Microprobe

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A microprobe is an instrument that applies a stable and well-focused beam of charged particles (electrons or ions) to a sample.

Contents

Types

When the primary beam consists of accelerated electrons, the probe is termed an electron microprobe, when the primary beam consists of accelerated ions, the term ion microprobe is used. The term microprobe may also be applied to optical analytical techniques, when the instrument is set up to analyse micro samples or micro areas of larger specimens. Such techniques include micro Raman spectroscopy, micro infrared spectroscopy and micro LIBS. All of these techniques involve modified optical microscopes to locate the area to be analysed, direct the probe beam and collect the analytical signal.

A laser microprobe is a mass spectrometer that uses ionization by a pulsed laser and subsequent mass analysis of the generated ions. [1] [2] [3]

Uses

Scientists use this beam of charged particles to determine the elemental composition of solid materials (minerals, glasses, metals). [4] The chemical composition of the target can be found from the elemental data extracted through emitted X-rays (in the case where the primary beam consists of charged electrons) or measurement of an emitted secondary beam of material sputtered from the target (in the case where the primary beam consists of charged ions).

When the ion energy is in the range of a few tens of keV (kilo-electronvolt) these microprobes are usually called FIB (Focused ion beam). An FIB makes a small portion of the material into a plasma; the analysis is done by the same basic techniques as the ones used in mass spectrometry.

When the ion energy is higher, hundreds of keV to a few MeV (mega-electronvolt) they are called nuclear microprobes. Nuclear microprobes are extremely powerful tools that utilize ion beam analysis techniques as microscopies with spot sizes in the micro-/nanometre range. These instruments are applied to solve scientific problems in a diverse range of fields, from microelectronics to biomedicine. In addition to the development of new ways to exploit these probes as analytical tools (this application area of the nuclear microprobes is called nuclear microscopy), strong progress has been made in the area of materials modification recently (most of which can be described as PBW, proton beam writing).

The nuclear microprobe's [5] beam is usually composed of protons and alpha particles. Some of the most advanced nuclear microprobes have beam energies in excess of 2 MeV. This gives the device very high sensitivity to minute concentrations of elements, around 1  ppm at beam sizes smaller than 1  micrometer. This elemental sensitivity exists because when the beam interacts with the a sample it gives off characteristic X-rays of each element present in the sample. This type of detection of radiation is called PIXE. Other analysis techniques are applied to nuclear microscopy including Rutherford backscattering(RBS), STIM, etc.

Another use for microprobes is the production of micro and nano sized devices, as in microelectromechanical systems and nanoelectromechanical systems. [6] The advantage that microprobes have over other lithography processes is that a microprobe beam can be scanned or directed over any area of the sample. This scanning of the microprobe beam can be imagined to be like using a very fine tipped pencil to draw your design on a paper or in a drawing program. Traditional lithography processes use photons which cannot be scanned and therefore masks are needed to selectively expose your sample to radiation. It is the radiation that causes changes in the sample, which in turn allows scientists and engineers to develop tiny devices such as microprocessors, accelerometers (like in most car safety systems), etc.

Related Research Articles

Analytical chemistry Study of the separation, identification, and quantification of the chemical components of materials

Analytical chemistry studies and uses instruments and methods used to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separation isolates analytes. Qualitative analysis identifies analytes, while quantitative analysis determines the numerical amount or concentration.

Spectroscopy Study involving matter and electromagnetic radiation

Spectroscopy is the study of the interaction between matter and electromagnetic radiation as a function of the wavelength or frequency of the radiation. Historically, spectroscopy originated as the study of the wavelength dependence of the absorption by gas phase matter of visible light dispersed by a prism. We can also consider matter waves and acoustic waves as forms of radiative energy, and recently gravitational waves have been associated with a spectral signature in the context of the Laser Interferometer Gravitational-Wave Observatory (LIGO).

Inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) is a type of mass spectrometry that uses an Inductively coupled plasma to ionize the sample. It atomizes the sample and creates atomic and small polyatomic ions, which are then detected. It is known and used for its ability to detect metals and several non-metals in liquid samples at very low concentrations. It can detect different isotopes of the same element, which makes it a versatile tool in Isotopic labeling.

Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of ions. The results are typically presented as a mass spectrum, a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures.

Particle-induced X-ray emission or proton-induced X-ray emission (PIXE) is a technique used in the determining of the elemental make-up of a material or sample. When a material is exposed to an ion beam, atomic interactions occur that give off EM radiation of wavelengths in the x-ray part of the electromagnetic spectrum specific to an element. PIXE is a powerful yet non-destructive elemental analysis technique now used routinely by geologists, archaeologists, art conservators and others to help answer questions of provenance, dating and authenticity.

Ion source Device that creates charged atoms and molecules (ions)

An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.

Secondary ion mass spectrometry surface chemical analysis and imaging method

Secondary-ion mass spectrometry (SIMS) is a technique used to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions. The mass/charge ratios of these secondary ions are measured with a mass spectrometer to determine the elemental, isotopic, or molecular composition of the surface to a depth of 1 to 2 nm. Due to the large variation in ionization probabilities among different materials, SIMS is generally considered to be a qualitative technique, although quantitation is possible with the use of standards. SIMS is the most sensitive surface analysis technique, with elemental detection limits ranging from parts per million to parts per billion.

Gold fingerprinting is a method of identifying an item made of gold based on the impurities or trace elements it contains.

