ZnTiN2 AS A CARRIER-SELECTIVE PROTECTIVE LAYER

Abstract

The present disclosure relates to a composition that includes a silicon layer having a first surface and a ZnTiN.sub.2 layer having a second surface, where the first surface and the second surface are physically in contact, and the composition is capable of photovoltaic properties when irradiated with light having a wavelength less than 1200 nm.

Claims

1. A composition comprising: a silicon layer having a first surface; and a ZnTiN.sub.2 layer having a second surface, wherein: the first surface and the second surface are physically in contact, and the composition is capable of photovoltaic properties when irradiated with light having a wavelength less than 1200 nm.

2. The composition of claim 1, wherein there is no intervening layer between the first surface and the second surface.

3. The composition of claim 1, wherein the silicon layer is p-type.

4. The composition of claim 1, wherein the ZnTiN.sub.2 layer has the characteristics of an n-type material.

5. The composition of claim 1, wherein the ZnTiN.sub.2 layer has a thickness between 10 nm and 1000 nm.

6. The composition of claim 1, wherein the ZnTiN.sub.2 layer has a wurtzite crystal structure.

7. The composition of claim 1, wherein the ZnTiN.sub.2 layer has a ratio of Zn/(Zn+Ti) between 0.4 and 0.55.

8. The composition of claim 1, further comprising an oxide layer, wherein the ZnTiN.sub.2 layer is positioned between the oxide layer and the silicon layer.

9. The composition of claim 8, wherein the oxide layer comprises at least one of a zinc oxide, a titanium oxide, or a combination thereof.

10. The composition of claim 9, wherein the zinc oxide comprises ZnO.

11. The composition of claim 9, wherein the titanium oxide comprises TiO.sub.2.

12. The composition of claim 8, wherein the oxide layer has a thickness between 5 nm and 1000 nm.

13. The composition of claim 8, wherein the oxide layer has a root-mean-square surface roughness of less than 10 nm.

14. A device comprising: a composition comprising: a silicon layer having a first surface; an oxide layer; and a ZnTiN.sub.2 layer having a second surface; and an electrolyte, wherein: the device is at least partially immersed in an electrolyte, and the oxide layer is positioned such that the oxide layer can be irradiated with light.

15. The device of claim 14, further comprising: an anode and a circuit, wherein: the composition is configured to function as a cathode.

16. The device of claim 14, further comprising: an additional layer comprising a III-V alloy having a bandgap between 1.5 eV and 2.0 eV.

17. The device of claim 16, wherein the additional layer comprises at least one of gallium, indium, and at least one of nitrogen, phosphorus, or a combination thereof.

18. A method utilizing a device, the method comprising: contacting the device with an electrolyte having a pH between 2 and 12; irradiating the device with light; and generating a photovoltage that is substantially independent of the solution potential of a redox couple in the electrolyte.

19. The method of claim 18, wherein the device is configured as a photocathode for water splitting or CO.sub.2 reduction.

20. The method of claim 18, further comprising maintaining an applied potential between +0.5 V and 0.5 V versus RHE at the working electrode while performing a fuel-forming electrochemical reaction.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0009] Some embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting.

[0010] FIG. 1A illustrates a device that includes a silicon layer and a ZnTiN.sub.2 layer, according to some embodiments of the present disclosure. Panel A) illustrates the surfaces of the silicon layer and the ZnTiN.sub.2 layer. Panel B) illustrates the interface resulting from physically contacting the silicon layer with the ZnTiN.sub.2 layer. The device is not drawn to scale.

[0011] FIG. 1B illustrates a device that includes a silicon layer, a ZnTiN.sub.2 layer, and an oxide layer, according to some embodiments of the present disclosure.

[0012] FIG. 2A illustrates an X-ray diffraction pattern of ZnTiN.sub.2 layer on Si, according to some embodiments of the present disclosure.

[0013] FIG. 2B illustrates a scanning electron micrograph of ZnTiN.sub.2 layer on a Si surface tilted at 30 degrees to show texture, according to some embodiments of the present disclosure.

[0014] FIG. 2C illustrates a plot of absorption coefficient vs incident photon energy for ZnTiN.sub.2 layer on Si, determined by spectroscopic ellipsometry, according to some embodiments of the present disclosure. The dashed line corresponds to the approximate bandgap.

[0015] FIG. 3A illustrates cyclic voltammograms for ZnTiN.sub.2/Si and bare Si in aqueous methyl viologen (MV) at pH 3.5, according to some embodiments of the present disclosure.

[0016] FIG. 3B illustrates cyclic voltammograms for ZnTiN.sub.2/Si and bare Si in aqueous methyl viologen (MV) at pH 9, according to some embodiments of the present disclosure.

[0017] FIG. 3C illustrates cyclic voltammograms for ZnTiN.sub.2/Si and bare Si in non-aqueous ferrocenium/ferrocene (Fc) solutions in the dark and under simulated AM1.5G illumination, according to some embodiments of the present disclosure.

[0018] FIG. 4A illustrates a plot of the open circuit voltage (V vs E.sub.sol) of ZnTiN.sub.2/Si and Si photoelectrodes in designated redox couple solutions under simulated AM1.5G illumination, according to some embodiments of the present disclosure. Raw data for representative scans can be found in FIGS. 3A-3C and contents of electrolyte solutions are described in the methods section.

[0019] FIG. 4B illustrates a schematic energy band diagram depicting the junction between ZnTiN.sub.2 and p-type Si in contact with a redox couple, according to some embodiments of the present disclosure. Minimal band bending is expected in the ZnTiN.sub.2 due to the high carrier concentration.

[0020] FIG. 5 illustrates a scanning electron micrograph of the cross-section of ZnTiN.sub.2 layer on Si substrate to corroborate layer thickness extracted from ellipsometry modeling, according to some embodiments of the present disclosure. Accelerating voltage and current were 3 kV and 1.3 nA, respectively.

[0021] FIG. 6 illustrates incident photon to current efficiency measurements for ZnTiN.sub.2/Si and bare Si in 1 mM methyl viologen in pH 3.5 potassium hydrogen phthalate buffer at 0.35 V vs Ag/AgCl applied bias, according to some embodiments of the present disclosure. The solution was not pre-electrolyzed before the IPCE experiment. Dashed line indicates the approximate bandgap of ZnTiN.sub.2 based on the absorption coefficient from spectroscopic ellipsometry. The light source was a Xe arc lamp passed through a monochromator. Spikes at wavelengths >800 nm correspond to Xe emission lines and are the result of a non-linear relationship between the light intensity and the photocurrent response of the photoelectrodes.

