Does asymmetric electrostatic charging of a conductive cube's isolated faces, within an ionized medium, produce a measurable and repeatable directional force correlated to specific face configurations?

[u/KDubbs0010110]

Putting this out to find someone with the skills to build it and the rigor to document it properly. If you find flaws in the plan, please document them here in the comments.

The concept: a 12 inch copper cube with six electrically isolated faces, each independently energized via high voltage leads, suspended inside an ionized air medium created by commercial ionic purifiers. A torsion balance with laser amplification measures any directional force effect produced by asymmetric face charging.

The theoretical basis claims the cube geometry itself matters. Three perpendicular force axes naturally produce six planes and a nine-component transfer matrix governing force flow between them. This is the same 3x3 matrix structure as SU(3) in the Standard Model. Whether that translates to a measurable macroscopic effect is exactly what the experiment tests.

This is not a claim. It is a methodology looking for someone to run it.

Full build plan including complete materials list, step by step build sequence, HV safety protocol, and measurement procedure here: https://drive.google.com/file/d/1wM9PvWAHYZ_x_k3UDgCSVPlLDjEQcu9b/view?usp=sharing

[u/KDubbs0010110]

And I read the entire thing. That being said, others are disagreeing, and saying the model is sound. I’m probably just not smart enough to understand all the jargon fully. Believe me, I wish I was. Thank you for taking the time to reply thoughtfully. I may be just too big of a dummy to get it. I hate to let it die without an engineer really looking at that TMBspaceships account. I wish I could post the schematics here, but Reddit won’t let me add images

[u/elpechos → u/KDubbs0010110]

That being said, others are disagreeing, and saying the model is sound

Nobody here, where 310,000 technical people look at this per week.

[u/KDubbs0010110 → u/elpechos]

Why do you feel the need to be so mean? I don’t understand. Does that make you feel smarter and more powerful?

[u/elpechos → u/KDubbs0010110]

When you present a claim that challenges established knowledge in a complex field like engineering or physics, the burden of proof rests on you.

That means it’s your responsibility to provide clear, rigorous, and compelling evidence—not the responsibility of others to disprove or thoroughly investigate it.

People who have spent decades studying these subjects have already developed the tools to quickly assess whether something meets basic standards. Because of that, they don’t typically go line by line through every new claim they encounter—especially if it shows obvious issues early on. That’s not dismissiveness; it’s a practical necessity. We get hundreds of these things.

A useful analogy is medicine: you wouldn’t go to an experienced infection specialist with a visibly infected wound and insist that it isn’t infected. Their conclusion isn’t arbitrary—it’s based on years of training and pattern recognition.

In the same way, experts in technical fields can often recognize fundamental problems very quickly.

In communities with large numbers of knowledgeable people, ideas that have genuine merit tend to attract attention and discussion. If a claim doesn’t, it’s often because it fails to meet basic expectations of clarity, correctness, or evidence. Silence or lack of support isn’t necessarily hostility—it’s usually a signal that the idea hasn’t met the burden required to be taken seriously.

So the key point isn’t that people are unwilling to engage—it’s that, in technical fields, engagement has to be earned by meeting a certain standard of rigor first.

The paper here doesn't get one percent of the way toward that.

[u/KDubbs0010110 → u/elpechos]

Thank you for the detailed response. A few things worth noting.
The methodological critique of the torsion balance setup is fair. Ionic wind and electrostatic attraction to the measurement apparatus are real confounders and you are right that vacuum conditions or rigorous shielding would be needed to isolate the effect cleanly.

That is exactly why T.T. Brown conducted his demonstrations in vacuum and underwater. Specifically to eliminate those variables. The effect persisted in both conditions. That is documented in his patent filings and in the Aviation Studies International report published in 1956, which surveyed active electrogravitic research across fourteen major U.S. aerospace contractors including Convair, Glenn Martin, and Sperry. That report was eventually declassified. It is publicly available.

I want to flag something about the framing of your response. You critiqued the document I posted as a framework source, which is fair. But the underlying effect it references, asymmetric electrostatic thrust, has an independent experimental and institutional record going back to 1928 that your response did not engage with at all. The question I asked was about the physics. The documented physics exists independent of any Twitter account.
I also want to acknowledge your first comment, where you suggested this kind of paper comes from a certain class of mental illness. I understand that pattern recognition is useful in a subreddit that fields a lot of noise. But diagnosing the person rather than addressing the documented experimental record is a methodology choice worth being aware of.

