BERKELEY, Calif. -- Scientists at the University of California, Berkeley said Monday that they have taken a big step on the long road to developing materials that could render people and objects invisible to the human eye.

Speaking at a news conference at Etcheverry Hall on campus, several graduate students said the development of an invisibility cloak, a popular subject in science fiction and Harry Potter novels, is probably still many years away.

But they said their success in engineering for the first time three-dimensional materials that can reverse the natural direction of visible and near-infrared light could help form the basis for higher resolution optical imaging and nanocircuits for high-powered computers.

Previously, researchers have only been able to cloak very thin two-dimensional objects.

The findings by research teams headed by Xiang Zhang, professor at UC-Berkeley's Nanoscale Science and Engineering Center, will be published this week in the journals "Nature" and "Science."

Researcher Guy Bartal said, "We are excited because this is a building block for the future."

However, Bartal said developing an invisibility cloak is "a very big challenge" and "will take a lot of energy and time."

Jie Yao, a graduate student, said developing an invisibility cloak is "a very important goal" but one that hasn't yet been achieved.

Jason Valentine, another graduate student, said it's difficult to predict how long it will take to finish developing an invisibility cloak because the field of metamaterials, which are composite materials with extraordinary capabilities of bending electromagnetic waves, is very new, as it's only about 10 years old.

Valentine said the most immediate application from the research being done at UC-Berkeley will involve biological research, such as understanding how cells work.

Bartal said the common thread in metamaterials is negative refraction.

In contrast, he said, all materials found in nature have a positive refractive index, a measure of how much electromagnetic waves are bent when moving from one medium to another.

As an example of negative refraction, Valentine displayed an illustration of a fish swimming underwater which instead appeared to be moving in the air above the water's surface.

He said applications for a metamaterial entail altering how light normally behaves.

In the case of invisibility cloaks or shields, the material would need to curve light waves completely around the object, like a river flowing around a rock.

Valentine said UC-Berkeley researches took two very different approaches to the challenge of creating bulk metamaterials that can exhibit negative refraction in optical frequencies.

Valentine said that in the paper he and several colleagues published in "Nature," researchers stacked together alternating layers of silver and non-conducting magnesium fluoride and cut nanoscale-sized fishnet patterns into the layers to create a bulk optical metamaterial.

Yao said that in the paper he and several other colleagues published in "Science," the metamaterial is composed of silver nanowires grown inside porous aluminum oxide.

The National Science Foundation helped support research into both metamaterials.

The U.S. Army Research Office helped support the work reported in "Nature" and the U.S. Air Force Office of Science Research helped fund the project described in "Science."

Valentine said, "Obviously, there are some military applications" from the research being done at UC-Berkeley and elsewhere.

He said, "The military is interested in metamaterials because it's a new material and has a flexible platform."