= Solution
The main characteristic peaks identify \b[<nickel> and <phosphorus>]: the spectrum has a strong Ni $K\alpha$ peak near $7.48\,\mathrm{keV}$, the Ni $L$ region near $0.85\,\mathrm{keV}$ and P $K\alpha$ near $2.01\,\mathrm{keV}$. Weaker associated lines, including Ni $K\beta$ near $8.26\,\mathrm{keV}$, can accompany them. The continuous background is <bremsstrahlung> from decelerated <electrons>.
Small <carbon> and <oxygen> signals at low <energy> can arise from contamination, surface <oxide> or preparation materials; a <copper> contribution can arise from the adjacent substrate within the finite interaction volume. The Cu $L$ region lies close to Ni $L$, so overlap is particularly troublesome at low <energy>. A weak Cu $K\alpha$ contribution near $8.04\,\mathrm{keV}$ is better separated, though still close to Ni $K\beta$. At $30\,\mathrm{kV}$ the beam can excite these K lines.
Peak height is not an <atomic fraction>: <ionization> cross-sections, <fluorescence> yields, absorption, detector response, background and line overlap require correction. The large <nickel> peak therefore supports the nickel-rich assignment but does not directly give the nickel-to-phosphorus atomic ratio.
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