Single crystal YIG nanofilm fabricated by a metal organic decomposition epitaxial growth process

Abstract

A MOD YIG epitaxial process for fabricating YIG nanofilms which, when deposited on GGG substrates, have single crystal epitaxial properties. The films may have thicknesses of 50 nm for a single layer, 100 nm for two layers, and 130 nm for three layers, and have a gyromagnetic ratio of 2.80 MHz per Oe, Gilbert damping ranges from 0.0003 to 0.001, 4M$ values between 1650 G to 1780 G, coercivity from 1 Oe. to 5 Oe, and surface roughness of RMS 0.20 nm for up to 10 layers. Fabrication is economical and uses only a spinner, a drying station (RT to 150 C temperature control), and a quartz tube furnace that accommodates a flowing atmosphere of research grade oxygen, thereby eliminating the need for high vacuum deposition chambers.

Claims

1. A metallic organic decomposition (MOD) epitaxial growth process for making a Y3Fe5O12 (YIG) nanofilm having at least one layer, the method comprising the steps of: providing a crystalline substrate having a planar surface; coating the planar surface of the crystalline substrate with a precursor liquid mixture consisting of yttrium oxide, iron oxide, one or more acids, and one or more organic substances; evenly distributing the precursor liquid to evenly coat the crystalline substrate surface; drying the precursor liquid on the crystalline substrate surface to form a thin film YIG layer; pyrolyzing the thin film YIG layer in a furnace; crystallizing the thin film YIG layer in an annealing furnace at high temperature to remove all organic material from the thin film YIG layer and to promote single crystal crystallization to occur across the entire thin film YIG layer; wherein the resulting nanofilm has a surface roughness between RMS 0.10 nm and 0.20 nm regardless of the number of YIG nanofilm layers; and wherein the resulting multilayer nanofilm the YIG nanofilm ferromagnetic resonance linewidth at frequencies above 10 GHz is reduced due to two magnon scattering, and further wherein the Q factor of the YIG nanofilm's ferromagnetic resonance rises as a function of frequency.

2. The method of claim 1, further including making a plurality of stacked thin film YIG layers to yield a multilayer YIG nanofilm having a total thin film thickness in the range of 50 nm to 500 nm, in steps of approximately 50 nm.

3. The method of claim 1, where the crystalline substrate is a synthetic crystalline substrate having a lattice constant substantially identical to that of YIG.

4. The method of claim 3, wherein the crystalline substrate is gadolinium gallium garnet (Gd3Ga5O12, GGG) 111-oriented substrate.

5. The method of claim 4, further including pre-annealing the GGG substrate in oxygen before the coating step.

6. The method of claim 1, wherein the crystalline substrate is a synthetic crystalline substrate having a surface roughness of RMS 0.10 nm to RMS 0.25 nm.

7. The method of claim 1, wherein the coating step involves using a spinner at speeds between 3000 rpm to 6000 rpm.

8. The method of claim 7, wherein the coating step includes a first spinning step to evenly coat the substrate with the liquid precursor, said first spinning step carried out at speeds at a first spinning speed and a second spinning step carried out at a second spinning speed higher than the first spinning speed to remove dried precursor from the edges of the substrate.

9. The method of claim 1, wherein the drying step involves heating the thin film YIG layer from 1 hour to 24 hours at a temperature of between room temperature of 20 C to 150 C, inclusive.

10. The method of claim 1, wherein the crystalizing step involves annealing involves heating the YIG thin film to approximately 1100 C for approximately 4 hours.

11. The method of claim 10, wherein the annealing is conducted in a quartz tube furnace with a flowing research grade oxygen.

12. The YIG nanofilm of 1, wherein the in-plane ferromagnetic saturation magnetization of the YIG nanofilm is within the range of 1600 gauss to 1800 gauss.

13. The YIG nanofilm of claim 1, wherein in-plane gyromagnetic ratio of the YIG nanofilm is in the range of 2.78 MHz/Oe to 2.82 MHz/Oe.

14. The YIG nanofilm of claim 1, wherein the in-plane ferromagnetic inhomogeneous linewidth of the YIG nanofilm is in the range of 6 Oe to 20 Oe.

15. The YIG nanofilm of claim 1, wherein the in-plane magnetic coercivity of the YIG nanofilm is within the range of 1 Oe to 5 Oe.

16. The YIG nanofilm of claim 1, wherein the Gilbert damping ratio of the YIG nanofilm is in the range of 0.0003 to 0.0010.

