1.1  What is Vacuum

From the practical point of view, a vacuum is defined as a space in which the pressure of gas is low compared with normal or atmospheric pressure presure.

This definition correctly allows a rather broad interpretation because the vacuums encountered cover a wide range of pressure values.

1.2  Unit of Vacuum measurement

Vacuum is measured in terms of pressure. The SI unit of pressure is the Pascal (Pa) or N/m2. Other units of pressure are Torr, mmHg and mbar.

         Standard Atmospheric Pressure = 101325 Pa = 760 torr  = 760 mmHg= 1013mbar

                                                   1 mbar = 100 Pa = 0.75 torr

1.3 The Ranges of Vacuum

The range of vacuum presently explored and utilized covers a range of about 15 orders of magnitude below atmospheric pressure. This corresponds therefore to pressures from 1000 mbar down to 10-12 mbar. This range is subdivided into smaller ranges as defined below.

Low (rough) vacuum                    Atmospheric pressure (1000 mbar) to 1 mbar

Medium vacuum                           1 to 10− 3 mbar

High vacuum (HV)                       10− 3 to 10− 8 mbar

Ultrahigh vacuum (UHV)             10− 8 to 10− 12 mbar

Extreme high vacuum (XHV)     Less than 10− 12 mbar

Vacuum from 1000 or 103 mbar 10− 3 mbar also called Primary Vacuum, from 10−3 mbar to 10−8 mbar Secondary Vacuum and from 10−8 mbar to 10−12 mbar Ultra High Vacuum (UHV).

Under standard conditions of temperature and pressure (T = 0°C = 273 K and atmospheric pressure  p = 101.3 kPa= 1000 mbar), a cubic meter of gas contains molecules, n=2.5  × 1025/ m3, where n is called molecular number density.

The lowest laboratory-made vacuum achieved thus far, under very specialized conditions, corresponds to  n being of the order 107 molecules per m3 and pressure or vacuum of the order of 10-15 mbar.

At altitudes of about 800 km where observational earth satellites typically orbit in a virtually friction-free atmosphere, vacuum is approximately 10-7 mbar (n = 2.5  × 1015 molecules/m3)

In interplanetary space n is about 107/m3, vacuum is approximately 10-15 mbar due mainly to the solar wind. In the space between galaxies there is thought to be on average less than one atom of hydrogen per cubic meter.

1.4  Applications of Vacuum

Primary Vacuum Applications

Many applications in the low-vacuum region exploit the force created by the pressure difference with atmospheric pressure for example, in vacuum molding and mechanical handling or lifting heavy luggage or things using suction pads. Also, oils may be degassed to rid them of dissolved air.

Applications in the medium vacuum range include vacuum and freeze-drying in the pharmaceutical industries in which vacuums have to be sufficiently low to permit relatively free evaporation from surfaces, and sputtering and chemical vapor deposition processes, to coat ultrathin films of thickness in nanometer range.

Secondary Vacuum Applications

High vacuum has a very large number of applications that include the manufacture of television tubes; the deposition of thin  film coatings by evaporation of materials from the bulk, as in lens blooming; and semiconductor technology in which there is an additional strict requirement for “clean” vacuum, free of critical impurities.

Instruments such as electron microscopes and mass spectrometers for chemical and forensic analysis operate in this region.

A significant property of the high vacuum is that it is sufficiently rarefied to allow free passage of particles e.g, atoms, molecules, or electrons from one place to another within it.

Ultrahigh Vacuum Applications

Ultrahigh vacuum is widely used in research applications where it is important that surfaces are subject to minimal contamination by capture of molecules of the residual gas. Surface science was one of the early driving forces that stimulated progress in this field.

Such vacuums are also a prerequisite in thermonuclear fusion experiments, prior to their back- filling with ultrapure gases for fusion studies, and vacua of 10−12 mbar are necessary in order that charged particle beams can be accelerated to very high energies and stored for reasonable times with acceptable rates of attenuation due to scattering, as in the large hadron collider, the LHC, at the CERN laboratories.

As is pointed out by O’Hanlon (2003), manufacturing processes for some sophisticated semiconductor and optoelectronic devices now necessitate the ultraclean conditions of the UHV environment, a trend that will continue.

Ultrahigh Vacuum Applications

Ultrahigh vacuum is widely used in research applications where it is important that surfaces are subject to minimal contamination by capture of molecules of the residual gas. Surface science was one of the early driving forces that stimulated progress in this field.

Such vacuums are also a prerequisite in thermonuclear fusion experiments, prior to their back- filling with ultrapure gases for fusion studies, and vacua of 10−12 mbar are necessary in order that charged particle beams can be accelerated to very high energies and stored for reasonable times with acceptable rates of attenuation due to scattering, as in the large hadron collider, the LHC, at the CERN laboratories.

