Ions & electrons detection technology

Photonis and El-Mul Time-of-Flight Detector Technology

Time-of-Flight (TOF) Mass Spectrometers (TOF-MS) operate on the principle of measuring the time it takes for ions to travel a fixed distance in an electric field. In a typical setup, ions are accelerated by an electric field towards a detector. The velocity of each ion is directly proportional to its mass-to-charge ratio. Lighter ions reach the detector faster than heavier ones. As the ions land on the detector, their arrival times are recorded, and the resulting data is used to construct mass spectra. TOF-MS offers high sensitivity and a wide mass range, making it valuable in various applications, including analyzing complex mixtures and identifying unknown compounds in fields such as chemistry, biology, and environmental science.

Photonis and El-Mul offer a portfolio of TOF detection platforms, each with distinct functionalities. One common approach, the Photonis BPTOF, couples a Microchannel Plate (MCP) to a scintillator and then to a Photomultiplier Tube (PMT). When ions strike the surface of the MCP, the electrical signal is amplified as freed electrons collide with the channel walls of the MCP. These electrons are focused onto a scintillator, which produces photons. These photons from the scintillator are focused onto a photocathode in a PMT. The photocathode converts photons back to electrons and the electrons are subsequently multiplied by secondary emission in the dynode stage of the PMT. This electrical signal emanating from the PMT is sent to the data acquisition system.

Photonis and El-Mul Quadrupole Detector Technology

A Quadrupole Mass Spectrometer is a crucial component in Mass Spectrometry, designed to separate and analyze ions based on their mass to charge ratio. Comprising of four parallel rods, the analyzer applies a combination of radio frequency and direct current (DC) voltages to create a stable quadrupole field. Ions with specific mass-to-charge ratios traverse this field, experiencing stable trajectories while others are selectively filtered out. By adjusting the voltages, only ions within a defined mass range reach the detector, allowing for precise identification and quantification of compounds in a sample. This dynamic sensitivity and high-resolution capability make quadrupole mass analyzers indispensable tools in various scientific fields, including chemistry, biology, and environmental science.

Quadrupole Mass Spectrometers commonly use continuous dynode electron multipliers to detect ions that have been separated by the mass analyzer. Molecules are ionized, focused, filtered through a mass analyzer, then focused into the detector. An ion striking the input face of the CEM typically produces 2-3 secondary electrons. These electrons are accelerated down the channel by a positive bias. The electrons strike the channel walls, producing additional electrons (and so on) until, at the output end pulse of 107 to 108 electrons emerges. This pulse of electrons is processed by the data acquisition system. 

An alternative detection platform, El-Mul’s Vega technology, had the ions from the mass analyzer striking a conversion dynode. Secondary electrons generated at the dynode are pulled onto a scintillator, converting them to photons. Photons collected via a light guide are then detected by a PMT which amplifies the signal. The Vega detection platform provides the advantage of gain stability, reducing need to recalibrate or exchange detectors and increasing instrument uptime.

At its core, Ion & Electron detection technology focuses on the precise and sensitive detection of charged particles such as ions and electrons, as well as photons, which are fundamental building blocks in the study of matter and energy. These charged particles carry valuable information about the properties and interactions of substances, making their accurate detection essential in numerous scientific research.

MCP Based Detectors (Advanced Performance Detectors)

Each Photonis MCP-based detector is designed with LongLife™ Microchannel Plates, which provide the highest level of sensitivity available to the market. These complete detector assemblies can be used in a wide variety of applications to detect charged particles and electromagnetic radiation, ranging from Mass Spectrometry to UV and X-Ray Astronomy. The detectors are designed for use in vacuum systems and continue to operate efficiently in elevated temperature conditions (300°C – the temperature reached during chamber cleaning) therefore saving time that would otherwise be required to remove the detector from the instrument.

Channeltron™ Channel Electron Multipliers

Channeltron™ Channel Electron Multipliers (CEMs) use the same operating principle as Microchannel Plates but are designed to operate using a single channel for electron multiplication rather than an array. Photonis has a wide variety of Channeltrons™ constructed from a specially formulated glass developed and produced in-house. Due to their low mass and high gain, Channeltrons® are also used in many nuclear physics labs and space applications to count electrons and charged particles in pulse mode operation. Other applications include residual gas analysis, plasma analysis, Auger, electron spectrometers, SEM, FIB and leak detectors.

Detectors for electron microscopy and e-beam systems

Exosens offers a variety of detection platforms for electrons and ions, applicable for scanning electron microscopes, transmission electron microscopes, focused ion beam tools and e-beam systems for the semiconductor industry.

Scintillator-based electron detectors attract electrons to a scintillator plate, which creates an amplified photon signal. The photos are then directed to photon sensor which converts the signal back to electrons and amplifies it.

This basic detection scheme can be implemented with a variety of scintillators and a variety of photon sensors. A traditional implementation is the Everhart Thornley detection scheme often used to detect secondary electrons in SEM chambers and provide a topographic image of the specimen.

A more advanced implementation is an in-column backscattered electron (BSE) detector which can filter out low energy electrons and provide a clean BSE signal, giving material-contrast in the SEM’s image. 
Other implementations split the signal into several segments and use ScintiFast™, and ultra-fast inorganic scintillator, to support fast scanning and imaging. Such implementations are common for metrology and inspection e-beam systems in the semiconductor industry.

Solid state detection technology is also available. This technology allows for flexible design and segmentation of the detector’s active area. It is frequently used for BSE detectors and for transmitted electron detectors in both SEMs and high energy scanning transmission electron microscopes (TEM).