Scanning probe microscopy: AFM (Atomic Force Microscopy)

Ntegra Aura platform (NT-MDT) allows the characterization of surfaces using the technique of scanning probe microscopy (Scanning Probe Microscopy, SPM).
Such microscopy allows visualization of nanoscale surfaces using a physical probe that scans the specimen.
The scanning probe microscopy is subdivided in numerous techniques, among which are:
Atomic Force Microscopy (AFM)
Tunneling Microscopy (STM)
Near Field Optical Microscopy (SNOM)
Applications:
1. Topography
Imaging in three dimensions with nanometer resolution: profilometry, roughness data in 2D and 3D, statistical studies of the grain surface, ...
2. Phase
Detects variations in composition, adhesion, friction and viscoelasticity, among other characteristics of the sample surface.
3. Electrical properties
Qualitative Measures (SRI, Spreading Resistance Imaging) detects differences in resistivity and electrical conductivity on the surface of the sample qualitatively in the nanometric range
Quantitative Measures (KPM, Kelvin Probe Microscopy) Study of the distribution of the electric potential on the surface of the sample.
4. Nanolithography
Can produce changes in the properties of the sample surface. Such modifications may be of various kinds: in the topography of the sample, in the physical properties without altering the topography.
5. Tunneling microscopy (STM, Scanning Tunneling Microscopy).
The scanning tunneling microscopy allows the study of different surface properties (topography, work function, local density of states) of conductive materials at the atomic scale. Detected tunnel current is sufficiently small (0.5pA-50nA) to investigate samples of low conductance.
6. Near-field optical microscopy (SNOM Scanning Near field Optical Microscopy).
This technique allows the study of the topography and optical properties of nanoscale opaque samples.
The system has 4 lasers with different wavelengths (473nm, 532nm, 635nm and 785nm).
The equipment is located in the Department of Condensed Matter Physics at the Faculty of Sciences (Campus San Francisco ) .

Service Guidelines
Before applied for any AFM-STM service offered in ICP, it is stronglyrecommended to read carefully the Service Guideline (Guía de servicio_AFM-STM.pdf, only available in Spanish). Its reading is mandatory if the service is demanded for the first time or if the user is not familiarized with the technique and/or the instrument.
Likewise, before processing any application, we recommend to contact the staff members in charge, either the scientific advisor or the technician (Marisela Vélez: marisela.velez@icp.csic.es, Tel. 915854802; and Manuel Sánchez: manuel.sanchez@icp.csic.es, Tel. 915854795, respectively).
Users (either internal or external) are not allowed to handle the AFM-STM equipment. The technician or otherwise the scientific advisor are required to be y present during all the measurement process.
Applications
Once the applicant has read the Service Guidelines carefully and contacted the staff in charge of this service, it is necessary to download the application form (Solicitud_AFM-STM.doc, only available in Spanish). It must be filled in and sent to the email address (manuel.sanchez@icp.csic.es). Later, the technician will contact the applicant / user in order to set a date and time for the experiments.
Kind of measurements
The offered experimental measurements can be classified as follows:
1. Conventional: AFM and/or STM measurements of liquid or solid samples, with no control of temperature or atmosphere.
2. Advanced. They include all kind of measurements requiring the use of controlled atmosphere, temperature and/or electrochemical cells.
Image treatment is also offered as additional service, as well as support for interpretation of results.
A conventional laboratory of sample preparation is also available. It is equipped with an ultrasonic equipment, micropipettes, frequently used solvents (ethanol, acetone, etc.) and different supports: f hydrophobic (graphite), hydrophilic (mica) and conducting (graphite and gold).

In this service it is possible to measure the topography by scanning the sample surface with the tip in contact. Additionally, in the contact mode it is possible to obtain phase images; their contrast is caused by differences in properties such as adhesion and viscoelasticity of the sample surface.
The measurements can be carried out in air or in liquid.Maximum scan size is 100 microns.
In any case it is necessary to contact the service staff in order to determine the optimal preparation methodology for the correspondin sample in order to perform the AFM measurement.

Atomic force microscopy of construction materials

The atomic force microscopy provides three-dimensional images with atomic or molecular resolution, of the surface of conductive or non-conductive samples without special preparation. It is also possible to perform measurements of modulations of forces as well as images of "volume of forces" to have information about differences in the elastic properties. Testing may be done under ambient conditions or in a liquid medium.

Scanning Probe Microscopy, mode "Atomic Force Microscopy" under controlled conditions

Topography images in dynamic and contact mode can be provided.
In dynamic mode, amplitude modulation is used. Besides topography image, images of phase contrast can be also provided.
With the contact mode, friction maps can be also obtained using the Lateral Force Microscopy mode.
Tests in low relative humidity, less than 3%, and in nitrogen gas environment can be performed.
Special modules are available, being one of them an especial cell to analyze samples in liquids. The equipment is compatible with various solvents, including acetone.
The largest image size is 80 microns x 80 microns, with a maximum resolution of 8192 x 8192 points.
Besides acquiring images, the service can perform spectroscopy experiments, where force-distance curves are plotted, obtaining the adhesion of the material as well as a relative measure of the hardness of the various materials present in the sample.
In the AFM Lab, the following equipment is available:
Agilent 5500LS, scanner 80 x 80 um2 in X / Y and 15 microns in the Z axis, is equipped with the Mac MODE III access module and the Signal Access Box, which allows to perform the Bimodal AFM mode. It also has Closed Loop capabilities that significantly improve the positioning in X and Y. Moreover, the system has a motorized stage with accuracy of ~3 microns and a range of ~15 cm in X / Y and 3 cm in Z, where samples can be as large as 25 x 25 cm2 and 3 cm thick. The device has the Q-Control option for the enhancement of images obtained in liquid. It has also a device for measuring humidity and temperature, and a sample heater module. Equipment¿s electrical noise is about 0.05 nm.
Agilent 5100 with scanner of 70 x 70 um2 in X / Y and 6 microns in the Z axis is equipped with a special cell fluid and controlled environment chamber for conducting analyses in nitrogen or argon environments. The maximum sample size is 3x3 cm2 in X / Y and 1 cm thick. This machine can use a generator module for applying external magnetic fields up to 800 Oe to the sample during the measurement. The main use of the equipment is getting high resolution topography images with an average electrical noise of 0.02 nm.