17. A metallic organic decomposition (MOD) epitaxial growth process for making a Y3Fe5O12 (YIG) nanofilm, the method comprising the steps of: (a) providing a GGG(111) substrate having a substantially planar substrate surface; (b) coating the GGG(111) substrate surface with a precursor liquid mixture consisting of yttrium oxide, iron oxide, one or more acids, and one or more organic substances; (c) evenly distributing the precursor liquid mixture across the GGG(111) substrate surface; (d) drying the precursor liquid on the crystalline substrate surface to form a thin film YIG layer; (e) crystallizing the thin film YIG layer at high temperature in an annealing furnace such that in a single process the YIG layer is pyrolyzed to remove all organic material, annealed to remove any remaining organic material, and crystallize the YIG layer such that the elemental meal atoms of the YIG lattice combine with oxygen atoms to form a single crystal YIG film according to the lattice pattern of the substantially identical GGG(111) substrate; and further including the step of repeating (b) through (e) to make a YIG nanofilm having multiple layers, wherein steps (c) and (d) involve using a previously crystallized layer of YIG nanofilm as the substrate surface.

18. A metallic organic decomposition (MOD) epitaxial growth process for making a Y3Fe5O12 (YIG) nanofilm, the method comprising the steps of: (a) providing a GGG(111) substrate having a substantially planar substrate surface; (b) coating the GGG(111) substrate surface with a precursor liquid mixture consisting of yttrium oxide, iron oxide, one or more acids, and one or more organic substances; (c) evenly distributing the precursor liquid mixture across the GGG(111) substrate surface; (d) drying the precursor liquid on the crystalline substrate surface to form a thin film YIG layer; (e) crystallizing the thin film YIG layer at high temperature in an annealing furnace such that in a single process the YIG layer is pyrolyzed to remove all organic material, annealed to remove any remaining organic material, and crystallize the YIG layer such that the elemental meal atoms of the YIG lattice combine with oxygen atoms to form a single crystal YIG film according to the lattice pattern of the substantially identical GGG(111) substrate; and wherein after a first crystallization step (e), the method further includes repeating steps (b) through (d) to make a YIG nanofilm having multiple layers, wherein steps (c) and (d) involve using a previously dried layer of YIG nanofilm as the substrate surface, and after a predetermined number of layers have been deposited and dried, a final crystallization step (e) is performed to merge all layers into a single crystal layer.

Description

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

(1) The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

(2) FIG. 1 is a schematic block diagram of a prior art MOD epitaxial YIG fabrication process;

(3) FIG. 2 is a schematic block diagram of the inventive MOD epitaxial YIG nanofilm fabrication process;

(4) FIG. 3 is a top plan schematic view of a spinner apparatus for carrying out the spin coating step for deposition of a precursor liquid onto a GGG(111) substrate;

(5) FIG. 4 is schematic diagram showing a quartz tube annealing furnace of the kind employed in the annealing step in the inventive MOD YIG epitaxial nanofilm fabrication process of the present invention;

(6) FIG. 5 is a highly schematic diagram showing the structural composition of single layer of epitaxial YIG nanofilm as produced in the inventive process;

(7) FIG. 6A is a graphical display of the distribution of the orientation of individual grains of the polycrystalline structure of an MOD epitaxial nanofilm fabricated on a silicon substrate;

(8) FIG. 6B, to contrast with FIG. 6A, is a graphical display of the distribution of the orientation of individual grains of the single crystal structure of an MOD epitaxial nanofilm fabricated on a GGG(111) substrate as in the inventive process;

(9) FIG. 7 is a graph illustrating XRD data of a single layer of YIG nanofilm epitaxially produced on a GGG(111) substrate;

(10) FIG. 8 is a graph showing FMR Gilbert damping constant measurements of single layer YIG on GGG sample, the low damping constant further validating the single crystal structure of the MOD YIG film under test;

(11) FIG. 9 is a graph showing FMR Gilbert damping constant measurement results and inhomogeneous damping constant H0 of a MOD epitaxial sample on GGG (different from that of the sample measured in FIG. 8) as measured at a different test facility;

(12) FIG. 10 includes side-by-side graphs showing, respectively, gyromagnetic ratio and 4Ms as measured by FMR and VSM techniques, showing an extremely low value of coercivity, indicating that epitaxial YIG/GGG nanofilms are extremely soft magnetics;

(13) FIG. 11 is a graph showing XRD data for both one-layer and three-layer epitaxial YIG/GGG nanofilms indicating layer thicknesses of 57 nm for a single layer and 130 nm for three layers;

