Ion Track Technology

PhysicsConsult

Reimar Spohr
Test image

Introduction to Ion Tracks

Ion acceleration
Push or pull for ion acceleration? From everyday life we are familiar with attractive and repulsive forces between atoms. Whenever we push an object we use repulsive forces. Whenever we pull it we use attractive forces. These forces have short range. They vanish after few atomic distances. Click on image to show ion.
Electrostatic accelerators use a constant electric field. The total ion energy gain corresponds to the product of the charge state of the ion times the acceleration voltage and is measured in Mega Electron Volt (MeV = 1 Mio eV). DC accelerators provide constant-current ion beams with well defined energy and narrow angular spread. They are known as Van de Graaff accelerators. Click on image to show tandem accelerator.
Cyclotrons consist of two hollow D-shaped electrodes separated by an accelerating gap. A magnetic field bends the ion path. The bending radius increases proportional to the ion speed. The spiral path reflects the gradual increase of energy. Click on image to animate.
Linear high frequency accelerators consist of a series of drift tubes separated by acceleration gaps. Alternating voltage is applied to neighboring drift tubes. Ions arriving at the acceleration gap at the right time (phase) are accelerated. The requirement leads to the formation of discrete ion bunches of similar speed. This condition is comparable to the situation of wave surfers adjusting their speed to the wave speed. Ions reaching the gap at the right time are accelerated. Click on image to show equivalent potential.
Irradiation systems
Wide field irradiations at 90 degree are performed by defocusing the ion beam with a magnetic lens. The beam parallelism increases with the distance between the lens and the target. Click image to show 45 degree irradiation.
Parallel beam irradiations at 90 degree are performed using beam broadening with two magnetic lenses. The first lens is widening the beam. The second lens is refocusing the beam. Click image to show 45 degree irradiation.
Raster scanners consist of two pairs of deflector magnets placing a parallel ion beam at a predetermined location. Click image to switch deflection on.
Single ion irradiations require a beam shutter and a particle detector (not shown). Click image to switch beam on.
Ion microbeam comprising (not shown) beam defining aperture, antiscattering aperture and particle detector. Click image to switch to 45 degree irradiation.
Radiation effect
Importance of mass for particle collision. Click to swap.
Collision cascade. The ion collides with target electrons which in turn collide with further target electrons. The motion expands radial from the ion path. The number of moving electrons increases while their average energy decreases. The motion dies out when the energy becomes too small to knock-off further electrons. Click image to show average effect.
Importance of conductivity. Insulators have low electron mobility. The collision cascade is confined in a small volume. The local radiation effect is high. Click to show metal.
Thermal spike model of track creation. Along the ion path a hot cylinder is formed. The cylinder expands rapidly while cooling down. Material heated above a certain temperature (for example the melting point) retains a radiation effect (for example disorder). Click image to animate.
Ion track etching
Etch geometry at track etch ratio 5:1 where etching proceeds five times faster along the track axis (long arrow) than in the base material (short arrow). The track etch ratio corresponds to the ratio of the arrow lengths. Click image to animate etch process.
Influence of track etch ratio. Conical pore at track etch ratio 5:1. Click to increase track etch ratio.
Diabolo shaped etch channel at track etch ratio 5:1. Click to increase track etch ratio.
Track replication
Electroreplication template. Click to animate replication.
Embedded diabolo at track etch ratio 50:1. Click to show free standing replica.
Embedded conical pin at track etch ratio 5:1. Click to show free standing replica.
Track texture
Conical troughs at track etch ratio 2:1. Click to show pin replica.
Cylindrical channels at high track etch ratio (above 100:1). Click to show replica.
Cylindrical channels at high track etch ratio (above 100:1). Click to show thin-walled cylinder replica.
Tilted cone troughs at track etch ratio 5:1. Click to show replica texture.
Spherical section troughs. Click to show replica.
Applications
Current rectifying asymmetric pore obtained by one-sided etching. Preferential transport of positive ions in direction of arrow. Click to show diode-like current characteristic.
Application: pH and self-oscillating sensors.
Counting and sizing of nanoparticles by supported nanopore. Click to show particle transit pulse.
Application: Real-time protein and DNA analysis.
Asymmetric filter pores with low flow resistance. Click to show cylindrical filter channels with high resistance.
Application: High flow nano filtration.
Responsive channel. Closed state. Channel closed below critical temperature of hydrogel. Hydrogel attached to channel wall. Click to show open channel.
Application: Self-regulating drug delivery controlled by body temperature.
Bio-specific channel. Sensor-molecules attached to wall. No complementary molecules present in solution. Low electrical resistance. Click to show high resistance state.
Application: DNA- and protein analysis.
Multilayer magnetic sensor at zero external field. Neighboring layers antiparallel. Electrical resistance high. Click to show low resistance state.
Application: Magnetometer; hard disk reading head; spintronic devices.
Field emitter array at zero electric field. No electron emission. Click to switch field emission on.
Application: Large area electron emitter; microwave generation; displays.
Superhydrophobic texture. Low friction. Click to show wetted state.
Application: Non-wetting self-cleaning surface.
Asymmetric-drag texture. Click to show replica.
Application: Asymmetric stick-slip for sport gear. Drag reduction. Converting vibration to motion.