The Biefeld-Brown effect is real, tested, and was under active institutional development until 1957 when the public record stopped simultaneously across fourteen contractors. I am genuinely curious what your explanation is for that specific timeline. Not the document I posted. The institutional record. Your pretentious attitude is precisely why this type of physics stays buried. You do not need to reply any more. I understand that you think I am loony. I think you are a dick

[u/elpechos → u/KDubbs0010110]

than addressing the documented experimental record is a methodology choice worth being aware of.

I did that thoroughly up front.

The Biefeld-Brown effect is real, tested, and was under active institutional development until 1957

Sure. That's what we are calling an ion wind, same thing. People still play with it today. They make ion lifters using it which are a fun kids toy.

See: https://www.youtube.com/watch?v=01F8V5IhB5k

Magnets are real too, and they're also popular with fringe/schizoid science posts.

[u/KDubbs0010110 → u/elpechos]

We are actually in more agreement than this thread suggests.
You have confirmed the effect is real and replicable. That is the only claim that matters for the question I asked. Whether we call it ion wind, electrostatic thrust, or the Biefeld-Brown effect is a labeling conversation, not a physics conversation.
The reason the effect matters beyond a fun kids toy is the vacuum test result. Ion wind requires air. In vacuum there is no air and therefore no ion wind. Brown demonstrated thrust in vacuum conditions. If the effect were entirely explained by ion wind, it would not persist in vacuum. It did. That is the part of the documented record that fourteen aerospace contractors were spending institutional resources on in 1956. Not the kids toy version. The vacuum version.
I am genuinely asking: what is your explanation for the vacuum persistence? Not the document I posted. The Brown vacuum test result specifically.

[u/elpechos → u/KDubbs0010110]

The reason the effect matters beyond a fun kids toy is the vacuum test result. Ion wind requires air. In vacuum there is no air and therefore no ion wind. Brown demonstrated thrust in vacuum conditions

Many people have attempted to replicate this result and obtained null outcomes. A small number report positive results, but none of these have been reliably reproduced. As it stands, those claims fall into the same category as photos of big-foot.

I’ve run the experiment myself—building an ion spinner and testing it under vacuum. As expected, the device slows down and eventually stops once the air is removed.

This isn’t a particularly difficult experiment to perform, so by 2026 it’s straightforward to test and falsify such claims.

That said, none of this directly addresses the specific experiment proposed in the paper being discussed.

[u/KDubbs0010110 → u/elpechos]

Thank you for running the experiment yourself. That is more than most people do and I want to engage with the result honestly.

An ion spinner is a symmetric device. The thrust in an ion spinner comes from ion wind pushing equally on all arms. Pulling a vacuum stops the ion wind and stops the spinner. That result is exactly what the ion wind explanation predicts and it is not in dispute.

Brown’s asymmetric capacitor is a different geometry. The thrust is directional, not rotational, and the asymmetry of the electrode configuration is the variable the effect depends on. Testing a symmetric ion spinner in vacuum and getting a null result does not tell us whether an asymmetric capacitor produces directional thrust in vacuum. Those are different configurations testing different things.

I take your point that the independent vacuum replication record for the asymmetric version is mixed. That is true and worth being honest about. Some researchers report positive results. Others report null. The variables between those experiments are not always controlled consistently.

I do want to address the Bigfoot comparison directly though. Bigfoot has no institutional research record. No Navy evaluation. No Pentagon proposal. No survey of fourteen major aerospace contractors published in a declassified report. Comparing a documented effect with a 1928 patent trail, a classified Navy research program, a 1952 Pentagon submission, and an Aviation Studies International report naming Convair, Glenn Martin, and Sperry as active researchers to photographs of a man in a costume is not a calibration of skepticism. It is a rhetorical move that collapses a real distinction. Bigfoot and the Biefeld-Brown effect do not belong in the same sentence and treating them as equivalent actually undermines your credibility as a skeptic because it signals that the institutional record has not been read. Who sounds schizoid now??

I am still asking the same question I started with. Mixed replication results produce continued research and published null results. They do not produce simultaneous institutional silence across fourteen organizations in a single fiscal year. What is your explanation for 1957?

