 2014

3. About Pattern and Form in Electrochemical Behavior of L-Cysteine-

thiolate Self-assembled Monolayers at GaAs(100),

V. Lazarescu, On Form and Pattern, Humboldt Kolleg, Bucharest. May, 29-3, 2014