You will be provided with a reference and some statements. Please determine whether each statement is 'supported', 'unsupported', or 'unknown' with respect to the reference. Please note:
First, assess whether the reference contains any valid content. If the reference contains no valid information, such as a 'page not found' message, then all statements should be considered 'unknown'.
If the reference is valid, for a given statement: if the facts or data it contains can be found entirely or partially within the reference, it is considered 'supported' (data accepts rounding); if all facts and data in the statement cannot be found in the reference, it is considered 'unsupported'.

You should return the result in a JSON list format, where each item in the list contains the statement's index and the judgment result, for example:
[
    {
        "idx": 1,
        "result": "supported"
    },
    {
        "idx": 2,
        "result": "unsupported"
    }
]

Below are the reference and statements:
<reference>
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</reference>

<statements>
1. Below 400°C, the kinetic activation barrier for oxygen migration into the lattice is insufficiently overcome, leaving deep-level amorphization largely unhealed
2. Fluorine radicals react with niobium to generate volatile niobium pentafluoride (NbF5, boiling point 234°C).
3. Atomic Layer Etching represents the ideal approach for damage-free pattern transfer.
4. An exposure of low-pressure reactant gas (for example, O2 plasma or SF6) modifies and chemically saturates the topmost atomic monolayer.
</statements>

Begin the assessment now. Output only the JSON list, without any conversational text or explanations.