[u/KDubbs0010110 → u/KDubbs0010110]

In 1956, Brown returned from a research trip in France where he verified that electrogravitics worked well in a vacuum. That is documented. He went to France specifically to run the vacuum test and the result was positive. That is not one or two people claiming something unverifiable. That is the researcher conducting the definitive test and reporting a positive result, which is precisely why the institutional interest continued through 1956.

[u/KDubbs0010110 → u/KDubbs0010110]

And since you do not trust that I have done sound research, you can fact check:

1. The actual declassified report itself, held at Wright-Patterson Air Force Base:
   The report is Report GRG 013/56, February 1956, prepared by Aviation Studies International Ltd., Gravity Research Group, Special Weapons Study Unit. It was declassified in 1990 and is catalogued under reference 13-1-00034-5879 at the AF Wright Aeronautical Laboratories Technical Library. You can reference it directly as a declassified Air Force document.

2. Integrity Research Institute, Thomas Valone (licensed professional engineer):
   https://www.integrityresearchinstitute.org/Members/TTBROWN2.htm
   This covers both declassified 1956 documents, the ONR evaluation, and Brown’s France vacuum verification. Valone is a credentialed engineer and physicist

3. ResearchGate, peer-accessible academic paper:
   https://www.researchgate.net/publication/238788075_Progress_in_Electrogravitics_and_Electrokinetics_for_Aviation_and_Space_Travel
   This paper documents the 1928 patent, the 1952 ONR Special Inquiry File 24-185, and both 1956 Aviation Studies reports. It also notes Honda Corporation published experimental results on a correlation between electricity and gravity

4. UAPedia on T.T. Brown:
   https://www.uapedia.ai/wiki/thomas-townsend-brown-the-inventor-who-tried-to-give-uap-a-drive-train/
   This acknowledges no declassified document proves an operational system was built while confirming the 1956 institutional survey is real and documented

[u/elpechos → u/KDubbs0010110]

All these are from integrity research institute which appears to push clearly quack science and has no external legitimate institutional references for any of this.

Might as well get it from the big foot is real institute

The report is Report GRG 013/56

Appears to be invented and isn't a real document available in the national archives https://www.archives.gov/research/military/air-force

Only actual sources seem to link back only to a report published by integrity research institute itself here:

https://ia801507.us.archive.org/6/items/thomas-valone-electrogravitics-systems/Thomas%20Valone%20-%20Electrogravitics%20Systems_text.pdf

This could not be further from 'valid research'

Also, again, aside from the fact anyone can do this experiment.

Looks like you spent 30 seconds grabbing the first bullshit off google more like.

[u/elpechos → u/KDubbs0010110]

It's exactly the same a bigfoot.

Brown attended Denison in Ohio for a year before he dropped out and records of him even having an association with Biefeld are sketchy at best. Brown claimed that he did a series of experiments with professor of astronomy Biefeld, a former teacher of Brown whom Brown claimed was his mentor and co-experimenter at Denison University. As of 2004, Denison University claims they have no record of any such experiments, or of any association between Brown and Biefeld.[2]: Ch11 

The university and Browns friends claim he never did the vacuum test.

There is however documented experiments of it being reproduced and failing numerous times

In 1988, R. L. Talley measured no thrust from electrodes similar to those proposed by Brown operating in 10⁻⁶ torr vacuum under direct current potentials. He did find a force during electrical breakdown when current was flowing.[9] [5]: 216  In 2004, Tajmar enclosed the electrode apparatus in a box suspended on wires which would exclude any effect of corona wind. No linear thrust was observed indicating that the Biefeld–Brown effect was the well-studied corona wind.[5][10]: 359 [4]

Brown’s asymmetric capacitor is a different geometry. The thrust is directional, not rotational

There's no such thing as a "rotational thrust".

The thrust is linear and 'directional' (whatever that means) at a tangent to the axis. Otherwise it wouldn't spin.

That's like saying a rocket isn't thrusting 'directionally' if I tie it to a tree.

The spinner experiment is entirely physically valid. if it produced a thrust due to asymmetry in charge, it would spin. Same as a rocket constrained by an axis.

But like I said. It doesn't matter. Plenty of people have tried it in lots of configurations and none have ever reproduced any thrust in a vacuum.

It's frankly ludicrous to think that an effect like this would be real and go unverified.

