Bradbury-Nielsen shutter
Encyclopedia
A Bradbury-Nielsen shutter (or Bradbury-Nielsen gate) is a type of electrical ion gate, which was first proposed in an article by Norris Bradbury
and Russel A. Nielsen, where they used it as an electron
filter. Today they are used in the field of mass spectrometry
where they are used in both TOF
mass spectrometers and in ion mobility spectrometer
s
, as well as Hadamard transform
mass spectrometers (a variant of TOF-MS). The Bradbury-Nielsen shutter is ideal for injecting short pulses of ions and can be used to improve the mass resolution of TOF instruments by reducing the initial pulse size as compared to other methods of ion injection.
voltage
in an 180° out-of-phase manner to alternate wires in a grid which is orthogonal to the path of the ion beam. This results in charged particles only passing directly through the shutter at certain times in the voltage phase (φ=nπ/2), when the potential difference between the grid wires is zero. At other times the ion beam is deflected to some angle by the potential difference between the neighboring wires. This deflection is divergent with ions that pass through alternate slits being deflected in opposite directions. The maximum deflection angle can be calculated by
tan α = k Vp / V0
where α is the deflection angle, k is a deflection constant, Vp is the wire voltage (+Vp on one wire set and -Vp on the other), and V0 is the ion acceleration voltage in eV. The deflection constant k can be calculated by
k = π / 2ln[cot(πR/2d)]
where R is the wire radius and d is the wire spacing.
wafer has been reported.
Norris Bradbury
Norris Edwin Bradbury , was an American physicist who was born in Santa Barbara, California. He served as director of the Los Alamos National Laboratory for 25 years , succeeding J. Robert Oppenheimer, who personally chose Bradbury for the position of director after working closely with him on the...
and Russel A. Nielsen, where they used it as an electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
filter. Today they are used in the field of mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
where they are used in both TOF
Time-of-flight
Time of flight describes a variety of methods that measure the time that it takes for an object, particle or acoustic, electromagnetic or other wave to travel a distance through a medium...
mass spectrometers and in ion mobility spectrometer
Ion mobility spectrometer
Ion-mobility spectrometry is an analytical technique used to separate and identify ionized molecules in the gas phase based on their mobility in a carrier buffer gas...
s
, as well as Hadamard transform
Hadamard transform
The Hadamard transform is an example of a generalized class of Fourier transforms...
mass spectrometers (a variant of TOF-MS). The Bradbury-Nielsen shutter is ideal for injecting short pulses of ions and can be used to improve the mass resolution of TOF instruments by reducing the initial pulse size as compared to other methods of ion injection.
Theory of Operation
The concept behind the Bradbury-Nielsen shutter is to apply a high frequencyHigh frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
in an 180° out-of-phase manner to alternate wires in a grid which is orthogonal to the path of the ion beam. This results in charged particles only passing directly through the shutter at certain times in the voltage phase (φ=nπ/2), when the potential difference between the grid wires is zero. At other times the ion beam is deflected to some angle by the potential difference between the neighboring wires. This deflection is divergent with ions that pass through alternate slits being deflected in opposite directions. The maximum deflection angle can be calculated by
tan α = k Vp / V0
where α is the deflection angle, k is a deflection constant, Vp is the wire voltage (+Vp on one wire set and -Vp on the other), and V0 is the ion acceleration voltage in eV. The deflection constant k can be calculated by
k = π / 2ln[cot(πR/2d)]
where R is the wire radius and d is the wire spacing.
Micromachined ion gates
A Bradbury-Nielsen Gate micromachined from a silicon on insulatorSilicon on insulator
Silicon on insulator technology refers to the use of a layered silicon-insulator-silicon substrate in place of conventional silicon substrates in semiconductor manufacturing, especially microelectronics, to reduce parasitic device capacitance and thereby improving performance...
wafer has been reported.