Shielding effectiveness (dB)

In plain words

How much a protective layer weakens electromagnetic signals passing through it, on a logarithmic scale: 20 dB blocks 99 % of the power, and 60 dB lets through only a millionth.

Going deeper

Shielding effectiveness measures how much of an electromagnetic wave a barrier stops, in decibels: every 10 dB is another factor of ten. Films of conductive 2D flakes reach values that normally require metal sheets, at a fraction of the thickness.

Reflection, absorption and what is left

A wave meeting a conductive film loses energy in three ways. Some is reflected at the front surface, because the impedance mismatch is large. Some is absorbed as it travels through, over a characteristic skin depth that shrinks with conductivity and frequency. And some bounces between the internal surfaces, giving further chances to be absorbed – which matters most in films made of many stacked .

Shielding effectiveness sums these contributions on a logarithmic scale: 20 dB means 99% of the power is blocked, 40 dB means 99.99%, 60 dB means all but a millionth. Commercial requirements are often around 20–40 dB; higher figures matter for sensitive instruments and for isolating components inside a dense package.

Why MXene films are good at it

A good shield needs conductivity and, for a thin one, many internal interfaces. films have both: flakes of Ti₃C₂T_x conduct like a metal – around 4600 S per cm in the films measured – and a film built from stacked flakes provides repeated internal reflections that trap the wave long enough to be absorbed.

The reported numbers are high for the thickness: 92 dB from a 45 µm film, and more than 50 dB from a film only 2.5 µm thick, the best among synthetic materials of comparable thickness at the time. Because the material disperses in water, films can be sprayed, printed or coated onto shapes that metal foil cannot follow, and with polymers trade some performance for flexibility.

Reading the numbers with care

Shielding effectiveness is frequency-dependent, and most reports are for the X band, around 8–12 GHz. Values do not transfer to other bands, and low-frequency magnetic shielding is a different problem that conductivity alone does not solve. Measurement geometry matters too, and thin films are sensitive to how they are clamped and contacted in the .

The comparison should also be fair on what is being ranked: per thickness, per weight, or per volume of material. Copper foil beats these films on absolute performance; the case for 2D films rests on thinness, weight, flexibility and processability. And the same oxidation that limits MXenes elsewhere limits them here, since conductivity falls as films age.

For specialists

The attenuation of electromagnetic radiation by a shield; 20 dB blocks 99% of power, 60 dB blocks 99.9999%.

Where this comes from

Electromagnetic interference shielding with 2D transition metal carbides (MXenes) Shahzad et al. · Science 353, 1137 (2016) cited by 5,242

Composites and coatings

The biggest market for 2D materials so far: flakes of graphene or other layered materials mixed in small amounts into plastics, rubber, concrete, paints or battery electrodes, to make them stiffer, tougher, more conductive or less permeable. Sold by the tonne, these products use cheap flakes made in bulk rather than perfect single layers. Whether a few percent of flakes really helps depends on how well they are spread out, how they line up and how firmly they hold on to the material around them.

Bulk uses in which exfoliated or chemically derived flakes – graphene nanoplatelets, reduced graphene oxide, hBN, MXenes, clays – are dispersed in a matrix or applied as a film. In polymer composites a few weight percent can raise stiffness and toughness, cross the percolation threshold for electrical conduction – as low as about 0.1 percent by volume for thin, wide flakes – and raise thermal conductivity; aligned flakes in barrier coatings lengthen the diffusion path of water, oxygen and ions and slow corrosion; flakes used as conductive additives replace part of the carbon black in battery electrodes; MXene films give strong electromagnetic shielding. Performance depends on flake size and thickness, dispersion without restacking, alignment and bonding to the matrix, and on powders whose properties vary widely between suppliers.

Full explanation

Silicon photonics

Guiding light instead of electricity through tiny channels on a silicon chip, made with the same factories and tools as ordinary computer chips. Light carries data faster and with less loss over distance, so such chips already connect the servers in data centres. Silicon itself is poor at a few jobs – it hardly emits light, cannot detect the infrared light used in fibre networks, and switches light only weakly – and 2D materials laid on top of the light channels are one way to add the missing functions.

Photonic integrated circuits in silicon-on-insulator, in which submicron silicon waveguides, with their high index contrast to the buried oxide, route light at telecom wavelengths through splitters, rings and gratings made with CMOS tools; germanium detectors and silicon carrier-depletion modulators are standard, and lasers are bonded or grown from III–V semiconductors. 2D materials couple to the evanescent field of the waveguide: graphene gives broadband, fast modulators and photodetectors that can be integrated at wafer scale, thin MoTe₂ and black phosphorus emit and detect in the near infrared, and low-loss phase-change Sb₂S₃ and Sb₂Se₃ give non-volatile switches and tuning. The obstacles are wafer-scale transfer or growth, contacts, optical loss and reproducibility to foundry standards.

Full explanation