VersaProbe III (XPS) Surface Analysis Instrument

The VersaProbe III is a highly versatile, multi-technique instrument with PHI’s patented, monochromatic, micro-focused, scanning X-ray source. The instrument offers a true SEM-like ease of operation with superior micro area spectroscopy and excellent large area capabilities. The fully integrated multi-technique platform of the VersaProbe III offers an array of optional excitation sources, sputter ion sources, and sample treatment and transfer capabilities. These features are essential in studying today’s advanced materials and in supporting your material characterization and problem-solving needs.

Features of the VersaProbe III

New SmartSoft Software for VersaProbe III
Micro-focused X-ray source for SEM like navigation and operation
Optimized configuration and multiple options for thin film depth profile analysis
- Flexible monatomic Ar ion beam
- Cluster ion guns available: GCIB with New cluster size measurement tool and C60
Excellent Auger performance providing high energy resolution and good signal to noise
Complete electronic band structure characterization:
- UPS with high sensitivity and energy resolution
- New Low Energy Inverse Photoemission Spectroscopy (LEIPS)
- Reflection Electron Energy Loss Spectroscopy (REELS)
Analyzer input lens with high sensitivity for all analysis conditions
Multichannel detector for fast elemental and chemical imaging
Unique Angle dependent technology for +/- 5 degree solid angle collection for ADXPS measurements
New StrataPHI software for thin-film structure analysis
Fully integrated multi-technique system with optional accessories:
- Hot/cold stage
- 4-contact sample mount for in-situ electrochemical experiments
- Transfer vessel: easy loading of samples under inert atmosphere from glove box or under vacuum

Micro-Focused Scanning X-ray Source and SEM-Like Operation

Ease of navigation and operation in SEM-like mode

SEM-Like XPS Microprobe

Unique Capabilities

PHI’s scanning XPS microprobe instrument platform provides scanning X-ray induced secondary electron images (SXI) generated by scanning a focused sub-10 μm X-ray beam across the sample. Just like an SEM, SXI’s can be used to navigate to areas of interest and to select areas for analysis in real time. SXI images provide 100% confidence in locating small features of interest and in avoiding areas with contamination and inhomogeneities for analysis. SXI images have a contrast mechanism that is dominated by photoelectron yield (composition), and therefore often reveal features that are not optically visible or related to topography.

SEM-Like Operation

SEM-Like Workflow

A typical XPS analysis on the PHI VersaProbe III begins by collecting an SXI image that is quickly generated using a sub-10 μm diameter raster scanned X-ray beam. Areas of interest for small or large spectral analysis or imaging are used to guide the next steps which may include: obtaining high energy resolution spectra for chemical state analysis, chemical state images, or compositional sputter depth profiles.

Single Crater Multi-Point Depth Profiling

A powerful capability enabled by PHI's unique scanning XPS microprobe technology is the ability to define analysis points on an SXI image and then obtain sputter depth profiles from multiple locations in a single sputter crater. For samples where sputtering area should be minimized, this is a powerful tool for analysis of neighboring features or on and off defect sites.

Thin Film Depth Profile Analysis

Optimized Configuration

A focused X-ray beam, high sensitivity spectrometer, high performance floating column argon ion gun, turnkey dual beam charge neutralization, compucentric Zalar™ rotation, and advanced data reduction algorithms provide the highest performance XPS depth profiling capability available. The standard monatomic argon ion gun is capable of generating 5 eV to 5 keV Ar ion beams and is ideally suited for most inorganic depth profiling applications.

Argon Gas Cluster Ion Beam (GCIB) Option for Organic Depth Profiling

It is well known that monatomic Ar ion guns used for inorganic thin film analysis typically cause severe chemical damage when sputtering most polymer and organic materials. PHI has led the way in developing and applying cluster source ion guns for the successful thin film analysis of polymer and organic materials. Our optional 20 kV Argon gas cluster ion beam (GCIB) and optional C60 ion gun have proven performance for depth profiling many polymer and organic films while minimizing the potential for chemical damage.

C60 Cluster Source Ion Gun Option for Mixed Matrix Depth Profiling

With the introduction of cluster source ion guns for organic and polymer thin film depth profiling, interest has grown in applying these ion guns to inorganic structures that sustain chemical damage with monatomic Ar ion beam sputtering. Our experience has shown that some metalloids, oxides, and thin film structures that contain both organic and inorganic materials sustain less chemical damage and differential sputtering artifacts when depth profiled using a 20 kV C₆₀ cluster source ion gun.

Multi-Point Auger Spectroscopy & Elemental Mapping

The convergence of the optical, SXI, and SEM images allows for an intuitive approach to identifying regions of interest for analysis
Fully integrated user interface for in-situ analysis using both techniques at the same region of interest without moving sample
Multipoint surveys and high-resolution spectra
Multipoint sputter depth profiles
Compositional mapping
Image registration for image drift correction during the prolonged analysis
High spatial and energy resolution analysis

Complete Electronic Band Structure Characterization

Measurement at the Same Location for XPS, UPS, LEIPS and REELS

In the VersaProbe III, LEIPS, UPS, Argon and GCIB ion beams, and neutralization beams are all aligned to the XPS measurement position. This allows for comprehensive evaluation of organic semiconductor materials.

Ultraviolet Photoelectron Spectroscopy (UPS) - Valence Band

Design of complex electronic material systems for display panels, flexible circuitry, and photovoltaics require knowledge of the basic properties of each component’s band structure in order to achieve efficient charge transport.

