before describing exemplary embodiments of the invention , it is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description . the invention is capable of other embodiments and of being practiced or being carried out in various ways . aspects of the present invention provide methods and apparatus for chemical vapor deposition , which may be used , for example , for forming thin films on a substrate . referring to fig2 , an exemplary chemical vapor deposition apparatus 210 is shown . cvd apparatus 210 includes an ampoule or vessel 212 containing a liquid reactant or precursor 211 . the ampoule or vessel 212 may be cylindrical or any other suitable shape . as shown in fig2 , vessel 212 is a closed vessel bounded by interior walls 218 and bottom surface 222 . the liquid reactant 211 is contained within a bottom portion of the vessel 212 . non limiting examples of liquid reactants include such as teos , trimethyl borate , tetraethyl borate , tetraethyl phosphate , tetraethyl phosphite , tetrakis ( dimethylamino ) titanium diethyl analog , water or the like is delivered from a liquid bulk delivery tank . gas inlet conduit 214 provides an inlet port which is connected to a source 250 of carrier gas 230 . the carrier gas may be stored in pressurized containers and the flow of the gas may be controlled by flow regulators and / or mass flow controllers as is known in the art . a diffuser element 232 , which may be in the form of a plate or a disk is inserted in the vessel 212 and extends between interior walls 218 and adjacent bottom surface 222 . the distance “ d ” between the diffuser element 232 and bottom surface 222 according to one or more embodiments is less than about 2 mm . the outer diameter or other cross - sectional dimension of the diffuser element 232 is substantially equal to the inner diameter or other cross - sectional dimension of the vessel 212 . as such , the diffuser element 232 can either be press fit or welded into the vessel and placed at the desired distance from the bottom surface 222 of the vessel so that the outer edges of the diffuser element 232 is in contact with the interior lateral walls of the vessel 212 . the gap or spacing between the bottom surface 222 of the vessel 212 and the diffuser element 232 defines a plenum 226 . gas delivered into this plenum , being confined by the edge of the diffuser plate in contact with the walls , escapes mostly through the pores of the diffuser plate . the diffuser element 232 is made from a porous material . an example of a porous material is a sintered frit . a sintered metal frit may be used to make the diffuser element 232 . an example of a suitable sintered metal is stainless steel . sintered stainless steel porous frits are available from mott corporation , farmington , conn . in one embodiment , the diffuser element is in the form of a disk having a diameter of about 5 . 75 inches , a thickness of about 0 . 078 inches and a pore size of about 40 microns . however , it will be understood that the present invention is not limited to a diffuser element having particular dimensions or pore size . the diffuser element 232 is located in the lower portion of the vessel and submerged in the liquid reactant 211 . gas inlet conduit 214 extends beneath the level of liquid reactant 211 and through the diffuser element 232 . pressurized delivery of carrier gas 230 provides a mixture 32 of vaporized liquid precursor and carrier gas , which then exits the vessel 212 through outlet conduit or port 216 , which is connected to a cvd chamber 260 . it will be appreciated that one or more mass flow controllers or regulators may be connected between the vessel 212 and cvd chamber 260 , which may be a conventional thermal or plasma - enhanced type . for example , such a chamber 260 is described in the following commonly owned issued u . s . pat . no . 5 , 000 , 113 , issued mar . 19 , 1991 to adamik et al . ; u . s . pat . no . 4 , 668 , 365 , issued may 26 , 1987 to foster et al . ; u . s . pat . no . 4 , 579 , 080 , issued apr . 1 , 1986 to benzing et al . ; u . s . pat . no . 4 , 496 , 609 , issued jan . 29 , 1985 to benzing et al . and u . s . pat . no . 4 , 232 , 063 , issued nov . 4 , 1980 to east et al ., the disclosures of which are incorporated by reference herein . in use , the cvd apparatus described immediately above can be used for the manufacture of films or layers on substrates , such as semiconductor substrates . thus a chemical vapor deposition method includes flowing a carrier gas from a gas supply through the liquid reactant 211 via inlet conduit or tube 214 . the flow of carrier gas through the liquid reactant causes the carrier gas and the liquid reactant to flow through the porous member to create a vapor from the liquid and transporting the vapor to a chamber under conditions to convert the liquid reactant to form a layer on a substrate contained within the chamber 260 . according to embodiments of the present invention , the use of a porous member extending across the cross section of the vessel 212 results in negligible microdroplet formation and incorporation in the mixed gas stream of carrier and liquid precursor vapor . this also permits more effective consumption of the liquid reactant by utilizing any remaining volume of the liquid precursor due to displacement of the liquid by the fritted disk , and the liquid is absorbed into the pores and microchannels of the porous member . this porous member displaces liquid into a fixed 2 mm gap or plenum between the bottom of the porous member and vessel or ampoule bottom surface . although the invention herein has been described with reference to particular embodiments , it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention . it will be apparent to those skilled in the art that various modifications and variations can be made to the method of the present invention without departing from the spirit and scope of the invention . thus , it is intended that the present invention include modifications and variations that are within the scope of the appended claims and their equivalents .