Patent Publication Number: US-7910882-B2

Title: Apparatus and method for cooling ions

Description:
This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 60/885,788, filed Jan. 19, 2007. 
    
    
     FIELD 
     The applicant&#39;s teachings relate to an apparatus and method for cooling secondary ions in a secondary ion mass spectrometer. 
     INTRODUCTION 
     Secondary Ion Mass spectrometry (SIMS) is a surface analysis technique whereby a sample is bombarded with primary ions to sputter secondary ions and neutral particles. The secondary ions typically have high internal excitation leading to fragmentation of ions of interest. The secondary ions need to be stabilized to prevent fragmentation. Also, the primary ions can collide with gas molecules thereby slowing down and scattering rather than bombarding the sample. 
     SUMMARY 
     In accordance with an aspect of the applicant&#39;s teachings, there is provided an apparatus for performing secondary ion mass spectrometry. The apparatus comprises a target surface for supporting a sample deposited on the target surface and an ion source configured to direct a beam of primary ions toward the sample to sputter secondary ions and neutral particles from the sample, at least a portion of the ion source can be configured to operate in vacuum. The beam of primary ions can be continuous or it can be pulsed. The primary ions can comprise cluster ions, such as C 60  ions. The apparatus also comprises a first chamber surrounding the target surface and the sample. The first chamber having an inlet for providing a gas to maintain high pressure at the sample for cooling the secondary ions and neutral particles, the high pressure being in the range of about 10 −3  to about 1000 Torr, and preferably at about 10 mTorr. The high pressure can also be in the range of about 10 −1  to about 100 Torr. The gas provided for cooling the secondary ions and neutral particles can be pulsed into the chamber or introduced continuously. The apparatus can further comprise a cooling path for receiving the secondary ions and neutral particles from the sample wherein the secondary ions and neutral particles are cooled along the cooling path. A product obtained by multiplying the high pressure at the sample by a length of the cooling path can be greater than 10 −3  Torr*cm. The neutral particles can be post-ionized, for example, with a laser light, by ion-ion charge transfer, by photo-ionization using VUV light, or by other techniques as known in the art. The inlet into the first chamber can be a conduit for directing gas at the sample. An output end of the ion source can be less than 1 cm from the sample. The output end of the ion source can also be 1 mm or less from the sample. The apparatus can further comprise a skimmer having an aperture, the skimmer being configured to receive and direct the secondary ions, which can include the ions generated by post-ionization of the neutral particles, through the aperture of the skimmer into an RF ion guide. Furthermore, the ion source can be configured to direct the beam of primary ions through the aperture of the skimmer toward the sample to sputter secondary ions and neutral particles from the sample. Also, the ion source can be integral with a portion of the skimmer. 
     In another aspect, there is provided a method of secondary ion mass spectrometry. The method comprises providing a target surface for supporting a sample deposited on the target surface. The method also comprises directing a beam of primary ions toward the sample to sputter secondary ions and neutral particles from the sample and providing a high pressure at the sample for cooling the secondary ions and neutral particles, the high pressure being in the range of about 10 −3  to about 1000 Torr, and preferably at about 10 mTorr The high pressure can also be in the range of about 10 −3  to about 100 Torr. The beam of primary ions can be continuous or it can be pulsed. The primary ions can comprise cluster ions, such as C 60  ions. The method further comprising providing gas to maintain the high pressure. The gas can be provided continuously or it can be a pulsed gas. The method further comprising directing the secondary ions and neutral particles sputtered from the sample into a cooling path and subjecting the secondary ions and neutral particles to cooling along the path. A product obtained by multiplying the high pressure at the sample by a length of the cooling path can be greater than 10 −3  Torr*cm. The neutral particles can be post-ionized, for example, with a laser light, by ion-ion charge transfer, by photo-ionization using VUV light, or by other techniques as known in the art. The method can further comprise delivering gas at the sample. The beam of primary ions can be directed at the sample. The method can further comprise providing a skimmer having an aperture and receiving and directing the secondary ions, which can include the ions generated by post-ionization of the neutral particles, through the aperture into an RF ion guide. Furthermore, the ion source can be configured to direct the beam of primary ions through the aperture of the skimmer toward the sample to sputter secondary ions and neutral particles from the sample. Also, the ion source can be integral with a portion of the skimmer. 