[0022] FIG. 7A illustrates current-voltage curves of ZnTiN.sub.2/Si and Si in pH 9 aqueous MV electrolyte under AM1.5G illumination, according to some embodiments of the present disclosure. Electrodes were stored in 0.1 M KHCO.sub.3 solution at pH 10.5 without N.sub.2 purging for the designated amounts of time in between measurements in the MV solution. Electrodes were disconnected from the potentiostat while stored in 0.1 M KHCO.sub.3.

[0023] FIG. 7B illustrates open circuit voltage (V.sub.OC) vs E.sub.sol of ZnTiN.sub.2/Si and Si in pH 9 MV solution after storage in pH 10.5, 0.1 M KHCO.sub.3 solution for the designated amounts of time, according to some embodiments of the present disclosure.

[0024] FIG. 8A illustrates normalized photocurrent for ZnTiN.sub.2/Si and Si under simulated AM1.5G at +0.1 V vs E.sub.sol in pH 3.5 aqueous MV, according to some embodiments of the present disclosure.

[0025] FIG. 8B illustrates current-voltage curves at designated time points during the illuminated chronoamperometry experiment, according to some embodiments of the present disclosure.

[0026] FIG. 8C illustrates a plot of the change in V.sub.OC over the course of the chronoamperometry experiment, according to some embodiments of the present disclosure.

[0027] FIG. 9A illustrates a bar plot depicting the bulk elemental abundance of Zn, Ti, N, and O by EDS on ZnTiN.sub.2/Si photoelectrodes without exposure to electrolyte (control; left) and after photoelectrochemical operation in pH 3.5 (middle) and pH 9 (right) MV electrolyte, according to some embodiments of the present disclosure. Data were taken using an accelerating voltage of 3 kV.

[0028] FIG. 9B illustrates a bar plot depicting the surface elemental composition of Zn, Ti, N, and O by XPS on a ZnTiN.sub.2/Si layer that was not made into an electrode or placed in electrolyte (No electrolyte; left) and on ZnTiN.sub.2/Si photoelectrodes after PEC operation in pH 3.5 (middle) and pH 9 (right) electrolyte, according to some embodiments of the present disclosure. All data were normalized to the sum of Zn, Ti, N, and O.

[0029] FIG. 10 illustrates a schematic diagram of a process for fabricating deconstructable photoelectrodes for post-PEC characterization, according to some embodiments of the present disclosure. Step 4 is outlined as the point the photoelectrode can be returned to as a flat geometry for characterization.

[0030] FIG. 11A-11D illustrates XPS spectra for elements for Zn, Ti, N, and O, accordingly, in ZnTiN.sub.2/Si photoelectrodes after photoelectrochemical operation in pH 3.5 (magenta) and pH 9 (orange) MV electrolyte, according to some embodiments of the present disclosure. A layer of ZnTiN.sub.2/Si that was not made into an electrode or exposed to electrolyte was included as a negative control for comparison. The light bars are a guide for the eye based on peak position in the control sample.

[0031] FIG. 12A illustrates current-voltage curve of ZnTiN.sub.2/Si framed to show the small cathodic current at low applied potential and the point at which the current crosses the x-axis, according to some embodiments of the present disclosure.

[0032] FIG. 12B illustrates open circuit voltage measurements at designated time points over 72 hours with the light turned on and off at the designated points, according to some embodiments of the present disclosure. The vertical, dashed line in FIG. 12A corresponds to the voltage of the horizontal, dashed line in FIG. 12B to aid comparison of the data. Illumination was provided by an LED solar simulator.

[0033] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

TABLE-US-00001 REFERENCE NUMERALS 100 composition 110 silicon layer 115 first surface 120 ZnTiN.sub.2 layer 125 second surface 130 interface 140 oxide layer

DETAILED DESCRIPTION

[0034] The embodiments described herein should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein. References in the specification to one embodiment, an embodiment, an example embodiment, some embodiments, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0035] The present disclosure relates to a new type of passivating, protective layer for silicon, that can be used in photovoltaic or photoelectrochemical applications. As shown herein, ZnTiN.sub.2 can produce a heterojunction with p-Si (p-type silicon) that creates a photovoltage independent of the environment in contact with the ZnTiN.sub.2. As a material itself, ZnTiN.sub.2 is promising in that it can form a stable oxide at the surface exposed to the environment, e.g., a gaseous atmosphere or a liquid electrolyte, without the oxide hindering charge transfer.

[0036] FIG. 1A illustrates a composition 100A, according to some embodiments of the present disclosure. The composition 100A includes a silicon layer 110 having a first surface 115 and a ZnTiN.sub.2 layer 120 having a second surface 125. Panel A of FIG. 1A illustrates the silicon layer 110 and the ZnTiN.sub.2 layer 120 separated to clearly indicate the first surface 115 and the second surface 125, whereas Panel B of FIG. 1A illustrates an interface 130 resulting from placing the first surface 115 and the second surface 125 in physical contact with each other, as would be present in an actual device. As illustrated, the first surface 115 and the second surface 125 form a solid/solid interface. The composition 100A does not have an intervening layer between the first surface 115 and the second surface 125. Further, as shown herein, the composition 100A is capable of demonstrating photovoltaic properties when irradiated with light having a wavelength longer than 500 nm or between 500 nm and 1100 nm. Referring again to FIG. 1A, for water-splitting applications, the ZnTiN.sub.2 layer 120 is both irradiated with light and immersed in an electrolyte. For PV applications, the ZnTiN.sub.2 layer 120 is both irradiated with light and exposed to the local environment, e.g., the atmosphere for terrestrial applications or space for space applications.

[0037] In some embodiments of the present disclosure, a silicon layer 110 may be p-type, due to the presence of a dopant. In some embodiments of the present disclosure, a silicon layer 110 may include a p-type dopant, with examples including at least one of gallium and/or boron. In some embodiments of the present disclosure, a ZnTiN.sub.2 layer 120 may have the characteristics of an n-type material. In some embodiments of the present disclosure, a p-type silicon layer 110 and an n-type ZnTiN.sub.2 layer 120 may form a heterojunction capable of creating a photovoltage. In some embodiments of the present disclosure, a silicon layer 110 may have a thickness between 10 m and 1000 m, or between 100 m and 1000 m, or between 150 m and 250 m. In some embodiments of the present disclosure, a ZnTiN.sub.2 120 layer may have a thickness between 10 nm and 1000 nm or between 50 nm and 100 nm.