(14) FIG. 12 is a graph showing the FMR wave form as measured for a single layer of epitaxial YIG/GGG nanofilm at 5 GHz;

(15) FIG. 13 Initial MOKE data is a qualitatively related to the VSM coercivity data shown in FIG. 10;

(16) FIG. 14 is a printout of measured surface roughness of a single layer sample YIG/GGG nanofilm indicating an RMS of 0.177 nm as measured by AFM;

(17) FIG. 15 is a printout showing the surface roughness of a three-layer sample similarly measured; RMS of 0.202 nm;

(18) FIG. 16 is printout of measured parameters showing the surface roughness of a ten-layer sample; RMS of 0.209 nm;

(19) FIG. 17 is a graphical display showing the ten-layer YIG/GGG sample as measured in FIG. 16; and RMS surface roughness of 0.209 nm as measured by AFM methods; and

(20) FIG. 18 is a table comparing the MOD YIG epitaxial nanofilm as fabricated by the inventive method compared with FMR data of other leading YIG epitaxial processes.

DETAILED DESCRIPTION OF THE INVENTION

(21) Referring now to FIGS. 2 through 4, wherein like reference numerals refer to like components in the various views, there is illustrated therein a new and improved metal organic decomposition epitaxial growth process for making YIG nanofilms. The process is generally denominated 10 herein [see FIG. 2].

(22) FIG. 2 schematically illustrates the basic method steps of an embodiment of the inventive method. As can be seen, the method includes: (1a) providing a suitable crystalline substrate, the substrate having a surface with a lattice constant substantially identical to that of YIG, the preferred substrate being GGG(111), and (1b) annealing the substrate surface in an annealing furnace 12; (2) providing and then depositing onto the substrate surface a precursor liquid mixture containing yttrium, iron, and oxygen in predetermined proportions 14; (3) evenly distributing the precursor liquid using a spin coating process to completely and evenly coat the substrate surface 16; (4) drying the precursor liquid on the substrate surface to form a thin film YIG layer; and (5) crystallizing the thin film YIG layer 20 by heating the thin film YIG layer at a first high temperature to pyrolize the layer to remove all organic material from the thin film YIG layer 22, and to anneal the thin film layer at a higher second temperature to remove any remaining organic materials, and to promote single crystal, crystallization to occur across the entire thin film YIG layer 24.

(23) In embodiments, the precursor liquid consists of yttrium oxide, iron oxide, and one or more acids and one or more organic substances.

(24) In embodiments, the precursor composition is a solution comprising:

(25) TABLE-US-00001 Ingredient Formula Conc. by % Wt Iron Oxide (III) Fe2O3 1.1 TO 1.3 Yttrium Oxide Y2O3 1.7 TO 1.9 2-Ethylhexanoicacid C4H9CH(C2H5) COOH 13 TO 18 Stabilizer A, B CxHyOz 8 TO 13 Turpentine 41 TO 46 N-Butylacetate CH3COOC4H9 19 TO 24 Ethylacetate CH3COOC2H5 6 TO 8

(26) Alternative (variant) formulations for the liquid precursor solution include:

(27) TABLE-US-00002 Ingredient Formula Conc. by % Wt Variant #1 Iron Oxide (III) Fe2O3 2.2 to 2.6 Yttrium Oxide Y2O3 1.7 to 1.9 Turpentine 40 to 45 Variant #2 Iron Oxide (III) Fe2O3 1.1 to 1.3 Yttrium Oxide Y2O3 2.4 to 3.3 Turpentine 40 to 45 Variant #3 Iron Oxide (III) Fe2O3 2.2 to 2.6 Yttrium Oxide Y2O3 2.4 to 3.3 Turpentine 39 to 44

(28) In embodiments, the crystalline substrate is GGG, and in further embodiments, GGG(111).

(29) FIG. 3 is a schematic view of the spinner apparatus employed in the spinning step 16 shown in FIG. 2. The step includes using a dropper 32 to deposit a drop of precursor liquid 34 onto a pre-annealed GGG(111) substrate surface 36 disposed on a spinner vacuum plate 38, to evenly coat the GGG(111) substrate surface. The spinning may be carried out in two steps, including an initial spincoat at a first speed (e.g., 3000 rpm) to allow the precursor liquid solvent to evaporate and the liquid to dry, and a second step at a second speed (e.g., 6000 rpm) to remove excess dried precursor from the edges of the substrate surface.