     These and other features of the applicants&#39; teachings are set forth herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The skilled person in the art will understand that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the applicant&#39;s teachings in any way. 
         FIG. 1  schematically illustrates a secondary ion mass spectrometry system in accordance with various embodiments of the applicant&#39;s teachings. 
         FIG. 2  schematically illustrates a secondary ion mass spectrometry system, including a skimmer having an aperture, in accordance with various embodiments. 
         FIG. 3  schematically illustrates a secondary ion mass spectrometry system, including an ion source integral with a portion of the skimmer, in accordance with various embodiments. 
         FIG. 4  schematically illustrates a secondary ion mass spectrometer system, including a chamber having an inlet that is a conduit delivering gas at the sample, in accordance with various embodiments. 
         FIG. 5  schematically illustrates a secondary ion mass spectrometer system, including an output end of the ion source located in close proximity to the sample, in accordance with various embodiments. 
         FIG. 6  schematically illustrates a secondary ion mass spectrometry system, including a conduit delivering gas at the sample and an output end of the ion source located in close proximity to the sample. 
     
    
    
     DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS 
     It should be understood that the phrase “a” or “an” used in conjunction with the applicant&#39;s teachings with reference to various elements encompasses “one or more” or “at least one” unless the context clearly indicates otherwise. Referring to  FIG. 1 , in various embodiments in accordance with the applicant&#39;s teachings, a schematic diagram illustrates a secondary ion mass spectrometry system  10  having an ion source  12  configured to direct a beam of primary ions  14  toward a sample  16  to sputter secondary ions  18  and neutral particles  19  from the sample  16 . In various embodiments, the beam of primary ions can be continuous or it can be pulsed. The primary ions can comprise cluster ions that can be metal or organic clusters, as known in the art, or any other suitable projectile ions. Projectile ions can comprise different charge states. For example, the primary ions can comprise of C 60  ions that are stable, robust large molecules that leave no residues when bombarding the sample. At least a portion of the ion source  12  can be configured to operate in vacuum. The sample  16  is supported on a target surface  20 . High pressure can be provided at the sample  16  for cooling and stabilizing the secondary ions which can have high internal excitation leading to fragmentation of ions of interest. Rapid cooling of the secondary ions can prevent such fragmentation. High pressure at the sample can facilitate rapid cooling of the secondary ions and the neutral particles. In various aspects, the high pressure can comprise a pressure in the range of about 10 −3  to about 1000 Torr, and preferably at about 10 mTorr. In various aspects, the high pressure can be in the range of about 10 −1  to about 100 Torr. In various embodiments, the neutral particles can be post-ionized as is well known in the art. For example, the neutral particles can be, but are not limited to be, post-ionized with a laser light, by ion-ion charge transfer ionization, or by photo-ionization using VUV light. A chamber  22  can surround the target surface and the sample. In various embodiments, the chamber  22  comprises an inlet  24  providing gas to maintain the high pressure as well as direct and focus the secondary ions, which can include the ions generated by post-ionization of the neutral particles, into an RF ion guide  26 . The gas typically can be a non-reactive gas, including, but not limited to, nitrogen, helium, or argon, as well known in the art. In various aspects, the gas can be provided continuously or it can be pulsed. Pumps  28  can regulate the pressure of the ion source  12 , which can be from about 10 −2  to about 10 −10  Torr, and the chamber  22 . A cooling path can receive the secondary ions and neutral particles from the sample, and the secondary ions and neutral particles can be cooled along the cooling path. At least a portion of the cooling path can lie along an RF ion guide. The secondary ions, which can include the ions generated by post-ionization of the neutral particles, can pass through the RF ion guide  26  into a mass analyzer, including, but not limited to, a quadrupole, time-of-flight, ion trap, or Fourier transform mass spectrometer. 
