It seems that every few months, we hear about a new material that may be a wonder semiconductor. We've talked about molybdenum disulfide, borophene, diamond, carbon nanotubes, and graphene. It's clear that researchers are hard at work trying to safeguard the future of the electronics industry, but silicon has stayed the staple of our semiconducting needs—a fact that does not seem likely to change anytime soon.
Still, though, we keep our eyes turned towards the future. And metallic hydrogen has recently joined the race as a possible semiconductor material.
Metallic hydrogen is a form of hydrogen that was theorized to exist almost 100 years ago. Due to the immense pressure needed to get hydrogen into a metallic state, it was believed to only exist in the most inhospitable environments such as the core of a gas giant such as Jupiter. Scientists have tried to produce metallic hydrogen with little success using methods including shock-wave compression and pulsed laser heating.
On October 5th of 2016, two researchers from Harvard University, Ranga Dias and Isaac F. Silvera, released claims that they had produced metallic hydrogen in the laboratory for the first time. The claim mainly comes from the experimental changes found in a hydrogen sample as the pressure was increased on it.
The sample was transparent at first and then turned black as the pressure increased. Finally, the sample became reflective when a pressure of 495GPa was reached.
The two diamonds that created the metallic hydrogen sample. Image credit: R. Dias and I.F. Silvera
So why is metallic hydrogen being called the next wonder material? What makes metallic hydrogen so special and was this sample really metallic hydrogen?
The So-Called “Wonder Material”
As mentioned above, metallic hydrogen was predicted to exist nearly 100 years ago. If the scientists who theorized its existence were right, then they may also have been correct about its potential properties.
Hydrogen on the periodic table of elements sits in the same column as the alkali metals (all having one valence electron in the outermost shell). But, unlike alkali metals, hydrogen forms diatomic bonds instead of metallic bonds and is a non-conductive substance. If hydrogen, however, where to be compacted into some solid material, what properties would it have?
Superconductor phenomena of levitation. Image courtesy of Julian Litzel [CC BY-SA 3.0]
Well, it has been theorized that such a metallic hydrogen substance could be a superconductor at room temperature which would revolutionize modern tech. Such a material could potentially end helium dependence (for devices that require sub-zero cooling such as MRI machines), provide power line distribution with virtually no loss, and enable future semiconductors to operate at ridiculous speeds.
It is also believed that metallic hydrogen may have semiconducting properties which would make it a candidate for the next generation semiconductor materials when the limits of silicon have been reached. But how much of this is true and what are the implications of such a material?
The Substance Sublimes out of the Spotlight
Unfortunately, the sample of metallic hydrogen was lost when one of the diamonds that applied the pressure on the metallic hydrogen sample shattered into a fine dust.
What’s worse is that, despite looking intensively through the diamond dust, the sample was not present anywhere. This has raised questions on whether metallic hydrogen can exist in normal pressures (such as our atmosphere) once it has been produced.
If metallic hydrogen sublimates once created, then such a material may never leave the laboratory and hence remain in the world of researchers rather than designers.
Steps of producing metallic hydrogen. Image credit: R. Dias and I.F. Silvera
There is one controversy about the metallic hydrogen sample that still remains up in the air: how it was created.
The diamond pieces that apply the pressure cannot be directly exposed to the hydrogen sample because there is a chance that hydrogen atoms could enter the diamond structure and weaken it. This is less than ideal when the diamonds have to withstand gigapascals of pressure. Therefore, the research team coated the diamonds in alumina (aluminum oxide) to prevent such diffusion of hydrogen into the diamond structure.
This preventative measure has lead to skepticism regarding the metallic hydrogen sample. The researchers claim that the “shininess” of the sample is evidence of its metallic nature but this may only be due to the alumina coating on the diamonds interfering with the sample.
- Molybdenum Disulfide Transistors Could Be the Next Leap in Microelectronics
- Diamonds Vie to Replace Silicon as Next Semiconductor Material
- Borophene Could Trump Graphene in Flexible Electronics Applications
Is metallic hydrogen, as a superconductor or a potential semiconductor, the future in electronics? Or is this another player in the "next top semiconductor" game? More importantly, was the metallic hydrogen experiment even genuine or just a simple mistake with the alumina coating?
For now, all we can say is that metallic hydrogen is still the stuff of science fiction and a second sample will need to be created before any more claims can be made. One experiment I personally would like to see is the sample being removed from the diamond anvil once produced to see if the sample is stable in normal atmospheric conditions. A material that has to be kept between a pair of diamonds may have great properties but it must be more durable if it's to come outside to play with the big boys such as silicon, graphene, and borophene.