Conductive atomic force microscopy

Conductive atomic force microscopy

Conductive atomic force microscopy (C-AFM) is a variation of atomic force microscopy (AFM) and scanning tunneling microscopy (STM), which uses electrical current to construct the surface profile of the studied sample. The current is flowing through the metal-coated tip of the microscope and the conducting sample. Usual AFM topography, obtained by vibrating the tip, is acquired simultaneously with the current. This enables to correlate a spatial feature on the sample with its conductivity, and distinguishes C-AFM from STM where only current is recorded. A C-AFM microscope uses conventional silicon tips coated with a metal or metallic alloy, such as Pt-Ir alloy.[1]

The C-AFM can be operated in the imaging mode and spectroscopic mode.

Contents

Imaging mode

In the conventional imaging mode, vibrating tip is scanned over a small sample area (typically square micrometres); a negative voltage bias is applied to the sample, and the electrons tunneling from the sample to the tip are being collected. This polarity is chosen for several reasons:

  • The electron barrier in this case is the conduction band onset at the Si/oxide interface, which is better known than the tip/oxide interface.
  • The emission area for substrate injection is homogeneous and depends mostly on the tip/sample contact area. On the contrary, the emission area in the case of tip injection depends on the shape of the tip.
  • During the measurement, the tip is in contact with the sample, and many studies materials are hydrophilic. Therefore, the tip drags along water and other contaminants adsorbed at the sample surface. The applied voltage induces a high electrical field between the tip and the substrate. This field ionizes water, producing the OH-. If a negative voltage is applied to the tip, the OH- ions are attracted to the surface of the sample; they oxidize it thereby permanently blocking the current flow. If a positive voltage is applied to the tip, the OH- ions are dragged to the tip, oxidizing it and breaking the electrical circuit. However, whereas the studied sample may be unique, the tips are disposable and easy to replace, but after replacement, it is difficult to relocate exactly the same area. The tip degradation, as well as image quality, also depend on the scanning parameters.[1]

Spectroscopic mode

In the spectroscopic mode, the tip is stationary, while the voltage is being swept. This allows recording conventional current–voltage characteristic from tiny areas of the sample, and thereby to extract information on the local electronic properties, such as local density of states.[1]

References

  1. ^ a b c Zhang, L.; T. Sakai, N. Sakuma, T. Ono, K. Nakayama (1999). "Nanostructural conductivity and surface-potential study of low-field-emission carbon films with conductive scanning probe microscopy". Applied Physics Letters 75 (22): 3527–3529. doi:10.1063/1.125377. 

See also


Wikimedia Foundation. 2010.

Поможем решить контрольную работу

Look at other dictionaries:

  • Photoconductive atomic force microscopy — (pc AFM) is a scientific technique.. Multi layer photovoltaic cells have gained popularity since mid 1980s.[1] At the time, research was primarily focused on single layer photovoltaic (PV) devices between two electrodes, in which PV properties… …   Wikipedia

  • Scanning probe microscopy — Part of a series of articles on Nanotechnology …   Wikipedia

  • Magnetic force microscope — MFM images of 3.2 GB and 30 GB computer hard drive surfaces. Magnetic force microscope (MFM) is a variety of atomic force microscope, where a sharp magnetized tip scans a magnetic sample; the tip sample magnetic interactions are detected and used …   Wikipedia

  • Scanning voltage microscopy — (SVM) sometimes also called nanopotentiometry is a scientific experimental technique based on atomic force microscopy. A conductive probe, usually only a few nanometers wide at the tip, is placed in full contact with an operational electronic or… …   Wikipedia

  • Kelvin probe force microscope — Kelvin probe force microscopy ( KPFM ), also known as surface potential microscopy, is a noncontact variant of atomic force microscopy (AFM) that was [http://dns.ntu ccms.ntu.edu.tw/references/APPL PHYS LETT 58 2921 1991.pdf invented] in 1991.… …   Wikipedia

  • Electrostatic force microscope — Electrostatic force microscopy (EFM) is a type of dynamic non contact atomic force microscopy where the electrostatic force is probed. ( Dynamic here means that the cantilever is oscillating and does not make contact with the sample). This force… …   Wikipedia

  • Scanning gate microscopy — (SGM) is a scanning probe microscopy technique with an electrically conductive tip used as a movable gate that couples capacitively to the sample and probes electrical transport on the nanometer scale. Typical samples are mesoscopic devices,… …   Wikipedia

  • Physical Sciences — ▪ 2009 Introduction Scientists discovered a new family of superconducting materials and obtained unique images of individual hydrogen atoms and of a multiple exoplanet system. Europe completed the Large Hadron Collider, and China and India took… …   Universalium

  • Carbon nanotube — Not to be confused with Carbon fiber. Part of a series of articles on Nanomaterials Fullerenes …   Wikipedia

  • Optical tweezers — (originally called single beam gradient force trap ) are scientific instruments that use a highly focused laser beam to provide an attractive or repulsive force (typically on the order of piconewtons), depending on the refractive index mismatch… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”