The combination of ultraviolet photoelectron spectroscopy (UPS) and low energy inverse photoemission spectroscopy (LEIPS) provides a complete characterization of the valence and conduction bands, as well as useful parameters such as the band gap, ionization energy, work function, and electron affinity.

Samples provided by: Organic Optoelectronics Practical Development Center（i3-opera)

Combined measurements from UPS and LEIPS

UPS and LEIPS measurement of electronic band for CuPc

LEIPS provides accurate values of electron affinity (EA) which is required for designing organic light-emitting diode, understanding band structure at metal-semiconductor and heterojunctions and in studies of charge-transfer processes.semiconductor

Low energy incident electrons (<5 eV) used in this technique are well-suited for analysis of organic materials with minimal damage.

The ionization energy can be obtained from the highest occupied molecular orbital (HOMO) of the UPS measurement. The electron affinity can be obtained from the lowest unoccupied molecular orbital (LUMO) of the LEIPS measurement. From the difference in those two values, the semiconductor bandgap energy can be calculated.

Unique features of LEIPS

LEIPS is the inverse process of XPS/UPS
A sample is irradiated with low energy (< 5 eV) electrons. Photons are emitted from the sample as electrons fill unoccupied states in the conduction band. Photon flux at fixed energy is measured relative to incident electron energy.
Information obtained from LEIPS:
- Obtain information on the unoccupied electronic energy levels
- Measurement of the electron affinity of the sample

Item	LEIPS	A Conventional Inverse Photoemission Spectroscopy
Analysis positions	Same position as XPS, UPS, Ar/C₆₀/GCIB ion guns, and AES/REELS	For dedicated IPES tool, sample transport required for XPS analysis
Energy or electrons	≤ 5 eV Near ultraviolet Low Damage to organic material	10 eV Vacuum ultraviolet Heavy sample damage
Selection of photon energy	Bandpass filter can be changed outside of bell jar	Bandpass filter is in an ultra-high vacuum chamber, difficult to replace
Energy Resolution	≤ 0.45 eV	0.6 eV

Low Damage Analysis of Organic Matter

A comparison of the degree of electron beam damage on a thin film C₆₀ sample using LEIPS electron energies and conventional IPES energies is shown. When the sample was irradiated with 10 eV electrons, equivalent to conventional IPES, the spectral shape changed, indicating that electronic damage had occurred. On the other hand, in the LEIPS measurement using 5 eV of electron energy, there is no change in the spectrum after extensive measurement time, suggesting that no sample damage has occurred.

LEIPS spectrum of a C₆₀ thin film sample measured at an electron energy of: (left) less than 5 eV with LEIPS, (right) 10 eV, similar to conventional IPES

REELS

REELS is a surface analysis technique in which a specimen is bombarded with an electron beam (≤ 1500 eV) and the energy distribution of the reflected electrons is measured. This energy distribution contains features corresponding to discrete losses of the energy of the reflected electrons due to excited atomic states, valence band transitions and material bandgaps.

REELS capabilities

Electronic state and bonding state of the surface
Bandgap measurement of semiconductors
Compare the relative hydrogen content of materials
Observe evidence of conjugation/aromaticity in materials
Discrimination of sp² / sp³ bond of carbon

REELS for band gap, hydrogen and sp2 character

Hydridization Measurements by REELS for 2D materials

REELS is sensitive to the hybridization of carbon. Energy loss peak due to π-->π* transition in graphene appears 6-8 eV lower than the elastic peak.

Intensity of peak increases for higher sp² character of carbon

Features of REELS

REELS measurement can be made by selecting one of the two electron guns as an option of VersaProbe III. Both electron guns can perform REELS measurement with high energy resolution of 0.5 eV or less according to FAT mode (constant energy resolution).

The first option for REELS is to get the "add-on" for the AES option by using the LAB6 electron gun as the source of energy. If the AES option is not available on your system, then second option for REELS is a newly developed, low-cost electron gun with a tungsten source is available.

Fully Integrated Multi-Technique System with Optional Accessories

Versatile Test Chamber Configuration

Integrated Optional Accessories

VersaProbe III test chamber is designed to accept multiple photon and ion sources that are focused at a common point on the sample and controlled from the SmartSoft-VersaProbe user interface

1) Scanning x-ray source
2) Sample introduction chamber Optional intro/prep chamber
3) Argon sputter ion gun
4) Electron energy analyzer
5) Optical Microscope
6A) Five axis automated sample manipulator Optional hot / cold version shown
6B) LN2 dewar for sample cooling
7) Optional sample preparation chambers
8) Optional C₆₀ sputter ion gun
9) Optional UV light source for UPS
10) Optional dual anode x-ray source
11) Optional electron gun for SAM
12) Optional 20 kV Ar₂₅₀₀⁺ gas cluster ion gun

MultiPak Data Reduction Software

Data Reduction for XPS and AES

PHI MultiPak is the most comprehensive data reduction and interpretation software package available for electron spectroscopy. The tasks of spectral peak identification, extracting chemical state information, quantification, and detection limit enhancement are addressed with an array of powerful and easy-to-use software tools for spectra, line scans, images and sputter depth profiles. MultiPak can be used on the instrument PC to process data in real time or on an off line PC for report generation.

Advanced Data Reduction Tools

Auto peak identification
XPS chemical state database
XPS spectral deconvolution
Quantitative analysis
Non-linear least squares fitting
Linear least squares fitting
Target factor analysis
Retrospective chemical imaging
Batch mode data processing

Multipak Data Reduction Software — Chemical depth profile of a multi-layer Ni-Cr thin film structure showing the presence of Cr metal and Cr oxide layers.

PHI VersaProbe III Scanning XPS Microprobe