EPFL and MIT Researchers Discover the ‘Holy Grail’ of Nanowire Production


Holy Grail Nanowire 5c6d75008f989

EPFL researchers have found a way to control and standardize the production of nanowires on silicon surfaces. Credit: Ecole Polytechnique Federale de Lausanne (EPFL)

Nanowires have the potential to revolutionize the technology around us. Measuring just 5-100 nanometers in diameter (a nanometer is a millionth of a millimeter), these tiny, needle-shaped crystalline structures can alter how electricity or light passes through them.

They can emit, concentrate and absorb light and could therefore be used to add optical functionalities to electronic chips. They could, for example, make it possible to generate lasers directly on  and to integrate single-photon emitters for coding purposes. They could even be applied in  to improve how sunlight is converted into electrical energy.

Up until now, it was impossible to reproduce the process of growing nanowires on silicon semiconductors – there was no way to repeatedly produce homogeneous nanowires in specific positions.

But researchers from EPFL’s Laboratory of Semiconductor Materials, run by Anna Fontcuberta i Morral, together with colleagues from MIT and the IOFFE Institute, have come up with a way of growing nanowire networks in a highly controlled and fully reproducible manner. The key was to understand what happens at the onset of nanowire growth, which goes against currently accepted theories. Their work has been published in Nature Communications.

“We think that this discovery will make it possible to realistically integrate a series of nanowires on silicon substrates,” says Fontcuberta i Morral. “Up to now, these nanowires had to be grown individually, and the process couldn’t be reproduced.”

The holy grail of nanowire production
Two different configurations of the droplet within the opening – hole fully filled and partially filled and bellow illustration of GaAs crystals forming a full ring or a step underneath the large and small gallium droplets. Credit: Ecole Polytechnique Federale de Lausanne (EPFL)

 

Getting the right ratio

The standard process for producing nanowires is to make  in  monoxide and fill them with a nanodrop of liquid gallium. This substance then solidifies when it comes into contact with arsenic. But with this process, the substance tends to harden at the corners of the nanoholes, which means that the angle at which the nanowires will grow can’t be predicted. The search was on for a way to produce homogeneous nanowires and control their position.

Research aimed at controlling the  has tended to focus on the diameter of the hole, but this approach has not paid off. Now EPFL researchers have shown that by altering the diameter-to-height ratio of the hole, they can perfectly control how the nanowires grow. At the right ratio, the substance will solidify in a ring around the edge of the hole, which prevents the nanowires from growing at a non-perpendicular angle. And the researchers’ process should work for all types of .

“It’s kind of like growing a plant. They need water and sunlight, but you have to get the quantities right,” says Fontcuberta i Morral.

This new production technique will be a boon for nanowire research, and further samples should soon be developed.

 Explore further: Nanowires have the power to revolutionize solar energy (w/ video)

More information: J. Vukajlovic-Plestina et al. Fundamental aspects to localize self-catalyzed III-V nanowires on silicon, Nature Communications (2019). DOI: 10.1038/s41467-019-08807-9

 

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Global Renewable Energy Trends From NREL


NREL 20140609_buildings_26954_hpJanuary 26th, 2015  Silvio Marcacci

Accurately assessing renewable energy growth, especially compared to fossil fuels, is one of the biggest challenges facing our clean energy transition. After all, how can you measure progress without adequate benchmarks?

Industry tallies and analyst updates provide the quickest summaries, but they’re either piecemeal or criticized for being slanted. Government data is more reputable and comprehensive, but often lags behind – case in point the National Renewable Energy Laboratory’s (NREL) 2013 Renewable Energy Data Book.

Most of the trends highlighted in NREL’s data are already known, but still this is among the most comprehensive resources available and many of the charts within are incredible reference points. The full report is definitely worth reading, but since most people don’t have time to read through 135 pages, I’ve pulled a few of the most impressive statistics and charts for you.

US renewable electricity generation

American Renewable Energy Grows, But Unevenly

NREL reports renewable energy represented 61% of all new U.S. electricity capacity installations in 2013 to reach 14.8% of total electric capacity and 13.1% of actual power generation. Good stuff, considering renewables were just 9.5% of total generation in 2004, but that growth may slip a bit as renewables only represented 41% of new capacity additions across the first three quarters of 2014.

US electric power and generation 2013

Still, compare renewable energy capacity and generation increases from 2000-2006 to 2007-2013, and it’s clear just how much momentum and traction renewables are generating across the U.S.

US renewable electricity capacity and generation

It’s also worth noting where America’s renewable growth exists. Saying wind and solar are growing fast (more on that later) isn’t news, but seeing those two compared to other technologies like hydropower or geothermal underscores where the action’s at for U.S. renewables. Wind and solar are expanding rapidly while other technologies essentially stay flat.

