Yes. Caping agent affect on geometry. Here keep in mind on concentration of capping agent to prevent the agglomeration. eg. silver nanoparticles capped with 0.1% of PGA shows that the particles have a nearly spherical shape, are smooth-surfaced, and have a low level of agglomeration and a high level of uniformity. But when capped with 0.4% of PGA, particles are much agglomerated and have formed a film.

Yes. Caping agent affect on geometry. Here keep in mind on concentration of capping agent to prevent the agglomeration. eg. silver nanoparticles capped with 0.1% of PGA shows that the particles have a nearly spherical shape, are smooth-surfaced, and have a low level of agglomeration and a high level of uniformity. But when capped with 0.4% of PGA, particles are much agglomerated and have formed a film.

you should choose a capping agent that caps with sulphur/oxygen  for synthesis of semiconductor nano particles. these capping agents ( soft base)  are suitable for  capping semiconductor nanoparticles i.e mainly d block elements ( soft acid). you should also take into the account redox potential of the capping agent for  achieving narrow distribution of nanoparticles.

I like the two answers.

Yes. Capping ligand concentration in the synthesis solution greatly effects the growth dynamics of nanocrystal. In simple words, ligand concentration effects the size and the shape of nanocrystals.

Choice of ligand greatly depends on the application of the nanocrystals (photo voltaic/ photo luminescent). Ligand selection is often linked with the synthesis procedures, because, the procedures are often designed for one (specific) ligand.  

Yes. Surely the capping ligand has the role in controlling the shape of the nanomaterials. you can choose a ligand with thiol or amine groups which can be attached to the nanomaterials and also to prevent the nanomaterials from aggregation, the ligand should have an additional functional groups like amine, carboxylic acid, thiol or any bulky moieties.. These additional groups will prevent the nanomaterials from aggregation by electrostatic repulsion or steric hindrance. for instance, 4-aminothiophenol can be used as stabilizing agent for gold nanoparticles. The thiol moiety will bind to the AuNPs and the amine moiety will prevent the AuNPs from aggregation via amine groups (lone pair-lone pair repulsion between amine groups). 

yes obliviously they affect the particles geometry if we add them while the synthesis  procedure . If we add capping agent just after the synthesis procedure or after the formation of particles it may not have any or much effect on particles geometry because particles already got it shape.  Actually these capping agent assembled and form different type of geometry when dissolved in polar or non polar solvent such as rod, vesicles, and so on...these assembly provide as substrate and result different shape nanoparticle if nucleation and growth take place in presence of them. soft acid as explained in answer 2 are commonly used as capping agent. 

Dear Umer,

Yes, it surely does affect the geometry of the synthesized nanoparticles. The most important step is the concentration of the capping agent used. You need to optimize this concentration by carrying out different experiments. Just say it as you need to use the concentration ranging from 0.1-1% and then observe the change in morphology/geometry. From here you can develop a better understanding. The second part that which kind of capping agent should you use doesn't have a specific answer. Different scientists have used different capping agents and you can try accordingly based on your requirements for a desired geometry.

Good luck!

Yes. Sure. I have an experience in using silica (SiO2) as capping agent for preparation of Magnetite (Fe3O4) nanoparticle. contrastly, without using capping agent, the magnetite particle exist on aggregate form.

Dear Yusran Yusran , particularly In your case (as u said above) it helped to reduce the agglomeration of particles. Then how you concluded capping agent  has effect on geometry.

Many capping ligands act as a shape regulating agents also.. Due to this, capping ligands not only prevent the aggregation but also regulates the shape of nanomaterials.