(30) FIG. 4 is schematic diagram showing the annealing furnace 40 that may be employed in the substrate pre-annealing step 12 and the YIG/GGG annealing step 20 in the inventive MOD YIG epitaxial nanofilm fabrication process of the present invention as shown in FIG. 2. While countless sintering and annealing furnace configurations and variations are known, in a most essential aspect the furnace used in the present inventive process is a quartz tube annealing furnace that includes a supply of high purity research grade oxygen 41 fed through a process and control valve, such as a mass flow controller 42, which measures and controls the flow of the oxygen into the inner passage 43 of the furnace quartz tube 44. Heating elements 45 surround a portion of the quartz tube and provide a constant working temperature of 1100 C. under the control of a programmable furnace control box 46. Oxygen flowing out from the furnace is passed through a gas bubbler 47 and then discharged as exhaust into the atmosphere 48.

(31) Looking next at FIG. 5, there is shown in a schematic perspective view the crystal structures 50 of a single crystal layer epitaxial YIG nanofilm 52 on a GGG substrate also having a crystal substrate 54. During fabrication, the YIG epitaxial layer forms during the high temperature annealing step during crystallization (24 and 20, respectively, in FIG. 2). Testing and analysis reveal that the individual grains of the YIG crystal and GGG crystal structures, 56, 58, are aligned in their orientations.

(32) The single crystal YIG on GGG epitaxial growth structure on single layer 50 nm thick YIG nanofilms was confirmed by several well-known measurement techniques. FIG. 6B and FIG. 7 provide EBSD and XRD measurement proof of the single crystal nature of the MOD YIG epitaxial crystal (YIG/GGG) samples produced by the present invention.

(33) FIGS. 6A and 6B provide contrasting graphic displays of the polycrystalline structure of a MOD YIG nanofilm disposed on a silicon substrate 60 (FIG. 6A) and a MOD YIG epitaxial nanofilm disposed on a GGG(111) substrate 62 made using the inventive process. EBSD measurements demonstrate the single crystal nature of the inventive MOD EPI YIG film. FIG. 6B is a black-and-white copy of a color display in which the single crystal nature of the sample was indicated by a nearly uniform color record within the EBSD measurement. By contrast, the sample measurement shown in FIG. 6A is clearly polycrystalline, as demonstrated in the myriad shade variations (color variations in the original graphic display).

(34) FIG. 7 is a graph 70 showing XRD data of a single layer YIG/GGG sample, clearly showing a YIG(444) peak (i.e., a shoulder) 72 next to a much larger peak of GGG(444) 74. YIG layer thickness is calculated from the XRD data to be 57 nm based on the measured fringes.

(35) FIG. 8 is a graph showing an FMR Gilbert damping constant measurement of single layer YIG/GGG sample. The low damping constant found here provides still further proof of the single crystal nature of the MOD YIG/GGG film.

(36) FIG. 9 is another graph 90 showing an FMR Gilbert damping constant as measure at a facility different from the facility that tested the samples for the FIG. 8 graph. With FIG. 8, this graph validates the finding that the Gilbert damping ratios of the YIG/GGG is in the range of 0.0003 to 0.0004. Such low damping ratio numbers again demonstrate the single crystal nature of the MOD YIG/GGG epitaxial samples.

(37) Test Results: It should be noted that FMR measurements are the combined results of magnetic and RF microwave measurements. The measured FMR data is reduced by a curve-fitting procedure involving the Kittel equation and the Landau-Lifshitz linearized model relationship between AH and excitation frequency

(38) The Kittel equation is Fr=(/2)[H(H+4Ms)]

(39) The Landau Lifshitz linearized model relationship is H=H0+(4Fr/3)/

(40) In the Kittel equation, Fr is the ferromagnetic resonant frequency, H is the DC magnetic bias field, 4Ms is the saturation magnetization, is the gyromagnetic ratio, H0 is the inhomogeneous line broadening, and is the Gilbert damping ratio. The Kittel equation is used to determine and 4Ms, the Landau-Lifshitz linear relationship is used to determine H0 and .

(41) Looking ahead to FIG. 12 as an example, experimental FMR waveform data is first mathematically fitted to a perfect Lorentzian wave form, as shown in the graph 120 of FIG. 12. The numerous circles 122 represent experimental data points. The solid line 124 is a Best fit Lorentzian wave form corresponding to the experimental FMR waveform data. A second solid line 126, just below the waveform line, is a measure of the deviation between the experimental data points and the Best fit Lorentzian waveform. With fitting accomplished, the FMR parameters associated with each of the fundamental equations are extracted and presented as a part of the final data. In this way, experimental data is converted into a sample's FMR parameters such as 4Ms, , H0, and a.