     As shown in  FIG. 2 , in various embodiments in accordance with the applicant&#39;s teachings, a schematic diagram illustrates a secondary ion mass spectrometry system  30  having an ion source  32  configured to direct a beam of primary ions  34  toward a sample  36  to sputter secondary ions  38  and neutral particles  39  from the sample  36 . In various embodiments, the beam of primary ions can be continuous or it can be pulsed. The primary ions can comprise cluster ions that can be metal or organic clusters, as known in the art, or any other suitable projectile ions. Projectile ions can comprise different charge states. For example, the primary ions can comprise of C 60  ions that are stable, robust large molecules that leave no residues when bombarding the sample. At least a portion of the ion source  32  can be configured to operate in vacuum. The sample  36  is supported on a target surface  40 . High pressure can be provided at the sample  36  for cooling and stabilizing the secondary ions which can have high internal excitation leading to fragmentation of ions of interest. Rapid cooling of the secondary ions can prevent such fragmentation. High pressure at the sample can facilitate rapid cooling of the secondary ions and the neutral particles. In various aspects, the high pressure can comprise a pressure in the range of about 10 −3  to about 1000 Torr, and preferably at about 10 mTorr. In various aspects, the high pressure can be in the range of about 10 −1  to about 100 Torr. In various embodiments, the neutral particles can be post-ionized as is well known in the art. For example, the neutral particles can be, but are not limited to be, post-ionized with a laser light, by ion-ion charge transfer ionization, or by photo-ionization using VUV light. A first chamber  42  can surround the target surface and the sample. In various embodiments, the first chamber  42  comprises an inlet  44  providing gas to maintain the high pressure. In various aspects, the system  30  comprises a skimmer  50  having apertures  52  and  53 . Primary ions pass into chamber  42  through an opening  53 . The gas can direct and focus the secondary ions, which can include the ions generated by post-ionization of the neutral particles, through the aperture  52  of the skimmer  50  into an RF ion guide  46  located in a second chamber  54 . In various embodiments, the ion source  32  can be configured to direct the beam of primary ions  34  through the aperture  53  of the skimmer  50  to sputter secondary ions and neutral particles from the sample  36 . The pressure of the second chamber  54  can be lower than in the first chamber  42 , for example, 10 mTorr. The gas typically can be a non-reactive gas, including, but not limited to, nitrogen, helium, or argon, as well known in the art. In various aspects, the gas can be provided continuously or it can be pulsed. Pumps  48  can regulate the pressure of the ion source  32 , which can be 10 −2  to 10 −10  Torr, and the second chamber  54 . A cooling path can receive the secondary ions and neutral particles from the sample, and the secondary ions and neutral particles can be cooled along the cooling path. At least a portion of the cooling path can lie along an RF ion guide. The secondary ions, which can include the ions generated by post-ionization of the neutral particles, can pass through the RF ion guide  46  into a mass analyzer, including, but not limited to, a quadrupole, time-of-flight, ion trap, or Fourier transform mass spectrometer. 
     Referring to  FIG. 3 , in various embodiments in accordance with the applicant&#39;s teachings, a schematic diagram illustrates a secondary ion mass spectrometry system  60  having an ion source  62  configured to direct a beam of primary ions  64  toward a sample  66  to sputter secondary ions  68  and neutral particles  69  from the sample  66 . In various embodiments, the beam of primary ions can be continuous or it can be pulsed. The primary ions can comprise cluster ions that can be metal or organic clusters, as known in the art, or any other suitable projectile ions. Projectile ions can comprise different charge states. For example, the primary ions can comprise of C 60  ions that are stable, robust large molecules that leave no residues when bombarding the sample. At least a portion of the ion source  62  can be configured to operate in vacuum. The sample  66  is supported on a target surface  70 . High pressure can be provided at the sample  66  for cooling and stabilizing the secondary ions which can have high internal excitation leading to fragmentation of ions of interest. Rapid cooling of the secondary ions can prevent such fragmentation. High pressure at the sample can facilitate rapid cooling of the secondary ions and neutral particles. In various aspects, the high pressure can comprise a pressure in the range of about 10 −3  to about 1000 Torr, and preferably at about 10 mTorr. In various aspects, the high pressure can be in the range of about 10 −1  to about 100 Torr. In various embodiments, the neutral particles can be post-ionized as is well known in the art. For example, the