A microwave capillary nanodiamond reactor assembly, and methods of making and using same, are provided. In another aspect, a reactor and method use less than 100 W of microwave power within a cavity to create a plasma therein, so a substrate or workpiece is placed in a cool plasma zone of about 350-400° C., while growing diamond on the workpiece in a low temperature synthesis manner. In another aspect, a workpiece is moved within a diamond-growing reactor while plasma is in a plasma cavity of the reactor. Furthermore, an aspect of the present reactor and method moves a plasma generating head of a reactor relative to a workpiece while the workpiece is in the reactor.

BACKGROUND AND SUMMARY

The present disclosure generally pertains to nanodiamond reactors and more particularly to a microwave capillary nanodiamond reactor.

It is known to use chemical vapor deposition (“CVD”) reactors for nanodiamond deposition. For example, commonly owned U.S. Pat. No. 9,890,457 is entitled “Microwave Plasma Reactors” and issued to Asmussen, et al. on Feb. 13, 2018. This patent is incorporated by reference herein. While this patent is a significant advancement in the industry, further improvements are desired.

Other conventional nanodiamond CVD reactors are discussed in Kumar, A., et al., “Formation of Nanodiamonds at Near-Ambient Conditions via Microplasma Dissociation of Ethanol Vapour,” Nature Communications, 4:2618 (Oct. 21, 2013), and Hemanwan, K., et al., “Diamond Synthesis at Atmospheric Pressure by Microwave Capillary Plasma Chemical Vapor Deposition,” Appl. Phys. Lett., 107, 181901 (Nov. 2, 2015). Traditional canonical CVD reactors are connected to a high power magnetron through a rigid waveguide network, and the power levels required for diamond synthesis are approximately 1 KW. Since the substrate is in direct contact with the outer hot plasma zone, diamond deposition can only be formed on a substrate having a melting point well in excess of 1,000° C. Such conventional CVD reactors are very large, stationary and expensive to manufacture and use. Furthermore, there is typically no ability to reposition workpieces relative to plasma within traditional nanodiamond CVD reactors. Additionally, structural and electrical properties of ultra-nano-crystalline diamond films grown in a microwave plasma assisted CVD reactor are discussed in Nikhar, T. and Baryshev, S., et al., “Dynamic Graphitization of Ultra-Nano-Crystalline Diamond and its Effects on Material Resistivity,” J. Appl. Phys., 128, 235305 (Dec. 21, 2020).

In accordance with the present invention, a microwave capillary nanodiamond reactor assembly, and methods of making and using same, are provided. In another aspect, a reactor and method use less than 100 W of microwave power within a cavity to create a plasma therein, so a substrate or workpiece is placed in a cool plasma zone of about 350-400° C., while growing diamond on the workpiece in a low temperature synthesis manner. A further aspect of the present reactor assembly includes a flow-through reactor having a hollow tube intersecting a plasma cavity, connected to a microwave power supply and reaction gas tank, with a workpiece holder movable along the tube.

In another aspect, a workpiece is moved within a diamond-growing reactor while plasma is in a plasma cavity of the reactor. Furthermore, an aspect of the present reactor and method moves a plasma generating head of a reactor relative to a workpiece while the workpiece is in the reactor. Yet another aspect employs a method of using a diamond reactor including depositing a first layer within a microwave powered plasma directly on a substrate, depositing at least a second layer within the microwave powered plasma onto the first layer, at least one of the layers being diamond and at least one of the layers being a different material (for example, sp3 or sp2 hybridization, or a mixture thereof), such as but not being limited to a buffer material or a graphite material; all of the layers being deposited while the substrate remains in the plasma, and/or outside the plasma, and/or while the reactor is operating.

