typically 3±5 nm in size, were used for growing the nanostructures. After the evacuation process was completed, the temperature of the system was elevated to 750 C at a rate of 20 C min ±1 and the pressure was maintained at 30 kPa. Nitrogen was sent through the system at a rate of 50 mL min ±1 to act as a carrier gas to transport the sublimated vapor to cooler regions within the tube furnace for deposition. The asproduced materials were analyzed by scanning electron microscopy and high-resolution transmission electron microscopy. The shape of a crystal is determined by the crystallographic planes that form the surface. The density and symmetry of atoms in different crystallographic planes are not identical, and neither are their electronic structure, bonding, surface energy, and chemical reactivities. Therefore, the ability to tune the shapes of materials directly relates to the ability to tune their properties and stabilities. While many successful attempts have been reported to manipulate the shape of isolated inorganic particles, [1±5] it remains a challenge to systematically modify the shape of particles that are composed of polycrystalline films, or electrode materials. A synthetic method that possesses such an ability is critical to elucidate any shape-dependence of chemical and physical properties. It will also generate many possibilities of improving the efficiency of devices based on semiconducting/metallic electrodes (e.g., photovoltaics, fuel cells, sensors, and battery applications). In this study, we demonstrate a synthetic method that can precisely and homogeneously control the shape of micrometersize cuprous oxide (Cu 2 O) crystals grown onto a conducting substrate. When inorganic crystals are formed under equilibrium conditions, their crystal habit is determined by the relative order of surface energies. Received[6] The fastest crystal growth will occur in the direction perpendicular to the face with the highest surface energy. This results in the elimination of higher-energy surfaces while the lower-energy surfaces increase in area. When organic or inorganic additives are added during the crystal growth process, the relative order of surface energies can be modified. [7] Due to anisotropy in adsorption stability, these additives adsorb onto a certain crystallographic plane more strongly than others. This preferential adsorption lowers the surface energy of the bound plane and hinders the crystal growth perpendicular to this plane, resulting in a change in the final morphology (as depicted in Scheme 1).We are interested in combining this concept with an electrodeposition method in order to produce semiconducting materials as polycrystalline electrodes with a precisely controlled morphology. Although it has been widely accepted that additives in plating solutions generally modify the surface features of inorganic deposits, [8] not many systematic attempts have been made to investigate preferential adsorption of additives to methodically tune particle shapes. Our interest lies specifically in uti...
Morphological control of crystals provides a means of tailoring the interfacial arrangement of atoms and has a vital role in enhancing the desired reactivity or stability of a material. 1 A common method to manipulate crystal habit is to employ a growth medium containing additives that can preferentially adsorb on specific crystallographic planes. [2][3][4][5][6] This changes the direction and rate of crystal growth and results in crystals with different final morphologies. 7,8 Preferential adsorption has been studied by carrying out the crystallization process with various additives and examining the resulting morphologies, from which the effect of additives can be deduced. However, this method cannot methodically elucidate how the relative stabilities of various crystallographic planes change upon the addition of additives. Furthermore, if several additives result in identical final morphologies, it is difficult to study their abilities to stabilize a specific plane in a comparative manner.In this study, we introduce a simple and straightforward approach for systematically studying additives' effects on the stability and growth of various crystallographic planes of growing crystals. In our method, we pre-form crystals with well-defined shapes (e.g., cubic, octahedral) and resume their crystallization in a medium that contains the additive to be studied. This method makes it possible to study additives' interactions with specific planes (e.g., {100} of a cube and {111} of an octahedron) that already exist. By monitoring how the original shapes transform over time, the role and strength of habit modifiers can be studied in a more methodical manner. Here, we describe our approach for the electrocrystallization of Cu 2 O crystals, which enabled us to determine the relative stabilities of the {100}, {111}, and {110} planes of Cu 2 O in various growth media. Through this study, a scheme to create new crystal morphologies that cannot be formed via preferential adsorption alone is also devised.The cubic Cu 2 O crystals used in this study were first galvanostatically deposited (constant current deposition, I ) 0.3 mA/cm 2 ) in a 0.02 M Cu(NO 3 ) 2 solution for 5 min. 9 The effect of NO 3 -ions on stabilizing {100} planes of Cu 2 O has been reported previously. 10 The resulting cubic crystals are uniform in shape and size, but their orientations are random due to the polycrystalline nature of the ITO electrodes used as working electrodes (Supporting Information). Therefore, crystal images with two different orientations ({100} and {111} planes parallel to the substrate) are shown for results discussed in this study to best demonstrate the crystal morphologies. Figure 1 shows scanning electron micrographs (SEM) of Cu 2 O crystals obtained when the galvanostatic deposition (I ) 0.3 mA/ cm 2 for 5 min) was resumed with the addition of 0.17 M NaNO 3 , Na 2 SO 4 , NH 4 NO 3 , or (NH 4 ) 2 SO 4 as a habit modifier to the original plating medium. Crystals grown in the presence of NaNO 3 maintain the same cubic morphology, ind...
A basic crystal shape is determined by habit formation and branching growth. Control of these processes leads to an enormous degree of synthetic freedom in generating crystal shapes. The vast array of architectures obtained for cuprous oxide during electrochemical growth is shown. For more details see the Communication by K.-S. Choi and M. J. Siegfried on the following pages. 3218
Ein neues Niveau in der Programmierbarkeit und Freiheit beim Steuern des Kristallwachstums von Kupfer(I)‐oxid wurde durch die systematische Einstellung des Verzweigungsgrades und des Kristallhabitus während der Elektroabscheidung erreicht. Beispiele von Cu2O‐Kristallen, in denen diese Merkmale mithilfe rational entworfener Wachstumsbedingungen und ‐geschichten festgelegt wurden, sind gezeigt (Maßstab: 1 μm).
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