[0038] FIG. 1B illustrates a composition 100B that is similar to the composition 100A illustrated in FIG. 1A, except that composition 100B further includes an oxide layer 140, where the ZnTiN.sub.2 layer 120 is positioned between the oxide layer 140 and the silicon layer 110. In some embodiments of the present disclosure, an oxide layer 140 may be constructed of at least one of a zinc oxide (e.g., ZnO), a titanium oxide (e.g., TiO.sub.2), or a combination thereof. In some embodiments of the present disclosure, an oxide layer 140 may have a thickness between 5 nm and 1000 nm or between 5 nm and 25 nm. Referring again to FIG. 1B, for water-splitting applications, the oxide layer 140 is both irradiated with light and immersed in an electrolyte. For PV applications, the oxide layer 140 is both irradiated with light and exposed to the local environment, e.g., the atmosphere for terrestrial applications or space for space applications.

[0039] As described in more detail below, a composition 100 having a silicon layer 110 and a ZnTiN.sub.2 layer 120 may be incorporated into a photovoltaic device, i.e., a solar cell or solar module, and/or a photoelectrochemical device, e.g., a water-splitting device. For the example of photoelectrochemical devices, an oxide layer 140 may provide the benefit of providing a barrier between the oxide layer 140 and underlying device layers; e.g., a silicon layer 110 and a ZnTiN.sub.2 layer 120. Thus, in some embodiments of the present disclosure, an oxide layer 140 may prevent or minimize the chemical degradation of a device when the device is immersed in an electrolyte. As some electrolytes are acidic or basic, with pH values between 4 and 12, such barrier layers can be very advantageous and, as shown herein, by significantly increasing the operational life-span of photoelectrochemical devices that include an oxide layer 140 in their device stack architecture.

[0040] Devices as described above have been constructed and tested. ZnTiN.sub.2 layers 120 were deposited on p-type silicon layers 110 to form ZnTiN.sub.2/Si (120/110) compositions 100A by radio-frequency (RF) co-sputtering to assess the ability of the ZnTiN.sub.2 layers 120 to act as electron-selective and protective layers on silicon photocathodes. Regenerative photoelectrochemical cell (PEC) measurements in aqueous methyl viologen electrolytes of different pH and in non-aqueous ferrocene electrolyte revealed a constant open circuit voltage (V.sub.OC) of 400 mV versus the solution potential (E.sub.sol) for photocathodes having ZnTiN.sub.2/Si compositions (like 110A illustrated in FIG. 1A), while the V.sub.OC of bare Si varied from 220 to 480 mV versus E.sub.sol under the same test conditions. Photocathodes with ZnTiN.sub.2/Si compositions also showed greater durability in the measured V.sub.OC and fill factor (FF) over 72 hours in a 0.1 M KHCO.sub.3 solution at pH 10.5, compared to bare Si photocathodes. Improved photocurrent and photovoltage stability of photocathodes of ZnTiN.sub.2/Si was also demonstrated during aqueous methyl viologen reduction at pH 3.5 over 21 hours under illumination. Energy-dispersive X-ray spectroscopy (EDS) indicated an increase in oxygen content after PEC operation and a pH-dependent change in the cation ratio. This was also supported by X-ray photoelectron spectroscopy (XPS) data (see FIGS. 11A-11D). These results highlight the possibility of using a ZnTiN.sub.2 layer 120 as a carrier-selective, protective layer on silicon photocathodes.

[0041] ZnTiN.sub.2 layers were synthesized for PEC testing using a previously demonstrated synthetic method, described in the following journal article, which is incorporated herein by reference in its entirety: J. Am. Chem. Soc. 2022, 144 (30), 13673-13687. ZnTiN.sub.2 layers 120 were deposited by radiofrequency (RF) co-sputtering onto the polished side of (100)-oriented p-type Si substrates (i.e., silicon layers 110) after removal of surface oxide with dilute HF. The cation ratio (Zn/(Zn+Ti)) across ZnTiN.sub.2 layers 120 was measured by X-ray fluorescence spectroscopy (XRF). Areas of layers chosen as samples for PEC testing were nominally stoichiometric, having a cation ratio of Zn/(Zn+Ti)=(491) %. X-ray diffraction (XRD) patterns were nominally identical across the deposited layers of ZnTiN.sub.2, with a representative pattern illustrated in FIG. 2A. The morphology of a ZnTiN.sub.2 layer is shown in the scanning electron micrograph in FIG. 2B. The absorption spectrum of ZnTiN.sub.2 was modeled from spectroscopic ellipsometry (see FIG. 2C), and the absorption onset around 1.8-2.0 eV indicates an optical bandgap in this range. Modeling of the sub-bandgap free carrier absorption from spectroscopic ellipsometry revealed that the deposited ZnTiN.sub.2 layers had a carrier concentration ca. 210.sup.20 cm.sup.3. As a result of this high carrier concentration, reference ZnTiN.sub.2 layers grown on n-type GaN under similar conditions behaved like conductors rather than semiconductors in PEC current-voltage sweeps.

[0042] Regenerative PEC measurements were performed to study the photocurrent and photovoltage characteristics of unprotected p-type Si photocathodes (i.e., unprotected silicon layers 110, hereafter, Si) and Si photocathodes with a ZnTiN.sub.2 surface layer (i.e., compositions 100A, hereafter, ZnTiN.sub.2/Si). In regenerative photoelectrochemistry, a semiconductor photoelectrode is placed in contact with a solution that contains an outer-sphere, single-electron redox couple to easily create a charge carrier-separating junction without the kinetic complications of multi-electron reactions. For the data reported herein, all working electrode potentials are referenced to E.sub.sol set by the concentrations of the reduced and oxidized species of the redox couple. The V.sub.OC for test photoelectrodes is quoted in mV as shorthand for mV vs E.sub.sol. The ferrocenium/ferrocene redox couple (Fc.sup.+/0, simply referred to as Fc) was prepared by dissolving the reduced and oxidized forms in acetonitrile (0.5 mM Fc.sup.+, 10 mM Fc.sup.0). The methyl viologen couple (MV.sup.2+/+, simply referred to as MV) was prepared in situ by pre-electrolysis of MV.sup.2+ in water to reach approximate concentrations of 49.75 mM and 0.25 mM of MV.sup.2+ and MV, respectively (calculated from the electrochemical potential of 0.507 V vs Ag/AgCl of the resulting electrolyte). Under regenerative conditions such as these with a well-defined solution potential, the V.sub.OC of the illuminated semiconductor electrode is taken to be its photovoltage.

