XPEEM Spectro-microscope

The NanoESCA XPEEM instrument is a spectroscopic photoemission electron microscope fitted with multiple excitation sources from UV to soft X-rays (AlKα X-ray, 1487eV) providing energy-filtered, surface-sensitive images with various specific contrasts: elemental, chemical, work function and electronic band structure contrasts.

XPEEM/kPEEM XPS/UPS NanoESCA MkI spectro-microscope (Scienta Omicron)

The NanoESCA XPEEM spectromicroscope is intended for surface imaging by photoemission with elemental, chemical and electronic contrasts using specific such as local work function and band structure. The advantage of imaging with a microscope (PEEM) is that the practical lateral resolution is determined by optical aberration rather than probe size as in scanning-based imaging processes, thereby allowing much higher magnifications and resolutions. The key of the NanoESCA instrument is that very high resolutions can be reached (1µm and below) but maintaining the high energy resolutions of XPS (typically 0.5eV) necessary for chemical-state analysis.

Real-space imaging (XPEEM) enables elemental, chemical and work function XPS and UPS analysis at the micron scale.

Reciprocal-space imaging (kPEEM) enables µ-ARPES analysis, i.e. provides the band structure of a crystalline material (e.g, a two-dimensional material such as graphene) over an area larger than 10×10µm2, with a high momentum resolution (typically 0.05Å-1) and at high energy resolution (better than 200meV).


Keywords
Imaging XPS, UPS, XPEEM, kPEEM


Specifications

  • Sample size <1cm2, sample height <3mm, in-situ sample preparation (heating, ion-beam sputtering)
  • Excitations
    • Monochromatic AlKα source (1486.6eV, 30-300µm)
    • VUV He discharge lamp: He I (21.22 eV), He II (40.8 eV)
    • UV sources (Hg: 4.9 eV – D2: 6.2 eV)
  • Microscope field-of-view: 9-300µm (real space); 2-7 Å-1 (reciprocal space)
  • Instrumental/practical lateral resolutions: 50nm-150nm (secondary electrons) – 0.5/1µm (core-level electrons)
  • Elemental sensitivity: 1% at
  • Work function sensitivity: 25 meV
  • Good conducting, low-surface roughness sample preferable

Ascent+ facility
CEA-Leti

Platform Technologies

  • Nano for Quantum Technologies
  • Disruptive Devices
  • Advanced Integration

Key Enabling Technologies

  • Metrology / Characterisation: Physical

Case Study

A typical case study for real-space chemical-state mapping, with complementary work function analysis is provided in figure 1 [1]. Figure 1(a) is a secondary-electron PEEM image of the area of interest, where 1-layer (1L) and 2-layer (2L)-thick graphene were transferred onto a patterned substrate for electrical testing, and then exposed to gaseous iodine for promoting doping by adsorption. The XPEEM analyses provides an understanding of the doping mechanism. The iodine elemental image in figure 1(b) provides the evidence that I is 1at.% and 2 at.% concentrated in the 1L and 2L domains respectively, evidencing not only adsorption but also intercalation due to the overlapped character of the 2L domain (not shown). The XPS core-level spectrum of I in the 2L domain (figure 1(d)) shows the chemistry of iodine in the form of negatively-charged complexes. These species act as p-doping species, which is in agreement with the work function analysis (figure 1(c)). Another example of high-resolution chemical-state mapping can be found in [2].

Figure 2 depicts the principle of band structure measurement at the micron-scale with kPEEM with an example of 2D material heterostructures heterogeneously distributed at the surface. Other exmaples can be found in [3] and [4].

Publications
The use of the NanoESCA XPEEM/kPEEM spectrometer is illustrated on several typical cases in the following papers:
[DOI: 10.1063/1.4889747]
[DOI: 10.1016/j.apsusc.2012.06.078]
[DOI: 10.1103/PhysRevB.94.081401]
[DOI: 10.1021/acsanm.8b02249]

Key Enabling Capability

Metrology / Characterisation

Platform Technology

Advanced Integration, Disruptive Devices, Nano for Quantum Technologies

Facility

CEA-Leti