A N T O N M A N A K H O V P H D I N P H Y S I C S Surface Analysis - XPS Why we need to know surface chemistry?  Surface properties affects interaction of material (metals, plastic, powder, etc.) with the environment (water, polymers, in vivo…) and specific chemical composition and morphology is required for particular application.  Surface Chemistry influences cell adhesion, fouling of bioorganisms, adhesion between different phases of composite materials.  Often the application of material with noble bulk properties (hardness, flexibility, chemical stability) is not possible due to low surface free energy, or too reactive surface instead.  Deposition of thin film can tune surface properties without degradation of the bulk of the material Surface analysis methods : Technique Probe In/Out Depth resolu- tion, nm Lateral resolution, nm Informa- tion Advantage (+) and drawback (-) Contact angle Liquid water droplet 0.1 1000 Surface energy + Fast acquisition - No molecular information X-Ray photoelectron spectroscopy XPS X-Ray/ electrons 5 3000 Elemental composition (except H), binding state + Quantitative + Information about the neighbours of the atoms - Limited Molecular information - sensitivity >0.1 at% Scanning electron microscopy , SEM Electrons/ electrons 3 2 Surface image - No direct information regarding the topography. Technique Probe In/Out Depth resolu- tion, nm Lateral resolution, nm Informa- tion Advantage (+) and drawback (-) Energy Dispersive analysis Electrons/ X-Ray 2000 100 Elemental information - Low precision of quantification IR attenuated total reflection ATR-FTIR IR/IR ~2000 2000 Surface composition binding state + Fast acquisition +Information regarding the molecular functions information X-Ray photoelectron spectroscopy XPS X-Ray/ electrons 5 3000 Elemental composition (except H), binding state + Quantitative + Information about the neighbours of the atoms - Limited Molecular information - sensitivity >0.1 at% Scanning electron microscopy , SEM Electrons/ electrons 3 2 Surface image - No direct information regarding the topography. Technique Probe In/Out Depth resolu- tion, nm Lateral resolution, nm Informa- tion Advantage (+) and drawback (-) Energy Dispersive analysis Electrons/ X-Ray 2000 100 Elemental information - Low precision of quantification IR attenuated total reflection ATR-FTIR IR/IR ~2000 2000 Surface composition binding state + Fast acquisition +Information regarding the molecular functions - Overlap of some chemical domains -Quantification is not possible Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) Ions/Ions 1 100 Surface composition + Highly Sensitive (>1 ppm) +Molecular information is possible + 3D reconstruction of the layer - non quantitative  Methods based on the radiation of material by photons :  XPS  XRD  UPS  UV-Vis spectrophotomentry  IR spectroscopy Interaction of photons with matter X-ray Photoelectron Spectroscopy XPS X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA) is a widely used technique to investigate the chemical composition of surfaces. X-ray Photoelectron spectroscopy, based on the photoelectric effect, was developed in the mid-1960’s by Kai Siegbahn and his research group at the University of Uppsala XPS involves irradiating a sample with X-rays of a characteristic energy and measuring the flux of electrons leaving the surface. The energy spectrum for the ejected electrons is a combination of an overall trend due to transmission characteristics of the spectrometer, energy loss processes within the sample and resonance structures that derive form electronic states of the material under analysis. The instrumental contribution is an unwelcome fact of the measurement process, but the background and resonance peaks offer information about the sample surface XPS  kinb EEh  Chemical Shifts Chemical Shifts Final Effects - Coupling Angular Momentum Coupling L-S coupling J-J coupling Light elements Heavy elements Final Effects – shake-up In metals the free electrons are constrained to move within energy bands that are characteristic of the material and these material properties influence the shape of the energy loss distribution, namely, scattering of the photoelectric electrons by free electrons with discrete energy bands produces energy loss distributions with relatively narrow structures. Depth of analysis and Mean Free Path Quantification C- concentration RSF -relative sensitivity factor C Survey Spectra O1s C1s N1s Atomic Concentrations : C= ? at.% O= ? at.% N= ? at.% I (C1s) = 181 080 RSF C1s = 1 I (N1s) = 53 240 RSF (N1s)= 1.8 I (O1s) = 37 700 RSF (O1s) = 2.95 Narrow Scan C1s 292 290 288 286 284 282 Intensity BE, eV Experiment C-C C-COO C-O C=O/O-C-O C(O)=O Envelope a) Carboxyl Layer 290 288 286 284 282 0 500 1000 1500 2000 2500 3000 a) C-CN/ CN NHx Intensity,counts BE, eV CHx N-C=O/ C=O Amine Layer C1s Narrow Scan -> Environments O1s N1sCarboxyl Layer 404 402 400 398 396 394 2000 3000 4000 5000 6000 CN Intensity,counts BE , eV NHx N-C=O N1s XPS Amine Layer HI MagPE 25.000KE/1 Ex=1486.599eV WF=0.000eV Ck=XL Det=SUM Ent=6x12mm Exit=6mm C-O/C=O O-C=O O1s x 10 1 20 30 40 50 60 70 CPS 536 532 528 524 Binding energy (eV) Chemical derivatization CD-XPS Derivatization of Primary Groups           %100 3/8 3/2    FC F С NH Derivatization of Carboxyl Groups         %100 23    FC F OOHC         %100 3/2  N F N NH PECVD of C2H4+NH3 More nitrogen – more amines but higher thickness loss. Stability of amine films prepared from NH3 / C2H2 mixture More nitrogen – more amines but higher thickness loss. Angel Contreras-Garcıa • Michael R. Wertheimer Plasma Chem Plasma Process (2013) 33:147–163 C2H4 C2H4 C2H4 C2H4 C2H2 C2H2 C2H2 C2H2 C2H2 AllylAmine Plasma Polymers High concentration of amines in AA pp can be obtained only at low plasma power but it leads to huge loss of material. Cell Adhesion Cell Proliferation