[0043] Cyclic voltammetry scans (CVs) of ZnTiN.sub.2/Si and bare Si in aqueous MV and non-aqueous Fc solution are illustrated in FIGS. 3A-3C with markers indicating the V.sub.OC. Reference electrode (RE) was a small carbon cloth for aqueous measurements and a Pt wire for non-aqueous measurements. Counter electrode (CE) was a large carbon cloth for aqueous measurements and a Pt mesh for non-aqueous measurements. Scan speed was 50 m V/s, and the forward scan proceeded from +0.6 V to 0.2 V. Square (ZnTiN.sub.2/Si) and circular (Si) markers indicate the V.sub.OC of the photoelectrode on the forward scan. Under all conditions, ZnTiN.sub.2/Si and Si both produced negative (reducing) photocurrent under illumination and their illuminated open circuit voltages moved to more positive potentials compared to the dark. This indicates that they both acted as photocathodes. Note that ZnTiN.sub.2/Si showed a lower photocurrent than Si due to parasitic absorption by ZnTiN.sub.2, which is expected based on the absorption onset of ZnTiN.sub.2 illustrated in FIG. 2C and is discussed further below. In pH 3.5 MV, the V.sub.OC for Si and ZnTiN.sub.2/Si was 490 mV and 440 mV, respectively. In pH 9 MV, the Si V.sub.OC decreased to 290 mV, while the ZnTiN.sub.2/Si remained similar at 390 mV. In non-aqueous Fc, the Si V.sub.OC further decreased to 200 mV, while ZnTiN.sub.2/Si remained at 430 mV. The significantly lower photocurrent for both photocathodes in Fc is due to the low concentration of the reducible Fc.sup.+ at 0.5 mM.

[0044] The three electrolyte conditions chosen here help characterize the nature of the carrier-separating junction (solid-liquid vs solid-solid) for each electrode type. For a solid-liquid junction with MV, the V.sub.OC of Si varies with pH because the energy band positions of Si depend on the pH, while the electrochemical potential of MV is independent of the pH, as no protons or hydroxide ions are involved in the redox reaction. This leads to a larger difference between the Fermi level of p-type Si and the electrochemical potential of MV at low pH compared to high pH, leading to more band bending and a larger photovoltage at low pH. This pH dependence was observed for the bare Si photocathode. The V.sub.OC of ZnTiN.sub.2/Si did not change with pH, which indicates the presence of a solid-state heterojunction. In non-aqueous Fc, a small photovoltage from the bare Si photocathode was observed because Fc makes a poorly rectifying junction with p-type Si. This is again a result of the difference between the Fermi level of the photoelectrode and the electrochemical potential of the redox couple. ZnTiN.sub.2/Si preserved its V.sub.OC in these conditions, further supporting the interpretation that a solid-state heterojunction has formed.

[0045] FIG. 4A illustrates the average V.sub.OC for ZnTiN.sub.2/Si and bare Si across the three different redox couple and electrolyte conditions. While the V.sub.OC of Si varied by 260 mV across the three solutions, the V.sub.OC of ZnTiN.sub.2/Si remained steady within error around 400 mV vs E.sub.sol. For a solid-liquid junction, the amount of charge carrier separation (i.e., photovoltage) depends on the solution potential (determined by the redox couple and the pH) and the Fermi level position (e.g., p-type vs n-type doping) of a given semiconductor sample. Since the V.sub.OC of ZnTiN.sub.2/Si is independent of the solution potential, the main charge separation mechanism cannot be the solid-liquid junction. This demonstrates that ZnTiN.sub.2 and Si have formed a carrier-separating heterojunction, with the ZnTiN.sub.2 facilitating electron movement toward the photoelectrode surface, as depicted qualitatively in FIG. 4B. Having a V.sub.OC independent of E.sub.sol is desirable for photoelectrodes that will perform fuel-forming reactions because the attainable V.sub.OC would otherwise be limited by the given semiconductor-redox couple pair.

[0046] As seen in the absorption spectrum in FIG. 2C, ZnTiN.sub.2 absorbs light strongly above 2 eV. The ZnTiN.sub.2 layers were between 180 nm and 190 nm thick, as determined by ellipsometry and confirmed by cross-sectional SEM (see FIG. 5), meaning that at 2.75 eV about 98% of the light was absorbed and could not reach the silicon layer. This reduced the ZnTiN.sub.2/Si photocurrent at shorter wavelengths (confirmed by incident photon to current efficiency measurements, see FIG. 6). This contributes to the lower photocurrent observed for ZnTiN.sub.2/Si in FIGS. 3A-3C. It may be possible to limit thespHAFe optical losses by using a thinner ZnTiN.sub.2 layer (e.g., between 50 nm and 100 nm), although the stability and charge transport implications of a thinner layer would then need to be assessed. Note that in a fuel-forming system, a Si photoabsorber may operate in tandem with a wide bandgap photoabsorber to generate sufficient photovoltage to drive the hydrogen evolution reaction or the CO.sub.2 reduction reaction in concert with oxygen evolution. For example, referring to FIGS. 1A and 1B, a device utilizing a composition (110A and/or 110B) may further include a layer constructed of a III-V semiconductor, where the additional layer may be positioned adjacent and/or in physical contact with the silicon layer 110. For example, such an additional layer may be constructed using an alloy constructed of gallium, indium, and at least one of nitrogen and/or phosphorus having a bandgap between 1.7 eV and 1.8 eV. The photocurrent obtained using a ZnTiN.sub.2/Si composition 110 is thus relevant to more realistic PEC systems, unlike the photocurrent from Si alone. Note that this composition did not include an intentionally deposited oxide layer. However, exposure to the atmosphere will result in at least a monolayer thick ZnO layer due to oxygen in the air.