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Electron microprobe

An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. It works similarly to a scanning electron microscope: the sample is bombarded with an electron beam, emitting x-rays at wavelengths characteristic to the elements being analyzed. This enables the abundances of elements present within small sample volumes to be determined, when a conventional accelerating voltage of 15-20 kV is used. The concentrations of elements from lithium to plutonium may be measured at levels as low as 100 parts per million (ppm), material dependent, although with care, levels below 10 ppm are possible The ability to quantify lithium by EPMA became a reality in 2008..

Focused ion beam device

Focused ion beam, also known as FIB, is a technique used particularly in the semiconductor industry, materials science and increasingly in the biological field for site-specific analysis, deposition, and ablation of materials. A FIB setup is a scientific instrument that resembles a scanning electron microscope (SEM). However, while the SEM uses a focused beam of electrons to image the sample in the chamber, a FIB setup uses a focused beam of ions instead. FIB can also be incorporated in a system with both electron and ion beam columns, allowing the same feature to be investigated using either of the beams. FIB should not be confused with using a beam of focused ions for direct write lithography. These are generally quite different systems where the material is modified by other mechanisms.

Characterization (materials science) process by which a materials structure and properties are probed and measured

Characterization, when used in materials science, refers to the broad and general process by which a material's structure and properties are probed and measured. It is a fundamental process in the field of materials science, without which no scientific understanding of engineering materials could be ascertained. The scope of the term often differs; some definitions limit the term's use to techniques which study the microscopic structure and properties of materials, while others use the term to refer to any materials analysis process including macroscopic techniques such as mechanical testing, thermal analysis and density calculation. The scale of the structures observed in materials characterization ranges from angstroms, such as in the imaging of individual atoms and chemical bonds, up to centimeters, such as in the imaging of coarse grain structures in metals.

Rutherford backscattering spectrometry (RBS) is an analytical technique used in materials science. Sometimes referred to as high-energy ion scattering (HEIS) spectrometry, RBS is used to determine the structure and composition of materials by measuring the backscattering of a beam of high energy ions impinging on a sample.

Instrumental chemistry

Instrumental analysis is a field of analytical chemistry that investigates analytes using scientific instruments.

Nuclear forensics is the investigation of nuclear materials to find evidence for the source, the trafficking, and the enrichment of the material. The material can be recovered from various sources including dust from the vicinity of a nuclear facility, or from the radioactive debris following a nuclear explosion.

A laser microprobe mass spectrometer (LMMS), also laser microprobe mass analyzer (LAMMA), laser ionization mass spectrometer (LIMS), or laser ionization mass analyzer (LIMA) is a mass spectrometer that uses a focused laser for microanalysis. It employs local ionization by a pulsed laser and subsequent mass analysis of the generated ions.

Nanoscale secondary ion mass spectrometry

Nanoscale secondary ion mass spectrometry (nanoSIMS) is an analytic technique used to gather nanoscale resolution measurements of the elemental and isotopic composition of a material using a sector mass spectrometer. This instrument is based on secondary ion mass spectrometry. NanoSIMS is able to create nanoscale maps of elemental composition, parallel acquisition of seven masses, isotopic identification, combining the high mass resolution, subparts-per-million sensitivity of conventional SIMS with spatial resolution down to 50 nm and fast acquisition.

Resonance ionization

Resonance ionization is a process in optical physics used to excite a specific atom beyond its ionization potential to form an ion using a beam of photons irradiated from a pulsed laser light. In resonance ionization, the absorption or emission properties of the emitted photons are not considered, rather only the resulting excited ions are mass-selected, detected and measured. Depending on the laser light source used, one electron can be removed from each atom so that resonance ionization produces an efficient selectivity in two ways: elemental selectivity in ionization and isotopic selectivity in measurement.

References

  1. ↑ Hillenkamp, F.; Unsöld, E.; Kaufmann, R.; Nitsche, R. (1975). "A high-sensitivity laser microprobe mass analyzer". Applied Physics. 8 (4): 341–348. Bibcode:1975ApPhy...8..341H. doi:10.1007/BF00898368. ISSN   0340-3793. S2CID   135753888.
  2. ↑ Denoyer, Eric.; Van Grieken, Rene.; Adams, Fred.; Natusch, David F. S. (1982). "Laser microprobe mass spectrometry. 1. Basic principles and performance characteristics". Analytical Chemistry. 54 (1): 26–41. doi:10.1021/ac00238a001. ISSN   0003-2700.
  3. ↑ Van Vaeck, L (1997). "Laser Microprobe Mass Spectrometry: Principle and Applications in Biology and Medicine". Cell Biology International. 21 (10): 635–648. doi:10.1006/cbir.1997.0198. ISSN   1065-6995. PMID   9693833. S2CID   7601994.
  4. ↑ S. J. B. Reed (25 August 2005). Electron Microprobe Analysis and Scanning Electron Microscopy in Geology. Cambridge University Press. ISBN   978-1-139-44638-9.
  5. ↑ Yvan Llabador; Philippe Moretto (1998). Applications of Nuclear Microprobe in the Life Sciences: An Efficient Analytical Technique for the Research in Biology and Medicine. World Scientific. ISBN   978-981-02-2362-5.
  6. ↑ Juan Jimenez (15 November 2002). Microprobe Characterization of Optoelectronic Materials. CRC Press. ISBN   978-1-56032-941-1.
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