Versions Compared

Old Version 3

changes.mady.by.user Microscopy Cluster

Saved on

compared with

New Version Current

changes.mady.by.user Microscopy Cluster

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

← Back to IRM homepage

Expand
titleTransmission

Transmission IRM is recommended where possible and can be is predominantly used for solid , samples. If you’re interested in liquid or gaseous samples, please contact the IRM team. Transmission requires that samples be very thin (between 5-10 µm), flat and highly polished where applicable. Solid samples should be microtomed to the correct thickness ranged for analysis, either freestanding or deposited onto an IR transmitting window such as CaF2, BaF2, ZnSe (preferably 0.5 mm in thickness) depending on the window properties and your required wavenumber coverage. Less frequently, Si or silicon nitride (Si3N4) may be used as substrates for transmission IR.

A micro-compression cell with diamond or CaF2 windows, to sandwich your sample in place under the beam, is also available for use. 

Examples of samples for transmission:

  • Biological tissues – microtomed and mounted onto an IR transmitting window

  • Cultured cells – grown on a substrate such as CaF2 or Si3N4 windows, and freeze-dried or fixed and air dried

  • Polymer multilayers – microtomed and placed in a compression cell between two windows of diamond or CaF2

Info

Combined IR transmission studies & X-ray Fluorescence Microscopy

Samples can be analysed by both transmission IRM and X-ray fluorescence microscopy at the X-ray Fluorescence Microprobe (XFM) beamline when they are deposited on silicon nitride (Si3N4) windows.

NOTE: Window thickness is restricted to a maximum of 500 nm and the material shows a lower wavenumber cut-off in the mid-IR at 1100 cm-1.  Please contact a Beamline Scientist for more information.

Expand
titleAttenuated Total Reflection (ATR)

ATR relies on a form of internal reflection to enable the analysis of more difficult samples with IR spectroscopy, e.g. samples that cannot be microtomed for transmission measurements or that do not adequately reflect IR for reflection. Compared to transmission and reflectance FTIR, ATR offers the advantage of enhanced spatial resolution (where a crystal with a high refractive index is used such as Ge).  Furthermore, the total internal reflectance phenomenon that ATR relies on (occurs when IR radiation travels through a high refractive index crystal a onto a low refractive index sample surface), results in an evanescent wave that penetrates the surface of the sample, rather than the bulk

The IRM beamline has a Bruker single-bounce micro-ATR accessory with a Germanium crystal tip (diameter=100 microns, refractive index=4). Traditional microscopic ATR methods often cause sample damage, contamination and re-positioning issues, where the ATR crystal is attached to the objective. However, with the macro-ATR methods developed in-house and described below, these issues are avoided by single contact ATR mapping.

Two models of the macro-ATR are available for use:

“hybrid” macro-ATR

  • The hybrid macro-ATR accessory presents a Germanium crystal tip (refractive index = 4) mounted on a macro-ATR cantilever arm (see figure below).

  • 3 sizes of ATR tip are available. The largest tip, which is 1 mm, works well with softer materials that do not require a high pressure to achieve a good contact. The small tips, which are 250 µm and 100 µm in diameter, can provide higher pressure and allow measurements inside smaller regions with limited access suitable for hard/rough surfaces.

  • The macro-ATR device allows users to manually adjust the pressure between the sample and Ge crystal and only requires a single contact throughout the measurement thereby preventing damage to the sample and increasing the scanning speed compared to micro-ATR technique.

Examples of samples for hybrid macro-ATR:

  • single fibre analysis (carbon fibres, wool)

  • dairy products (cheeses)

  • biological samples such as cells, tissue sections and skin biopsies

  • insect wings

  • polymeric materials

  • eucalyptus leaves

If you are interested in using the macro-ATR acquisition mode, please read the instructions on sample preparation HERE

Tip

“soft-contact” piezo controlled macro-ATR

  • For this model, we use ZnSe or Ge hemispheres which have a 1 mm diameter flat sensing surface at the bottom. The hemispherical crystal is then held inside a magnetic mount, which provide precise positioning of the crystal when changing the sample (see figure below)

  • The attractive feature of this device is the unique combination of piezo-controlled linear translation stages used for both xy and z directions

  • The step interval of the piezo drive can be set as small as 50 nm, allowing the sample to gently approach the flat sensing bottom of the ATR crystal

  • the soft contact-piezo controlled system is ideal for very soft, delicate or more fragile samples

Examples of samples for soft-contact piezo-controlled macro-ATR:

  • insect wings and gecko skin (superhydrophobic wax coatings)

  • biopolymer gels

Sample preparation and mounting for this technique is largely sample specific, so please discuss your project with a member of the Beamline Team if you are considering “soft-contact” ATR

 

...

Expand
titleGrazing Incidence

The IRM beamline has a Bruker Vis/IR Grazing Angle Objective (GAO, 15×) for grazing incidence analyses. This objective is specifically designed to analyse thin layers or films <1 µm thick that are deposited onto non-IR absorbing, reflecting surfaces e.g. highly polished metal slides (Au or Al) or indium tin oxide (ITO) coated glass, for example. GAOs increase the optical path length of a sample by essentially skimming the beam across the surface using high angles of incidence. This objective uses an incident angle of ~84° and shows excellent sensitivity down to monolayer thicknesses, particularly when used with polarised light, and good spatial resolution. The Bruker design relies on transflectance from the sample surface, effectively increasing the sample path length to again assist sensitivity, and uses a polariser in the IR beam; p-polarised light is polarised perpendicular to the surface of the sample and shows enhanced IR absorption when large angles of incidence are used.

Image RemovedImage Added

Examples of samples grazing angle experiments:

  • Thin (sub micron) coating on metallic or other highly IR-reflective surfaces

  • Corrosion products on metallic surfaces

Expand
titleFTIR Rapid Scan; Time-Resolved Spectroscopy

Time resolved spectroscopy (TRS) using a FTIR spectrometer offers the advantage of being able to monitor rapidly changing chemical or physical properties of a system in high temporal resolution (up to 65 spectra/sec using a 160 kHz scan velocity @ 16 cm-1). It allows for the simultaneous observation of the progression and/or decay of various chemical species during an event.

The rapid scan experiments can be initiated by an external trigger, such as a change in voltage, which can be programmed into the rapid-scan method editor in OPUS, making it ideal for the observation of kinetic chemical changed induced by an electrochemical potential event, to provide an example, More information on rapid scan FTIR spectroscopy can be found on the Bruker website.

← Back to IRM homepage