[0047] The ability of ZnTiN.sub.2 to act as a protective coating as well as an electron-selective contact layer for Si was assessed through comparative PEC durability studies with unprotected Si. Photoelectrode performance was assessed by periodically taking CVs over a 72-hour period in a regenerative pH 9 MV PEC cell. In between CVs, the photoelectrodes were stressed by placing them in a 0.1 M KHCO.sub.3 electrolyte at pH 10.5 without N.sub.2 purging, and without electrical connection to the potentiostat (an ungrounded condition). This stress solution was chosen to have a bicarbonate concentration and pH relevant to CO.sub.2 reduction reaction (CO.sub.2RR) conditions during operation, where the H concentration can significantly decrease at the electrode surface. The CVs taken at each time point for each electrode are illustrated in FIG. 7A (only cathodic scan shown for clarity). The onset of the photocurrent for Si is shown to shift to more cathodic potentials over time, degrading the V.sub.OC and FF. This is due to the formation of highly resistive zinc oxide surface between the photoelectrode and the solution, resulting in higher applied bias to extract charge carriers. By contrast, the shape of the ZnTiN.sub.2/Si current-voltage curve is more stable, with minimal change to the V.sub.OC and FF. This demonstrates protection to the underlying Si. The quantitative change in the V.sub.OC for ZnTiN.sub.2/Si and Si over 72 hours is illustrated in FIG. 7B. The V.sub.OC of ZnTiN.sub.2/Si only slightly decreases, by about 10 mV over 72 hours, with a relatively flat continuing trend. By contrast, the Si V.sub.OC shows a downward trend going from ca. 240 mV to ca. 200 mV after 72 hours. These results demonstrate a protective function of ZnTiN.sub.2 in addition to the added charge carrier separation provided by the layer.

[0048] The stability of ZnTiN.sub.2/Si and Si was further compared under active MV reduction conditions. Chronoamperometry was performed at +0.1 V vs E.sub.sol under AM1.5G illumination for 21 hours in pH 3.5 MV solution; the normalized photocurrent over time is illustrated FIG. 8A. The current for ZnTiN.sub.2/Si decreased by 7% and Si by 19%. CVs were taken at designated time points and forward cathodic scans are plotted in FIG. 8B. Si showed a notable decrease in V.sub.OC and FF within the first hour, and then a second large decrease occurred between hour 6 and 21. By contrast, ZnTiN.sub.2/Si showed a minor decrease in photocurrent in the first hour but remained relatively unchanged over the course of the 21 hours. The quantitative change in V.sub.OC over 21 hours is illustrated in FIG. 8C. The V.sub.OC for ZnTiN.sub.2/Si and Si decreased by about 12 mV and 120 mV, respectively. These data further support a protective effect of the ZnTiN.sub.2 and demonstrate the stability of the layer.

[0049] The ZnTiN.sub.2/Si PEC results presented here (see FIGS. 7A, 7B and FIGS. 8A-8C) indicate that ZnTiN.sub.2 forms protective surface oxides in aqueous solutions under pH and applied bias conditions that are relevant for fuel-forming electrochemical reactions; e.g., a pH between 2 and 12 and an applied bias between +0.5 and 0.5 V versus RHE, with the voltage at the working electrode rather than the full cell potential. To further investigate the formation of surface layers under the photoelectrochemical conditions used here, EDS and XPS were performed on ZnTiN.sub.2/Si samples to determine respective bulk and surface elemental compositions after cumulative exposure to electrolyte for 1 hour at open circuit in the dark and 1 hour at 0 V vs E.sub.sol under illumination in pH 3.5 or pH 9 MV. In these samples, a tape mask was used to define the area exposed to electrolyte, rather than epoxy (modified electrode fabrication scheme illustrated in FIG. 10). For bulk techniques like EDS, this enabled an area never exposed to electrolyte to be directly compared as a control to an area exposed to electrolyte on the same electrode. Surface-sensitive techniques such as XPS used a ZnTiN.sub.2/Si layer that was not made into an electrode or exposed to electrolyte as a control due to potential surface contamination by the tape.

[0050] The bulk elemental abundance of Zn, Ti, N, and O (normalized to the sum of those elements) of ZnTiN.sub.2/Si exposed to pH 3.5 and pH 9 electrolyte was measured by EDS (see FIG. 9A). EDS results from an area unexposed to electrolyte are presented for comparison. The area tested in pH 3.5 MV showed a reduction in the amount of Zn compared to the unexposed area, while the sample tested in pH 9 MV showed no significant change in the cation composition compared to the unexposed area. Both areas exposed to electrolyte showed a higher O content.

[0051] EDS was performed at accelerating voltages of 3 kV and 10 kV for increased surface sensitivity and improved quantitative certainty, respectively. The same trends in elemental composition were observed for both accelerating voltages, and values obtained at 10 kV are illustrated in FIG. 10 and the full elemental percentages are summarized below in Table 1.

TABLE-US-00002 TABLE 1 EDS elemental composition of all observed elements in ZnTiN.sub.2/Si samples in areas unexposed and exposed to electrolyte (All values 5%) Zn/(Zn + Ti) Zn Ti N O C Si 3 kV pH 3.5 Unexposed 0.49 17.89 18.91 36.26 9.88 16.25 0.81 Exposed 0.38 12.30 19.73 33.01 13.81 20.24 0.90 pH 9 Unexposed 0.49 17.98 18.45 34.27 10.31 18.49 0.50 Exposed 0.51 18.36 17.68 33.51 16.44 12.71 1.30 10 kV pH 3.5 Unexposed 0.49 7.95 8.22 25.70 5.63 23.02 29.48 Exposed 0.36 4.29 7.71 23.87 6.84 21.65 35.64 pH 9 Unexposed 0.51 9.33 9.10 27.97 5.82 19.93 27.85 Exposed 0.48 8.69 9.43 27.26 8.21 15.85 30.56

[0052] Surface elemental composition data from XPS are illustrated FIG. 9B for Zn, Ti, N, and O, normalized to the sum of these elements (full results provided in Table 2). The elemental composition from XPS was generally in line with the findings from EDS, with Zn becoming less prevalent on the surface after exposure to pH 3.5 MV and minimal change in the surface cation concentrations after PEC operation in pH 9 MV. The oxygen content was high in all samples, resulting in no significant change in surface oxygen after exposure to electrolyte. High surface oxygen content on the no electrolyte sample is likely due to handling and storage in air for long periods of time (days). XPS also showed that the surface of the no electrolyte control sample was Zn-rich (see FIGS. 11A-11D).