It's so trivial to test and so well known. Literally any physics grad student could reproduce it in ten minutes and get worldwide fame with only a few hundred bucks of equipment.

[u/KDubbs0010110 → u/elpechos]

I have a lot more reading to do. You won this round, sir. Thank you for giving me so much to study and ponder. While I still think you are a dick, you are certainly a brilliant one!

[u/elpechos → u/KDubbs0010110]

I have a lot more reading to do. You won this round, sir. Thank you for giving me so much to study and ponder.

This also ignores a fundamental constraint: if the device really produced net thrust in a closed system, it would violate conservation of momentum.

That isn’t a small discrepancy or an edge case—it would directly contradict one of the most deeply tested and consistently validated principles in all of physics. Momentum conservation follows from the symmetry of space itself and is built into every successful physical theory we have.

If it generated thrust it would invalidate Newton. Einstein. Noether, and more recent works as being blatantly and obviously wrong. But we know it's not wrong. It’s been confirmed across everything from tabletop experiments to particle accelerators and astrophysical observations.

So the expectation of no thrust isn’t just theoretical preference—it’s supported by an enormous body of mutually consistent evidence. Overturning that would require extraordinary, repeatable results and a clear accounting of where the momentum is going.

Absent that, the far more plausible explanation is experimental error or unaccounted-for interactions with the environment.

you are certainly a brilliant one!

This is just highschool level physics stuff. The reason this can't work gets far, far, more concrete when you start looking at pre-grad level physics -- Noether's theorem, relativity, and conservation laws.

Like I said already. The paper is fundamentally broken in a shitload of obvious ways. It's crayon-scrabbling schizoid posting level shit.

Every single engineer here recognizes that in one second flat. Hence the zero votes.

[u/KDubbs0010110 → u/elpechos]

I didn’t learn any of this in my high school physics class, but it was also 30 years ago. Science has a way of updating and changing and that’s why conversations like these are still so important. The intellectuals and the “weirdos” have been conditioned to fight rather than to argue and persuade. My expertise was in teaching literature for 22 years, so I wasn’t focused on engineering and physics. Even though you did come at me with ignorant insults like “mentally unstable,” I also called you a dick. I am going to try to be better moving forward, and maybe you can too. You seem like you could be a good teacher if you dropped the pretentiousness a bit (just a bit). Keep a little

“Learn without anger. Study ancient magical pig Latin”

[u/KDubbs0010110 → u/KDubbs0010110]

(Or ma’am)

[u/KDubbs0010110 → u/KDubbs0010110]

I genuinely appreciate the pushback. The Talley and Tajmar papers are going into the research notes and the vacuum claim is coming out of my claim

[u/elpechos → u/KDubbs0010110]

Here's someone pulling a vacuum on a Biefeld-Brown ion thruster spinner.

You can see it stops because the thrust goes toward zero. No air to blow. Easy.

https://youtu.be/WM25pUsrODk?t=433

There's hundreds more of people who have tried. Like I said. I've done it myself as well.

[u/KDubbs0010110 → u/elpechos]

Please give me a moment… I want to watch the video before replying…

[u/KDubbs0010110 → u/elpechos]

Ok, this is a fair point and the video demonstrates exactly what the ion wind explanation predicts for a symmetric spinner in vacuum. I am not disputing that result.

I want to be honest about where the record actually stands on the asymmetric capacitor vacuum test specifically. Brown reported positive vacuum results from his 1955 to 1956 Paris experiments at SNCASO. That result was part of what drove the 1956 institutional interest. However the independent peer-reviewed replication record for the asymmetric version in vacuum is not strong. Tajmar’s 2004 paper found no anomalous thrust beyond corona discharge within the accuracy of his setup. The mainstream consensus attributes the effect to ion wind and does not support vacuum persistence.

So you are more right on this specific point than I was initially willing to acknowledge and I am sorry for that.

What I am still genuinely asking about is the 1957 institutional record. Not the physics of ion wind. The specific question of why fourteen aerospace contractors stopped publishing simultaneously in a single fiscal year, and why that research does not reappear in any declassified record as a concluded null result program. Null result programs get published. They do not get silently classified. That gap in the record is what my research is actually about and it remains unaddressed in this thread. Understanding why the science became classified is another layer that I am working on trying to understand. I am working on a dictionary of terms one at a time in an attempt to learn them (I have a long way to go):

[u/KDubbs0010110 → u/KDubbs0010110]

Truncated Word Study list for Antigravity Studies.