The present reactor is advantageous over traditional systems. For example, the present reactor and method beneficially allow for changes in diamond growth on the workpiece by moving the workpiece-holder in the plasma and tube. The present reactor is well suited for the deposition of diamond films on polymeric substrates for use in biomedical implants, bionic devices, and electrochemical devices, due to the lower manufacturing temperatures. The present reactor (excluding a gas tank and a microwave power supply) has a maximum exterior dimension no greater than 20 cm3as compared to conventional CVD reactors greater than 1 m3, thereby allowing the present reactor to be portable and/or useable in an additive manufacturing machine such as one having a moveable plasma head on a gantry, while accommodating an exposed substrate surface of at least 1 cm2. Additional advantages and features will be disclosed in the following description and appended claims, taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION

A preferred embodiment of a microwave capillary nanodiamond reactor assembly21is illustrated inFIGS.1-4. Reactor assembly21includes a stationary workbench or table23having a horizontal surface25thereon, a microwave power source27, gas supply tanks29, a vacuum pump31, a programmable computer controller33and a reactor35. An upstanding bracket36stationarily couples reactor35to surface25. Reactor35has a plasma cavity37internal to a generally cylindrical and upstanding housing39. An ignitor initiates plasma40in precursor reaction gases, such as H2and/or CH4, from tanks29, within cavity37. The gas pressure within cavity37is about 1-100 Torr, and more preferably about 50-70 Torr, for gas flow of approximately 10 to 500 sccm.

Pressure gauges41, power gauges42, optionally temperature sensors and optionally valves43, are electrically connected to controller33to allow for automated real-time adjustable control of the valves based in-part on output signals from the gauges and sensors. Controller33includes a microprocessor to run programmed software instructions stored in non-transient RAM or ROM memory, to receive input signals, compare the input signals to desired stored values, display output data, and optionally automatically send output signals to adjust the valves and associated plasma.

A hollow, quartz capillary tube51is elongated in a generally horizontal direction, substantially perpendicular to and intersecting housing39at cavity37. The side arms of tube51and housing39define a generally+ (cross) shape. Tube51may be longer or shorter depending on the gas used and/or substrate size. However, it is preferred that the entire longitudinal length of tube from one side of housing39to the other, be longer than a total exterior length of housing39from its top to its bottom ends. For one example, a uniform internal diameter of tube51is 12.7 mm.

End caps71and72hold distal ends of tube51and include internal passages, and fittings or clamps, for coupling a gas inlet hose73, pressure gauge41and pump outlet hose75thereto. Upstanding brackets77secure end caps71and72to surface25. This embodiment reactor which includes housing39and tube51, but excludes the gas tanks, microwave power supply, pump and controller, preferably has a maximum exterior dimension no greater than 20 cm3. This size and relatively simple mechanical structure advantageously allow for ease of assembly and disassembly, and a light weight and small size, thereby making it portable for transporting to different facilities, use in compact laboratory or manufacturing spaces, and of lower cost as compared to conventional CVD machines.

This reactor configuration serves as a 2.45 GHz microwave discharge cavity (cylindrical/pillbox cavity type) used to transfer the microwave power to the gas mixture, which is contained in the quartz tube acting as a vacuum chamber. An impedance matching stub53is used to match the impedance of the resonant cavity filled with conductive plasma medium to that of a coaxial line55of microwave power supply27. The resonant frequency of this cavity is adjusted by a frequency tuning stub57, and together with the impedance matching, power reflected from the cavity is minimized. In an example, the tubular side arms of the microwave cavity beneficially improve the coupling of the input power to the discharge, and reduce the tendency of arcing between the frequency and impedance matching stubs at optimum tuning conditions. Moreover, a fan79can be employed to externally air-cool reactor35.

A workpiece holder81is a longitudinally elongated rod of approximately 3.18 mm diameter with spaced apart flats for holding multiple substrates or workpieces83thereon. A distal end of holder81is inserted into a sealed aperture of end cap72, and linearly moved into an associated one of the side arms of tube51. In one example, the holder is stainless steel. Holder81may be manually moved or automatically moved via an electromagnetic actuator, such as a stepper motor, solenoid or the like, controlled by controller33. The present assembly and method may optionally move holder81and substrate(s)83thereon in linear and/or rotational directions while the plasma is within the reactor/cavity35and while the diamond layer is being grown upon the substrate. This in-process movement can beneficially create different diamond layer thicknesses across the substrate, if such a design is desired for a specific end use.

The leading substrate83, located closest to the distal end of holder81, is located within a cool zone Bin tube51, which is about 5 cm long and spaced about 1 cm outward from cavity40internal to housing39, shown as a spacing zone A which includes some of plasma40therein. Less than 100 W of microwave power is used to create a plasma within cavity37such that the deposition cool zone B is preferably 350-400° C., which is adjacent to but outside of the plasma cavity. Therefore, this temperature is ideally suited for growing a diamond layer of approximately 5-20 nm grain sizes upon a biomedical polymeric substrate, such as one made from at least one of: parylene, polyethylene, polyketone, polylactide, polyglycolide or the like, which can be subsequently implanted into a human or animal patient. In another configuration, one or more of the substrates83may be of a silicon material. Furthermore, each substrate may optionally have an exposed (to layering) surface area of at least 1 cm2.