neutral particles can be, but are not limited to be, post-ionized with a laser, by ion-ion charge transfer ionization, or by photo-ionization using VUV light. A first chamber  72  can surround the target surface and the sample. In various embodiments, the first chamber  72  comprises an inlet  74  providing gas to maintain the high pressure. In various aspects, the system  60  comprises a skimmer  80  having an aperture  82 . In various embodiments, the ion source  62  can be integral with a portion of the skimmer  80 . The output end  81  of the ion source  62  can be located in close proximity to the sample  66 . Such an arrangement can alleviate the undesired consequences of the primary ions colliding with the gas, slowing down, scattering and breaking down, thereby affecting the trajectory of the primary ions toward the sample and efficiency of generation of secondary ions. The gas can direct and focus the secondary ions, which can include ions generated by post-ionization of the neutral particles, through the aperture  82  of the skimmer  80  into an RF ion guide  76  located in a second chamber  84 . The pressure of the second chamber  84  can be lower than in the first chamber  72 , for example, 10 mTorr. The gas typically can be a non-reactive gas, including, but not limited to, nitrogen, helium, or argon, as well known in the art. In various aspects, the gas can be provided continuously or it can be pulsed. Pumps  78  can regulate the pressure of the ion source  62 , which can be 10 −2  to 10 −10  Torr, and the second chamber  84 . A cooling path can receive the secondary ions and neutral particles from the sample, and the secondary ions and neutral particles can be cooled along the cooling path. At least a portion of the cooling path can lie along an RF ion guide. The secondary ions, which can include the ions generated by post-ionization of the neutral particles, can pass through the RF ion guide  76  into a mass analyzer, including, but not limited to, a quadrupole, time-of-flight, ion trap, or Fourier transform mass spectrometer. 
     Referring to  FIG. 4 , in various embodiments in accordance with the applicant&#39;s teachings, a schematic diagram illustrates a secondary ion mass spectrometry system  90  having an ion source  92  configured to direct a beam of primary ions  94  toward a sample  96  to sputter secondary ions  98  and neutral particles  99  from the sample  96 . In various embodiments, the beam of primary ions can be continuous or it can be pulsed. The primary ions can comprise cluster ions that can be metal or organic clusters, as known in the art, or any other suitable projectile ions. Projectile ions can comprise different charge states. For example, the primary ions can comprise of C 60  ions that are stable, robust large molecules that leave no residues when bombarding the sample. At least a portion of the ion source  92  can be configured to operate in vacuum. The sample  96  is supported on a target surface  100 . High pressure can be provided at the sample  96  for cooling and stabilizing the secondary ions which can have high internal excitation leading to fragmentation of ions of interest. Rapid cooling of the secondary ions can prevent such fragmentation. High pressure at the sample can facilitate rapid cooling of the secondary ions and neutral particles. In various aspects, the high pressure can comprise a pressure in the range of about 10 −3  to about 1000 Torr, and preferably at about 10 mTorr. In various aspects, the high pressure can be in the range of about 10 −1  to about 100 Torr. In various embodiments, the neutral particles can be post-ionized as is well known in the art. For example, the neutral particles can be, but are not limited to be, post-ionized with a laser, by ion-ion charge transfer ionization, or by photo-ionization using VUV light. A chamber  102  can surround the target surface and the sample. In various embodiments, the chamber  102  comprises a conduit  104  providing gas to maintain the high pressure as well as direct and focus the secondary ions, which can include ions generated by post-ionization of the neutral particles, into an RF ion guide  106 . The conduit  104  can deliver the gas at the sample to facilitate rapid cooling of the secondary ions and neutral particles. The gas typically can be a non-reactive gas, including, but not limited to, nitrogen, helium, or argon, as well known in the art. In various aspects, the gas can be provided continuously or it can be pulsed. Pumps  108  can regulate the pressure of the ion source  92 , which can be from about 10 −2  to about 10 −10  Torr, and the chamber  102 . A cooling path can receive the secondary ions and neutral particles from the sample, and the secondary ions and neutral particles can be cooled along the cooling path. At least a portion of the cooling path can lie along an RF ion guide. The secondary ions, which can include ions generated by post-ionization of the neutral particles, can pass through the RF ion guide  106  into a mass analyzer, including, but not limited to, a quadrupole, time-of-flight, ion trap, or Fourier transform mass spectrometer. 