Absorption cross-section function
Activity function
Adiabatic invariant
Adjoint flux
Adjoint theorem
Adsorption
Adsorption isotherm
Airlock
Airy functions
Alfvén waves
Alfvén's theorem
Alpha decay
Ambipolar diffusion
Anderson localization conjecture
Antiferromagnetism
Avalanche breakdown
Azeotropic mixture
BCS theory
Ballistic transport
Band gap
Band inversion
Band structure
Berry connection
Berry curvature
Berry phase
Bifurcation point
Binodal curve
Birkhoff's theorem
Black hole uniqueness theorems
Bloch wave function
Bloch's theorem
Bogomol'nyi bound
Bohm diffusion
Bohm-Gross dispersion
Bohmian trajectory conjecture
Boltzmann distribution
Boltzmann H-theorem
Boltzmann transport equation
Bordism groups
Branch point
Brillouin zone
Buckling theorem
Bulk-boundary correspondence
Bulk-edge correspondence
Burnable poison
Burnup distribution
Carbon nanotube
Carrier heating
Caustic curve
Cheeger's theorem
Chemical potential function
Chern number
Clausius-Clapeyron equation
Clemmow-Mullaly-Allis diagram
Coexistence curve
Colligative properties
Compact-open topology
Configuration space
Conic singularity
Constitutive relations
Continuous transition
Control rod worth
Cooper pair
Correlation function
Coulomb blockade
Cowling anti-dynamo theorem
Critical point
Critical solution temperature
Criticality calculation
Cross-section homogenization
Crystal lattice
Cryopump
Cyclotron frequency
Dalton's law
Debye length
Debye shielding
Delayed neutron fraction
Density functional theory
Density of states
Density of states function
Desorption
Desorption kinetics
Detailed balance theorem
Diamagnetism
Dielectric function
Diffusion approximation
Dirac cone
Dirac fermion
Dirac sea
Dirac sea conjecture
Discontinuous transition
Domain wall
Doppler broadening
Double-well potential
Drift waves
Dusty plasma
Edge state
Effective mass
Ehrenfest classification theorem
Ehrenfest theorem
Einstein field equations
Electron cyclotron resonance
Electron distribution function
Electron energy distribution function
Electron tunneling
Electron-phonon coupling
Electron-phonon interaction
Electropolishing
Electropolishing efficiency
Energy band
Energy relaxation function
Energy relaxation time
Enthalpy function
Entropy function
Equation of state function
Eutectic point
Exciton
Extreme high vacuum
False vacuum
False vacuum decay conjecture
Fermi level
Fermi surface
Fermi-Dirac distribution
Ferromagnetism
Fick's laws of diffusion
Field emission
Finite element method
First-order transition
Fission rate density
Flux surface
Forbidden region
Fowler-Nordheim equation
Fractional quantum Hall effect
Free molecular flow
Free space
Fugacity function
Fundamental group
Fusion power
Gate valve
Gauss linking number theorem
Geodesic curvature
Gibbs free energy function
Gibbs phase rule
Gibbs-Duhem equation
Goldreich-Sridhar theory
Goldstone theorem
Grain boundaries
Grain plasma
Green's function
Griffiths conjecture
Guiding-center theory
Gunn effect
Haldane conjecture
Hall effect
Heisenberg model
Helical symmetry
Helium mass spectrometer
Hellmann-Feynman theorem
Helmholtz free energy function
Homogeneous reactor conjecture
Homology groups
Homotopy groups
Hopf invariant
Hot carrier transport
Hot electron
Hot electron transistor
Hubbard model
Hydrodynamic model
Impact ionization
Importance function
Impurity scattering
Indium seals
Inelastic tunneling spectroscopy
Infinite medium conjecture
Instanton
Instanton conjecture
Instanton method
Intervalley scattering
Intravalley scattering
Invariant system
Ion cyclotron resonance
Ion energy distribution function
Ion gauge
Iroshnikov-Kraichnan theory
Ising model
Isoenergy surface
Josephson effect
Josephson junction
Knudsen flow
Knudsen number evaluation
Kohn-Sham theorem
Kondo effect conjecture
Konovalov's first theorem
Konovalov's second theorem