In one example using the present reactor assembly, a gas mixture of CH4and H2is used to ignite the plasma under following conditions:Pressure: 1-60 TorrTotal Flow Rate: 10-500 sccmForward Power: 10-70 WReflected Power: 0-2 WVolume % of CH4in total gas mixture: 5-20%.Duration: 2-5 hrsSubstrate: intrinsic Si with and without surface pretreatment (which refers to scratching or seeding the substrate surface by ultrasonically attaching nanodiamond seeds to it in a nano-diamond aqueous solution for 2 minutes).

An alternate embodiment of a microwave capillary nanodiamond reactor assembly121is shown inFIG.5. A sealed vacuum chamber or enclosure122has a bed or holder surface125on a floor thereof. One or more substrates or workpieces183are stationarily mounted upon surface125. A gantry124spans above bed surface125within enclosure122, and is slidable back and forth in longitudinal horizontal directions along outboard rails126, driven by an electromagnetic or fluid powered actuator. A reactor head139, having a partially-internal plasma cavity, and intersecting capillary tube151, are movable in transverse horizontal directions along gantry124. An electromagnetic or fluid powered actuator156drives a transmission, such as a cable or belt and pulley assembly to move reactor head129along the gantry. The reactive gases enter the capillary tube and microwave power is supplied to reactor head139via a cable155. A programmable controller133automatically controls movement of the gantry, head, gas flow, pump, plasma and ignition.

The operating principle and structure are similar to that of the previous embodiment, however, plasma is emitted from an open end of reactor head139toward substrate183. This creates diamond growth and layering184upon substrate183. Notably, a large sized substrate (e.g., with a surface area greater than 1 cm2and more preferably greater than 10 cm2) can be processed with the present reactor head which is beneficially light weight, of small size and portable.

FIG.6shows a different workpiece configuration using any of the previously discussed reactor assemblies. A polymeric or silicon substrate283has a first diamond layer284directly grown thereon, and then a buffer of conductive or insulating layer286deposited thereon, and then a second diamond layer288grown on top of the buffer layer. The present reactor beneficially allows for an automatic controller-varied gas change during the plasma processing, without removal of the workpiece, to cause the different material layering.

Another different workpiece example, using any of the previously discussed reactor assemblies, can be observed with reference toFIG.7. Here, a polymeric or silicon substrate383has a graphite layer384directly grown thereon, and then a diamond layer286is grown thereon. Additional layers may also be deposited. Again, the present reactor beneficially allows for an automatic controller-varied gas change during the plasma processing, without removal of the workpiece, to cause the different material layering. For example, methane plus argon for graphite layering and then methane plus hydrogen for diamond layering, may be used.

Another exemplary configuration provides a method for using a chemical vapor deposition flow through reactor, the method comprising: (a) supplying microwave power of less than 100 W to a cavity within the reactor; (b) creating a plasma within the cavity; (c) locating a workpiece within a zone in a hollow tube intersecting the cavity, the zone comprising at least one of: (i) a cool zone having an internal temperature no greater than 400° C. during step (b); or (ii) a hot zone having an internal temperature no greater than 1,000° C. during step (b); and (d) growing at least one of: a diamond or graphitic layer, on the workpiece within the zone.

While various embodiments have been disclosed, it should be appreciated that additional variations of the reactor and method are also envisioned. For example, different materials, layering combinations and gas combinations may be employed, however, some of the preferred benefits may not be obtained. Additional or different electrical hardware components may be used although certain of the present advantages may not be fully realized. While certain sizes and shapes have been disclosed it should be appreciated that alternate sizes and shapes may be used, although all of the present advantages may not be fully achieved. It is also noteworthy that any of the preceding features may be interchanged and intermixed with any of the others. Accordingly, any and/or all of the dependent claims may depend from all of their preceding claims and may be combined together in any combination. Variations are not to be regarded as a departure from the present disclosure, and all such modifications are entitled to be included within the scope and spirit of the present invention.