TABLE-US-00003 TABLE 2 XPS elemental composition of all observed elements in ZnTiN.sub.2/Si samples (All values 5%) Zn/(Zn + Ti) Zn Ti N O C Si Cl NO 0.763 8.55 2.65 4.97 32.34 50.02 n.d. 1.47 ELECTROLYTE PH 3.5 0.289 1.99 4.90 6.05 25.99 55.92 4.62 0.52 PH 9 0.837 6.64 1.29 4.11 23.04 54.98 3.95 5.99

[0053] These data indicate that surface oxides form on ZnTiN.sub.2, but as shown in the PEC data, they do not appear detrimental to charge transfer, unlike what would be expected for highly insulating SiO.sub.x. While the durability data support the formation of protective surface oxides (e.g., ZnO.sub.x and/or TiO.sub.y where 0<x2 and 0<y2 independently of each other), the small cathodic current seen before the onset of MV reduction in the CVs also suggests that slow reactions may be taking place that could be causing long-term corrosion of the layer. The EDS data possibly indicate some thinning of the layer in areas exposed to electrolyte compared to areas not exposed to electrolyte, as the Si abundance appears higher in the electrolyte-exposed areas (see Table 3). However, atomic force microscopy (AFM) does not show a significant change in roughness for ZnTiN.sub.2/Si exposed to electrolyte compared to an as-grown ZnTiN.sub.2/Si layer and overall, the layers remain rather smooth, with post-PEC roughness less than 10 nm.

TABLE-US-00004 TABLE 3 EDS atomic percent of Si in ZnTiN.sub.2/Si samples (All values 5%) 3 kV 10 kV TREATMENT Unexposed Exposed Unexposed Exposed PH 3.5 0.81 0.90 29.48 35.64 PH 9 0.50 1.30 27.85 30.56 AIR EXPOSED 0.32 0.11 23.61 25.40

[0054] Physical and Optoelectronic Characterization: The single XRD peak at 2=36 in FIG. 2A is consistent with the (002) reflection of the wurtzite crystal structure typically adopted by cation-disordered ZnTiN.sub.2. The prominence of this peak indicates a preferential growth in this direction, with the (002) planes oriented nominally parallel to the substrate growth surface. No silicon substrate peaks were observed in this region of 2 as the single (h00) peak occurs at 69 (PDF file No. 01-070-5680). Nanocolumnar growth with triangular faceting is seen in the scanning electron micrograph (see FIG. 2B). This morphology is typical of sputtered metal nitrides grown on non-templating substrates. The absorption spectrum in FIG. 2C was extracted by modeling the raw change in light polarization data with a PSemi-M0 oscillator and a Drude oscillator. The absorption onset around 1.8-2.0 eV indicates an optical bandgap in this range (i.e., light having a wavelength between 619 nm and 289 nm). Fitting the Drude oscillator to the sub-bandgap region revealed a charge carrier concentration of 210.sup.20 cm.sup.3.

[0055] Current-Voltage Behavior of ZnTiN.sub.2 Grown on n-GaN: ZnTiN.sub.2 layers were grown by radio-frequency co-sputtering on GaN substrates (GaN layer grown by MBE on sapphire). To prepare samples as photoelectrodes, an ohmic back contact to GaN was made using electron beam deposition of Ti/Al/Ni/Au, and conductive contacts and wire were electrically insulated from the electrolyte solution using epoxy and a glass tube. A bare n-type GaN substrate was used as a comparison photoelectrode. Current-voltage sweeps for GaN, a conductive carbon electrode, and ZnTiN.sub.2/GaN in non-aqueous Fc were evaluated. These showed that bare GaN acts as a photoanode, passing oxidizing current upon illumination. ZnTiN.sub.2/GaN appears similar to the carbon electrode, with reducing and oxidizing current flowing regardless of illumination. This shows that ZnTiN.sub.2 acts more like a conductor than a semiconductor, a result of its high dopant density.

[0056] Determining the V.sub.OC from Current-Voltage Curves of Si and ZnTiN.sub.2/Si Samples: The open circuit voltage (V.sub.OC) is typically taken as the onset of the photocurrent. For the Fc data, this was determined as the point where the photocurrent crosses the x-axis. In the MV solutions, the oxidative (positive) current was nearly zero at applied potentials positive of the oxidation potential of MV, such that searching for the point where current equals zero does not necessarily yield an accurate result. Additionally, ZnTiN.sub.2/Si displayed a very small (<0.25 mA/cm.sup.2) cathodic current before the onset of MV reduction, so the point where the current crosses the x-axis in the CV does not correspond to the V.sub.OC. This was confirmed by measuring the potential at open circuit under illumination (see FIGS. 12A and 12B). Measurements at open circuit conditions were not taken every hour for bare Si photoelectrodes, so the point where the CV inflected downward was chosen as the V.sub.OC. To determine this point, a numerical approximation of the derivative of the current-voltage curve was taken for both samples and a Savitzky-Golay filter was applied to reduce the noise that is inherently introduced by this mathematical procedure. The voltage at which the derivative or slope was equal to 0.1 mAcm.sup.2/V was found to reasonably approximate (within 30 mV) and follow the same trend of the V.sub.OC as measured by other methods (i.e., by the open circuit measurements for ZnTiN.sub.2/Si and where the CV crossed 0 mA/cm.sup.2 for Si). Therefore, the V.sub.OC in MV plotted in FIGS. 3A-3C, 4A, 4B, 7A, 7B and 8A-8C was taken as the point where the current-voltage curve inflected downward in the cathodic sweep (slope equal to 0.1 mAcm.sup.2/V).

[0057] Cross-sectional SEM to Corroborate Layer Thickness: ZnTiN.sub.2 layer thickness on Si was found to be 190 nm by modeling of spectroscopic ellipsometry data. Cross-sectional SEM imaging corroborated this result, showing a layer thickness of 180 nm (see FIG. 5).

