Project

Back to overview

Positive or negative? Selecting the charge state of ions during pulsed laser deposition of thin films

English title Positive or negative? Selecting the charge state of ions during pulsed laser deposition of thin films
Applicant Wokaun Alexander
Number 152553
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Inorganic Chemistry
Start/End 01.07.2014 - 31.07.2018
Approved amount 238'573.00
Show all

All Disciplines (2)

Discipline
Inorganic Chemistry
Other disciplines of Physics

Keywords (6)

pulsed laser deposition (PLD); negative ions; thin films; plasma analysis; charge selection; oxides

Lay Summary (German)

Lead
Für ein grundlegendes Verständniss des Prozesses der gepulsten Laserablation (PLD) und warum es häufig nur in einem sehr eng begrenzten Parameterfenster möglich ist qualitativ hochwertige Filme herzustellen, werden in situ Diagnosetechniken eingesetzt. Wichtige Plasmaparameter sind die kinetische Energie von Plasmaspezien, Metall-Sauerstoff Spezien als Reaktionsprodukte nach der Wechselwirkung von Targetspezien mit dem Hintergrundsgas, oder die Bildung von ausgeprägt vielen negativen Ionen, die bei der Filmformation wichtig sein können. Diese Plasmaspezien können mit Hilfe spektroskopischer Methoden untersucht werden. In diesem Project wird die Bedeutung von geladenen Plasmaspezien bzgl. der Filmzusammensetztung systematisch untersucht, in dem selektive geladene Plasmaspezien mit Hilfe eines elektischen Feldes ausgeblendet werden.
Lay summary

Hintergrund

Das Wachstum dünner Filme ist ein wichtiges Feld für Grundlagen- und Angewandte Forschung sowie industrieller Anwendungen. PLD hat sich zu einer industriellen Technik für einige spezielle Anwendungen weiterentwickelt. PLD ist ein Dreischrittprozess: Licht-Materie Wechselwirkung zur Erzeugung des Plasmas, Plasmaausdehnung, und die Abscheidung der Plasmaspezien auf einem Substrat als dünne Beschichtung. Zur Herstellung qualitativ hochwertiger Filme werden verschiedene Parameter, wie z.B. Laser-Energiedichte, Wellenlänge, etc., variiert. Der Optimierungsprozess ist aber oft sehr zeitaufwändig und wird in der Regel wie eine „black-box“ behandelt.

 

Ziel des Projects

Das Ziel des Projektes ist es festzustellen wie wichtig der Beitrag von negativen Ionen zur Herstellung von qualitativ hochwertigen Oxidfilmen mit PLD ist. Zur Selektierung von positiven und neutralen sowie negativen und neutralen Plasmaspezien wird eine elektrostatische Iris eingesetzt mit deren Hilfe es möglich sein sollte den Einfluss dieser Spezienkombinationen zu studieren, und zu sehen ob es von Vorteil wäre solch eine Ladungstrennung generell für PLD zu benutzen.

 

Bedeutung der Forschung

Die gepulste Laserablation ist eine sehr vielseitige Technik die erfolgreich zum Wachstum von oxidischen Filmen und Mehrlagenschichten eingesetzt wird. Für einige Materialien wurde festgestellt, dass für optimiertes Filmwachstum die Menge an negativen Ionen im Plasma, insbesondere O- und MeOx- besonders hoch ist. Allerdings steigt hier auch der Anteil der positiven Plasmaspezien, sodass sich nicht eindeutig entscheiden lässt welche der Spezien die größere Relevanz für die Filmherstellung besitzt. Um diese Fragestellung zu beantworten, wird eine elektrostatische Iris zur Trennung der geladenen Spezien im Plasma eingesetzt. Ein signifikanter Einfluss der Ladungstrennung hätte auch nützliche Auswirkungen für das zukünftige Arbeiten mit PLD als Depositionsmethode.