     Referring to  FIG. 5 , in various embodiments in accordance with the applicant&#39;s teachings, a schematic diagram illustrates a secondary ion mass spectrometry system  110  having an ion source  112  configured to direct a beam of primary ions  114  toward a sample  116  to sputter secondary ions  118  and neutral particles  119  from the sample  116 . In various embodiments, the beam of primary ions can be continuous or it can be pulsed. The primary ions can comprise cluster ions that can be metal or organic clusters, as known in the art, or any other suitable projectile ions. Projectile ions can comprise different charge states. For example, the primary ions can comprise of C 60  ions that are stable, robust large molecules that leave no residues when bombarding the sample. At least a portion of the ion source  112  can be configured to operate in vacuum. The sample  116  is supported on a target surface  120 . High pressure can be provided at the sample  116  for cooling and stabilizing the secondary ions which can have high internal excitation leading to fragmentation of ions of interest. Rapid cooling of the secondary ions can prevent such fragmentation. High pressure at the sample can facilitate rapid cooling of the secondary ions and neutral particles. In various aspects, the high pressure can comprise a pressure in the range of about 10 −3  to about 1000 Torr, and preferably at about 10 mTorr. In various aspects, the high pressure can be in the range of about 10 −1  to about 100 Torr. In various embodiments, the neutral particles can be post-ionized as is well known in the art. For example, the neutral particles can be, but are not limited to be, post-ionized with a laser, by ion-ion charge transfer ionization, or by photo-ionization using VUV light. A first chamber  122  can surround the target surface and the sample. In various embodiments, the first chamber  122  comprises an inlet  124  providing gas to maintain the high pressure. In various aspects, the system  110  comprises a skimmer  130  having an aperture  132 . In various embodiments, the output end  131  of the ion source  112  can be located in close proximity to the sample  116 . In various embodiments, the output end  131  of the ion source  112  can be, but is not limited to, less than 1 cm from the sample. In various embodiments, the output end  131  of the ion source  112  can be, but is not limited to, 1 mm or less from the sample. In various aspects, depending on the configuration of the system, the output end of the ion source can be located as close as possible to the sample without touching the sample. Such arrangements can alleviate the undesired consequences of the primary ions colliding with the gas, slowing down, scattering, and fragmenting thereby affecting the trajectory of the primary ions toward the sample and the yield of secondary ions. The gas can direct and focus the secondary ions, which can include the ions generated by post-ionization of the neutral particles, through the aperture  132  of the skimmer  130  into an RF ion guide  126  located in a second chamber  134 . The pressure of the second chamber  134  can be lower than in the first chamber  122 , for example, 10 mTorr. The gas typically can be a non-reactive gas, including, but not limited to, nitrogen, helium, or argon, as well known in the art. In various aspects, the gas can be provided continuously or it can be pulsed. Pumps  128  can regulate the pressure of the ion source  62 , which can be 10 −2  to 10 −10  Torr, and the second chamber  134 . A cooling path can receive the secondary ions and neutral particles from the sample, and the secondary ions and neutral particles can be cooled along the cooling path. At least a portion of the cooling path can lie along an RF ion guide. The secondary ions, which can include the ions generated by post-ionization of the neutral particles, can pass through the RF ion guide  126  into a mass analyzer, including, but not limited to, a quadrupole, time-of-flight, ion trap, or Fourier transform mass spectrometer. 
