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 descriptionThe project aims to explore the control exerted by the adsorbed cysteine over the electronic properties of the GaAs (100) 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 (100) 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 (Mg+), anions (Cl-) and redox probes (hemine/hem) on the electrochemical properties of the self-assembled monolayer of cysteine on GaAs(100) electrodes. Electrochemical response of the cysteine-modified GaAs (100) electrodes in the presence of two important neurotransmitters (dopamine / epinephrine) will be also examined.

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(100) electrodes

2013: Examination of the influence exerted by metal cations (Mg2+) and anions (Cl-, CH3(CH2)11OSO3

-) on the electrochemical properties of the self-assembled monolayers of cysteine on GaAs(100) electrodes

2014: Evaluation of the electrochemical response of the cysteine-modified GaAs(100) electrodes in the presence of dopamine

2015: Evaluation of the electrochemical response of the cysteine-modified GaAs(100) electrodes in the presence of epinephrine

2016 Examination of the influence exerted by redox probes (Hemine/Hem) on the electrochemical properties of the self-assembled monolayers of cysteine on GaAs(100) electrodes

BudgetBudget

chapter

2012 (lei) 2013 (lei) 2014 (lei) 2015 (lei) 2016(lei) Total (lei)

Salaries 150000.00 132400.00 70000.00 75411.50 24588.50 452400.00

Inventory 254067.13 86343.48 36679.18 42180.00 230190.35 649460.14

Mobility 45932.87 27319.04 20820.82 20000.00 34067.13 148139.86

Overhead 90000.00 49212.50 25500.00 27518.5 57769.00 250000.00

Total 540000.00 295275. 02 153000.00 165110.00 346614.98 1 500 000

2012: Objectives Preparation of GaAs(100) electrodes from n- and p-doped wafers Chemical modification of GaAs(100) electrodes with self-

assembled monolayers (SAM) of cysteine Microstructural (STM/AFM, VASE, fractal analysis) investigations

on GaAs(100) substrate before and after the chemical modification with cysteine

Electrochemical investigations (CV, EIS) on pH-and doping-effects at cysteine-modified GaAs(100) 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 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 prevailing on the semiconducting surface

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. LazarescuElectrochimica Acta 104 (2013) 1-11 (IF: 4.09)

(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, Romania2. 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. 20123. 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

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: Objectives

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(100) 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 Mg2+ 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 to n-GaAs(100) substrate

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, CH3(CH2)11SO4

- 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 DFT calculations on the chemical interaction of L-cysteine with Ga8As7H12 and Ga7As8H12 clusters modeling the As-rich and Ga-rich (100) surfaces showed significant differences between them

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: 4.5)

(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: ObjectivesEvaluation of the electrochemical response of the cysteine-modified GaAs(100) 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(100) 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 176 (2015) 112-124 (IF: 4.5)

(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, 20142. 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, 20143. 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

2015: ObjectivesEvaluation of the electrochemical response of the cysteine-modified GaAs(hkl) electrodes in the presence of the neuro-transmitter epinephrine

Electrochemical investigations (CV, EIS)

XPS investigations

Microstructural investigations (AFM, fractal analysis)

Dr. Mirela Enache Dr. Loredana Preda Dr. Ana Maria Toader Dr. Mihai Anastasescu Dr. Gianina Dobrescu Cristian Ionita (Technician)

2015: Working team

INCFM- Bucharest: Dr. Mihail F. Lazarescu; Dr. Catalin Negrila (GaAs(100) electrodes preparation and XPS

investigations)

Universität Ulm, Institut für Theoretische Chemie:Dr. Elizabeth Santos; Dr. Fernanda Juarez

(theoretical estimation of the L-cysteine-thiolate bonding at GaAs(100) substrates)

2015: Scientific cooperation

CV & EIS investigations performed at pH 7 revealed that epinephrine has different effects on the interfacial impedance: it becomes more resistive at the p-doped but less resistive at the n-doped cysteine-thiolate covered GaAs(100) electrodes at both limits of the potential window; besides, the potential dependence of the main electrical contributions of the interfacial impedance is different under the anodic and cathodic bias only at the p-doped electrodes.

XPS & AFM measurements performed both before and after the electrochemical bias pointed out distinct chemical and structural changes brought about by the interaction of epinephrine with cysteine-thiolate formed at p- and n-GaAs(100) electrodes.

Experimental data suggest that epinephrine interaction with cysteine-thiolate self-assembled on GaAs(100) is mainly electrostatic at the p-doped substrates whereas at the n-doped ones, it involves also field-dipole and chemical forces.

For a better understanding of such complex interfacial phenomena, additional experimental and theoretical studies were performed:

2015: Activity Report

2015: Activity Report EIS, XPS and AFM investigations on the chemical and

electrochemical interactions of the p- GaAs(100) electrode with ionic species and dipoles in SDS acidic solutions

They revealed that the surface As and Ga atoms keep their chemical individuality in their contact with all the electrically active species in solution and the applied field effects control both the adsorption and the self-assembling processes

Density-functional theory calculations on the adsorption of the L-cysteine on GaAs(100) from ethanol solutions carried out in cooperation with University of Ulm (Germany) using slabs instead clusters to describe better the surface

They pointed out that an important contribution for the stabilization of the adsorbate originates in the interaction of the functional groups with the surface. The distinct interaction of the molecular dipole of the adsorbed species with the electrostatic field driven by the diffuse distribution of the semiconductor space charge region turned out to be the cause of the prevalence of the As-bound L-cysteine thiolate species at the p-doped samples and that of the Ga-bound L-cysteine thiolate species at the n-doped samples.