(42) FMR tests for the inventive YIG/GGG samples have resulted in very small sample-to-sample measurement variations in and 4Ms for samples of up to three YIG layers. However, significant sample-to-sample variations in the Gilbert damping ratio, , and the inhomogeneous line broadening parameter H0 have been observed. All of the conforming FMR parameters agree closely with well-established values for those parameters using PLD, LPE, and sputtered nanofilm deposition reported by researchers. Initially, measurements of the Gilbert damping ratio was 0.0003, a very good number relative to other types of epitaxial YIG films. Recent measurements closer to the time of filing the instant application have indicated a Gilbert damping ratio spread over the range of 0.0003 to 0.006, slightly higher than data obtained with PLD and LPE techniques. Looking ahead to the table 180 of FIG. 18 (discussed more fully below), there is shown a summary of the measured data, which is based on in-plane magnetic field biasing.

(43) Looking back now at FIG. 10, there is shown side-by-side graphs 100 including a first graph showing gyromagnetic ratio (right graph 102) and a second graph showing saturation magnetization, 4Ms, (left graph 104), as measured by FMR and VSM techniques. The extremely low value of coercivity indicates that the tested epitaxial YIG/GGG nanofilms are extremely soft magnetics. YIG/GGG samples were able to be lifted by small permanent magnets, thus indicating the presence of soft magnetic properties in the samples.

(44) 4Ms data was consistent from sample to sample for up to three YIG layers, using both 5 mm5 mm and 10 mm10 mm samples. Values range from 1650 to 1750 Gauss, corresponding closely to established bulk YIG values (1750 Oe.). Coercivity data was low and consistent for all samples, in the range of (1 to 5 Oe). Low coercivity data indicates that epitaxial YIG film is a very soft magnetagain, see FIG. 10, and FIG. 11, discussed below.

(45) The gyromagnetic ratio data was very consistent for all samples (2.80 MHz per Oe.)

(46) The best values of H0 (inhomogeneous linewidth) and a (Gilbert damping) data were obtained with 5 mm5 mm samples. Larger sample sizes have higher values, and it is hypothesized that the larger sizes may be introducing inhomogeneities in the YIG film, affecting the values of and inhomogeneous linewidth.

(47) XRD measurements of both single layer and three-layer YIG/GGG samples are shown in the graphs 110 of FIG. 11. The data was used to calculate layer thickness, which is 57 nm for a single layer and 130 nm for three layers. FIG. 11 shows the FMR wave 112 form as measured for a single layer of epitaxial YIG/GGG nanofilm at 5 GHz, as well as the wave form 114 measured for three layers of YIG/GGG.

(48) The coercivity data measured by VSM, as shown in FIG. 10, is clearly visible in the graph 130 of FIG. 13, where an uncalibrated measurement was made by MOKE (i.e., Magnetic Optical Kerr Effect) techniques. In MOKE measurements a beam of light is shined at a given angle of incidence on to a sample while a magnetic field is simultaneously applied to the sample at a given angular relationship to the light beam. There are several different relationships that may exist in the angular relationship between the light beam and the magnetic field. It is these angular relationships that determine the MOKE measurement explored. FIG. 13 shows a strong qualitative relationship between the MOKE measurement and the VSM data presented in FIG. 10. However, at present there is no MOKE calibration data, and it is therefore not yet possible to quantitively relate the data in FIG. 10 with the data in FIG. 13.

(49) The surface roughness of multilayer YIG/GGG samples ranges from RMS 0.10 nm to 0.20 nm, as shown in the printouts of the quantitative data, 140, 150, and 160, respectively, of FIGS. 14-16. Up to 10 layers of YIG have been fabricated, and the measured surface roughness indicates a surface roughness of less than RMS 0.20 nm occurring at the top layer of the stack, no matter how many layers of YIG/GGG are measured.

(50) In order, the data 140 of FIG. 140 shows a surface roughness of a single layer sample to be RMS 0.15, as measured by AFM.

(51) The data 150 of FIG. 15 shows the measured surface roughness of a three-layer sample to be RMS 0.20 nm, also as measured by AFM.

(52) The data 160 of FIG. 16, shows the measured surface roughness of a ten-layer sample of YIG/GGG to be RMS 0.20 nm, as measured by AFM. FIG. 17 is a graphic display 170 of the surface of the ten-layer YIG/GGG sample.

