Patent Number: 
Section: claims

1. An apparatus for generating a gas-cluster beam, comprising:a gas expansion nozzle mounted in a chamber to cause gas clusters from the expansion nozzle to form a beam passing through the chamber in a predetermined direction and through an aperture at an end of the chamber,wherein the chamber is formed by one or more surfaces surrounding the beam and aperture and located to deflect gas clusters and molecules from the nozzle that are not traveling within and aligned with the beam away from the beam and towards an opposing predetermined direction. 2. The apparatus of claim 1, wherein the one or more surfaces include a conical first surface coaxially surrounding the beam and angled towards the opposing predetermined direction. 3. The apparatus of claim 2, wherein the one or more surfaces include a second flat surface surrounding the aperture and facing the opposing predetermined direction. 4. The apparatus of claim 1, wherein the one or more surfaces include one or more third surfaces facing away from the beam and located immediately surrounding the beam to deflect gas molecules and clusters traveling at more than a predetermined distance from the beam away from the beam. 5. The apparatus of claim 1, further comprising a vacuum apparatus located behind the expansion nozzle for evacuating deflected gas molecules and clusters that are not part of the beam from the chamber in the opposing predetermined direction. 6. The apparatus of claim 1, wherein the gas expansion nozzle is mounted at opposing input and outlet ends using a limited number of elongated members extending from sides of the chamber to allow easy flow of gas molecules and clusters that are not part of the beam in the opposing predetermined direction. 7. The apparatus of claim 6, wherein the gas expansion nozzle is adjustably mounted at the outlet end of the nozzle to enable adjustment of the predetermined direction. 8. The apparatus of claim 7, wherein the gas expansion nozzle is tiltably mounted at the input end of the nozzle to support adjustment of the predetermined direction at the outlet end of the nozzle. 9. The apparatus of claim 1, wherein the one or more surfaces has substantially the shape of a cone or a pyramid or a elliptic paraboloid or an ellipsoid. 10. The apparatus of claim 1, further comprising a second chamber surrounding the gas cluster beam beyond the aperture and the first said chamber and having a second aperture located for allowing further flow of the gas cluster beam. 11. The apparatus of claim 10, further comprising one or more fourth surfaces facing away from the beam and located immediately surrounding the beam at the second aperture for deflecting gas molecules and clusters traveling at more than a predetermined distance from the beam away from the beam. 12. The apparatus of claim 11, wherein the gas expansion nozzle is mounted at input and outlet ends, and further wherein the outlet end is adjustably mounted to enable adjustment of the predetermined direction. 13. The apparatus of claim 10, wherein the second chamber is formed by at least one plane surface oriented at an angle of from 30° to about 60° with respect to the gas cluster beam and adapted to direct gas molecules and clusters that are not part of the beam away from the beam. 14. The apparatus of claim 1, wherein the one or more surfaces surrounds substantially all of the beam located within the chamber. 15. A gas-cluster ion-beam processing apparatus comprisingthe gas-cluster beam generator apparatus of claim 1 for generating a gas-cluster beam;an ionizer for ionizing at least a portion of the gas-cluster beam to form a gas-cluster ion-beam having a path; anda workpiece holder for supporting a workpiece in the path of the gas-cluster ion-beam. 16. The gas-cluster ion-beam processing apparatus of claim 15, further comprising a differential pumping chamber having a plane surface oriented at an angle of from about 30 degrees to about 60 degrees with respect to a gas-cluster beam trajectory and adapted to direct at least a portion of un-clustered gas into a vacuum pump. 17. A method for generating a gas-cluster beam, comprising the steps of:directing a gas expansion nozzle into a chamber to cause gas clusters from the expansion nozzle to form a beam passing through the chamber in a predetermined direction and through an aperture at an end of the chamber;deflecting gas clusters and molecules from the nozzle that are not traveling within and aligned with the beam away from the beam and towards an opposing predetermined direction using walls of the chamber that surround the beam and aperture; andcreating a vacuum behind the expansion nozzle for evacuating deflected gas molecules and clusters that are not part of the beam from the chamber. 18. The method of claim 17, wherein the step of directing includes adjustably mounting the outlet end of the nozzle and adjusting the predetermined direction.