[0058] Incident Photon-to-Current Efficiency (IPCE) Measurement: ZnTiN.sub.2/Si samples exhibited lower photocurrent densities compared to bare Si photocathodes, so IPCE was performed to assess the contribution of parasitic light absorption by the ZnTiN.sub.2 layer. As seen in FIG. 6, the IPCE of ZnTiN.sub.2/Si decreased around the bandgap of ZnTiN.sub.2 identified in the absorption spectrum. These data confirm that Si was the active photoabsorbing material in ZnTiN.sub.2/Si photocathodes and absorption by ZnTiN.sub.2 did not add to the photocurrent, but rather decreased it.

[0059] Deconstructable Photoelectrode Preparation: To more easily characterize ZnTiN.sub.2/Si samples after photoelectrochemical (PEC) treatment, a so-called deconstructable photoelectrode design was developed. As illustrated in FIG. 10, electrodeposition tape was used as a mask to delineate the area that would be exposed to the electrolyte during photoelectrochemical testing. The same GaIn eutectic with Ag paste back contact was used on the unpolished side of the Si wafer. A flat wire coil was attached to the back and epoxied in place. A wire connection and glass tube could then be reversibly attached using electrodeposition tape and parafilm to protect the back contact from the electrolyte. This design allowed disassembly of the electrode to the flat geometry (Step 4 in FIG. 10) for characterization by SEM, XPS, and AFM.

[0060] Energy Dispersive X-Ray Spectroscopy (EDS) of deconstructable electrodes: EDS was used to measure the elemental abundance of Zn, Ti, N, and O in areas of the same electrode that were either unexposed or exposed to electrolyte due to masking with electrodeposition tape. Deconstructable electrodes (fabrication scheme illustrated in FIG. 10) were subjected to 1 h at open circuit in the dark and 1 h at short circuit under simulated sunlight. The EDS measurements taken with a 10 kV accelerating voltage (see FIG. 10) agree with the measurements taken using a 3 kV accelerating voltage (see FIG. 9A), showing a decrease in Zn content in areas exposed to pH 3.5 electrolyte/PEC operation and an increase in O content in areas exposed to electrolyte of either pH. In these plots, the Zn, Ti, N, and O are normalized to the sum of these elements. Table 1 shows the full EDS values summed to the total of all elements detected.

[0061] Note on EDS quantification of Si on ZnTiN.sub.2/Si electrodes in unexposed vs exposed areas: a slight tendency was observed for the exposed areas of samples to have a higher atomic percentage of Si by EDS (Table 3). This included a ZnTiN.sub.2/Si electrode that was prepared with a tape mask but not exposed to electrolyte (air exposed), but the difference was slightly larger in samples exposed to electrolyte. This higher Si signal might suggest that the ZnTiN.sub.2 layer was thinning. Measurements after more prolonged PEC operation would be needed to increase the certainty of this interpretation.

[0062] XPS Characterization of ZnTiN.sub.2/Si: XPS was performed on the same ZnTiN.sub.2/Si photoelectrodes as measured by EDS. XPS was also performed on a control ZnTiN.sub.2/Si layer that was not made into an electrode or exposed to electrolyte for comparison. The elemental composition data is provided in Table 2. XPS indicated that without electrolyte exposure, the ZnTiN.sub.2 layer surface was Zn-rich, while EDS and XRF showed that the bulk cation ratio was near 50:50. After photoelectrochemical testing in pH 3.5 MV, the cation ratio (Zn/(Zn+Ti)) was lower compared to the control sample, consistent with the EDS data. After PEC testing in pH 9 MV, the cation ratio was similar compared to the control sample due to the high starting concentration of Zn in the control. O content was not higher in the samples exposed to electrolyte, likely because the control sample was exposed to air for long periods of time (days), resulting in a high surface O content.

[0063] XPS spectra for Zn, Ti, N, and O are provided in FIGS. 11A-11D. The range of values displayed by the Zn 2p peaks (see FIG. 11A) were consistent with a Zn.sup.2+ oxidation state, which would be expected in ZnO and ZnTiN.sub.2. The slight difference in position as a function of pH might relate to a more ZnO-like or Zn(OH).sub.2-like surface on the control and pH 9 samples and a more ZnN-like contribution to the surface of the pH 3.5 sample. This aligns with expectations from the Pourbaix diagram, as ZnO is not expected to be stable at pH 3.5. The Ti 2p region of FIG. 11B clearly showed multiple peaks, indicating multiple chemical environments around Ti.sup.4+, and the ratio of peak heights depended on sample treatment. The lower energy peak was more prominent in the control sample, whereas the higher energy peak became more prominent after pH 3.5 electrolyte treatment. The high energy peak is consistent with the expectation for TiO.sub.2, as is the appearance of a lower energy peak in the O Is spectrum (see FIG. 11D), providing further evidence for the formation of a TiO.sub.2-like surface after operation in pH 3.5. The Ti 2p peaks became overall less prominent after exposure to pH 9 electrolyte, consistent with the loss of Ti from the surface. The N Is peak around 396 eV (see FIG. 11C) could be consistent with either a nitride or an oxynitride phase. The small peak at higher energy also suggests an oxynitride contribution, which might have become more oxidized after PEC operation at pH 9 to shift the peak to higher binding energy.

[0064] Atomic force microscopy (AFM) roughness of ZnTiN.sub.2/Si after exposure to electrolyte: AFM was performed on ZnTiN.sub.2/Si electrodes that were operated in pH 3.5 and pH 9 MV (described previously) and on a ZnTiN.sub.2/Si layer that was not made into an electrode or exposed to electrolyte as a control. Table 4 provides the average root mean squared (RMS) roughness. There was no significant change in the RMS roughness after operation in pH 3.5 or pH 9 MV for 1 hour in the dark at open circuit and 1 hour under illumination at short circuit. This either indicates that the layers were robust to degradation during PEC operation or that layer degradation occurred uniformly across the surface topography, leaving surface features intact.

TABLE-US-00005 TABLE 4 AFM RMS roughness of ZnTiN.sub.2/Si samples without and with electrolyte exposure TREATMENT Roughness (nm) NO ELECTROLYTE 5.32 PH 3.5 6.07 PH 9 5.14

EXAMPLES

[0065] Example 1. A composition comprising: a silicon layer having a first surface; and a ZnTiN.sub.2 layer having a second surface, wherein: the first surface and the second surface are physically in contact, and the composition is capable of photovoltaic properties when irradiated with light having a wavelength less than 1200 nm or between 300 nm and 1200 nm or between the optical band gap of ZnTiN.sub.2 and 1200 nm.