(a) Papers (1) V. Lazarescu, M. Enache, G. Dobrescu, M. Anastasescu, C. Negrila, M.F. Lazarescu, Potential-Driven Effects at p-GaAs (100) Electrode in Sodium Dodecyl Sulfate Acid Solution, Journal of Electroanalytical Chemistry (under review) (2) M.F. Juarez, A.M. Toader, C. Negrila, E. Santos, V. Lazarescu, Combined ab initio and XPS investigations of the electronic interactions of L-Cysteine adsorbed on GaAs(100) Chemistry Select (to be submitted)(b) Communications(1) V. Lazarescu, M. Enache, G. Dobrescu, M. Anastasescu, C. Negrila, M.F. Lazarescu, Field Effects at p-GaAs (100) Electrode in Sodium Dodecyl Sulfate Acid Solution, 228th ECS Meeting Phoenix, AZ, 11-15 Oct., 2015(2)M. Enache, M. Anastasescu, G. Dobrescu, C. Negrila, M. F. Lazarescu, V. Lazarescu, Electrochemical Behaviour of Dopamine on GaAs(100) Electrodes in Acidic Media, 10th International Frumkin Symposium on Electrochemistry, 21-23 Oct. 2015, Moscova, Rusia

2015: Papers & Communications

2016: ObjectivesEvaluation of the electrochemical response of the cysteine-modified GaAs(100) electrodes in the presence of a redox couple (hemine/hem)

Electrochemical investigations (CV, EIS)

XPS investigations

Microstructural investigations (AFM, fractal analysis)

2016: Working team Dr. Mirela Enache Dr. Loredana Preda Dr. Mihai Anastasescu Dr. Gianina Dobrescu Cristian Ionita (Technician)

2016: Scientific cooperation INCFM- Bucharest: Dr. Mihail F. Lazarescu; Dr. Catalin Negrila (GaAs(100) electrodes preparation and XPS

investigations)

Universität Ulm, Institut für Theoretische Chemie:Dr. Elizabeth Santos; Dr. Fernanda Juarez

(theoretical estimation of the L-cysteine-thiolate bonding at GaAs(100) substrates)

2016: Activity Report CV & EIS investigations performed at pH 7.5 revealed that

the redox couple hemine/hem occurs reversibly at the p-doped cysteine-thiolate covered GaAs(100) electrode and irreversibly at the n-doped one

XPS & AFM measurements performed both before and after the electrochemical bias pointed out distinct chemical and structural changes brought about by the interaction of the hemine/hem species with the cysteine-thiolate formed at p- and n-GaAs(100) electrodes.

Experimental data suggest that hemine/hem species adsorbed in a stand-up position on the cysteine-thiolate self-assembled on p-GaAs(100) keeps the high spin configuration before and after the charge transfer step whereas these species undergo a spin transition to a lower configuration at the n-doped substrates, resulting in strong adsorbed species which inhibit the subsequent re-oxidation process.

2016: Activity Report For a better understanding of such complex interfacial

phenomena, we performed additional EIS, XPS and AFM investigations on the chemical and electrochemical interactions of the redox couple hemine/hem with bare p- and n-GaAs(100) at pH 7.5

They revealed that the redox couple exhibits a reversible behavior at the p-doped electrode and a irreversible one at the n-doped one, but only in the voltammetric data.

EIS and XPS investigations proved that the couple redox operates reversibly at both types of electrodes within the adsorbed layer,

XPS data evidenced significant changes in the Cl-2p core level region observed at n-GaAs(100) after the cathodic reduction process which suggest a potential-induced spin transition from high to low spin state, resulting in strong adsorbed hem species which limits the process of re-oxidation to only the adsorbed species.

2016: PapersM.F. Juarez, A.M. Toader, C. Negrila, E. Santos, V.

Lazarescu, Combined ab initio and XPS investigations of the electronic interactions of L-Cysteine adsorbed on GaAs(100), ChemistrySelect 1 (2016) 3623 – 3634.

V. Lazarescu, M. Enache, M. Anastasescu, G. Dobrescu, C. Negrila, M. F. Lazarescu, Combined EIS, XPS, and AFM study of the distinct behavior of L-Cysteine-thiolate formed at p- and n-GaAs(100) electrodes in SDS solution, Electrochimica Acta (under evaluation)

2016: Communications Combined EIS and XPS study of the distinct behavior of L-cysteine-thiolate

formed at p- and n-GaAs(100) electrodes in SDS solution,V. Lazarescu, M. Enache, M. Anastasescu, G. Dobrescu, C. Negrila, M. F. Lazarescu, 10th International Symposium of Electrochemical Impedance Spectroscopy, A Toxa (Spania), iunie 2016

Electrochemical behavior of epinephrine on L-Cysteine modified GaAs(100) electrode, M. Enache, M. Anastasescu, C. Negrila, M. F. Lazarescu, V. Lazarescu, 67th Annual Meeting of the International Society of Electrochemistry, Hague (Olanda) August, 2016.

Dopamine effects on self-assembled monolayers of L-cysteine on GaAs (100) electrodes, M. Enache, M. Anastasescu, C. Negrila, M. F. Lazarescu, V. Lazarescu, ROMPHYSCHEM-16, Galati (Romania), Sept. 2016

Fractal analysis of self-assembled monolayers of L-cysteine on GaAs (100) electrodes, G. Dobrescu, M. Anastasescu, I. Fangli, V. Lazarescu, ROMPHYSCHEM-16, Galati (Romania), Sept. 2016