     Referring to  FIG. 6 , in various embodiments in accordance with the applicant&#39;s teachings, a schematic diagram illustrates a secondary ion mass spectrometry system  140  having an ion source  142  configured to direct a beam of primary ions  144  toward a sample  146  to sputter secondary ions  148  and neutral particles  149  from the sample  146 . In various embodiments, the beam of primary ions can be continuous or it can be pulsed. The primary ions can comprise cluster ions that can be metal or organic clusters, as known in the art, or any other suitable projectile ions. Projectile ions can comprise different charge states. For example, the primary ions can comprise of C 60  ions that are stable, robust large molecules that leave no residues when bombarding the sample. At least a portion of the ion source  142  can be configured to operate in vacuum. The sample  146  is supported on a target surface  150 . High pressure can be provided at the sample  146  for cooling and stabilizing the secondary ions which can have high internal excitation leading to fragmentation of ions of interest. Rapid cooling of the secondary ions can prevent such fragmentation. High pressure at the sample can facilitate rapid cooling of the secondary ions and neutral particles. In various aspects, the high pressure can comprise a pressure in the range of about 10 −3  to about 1000 Torr, and preferably at about 10 mTorr. In various aspects, the high pressure can be in the range of about 10 −1  to about 100 Torr. In various embodiments, the neutral particles can be post-ionized as is well known in the art. For example, the neutral particles can be, but are not limited to be, post-ionized with a laser, by ion-ion charge transfer ionization, or by photo-ionization using VUV light. A first chamber  152  can surround the target surface and the sample. In various embodiments, the first chamber  152  comprises a conduit  154  providing gas to maintain the high pressure as well as direct and focus the secondary ions, which can include ions generated by post-ionization of the neutral particles, into an RF ion guide  156 . The conduit  154  can be located near the ion source  142 , and the conduit  154  can deliver the gas at the sample to facilitate rapid cooling of the secondary ions and neutral particles. In various aspects, the system  140  comprises a skimmer  160  having an aperture  162 . In various embodiments, the output end  161  of the ion source  142  can be located in close proximity to the sample  146 . In various embodiments, the output end  161  of the ion source  142  can be, but is not limited to, less than 1 cm from the sample. In various embodiments, the output end  161  of the ion source  142  can be, but is not limited to, 1 mm or less from the sample. In various aspects, depending on the configuration of the system, the output end of the ion source can be located as close as possible to the sample without touching the sample. Such arrangements can alleviate the undesired consequences of the primary ions colliding with the gas, slowing down, scattering and fragmenting, thereby affecting the trajectory of the primary ions toward the sample and the yield of secondary ions. The gas can direct and focus the secondary ions, which can include ions generated by post-ionization of the neutral particles, through the aperture  162  of the skimmer  160  into an RF ion guide  156  located in a second chamber  164 . The pressure of the second chamber  164  can be lower than in the first chamber  152 , for example, 10 mTorr. The gas typically can be a non-reactive gas, including, but not limited to, nitrogen, helium, or argon, as well known in the art. In various aspects, the gas can be provided continuously or it can be pulsed. Pumps  158  can regulate the pressure of the ion source  142 , which can be 10 −2  to 10 −10  Torr, and the second chamber  164 . A cooling path can receive the secondary ions and neutral particles from the sample, and the secondary ions and neutral particles can be cooled along the cooling path. At least a portion of the cooling path can lie along an RF ion guide. The secondary ions, which can include the ions generated by post-ionization of the neutral particles, can pass through the RF ion guide  156  into a mass analyzer, including, but not limited to, a quadrupole, time-of-flight, ion trap, or Fourier transform mass spectrometer. 
     The embodiments shown in  FIGS. 1 to 6  are interfaced to an ion guide, which may not be necessary. Various embodiments may not require an ion guide. 
     The following describes a general use of the applicant&#39;s teachings which is not limited to any particular embodiment, but can be applied to any embodiment. In operation, an ion source, which can be configured to operate in vacuum, bombards a sample, deposited on a target surface, with a beam of primary ions which sputters secondary ions and neutral particles from the sample. In various aspects, the beam of primary ions can be continuous or it can be pulsed. The ion source typically operates from about 10 −2  to about 10 −10  Torr. Since the secondary ions typically can have high internal excitation, which can lead to fragmentation of ions of interest, the secondary ions can be stabilized by providing high pressure at the sample to facilitate rapid cooling of the secondary ions and neutral particles. The high pressure can comprise a pressure in the range of about 10 −3  to about 1000 Torr, and preferably at about 10 mTorr. In various aspects, the high pressure can comprise a pressure in the range of about 10 −1  to about 100 Torr. In various embodiments, the neutral particles can be post-ionized as is well known in the art. For example, the neutral particles can be, but are not limited to be, post-ionized with a laser, by ion-ion charge transfer