Characterization


  • A Scanning Probe Microscope (SPM)

Microscope characteristics

AFM techniques

Surface modification techniques

  • Optical Spectroscopy Facilities

UV-Vis spectrophotometer

Fluorescence spectrometer

Micro-Raman spectrometer for Raman and PL analysis

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SCANNING PROBE MICROSCOPE

 


Microscope characteristics

  • VEECO THERMOMICROSCOPE CP-RESEARCH
  • The microscope is equipped with a large area scanner (100 mm)
  • A ScanMaster closed-loop scan-linearization is used to assist scanner non-linearity during large area imaging.
  • The system uses an integrated optical microscope with zoom capability up to 50x to image features with 50mm resolution, helping to locate the AFM tip over the desired sample feature.
  • The microscope is lodged in a glove box (Veeco supplier) to control environmental humidity and gas composition
  • Available SPM techniques:
    • STM modes: STM; I/V Spectroscopy
    • AFM modes: Contact mode; Lateral Force; Force vs Distance Spectroscopy; Non contact / Intermittent contact (tapping); Phase imaging; Electric force Microscopy (EFM); Kelvin Probe Force Microscopy (KPFM);


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AFM techniques

Most of AFM methods have been developed to characterize surface morphology by three-dimensional images. This allows calculating parameters such as particle size, surface to volume ratio, roughness, bearing ratio, fractals and so on.

Different techniques (contact, non contact, tapping) work on different sample-tip force regime in order to optimize such an interaction according to sample properties.

Techniques such as phase detection microscopy (PDM) or lateral force microscopy (LFM) can be used to map surface properties such as elasticity (PDM) or friction (LFM).

Force vs distance spectroscopy is used to measure the vertical force that the tip applies to the surface while working in contact-AFM mode. This technique can be used to analyze features such as lubrication thickness, viscosity of surface contaminants or elastic properties of the surface.

AFM (tapping mode) image of ZnO layer, as grown on a LiTaO3 substrate.


AFM (tapping mode) image of ZnO layer deposited on a LiTaO3 substrate after an annealing treatment carried out at 300°C for 24 hours

The AFM can be used also to map the electrical properties of a given material. In our laboratory, the following electrical characterization are available:

  • ELECTRIC FORCE MICROSCOPY (EFM).  EFM is used to obtain a map of the electric-field gradient between a conductive AFM-tip and the underneath sample area;
  • KELVIN PROBE FORCE MICROSCOPY (KPFM). KPFM is used to obtain the space (x-y) distribution of a sample surface potential. It is a nulling technique, in which a feedback loop is used to null the force arising by the difference in surface potential between the tip and the underneath sample area.

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Surface modification techniques

  • NANOMANIPULATION.  The nanomanipulation tool allows moving objects laying on a flat surface.
  • NANOLITHOGRAPHY. Nanolithography can be performed by AFM in different ways. Two of the most common methods are:
    • Scratch Mode: It uses a hard tip (usually a diamond tip) to scratch a sample and designing lithographic patterns. On soft substrates (or substrates covered by a soft layer to be patterned) the usual Si AFM tips can work as well as the diamond ones.
    • Voltage Pulse Mode: It requires a humid environment and a conductive AFM tip. It is a surface oxidation process induced by a bias applied between the tip and sample surface. The process occurs within the water meniscus naturally forming at the tip-sample interface.

Humidity degree, voltage amplitude and tip speed are the most important parameters controlling the dimensions of the oxide pattern.

Pt and SiOx nanostructures patterned over a Si substrate by electrochemical Dip Pen Nanolithography (E-DPN) and Local Anodic Oxidation (LAO)

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A High resolution Field Emission SEM
The SEM is capable of detection of transmitted electrons, thus providing compositional imaging at the nanoscale associated to semi-quantitative EDX elemental analysis. The SEM was also equipped in 2006 with two-independently operated piezo-actuators for manipulation of nanowires and in-situ probing of the electrical conductance of nanostructures.

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UV-Vis spectrophotometer
T80 PGInstruments

Figure 1. UV-Vis spectrophotometer.

Double beam optics
WL range: 190-900 nm
Slit width : 2 nm (fix)
Multi-cells sample holder: up to 8 samples
Thin film sample holder: 1 sample
2 operating lamps: Deuterium and Tungsten

Anodic Oxidation (LAO)

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Fluorescence spectrometer
LS55 Perkin-Elmer


Figure 1. Fluorescence spectrometer

WL range: 200-900
High energy pulsed Xenon source for excitation
Measurement modes:
Fluorescence, phosphorescence and bio- and chemi-luminescence measurement
Excitation, emission, constant wavelength synchronous, and constant energy synchronous spectral scanning
3D excitation/emission scans, 3D synchronous and kinetic scans
Single and multiple wavelength kinetics
Simultaneous kinetics for multiple samples
Simple quantitation by curve fitting with a number of fit algorithms

Anodic Oxidation (LAO)

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Micro-Raman spectrometer for Raman and PL analysis

Raman micro-spectrometer (modular system) Jobin-Yvon Horiba
Single 320 f /4.1 monochromator+front illuminated CCD

Objectives:

RAMAN: 10x-100x-20xLWD
PL (325nm) 10x-40xUV

Equipped with:

   confocal microscope:
•    Micro-motorized x-y stage
•    Spatial resolution : diffraction limited
•    Raman imaging
•    Excitation:
            - He-Cd laser: UV 325 nm/Blue 442 nm
            - Solid state laser @ 532 nm

  • Linkam cell THMS600 for low and high temeparture measurements; gas measurements; two electrical contacts inside.
Linkam cell THMS 600
Raman system

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X-Ray Diffraction Spectroscopy

Empyrean diffractometer (PANalytical, Almelo, The Netherlands):

  • Cu-LFF tube operated at 40kV-40mA
  • Two indipendent arms, each with own detector
  • PIXcel 1D detector with 255 channel for fast linear acquisition
  • Parallel-plate collimated proportional Xe detector with a nickel large-β filter
  • Sample holder for powder spectroscopy
  • Micro-Mechanized Z-Axis sample holder for planar and 3D objects
  • Bragg-Bentano and Glancing-Angle Mode
  • Full set of Front and Anti-Scattering slits