Chemical Bath Deposition of ZnO Nanowires Using Copper Nitrate as an Additive for Compensating Doping

Abstract

The controlled incorporation of dopants like copper into ZnO nanowires (NWs) grown by chemical bath deposition (CBD) is still challenging despite its critical importance for the development of piezoelectric devices. In this context, the effects of the addition of copper nitrate during the CBD of ZnO NWs grown on Au seed layers are investigated in detail, where zinc nitrate and hexamethylenetetramine are used as standard chemical precursors and ammonia as an additive to tune the pH. By combining thermodynamic simulations with chemical and structural analyses, we show that copper oxide nanocrystals simultaneously form with ZnO NWs during the CBD process in the low-pH region associated with a large supersaturation of Cu species. The Cu(II) and Zn(II) speciation diagrams reveal that both species show very similar behaviors, as they predominantly form either X 2+ ions (with X = Cu or Zn) or X(NH3)4 2+ ion complexes, depending on the pH value. Owing to their similar ionic structures, Cu 2+ and Cu(NH 3 ) 4 2+ ions preferentially formed in the low-and high-pH regions, respectively, are able to compete with the corresponding Zn 2+ and Zn(NH3)4 2+ ions to adsorb on the c-plane top facets of ZnO NWs despite repulsive electrostatic interactions, yielding the significant incorporation of Cu. At the highest pH value, additional attractive electrostatic interactions between the Cu(NH 3 ) 4 2+ ion complexes and negatively charged c-plane top facets further

Modulating the growth of chemically deposited ZnO nanowires and the formation of nitrogen- and hydrogen-related defects using pH adjustment

“…As shown by Lausecker et al, the drastic increase in the axial growth rate prevents the complete formation of the nonpolar m-planes on their sidewalls, hence reducing the size of the NW tip. 14 Simultaneously, an erosion process of the NW top facets by HO À ions at high pH has also been shown. 46 However, the extended growths under dynamic conditions cause the depletion of chemical reactants, promoting a decrease in the axial growth rate and giving the opportunity for the nonpolar m-planes to form.…”

“…ZnO NWs also possess the advantage to be grown by the low-temperature and low-cost solution route of chemical bath deposition (CBD), where their crystallization follows the thermally-activated dehydration of [Zn(H 2 O) 6 ] 2+ ions coming from the Zn(II) ions representing the limiting reactant at low pH, and where their growth is kinetically controlled by the thermally-activated decomposition of hexamethylenetetramine (HMTA) that slowly releases hydroxide ions in an aqueous solution. [6][7][8][9][10] Hence, the understanding of the different experimental parameters such as the chemical precursor concentration, 8,9,11,12 nature of the species present in the solution, 11,[13][14][15][16][17] pH of the solution, 11,18,19 temperature and growth time, 10,20 have shown to play a key role on the morphology, structural, chemical, optical, and electrical properties of ZnO NWs. Universally, the hydronium and hydroxide ions are referred to as the water ions,…”

“… 11 Dahiya et al showed that the addition of ammonium hydroxide (NH 4 OH) slowly degrades the optical response of ZnO NWs through the increase in the concentration of point defects within the pH range of 6.6 to 7.1. 18 Additionally, the intentional doping of ZnO NWs with Al, 15 Ga, 13 and Cu, 14 has been developed through the addition of their respective chemical precursors into the CBD solution with different amounts of ammonia (NH 3 ) within the pH range of ∼7 to ∼11.…”

In situ analysis of the nucleation of O- and Zn-polar ZnO nanowires using synchrotron-based X-ray diffraction

“…[12][13][14] It relies on the heterogeneous formation of ZnO NWs on a dedicated polycrystalline Au 15,16 or ZnO 17,18 seed layer in an aqueous solution containing a zinc salt (e.g., zinc nitrate, zinc acetate, zinc sulfate) with a source of hydroxide ions and complexing agents (e.g., sodium hydroxide, ammonia, hexamethylenetetramine (HMTA)). 19,20 Chemical additives such as polyethylene-imine, 21 chorine ions, 22 citrate ions, 23 and metal nitrate [24][25][26][27] have previously been employed to tune the aspect ratio and electronic conductivity. Importantly, the polarity of the NWs can be controlled by the nucleation surface, 28,29 enabling the formation of O-and Zn-polar ZnO NWs along the 0001 and 0001 directions, respectively.…”

Ab initio расчеты электронных свойств и перенос заряда в Zn-=SUB=-1-x-=/SUB=-Cu-=SUB=-x-=/SUB=-O со структурой вюртцита

“…На свойства нанопорошков ZnO, легированных медью, влияют эффекты отжига, температура и концентрация легирующей примеси Cu [9] Степень растворимости акцепторных примесей, например (Na, Li и N), ограничивает концентрацию дырок в аналогичных с ZnO соединениях ZnSe и ZnTe [11]. Поэтому изучение закономерностей влияния меди на электронную структуру [12], диэлектрические [13], оптические [14,15], магнитные [16][17][18] и другие физические свойства [19] материалов на основе ZnО n-и p-типа также остается проблемой. В связи с возможностью создания миниатюрных приборов, внимание уделяется также легированным нанокристаллическим порошкам и тонким пленкам ZnO [20].…”