US renewable electricity capacity by source

Renewables Are Nearly A Quarter Of Global Power

Here are two stats to bookmark – cumulative installed global renewable electricity capacity grew 108% from 2000 to 2013, and contributed 23% of all global power generation in 2013.

Global renewable electricity generation

Again, wind and solar grew fastest among all renewable energy technologies. Wind generation grew by a factor of 18 while solar grew by a factor of 68 between 2000 and 2013. The same trend is apparent worldwide as in America – while hydropower remains the largest source of renewable energy, it’s staying flat.

Global renewable electricity capacity

How High Can Wind Power Soar?

Time for another common theme in NREL’s stats: China is crushing it on wind energy additions. At the end of 2013, China had 91.4GW of cumulative wind power capacity, America 61.1GW, Spain 23GW, India 20.2GW, and a host of others in the 5-10GW range.

Total global wind electricity capacity

If that sounds like a big lead now, consider China added another 20.7GW of wind power in 2014 while America installed just 4.7GW, according to Bloomberg New Energy Finance (BNEF). This yawning gap may narrow a bit in 2015, considering 13.6GW of new wind was under construction in America as of October 2014, but China could set another record this year with 20-23GW new installed wind capacity. 

US wind electricity capacity and generation

Solar Growing Faster Than NREL Can Track

The lag time from industry assessments to government reports is most evident with solar power. NREL reports U.S. solar photovoltaic installed capacity jumped from 7.3GW in 2012 to 12.1GW in 2013, and solar’s growth over time looks truly exponential, but it’s still growing. Just under 4GW new solar PV came online in the U.S. through third quarter 2014, meaning another exponential jump is on the way.

US solar electricity capacity and generation

Even so, America lags in global solar capacity. NREL ranks Germany as the world’s undisputed solar leader with 35.9GW at the end of 2013, but that number only rose to 38.1MW through October 2014, while China and Japan are gaining fast. NREL ranked China second overall with 19.9GW and Japan fourth overall with 13.6GW at the end of 2013, but BNEF forecast 13-14GW new solar in China and 9-11GW new solar in Japan during 2014.

Total global solar electricity capacity

NREL’s data also highlights Asia’s complete dominance in solar manufacturing. Asian nations led all markets with a whopping 86% of the world’s 40GW total PV module production at the end of 2013, and China represented 64% of global production. Europe and America check in at 9% and 2% respectively – still wonder why solar trade wars are raging across the Atlantic and Pacific Oceans?

Global solar PV manufacturing

America Has A Long Way To Go On Energy Efficiency

We’ve long known buildings are the largest energy consumers in America, and NREL’s data once again reminds us of the potential for energy efficiency to cut demand and emissions. U.S. buildings consumed 40.1% of national energy supply in 2013, with residential buildings just a bit higher than commercial buildings.

US energy consumption 2013

Now here’s the interesting part of NREL’s data:. 52.1% of commercial energy consumption and 46% of residential energy consumption in 2013 was due to electrical system energy losses – roughly half of U.S. power demand is wasted! NREL doesn’t strictly define this term, but it generally refers to losses as electricity moves across power lines. Not only is this a huge opportunity for smart grid technologies, but it’s also a powerful reason to shift toward distributed generation away from centralized power supplies.

US residential and commercial energy consumption 2013

Biofuels Dominate Alternative Fuel Consumption

America led worldwide biofuels production (13.3 billion gallons ethanol, 1.8 billion gallons biodiesel) in 2013, more than twice Brazil’s output (6.2 billion gallons ethanol, 766 million gallons biodiesel), so it makes sense biofuels would also dominate U.S. alternative fuel consumption.

Global ethanol production

US renewable and alternative fuel consumption

But while renewable and alternative fuels (including electric vehicles) are growing fast, they’re still minuscule compared to petroleum-based fuels. America’s fuel consumption is at the same time a daunting challenge and a massive opportunity for clean energy technologies.

US traditional fuel consumption

Wait, Why Are We So Excited About Fuel Cells?

Fuel cell vehicles have dominated recent headlines, but NREL’s data is a sobering look at how hydrogen and fuel cells are actually deploying across the global energy system. Stationary fuel cells, used primarily for backup power, grew 25% in 2013 but still only totaled 160MW of installed capacity in 1,137 total systems.

Global fuel cell systems shipped

Fuel cell vehicles are an even smaller piece of this pie. NREL shows transportation fuel cell system capacity holding flat even as stationary fuel cell system capacities have surged in volume. This lack of growth is clearly shown by the number of operational U.S. hydrogen fueling stations – just 53 through December 2013.

Total US hydrogen fueling stations