||Atomic force microscopy (AFM)
Considered as one of the few ways to “feel” a nano patterned surface, AFM techniques rely on surface forces and electronic feedback loops to convert mechanical interference of the scanning probe into an electrical signal. Interferences are usually atomic forces such as van der Waals. Magnetic and electrostatic effects may also be registered, as well as surface reactions to applied voltages (e.g. Kelvin probe) and forces (e.g. nano-indentation). Both organic and inorganic substances have found their way under the AFM scans.
A new friction mechanism has been discovered in part due to AFM. The expected sticking and sliding of a polymer chain was accompanied by a desorption stick: that is independent of normal force, velocity, and adsorbed polymer length.
A variation of AFM is also being developed as hydrothermal AFM. In this case, the scanning probe is submerged. The novelty of this method is being able to study surface interactions at 250 deg C and at a pressure of 80 atm, including hydrofracturing and storage of radioactive wastes.
The micro-AFM tip has also been developed as a possible liquid despencer by 2013. The liquid drops may be delivered in the microscale to specific areas of interest during the scanning procedure.
||Cold ion laser spectroscopy
Molecules are cooled close to absolute zero and ionized. Angle variant IR and UV laser excitation produces specific of molecular fragments which may ultimately reveal information about the different energy levels. Two isomers may be differentiated due to unique vibrational frequencies and light absorption characteristics.
An effective way to simulate a nano device’s electrical properties is to derive the electrical properties from the first-principles method, which accurately calculates the behavior of each atom. A massively parallel supercomputer is required for this task and is still limited to models on the scale of 3,000 atoms.
Density Functional Theory (DFT) is a modeling tool as useful as a hammer and screwdriver around the house. It assists chemists and physicists at understanding the properties of matter on the nanoscale. It must still be used with caution. For one, it is based on the Schrödinger formalism (complex valued wave-functions which have no counterpart in the real world). Secondly, finite element and/or difference solutions make is difficult to scale these deterministic algorithms.
Monte Carlo is often a competitive simulation tool to DFT. Monte Carlo is a mathematical method relying on independent number generation to solve complex integro-differential equations.
A gas electron diffractometer can be used to measure the undisturbed molecular bond lengths and angles. It is more accurate than solid state experimentation because of reduced crystal packing interactions. About halfway to costing half a billion USD, equipment owners include Europe, Japan, New Zealand, the USA and two for Russia.
If an electron is excited, it may hop into a different energy state. On the return path, an electron may emit different kinds of energies. The collection of such energies is the basis of many spectroscopy techniques, including one of the most popular being fluorescence. Ultra-fast techniques can resolve changes in fluorescence on 60 – 450 fs time scales.
Often compared with EM simulations for the presence of localized plasmonic resonance. Near-field allows measurement of individual parts of a system. Such is also possible when coupled with atomic force microscopy.
A suspended nanochannel resonator (SNR) measures the mass of particles as they flow through a 400 nm channel. It is possible to weigh small viruses, extracellular vesicles, and most of the engineered nanoparticles that are being used for nanomedicine. Nearly 30,000 particles in about 90min could be measured.
Half a billion electrons to can now be accelerated to 2 giga-electronvolts over a distance of about 1 inch, a size reduction of approximately 10,000. This energy may be converted to hard x-rays on a femtosecond time resolution. What made this possible is the laser-plasma acceleration which involves firing a brief but intensely powerful (petawatt) laser pulse into a puff of gas.
Pulsed laser light offers a wide array of imaging and synthesis options. Ultra-short pulses provide the ability to measure responses at small time scales. Compressing femtosecond and attosecond is possible through optical design. More recently another complimentary method was developed by modifying the fiber amplification class of lasers with nanostructured basket-weave cores that are filled with noble gas. The nonlinear interaction between the gas and the pulses generate a variety of pulse rates that act to compress into shorter pulses.
Modes of vibration are experienced not only by macroscopic objects like cars, but also by nanoscopic species like molecules. The vibrations occur due to excitation (usually by visible light) that will shift the energy of the excitation source by amounts proportional to the molecular bond energies.
Hyperspectral imaging adds more information to Raman scanning as it allows spatial data to be collected simultaneously. An added benefit is that larger areas may be sampled: square cm and larger vs. square micrometre with traditional equipment. The resultant images are then typically scaled as an intensity graph based on a selected wavenumber.
||Scanning electron microscopy (SEM)
SEM is essentially the bread and butter of many nano investigations. It is a microscope that is not limited by diffraction as optical microscopes are and hence may comfortably reach 50,000x magnification as opposed to a common 100x by a basic light microscope. With electron microscopy, individual planes of atoms may actually be resolved. Much like Galileo saw the defects on the moon with his telescope, we can now see defects on coherent twin boundaries, often described as “perfect,” appearing like a perfectly flat, one-atom-thick plane in computer models and electron microscope images. It is also becoming more common to scan in 3D and provide corresponding computer models with a resolution as small as 25 nm.
A variation of SEM is Scanning Transmission Electron Holography Microscope (STEHM). Au atoms were scanned with a resolution of 35 picometres deeming it the world’s most powerful microscope (2013, 7 tonne, 4.3m tall, $9.2 M CAD, Hitachi).
For monitoring catalytic reactions, in-situ aberration corrected environmental scanning transmission electron microscopy technology (in-situ AC-ESTEM) is developed. Reactions up to 500 degC could be facilitated under transient conditions.