1次元構造とは，その中の電子が一方向にしか動けないよrnうに閉じ込められている状態であり，量子細線，原子・分子rn鎖，ナノチューブ，エッジ状態，あるいは異方的な有機・無rn機結晶など，さまざまな物質系で実現されている．しかし，rn厳密に1次元である系はほとんどなく，隣接する1次元ワrnイヤの間で電子の飛び移りが起こったり，ワイヤの幅が有限rnであったりする「擬1次元」系であることが多い．%Several examples are known in which massive arrays of metal atomic chains are formed on semiconductor surfaces that show quasi-one-dimensional electronic structures. Here, Au chains on Si(557) and Si(553), and In chains on Si(111) surfaces are introduced and discussed with experimental data of scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and electrical conductance measurements. They show quasi-one-dimensional Fermi surfaces and parabolic band dispersion along the wires. All of them exhibit metal-insulator transitions and charge-density wave formation due to Peierls instability of the metallic chains. The electrical conductivity, however, reveals the metal-insulator transition only on the less-defective surfaces, while a defective surface does not. The importance of atomic-scale defects on quasi-one-dimensional systems is demonstrated by showing the dramatic decrease of conductivity along the metallic wires with increase of the defect density.
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