(53) Conclusions: a fully functional YIG oscillator or YIG filter requires the presence of a magnet to provide a tunable source of the magnetic bias field necessary for adjusting the oscillators or filter's ferromagnetic resonance (FMR) to a desired operating frequency. Magnetic bias field can be supplied in one of three ways: (1) an electromagnet; (2) a permanent magnet; and (3) a combination of electromagnetic and permanent magnets.

(54) The advantages and disadvantages of each are as follows. Electromagnets are current tunable for selecting the FMR frequency of choice. However, at high frequencies, tuning currents may become excessive, generating undesirable amounts of heat. Permanent magnets require no tuning current but are confined to a single FMR frequency of operation. The combination of an electromagnet and a permanent magnet allows for low tuning current operation near the FMR frequency associated with the permanent magnet, but can be tuned to higher or lower frequencies, using a minimum of electromagnet current.

(55) The MOD process is well known for growing crystals of various materials. However, the MOD YIG epitaxial fabrication process disclosed herein produces single crystal epitaxial YIG nanofilms, and this is the first instance of such an achievement. The advantages of the nanofilm produced by the inventive fabrication process over the known MOD YIG epitaxial fabrication processes may be appreciated by reference to FIG. 18, which is a comparison table 180 comparing FMR data for the YIG/GGG epitaxial nanofilm as fabricated by the inventive method with other leading YIG epitaxial processes.

(56) Electroless Gold Plating: Once fabricated, gold deposition may be employed to connect the YIG nanofilm to other circuit elements, such as amplifiers and oscillators, making thereby incorporating the nanofilm into a complete working system. Gold depositions makes this interconnection possible. In purpose and effect, the gold is an enabler by connecting the nanofilm to other components that make it truly useful.

(57) To that end, the YIG/GGG nanofilm can be electroless plated with gold metal using the following process:

(58) First, the following chemicals and supplies are provided: (1) gold(I) sodium thiosulfate hydrate; (2) L-ascorbic acid sodium salt; (3) diammonium hydrogen phosphate (DAP); and (4) ammonium dihydrogen phosphate (ADP).

(59) Buffer Solution: Next, a pH 6 buffer stock solution is prepared as follows: (1) preparing 400 mL distilled water (DIW) in a beaker, controlling the temperature to hold at with a hotplate and a pH probe; (2) then 12.3 g of DAP is added into the water with magnetic stirring until fully dissolved.

(60) While monitoring the pH level, the ADP is added into the solution until the pH probe reads 5.9-6.1.

(61) Substrate Preparation: Next, the substrate is prepared as follows: (1) first it is cleaned with a 3 minute ultraviolet light (UV) clean; (2) next it is rinsed with DIW, isopropyl alcohol (IPA), and acetone; (3) then it is dried with nitrogen flow.

(62) Next, the substrate is spincoated and pattern photoresist with UV lithography, and then developed.

(63) An electron beam is then used to evaporate 1 nm Ti+175 nm Au, keeping the chamber under vacuum between Ti and Au layers to prevent the formation of titanium oxide.

(64) The photoresist is stripped and the sample cleaned. Observations are recorded as necessary.

(65) Electroless plating process: (1) a 50 mL pH 6 buffer stock is prepared, the temperature controlled by holding it at 30 C. with a hotplate and a magnetic stirrer. (2) of ascorbic acid salt is slowly added into solution until fully dissolved. (3) 0.1225 g of gold sodium thiosulfate is slowly added into solution and allowed to fully dissolve. (4) Using a holding apparatus, the prepared sample is immersed into solution with normal of Au-deposited side being antiparallel to flow of the stirred liquid. (5) Plating is allowed to occur for 1 hour. (6) Finally, the plated nanofilm is rinsed with DIW, IPA, and acetone.

(66) The above disclosure is sufficient to enable one of ordinary skill in the art to practice the invention and provides preferred modes of practicing the invention presently contemplated by the inventors. While there is provided herein a full and complete disclosure of the preferred embodiments, the description is not desired to limit the invention to the exact process steps nor the exact resulting product made by the inventive process. Various modifications, alternative steps, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true spirit and scope of the invention. Such changes might involve alternative materials, components, structural arrangements, sizes, shapes, forms, functions, operational features or the like.

(67) For instance, the variant liquid precursor compositions are contemplated and within the scope of the present invention.

(68) Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is defined by the appended claims.