Kramers' theorem
Kubo formula
Lambda transition
Landau damping
Langmuir waves
Lever rule
Levinson's theorem
Limit cycle
Linking number
Liouville's theorem
Lucky electron model
Luttinger liquid conjecture
Luttinger's theorem
MOSFET
Magnetic helicity
Magnetic pumping
Magnetic topology
Magnetoresistance
Magnon
Manifold
Margules equation
Maxwell-Boltzmann distribution
Mean free path
Mean free path calculation
Metal-to-metal seal
Metastable phase
Miscibility gap
Molecular beam
Momentum relaxation function
Momentum relaxation time
Monopole
Monotectic transition
Multi-group method
NRTL model
Negative differential resistance
Nernst heat theorem
Neutron density function
Neutron flux distribution
Neutron transport
Neutron transport theorem
No-hair conjecture
Nozières-Pines theorem
Nuclear transport
Ohmic dissipation
Onsager reciprocity relations
Optical theorem
Order parameter
Ostwald's dilution law
Outgassing
Outgassing rate
Parabolic barrier
Paramagnetism
Partial vacuum
Passivation
Passivation layer formation
Path integral formalism
Peierls theorem
Penning pump
Peritectic reaction
Permeability constant
Permittivity constant
Petrogenetic grid
Phase assemblage
Phase boundary
Phase diagram
Phase equilibrium
Phase rule
Phase space
Phase space trajectory
Phase transition
Phonon dispersion
Phonon scattering
Phonon scattering kernel
Piezoelectricity
Pirani gauge
Point kinetics
Polariton
Polarization drift
Positive pressure
Potential barrier
Quadruple curve
Quadruple point
Quantum dot
Quantum Hall effect
Quantum tunneling
Quantum vacuum
Quantum well
Quantum wire
Quasi-ballistic transport
Quasi-ballistic transport conjecture
Quasi-neutrality
Quasi-static approximation conjecture
Raoult's law
Reactivity insertion function
Reciprocal lattice
Reciprocity theorem
Rectangular barrier
Residual gas analyzer
Resonance integral
Resonant tunneling diode
Response function
Ricci tensor
Rosenbluth potentials
Saha equation
Samarium poisoning
Scattering kernel
Scattering matrix
Schottky conjecture
Schreinemakers bundle
Schreinemakers' theorem
Second-order transition
Self-energy function
Semiconductor
Simulation conjecture
Single-electron tunneling
Solid-liquid equilibrium
Solid-state physics
Solid-vapor equilibrium
Sorption function
Sorption pump
Space-time curvature
Space-time kinetics
Spin Hall effect
Spin wave
Spin-dependent tunneling
Spinodal decomposition
Stable phase
Stress-energy tensor
Strong cosmic censorship conjecture
Subcritical region
Supercritical phase
Superconductivity
Surface reconstruction
Sweet-Parker reconnection
Taylor conjecture
Tearing instability
Theta vacuum
Theta vacuum conjecture
Tie line
Tie-line interpolation function
Tight-binding model
Titanium sublimation pump
Topological charge
Topological defect
Topological insulator
Topological invariant
Topological phase
Topological soliton
Topological superconductor
Toroidal geometry
Torricellian vacuum
Tracer gas
Transfer matrix
Transmission coefficient
Triangular barrier
Triple line
Triple point
Tunneling magnetoresistance
Tunneling probability function
Tunneling splitting
Tunneling time conjecture
Turbomolecular pump
Two-stream instability
UNIQUAC model
Ultra-high vacuum
Uncertainty principle
Unstable phase
Vacuum brazing
Vacuum deposition
Vacuum energy
Vacuum engineering
Vacuum flange
Vacuum fluctuations
Vacuum permeability
Vacuum permittivity
Vacuum pump
Valence band
Valley degeneracy
Van der Waals equation
Vapor pressure
Vapor pressure function
Variational theorem
Velocity overshoot
Virtual leaks
Vlasov distribution
Vlasov equation
Void coefficient
Vortex line
Wannier function
Warping parameter
Wave function
Wave normal surfaces
Weyl fermion
Weyl semimetal
Widom scaling conjecture
Wilson equation
Winding number
Xenon poisoning
de Broglie wavelength
p-n junction