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Rev. Materials"],"accepted":{"date-parts":[[2025,8,12]]},"abstract":"<jats:p>\n                    Superconducting radio-frequency cavities, critical components of modern particle accelerators and quantum computing hardware, fundamentally rely on the surface properties of niobium. However, native oxide formation and impurity uptake in the near-surface region can degrade superconducting performance and increase radio-frequency losses during operation. In this study, we present a systematic  x-ray reflectivity investigation of (110) niobium single-crystal surfaces with and without an atomic layer deposited\n                    <a:math xmlns:a=\"http:\/\/www.w3.org\/1998\/Math\/MathML\">\n                      <a:mrow>\n                        <a:msub>\n                          <a:mtext>Al<\/a:mtext>\n                          <a:mn>2<\/a:mn>\n                        <\/a:msub>\n                        <a:msub>\n                          <a:mtext>O<\/a:mtext>\n                          <a:mn>3<\/a:mn>\n                        <\/a:msub>\n                      <\/a:mrow>\n                    <\/a:math>\n                    capping layer under ultrahigh-vacuum conditions up to\n                    <b:math xmlns:b=\"http:\/\/www.w3.org\/1998\/Math\/MathML\">\n                      <b:mrow>\n                        <b:mn>650<\/b:mn>\n                        <b:msup>\n                          <b:mspace width=\"0.16em\"\/>\n                          <b:mo>\u2218<\/b:mo>\n                        <\/b:msup>\n                        <b:mi mathvariant=\"normal\">C<\/b:mi>\n                      <\/b:mrow>\n                    <\/b:math>\n                    . Our results reveal a temperature-dependent reduction of the native niobium oxide layers in both capped and uncapped samples, with similarities in the overall behavior but clear differences in the reduction pathways. The\n                    <e:math xmlns:e=\"http:\/\/www.w3.org\/1998\/Math\/MathML\">\n                      <e:mrow>\n                        <e:msub>\n                          <e:mtext>Al<\/e:mtext>\n                          <e:mn>2<\/e:mn>\n                        <\/e:msub>\n                        <e:msub>\n                          <e:mtext>O<\/e:mtext>\n                          <e:mn>3<\/e:mn>\n                        <\/e:msub>\n                      <\/e:mrow>\n                    <\/e:math>\n                    capping layer modifies the reduction process, prevents oxide regrowth upon air exposure, and protects the niobium surface against impurity uptake during thermal treatment. These findings demonstrate that\n                    <f:math xmlns:f=\"http:\/\/www.w3.org\/1998\/Math\/MathML\">\n                      <f:mrow>\n                        <f:msub>\n                          <f:mtext>Al<\/f:mtext>\n                          <f:mn>2<\/f:mn>\n                        <\/f:msub>\n                        <f:msub>\n                          <f:mtext>O<\/f:mtext>\n                          <f:mn>3<\/f:mn>\n                        <\/f:msub>\n                      <\/f:mrow>\n                    <\/f:math>\n                    capping is an effective strategy to suppress native oxide formation during thermal cycling, offering clear benefits for the performance and operational lifetime of superconducting radio-frequency cavities and related quantum computing technologies.\n                  <\/jats:p>","DOI":"10.1103\/48mp-wypj","type":"journal-article","created":{"date-parts":[[2025,9,24]],"date-time":"2025-09-24T17:30:44Z","timestamp":1758735044000},"update-policy":"https:\/\/doi.org\/10.1103\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Influence of an\n                    <mml:math xmlns:mml=\"http:\/\/www.w3.org\/1998\/Math\/MathML\">\n                      <mml:mrow>\n                        <mml:msub>\n                          <mml:mi>Al<\/mml:mi>\n                          <mml:mn>2<\/mml:mn>\n                        <\/mml:msub>\n                        <mml:msub>\n                          <mml:mi mathvariant=\"normal\">O<\/mml:mi>\n                          <mml:mn>3<\/mml:mn>\n                        <\/mml:msub>\n                      <\/mml:mrow>\n                    <\/mml:math>\n                    capping layer on the thermal reduction of the native niobium oxide: An in situ x-ray reflectivity 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