[0066] Example 2. The composition of Example 1, wherein the optical band gap is between 1.8 eV and 2.0 eV.

[0067] Example 3. The composition of either Example 1 or Example 2, wherein there is no intervening layer between the first surface and the second surface.

[0068] Example 4. The composition of any one of Examples 1-3, wherein the silicon layer is p-type.

[0069] Example 5. The composition of any one of Examples 1-4, wherein the silicon layer comprises at least one of gallium, boron, or a combination thereof.

[0070] Example 6. The composition of any one of Examples 1-1, wherein the silicon layer has a thickness between 10 m and 1000 m, or between 100 m and 1000 m, or between 150 m and 250 m.

[0071] Example 7. The composition of any one of Examples 1-1, wherein the ZnTiN.sub.2 layer has the characteristics of an n-type material.

[0072] Example 8. The composition of any one of Examples 1-1, wherein the ZnTiN.sub.2 layer has a thickness between 10 nm or 1000 nm, or between 100 nm and 300 nm, or between 180 nm and 190 nm, or between 50 nm and 100 nm.

[0073] Example 9. The composition of any one of Examples 1-1, wherein the ZnTiN.sub.2 layer has a wurtzite crystal structure.

[0074] Example 10. The composition of any one of Examples 1-9, wherein the ZnTiN.sub.2 layer has a nanocolumnar morphology.

[0075] Example 11. The composition of any one of Examples 1-10, wherein the nanocolumnar morphology comprises triangular faceting.

[0076] Example 12. The composition of any one of Examples 1-1, wherein the ZnTiN.sub.2 layer has a ratio of Zn/(Zn+Ti) between 0.4 and 0.55 or between 0.48 and 0.52 or between 0.49 and 0.51.

[0077] Example 13. The composition of any one of Examples 1-1, further comprising an oxide layer, wherein the ZnTiN.sub.2 layer is positioned between the oxide layer and the silicon layer.

[0078] Example 14. The composition of any one of Examples 1-13, wherein the oxide layer comprises at least one of a zinc oxide, a titanium oxide, or a combination thereof.

[0079] Example 15. The composition of any one of Examples 1-14, wherein the zinc oxide comprises ZnO.

[0080] Example 16. The composition of any one of Examples 1-14, wherein the titanium oxide comprises TiO.sub.2.

[0081] Example 17. The composition of any one of Examples 1-1, wherein the oxide layer has a thickness between 5 nm and 1000 nm, or between 5 nm and 25 nm.

[0082] Example 18. The composition of any one of Examples 1-13, wherein the oxide layer has a root-mean-square surface roughness of less than 10 nm.

[0083] Example 19. The composition of any one of Examples 1-1, wherein the composition is resistant to chemical degradation when immersed in an electrolyte.

[0084] Example 20. A device comprising: the composition as recited in any one of Examples 1-19, and an electrolyte, wherein: the device is at least partially immersed in an electrolyte, and the oxide layer is positioned such that the oxide layer can be irradiated with light.

[0085] Example 21. The device of 20, wherein the electrolyte has a pH between 2 and 12.

[0086] Example 22. The device of either Example 20 or Example 21, further comprising: an anode and a circuit, wherein: the composition is configured to function as a cathode.

[0087] Example 23. The device of any one of Examples 20-22, further comprising: an additional layer comprising a III-V alloy having a bandgap between 1.5 eV and 2.0 eV or between 1.7 eV and 1.8 eV.

[0088] Example 24. The device of any one of Examples 20-23, wherein the additional layer comprises at least one of gallium, indium, and at least one of nitrogen, phosphorus, or a combination thereof.

[0089] Example 25. The device of any one of Examples 20-24, wherein the additional layer comprises at least one of GaInN, GaInP, or a combination thereof.

[0090] Example 26. A method utilizing a device as recited in any one of Examples 20-25, the method comprising: contacting the device with an electrolyte having a pH between 2 and 12; irradiating the device with light; and generating a photovoltage that is substantially independent of the solution potential of a redox couple in the electrolyte.

[0091] Example 27. The method of Example 26, wherein the device is configured as a photocathode for water splitting or CO.sub.2 reduction.

[0092] Example 28. The method of either Example 26 or Example 27, wherein the oxide layer comprises TiO.sub.2 after operation in an aqueous solution.

[0093] Example 29. The method of any one of Examples 26-28, further comprising maintaining an applied potential between +0.5 V and 0.5 V versus RHE at the working electrode while performing a fuel-forming electrochemical reaction.

[0094] As used herein the term substantially is used to indicate that exact values are not necessarily attainable. By way of example, one of ordinary skill in the art will understand that in some chemical reactions 100% conversion of a reactant is possible, yet unlikely. Most of a reactant may be converted to a product and conversion of the reactant may asymptotically approach 100% conversion. So, although from a practical perspective 100% of the reactant is converted, from a technical perspective, a small and sometimes difficult to define amount remains. For this example of a chemical reactant, that amount may be relatively easily defined by the detection limits of the instrument used to test for it. However, in many cases, this amount may not be easily defined, hence the use of the term substantially. In some embodiments of the present invention, the term substantially is defined as approaching a specific numeric value or target to within 20%, 15%, 10%, 5%, or within 1% of the value or target. In further embodiments of the present invention, the term substantially is defined as approaching a specific numeric value or target to within 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1% of the value or target.

[0095] As used herein, the term about is used to indicate that exact values are not necessarily attainable. Therefore, the term about is used to indicate this uncertainty limit. In some embodiments of the present invention, the term about is used to indicate an uncertainty limit of less than or equal to 20%, 15%, 10%, 5%, or 1% of a specific numeric value or target. In some embodiments of the present invention, the term about is used to indicate an uncertainty limit of less than or equal to 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1% of a specific numeric value or target.

[0096] The foregoing discussion and examples have been presented for purposes of illustration and description. The foregoing is not intended to limit the aspects, embodiments, or configurations to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the aspects, embodiments, or configurations are grouped together in one or more embodiments, configurations, or aspects for the purpose of streamlining the disclosure. The features of the aspects, embodiments, or configurations, may be combined in alternate aspects, embodiments, or configurations other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the aspects, embodiments, or configurations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment, configuration, or aspect. While certain aspects of conventional technology have been discussed to facilitate disclosure of some embodiments of the present invention, the Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate aspect, embodiment, or configuration.