Reactive etching of GaxAs−y by HCl

The gas phase reactions of HCl with anionic gallium arsenide clusters, GaxAs−y, containing two to six atoms are presented. Reaction rates and product distributions for the primary, secondary, and tertiary reactions are tabulated. HCl etches GaxAs−y by loss of GaCl to form Gax−1AsyH−. These products are also etched by HCl through loss of GaCl to form Gax−2AsyH−2. Those clusters which do not contain gallium either react to lose AsCl (As2H− and As3H−) or react to abstract H+ and form Cl−(AsH−2). Three gallium-containing clusters (GaAs−4, Ga2AsH−, and GaAs2H−2) react by proton abstraction to form Cl− rather than lose GaCl. Two clusters (Ga3As−2 and Ga2As−3) have an additional reaction pathway open to form two neutrals (GaCl and As2) plus a smaller anionic cluster. Formation of GaCl and As2 mimics the etching of bulk gallium arsenide by HCl at elevated temperatures. Five clusters (GaAs−4, Ga2As−3, GaAs4H−, Ga4As−2, and Ga2As−4) exhibit dual populations that can be differentiated kinetically. There is an inverse correlation between bare cluster reactivity and its initial abundance from laser desorption. The only exception is Ga2As−3 which has ∼50% population of a very reactive species that is the most abundant cluster initially desorbed.