ionization, or by photo-ionization using VUV light. A first chamber can surround the target surface and the sample. The high pressure can be provided by delivering gas through an inlet in the first chamber. The gas can be delivered at the sample through a conduit in the first chamber. In various aspects, the gas can be provided continuously or it can be pulsed. The output end of the ion source can be in close proximity to the sample which can prevent the primary ions from colliding with the gas, slowing down, scattering, and fragmenting. In various embodiments, the output end of the ion source can be, but is not limited to, less than 1 cm from the sample. In various embodiments, the output end of the ion source can be, but is not limited to, 1 mm or less from the sample. In various aspects, depending on the configuration of the system, the output end of the ion source can be located as close as possible to the sample without touching the sample. A cooling path can receive the secondary ions and neutral particles from the sample, and the secondary ions and neutral particles can be cooled along the cooling path. At least a portion of the cooling path can lie along an RF ion guide. The gas can assist in directing and focusing the secondary ions, which can include ions generated by post-ionization of the neutral particles, into the RF ion guide. In various embodiments, an ion guide may not be required. A skimmer having an aperture can also be used to receive and direct the secondary ions, which can include ions generated by post-ionization of the neutral particles, through the aperture of the skimmer into the RF ion guide, which can be in a second chamber at a lower pressure than the first chamber, for example, 10 mTorr. The ion source can be integral with a portion of the skimmer. The ion source can be configured to direct the beam of primary ions through the aperture of the skimmer toward the sample to sputter secondary ions and neutral particles from the sample. In various aspects, the beam of primary ions can be continuous or it can be pulsed. The secondary ions, which can include ions generated by post-ionization of the neutral particles, can pass through the RF ion guide and can be mass analyzed. The RF ion guide can provide additional benefits, as described in U.S. Pat. No. 4,963,736 by Douglas and French, by focusing the ions. 
     Collisional cooling of secondary ions with the gas can be efficient if more than one collision occurs. Also, the secondary ion mass spectrometry process can be more efficient or better controlled if the primary ions do not collide with the gas and therefore do not fragment before they bombard the sample. Though, a small number of collisions may still be tolerated. The following equation can define the probability of the number of collisions: 
                   N   =     σ   ⁢       ∫   0   L     ⁢       n   ⁡     (   x   )       ⁢           ⁢     ⅆ   x                   (     Equation   ⁢           ⁢   1     )               
where N is the expected average number of collisions, σ is the collision cross-section, n(x) is the density of the gas molecules, x is the coordinate along the trajectory, and L is the length of the trajectory.
 
     In a simplified form, this requirement can be stated as pressure of the gas, the high pressure at the sample, in the first chamber times the length of the trajectory of the secondary ions from the target surface to downstream of the sampling region, from the target surface  40  to aperture  52  of the skimmer, the length of the cooling path, equals 10 −3  Torr*cm (Pressure*Length=10 −3  Torr*cm). This represents a lower border for collisional cooling to have any effect. The gas can be provided such that the product of the gas pressure, the high pressure at the sample, in the first chamber and length of the trajectory of the secondary ions from the target surface to downstream of the sampling region, the length of the cooling path, is greater than 10 −3  Torr*cm. It should be noted that this is an estimate since the pressure in most embodiments is not constant. Equation 1 can be used to obtain a more precise estimate of the number of collisions. The cooling can continue beyond the aperture  52 , depending on the pressure of chamber  54 . 
     While the applicant&#39;s teachings are described in conjunction with various embodiments, it is not intended that the applicant&#39;s teachings be limited to such embodiments. On the contrary, the applicant&#39;s teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those skilled in the art. 
     In various embodiments, primary ions can be, but are not limited to, cluster ions that can be metal or organic clusters. The primary ions can be C 60 , glycerol, water, gold, or elemental atomic ions. 
     In various embodiments, the gas typically can be a non-reactive gas, and can be, but is not limited to, nitrogen, argon, or helium. In various embodiments, the gas can be provided continuously or it can be pulsed. 
     In various embodiments, an ion guide can be, but is not limited to, a multipole. For example, an ion guide can be a quadrupole, a hexapole, or an octapole. An ion guide can be an RF ring guide or any RF guide in which RF fields are used to confine or focus ions radially to prevent radial escape of the ions. An ion guide can be, but is not limited to, a 2D trap, also known as a linear ion trap, or a collision cell. 
     In various embodiments, the mass analyzer can be, but is not limited to, a quadrupole mass spectrometer, a time-of-flight mass spectrometer, a fourier transform mass spectrometer, a linear ion trap, 3-D ion trap, or an orbitrap mass spectrometer. 
     All such modifications or variations are believed to be within the sphere and scope of the applicant&#39;s teachings as defined by the claims appended hereto.