As is pointed out by O’Hanlon (2003), manufacturing processes for some sophisticated semiconductor and optoelectronic devices now necessitate the ultraclean conditions of the UHV environment, a trend that will continue.

Ultrahigh Vacuum Applications

Ultrahigh vacuum is widely used in research applications where it is important that surfaces are subject to minimal contamination by capture of molecules of the residual gas. Surface science was one of the early driving forces that stimulated progress in this field.

Such vacuums are also a prerequisite in thermonuclear fusion experiments, prior to their back- filling with ultrapure gases for fusion studies, and vacua of 10−12 mbar are necessary in order that charged particle beams can be accelerated to very high energies and stored for reasonable times with acceptable rates of attenuation due to scattering, as in the large hadron collider, the LHC, at the CERN laboratories.

As is pointed out by O’Hanlon (2003), manufacturing processes for some sophisticated semiconductor and optoelectronic devices now necessitate the ultraclean conditions of the UHV environment, a trend that will continue.

Ultrahigh Vacuum Applications

Ultrahigh vacuum is widely used in research applications where it is important that surfaces are subject to minimal contamination by capture of molecules of the residual gas. Surface science was one of the early driving forces that stimulated progress in this field.

Such vacuums are also a prerequisite in thermonuclear fusion experiments, prior to their back- filling with ultrapure gases for fusion studies, and vacua of 10−12 mbar are necessary in order that charged particle beams can be accelerated to very high energies and stored for reasonable times with acceptable rates of attenuation due to scattering, as in the large hadron collider, the LHC, at the CERN laboratories.

As is pointed out by O’Hanlon (2003), manufacturing processes for some sophisticated semiconductor and optoelectronic devices now necessitate the ultraclean conditions of the UHV environment, a trend that will continue.

Ultrahigh Vacuum Applications

Ultrahigh vacuum is widely used in research applications where it is important that surfaces are subject to minimal contamination by capture of molecules of the residual gas. Surface science was one of the early driving forces that stimulated progress in this field.

Such vacuums are also a prerequisite in thermonuclear fusion experiments, prior to their back- filling with ultrapure gases for fusion studies, and vacua of 10−12 mbar are necessary in order that charged particle beams can be accelerated to very high energies and stored for reasonable times with acceptable rates of attenuation due to scattering, as in the large hadron collider, the LHC, at the CERN laboratories.

As is pointed out by O’Hanlon (2003), manufacturing processes for some sophisticated semiconductor and optoelectronic devices now necessitate the ultraclean conditions of the UHV environment, a trend that will continue.

Ultrahigh Vacuum Applications

Ultrahigh vacuum is widely used in research applications where it is important that surfaces are subject to minimal contamination by capture of molecules of the residual gas. Surface science was one of the early driving forces that stimulated progress in this field.

Such vacuums are also a prerequisite in thermonuclear fusion experiments, prior to their back- filling with ultrapure gases for fusion studies, and vacua of 10−12 mbar are necessary in order that charged particle beams can be accelerated to very high energies and stored for reasonable times with acceptable rates of attenuation due to scattering, as in the large hadron collider, the LHC, at the CERN laboratories.

As is pointed out by O’Hanlon (2003), manufacturing processes for some sophisticated semiconductor and optoelectronic devices now necessitate the ultraclean conditions of the UHV environment, a trend that will continue.

Ultrahigh Vacuum Applications

Ultrahigh vacuum is widely used in research applications where it is important that surfaces are subject to minimal contamination by capture of molecules of the residual gas. Surface science was one of the early driving forces that stimulated progress in this field.

Such vacuums are also a prerequisite in thermonuclear fusion experiments, prior to their back- filling with ultrapure gases for fusion studies, and vacua of 10−12 mbar are necessary in order that charged particle beams can be accelerated to very high energies and stored for reasonable times with acceptable rates of attenuation due to scattering, as in the large hadron collider, the LHC, at the CERN laboratories.

As is pointed out by O’Hanlon (2003), manufacturing processes for some sophisticated semiconductor and optoelectronic devices now necessitate the ultraclean conditions of the UHV environment, a trend that will continue.

Ultrahigh Vacuum Applications

Ultrahigh vacuum is widely used in research applications where it is important that surfaces are subject to minimal contamination by capture of molecules of the residual gas. Surface science was one of the early driving forces that stimulated progress in this field.

Such vacuums are also a prerequisite in thermonuclear fusion experiments, prior to their back- filling with ultrapure gases for fusion studies, and vacua of 10−12 mbar are necessary in order that charged particle beams can be accelerated to very high energies and stored for reasonable times with acceptable rates of attenuation due to scattering, as in the large hadron collider, the LHC, at the CERN laboratories.

As is pointed out by O’Hanlon (2003), manufacturing processes for some sophisticated semiconductor and optoelectronic devices now necessitate the ultraclean conditions of the UHV environment, a trend that will continue.