 

Direct link to Lay Summary Last update: 15.04.2014

Responsible applicant and co-applicants

Employees

Collaboration

Group / person Country
Types of collaboration
Solid State Chemistry and Catalysis/Empa Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
School of Physics/Trinity College Dublin Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Ion Beam Physics/ETH Zurich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Optoelectronic Research Center/University of Southampton Great Britain and Northern Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Trace Analysis and Microanalysis/ETH Zurich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Laser Processing Group/CSIC Madrid Spain (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Electrochemical Materials/ETH Zurich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Conference on Laser Ablation - COLA 2017 Individual talk An insight into the expansion of a laser-induced plasma in vacuum 03.09.2017 Marseille, France Lippert Thomas; Wokaun Alexander; Yao Xiang;
E-MRS 2016 Spring Meeting Poster Characterization of laser induced plasma 02.05.2016 Lille, France Wokaun Alexander; Yao Xiang; Lippert Thomas;


Associated projects

Number Title Start Funding scheme
142176 Small band-gap nanostructured perovskite materials for photovoltaic and photocatalytic hydrogen generation applications 01.01.2013 Romanian-Swiss Research Programme (RSRP)
170743 An ultra-high resolution scanning electron microscope (SEM) for low-energy imaging and analysis 01.02.2017 R'EQUIP
134577 Negative ions: the overlooked species in thin film growth by pulsed laser deposition 01.04.2011 Project funding (Div. I-III)
147190 Influence of Strain and Interfaces on the Properties of Ion Conducting Thin Films for micro-Solid-Oxide-Fuel-Cells 01.05.2013 Project funding (Div. I-III)
172708 Laser interaction with materials for thin film deposition: From fundamentals to functional films 01.08.2017 Project funding (Div. I-III)

Abstract

The growth of thin films is an important field of fundamental and applied research and has many industrial applications. Pulsed laser deposition (PLD) has become an industrial technique for selected applications (e.g. superconducting tapes), mainly due to its ability to grow films of complex materials with superior properties than otherwise achievable with other methods which justifies the larger cost of running such processes. PLD can be considered as a three-stage process, i.e. the laser-material interaction that generates a plume/plasma, the plasma expansion, and the deposi-tion of the plume species on a substrate to form the film. To obtain high quality films various parameters, such as laser fluence, laser wavelength, laser spot size, background gas and pressure, target-substrate distance and substrate temperature etc., are varied. This optimization process is often time consuming and treated like a black-box technique. For a fundamental understanding of the PLD process, in particular why sometimes high-quality films are only obtained in a very narrow parameter window, the application of various in situ analytical measurements is required. Over the last years various studies have been performed to analyze the laser-generated plume by different techniques, such as emission spectroscopy and imaging, ion probe measurements, and plasma mass spectrometry. These techniques yield data about the plume composition and reactions, expansion direction, and kinetic energies of the species. Important parameters that have been identified include the role of kinetic energies, the formation of metal-oxygen species by reactions of metallic plume species with oxygen from the background gas, and also the formation of a pronounced amount of negative ions (up to 40%). Strikingly, the “best” films have been obtained at least for a couple of material under conditions where the larg-est amount of negative ions, mainly in the form of O- and MeOx- species, is detected. This suggests that negative ions may play a very important role for thin film growth by PLD. Unfortunately, it was not possible to draw this conclusion decisively, because under the conditions where the high amounts of negative ions are formed, also an increase number of positively charged metal-oxygen species is generated.To conclusively answer now the question whether negative ions are really important for the film growth by PLD a modification of an existing PLD setup is planned: An iris to which an electric field can be applied is positioned in front of the substrate or a plasma mass spectrometer. This will allow to grow films (or analyze the plume composition) as function of the applied electric field (negative or positive), and therefore with a plume that ideally consists of negative or positive species, plus the neutral species. A fast AC-field may even allow growing films with mainly neutral species. The influence of this charge selection will be study by a detailed analysis of the films which are deposited under these conditions. The analysis will cover the composition, structural parameter, surface quality as well as properties, such as resistivity. Most studies will be per-formed with a material that has been extensively applied before, i.e. LaxCa1-xMnO3, but also less complex materials (Al2O3 and LuMnO3) will be studied. This new PLD setup and the film analysis should then answer the question on the importance of the charge of species, implying that it may be useful to implement a “charge selector” into PLD setups. Additionally complementary studies of the kinetic energies of up to 1 keV (using plasma mass spectrometry and emission spectroscopy) and the role of the geometry/dimensions (by plasma imaging) of the substrate are planned. The studies for the higher kinetic energies will be performed, because it was not possible for us previously to analyze kinetic energies higher than 100eV, and these high energies may play an important role for the quality of films.
-